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The Sheahan Diamond Literature Reference Compilation - Scientific and Media Articles based on Major Keyword - Geochemistry
The Sheahan Diamond Literature Reference Compilation is compiled by Patricia Sheahan who publishes on a monthly basis a list of new scientific articles related to diamonds as well as media coverage and corporate announcements called the Sheahan Diamond Literature Service that is distributed as a free pdf to a list of followers. Pat has kindly agreed to allow her work to be made available as an online digital resource at Kaiser Research Online so that a broader community interested in diamonds and related geology can benefit. The references are for personal use information purposes only; when available a link is provided to an online location where the full article can be accessed or purchased directly. Reproduction of this compilation in part or in whole without permission from the Sheahan Diamond Literature Service is strictly prohibited. Return to Diamond Keyword Index
Sheahan Diamond Literature Reference Compilation - Scientific Articles by Author for all years
Each article reference in the SDLRC is tagged with one or more key words assigned by Pat Sheahan to highlight the main topics of the article. In an effort to make it easier for users to track down articles related to a specific topic, KRO has extracted these key words and developed a list of major key words presented in this Key Word Index to which individual key words used in the article reference have been assigned. In most of the individual Key Word Reports the references are in crhonological order, though in some such as Deposits the order is first by key word and then chronological. Only articles classified as "technical" (mainly scientific journal articles) and "media" (independent media articles) are included in the Key Word Index. References that were added in the most recent monthly update are highlighted in yellow.
Geochemistry can be about the relative composition of elements and their isotopes within rocks, but also about the mechanisms that drive the movement of matter within the earth.
Application des Methodes Geochimiques (chromium et Nickel) a la Recherche de Pipes Kimberlitique: Relutats Obtenus sur un Pipe Deja Connu (kenieba) Soudan Francais.
Partition of oxygen isotopes and trace elements between carbonate and silicate melts at 1 kilobar, 800 degrees C and its bearing on the origin ofcarbonatite
Variacion Vertical Y Lateral de Ocho Perfiles Aluvionales De la Quebrada Grande, Afluente Del Rio Guaniamo, Comprendidos Entre Los Campos Mineros la Bicicleta Y
An Ultrapotassic Basaltic Suite from the Central Sierra Nevada, California: a Study of the Mineralogy, Petrology, Geochemistry and Isotopic Composition.
Ph.d. Thesis, University California, Santa Barbara., 100P.
United States, California, West Coast
Basanite, Whole Rock Geochemistry, Isotope, Geothermometry
Metasomatism and Chemical Heterogeneity in the Sub-continental Mantle: Sr and Nd Isotopic Analysis of Apatite Rich Xenoliths and Alkaline Magmas from Eastern Australia.
Proceedings of Third International Kimberlite Conference, TERRA COGNITA, ABSTRACT VOLUME., Vol. 2, No. 3, P. 231, (abstract.).
Observations on natural diamonds: geochemical analyses of inclusions indiamonds, especially clinopyroxene: contribution to mineralogy of blackdiamonds.*GE.
Ph.d. Thesis, University of Mainz, (in German), 335p
Geochemical and petrographic investigation of the genesis of the cancrinite-syenite niobium bearing carbonatite complex of Lueske Kivu Northeastern Zaire.*G
Ph.D. Thesis University of Berlin (in German), 330p
Detrital Minerals of Mantle Origin in the Green River Basin, Wyoming.
Society for Mining, Metallurgy and Exploration (SME)-American Institute of Mining, Metallurgical, and Petroleum Engineers (AIME)., SYMPOSIUM OUTLINE FALL MEETING DENVER OCTOBER 24TH. P. 13. (
Age and geochemical characteristics of a mafic dyke swarm in the Archean vestfold block Antarctica- inferences about Proterozoic dyke emplacement inGondwana
Journal of Petrology, Vol. 27, No. 4, August pp. 853-886
Geochemical characteristics of boninite and tholeiite series volcanic rocks of the Mariana forearc and the role of an incompatible element enrichedfluid
Mantle metasomatism and alkaline magmatism, edited E. Mullen Morris and, No. 215, pp. 151-164
Preliminary characterization of the supergene evolution of the carbonatite rocks of the Juquia (sp) Alkaline carbonatite complex with phosphateenrichment
Xiii International Geochemical Exploration Symposium, Rio 89 Brazilian, p. 219. Abstract
Metasomatized lower crustal and upper mantle xenoliths from North Queensland -chemical and isotopic evidence bearing on the composition and source of fluid phase
Geochimica et Cosmochimica Acta, Vol. 53, No. 3, March pp. 649-660
Eclogites with oceanic crustal and mantle signatures from the Bellsbankkimberlite, South Africa. Part I:Mineralogy, petrography, and whole rockchemistry
Mineralogy and geochemistry of island arc picrites, as illustrated by an example from the southern part of the Olyutorskaya zone of the KoryakHighlands
Doklady Academy of Sciences USSR, Earth Science Section, Vol. 306, No. 3, pp. 148-152
A convective cumulation model for crystallization differentiation of the melt and formation of the apatite deposits in Khibiny ijolite-urtite intrusion
Spinel chemistry as an indicator of magmatic processes in lamprophyres of Eastern British Columbia
Geological Association of Canada (GAC)/Mineralogical Association of Canada (MAC) Vancouver 90 Program with Abstracts, Held May 16-18, Vol. 15, p. A63. Abstract
Origin of clinopyroxene and amphibole megacrysts in the alkali basaltic rocks from western Taiwan as constrained by rare earth elements (REE) geochemistry
Proceedings of the Geological Society of China, Vol. 33, No. 3, July pp. 177-204
Geochemical, mineralogical and lithological analyses of glacial sediments for gold, base metals and kimberlite exploration Beardmore-Geraldton area, Thunder Bay Ont
Geological Survey of Canada Open File, No. 2266, 442p. $54.50 Geological Society of Canada (GSC) and (disk. from Ashley $ 25.00
Peraluminous metamorphic rocks from the Namaqualand Metamorphic Complex (South Africa): geochem. evidence for an exhalation related sed. origin in a Mid.Prot
Chemical Geology, Vol. 81, No. 3, January 30, pp. 221-240
Edwards, D., Rock, N.M.S., Taylor, W.R., Griffin, B.J., Sun, S-S.
The Aries Diamondiferous kimberlite pipe, central Kimberley block, westernAustralia: mineralogy, petrology and geochem. of the pipe rock and indicators
Proceedings of Fifth International Kimberlite Conference held Araxa June 1991, Servico Geologico do Brasil (CPRM) Special, pp. 82-84
A semi-quantitative model for fractionation of rhyolite from rhyodacite in a compositionally altered Archean volcanic complex, Superior Province, Canada
Precambrian Research, Vol. 50, No. 1-2. April pp. 49-67
Exploration Techniques, Saskatoon, Conference registration The Canadian Institute of Mining, Metallurgy and Petroleum (CIM) Xerox, Sept. 5-13, 1991 Fax 514 939-2714
Heavy mineral geochemical exploration for lamproite
The Canadian Mining and Metallurgical Bulletin (CIM Bulletin) ., Session on Diamonds at The Canadian Institute of Mining, Metallurgy and Petroleum (CIM) Annual Meeting April, Vol. 84, No. 947, March p. 99. Abstract
An analytical method for hydrogeochemical surveys: inductively coupled plasma atomic emission spectrometry after using enrichment coprecipitation with cobalt and amM.
Journal of Geochemical Exploration, Vol. 41, No. 3, November pp. 349-362
Oxygen isotope evidence for the origin of pyroxenites in the Beni Bousera peridotite massif, North Morocco: derivation from subducted oceaniclithosphere
Earth and Planetary Science Letters, Vol. 102, No. 3/4, March pp. 289-301
Argon isotope and halogen chemistry of phlogopite from South Africankimberlites: a combined step-heating, laser probe, electron microprobe and TEMstudy
Use of geochemistry as a guide to platinum group element potential of mafic ultramafic rocks- examples the West Pilbara block and Halls Creek Mobile Zone:
Precambrian Research, Vol. 50, No. 102, April pp. 1-35
Rock chem dat a sets. Alkaline rocks of Australia. 111 analyses ( 557lamproites and related rock types from Fitzroy and Argyle areas and 277 from alkaline rocks
Bmr Australia Rockchem Data Sets, Please note cost $ 1200.00
Australia
Data sets -rock chemistry, Geochemistry lamproites
Geochemical evolution of granitoids Archean Abitibi s volcanic zone and the Pontiac subprovince, Superior, : implications for tectonic history and sourceregions
Chemical Geology, Vol. 98, No. 1-2, July 10, pp. 23-70
Ontario
Geochemistry, Tectonics -Abitibi southern volcanic zone
Implications of HFS/LIL trace element variations for the mantle sources of recent alkaline volcanism in northern British Columbia and the Yukon, Canada
Eos Transactions, Vol. 73, No. 14, April 7, supplement abstracts p.325
The Canadian Mining and Metallurgical Bulletin (CIM Bulletin) , Annual Meeting Abstracts approximately 10 lines, Vol. 86, No. 968, March POSTER ABSTRACT p. 69
Diamondiferous kimberlite in Saskatchewan, Canada- a biogeochemical SOURCE[ Journal of Geochemical Exploration,Special issue Proceedings of geochemical Exploration 1991 held Reno
Journal of Geochemical Exploration, Special issue Proceedings of, Vol. 47, No. 1-3, pp. 131-142
Mathematics and the Buckyball.The elaborate symmetries of this soccer ball shaped molecule allow many of its properties to be calculated from firstprinciples
American Scientist, Vol. 81, January-February pp. 56-70
Reconnaissance till mineral and geochemical survey northern Alberta:preliminary results of orientation survey
Mid-continent diamonds Geological Association of Canada (GAC)-Mineralogical Association of Canada (MAC) Symposium ABSTRACT volume, held Edmonton May, pp. 101-106
Prairie indicator mineral and soil geochemical survey
The Canadian Mining and Metallurgical Bulletin (CIM Bulletin) , Annual Meeting Abstracts approximately 10 lines, Vol. 86, No. 968, March POSTER ABSTRACT p. 69
Mineralogical and group classification Program.. for diamond indicatorminerals. ( a listing of other minerals and include Gurney's classification of G9, G10
Saskatchewan Energy and Mines -Geological Survey, Data File No. 18, 3 p. text and disc
The track record for diamond indicator minerals: a summary of casehistories
The Canadian Mining and Metallurgical Bulletin (CIM Bulletin) , Annual Meeting Abstracts approximately 10 lines, Vol. 86, No. 968, March ABSTRACT p. 70
Laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS):rapid technique direct quantitative determination major, trace rareearth elements
Geochemistry, origin and provenance of upper Proterozoic to upper Cambrian alkaline to transitional basaltic rocks in and contiguous to sector Humberzone
American Journal of Science, Vol. 293, November pp. 980-1009
Lecuyer, C., Gruau, G., Anhaeusser, C.R., Fourcade, S.
The origin of fluids and the effects of metamorphism on the primary chemical compositions of Barberton komatiites: new evidence from geochemistry, isotopes
Economic Geology Research Unit, University of the Witwatersrand, Inf. Circular No. 272, 32p
Results of reconnaissance diamond indicator mineral sampling, Saskatchewan.
Mid-continent diamonds Geological Association of Canada (GAC)-Mineralogical Association of Canada (MAC) Symposium ABSTRACT volume, held Edmonton May, pp. 107-116.
Kimberlite indicator mineral tracing on the Canadian Prairie
The Canadian Mining and Metallurgical Bulletin (CIM Bulletin) , Annual Meeting Abstracts approximately 10 lines, Vol. 86, No. 968, March ABSTRACT p. 70.
Hidden gems in the NURE data: placer exploration potential for gold, PGM, rare earth elements (REE) and other metals in the Arctic coastal plain and Foothills Province, Alaska
The geochemistry (platinum group elements (PGE)) in kimberlites and constraints of the nature platinum group elements (PGE) insubcratonic lithospheric mantle.
International Symposium Upper Mantle, Aug. 14-19, 1994, Extended abstracts pp. 73-75.
Geochemistry of the rare lithophile elements Zirconium, Hafnium, Niobium, Tantalum, Thorium, and Uranium and variations in their ratios during fraction.
Alkaline Magmatism -problems mantle source, pp. 216-22.
Oxygen isotope contamination of carbonates, silicates and oxides in selected carbonatites: constraints on crystallization temperatures of carbonatitic magmas.
Composition of phengites in eclogites and their retrogressive derivatives of Dabie shan region: implication for the applicability of phengite geobarometre....
Chinese Journal of Geochemistry, Vol. 21, 1, pp.52-56.
Regional survey to identify potential blocks for occurrence of kimberlite/lamproite pipes in Indravati River Basin, Koraput and Nabarangapur Districts, Orissa
Records of the Geological Survey of India, Vol. 133, 3, eastern 1998-1999, pp.191-3.
Organic petrology, organic geochemistry, palynology and petrophysics dat a from Lac de Gras kimberlites and associated sedimentary rocks and xenoliths.
Geological Survey of Canada Open File, No. 4272, 1 CD $ 32.50
Regional survey to identify potential blocks for occurrence of kimberlite/lamproite pipes in Indravati Basin, Koraput and Nawarangpur district, Orissa.
Records of the Geological Survey of India, Vol. 132, 3, eastern 1997-1998, pp.209-11.
The Precambrian Earth, tempos and events, editors Eriksson, P.G., Altermann, W., Nelson, D.R., Mueller, W.U., Elsevier, Developments in Precambrian Geology No. 12, C
A comparison of selective leach signatures over kimberlites and other targets. B30,A4,A1.AM47,95-2,MR6, Seed, OPAP, Peddie carbonatites Firstbrook, Borden, Firesand,
Ontario Geological Survey Open File, No. 6142, 179p. $ 16.
Canada, Ontario, Kirkland Lake, New Liskeard, Wawa
A petrological and geochemical appraisal of the Mesoproterozoic Diamondiferous Majhgawan pipe of central India: evidence for transitional kimberlite - orangeite ( group II kimberlite) - lamproite rock type.
Preliminary investigation: sedimentology and provenance of the Wood Mountain Formation and derived glacial and glaciofluival sediments - context for KIM anomalies.
Saskatchewan Geological Survey Summary of Investigations 2004, Vol. 2, pp. A 1-12.
Kent, A.J.R., Stolper, E.M., Francis, D., Woodhead, J., Frei, R., Eiler, J.
