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The Sheahan Diamond Literature Reference Compilation - Technical Articles based on Major Region - Lesotho
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 Region 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 addition most references have been tagged with one or more region words. In an effort to make it easier for users to track down articles related to a specific region, KRO has extracted these region words and developed a list of major region words presented in the Major Region Index to which individual region words used in the article reference have been assigned. Each individual Region Report contains in chronological order all the references with a region word associated with the Major Region word. Depending on the total for each reference type - technical, media and corporate - the references will be either in their own technical, media or corporate Region Report, or combined in a single report. Where there is a significant number of technical references there will be a technical report dedicated to the technical articles while the media and corporate references are combined in a separate region report. References that were added in the most recent monthly update are highlighted in yellow within the Region Report. The Major Region words have been defined by a scale system of "general", "continent", "country", "state or province" and "regional". Major Region words at the smaller scales have been created only when there are enough references to make isolating them worthwhile. References not tagged with a Region are excluded, and articles with a region word not matched with a Major Region show up in the "Unknown" report.
Kimberlite - diamondiferous
Lamproite - diamondiferous
Lamprophyre - diamondiferous
Other - diamondiferous
Kimberlite - non diamondiferous
Lamproite - non diamondiferous
Lamprophyre - non diamondiferous
Other - non diamondiferous
Kimberlite - unknown
Lamproite - unknown
Lamprophyre - unknown
Other - unknown
Future Mine
Current Mine
Former Mine
Click on icon for details about each occurrence. Works best with Google Chrome.
CITATION: Faure, S, 2010, World Kimberlites CONSOREM Database (Version 3), Consortium de Recherche en Exploration Minérale CONSOREM, Université du Québec à Montréal, Numerical Database on consorem.ca. NOTE: This publicly available database results of a compilation of other public databases, scientific and governmental publications and maps, and various data from exploration companies reports or Web sites, If you notice errors, have additional kimberlite localizations that should be included in this database, or have any comments and suggestions, please contact the author specifying the ID of the kimberlite: [email protected]
Uplift, Faulting, Seismicity, Thermal Spring and Possible Incipient Volcanic Activity in the Lesotho-natal Region, Southeast Africa: the Quathlamba hotspot Hyopthesis.
Speculations concerning the importance of metasomatic melt migration In the formation of pyroxenite sheets in garnet peridotite xenoliths from MatsokuLes
Proceedings of the Fourth International Kimberlite Conference, Held Perth, Australia, No. 16, pp. 184-186
Hopp, J., Trieloff, M., Brey, G.P., Woodland, A.B., Simon, N.S.C., Wijbrans, J.R., Siebel, W., Reitter, E.
40 Ar 39 Ar ages of phlogopite in mantle xenoliths from South African kimberlites: evidence for metasomatic mantle impregnation during Kilbaran orogenic cycle.
Galloway, M., Nowicki, T., Van Coller, B., Mukodzani, B., Siemens, K., Hetman, C., Webb, K., Gurney, J.
Constraining kimberlite geology through integration of geophysical, geological and geochemical methods: a case study of the Mothae kimberlite, northern Lesotho.
Mitchell, R.H., Scott Smith, B.H., Skinner, E.M.W.
Mineralogy of magmaclasts and interclast matrices of Kimberley-type pyroclastic kimberlites from the Kao, Letseng-La-Terae, Lethlakane and Premier kimberlite pipes of southern Africa.
10th. International Kimberlite Conference Held Bangalore India Feb. 6-11, Poster abstract
Contrasting garnet lherzolite xenoliths suites from the Letseng kimberlite pipes: inferences for the northern Lesotho geotherm.
Proceedings of the 10th. International Kimberlite Conference, Vol. 1, Special Issue of the Journal of the Geological Society of India,, Vol. 1, pp. 29-44.
Gem Diamonds the owner of the highest average dollar-per-carat kimberlite diamond mine in the world continues to defy expectations with its exceptionally large and high-value stones from Botswan and Lesotho.