Mantle heterogeneity during the formation of the North Atlantic igneous province: constraints from trace element and Sr Nd Os O isotope - Baffin Island picrites
Geochemistry, Geophysics, Geosystems: G3, Vol. 5, pp. Q11004 10.1029/2004GC000743
Upper mantle temperature determined from combining mineral composition, electrical conductivity laboratory studies and magnetotelluric field observations:
Earth and Planetary Science Letters, Vol. 236, 1-2, pp. 258-268.
Canada, British Columbia, Alberta, Yukon, Cordillera
Roy, A., Sarkar, A., Jeyakumar, S., Aggrawal, S.K., Ebihara, M., Satoh, H.
Late Archean mantle metasomatism below eastern Indian Craton: evidence from trace elements, REE geochemistry and Sr Nd O isotope systematics of ultramafic dykes.
Proceedings National Academy of Sciences India , Vol. 113, 4, pp. 649-666. Ingenta 1045680437
Compositional variations (major and trace elements) of clinopyroxene and Ti and radite from pyroxenite, ijolite and nepheline syenite, Alno Island, Sweden.
The effect of temperature on the equilibrium distribution of trace elements between clinopyroxene, orthopyroxene, olivine and spinel in upper mantle peridotite.
Chemical geology, Vol. 221, 1-2, Sept. 5, pp. 65-101.
National geochemical Reconnaissance: regional stream sediment and water data: Travaillant Lake area.. analytical, mineralogical kimberlite indicator data
Geological Survey of Canada Open File, 4951, 1 CD May 17, $ 9.10
Geochemistry of late Mesozoic adakites from the Sulu belt, China: magma genesis and implications for crustal recycling beneath continental collisional orogens.
Preliminary release of kimberlite indicator mineral dat a from National geochemical Reconnaissance stream sediment samples in the Jackpine Lake area Buffalo Head Hills
Geological Survey of Canada Open File, 5267, 23p. 1 CD $ 26.00
Geology, petrology, geochemistry and mineral chemistry of new kimberlite fields in the Wajrakarur kimberlite field, Anantapur district, Andhra Pradesh.
National Seminar on Exploration Survey, Geological Society of India Special Publication, No. 58, pp. 593-602.
Modified ion exchange separation for tungsten isotopic measurements from kimberlite samples using multi-collector inductivity coupled plama mass spectrometry.
Analyst, ( Royal Society of Chemistry), Vol. 131, 3, pp. 434-439.
The upper continental crust, an aquifer and its fluid: hydraulic and chemical dat a from 4 km depth in fractured crystalline basement rocks at the KTB test.
Project 03-002. Synthesis of Archean geology and diamond bearing rocks in the Michipicoten Greenstone Belt: results from microdiamond extraction and geochronology.
Ontario Geological Survey Summary of Fieldwork 2005, O.F. 6172, pp. 8-1-13.
The diamonds and kimberlitic indicative minerals within the context of stratigraphy and source in Shefa Yamim drill SY-15, Pliocene-Pleistcene Qishon River Valley.
Major and trace element and Sr Nd, Hf, and Pb isotope compositions of the Karoo large igneous province, Botswana and Zimbabwe: lithosphere vs mantle plume...
Indicator mineralogy of kimberlite boulders and sand samples from the Lac Baby and Sharp Lake eskers, Lake Timiskaming field, western Quebec and northeast Ontario
Geological Survey of Canada Open File, No. 5050, 21p.
Geochemical, mineralogical and kimberlite indicator mineral electron microprobe dat a from sills, heavy mineral concentrates and waters Buffalo Head Hills.
Geological Survey of Canada Open File, No. 5057, 16p.
Portnyagin, M., Hoernie, K., Plechov, P., Mironov, N., Khubunaya, S.
Constraints on mantle melting and composition and nature of slab components in volcanic arcs from volatiles ( H2) S Cl F) and trace elements in melt inclusions from the Kamchatka Arc.
Earth and Planetary Science Letters, Vol. 255, 1-2, pp. 53-69.
Sader, J.A., Leybourne, M.I., McClenaghan, M.B., Hamilton, S.
Low temperature serpentinization processes and kimberlite groundwater signature Kirkland Lake and Lake Timiskaming kimberlite fields: implications diamond exploration.
Geochemistry: Exploration, Environment, Analysis, Vol. 7, 1, pp. 3-21.
Petrochemical characteristics of the kimberlites in the Middle Markha region with application to the problem of the geochemical heterogeneity of kimberlites.
Geochemistry International, Vol. 45, 12, Dec. pp. 1197-1209.
Refertilization of ancient lithosphere mantle beneath the central North Chin a craton: evidence from petrology and geochemistry of peridotite xenoliths.
Geochemical and kimberlite indicator mineral results for till samples from Nejanilini, Kasmere and Putahow lakes areas, northern Manitoba NTS 64N 64 O 64 P.
Nielsen, T.F.D., Jensen, S.M., Secher, K., Sand, K.K.
Distribution of kimberlite and aillikite in the diamond province of southern West Greenland: a regional perspective based on groundmass mineral chemistry and bulk compositions.
Stream sediment sampling for kimberlite indicator minerals in the western Canada sedimentary basin: the Buffalo Head Hills Survey, north central Alberta.
Geological Association of Canada Short Course, No. 18, pp. 111-124.
Steenfelt, A., Jensen, S.M., Nielsen, T.F.D., Sand, K.K.
Provinces of ultramafic lamprophyre dykes, kimberlite dykes and carbonatite in West Greenland characterised by minerals and chemical components in surface media.
Viljoen, K.S., Harris, J.W., Ivanic, T., Richardson, S.H., Whitehead, K.
Trace element geochemistry and Ni thermometry of garnet inclusions in peridotitic diamonds from Premier and Finsch, South Africa: implications - diamond formation
International Mineralogical Association meeting August Budapest, abstract p. 187.
Lower crustal melting via magma underplating: elemental Sr Nd Pb isotopic constraints from late Mesozoic intermediate felsic volcanic rocks in NE Chin a block.
Estudos com base em quimica semi-quantitativa atraves da microscopis eletronica de Varredura dos minerais satelites do corpo kimberlitico no minicipio de Ariquemes
5th Brasilian Symposium on Diamond Geology, Nov. 6-12, abstract p. 65.
Chemical composition, volatile components, and trace elements in the magmatic melt of the Kurama mining district, middle Tien Shan: evidence investigation of quartz inclusions
Vladykin, N.V., Deep Seated Magmatism: its sources and plumes, pp. 75-92.
Kahoui, M., Kemainsky, F.V., Griffin, W.L., Belousova, E., Mahdjoub, Y., Chabane, M.
Detrital pyrope garnets from the El Kseibat area, Algeria: a glimpse into the lithospheric mantle beneath the north-eastern edge of the West African Craton.
Journal of African Earth Sciences, In press available, 46p.
Kimberlite indicator minerals in terrigene sediments of lower part of Mackenzie River Basin, NWT, Canada: evidence of new craton with thick lithosphere.
10th. International Kimberlite Conference Feb. 6-11, Bangalore India, Abstract
Diamonds from the Poiskovaya, Zapolyarnaya and Leningrad kimberlite pipes, northern Yakutia: correlation of carbon isotopic composition and nitrogen content as an indicator of fluid diamond formation.
Diamond exploration and regional prospectivity of the Northern Territory of Australia.
Proceedings of the 10th. International Kimberlite Conference, Vol. 2, Special Issue of the Journal of the Geological Society of India,, Vol. 2, pp. 257-280.
Grunsky, E.C., Kjarsgaard, B.A., Kurzlaukis, S., Seller, M.
The use of statistical methods applied to multi-element geochemistry for phase discrimination in kimberlites - examples from the Star and Whiskey kimberlites.
GAC/MAC joint annual meeting, Vol. 36, p. 1. abstract
Grunsky, EC., Kjarsgaard, B.A., Kurzlaukis, S., Seller, M., Knight, R., Moroz, M.
Classification of whole rock geochemistry based on statistical treatment of whole rock geochemical analyses and portable XRF analyses at the Attawapiskat kimberlite field of Ontario.
Geological Survey of Canada, Scientific Presentation 15,, 1 sheet 10.4095/292446
Kimberlite indicator minerals in terrigine sediments of Arctic regions of Siberian and North American ancient platforms: evidence of new cratons with thick lithosphere.
Kleinhanns, I.C., Fullgraf, T., Wilsky, F., Nolte, N., Fliegel, D., Klemd, R., Hansen, B.T.
U-Pb zircon ages and (isotope) geochemical signatures of the Kamanjab In lier ( NW Namibia): constraints on Palaeoproterozoic crustal evolution along the southern Congo craton.
Geological Society of London Special Publication: Continent formation through time., No. 389, pp. 165-195.
43rd Annual Yellowknife Geoscience Forum Abstracts, abstract p. 22.
Canada, Northwest Territories
Geochemistry
Abstract: Attention is being focused on the development of deep penetrating geochemical exploration methods as the discovery rate of world class deposits decreases. Diamondiferous kimberlites located in the Lac de Gras region of the Northwest Territories are one of the many deposit types in Canada covered by glacial overburden, and are therefore challenging to detect. This paper presents initial results from an investigation of the DO-18 kimberlite (Peregrine Diamonds), buried under 5-20m of glacial cover, to identify surface geochemical responses directly related to the buried kimberlite and differentiate between physical and chemical transport mechanisms. A detailed grid of 150 samples over an area of 0.5km2 sampled the oxidized upper B soil horizon in till above and off the DO-18 kimberlite into background. Regolith mapping was conducted and included surficial soil type and rock fragments, topographic variation and physical features, e.g. bogs, swamps, vegetation and glacial direction indicators. This allows an assessment of surface controls on the geochemistry, including the generation of false anomalies from chemical traps such as swamps. Multi-element geochemistry comprising 4-acid, Aqua-Regia and distilled water extraction coupled with ICP-MS was undertaken using commercial techniques to identify and differentiate between those elements migrating by chemical process from those migrating by physical transportation. Hydrocarbons were analysed using the SGH-technique (ActLabs) and the Gore-sorber technique (AGI) to characterize type and abundance of complex hydrocarbons above the kimberlite relative to the host granite gneiss. Preliminary results from the 4-acid digestion data show a clastic dispersion of Nb, Ni, Mg, Co, Cr and Cs from directly above the kimberlite to the edge of the sampling grid 500 metres northwest of the buried kimberlite. Surface material exhibits a strong control on geochemistry with trace elements being controlled by major elements (Al, Fe, Mn) found within each surface material type, and in some cases are heavily influenced by the presence of organic carbon. Evaluation of these relationships allows clarification of the natural background noise and enhancement of the geochemical responses and contrasts.
43rd Annual Yellowknife Geoscience Forum Abstracts, abstract p. 86.
Canada, Northwest Territories
Geochemistry
Abstract: The Central Mackenzie Valley (CMV) area of the Northwest Territories (NWT) comprises a Phanerozoic sedimentary basin that lies between the western margin of the Slave craton and the Cordillera. Although the region is considerably outside the bounds of the exposed Slave craton, both LITHOPROBE and more recent regional-scale surface wave studies (e.g., Priestley and McKenzie, 2006) indicate the likely presence of lithospheric mantle extending into the diamond stability field. Recent work conducted by Olivut Resources Ltd. led to the discovery of 29 kimberlites in the CMV. However, the indicator mineral chemistry of discovered kimberlites does not appear to be a good match (www.olivut.ca) with those during regional till and stream sediment sampling by the Geologic Survey of Canada (GSC) and Northwest Territories Geologic Survey (NTGS) in August 2003 and July 2005. We present new geochemical data on the regional indicator minerals with the aim of obtaining geotherm and depth of mantle sampling constraints on those indicator minerals discovered to date. A statistical evaluation of the data will compare the similarities to indicator mineral chemistry with parts of the Slave craton to evaluate whether the CMV indicators may ultimately be derived from that region. In total 3600 kimberlite indicator mineral grains were picked from the 0.25-2.0 mm size fractions. Peridotitic garnet grains dominate (46%), followed by magnesium ilmenite (26%), with decreasing individual proportions >15% of chromite, low-chrome diopside, olivine, chrome-diopside and eclogitic garnet. A sub-sample of these grains (3143) were analysed by EPMA. Garnet grains classify (after Grütter et al., 2004) as 1015 (62.1%) G9, 270 (16.5%) G11, 113 (6.9%) G10, 103 (6.3%) G12, 57 (3.5%) G1, 46 (2.8%) G10D, and the remaining 31 (1.9%) as G0, G3, G3D, G4, and G5. A sub-set of garnet grains (~700) were selected for LA-ICP-MS trace element analysis. Of the grains selected 74% G9, 14% G10 (and G10D), and 8% G11, with only 4% G12 and G0 (Grütter et al., 2004). Nickel concentrations from these grains range from 2.6-168.2 ppm, with the majority (>80%) between 20-100 ppm, yielding TNi (Canil, 1999) values ranging from 643-1348°C, with the majority between ~1000-1200°C. Using a central Slave craton geothermal gradient (Hasterok and Chapman, 2011), equilibration pressures for these garnet grains range from 20-80 kbars with the majority between 40-60 kbars (120-185 km). Preliminary analysis has 581 (81%) of the erupted peridotitic mantle garnet grains plotting within the diamond stability field (Kennedy and Kennedy, 1976). Of the 128 clinopyroxene grains analysed, only a few represent garnet peridotite (lherzolite) facies KIM clinopyroxene grains following compositional screening. Thermobarometry of these grains (Nimis and Taylor, 2000), assuming they were all derived from the same lithospheric section, yields P-T arrays identical to the central Slave geotherm that was 220 km thick at the time of eruption. These results are encouraging for diamond exploration. We thank Overburden Drilling Management Ltd. for grain picking and recovery of the small diamond, SGS Lakefield Research for mounting grains, and the GSC for probing of the grains.
Journal of African Earth Sciences, Vol. 113, pp. 35-50.
Africa, Cameroon
Geochemistry
Abstract: Trace element abundances in three indicator minerals (corundum, chrysoberyl, and zircon grains) from the western Mamfe gem placers, as determined by LA-ICP-MS analytical techniques, are shown to be sensitive to their crystallization conditions and source rock types. Corundum is dominantly composed of Al (standardized at 529,300 ppm), Fe (2496-12,899 ppm), and Ti (46-7070 ppm). Among element ratios, Fe/Mg (73-1107), Fe/Ti (0.5-245.0), Ti/Mg (1-175), and Ga/Mg (4-90) are generally higher whereas, Cr/Ga (<0.072) is low. The Fe (?12,899), Ga (?398), Mg (2-62), Cr (1.1-33.0), and V (3.0-93.0) contents (in ppm) mostly typify corundum grains formed in magmatic rocks, although some are metamorphic affiliated. A very higher Ti and significantly low Ga, Ta and Nb contents in some blue grains, suggest interesting concentrations of those high-tech metals in their source rocks. Chrysoberyl is dominantly composed of Al (standardized at 425,000 ppm) and Be (62701-64371 ppm). Iron (7605-9225 ppm), Sn (502-3394 ppm), and Ti (33-2251 ppm) contents are high, whereas Ga (333-608 ppm), Ta (<456.0 ppm), and Nb (<3.0 ppm) are significantly low. The high (Be and Sn) and significantly low Ga-Rb abundances, and Ta > Nb in the western Mamfe chrysoberyls show that they were crystallized in granitic pegmatites, with some of those source rocks being enriched in Ta and Sn. Zirconium oxide (ZrO2: standardized at 66.1 wt.%)) is the only major oxide in analysed coarse-grained zircons. Within the minor elementary suites: Hf (4576-12,565 ppm) and Y (48-2805 ppm) contents are significantly high. The trace element suites include: Th (7-1565 ppm), U (13-687 ppm), and ?REE (50-2161 ppm), whose values are significantly low. The (Yb/Sm)N, Ce/Ce*, and Eu/Eu* anomalies range from 1.0 to 227.0, 0 to 308, and 0.08 to 1.7 respectively. They are Hf-Y-HREE enriched and depleted zircons mainly crystallized in magmatic oxidized environments. They were mainly sorted from granitoids, syenites and kimberlites.
Indicator mineral and geochemistry dat a for a till and alluvium sampling survey in the McFaulds Lake ( Ring of Fire) area, northern Ontario. Mentions KIMS.
Ontario Geological Survey Report and Data, Report 6309, Data release 322.
Journal of Geochemical Exploration, Vol. 165, pp. 159-173.
Canada, British Columbia
Geochemistry - carbonatites
Abstract: This orientation survey indicates that Quantitative Evaluation of Materials by Scanning electron microscopy (QEMSCAN®) is a viable alternative to traditional indicator mineral exploration approaches which involve complex processing followed by visual indicator mineral hand-picking with a binocular microscope. Representative polished smear sections of the 125-250 ?m fraction (dry sieved and otherwise unprocessed) and corresponding Mozley C800 table concentrates from the drainages of three carbonatites (Aley, Lonnie, and Wicheeda) in the British Columbia Alkaline Province of the Canadian Cordillera were studied. Polished smear sections (26 × 46 mm slide size) contained an average of 20,000 exposed particles. A single section can be analyzed in detail using the Particle Mineral Analysis routine in approximately 3.5-4.5 h. If only mineral identification and mineral concentrations are required, the Bulk Mineral Analysis routine reduces the analytical time to 30 min. The most useful carbonatite indicator minerals are niobates (pyrochlore and columbite), REE-fluorocarbonates, monazite, and apatite. Niobate minerals were identified in the 125-250 ?m fraction of stream sediment samples more than 11 km downstream from the Aley carbonatite (their source) without the need for pre-concentration. With minimal processing by Mozley C800, carbonatite indicator minerals were detected downstream of the Lonnie and Wicheeda carbonatites. The main advantages of QEMSCAN® over the traditional indicator mineral exploration techniques are its ability to: 1) analyze very small minerals, 2) quickly determine quantitative sediment composition and mineralogy by both weight percent and mineral count, 3) establish mineral size distribution within the analyzed size fraction, and 4) determine the proportions of monomineralic (liberated) grains to compound grains and statistically assess mineral associations in compound grains. One of the key advantages is that this method permits the use of indicator minerals based on their chemical properties. This is impossible to accomplish using visual identification.
Geochimica et Cosmochimica Acta, Vol. 191, pp. 187-202.
Australia
Geochemistry
Abstract: Despite the robust nature of zircon in most crustal and surface environments, chemical alteration, especially associated with radiation damaged regions, can affect its geochemistry. This consideration is especially important when drawing inferences from the detrital record where the original rock context is missing. Typically, alteration is qualitatively diagnosed through inspection of zircon REE patterns and the style of zoning shown by cathodoluminescence imaging, since fluid-mediated alteration often causes a flat, high LREE pattern. Due to the much lower abundance of LREE in zircon relative both to other crustal materials and to the other REE, disturbance to the LREE pattern is the most likely first sign of disruption to zircon trace element contents. Using a database of 378 (148 new) trace element and 801 (201 new) oxygen isotope measurements on zircons from Jack Hills, Western Australia, we propose a quantitative framework for assessing chemical contamination and exchange with fluids in this population. The Light Rare Earth Element Index is scaled on the relative abundance of light to middle REE, or LREE-I = (Dy/Nd) + (Dy/Sm). LREE-I values vary systematically with other known contaminants (e.g., Fe, P) more faithfully than other suggested proxies for zircon alteration (Sm/La, various absolute concentrations of LREEs) and can be used to distinguish primary compositions when textural evidence for alteration is ambiguous. We find that zircon oxygen isotopes do not vary systematically with placement on or off cracks or with degree of LREE-related chemical alteration, suggesting an essentially primary signature. By omitting zircons affected by LREE-related alteration or contamination by mineral inclusions, we present the best estimate for the primary igneous geochemistry of the Jack Hills zircons. This approach increases the available dataset by allowing for discrimination of on-crack analyses (and analyses with ambiguous or no information on spot placement or zircon internal structures) that do not show evidence for chemical alteration. It distinguishes between altered and unaltered samples in ambiguous cases (e.g., relatively high Ti), identifying small groups with potentially differing provenance from the main Jack Hills population. Finally, filtering of the population using the LREE-I helps to more certainly define primary correlations among trace element variables, potentially relatable to magmatic compositional evolution.
Geochemistry: Exploration, Environment, Analysis, Vol. 16, 3-4, pp. 181-192.
Technology
Geochemistry
Abstract: Three portable X-ray fluorescence (pXRF) methods were compared and tested in an exploration program using till in Sinoselkä, northern Finland. The use of one truck-mounted XRF unit and two handheld pXRF analysers were tested for basal till samples gathered using percussion drilling with a flow-through sampling bit. The datasets were compared to both conventional aqua regia based analyses and each other. The results prove that a correlation between the data generated by different pXRF methods was acceptable for some major (Ca, Fe) and most of the base metal elements (like As, Cr, Cu, Mn, Ni, Pb, Zn) in the Sinoselkä area. The pXRF analyses also correlate well with the aqua regia geochemical data of the same elements. Distribution of the elements was comparable to the lithological changes in the underlying bedrock that indicates a short glacial transport distance. It is also demonstrated that more than absolute values, the relative values and their changes are those which should be considered and carefully examined. The results reported here emphasize the usefulness of pXRF analysers in till geochemical exploration and demonstrate that they involve easy and fast methods to collect geochemical data for tracing sources of multi-metal mineralization. Furthermore, pXRF is applicable in gold exploration, although indicator elements like As, Bi, Cu, Mn and Sb have to be used instead of Au.
Abstract: One of the great problems in the history of Earth’s climate is how to reconcile evidence for liquid water and habitable climates on early Earth with the Faint Young Sun predicted from stellar evolution models. Possible solutions include a wide range of atmospheric and oceanic chemistries, with large uncertainties in boundary conditions for the evolution and diversification of life and the role of the global carbon cycle in maintaining habitable climates. Increased atmospheric CO2 is a common component of many solutions, but its connection to the carbon chemistry of the ocean remains unknown. Here we present calcium isotope data spanning the period from 2.7 to 1.9 billion years ago from evaporitic sedimentary carbonates that can test this relationship. These data, from the Tumbiana Formation, the Campbellrand Platform and the Pethei Group, exhibit limited variability. Such limited variability occurs in marine environments with a high ratio of calcium to carbonate alkalinity. We are therefore able to rule out soda ocean conditions during this period of Earth history. We further interpret this and existing data to provide empirical constraints for carbonate chemistry of the ancient oceans and for the role of CO2 in compensating for the Faint Young Sun.
Boletin del Museo Nacional de Historia Narural del Paraguay, Vol. 20, 2, pp. 188-204. pdf available in * Port
South America, Paraguay
Geochemistry - indicator minerals
Abstract: Many diamondiferous kimberlites in the Lac de Gras region of the Northwest Territories are concealed by glacial drift, rendering them challenging to detect by traditional exploration techniques that exploit residual surface chemistry. Much research has been aimed at the development of deep penetrating geochemical exploration technologies to increase the rate of discovery whilst reducing risk and exploration cost. However, results from a detailed study of soil geochemistry above the DO-18 kimberlite (Peregrine Diamonds) demonstrate the potential to apply conventional surface geochemical techniques coupled with surface material mapping and landscape evolution models to the evaluation of discrete targets. 50 soil samples from the oxidized upper B-horizon in a detailed grid crossing the concealed kimberlite were collected. Samples, screened to -180 microns, were analysed by multi-element ICP-MS following 4-acid, aqua-regia and deionized water extractions. Fp-XRF was utilised as an equivalent total method to evaluate its applicability. Sequential leach on selected samples was undertaken to understand the deportment of the elements of interest within the soils. Surficial mapping included soil type, topographic variation, landforms, environment and vegetation. This allows an assessment of surface controls on the geochemistry, in particular the generation of false anomalies from chemical traps such as swamps; and allows the generation of a landscape development model. Hydrocarbons, analysed using the SGH and Gore-sorber techniques, were evaluated to characterize the type and abundance of complex hydrocarbons above the kimberlite relative to above the host granitic gneiss. Geochemical data is subject to landform generation processes. The northern half of the grid comprises till with numerous frost boils. The southern half, at lower topography below a distinct break, is dominated by sand-rich material and fine clay. Results from the 4-acid and aqua regia extraction show a dispersion of Nb, Ni, Mg, Ce, Cr and Cs from directly above the northern part of the kimberlite to the edge of the sampling grid, approximately 500 metres to the northwest, following glacial dispersion. SGH-hydrocarbon results exhibit a similar pattern in light-alkyl benzenes. Fp-XRF data repeats the pattern in all elements except Mg, where the concentrations are too low for reliable detection. In the southern half of the grid, at a lower topographic level, geochemical responses are considerably more subtle. It is hypothesised that anomaly formation in the till followed standard glacial dispersion in the down ice trend. Material was entrained to the surface from deeper in the till, locally above the kimberlite, by frost boil action. The southern part of the area is considered to have been inundated with water, the remains of which comprise the current lake over the DO-27 kimberlite approximately 400m to the south. Sediments in this area are clay rich - comprising material deposited by the lake, or re-worked sandy material along the palaeo-lake margin and subsequent erosional channels. These later processes acted to further disperse, conceal and dilute the signal of the underlying body.
Abstract: Apatite-group phosphates are nearly ubiquitous in carbonatites, but our understanding of these minerals is inadequate, particularly in the areas of element partitioning and petrogenetic interpretation of their compositional variation among spatially associated rocks and within individual crystals. In the present work, the mode of occurrence, and major- and trace-element chemistry of apatite (sensu lato) from calcite and dolomite carbonatites, their associated cumulate rocks (including phoscorites) and hydrothermal parageneses were studied using a set of 80 samples from 50 localities worldwide. The majority of this set represents material for which no analytical data are available in the literature. Electron-microprobe and laser-ablation mass-spectrometry data (~ 600 and 400 analyses, respectively), accompanied by back-scattered-electron and cathodoluminescence images and Raman spectra, were used to identify the key compositional characteristics and zoning patterns of carbonatitic apatite. These data are placed in the context of phosphorus geochemistry in carbonatitic systems and carbonatite evolution, and compared to the models proposed by previous workers. The documented variations in apatite morphology and zoning represent a detailed record of a wide range of evolutionary processes, both magmatic and fluid-driven. The majority of igneous apatite from the examined rocks is Cl-poor fluorapatite or F-rich hydroxylapatite (? 0.3 apfu F) with 0.2-2.7 wt.% SrO, 0-4.5 wt.% LREE2O3, 0-0.8 wt.% Na2O, and low levels of other cations accommodated in the Ca site (up to 1000 ppm Mn, 2300 ppm Fe, 200 ppm Ba, 150 ppm Pb, 700 ppm Th and 150 ppm U), none of which show meaningful correlation with the host-rock type. Silicate, (SO4)2 ? and (VO4)3 ? anions, substituting for (PO4)3 ?, tend to occur in greater abundance in crystals from calcite carbonatites (up to 4.2 wt.% SiO2, 1.5 wt.% SO3 and 660 ppm V). Although (CO3)2 ? groups are very likely present in some samples, Raman micro-spectroscopy proved inconclusive for apatites with small P-site deficiencies and other substituent elements in this site. Indicator REE ratios sensitive to redox conditions (?Ce, ?Eu) and hydrothermal overprint (?Y) form a fairly tight cluster of values (0.8-1.3, 0.8-1.1 and 0.6-0.9, respectively) and may be used in combination with trace-element abundances for the development of geochemical exploration tools. Hydrothermal apatite forms in carbonatites as the product of replacement of primary apatite, or is deposited in fractures and interstices as euhedral crystals and aggregates associated with typical late-stage minerals (e.g., quartz and chlorite). Hydrothermal apatite is typically depleted in Sr, REE, Mn and Th, but enriched in F (up to 4.8 wt.%) relative to its igneous precursor, and also differs from the latter in at least some of key REE ratios [e.g., shows (La/Yb)cn ? 25, or a negative Ce anomaly]. The only significant exception is Sr(± REE,Na)-rich replacement zones and overgrowths on igneous apatite from some dolomite(-bearing) carbonatites. Their crystallization conditions and source fluid appear to be very different from the more common Sr-REE-depleted variety. Based on the new evidence presented in this work, trace-element partitioning between apatite and carbonatitic magmas, phosphate solubility in these magmas, and compositional variation of apatite-group minerals from spatially associated carbonatitic rocks are critically re-evaluated.