Sommer, H., Wan,Y., Kroner, A., Xie, H., Jacob, D.E.
Shrimp zircon ages and petrology of lower crustal granulite xenoliths from the Letseng-La-Terae kimberlite, Lesotho: further evidence for a Namaquanatal connection.
South Africa Journal of Geology, Vol. 116, 2, pp. 183-198.
MSA Group for Paragon Diamonds, April, 17p. Available pdf
Africa, Lesotho
Microdiamonds - responses
Abstract: The Motete Dyke is a diamondiferous kimberlite situated in the mountains of Lesotho. Total liberation diamond recovery methods were used to analyse representative samples from localities along the 1 500 m outcrop length of the dyke for grade modeling purposes. The microdiamond grade and stone density is remarkably consistent throughout the exposed area of the dyke. A grade of some 60 cpht at +1.18 mm and 90 cpht at +0.85 mm is estimated for the dyke at surface. In order to extend the estimate to deeper levels it will be necessary to drill into the dyke to obtain more sampling material for total liberation analysis. Initial tonnage calculations indicate that the dyke contains an estimated 525 000 carats at +0.85 mm with an additional 50 000 carats in every additional 10 m depth below 2450 m elevation, assuming an average dyke width of 1.44 m and density of 2.57 tons/m3. Bulk sampling of the dyke is recommended to recover a parcel of diamonds for valuation and to confirm the diamond size frequency and content model.
Abstract: Garnets from kimberlite-hosted mantle and a few xenoliths from the lower crust were investigated for water, major, minor, and trace elements. Xenoliths from the mantle comprise pyroxenite, eclogite, alkremite, and peridotite, and crustal xenoliths are mafic high-pressure granulites. Samples from South Africa, Lesotho, and Namibia comprise two principal settings, Kaapvaal Craton (‘on craton’) and Rehoboth terrane (‘off craton’). The composition of garnet depends on rock type but is unrelated to the setting, except for Ti and Cr. In garnets from ‘off craton’ mantle xenoliths, Ti positively correlates with Cr whereas those from ‘on craton’ samples reveal a negative correlation between both elements. Rare earth element patterns indicative of a metasomatic overprint are observed in garnets from both settings, especially in eclogitic garnet. Water contents in garnet are low and range from <1 to about 40 ppm. No setting-related difference occurs, but a weak correlation between water and rock type exists. Water contents in garnets from eclogite and mafic granulite are lower than those in pyroxenite, alkremite, and peridotite. All garnets are water under-saturated, i.e. they do not contain the maximum amount of water that can be accommodated in the mineral structure. Cratonic and non-cratonic samples also show the same characteristics in the infrared (IR) absorption spectra. An absorption band at 3650 cm-1 is typical for most mantle garnets. Bands at 3520 and 3570 cm-1 are present only in TiO2-rich garnets from the Rehoboth terrane and are ascribed to a Ti-related hydrogen substitution. A number of garnets, especially from the Kaapvaal Craton, contain molecular water in addition to structural water. Molecular water is inhomogeneously distributed at grain scale pointing to local interaction with fluid and to disequilibrium at grain scale. These garnets consistently reveal either submicroscopic hydrous phases or additional IR bands at 3630 and 3610-3600 cm-1 caused by structural water. Both features do not occur in garnets in which molecular water is absent. The observations imply (i) relatively late introduction of fluid, at least in cases where hydrous phases formed, and (ii) a relatively dry environment because only water-deficient garnets are able to incorporate additional structural water. Most importantly, they imply (iii) that the low water contents are primary and not due to water loss during upward transport. This late water influx is not responsible for the metasomatic overprint indicated by garnet REE patterns. The results of this study suggest dry conditions in the lithosphere, including mantle and crustal sections of both the Kaapvaal Craton (‘on craton’) and the Rehoboth terrane (‘off craton’). If the low water contents contributed to the stabilization of the Kaapvaal cratonic root (Peslier et al., 2010) the same should apply to the Rehoboth lithosphere where the same variety of rock types occurs. The extremely low water contents in eclogite relative to pyroxenite may be explained by an oceanic crust origin of the eclogites. Subduction and partial melting would cause depletion of water and incompatible elements. The pyroxenites formed by crystal accumulation in the mantle and did not suffer melt depletion. Such a difference in origin can be reconciled with the low Ti contents in eclogitic garnet and the high Ti contents in pyroxenitic garnet.