Abstract: The extent to which water and halogens in Earth’s mantle have primordial origins, or are dominated by seawater-derived components introduced by subduction is debated. About 90% of non-radiogenic xenon in the Earth’s mantle has a subducted atmospheric origin, but the degree to which atmospheric gases and other seawater components are coupled during subduction is unclear. Here we present the concentrations of water and halogens in samples of magmatic glasses collected from mid-ocean ridges and ocean islands globally. We show that water and halogen enrichment is unexpectedly associated with trace element signatures characteristic of dehydrated oceanic crust, and that the most incompatible halogens have relatively uniform abundance ratios that are different from primitive mantle values. Taken together, these results imply that Earth’s mantle is highly processed and that most of its water and halogens were introduced by the subduction of serpentinized lithospheric mantle associated with dehydrated oceanic crust.
Abstract: The Cana Brava complex is the northernmost of three layered complexes outcropping in the Goiás state (central Brasil). New field and geochemical evidences suggest that Cana Brava underwent hyper- to subsolidus deformation during its growth, acquiring a high-temperature foliation that is generally interpreted as the result of a granulite-facies metamorphic event. The increase along the stratigraphy of the incompatible elements abundances (LREE, Rb, Ba) and of the Sr isotopic composition, coupled with a decrease in ?Nd(790), indicate that the complex was contaminated by the embedded xenoliths from the Palmeirópolis Sequence. The geochemical data suggest that the contamination occurred along the entire magma column during the crystallization of the Upper Mafic Zone, with in situ variations determined by the abundance and composition of the xenoliths. These features of the Cana Brava complex point to an extremely similarity with the Lower Sequence of the most known Niquelândia intrusion (the central of the three complexes). This, together with the evidences that the two complexes have the same age (c.a. 790 Ma) and their thickness and units decrease northwards suggests that Cana Brava and Niquelândia are part of a single giant Brasilia body grown through several melt impulses.
Abstract: Drift prospecting has been a successful mineral exploration tool in previously glaciated terrains. Based on the concepts of glacial dynamics, and related sediment production, transport and deposition, drift prospecting surveys assess compositional variability within glacial sediments and trace indicators of mineralization back to a buried bedrock source. The time-transgressive nature of shifting ice flow direction and related till production is an important factor, controlling the shape and extent of dispersal patterns in till. The effect of changing ice flow on the composition of till has been well-studied in both map view, as well as longitudinally in cross section (i.e., dispersal curves). Fewer studies have looked at dispersal patterns holistically in three-dimensions. Here, we use 94 reverse circulation (RC) boreholes, yielding 254 till samples, to reconstruct the subsurface geometry of a dispersal train from a pair of buried kimberlite pipes (DO-27 and DO-18) in the Northwest Territories. Discrete smooth interpolation modeling in SKUA-GOCAD based on downhole data allows for visualization of geochemical anomalies within the till column, as well as the subsurface density of kimberlite indicator mineral grains. Through the combination of borehole data, field work, and modeling, we are able to compare three-dimensional dispersal patterns in the subsurface with local ice flow records, measured from erosional ice flow indicators in the field. This dataset allows us to evaluate the role that changing ice flow, as well as local bedrock surface topography, play in controlling dispersal and deposition of clastic sediment by past ice sheets. Our modeling documents buried palimpsest terrains along older ice flow trajectories, demonstrating lateral and vertical variability within a single, relatively thin and discontinuous till sheet. Furthermore, we observe relationships between local indicator mineral concentrations and bedrock topography, with indicator mineral dispersal concentrated along a bedrock-controlled topographic low aligned with the most recent ice flow. This work demonstrates the benefit of detailed mapping and visualization of a dispersal plume, even in areas of relatively thin and discontinuous till cover, highlighting the role basal topography and shifting ice flow plays on shaping the surface expression of a dispersal train.
Earth and Planetary Science Letters, Vol. 471, pp. 65-73.
Mantle
geochemistry, water cycle
Abstract: Subduction of hydrous and carbonated oceanic lithosphere replenishes the mantle volatile inventory. Substantial uncertainties exist on the magnitudes of the recycled volatile fluxes and it is unclear whether Earth surface reservoirs are undergoing net-loss or net-gain of H2O and CO2. Here, we use noble gases as tracers for deep volatile cycling. Specifically, we construct and apply a kinetic model to estimate the effect of subduction zone metamorphism on the elemental composition of noble gases in amphibole - a common constituent of altered oceanic crust. We show that progressive dehydration of the slab leads to the extraction of noble gases, linking noble gas recycling to H2O. Noble gases are strongly fractionated within hot subduction zones, whereas minimal fractionation occurs along colder subduction geotherms. In the context of our modelling, this implies that the mantle heavy noble gas inventory is dominated by the injection of noble gases through cold subduction zones. For cold subduction zones, we estimate a present-day bulk recycling efficiency, past the depth of amphibole breakdown, of 5-35% and 60-80% for 36Ar and H2O bound within oceanic crust, respectively. Given that hotter subduction dominates over geologic history, this result highlights the importance of cooler subduction zones in regassing the mantle and in affecting the modern volatile budget of Earth's interior.
Abstract: The goal of this work is to determine the effect of multiple glaciations on till composition, in a zone of transition from a multi-till stratigraphy within the Hudson Bay Lowland (HBL) to a single till stratigraphy over the Precambrian shield. The study area, in NE Manitoba, has access to numerous sections that expose multiple tills, in addition to interglacial and postglacial sediments. Sequences of thick till are not easily separated into different units, despite previous field attempts to define four named tills. The compositional transition to thin till overlying the Precambrian Shield in the west is also not well understood. Yet, the two different settings were affected by the same 3+ glacial cycles. The wide range in eastern- and/or northeastern-sourced calcareous clast concentrations, and ‘locally’-sourced shield clast concentrations, combined with variable concentrations of northern-sourced clasts, suggests that the tills of northeastern Manitoba are ‘provenance’ hybrids. Local tills result from the net effect of multiple glacial processes that underwent spatiotemporal variability. Mixed provenance applies not only to surface tills, but to the subsurface tills as well. Preliminary results suggest that carbonate transport across the shield was continuous throughout several glacial cycles, but the bulk of transport likely occurred prior to the most recent glacial cycle. Current work has established a northern-Manitoba ice-flow history using the erosional and depositional record, which encompasses 5 to 7 phases. This new compilation is used in conjunction with ‘till-clast’ stratigraphy and ‘till-geochemistry’ stratigraphy, to identify a new provenance framework for tills in northeastern Manitoba.
Geochemistry of the Namaqualand, Busmanland and Warmbad melillitite and kimberlite provinces of South Africa and Namibia: the southern extension of the African kimberlitic megalineament.
Abstract: The history of kimberlite magmatism in the Siberian craton comprised the Middle Paleozoic (Late Devonian), Triassic, and Jurassic-Cretaceouse events. The Middle Paleozoic event produced greatest amounts of diamond-bearing kimberlites; diamond contents in the Triassic rocks are much lower, while the Jurassic-Cretaceous kimberlites are actually barren [1]. Minerals derived from kimberlites of different ages often coexist in placers and dispersion trains, which poses problems to the use of mineralogical methods for diamond exploration. The problem can be solved by knowing the morphological features of kimberlite indicator minerals typical of each magmatic event [2]. Garnets from Middle Paleozoic kimberlites have the following features: a) chemistry corresponding to diverse parageneses, including those of diamond assemblage; b) weak to strong wear; predominant medium and high wear degrees; c)signatures of dissolution in Late Devonian laterite weathering profiles. Garnets from Triassic kimberlites differ in a) lower paragenetic diversity; few or absent garnets of diamond assemblage; b) only low wear degree; strong wear restricted to garnets from Triassic kimberlites hosted by coastal sediments; c) no dissolution signatures. Jurassic-Cretaceous ages of kimberlites can be inferred from a) changes in paragenetic diversity as a result of deep metasomatism and predominance of shallow lherzolite varieties; no diamond assemblage garnets; b) weak wear; c) no dissolution signatures. The approach was used to estimate the ages of kimberlites in some kimberlite provinces. As a result, we inferred the existence of Middle Paleozoic kimberlites in the Kyutyungde graben, in the catchments of the Mayat, Billakh (Anabar area), and Muna rivers, in the MarkhaMorkoka interfluve, and in the Tychan diamond province (Krasnoyarsk region); Triassic kimberlites in the northern slope of the Olenek uplift and within the Bulkur uplift; and Late Jurassic-Early Cretaceous kimberlites in the Kenkeme catchment north of Yakutsk city.
geochemicalperspectives.org, Vol. 6, 1, April, 187p. Pdf 28 MB
Global
geochemistry
Abstract: Some scientists and journalists, and many members of the general public, have been led to believe that the world is rapidly running out of the metals on which our modern society is based. Advocates of the peak metal concept have predicted for many decades that increasing consumption will soon lead to exhaustion of mineral resources. Yet, despite ever-increasing production and consumption, supplies of minerals have continued to meet the needs of industry and society, and lifetimes of reserves remain similar to what they were 30-40 years ago. In this volume, we discuss the reasons for this apparent paradox using our broad experience and expertise on both academic and industrial sides of the minerals sector. Many misconceptions arise from flawed estimates of the size of global mineral resources which stem from a lack of understanding of the critical difference between reserves and resources. Some authors use quoted reserves – the amount of metal proven to exist and to be economic for mining at present – when predicting imminent shortages. Resources – the amount that may be accessible in the upper few kilometres of the crust – are far larger.Over the last 150 years, improved technologies, economies of scale and increased efficiency have combined to reduce costs hence allowing lower-grade ore to be mined economically. The net result is that the long-term inflation-adjusted price of most metals has decreased more or less in parallel with increasing production, a second apparent paradox that frequently is not well understood. Using copper as the principal example and other metals as appropriate, we summarise the latest research on ore deposits and the activities of the minerals industry. Following a description of the numerous geological processes that form ore deposits, we outline the scientific methods used by the minerals industry to explore for new deposits. We also discuss how resources are mined and how minerals are processed, as well as recent efforts to reduce related environmental impacts. Economic and societal factors influence supply, and these are as important as the actual presence of a resource. Finally, we discuss the critical roles that geoscientists will play in assuring continued supplies of minerals. These include the development of new concepts and techniques that will assist the discovery, mining, processing, remediation, and management of mineral resources. It is essential that researchers help to educate the general public about the need for continued exploration to find new resources to meet growth in world living standards. We demonstrate that global resources of copper, and probably of most other metals, are much larger than most currently available estimates, especially if increasing efficiencies and higher prices allow lower-grade ores to be mined. These observations indicate that supplies of important mineral commodities will remain adequate for the foreseeable future.
45th. Annual Yellowknife Geoscience Forum, p. 67 abstract
Canada, Northwest Territories
geochemistry - indicator minerals
Abstract: Tracing surficial dispersal patterns of indicator minerals within glacial sediments in the main up-ice direction has greatly contributed to numerous mineral discoveries of economic value in the Northwest Territories. However, many cases have also reported perplexing scenarios of dispersal trains seemingly lacking a source, or known sources without a spatially associated dispersal train at the surface. These ‘special’ cases often hinder exploration efforts, and tend to remain poorly understood; yet these cases are becoming increasingly important to decipher as exploration moves into more complex terrains. We present an overview of our research done in the Lac de Gras area over the past few years in collaboration with the Northwest Territories Geological Survey and their partners investigating the effect of multiple ice flows, variable bedrock topography and drift thickness, and the complexities of glacial sedimentary environments on 2D and 3D mechanical (detrital) dispersion. Our research draws from surface and subsurface datasets from various sources at both the regional and local scales. We show that despite the occurrence of relatively long, continuous, surficial patterns extending in the direction of the latest-strongest ice flow event in the region, a subtle record of the time-transgressive glacial history is also frequently preserved. These records yield information about the net effect on sediment dispersion of multiple ice flow phases, bedrock geology, basal topography, and glacial depositional processes. Our findings suggest these geological factors played a key role in producing some of the most irregular and enigmatic dispersal patterns in the region. They also offer insights into how to best characterize and explain the signal (or lack thereof) from elusive buried sources of potential economic interest.
45th. Annual Yellowknife Geoscience Forum, p. 70 abstract
Canada, Northwest Territories
geochemistry - indicator minerals
Abstract: Kimberlite indicator mineral (KIM) concentrations in till are commonly used in glaciated areas such as Northwest Territories to identify glacial dispersal from a kimberlitic source. However, sampling of till that has been modified by post-depositional processes, or material that is not till, can obscure the original glacial dispersion and mislead exploration efforts. The recognition of subtle changes in material type or the occurrence of till modification is obstructed by periglacial processes that homogenize the landscape. Due to restrictions of scale, it is nearly impossible to identify and represent these subtle landscape variations in regional-scale surficial mapping. The uniform till cover depicted in the regional mapping does not reflect reality, and therefore does not provide the necessary surficial context to inform till sampling programs and evaluation efforts. The Northwest Territories Geological Survey and several private exploration companies have recognized the importance of identifying differences in material type and processes that can remobilize and alter the composition of till. Recent improvements in the availability of high-resolution imagery and digital elevation data have provided the means to perform more detailed surficial studies at a scale that is more applicable to diamond exploration. As a result, multiple high-resolution surficial mapping and associated sediment sample data evaluations have been initiated in and around the Lac de Gras region. These studies have reinforced that there is significant spatial variation in the suitability for till sampling, and found that subglacial meltwater corridors and glacial lakes were common. Furthermore, a many of the previously collected till samples were affected by these processes, which can have a significant influence on KIM concentrations and the shape of their dispersal patterns. Meltwater can truncate dispersals and concentrate heavy minerals. Glacial lakes can either dilute or concentrate heavy minerals depending on whether the environment was proximal or distal. Specific landform assemblages and characteristics have been documented that can be used to identify these dispersal-modifying processes, and used to produce a surficial context that is more suitable to exploration. This improved surficial context facilitates the collection of in situ till samples and the interpretation of existing surface sediment data resulting in lower-risk exploration targets.
Earth and Planetary Science Letters, Vol. 458, 1, pp. 252-262.
Mantle
geochemistry
Abstract: The Earth and other terrestrial planets formed through the accretion of smaller bodies, with their core and mantle compositions primarily set by metal -silicate interactions during accretion. The conditions of these interactions are poorly understood, but could provide insight into the mechanisms of planetary core formation and the composition of Earth's core. Here we present modeling of Earth's core formation, combining results of 100 N-body accretion simulations with high pressure -temperature metal -silicate partitioning experiments. We explored how various aspects of accretion and core formation influence the resulting core and mantle chemistry: depth of equilibration, amounts of metal and silicate that equilibrate, initial distribution of oxidation states in the disk, temperature distribution in the planet, and target:impactor ratio of equilibrating silicate. Virtually all sets of model parameters that are able to reproduce the Earth's mantle composition result in at least several weight percent of both silicon and oxygen in the core, with more silicon than oxygen. This implies that the core's light element budget may be dominated by these elements, and is consistent with ?1 -2 wt% of other light elements. Reproducing geochemical and geophysical constraints requires that Earth formed from reduced materials that equilibrated at temperatures near or slightly above the mantle liquidus during accretion. The results indicate a strong tradeoff between the compositional effects of the depth of equilibration and the amounts of metal and silicate that equilibrate, so these aspects should be targeted in future studies aiming to better understand core formation conditions. Over the range of allowed parameter space, core and mantle compositions are most sensitive to these factors as well as stochastic variations in what the planet accreted as a function of time, so tighter constraints on these parameters will lead to an improved understanding of Earth's core composition.
Abstract: This work examines the global distribution of Archaean and modern igneous rock's compositions, without relying on preconceptions about the link between rock compositions and tectonic sites (in contrast with “geotectonic” diagrams). Rather, Archaean and modern geochemical patterns are interpreted and compared in terms of source and melting conditions. Mafic rocks on the modern Earth show a clear chemical separation between arc and non-arc rocks. This points to the first order difference between wet (arc) and dry (mid-ocean ridges and hotspots) mantle melting. Dry melts are further separated in depleted (MORB) and enriched (OIB) sources. This three-fold pattern is a clear image of the ridge/subduction/plume system that dominates modern tectonics. In contrast, Archaean mafic and ultramafic rocks are clustered in an intermediate position, between the three main modern types. This suggests that the Archaean mantle had lesser amounts of clearly depleted or enriched portions; that true subductions were rare; and that the distinction between oceanic plateaus and ridges may have been less significant. Modern granitic rocks dominantly belong to two groups: arc-related granitoids, petrologically connected to arc basalts; and collision granitoids, related to felsic sources. In contrast, the Archaean record is dominated by the TTG suite that derives from an alkali-rich mafic source (i.e. altered basalt). The geochemical diversity of the TTG suite points to a great range of melting depths, from ca. 5 to > 20 kbar. This reveals the absence of large sedimentary accumulations, again the paucity of modern-like arc situations, and the importance played by reworking of an earlier basaltic shell, in a range of settings (including some proto-subduction mechanisms). Nonetheless, granitoids in each individual region show a progressive transition towards more modern-looking associations of arc-like and peraluminous granites. Collectively, the geochemical evidence suggests an Archaean Earth with somewhat different tectonic systems. In particular, the familiar distinction between collision, arcs, ridges and hotspots seems to blur in the Archaean. Rather, the large-scale geochemical pattern reveals a long-lived, altered and periodically resurfaced basaltic crust. This protocrust is reworked, through a range of processes occurring at various depths that correspond to a progressive stabilization of burial systems and the establishment of true subductions. A punctuated onset of global plate tectonics is unlikely to have occurred, but rather short-term episodes of proto-subduction in the late Archaean evolved over time into longer-term, more stable style of plate tectonics as mantle temperature decayed.
Contrasting termite transported indicator mineral concentrations in the Kgalafadi of central district Botswana: Macrotermes micaelseni vs Hodotermes mossambicus.
Vancouver Kimberlite Cluster, March 9, 1p. Abstract
International Journal of Earth Sciences, Vol. 107, 3, pp. 787-810.
Mantle
geochemistry
Abstract: Archean and Proterozoic subcontinental lithospheric mantle (SLM) is compared using 83 similarly incompatible element ratios (SIER; minimally affected by % melting or differentiation, e.g., Rb/Ba, Nb/Pb, Ti/Y) for >3700 basalts from ten continental flood basalt (CFB) provinces representing nine large igneous provinces (LIPs). Nine transition metals (TM; Fe, Mn, Sc, V, Cr, Co, Ni, Cu, Zn) in 102 primitive basalts (Mg# = 0.69-0.72) from nine provinces yield additional SLM information. An iterative evaluation of SIER values indicates that, regardless of age, CFB transecting Archean lithosphere are enriched in Rb, K, Pb, Th and heavy REE(?); whereas P, Ti, Nb, Ta and light REE(?) are higher in Proterozoic-and-younger SLM sources. This suggests efficient transfer of alkali metals and Pb to the continental lithosphere perhaps in association with melting of subducted ocean floor to form Archean tonalite-trondhjemite-granodiorite terranes. Titanium, Nb and Ta were not efficiently transferred, perhaps due to the stabilization of oxide phases (e.g., rutile or ilmenite) in down-going Archean slabs. CFB transecting Archean lithosphere have EM1-like SIER that are more extreme than seen in oceanic island basalts (OIB) suggesting an Archean SLM origin for OIB-enriched mantle 1 (EM1). In contrast, OIB high U/Pb (HIMU) sources have more extreme SIER than seen in CFB provinces. HIMU may represent subduction-processed ocean floor recycled directly to the convecting mantle, but to avoid convective homogenization and produce its unique Pb isotopic signature may require long-term isolation and incubation in SLM. Based on all TM, CFB transecting Proterozoic lithosphere are distinct from those cutting Archean lithosphere. There is a tendency for lower Sc, Cr, Ni and Cu, and higher Zn, in the sources for Archean-cutting CFB and EM1 OIB, than Proterozoic-cutting CFB and HIMU OIB. All CFB have SiO2 (pressure proxy)-Nb/Y (% melting proxy) relationships supporting low pressure, high % melting resembling OIB tholeiites, but TM concentrations do not correlate with % melting. Thus, the association of layered intrusion (plutonic CFB) TM deposits with Archean terranes does not appear related to higher metal concentrations or higher percentages of melting in Archean SLM. Other characteristics of these EM1-like magmas (e.g., S2 or O2 fugacity) may lead to element scavenging and concentration during differentiation to form ore deposits.
Abstract: In this study, we assess the diamond exploration potential of the northern East European Platform based on aeromagnetic survey results and the morphologic and geochemical analysis of 1513 grains of kimberlite indicator minerals (KIMs), such as purple pyrope garnet, olivine, and Cr-diopside. These minerals were recovered from samples collected from modern river and stream sediments in four areas located in the north-eastern (within the Arkhangelsk Diamondiferous Province) and south-western (hundreds of kilometers outside of the Arkhangelsk Diamondiferous Province) parts of the Arkhangelsk region in the European part of Russia. All the studied areas are located within ancient cratons, including the Kola, Karelian, and Shenkursk cratons. Based on the major element compositions of the KIMs and thermobarometric calculations, this study confirms that the lithospheric mantle beneath the studied areas is suitable for the formation and preservation of diamonds. The high percentage of KIMs with primary magmatic grain surface morphologies is evidence of the presence of local kimberlite sources within all of the studied areas. The significant amount of diamond-associated KIMs indicates that the potential sources are diamondiferous. Hence, the results suggest that the studied areas can be recommended for further diamond prospecting activity with a high probability of discovering new diamondiferous kimberlites.
Geochimica et Cosmochimica Acta, Vol. 232, pp. 82-100.
Mantle
geochemistry
Abstract: We have analyzed ancient atmospheric gases trapped in fluid inclusions contained in minerals of Archean (3.3?Ga) to Paleozoic (404?Ma) rocks in an attempt to document the evolution of the elemental composition and isotopic signature of the atmosphere with time. Doing so, we aimed at understanding how physical and chemical processes acted over geological time to shape the modern atmosphere. Modern atmospheric xenon is enriched in heavy isotopes by 30-40‰ u?1 relative to Solar or Chondritic xenon. Previous studies demonstrated that, 3.3?Ga ago, atmospheric xenon was isotopically fractionated (enriched in the light isotopes) relative to the modern atmosphere, by 12.9?±?1.2 (1?) ‰ u?1, whereas krypton was isotopically identical to modern atmospheric Kr. Details about the specific and progressive isotopic fractionation of Xe during the Archean, originally proposed by Pujol et al. (2011), are now well established by this work. Xe isotope fractionation has evolved from 21‰ u?1 at 3.5?Ga to 12.9‰ u?1 at 3.3?Ga. The current dataset provides some evidence for stabilization of the Xe fractionation between 3.3 and 2.7?Ga. However, further studies will be needed to confirm this observation. After 2.7?Ga, the composition kept evolving and reach the modern-like atmospheric Xe composition at around 2.1?Ga ago. Xenon may be the second atmospheric element, after sulfur, to show a secular isotope evolution during the Archean that ended shortly after the Archean-Proterozoic transition. Fractionation of xenon indicates that xenon escaped from Earth, probably as an ion, and that Xe escape stopped when the atmosphere became oxygen-rich. We speculate that the Xe escape was enabled by a vigorous hydrogen escape on the early anoxic Earth. Organic hazes, scavenging isotopically heavy Xe, could also have played a role in the evolution of atmospheric Xe. For 3.3?Ga-old samples, Ar-N2 correlations are consistent with a partial pressure of nitrogen (pN2) in the Archean atmosphere similar to, or lower than, the modern one, thus requiring other processes than a high pN2 to keep the Earth's surface warm despite a fainter Sun. The nitrogen isotope composition of the atmosphere at 3.3?Ga was already modern-like, attesting to inefficient nitrogen escape to space since that time.
Abstract: In this study, we compare the major- and trace-element compositions of olivine, garnet, and clinopyroxene that occur as single crystals (142 grains), with those derived from xenoliths (51 samples) from six kimberlites in the Lucapa area, northeastern Angola: Tchiuzo, Anomaly 116, Catoca, Alto Cuilo-4, Alto Cuilo-63 and Cucumbi-79. The samples were analyzed using electron probe microanalysis (EPMA) and laser-ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS). The results suggest different paragenetic associations for these kimberlites in the Lucapa area. Compositional overlap in some of the macrocryst and mantle xenolith samples indicates a xenocrystic origin for some of those macrocrysts. The presence of mantle xenocrysts suggests the possibility of finding diamond. Geothermobarometric calculations were carried out using EPMA data from xenoliths by applying the program PTEXL.XLT. Additional well calibrated single-clinopyroxene thermobarometric calculations were also applied. Results indicate the underlying mantle experienced different equilibration conditions. Subsequent metasomatic enrichment events also support a hypothesis of different sources for the kimberlites. These findings contribute to a better understanding of the petrogenetic evolution of the kimberlites in northeastern Angola and have important implications for diamond exploration.
Abstract: The results of experiments on dissolution of diamond in a Fe melt with variable concentrations of S at high P-T parameters are presented. It is established that the maximal degree of diamond dissolution occurs at a sulfur concentration of 15 wt %. With decreasing or increasing S content, dissolution of diamond slows down and almost does not occur during the period of the experiment (60 min), when the "eutectic" composition is gained. In contrast to a pure Fe melt, the presence of S decreases the carbon solubility and, therefore, reduces the aggressiveness of metal melt in relation to diamonds, thus, stimulating their preservation in the Earth’s mantle, especially if the concentration of S exceeds that in the "eutectic" composition.
European Journal of Mineralogy, Vol. 30, 2, pp. 231-236.
Mantle
geochemistry
Abstract: Correlations between chemical and structural complexities of minerals were analysed using a total of 4962 datasets on the chemical compositions and 3989 datasets on the crystal structures of minerals. The amounts of structural and chemical Shannon information per atom and per unit cell or formula unit were calculated using the approach proposed by Krivovichev with no Hcorrection for the minerals with unknown H positions. Statistical analysis shows that there are strong and positive correlations (R 2 > 0.95) between the chemical and structural complexities and the number of different chemical elements in a mineral. Analysis of relations between chemical and structural complexities provides strong evidence that there is an overall trend of increasing structural complexity with the increasing chemical complexity. Following Hazen, four groups of minerals were considered that represent four eras of mineral evolution: "ur-minerals", minerals from chondritic meteorites, Hadean minerals, and minerals of the post-Hadean era. The analysis of mean chemical and structural complexities for the four groups demonstrate that both are gradually increasing in the course of mineral evolution. The increasing complexity follows an overall passive trend: more complex minerals form with the passage of geological time, yet the simpler ones are not replaced. The observed correlations between the chemical and structural complexities understood in terms of Shannon information suggest that, at a first approximation, chemical differentiation is a major force driving the increase of complexity of minerals in the course of geological time. New levels of complexity and diversifcation observed in mineral evolution are achieved through the chemical differentiation, which favours local concentrations of particular rare elements and creation of new geochemical environments.
Philosphical Transactions of the Royal Society, rsta.royalsociety publishing.org 30p. Available
Mantle
tectonics, geochemistry
Abstract: Plate tectonics, involving a globally linked system of lateral motion of rigid surface plates, is a characteristic feature of our planet, but estimates of how long it has been the modus operandi of lithospheric formation and interactions range from the Hadean to the Neoproterozoic. In this paper, we review sedimentary, igneous and metamorphic proxies along with palaeomagnetic data to infer both the development of rigid lithospheric plates and their independent relative motion, and conclude that significant changes in Earth behaviour occurred in the mid- to late Archaean, between 3.2?Ga and 2.5?Ga. These data include: sedimentary rock associations inferred to have accumulated in passive continental margin settings, marking the onset of sea-floor spreading; the oldest foreland basin deposits associated with lithospheric convergence; a change from thin, new continental crust of mafic composition to thicker crust of intermediate composition, increased crustal reworking and the emplacement of potassic and peraluminous granites, indicating stabilization of the lithosphere; replacement of dome and keel structures in granite-greenstone terranes, which relate to vertical tectonics, by linear thrust imbricated belts; the commencement of temporally paired systems of intermediate and high dT/dP gradients, with the former interpreted to represent subduction to collisional settings and the latter representing possible hinterland back-arc settings or ocean plateau environments. Palaeomagnetic data from the Kaapvaal and Pilbara cratons for the interval 2780-2710?Ma and from the Superior, Kaapvaal and Kola-Karelia cratons for 2700-2440?Ma suggest significant relative movements. We consider these changes in the behaviour and character of the lithosphere to be consistent with a gestational transition from a non-plate tectonic mode, arguably with localized subduction, to the onset of sustained plate tectonics.