The 4th Colloquium on Diamonds - source to use held Gabarone March 1-3, 2010, 14p.
Africa, Lesotho
Deposit - Letseng
Abstract: Bateman Engineering managed the establishment of a second diamond treatment plant at the Letseng Mine in the Mokhotlong District of northern Lesotho, about 100 km from the town of Buthe Buthe. Letseng Diamonds Proprietary Limited, is owned 70 % by Gem Diamonds and 30 % by the Government of the Kingdom of Lesotho. The second plant, which commenced construction in late 2006, doubled Letseng Mines' hard rock processing capacity from 2.6 million t/yr to 5.2 million t/yr, making it the worlds' seventh largest diamond mine by throughput. Bateman Engineering provided the engineering design, procurement and construction management of the new plant.
Abstract: Uneconomical two decades ago, the Letseng diamond mine in Lesotho is today a major source of 50-carat-plus Type IIa diamonds. It is also the lowest-yielding diamond mine in the world, averaging about 1.5 carats of diamonds per hundred tons of ore against an industry average of one carat per ton. First opened in 1975, the previous operators of the mine (Rio Tinto and De Beers) struggled to maintain its operation because very large diamonds were mixed in with its very low production. The mine closed in 1982 after seven years of loss-making operation. In the 2000’s, three changes profoundly affected the diamond industry: 1. The price of large diamonds appreciated very strongly compared to more commercial sizes and qualities, 2. Improvements in ore processing technology that reduces potential damage or outright destruction of large crystals, and 3. Improvements in X-Ray technology that enhances the ability to identify low fluorescence, Type IIa and fancy color diamonds. This technology also allows for identification of very large diamonds in kimberlite before primary crushing. Letseng reopened in 2006 and has been operating at a profit despite its very low yield and relatively low volume, of about 100,000 carats yearly. The company continues to upgrade its technology which resulted in the recovery of 90 diamonds larger than 50 carats last year. Letseng also serves as a model for other small “boutique” mines such as Kerowe, the Botswana operation which yielded the 1109 ct Lesedi la Rona diamond in 2015 and the Lulo concession in Angola which have come on line recently.
Abstract: The Letšeng Diamond Mine comprises two adjacent kimberlites, the Main and Satellite pipes. Very low grade and low frequency of high value stones preclude use of standard evaluation methods, increasing the need for high confidence geology models. New results of drillcore investigations, including core logging, country rock dilution measurements, indicator mineral abundances and petrography are integrated with open pit mapping and macrodiamond production data to present updated 3D geological models of the Main and Satellite pipes. Letšeng was emplaced ~90 Ma and forms part of a Cretaceous kimberlite province extending across southern Africa. The Letšeng bodies are steep-sided volcanic pipes that are infilled with multiple asymmetric phases of kimberlite separated by near-vertical, sharp, cross-cutting internal contacts. There are associated marginal carbonate-cemented country-rock breccias and sub-vertical kimberlite dykes that can occur within a zone of well-developed carbonate veining adjacent to the pipes. The pipe infills are dominated by kimberlite closely resembling Kimberley-type pyroclastic kimberlite (KPK; formerly tuffisitic kimberlite; Scott Smith et al. 2013) that contains common large megaxenoliths of massive and brecciated country rock basalt. Other textural varieties include hypabyssal kimberlite (HK), transitional HK-KPK and resedimented volcaniclastic kimberlite (RVK). Each phase of kimberlite represents a separate magmatic system. In each KPK there is a continuum of crystallization from the magmaclast selvages to the intermagmaclast matrix. As documented elsewhere, the HK-KPK transition involves an increasing (i) degree of deuteric replacement of olivine, (ii) amount of incorporated country rock xenoliths and (iii) textural modification of the magma prior to solidification subsurface within the diatreme. These conclusions negate some other proposed modes of emplacement.