Diamond potential of the Dehcho region. Horn Plateau
2018 Yellowknife Geoscience Forum , p. 104. abstract
Canada, Northwest Territories
geochemistry
Abstract: Our knowledge of the diamond potential in the Dehcho region has progressed significantly in the past decade. We now recognize that the central Dehcho represents a world class diamond exploration district. Continued scientific and industry work in the area have clearly shown that the diamond potential of this area may be of the same magnitude as the Lac de Gras region, which hosts active diamond mines. The evidence for high diamond potential in the Dehcho, includes abundant Kimberlite Indicator Minerals (KIM) from stream sediment sampling work, a diamond found in a stream sediment sample, 39 drilled kimberlites, some of which are diamondiferous, and numerous untested kimberlite-like geophysical anomalies from both government and industry data. Recent work at the University of Alberta has shown that deep Earth conditions in the area of the Horn Plateau may be as favorable for diamond generation and preservation as the Lac de Gras region and that there that there may be multiple generations of kimberlites present in the region. Given the relative paucity of exploration work and geoscience data in the Dehcho region, the available evidence is strongly suggestive of the possibility of the presence of diamond deposits.
Ross, M., Kelley, S.E., Janzen, R., Stirling, R.A., Normandeau, P.X., Elliott, B.
Orphan and elusive glacial dispersal trains from kimberlites in the Lac de Gras area.
2018 Yellowknife Geoscience Forum , p. 65-66. abstract
Canada, Northwest Territories
geochemistry
Abstract: Numerous glacial dispersal trains, spatially and compositionally associated to kimberlites, have been characterized and mapped in the Lac de Gras region, Northwest Territories (NT). However, a small number of these trains have yet to be associated with a source. Additionally, a number of known sub-cropping kimberlites do not have well-defined, spatially associated, trains of indicator minerals. These issues suggest that local factors may be important in controlling the occurrence, shape, and strength of a dispersal pattern and its spatial association with a kimberlite. Identifying these factors and understanding their effect on the dispersion of indicator minerals could provide a road map for finding additional diamondiferous kimberlites in the NT and elsewhere. Here we examine contrasting dispersal trains from south and southwest of Lac de Gras, as well as situations where the source of known dispersal trains (e.g., Coppermine Train) continue to elude exploration geologists. Using both surface and subsurface datasets, we find that the bedrock geology and topography of the source area, as well as those of the dispersal area, are potential key controls on the type and shape of dispersal patterns. Even across discontinuous drift and subdued shield relief we find that bedrock topography and lithology modulated the effect of glacial dynamics on till production and provenance. These 'bedrock factors' have interacted in various ways during Quaternary glaciations, in combinations unique to each case, to generate complex dispersal patterns in three dimensions. Accounting for these factors, using both surface and subsurface data, could enhance the success of drift exploration programs and improve their outcome in the glaciated shield terrains of northern Canada.
Re-thinking diamond exploration tactics in the Slave Province: a surficial geology perspective. Lac de Gras area
2018 Yellowknife Geoscience Forum , p. 66-67. abstract
Canada, Northwest Territories
geochemistry
Abstract: It took several decades to develop the necessary understanding of glaciation, geochemistry and mineralogy to refine exploration strategies and find the first kimberlite in the Northwest Territories, Canada. These fundamental drift prospecting strategies followed by geophysics and drilling have been used to locate many kimberlite occurrences over the years. Indicator minerals in surface sediments are still the primary datasets used to identify kimberlite exploration targets; however, many of the kimberlite sources for the well-defined indicator mineral dispersals have been identified. Exploration must now focus on regions with more complex surficial geology where primary dispersal patterns in till are obscured by post-depositional modification. These patterns are largely defined using data from historical “˜till' surveys that often failed to properly scrutinize the sample media; reworked tills and other surficial materials were commonly collected. The regional surficial geology maps (e.g., 1:50,000 to 1:250,000) typically published by geological surveys to stimulate reconnaissance exploration in new areas are generally incapable of providing sufficient resolution to determine the genesis and post-glacial alteration of sample media or reconcile complex dispersal patterns. Furthermore, advances in analytical methods have yielded compiled datasets with results from multiple methods that are not always comparable. Without a new, more detailed and systematic approach to evaluating surface sediment data, exploration in areas with complex glacial, deglacial and post-glacial histories will be challenged to discover kimberlite. The accessibility, quality and variety of high-resolution aerial or satellite imagery and topographic data has improved significantly over the years, affording a more detailed interpretation of the surficial environment. These detailed interpretations have allowed us to evaluate historical data with a new perspective and target the collection of new, high-quality data. Throughout the Slave Province, we have tailored surficial interpretations to distinguish in-situ till from reworked till and other materials, which have altered dispersion and indicator mineral concentrations. Using examples from the Lac de Gras area, this presentation demonstrates how a detailed surficial framework, combined with an understanding of the varied analytical methods, is applied to historical datasets to refine indicator dispersal patterns and identify new exploration targets. By standardizing the data based on sediment genesis and transport mechanisms, the dataset becomes more suitable for statistical evaluation and anomaly threshold determinations that are unique to specific data subpopulations. As a result, anomaly contrasts are improved, and complex dispersals can be unravelled. In addition, areas with insufficient data coverage are identified and the necessary framework to complete informed, efficient infill or new sampling is provided. The examples we share highlight that there is no replacement for project-scale understanding of surficial geology and its varied effects on mineral dispersals in the development and interpretation of a surface sediment dataset used to identify kimberlite exploration targets.
Abstract: Multifractal features of element concentrations in the Earth’s crust have demonstrated to be closely associated with multiple probability distributions such as normal, lognormal and power law. However, traditional understanding of geochemical distribution satisfying normal, lognormal or power-law models still faces a serious problem in adjusting theoretical statistics with the empirical distribution. Given that the differences among different geochemical distribution populations may have considerable effects on the target estimation, a new perspective from the singularity of fractal density is adopted to investigate mixed geochemical distribution patterns within frequency and space domains. In the framework of fractal geometry, ordinary density such as volume density (e.g., g/cm3 and kg/m3) described in Euclidean space can be considered as a special case of the fractal density (e.g., g/cm? and kg/m?). According to the nature of fractal density, geochemical information obtained from Euclidean geometry may not sufficiently reflect inherent geochemical features, because some information might be hidden within fractal geometry that can be only revealed by means of a set of fractional dimensions. In the present study, stream sediment geochemical data collected from west Tianshan region, Xinjiang (China), were used to explore element distribution patterns in the Earth’s crust based on a fractal density model. Four elements Cu, Zn, K and Na were selected to study the differences between minor and major elements in terms of their geochemical distribution patterns. The results strongly suggest that element distribution patterns can be well revealed and interpreted by means of a fractal density model and related statistical and multifractal parameters.
Abstract: Large peralkaline complexes are ‘factories’ that have produced a variety of ‘exotic’ minerals including high field strength element minerals. In most cases, these minerals are secondary and crystallise in a hydrothermal paragenesis that is extremely difficult to decipher due to the complexity of the textural relationships. The Strange Lake pluton is one of these complexes, and contains 37 exotic minerals, most of which are secondary. Adding to the difficulty in establishing a comprehensive paragenesis for these minerals and an alteration/precipitation path for the pluton is the fact that there were several stages of crystallisation of the same exotic and common secondary minerals, e.g., bastnäsite, fluocerite, gadolinite, aegirine, fluorite, and zircon. In this paper, we present a model, which describes a detailed path for the alteration and precipitation of minerals in the closed hydrothermal system of a peralkaline granitic pegmatite, based on direct measurements of the evolving composition of the aqueous fluid that exsolved from the late-stage magma crystallising rare-metal pegmatites in the Strange Lake pluton. The driving force for this evolution was cooling-induced oxidation that ultimately transformed the CH4-H2 gas in this fluid to CO2. This led to a large drop in the pH, which was a major control on the composition of the fluid and the crystallisation of secondary minerals. Although large numbers of minerals formed and were replaced during the different stages of fluid evolution, the changing chemistry of the fluid was largely a response to the alteration of four minerals, namely arfvedsonite, elpidite, narsarsukite and fluorite. The earliest stage of alteration, which took place at ~360?°C, was marked by the replacement of arfvedsonite by aegirine. This alteration decreased salinity and released K, Li, and Rb to the fluid, causing K-metasomatism. At ~300?°C, CH4 and higher hydrocarbons reacted to produce CO2. This caused a massive drop in pH from a value?>?10 to a value of ~3 and intense alteration, which included the dissolution of fluorite, the breakdown of elpidite to zircon and quartz and the replacement of narsarsukite by titanite. With ongoing dissolution of fluorite, Ca activity reached a level sufficient to promote the alteration of elpidite to armstrongite or gittinsite. This was accompanied by alteration of arfvedsonite to ferroceladonite and microcline to Al-phyllosilicates, enriching the fluid in Na, Fe and F. Soon after, there was a near total loss of CO2 (at ~230?°C). This loss was catastrophic and was focused along conical fractures (these developed as a result of the collapse of the roof of the pluton), with resultant fragmentation of the rocks along the fluid path. Alteration to phyllosilicates continued after the loss of CO2, as the system cooled to ~190?°C. This marked the beginning of the final stage of alteration, which involved the replacement of arfvedsonite by aegirine and hematite. It also coincided with large scale hematisation within the pluton. Finally, it led to the cementation of the fragments along the fluid path to form the fluorite-hematite ring breccia that is now evident at the margins of the pluton. The model of fluid evolution presented here is potentially applicable to many other peralkaline complexes. The only requirements are that the system was closed until a relatively late stage and that the exsolved fluid was saline and contained a reduced carbonic component. This is a feature of many peralkaline complexes, most notably, the Khibiny and Lovozero complexes in Russia, and Ilímaussaq in Greenland.
Abstract: Painstaking measurements of isotopes and their relative abundance in rocks have illuminated the hidden inner Earth and our planet’s origins and shadowy past for much of the preceding century.
Abstract: Drift prospecting has been utilized throughout the Slave Province in the Northwest Territories for decades, where glaciation and erosion within the past 10 000 years has produced the dispersion of minerals from their original host to till in their surrounding areas. This study is part of the greater Slave Province geophysical, surficial materials and permafrost study: a Northwest Territories Geological Survey (NTGS) led government-academic-industry research program. The purpose of this particular research is to assess kimberlite indicator minerals (KIMs) for any potential signature that may coincide with glacial dispersal trains through quantitative mineralogical and geochemical analysis. The NTGS has recently published data on Southern Slave Province surficial materials, which is useful as a comparative tool in the analysis of potential dispersal trains. Samples were collected from surficial sediment at various targets throughout the 75N and M NTS zones. Sample locations were chosen based on their down-ice position with respect to known kimberlites and gravity anomalies previously identified by the NTGS. Samples were preferentially collected from active and recently inactive frost boils. Overall, twenty-one 10 kg samples were collected and examined for KIMs. Several samples contain KIMs in moderate to high concentrations. Positive identifications of Cr-pyrope, chromite, Mg-ilmenite, and Cr-diopside have been confirmed in preliminary analysis. Of the identified KIMs garnet is the most abundant at 78 %, followed by chromite at 13 %, ilmenite at 8.9 %, and Cr-diopside at 0.5 %. Quantitative analyses are reported on confirmed KIMs: Cr-pyrope, Mg-ilmenite, Cr-diopside, chromite, and olivine for each sample site. The results of the analyses will be used to make further insights into till and kimberlite geochemistry of the Southern Slave Province.
Journal of Metamorphic Geology, doi.org.10.1111/ jmg.12484
Global
geochemistry
Abstract: This essay in honour of Mike Brown addresses aspects of chemical equilibrium and equilibration in rocks, with a focus on the role that chemical potentials play. Chemical equilibrium is achieved by diffusive flattening of chemical potential gradients. The idea of equilibration volume is developed, and the way equilibration volumes may evolve along a pressure-temperature path is discussed. The effect of the environment of an equilibration volume is key to understanding the evolution of the equilibration volume with changing conditions. The likely behaviour of equilibration volumes is used to suggest why preservation of equilibrium mineral assemblages and mineral compositions from metamorphism tends to occur. This line of logic then provides the conceptual support to conventional equilibrium thermodynamic approaches to studying rocks, using, for example, thermobarometry and pseudosections.
Abstract: Complex ice flow history, variable bedrock topography, landform types, and drift thickness may lead to complex glacial sediment dispersal patterns that are difficult to interpret, with implications for subglacial sediment provenance and related ice sheet research, as well as for mineral (drift) exploration. This study investigates the controls of bedrock topography, drift thickness, and landforms on 3D dispersal patterns in two study areas located southeast of Lac de Gras, Northwest Territories. The two areas are situated only about 25 km apart and have a similar ice flow history (clockwise shift from SW to NW). However, study area #1 hosts kimberlites within low topographic relief, while area #2 hosts kimberlites on a small granitic hill. The distribution and type of sediment-landform assemblages, as well as drift thickness, also differ between the two areas. Sediment characteristics, matrix geochemistry, and kimberlite indicator minerals (KIM) from surficial samples (n = 51) were analyzed and compared with a sample subset (n = 2000, from 250 boreholes) from a large RC drilling dataset donated by industry. Digital elevation models and a surficial geology map were also used. Results show contrasting patterns between the two areas, despite a similar ice flow record. Area #1 has a well-developed, yet fragmented 3D dispersal train consistent with the clockwise ice flow shift record. Area #2's dispersal patterns are less clearly-defined and appear unrelated or only weakly related to the known local source within the granitic hill. We find relationships between: 1) the strength of dispersal patterns and the bedrock topography in the kimberlitic source area; and, 2) the dispersal style and 3D shape within sediment-landform landsystems. These relationships have implications for drift prospecting survey design, as well as the interpretation of dispersal train patterns.
Abstract: Earth Scientists have two ways of examining and mapping the structure and composition of the subcontinental lithospheric mantle (SCLM): geophysical surveys, and studies of mantle samples from volcanic rocks or exposed terranes. Interpretation of both types of data requires an understanding of some basic strengths and limitations of each approach.
Abstract: Stable isotope (?18O, ?13C) analyses were performed on well preserved belemnites, oysters, and rhynchonellid brachiopods from the Middle to Upper Jurassic of the Morondava Basin in southern Madagascar. Both brachiopods and oysters indicate similar average temperatures of 18.7 to 19.3?°C in the Early Callovian, followed by a temperature decrease towards the Middle Oxfordian (13.9?°C) and a minimum in the Early Kimmeridgian (12.3?°C). In contrast, belemnites from the Oxfordian show lower average temperatures of 10.0?°C, which is likely caused by specific conditions for these organisms (e.g., different fractionation or life habits). Additionally, three oysters from the Upper Oxfordian and Lower Kimmeridgian were used for high-resolution stable isotope analyses. The data show seasonal fluctuations of >6?°C around averages between 14.4 and 14.7?°C. Latitudinal temperature gradients for the Callovian and Kimmeridgian are similar to today at the examined low latitudes of the southern hemisphere. The observed cooling of around 5?°C from the Callovian to the Oxfordian/Kimmeridgian can be attributed to a concurrent southward drift of Madagascar during the break-up of Gondwana. Thus, the study underlines the importance of considering palaeogeography in interpreting stable isotope data as well as the potential of detecting and timing palaeogeographic events by using stable isotope analyses.
www.minsocam.org/ MSA/Centennial/ MSA_Centennial _Symposium.html The next 100 years of mineral science, June 20-21, p. 30. Abstract
Global
geochemistry
Abstract: The key to answering many compelling and complex questions in Earth, planetary, and life science lies in breaking down the barriers between scientific fields and harnessing the integrated, multi-disciplinary power of their respective data resources. We have a unique opportunity to integrate large and rapidly expanding “big data” resources, to enlist powerful analytical and visualization methods, and to answer multi-disciplinary questions that cannot be addressed by one field alone. Recent years have seen a dramatic increase in the volume of mineralogical and geochemical data available for study. These large and expanding data resources have created an opportunity to characterize changes in near-surface mineralogy through deep time and to relate these findings to the geologic and biologic evolution of our planet over the past 4.5 billion years [1-3]. Using databases such as the RRUFF Project, the Mineral Evolution Database (MED), mindat, and EarthChem, we explore the spatial and temporal distribution of minerals on Earth’s surface while considering the multidimensional relationships between composition, oxidation state, structural complexity [4], and paragenetic mode. These studies, driven by advanced analytical and visualization techniques such as mineral ecology [5-6], network analysis [7], and affinity analysis, allow us to begin tackling big questions in Earth, planetary, and biosciences. These questions relate to understanding the relationships of mineral formation and preservation with large-scale geologic processes, such as Wilson cycles, the oxidation of Earth’s atmosphere, and changes in ocean chemistry. We can also investigate the abundance and likely species of as-yet undiscovered mineral, as well as estimate the probability of finding a mineral or mineral assemblage at any locality on Earth or another planetary body. Given the spatial and temporal distribution of minerals on Earth, which was heavily influenced by life, we can explore the possibility that Earth’s mineral diversity and distribution is a biosignature that can be used for future planetary evaluation and exploration. These geologic resources also facilitate integration across disciplines and allow us to explore ideas that one field alone cannot fully characterize, such as how the geochemical makeup of our planet affected the emergence and evolution of life, and, likewise, how life influenced chemical composition and geological processes throughout Earth history.
www.minsocam.org/ MSA/Centennial/ MSA_Centennial _Symposium.html The next 100 years of mineral science, June 20-21, p. 31. Abstract
Global
geochemistry
Abstract: The successful utilization of big data has direct implications for field-based and laboratory-based petrological and geochemical studies as well as ever-growing “data mining” studies. In considering the major advances in the fields of mineralogy, petrology, and geochemistry, it is important to recognize the various styles and sizes of data that have been available to geologists through time. The petrologic and geochemical fields span tremendous scales, and major milestones in understanding have been contributed to the field across these scales through time. Goldschmidt’s (1937) classification of the elements was largely based on the preference of different elements to form distinct minerals within meteorites and predated the vast majority of experimental data on elemental behavior and partitioning. Dana’s monumental contribution, the System of Mineralogy (Third Edition, 1850), was developed using available chemical, atomic, and symmetry data even before Xray diffraction had been invented. As mineral classification became systematically defined, with further aid from continued technological advances, mineral assemblages could be used for even higher-level classification. The concept of metamorphic facies was introduced by Eskola (1915, 1920), stemming out of a study that focused on Norwegian eclogites. Tuttle and Bowen (1958) employed experimental techniques in order to replicate natural phenomena in a more controlled, observable, and reproducible way: these experiments resulted in the ability to understand the phase relations in granites. These early contributions laid the groundwork for the basic understanding of how elements behave, how minerals form, and how mineral assemblages reflect formation conditions of rocks on Earth. With the increasing availability of more forms of geochemical and petrological data, the compilation of data and application of these datasets to complex questions has become more prevalent. Trace element compositions have contributed to the development of discrimination plots that allow for not only the classification of rock types but the interpretation of, for example, magma sources and amount of crustal contamination. The compilation of zircon age dates, after the advent and common use of the U-Pb geochronologic technique, has allowed for massive compilations of ages across the world and contributed to the development of our current understanding of the supercontinent cycle through Earth’s history. Currently, there are significant, publicly sourced and publicly available datasets (e.g., NAVDAT, EarthChem, Georoc, etc.) that contain information ranging from whole rock chemical analyses to age dates to isotopic analyses. With the ever-increasing amount of available data, we are able to address more complex questions and look deeper back into geologic history. One such complex question being addressed with big-data approaches is the geochemical footprint of the supercontinent Rodinia and potential driving factors behind its apparent distinct igneous geochemistry. Further, this case study emphasizes the challenge facing any geologist utilizing big-data, in understanding the source of data and the persistent challenge of preservational bias through the rock record.
Journal of Earth Science System, doi:10.1007/s12040- 019-1228-0
India
geochemistry
Abstract: The mafic dyke swarm, newer dolerite dykes (NDDs) intrudes the Archaean Singbhum granite of the Singhbhum craton, eastern India. The present investigation focuses on the petrography and geochemistry of 19 NNE-SSW to NE-SW trending NDDs in two sectors in the northern and south-western part of Bahalda town, Odisha, Singhbhum. Chondrite normalised rare earth element (REE) patterns show light REE (LREE) enrichment among majority of the 13 dykes while the remaining six dykes show a flat REE pattern. Critical analyses of some important trace element ratios like Ba/La, La/Sm, Nb/Y, Ba/Y, Sm/La, Th/La, La/Sm, Nb/Zr, Th/Zr, Hf/Sm, Ta/La and Gd/Yb indicate that the dolerite dykes originated from a heterogeneous spinel peridotite mantle source which was modified by fluids and melts in an arc/back arc setting. REE modelling of these dolerite dykes were attempted on LREE-enriched representative of NDD which shows that these dykes might have been generated by 5-25% partial melting of a modified spinel peridotite source which subsequently suffered around 30% fractional crystallisation of olivine, orthopyroxene and clinopyroxene. The reported age of ~2.75-2.8 Ma seems to be applicable for these dykes and this magmatism appears to be contemporaneous with major scale anorogenic granitic activity in the Singhbhum craton marking a major event of magmatic activity in eastern India.
Geochemistry: Exploration, Environment, Analysis, Vol. 19, pp. 414-430.
Canada, British Columbia
geochemistry
Abstract: Using Rock Canyon Creek REE-F-Ba deposit as an example, we demonstrate the need for verifying inherited geochemical data. Inherited La, Ce, Nd, and Sm data obtained by pressed pellet XRF, and La and Y data obtained by aqua regia digestion ICP-AES for 300 drill-core samples analysed in 2009 were compared to sample subsets reanalysed using lithium metaborate-tetraborate (LMB) fusion ICP-MS, Na2O2 fusion ICP-MS, and LMB fusion-XRF. We determine that LMB ICP-MS and Na2O2 ICP-MS accurately determined REE concentrations in SY-2 and SY-4, and provided precision within 10%. Fusion-XRF was precise for La and Nd at concentrations exceeding ten times the lower detection limit; however, accuracy was not established because REE concentrations in SY-4 were below the lower detection limit. Analysis of the sample subset revealed substantial discrepancies for Ce concentrations determined by pressed pellet XRF in comparison to other methods due to Ba interference. Samarium, present in lower concentrations than other REE compared, was underestimated by XRF methods relative to ICP-MS methods. This may be due to Sm concentrations approaching the lower detection limits of XRF methods, elemental interference, or inadequate background corrections. Aqua regia dissolution ICP-AES results, reporting for La and Y, are underestimated relative to other methods.
Geochemistry: Exploration, Environment, Analysis, http://doi.org/10.1144/ geochem2019-031 16p. Pdf
Canada, Nunavut, Australia
geochemistry
Abstract: Multi-element geochemical surveys of rocks, soils, stream/lake/floodplain sediments and regolith are typically carried out at continental, regional and local scales. The chemistry of these materials is defined by their primary mineral assemblages and their subsequent modification by comminution and weathering. Modern geochemical datasets represent a multi-dimensional geochemical space that can be studied using multivariate statistical methods from which patterns reflecting geochemical/geological processes are described (process discovery). These patterns form the basis from which probabilistic predictive maps are created (process validation). Processing geochemical survey data requires a systematic approach to effectively interpret the multi-dimensional data in a meaningful way. Problems that are typically associated with geochemical data include closure, missing values, censoring, merging, levelling different datasets and adequate spatial sample design. Recent developments in advanced multivariate analytics, geospatial analysis and mapping provide an effective framework to analyse and interpret geochemical datasets. Geochemical and geological processes can often be recognized through the use of data discovery procedures such as the application of principal component analysis. Classification and predictive procedures can be used to confirm lithological variability, alteration and mineralization. Geochemical survey data of lake/till sediments from Canada and of floodplain sediments from Australia show that predictive maps of bedrock and regolith processes can be generated. Upscaling a multivariate statistics-based prospectivity analysis for arc-related Cu-Au mineralization from a regional survey in the southern Thomson Orogen in Australia to the continental scale, reveals a number of regions with a similar (or stronger) multivariate response and hence potentially similar (or higher) mineral potential throughout Australia.
Abstract: A drastically altered chemistry was recently discovered in the Fe-O-H system under deep Earth conditions, involving the formation of iron superoxide (FeO2Hx with x?=?0 to 1), but the puzzling crystal chemistry of this system at high pressures is largely unknown. Here we present evidence that despite the high O/Fe ratio in FeO2Hx, iron remains in the ferrous, spin-paired and non-magnetic state at 60-133?GPa, while the presence of hydrogen has minimal effects on the valence of iron. The reduced iron is accompanied by oxidized oxygen due to oxygen-oxygen interactions. The valence of oxygen is not -2 as in all other major mantle minerals, instead it varies around -1. This result indicates that like iron, oxygen may have multiple valence states in our planet’s interior. Our study suggests a possible change in the chemical paradigm of how oxygen, iron, and hydrogen behave under deep Earth conditions.
Abstract:
Kimberlites are ultrabasic, Si-undersaturated, low Al, low Na rocks rich in CO2 and H2O. The distinctive geochemical character of kimberlite is strongly influenced by the nature of the local underlying lithospheric mantle. Despite this, incompatible trace element ratios and radiogenic isotope characteristics of kimberlites, filtered for the effects of crustal contamination and alteration, closely resemble rocks derived from the deeper, more primitive, convecting mantle. This suggests that the ultimate magma source is sub-lithospheric. Although the composition of primitive kimberlite melt remains unresolved, kimberlites are likely derived from the convecting mantle, with possible source regions ranging from just below the lithosphere, through the transition zone, to the core-mantle boundary.
Abstract: Zircon provides one of the best records of the formation and reworking of continental crust in the early Earth. However, Hadean to Eoarchean zircons are relatively scarce worldwide. Here we present the first report of relict Eoarchean magmatic zircons in granitic gneisses from the Sulu Orogen, eastern China. Based on internal structures, trace element contents, and U-Pb ages, we identified four groups of zircon domains with U-Pb ages of?~?3.7?Ga (Group I), ~2.1?Ga (Group II), ~790?Ma (Group III), and?~720?Ma (Group IV). Group I domains exhibit variable Th/U ratios, steep HREE patterns, and negative Eu anomalies. They yield lower intercept U-Pb ages of 1.82-1.95?Ga and discordia upper intercept ages of 3.65-3.69?Ga that are similar to the oldest concordant spot age of 3680?±?29?Ma. This indicates their growth from an Eoarchean magma and reworking during the Paleoproterozoic. The oldest Eoarchean domains with U-Pb ages of 3606?±?28 to 3680?±?29?Ma have low P contents of 216-563?ppm and high (Y?+?REE)/P molar ratios of 1.13-3.34, consistent with an igneous source. They show ?Hf(t) values of -2.8 to -0.9 at 3.67?Ga and TCHUR2 ages of 3.7-4.0?Ga, suggesting the growth of juvenile crust during the early Eoarchean. Group II to IV domains have consistent TDM2 ages of 2.6-3.0?Ga, suggesting that they grew during multiple reworkings of the Archean crust. Group II domains have variable Th/U ratios and steep to flattened HREE patterns that suggest growth during Paleoproterozoic crustal anatexis. Groups III and IV zircon domains have Th/U ratios and trace element contents that indicate growth from magmas that formed during Neoproterozoic continental rifting. In view of the unique feature of Neoproterozoic rifting magmatism in South China, the relict Eoarchean magmatic zircons would have originated in the Yangtze Craton and then undergone multiple phases of reworking during the Paleoproterozoic and Neoproterozoic. The results indicate the presence of?~3.7?Ga relict magmatic zircons in the Sulu Orogen, and they represent the oldest remnants of crustal material in the Yangtze Craton.
Abstract: Canada exhibits many of the challenges involved with exploring for coloured stones in countries with very low population densities, temperate-to-arctic climates and a lack of infrastructure hindering access to most prospective areas. Despite this, a number of discoveries have occurred, mainly during the past two decades. These include emeralds from Northwest Territories (1997) and Yukon (1998); sapphire (2002) and spinel (from 1982)—including cobalt-blue stones—from Baffin Island in Nunavut; and ruby and pink sapphire (2002) from British Columbia. Such discoveries can be assisted by undertaking scientific research into gem formation, as well as by applying exploration criteria developed elsewhere to uncharted territory. Future exploration in Canada and other countries facing similar challenges will likely benefit from additional geological studies to identify prospective areas and features; innovative means of transportation, such as boats instead of aircraft; drones for exploring rugged terrain; hyperspectral imaging for mineral sensing; surveying with UV lamps to identify minerals associated with gem mineralisation; and careful prospecting (including field mapping and collecting heavy mineral concentrates) by experienced individuals. Quaternary geology fieldwork was conducted at a reconnaissance-scale in the Kaskattama highland area to document the Quaternary stratigraphy and till composition. The diamond potential of this region was investigated using kimberlite-indicator-mineral (KIM) counts from till samples. Indicator mineral results are the focus of this report and are combined with ice-flow and till-clast-lithology data to provide a context to interpret provenance. Kimberlite-indicator minerals were recovered from glacial sediments (till) in the Kaskattama highland area and KIM counts are elevated relative to data from the surrounding area. The lowest KIM counts were from till with a high Hudson Bay Basin (carbonatedominated) and low undifferentiated greenstone and greywacke (UGG) provenance signature. The highest KIM counts are associated with till samples that have a relatively elevated UGG or elevated granitoid provenance signature. Till samples with relatively elevated UGG concentration have an interpreted east or southeast provenance, which is supported by ice-flow data and the recovery of distinct east-sourced erratics. Till samples with a relatively elevated granitoid clast concentration have a correlation with the southwest- trending Hayes streamlined-landform flowset. Considering the likely provenance for granitoid clasts is to the northwest, the presence of relatively high concentrations of granitoid clasts in the Hayes flowset could be indicative of a higher inheritance from previous ice-flow events or a palimpsest dispersal pattern. Interpretation of till-composition and ice-flow data has indicated there are likely multiple sources for the KIMs recovered during this study. Detailed work is recommended to clarify local-scale dispersal patterns.