South African Institute of Mining and Metallurgy, Vol. 116, 8, pp. 723-731.
Africa, Lesotho
deposit - Letseng
Abstract: The steepening of slope angles on an open pit mining operation has a material impact on improving the economics of mining. Steepening of slope angles can also increase the risk of slope failure. Slope failures are inherently costly events, because they can be catastrophic, resulting in multiple fatalities, equipment damage, and temporary or permanent closure of a mine. The steepening of the basalt slope angles at Letseng Diamond Mine followed operational improvements that were introduced through improved blasting practices and geotechnical controls. The steeper slope design resulted in a 6 Mt/a reduction in the peak waste mining compared with the previous mine plan coupled with an increase in the net present value and life of mine. This paper is an outline of the steps that were taken at Letseng to increase slope angles in waste and the resulting improvements to the mine plan.
Mineralogy and Petrology, doi.org/10.1007/s00710-018-0624-5 12p.
Africa, Lesotho
deposit - Liqhobong
Abstract: The Cretaceous Liqhobong kimberlite cluster comprises at least six known diamondiferous Group 1 kimberlite bodies; namely the circular Main Pipe (8.5 ha), ovoid Satellite Pipe (1.6 ha), Discovery Blow (0.15 ha), Blow (0.1 ha), the Main Dike adjoining the blows and pipes, and one other recently exposed dike. The kimberlites intrude Jurassic Drakensberg lavas and outcrop at ~2650 masl in rugged Maluti Mountain terrain, and are emplaced along a strike of about 2.5km. The cluster represents at least three episodes of structurally controlled kimberlite intrusion; the first which comprised the dike(s?) and the two blows (the blows being dike enlargements emplaced 1km apart) and later the two separate emplacements of the Main and Satellite Pipes.
Contributions to Mineralogy and Petrology, Vol. 173, pp. 76- doi.org/10.1007/ s00410-018-1502-1
Africa, Lesotho
deposit - Letseng
Abstract: The Letšeng-la-Terae kimberlite (Lesotho), famous for its large high-value diamonds, has five distinct phases that are mined in a Main and a Satellite pipe. These diatreme phases are heavily altered but parts of a directly adjacent kimberlite blow are exceptionally fresh. The blow groundmass consists of preserved primary olivine with Fo86?88, chromite, magnesio-ulvöspinel and magnetite, perovskite, monticellite, occasional Sr-rich carbonate, phlogopite, apatite, calcite and serpentine. The bulk composition of the groundmass, extracted by micro-drilling, yields 24-26 wt% SiO2, 20-21 wt% MgO, 16-19 wt% CaO and 1.9-2.1 wt% K2O, the latter being retained in phlogopite. Without a proper mineral host, groundmass Na2O is only 0.09-0.16 wt%. However, Na-rich K-richterite observed in orthopyroxene coronae allows to reconstruct a parent melt Na2O content of 3.5-5 wt%, an amount similar to that of highly undersaturated primitive ocean island basanites. The groundmass contains 10-12 wt% CO2, H2O is estimated to 4-5 wt%, but volatiles and alkalis were considerably reduced by degassing. Mg# of 77.9 and 530 ppm Ni are in equilibrium with olivine phenocrysts, characterize the parent melt and are not due to olivine fractionation. 87Sr/86Sr(i)?=?0.703602-0.703656, 143Nd/144Nd(i)?=?0.512660 and 176Hf/177Hf(i)?=?0.282677-0.282679 indicate that the Letšeng kimberlite originates from the convective upper mantle. U-Pb dating of groundmass perovskite reveals an emplacement age of 85.5?±?0.3 (2?) Ma, which is significantly younger than previously proposed for the Letšeng kimberlite.
The Journal of the Southern African Institute of Mining and Metallurgy, Vol. 199, pp. 613-620.
Africa, Lesotho
deposit - Liqhobong
Abstract: Liqhobong Mining Development Company (LMDC) has been experiencing problems with boulders after blasting where the fragment sizes exceed the maximum of 800 mm as per mine standard. As a result, the mine has employed various methods to improve the fragmentation. The goal is to produce a run-of-mine (ROM) feed that does not choke the crusher and cause delays in production. In order to achieve this goal, fragmentation distribution within the fines and coarse envelope must be optimized through effective planning of blasting activities and accurate execution. The mine determined the fines-coarse envelope within which the entire crushing system can handle fragments using Split Desktop software. It is expected that both the predicted and actual fragmentation curves lie within that envelope for optimal fragmentation. The Kuz-Ram model with blast design parameters of 2.6 m for burden, 2.8 m for spacing, and 127 mm hole diameter was used to predict the fragmentation. The results show that the blast design parameters may need altering to achieve optimum fragmentation. Furthermore, the execution of the drilling and blasting may be the cause of the fragmentation problems. The mean fragmentation size (X50) differs greatly, unlike the uniformity index (n)s values which are relatively close to each other (0.6 to 2.2). The mean squared error (MSE) values have a large range. A proposed solution is a modified burden, spacing, and hole diameter. It is concluded that blast design parameters need to be reviewed in order to obtain correct predictions.
Contributions to Mineralogy and Petrology, Vol. 175, 9p. Pdf
Africa, Lesotho
olivine
Abstract: This paper highlights published and new field and petrographic observations for late-stage (crustal level) deformation associated with the emplacement of kimberlites and other mantle-derived magmas. Thus, radial and tangential joint sets in the competent 183 Ma Karoo basalt wall rocks to the 5 ha. Lemphane kimberlite blow in northern Lesotho have been ascribed to stresses linked to eruption of the kimberlite magma. Further examples of emplacement-related stresses in kimberlites are brittle fractures and close-spaced parallel shears which disrupt olivine macrocrysts. In each of these examples, there is no evidence of post-kimberlite regional tectonism which might explain these features, indicating that they reflect auto-deformation in the kimberlite during or immediately post-emplacement. On a microscopic scale, these inferred late-stage stresses are reflected by fractures and domains of undulose extinction which traverse core and margins of some euhedral and anhedral olivines in kimberlites and olivine melilitites. Undulose extinction and kink bands have also been documented in olivines in cumulates from layered igneous intrusions. Our observations thus indicate that these deformation features can form at shallow levels (crustal pressures), which is supported by experimental evidence. Undulose extinction and kink bands have previously been presented as conclusive evidence for a mantle provenance of the olivines—i.e. that they are xenocrysts. The observation that these deformation textures can form in both mantle and crustal environments implies that they do not provide reliable constraints on the provenance of the olivines. An understanding of the processes responsible for crustal deformation of kimberlites could potentially refine our understanding of kimberlite emplacement processes.
Abstract: By virtue of their exceptionally deep origin and unique geological histories, diamonds have been found to contain a variety of minerals that are otherwise rare or absent at Earth’s surface. During examination of a type IIa diamond sample from the Letseng mine, Lesotho, a new nickel sulfide mineral was found as part of a fine-grained multiphase inclusion. This nickel sulfide is the natural analogue of the synthetic nickel monosulfide known as ?-NiS, with a NiAs-type structure. This new mineral has been named crowningshieldite, after G.R. Crowningshield (1919 - 2006), whose many years of innovation at the Gemological Institute of America produced countless advances in the understanding and identification of natural, treated and synthetic diamonds and other gem materials. Crowningshieldite is the high-temperature polymorph of millerite, with an inversion temperature of 379 °C from previous experiments on pure NiS. The observed sample of crowningshieldite has an empirical formula of (Ni0.90Fe0.10)S. The host diamond is gemmy, colorless, and relatively pure (type IIa, containing less than ~5 ppm nitrogen). It belongs to a variety of sublithospheric/superdeep diamonds named CLIPPIR diamonds that are notable for their metallic Fe-Ni-C-S melt inclusions. In this case, the inclusion is interpreted to be an alteration assemblage produced when a primary metallic Fe-Ni-C-S inclusion with a surface-reaching fracture reacted with hot fluids, likely associated with kimberlite emplacement. Other phases identified in association with crowningshieldite in this fine-grained alteration assemblage are magnetite-magnesioferrite, hematite, and graphite. Unexposed inclusions within the same diamond are of original, unaltered Fe-Ni-C-S composition. The new mineral crowningshieldite is a good example of the complexity and breadth of geological processes recorded within diamonds and their inclusions.
The Journal of the Southern African Insitute of Mining and Metallurgy, Vol. 119, Feb, 9p. Pdf
Africa, South Africa, Zimbabwe, Namibia, Angola, DRC, Lesotho, Botswana, eSwatini
production
Abstract: Southern Africa is generally thought to be well explored, with only limited potential for major new diamond discoveries. However, Chiadzwa in Zimbabwe and reports of a significant new kimberlite find in Angola are testimony to the dangers attached to an attitude that 'there is nothing left to find'.
Since the major discoveries in the central interior of South Africa in the 1870s, diamond exploration in the region has been led by market and political factors that influence the key exploration drivers of opportunity and value proposition. Unexpected new discoveries by new players always impact on existing producers and, from time to time, denial of opportunity through political or protectionist policies has inhibited investment in exploration. Entrepreneurial exploration appetite in southern Africa will be tempered by the potential value equation and security of investment. Overlaid on this, developments in diamond recovery technologies provide opportunity to reinvigorate current mines and old prospects previously considered too difficult or costly to exploit. Position on the cost curve will remain a key factor for survival in an increasingly competitive environment.
Abstract: Crowningshieldite is the natural analog of the synthetic compound ?-NiS. It has a NiAs-type structure and is the high-temperature polymorph relative to millerite (?-NiS), with an inversion temperature of 379 °C. Crowningshieldite is hexagonal, space group P63/mmc, with a = 3.44(1) Å, c = 5.36(1) Å, V = 55.0(2) Å3, and Z = 2. It has an empirical formula (Ni0.90Fe0.10)S and dcalc = 5.47(1) g/cm3. The five strongest lines in the powder X-ray diffraction data are [dmeas in angstroms (I) (hkl)]: 1.992 (100) (102), 1.718 (55) (110), 2.978 (53) (100), 2.608 (35) (101), and 1.304 (17) (202). Crowningshieldite was found as part of a multiphase inclusion in a gem-quality, colorless, type IIa (containing less than ~5 ppm N) diamond from the Letseng mine, Lesotho. The inclusion contains crowningshieldite along with magnetite-magnesioferrite, hematite, and graphite. A fracture was observed that extended from the inclusion to the diamond exterior, meaning that fluids, possibly kimberlite-related, could have penetrated into this fracture and altered the inclusion. Originally, the inclusion might have been a more reduced, metallic Fe-Ni-C-S mixture made up of cohenite, Fe-Ni alloy, and pyrrhotite, akin to the other fracture-free, pristine inclusions within the same diamond. Such metallic Fe-Ni-C-S primary inclusions are a notable recurring feature of similar type IIa diamonds from Letseng and elsewhere that have been shown to originate from the sublithospheric mantle. The discovery of crowningshieldite confirms that the ?-NiS polymorph occurs in nature. In this case, the reason for its preservation is unclear, but the relatively iron-rich composition [Fe/(Fe+Ni) = 0.1] or the confining pressure of the diamond host are potential factors impeding its transformation to millerite. The new mineral name honors G. Robert Crowningshield (1919-2006) (IMA2018-072).
Geochemistry, Geophysics, Geosystems, 10.1029/2021GC009691 55p. Pdf
Africa, South Africa, Lesotho, Europe, Greenland
craton
Abstract: Understanding the rate at which temperature changes with increasing depth (geothermal gradients) within ancient continental crust and its underlying mantle (cratonic lithosphere) is essential for understanding the internal structure of Earth. However, understanding geothermal gradients requires a chemical and physical understanding of deep cratonic lithosphere (up to ?200 km depth) and samples from such depths are only available as fragments hosted in melts that originate there (e.g., kimberlites). This limited sample availability of the cratonic mantle roots has resulted in some properties of this domain, used in geothermal modeling, to be poorly constrained. Here we use samples of cratonic mantle lithosphere to determine one critical and poorly constrained parameter used in modeling geothermal gradients—the heat produced from the radiogenic decay of K, U, and Th to their daughter isotopes. We measure these elements in the samples via in situ laser ablation methods to quantify their potential heat production. Comparing our results to previous estimates of heat production, our new estimates produce differences in the thicknesses of cratonic lithosphere calculated from modeled geothermal gradients by >10 km depending on the chosen lithological model. The results from this study provide an important new data set for constraining heat production in cratonic mantle peridotites.
Abstract: In this series of New Mineral Names, a thematic approach is used to help provide context for advances and discoveries in mineralogy. Planet Earth is ever-changing, and unique crystals are found in the tiniest of micro-geologic niches. With emerging analytical techniques, the formerly inaccessible becomes accessible. New minerals inspire creative approaches to overcoming chemical and technological challenges and can reveal what the Earth was like billions of years ago. In this issue, we look at recently described minerals that are associated with diamonds, dumps, and fumaroles: crowningshieldite, goldschmidtite, breyite, cardite, grimmite, hrabákite, freitalite, dioskouriite, dobrovolskyite, ferroefremovite, and vasilseverginite.
Abstract: Large, high-quality type IIa diamonds such as the Cullinan and the Koh-i-Noor are among the most elusive of mined gem diamonds. These are called CLIPPIR diamonds, an acronym reflecting the distinguishing physical characteristics of this variety of diamonds (Cullinan-like, Large, Inclusion Poor, Pure, Irregular, Resorbed) [1]. There is currently no reliable method to predict the occurrence of CLIPPIR diamonds in a deposit, which remains a hurdle for exploration and mining [2]. Mineral inclusions reveal that these are sublithospheric diamonds [1], which explains why their occurrence is effectively independent from more common eclogitic and peridotitic lithospheric diamonds and their associated indicator minerals. More recently, an analysis of iron isotopes in the metallic inclusions sometimes found in CLIPPIR diamonds has provided additional insight into their formation, which may provide clues for exploration. Three measurements of metallic Fe-Ni-C-S inclusions from two diamonds from the Letseng mine, Lesotho reveal remarkably heavy iron isotopic compositions, ?56Fe = 0.79-0.90‰ [3]. These measurements lie far outside the range of known mantle compositions (near 0‰) or expected reaction products at depth. Instead, the heavy signature is ascribed to subducted iron sourced from magnetite and/or Fe-Ni alloys precipitated during seafloor serpentinization of oceanic peridotite. These metallic inclusions provide physical evidence that traces serpentinite subduction into the mantle transition zone. This finding is a step toward a genetic model for CLIPPIR diamonds. Their formation requires input from deeply subducted serpentinized peridotite. Furthermore, this input may come specifically from cold subducting slabs, whose serpentinized mantle portions can bypass the shallow sub-arc dehydration activity and instead transport serpentinite-derived components such as hydrous minerals and iron-rich phases to the transition zone/uppermost lower mantle [4]. The results suggest that geochemical signatures related to deeply subducted serpentinites may eventually provide a basis for targeting CLIPPIR diamonds in volcanic deposits at surface.