Abstract: The Earth’s mantle is currently divided into the African and Pacific domains, separated by the circum-Pacific subduction girdle, and each domain features a large low shear-wave velocity province (LLSVP) in the lower mantle. However, it remains controversial as to whether the LLSVPs have been stationary through time or dynamic, changing in response to changes in global subduction geometry. Here we compile radiogenic isotope data on plume-induced basalts from ocean islands and oceanic plateaus above the two LLSVPs that show distinct lead, neodymium and strontium isotopic compositions for the two mantle domains. The African domain shows enrichment by subducted continental material during the assembly and breakup of the supercontinent Pangaea, whereas no such feature is found in the Pacific domain. This deep-mantle geochemical dichotomy reflects the different evolutionary histories of the two domains during the Rodinia and Pangaea supercontinent cycles and thus supports a dynamic relationship between plate tectonics and deep-mantle structures.
Abstract: Mid-oceanic ridge basalts (MORBs) are depleted in incompatible elements, but ridge segments far from mantle plumes frequently erupt chemically enriched MORBs (E-MORBs). Two major explanations of E-MORBs are that these basalts are generated by the melting of entrained recycled crust (pyroxenite) beneath ridges or by the melting of refertilized peridotites. These two hypotheses can be discriminated with compatible element abundances from Sc to Ge, here termed the ScGe elements. Here, we demonstrate that E-MORBs have systematically lower Ge/Si and Sc contents and slightly higher Fe/Mn and Nb/Ta ratios than depleted MORBs (D-MORBs) due to the mixing of low-degree pyroxenite melts. The Ge/Si ratio is a new tracer that effectively discriminates between melts derived from peridotite sources and melts derived from mixed pyroxenite-peridotite sources. These new data are used to estimate the distribution of pyroxenite in the mantle sources of global MORB segments.
Abstract: The Earth’s mantle is currently divided into the African and Pacific domains, separated by the circum-Pacific subduction girdle, and each domain features a large low shear-wave velocity province (LLSVP) in the lower mantle. However, it remains controversial as to whether the LLSVPs have been stationary through time or dynamic, changing in response to changes in global subduction geometry. Here we compile radiogenic isotope data on plume-induced basalts from ocean islands and oceanic plateaus above the two LLSVPs that show distinct lead, neodymium and strontium isotopic compositions for the two mantle domains. The African domain shows enrichment by subducted continental material during the assembly and breakup of the supercontinent Pangaea, whereas no such feature is found in the Pacific domain. This deep-mantle geochemical dichotomy reflects the different evolutionary histories of the two domains during the Rodinia and Pangaea supercontinent cycles and thus supports a dynamic relationship between plate tectonics and deep-mantle structures.
Features of radioactive element distribution within the Arkhangelsk diamondiferous province: possible directions for development of isotope-radiogeochemical methods for kimberlite prospecting in complex landscape geology and climate conditions of the suba
Geochemistry: Exploration, Environment, Analysis, Vol. 20, pp. 269-279. pdf
Bol. Mus. Nac. Hist. Paraguay, , Vol. 20, 2, pp. 188-204. pdf
South America, Paraguay
geochemistry
Abstract: After some works of Jaime Baez-Presse that quoted the presence of diamonds in Eastern Paraguay, we have perfprmed a whole sampling a study relative to the indicator mineral for diamonds. Indicator minerals are mineral species that, when appearing as transported grains in clastic sediments, indicate the presence in bedrock of a specific type of mineralization, hydrothermal alteration or lithology. Their physical and chemical characteristics, including a relatively high density (heavy minerals), facilitate their preservation and identification. The heavy minerals represent an important exploration method for detecting a variety of ore deposit types including diamond, gold, Ni-Cu, PGE, and so on.. One of the most significant events in the application of indicator mineral methods in the past was the diamond exploration. This paper provides an overview of indicator mineral methods, i.e. presence of Cr-diopside, Pyrope-rich garnet and Picroilmenite, for diamond exploration along the Eastern Paraguay river. Unfortunately the above heavy mineraks, generally associated to the diamonds, do not appear in Eastern Paraguay, excluding this Country as a potential source for the diamond as economic potential source.
Drift prospecting for kimberlite in the Slave geological Province: why your KIM-bearing sediment samples may not lead you to kimberlite.
Vancouver Kimberlite Cluster, Sept. 30, 1p. Abstract
Canada, Northwest territories
geochemistry
Abstract: Drift prospecting has been used for decades in the Slave Geological Province, NWT, to identify kimberlite indicator mineral and geochemical dispersals. These dispersals, in conjunction with geophysics and drilling, have led to many kimberlite discoveries. The sources of most well-defined dispersal patterns have been identified, and exploration must now focus on inauspicious regions where primary dispersal from kimberlite has been obscured by post-depositional changes to the landscape. Detailed surficial interpretations from readily available, high-resolution imagery and digital elevation data are a powerful asset when working in these challenging environments. Interpretations tailored to exploration provide the necessary context to unravel the complexities in the surficial geology and reconcile complex dispersal patterns. This presentation will demonstrate how the understanding and recognition of unique depositional environments and post-depositional modification of sediments can provide new insight into historical data, reduce the effort and resources required to collect new high-quality samples and inform data evaluations, ultimately providing lower-risk exploration targets.
Bol. Mus. Nac. Hist. Parag. *** ENG, Vol. 20, 2, pp. 188-204. pdf
South America, Paraguay
geochemistry
Abstract: After some works of Jaime Baez-Presse that quoted the presence of diamonds in Eastern Paraguay, we have perfprmed a whole sampling a study relative to the indicator mineral for diamonds. Indicator minerals are mineral species that, when appearing as transported grains in clastic sediments, indicate the presence in bedrock of a specific type of mineralization, hydrothermal alteration or lithology. Their physical and chemical characteristics, including a relatively high density (heavy minerals), facilitate their preservation and identification. The heavy minerals represent an important exploration method for detecting a variety of ore deposit types including diamond, gold, Ni-Cu, PGE, and so on.. One of the most significant events in the application of indicator mineral methods in the past was the diamond exploration. This paper provides an overview of indicator mineral methods, i.e. presence of Cr-diopside, Pyrope-rich garnet and Picroilmenite, for diamond exploration along the Eastern Paraguay river. Unfortunately the above heavy mineraks, generally associated to the diamonds, do not appear in Eastern Paraguay, excluding this Country as a potential source for the diamond as economic potential source.
Geochemistry, Vol. 80, doi.org/10.1016/ j.chemer. 2019.125594 40p. Pdf
Mantle
geochemistry
Abstract: We review some issues relevant to volatile element chemistry during accretion of the Earth with an emphasis on historical development of ideas during the past century and on issues we think are important. These ideas and issues include the following: (1) whether or not the Earth accreted hot and the geochemical evidence for high temperatures during its formation, (2) some chemical consequences of the Earth’s formation before dissipation of solar nebular gas, (3) the building blocks of the Earth, (4) the composition of the Earth and its lithophile volatility trend, (5) chemistry of silicate vapor and steam atmospheres during Earth’s formation, (6) vapor - melt partitioning and possible loss of volatile elements, (7) insights from hot rocky extrasolar planets. We include tabulated chemical kinetic data for high-temperature elementary reactions in silicate vapor and steam atmospheres. We finish with a summary of the known and unknown issues along with suggestions for future work.
Contributions to mineralogy and Petrology, Vol. 175, 27p. Pdf
Mantle
mineralogy, geochemistry
Abstract: The interplay between stress and chemical processes is a fundamental aspect of how rocks evolve, relevant for understanding fracturing due to metamorphic volume change, deformation by pressure solution and diffusion creep, and the effects of stress on mineral reactions in crust and mantle. There is no agreed microscale theory for how stress and chemistry interact, so here I review support from eight different types of the experiment for a relationship between stress and chemistry which is specific to individual interfaces: (chemical potential)?=?(Helmholtz free energy)?+?(normal stress at interface)?×?(molar volume). The experiments encompass temperatures from -100 to 1300 degrees C and pressures from 1 bar to 1.8 GPa. The equation applies to boundaries with fluid and to incoherent solid-solid boundaries. It is broadly in accord with experiments that describe the behaviours of free and stressed crystal faces next to solutions, that document flow laws for pressure solution and diffusion creep, that address polymorphic transformations under stress, and that investigate volume changes in solid-state reactions. The accord is not in all cases quantitative, but the equation is still used to assist the explanation. An implication is that the chemical potential varies depending on the interface, so there is no unique driving force for reaction in stressed systems. Instead, the overall evolution will be determined by combinations of reaction pathways and kinetic factors. The equation described here should be a foundation for grain-scale models, which are a prerequisite for predicting larger scale Earth behaviour when stress and chemical processes interact. It is relevant for all depths in the Earth from the uppermost crust (pressure solution in basin compaction, creep on faults), reactive fluid flow systems (serpentinisation), the deeper crust (orogenic metamorphism), the upper mantle (diffusion creep), the transition zone (phase changes in stressed subducting slabs) to the lower mantle and core mantle boundary (diffusion creep).
Abstract: Laser-induced breakdown spectroscopy (LIBS) is a simple, straightforward, and versatile form of atomic emission spectroscopy that focuses a rapidly-pulsed laser beam onto a sample to form a plasma containing its constituent elements and then uses spectral analysis of the emitted light to detect the elements present. In theory, LIBS is capable of qualitative, semi-quantitative, and quantitative analysis of all elements in the periodic table. LIBS can be performed in the laboratory or outside in the ambient environment for on-site analysis in situ; LIBS can also be used for rapid microscale compositional imaging. This review first presents a description of the LIBS technique and then discusses and illustrates through a historic literature review how LIBS has been used to analyze gases, natural waters, minerals, rocks, sediments, and soils. Given the persistent need of analytical instrumentation for the rapid chemical analysis of geologic materials in the field, and the capability of LIBS to analyze any type of sample in real time with little to no preparation, there is a vast potential for the routine application of LIBS across a broad spectrum of the geosciences that is as yet only minimally realized.
Abstract: Geochemical exploration has provided significant clues for mineral exploration and has helped discover many mineral deposits. Although various methods, including classic statistics, multivariate statistics, geostatistics, fractal/multifractal models, and machine learning algorithms, have been successfully employed to process geochemical exploration data, efficient interpretation and visualization of geochemical exploration data in support of the discovery of mineral deposits remain challenging. In this study, a workflow for intelligent interpretation and visualization of geochemical exploration data, defined as processing geochemical survey data with support of a geographical information system (GIS) and machine learning algorithms, was proposed. The effectiveness of the intelligent interpretation and visualization of geochemical exploration data supported by GIS and machine learning algorithms was demonstrated using a case study of processing a regional-scale geochemical survey dataset collected from Sichuan Province, China. Future research should add more advanced mathematical and statistical models, such as deep learning algorithms, into GIS to support the intelligent interpretation and visualization of geochemical exploration data.
Geostandards and Geoanalysis Research, doi.org/10.1111/GGR.12419 34p. Pdf
Australia
geochemistry
Abstract: To promote a more efficient and transparent geochemistry data ecosystem, a consortium of Australian university research laboratories called the AuScope Geochemistry Network (AGN) assembled to build a collaborative platform for the express purpose of preserving, disseminating, and collating geochronology and isotopic data. In partnership with geoscience-data-solutions company Lithodat Pty Ltd, the open, cloud-based AusGeochem platform (https://ausgeochem.auscope.org.au) was developed to simultaneously serve as a geosample registry, a geochemical data repository, and a data analysis tool. Informed by method-specific groups of geochemistry experts and established international data reporting practices, community-agreed database schemas were developed for rock and mineral geosample metadata and secondary ion mass spectrometry U-Pb analysis, with additional models for laser ablation inductively-coupled mass spectrometry U-Pb and Lu-Hf, Ar-Ar, fission-track and (U-Th-Sm)/He under development. Collectively, the AusGeochem platform provides the geochemistry community with a new, dynamic resource to help facilitate FAIR (Findable, Accessible, Interoperable, Reusable) data management, streamline data dissemination and advanced quantitative investigations of Earth system processes. By systematically archiving detailed geochemical (meta-)data in structured schemas, intractably large datasets comprising thousands of analyses produced by numerous laboratories can be readily interrogated in novel and powerful ways. These include rapid derivation of inter-data relationships, facilitating on-the-fly data compilation, analysis, and visualisation.
Abstract: This paper provides a summary of traditional, current, and developing exploration techniques using indicator minerals derived from glacial sediments, with a focus on Canadian case studies. The 0.25 to 2.0 mm fraction of heavy mineral concentrates (HMC) from surficial sediments is typically used for indicator mineral surveys, with the finer (0.25-0.50 mm) fraction used as the default grain size for heavy mineral concentrate studies due to the ease of concentration and separation and subsequent mineralogical identification. Similarly, commonly used indicator minerals (e.g., Kimberlite Indicator Minerals—KIMs) are well known because of ease of optical identification and their ability to survive glacial transport. Herein, we review the last 15 years of the rapidly growing application of Automated Mineralogy (e.g., MLA, QEMSCAN, TIMA, etc) to indicator mineral studies of several ore deposit types, including Ni-Cu-PGE, Volcanogenic Massive Sulfides, and a variety of porphyry systems and glacial sediments down ice of these deposits. These studies have expanded the indicator mineral species that can be applied to mineral exploration and decreased the size of the grains examined down to ~10 microns. Chemical and isotopic fertility indexes developed for bedrock can now be applied to indicator mineral grains in glacial sediments and these methods will influence the next generation of indicator mineral studies.
