Hello Guest User, You are visiting this website from a computer with an IP address of 172.71.254.42 with the name of '?' since Wed Apr 24, 2024 at 12:44:31 PM PT for approx. 0 minutes now.
The Sheahan Diamond Literature Reference Compilation - Scientific and Media Articles based on Major Keyword - Microdiamonds
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.
Microdiamonds are diamonds that fall through a 0.85 mm sieve with anything larger described as a macrodiamond. The prevailing theory is that the formation of a diamond population follows a lognormal size frequency distribution which means that for any unit of rock there are going to be a lot more very small diamonds than big diamonds. But only "macrodiamonds" have commercial value in the jewelry sector, which is why historically the evaluation of a kimberlite for diamond grade required testing of large samples through dense media separation that recovered only stones bigger than 0.85 mm. Prior to the nineties the standard exploration strategy upon discovering a kimberlite was to analyze the chemistry of the kimberlite's minerals and compare it to a database De Beers developed during the 20th century by extracting inclusions from diamonds. Under this approach De Beers cataloged the chemistry of all the minerals found in a kimberlite as well as the diamond content established through bulk sampling. Over time it became apparent that garnets with certain chemical composition ranges recovered as diamond inclusions tended not to exist in barren kimberlites. The theory emerged that such minerals, of which pyrope garnets of the G10/G9 variety were the most diagnostic group, grew only in the same pressure-temperature regime in which diamonds formed. Because these minerals were far more abundant than diamonds it became cost effective to assess the diamond indicator mineral chemistry of a kimberlite before incurring the expense of testing for actual diamond content. The wisdom of this approach was called into question after Ashton discovered the Argyle pipe in Australia which had an unusually high macro grade of about 500 cpht. The problem it posed was that it was a lamproite whose minerals had a chemistry very different from that of the kimberlites derived from the peridotitic kimberlites that dominated the De Beers database. The Orapa pipe in Botswana, a true kimberlite but with a diamond content vastly superior to that of Argyle, was also problematic because it lacked G10/G9 pyrope chemistry. Exploration groups such as Ashton developed a strategy where once a kimberlite was found it was subjected to caustic fusion or acid dissolution for the recovery of any size of diamond. The more diamonds and the bigger the better the potential for a macro grade. This allowed exploration companies to use a sample smaller than 100 kg recovered through core drilling to assess the diamond potential of a new kimberlite. During the nineties when BHP and Dia Met discovered the Ekati kimberlite field in Canada's Arctic a reporting standard somewhat arbitrarily emerged where all of the diamonds were measured in their longest dimension and classified as either 0.5 mm or bigger, or smaller than 0.5 mm: the bigger ones were called "macros" and the smaller ones "micros". From this emerged the notion that the more macros per kg of sample, the better the macro grade potential. More dubious was the idea that the ratio of macro to micro counts was indicative of macro grade potential. This approach benefited from simply not recovering or counting the smallest diamonds. The 0.5 mm in the longest dimension distinction attracted criticism after several bulk samples in 1994 from supposedly promising pipes delivered disappointing low grades. Ironically, the infamous Tli Kwi Cho Bust was not the result of misinterpreting the grade potential of the DO27 pipe, but rather by a failure of the operator, Rio Tinto, to delineate the geology of the pipe and design an underground bulk sample to recover a representative sample of the different kimberlite units. The first scientist to push the idea that macro grade could be predicted from microdiamond size frequencies was Luc Rombouts, a theme further developed by John Chapman and Grant Boxer who worked with the Argyle data sets. Ironically, Ashton Canada only published micro diamonds according to the discredited 0.5 mm longest dimension classification. A multi-sieve based reporting system for micro diamonds first appeared when De Beers started reporting such results for the Gahcho Kue pipes optioned from Mountain Province. The driving force behind this approach was Johann Ferreira whose sieve system was modified through the publication of the CIM Diamond Exploration Reporting Guideline. Since then all "microdiamond" results have been reported according to a root two progression sieve system. This has enabled investors to plot on a log 10 scale the normalized counts per sieve size which should result in a straight line. The diamond grade is the area under this curve from the cut-off sieve size onwards. The shallower the slope of the microdiamond size frequency distribution curve, the "coarser" the distribution and thus the better the potential for large diamonds which is not necessarily related to the overall macro grade. Articles tagged with the key word "microdiamonds" tend to be about the method of using microdiamonds to predict grade and the associated pitfalls, which is relevant to diamond exploration. However, there is some controversy about the origin of microdiamonds under conditions not conducive to the formation of commercial size "macro" diamonds such as high pressure conditions created through meteor impacts or in subduction zones. Some articles thus deal with unusual rocks with high micro diamond counts such as the Dachine Massif and the Wawa conglomerates.
Paleoclimatic and structural environment at the end of the Cretaceous along the western flank of the Congo Basin, with application of undergroundmicrodiamonds.
Journal of African Earth Sciences, Vol. 10, No. 1/2. pp. 399-408
A new manifestation of micro-diamonds in metamorphic rocks as an evidence of the regional character of high-pressure metamorphism in KokchetavMassif.(in Russian)
Doklady Academy of Sciences Akademy Nauk SSSR, (Russian), Vol. 321, No. 1, pp. 189-193. # HB124
Morphological features of microdiamonds, sodium in garnet and potassium inpyroxenes content of two eclogite xenoliths from Udachnaya pipe(Yakutia).(Russian)
Doklady Academy of Sciences Akademy Nauk SSSR, (Russian), Vol. 321, No. 3, pp. 585-592
Russia, Commonwealth of Independent States (CIS), Yakutia
Some specific features of genesis of microdiamonds of octahedral and cubic habit from kimberlites of the Udachanaya pipe inferred from carbon isotopes - defect
Russian Geology and Geophysics, Vol. 48, pp. 299-304.
Abstract: The Variscan French Massif Central (FMC) is classically described as a stack of nappes with increasing metamorphism from the bottom (parautochthonous unit) to the top (lower and upper gneiss units). Ultra-high pressure (UHP) metamorphism was already recognized in the uppermost units, with notably coesite-bearing rocks. We report the first finding of metamorphic microdiamonds in the parautochthonous unit, revealing that the UHP event affected the whole stack of nappes and also that the pressures reached are above what was previously expected, since the presence of diamond, according to the peak temperature estimates for this unit, indicates pressures of ca. 3 GPa (i.e. 100 km depth). At the scale of the FMC, this finding adds complexity to the established models. On a broader scale, this adds evidence of similarity between this part of the belt and other UHP Variscan terranes such as the Erzgebirge and the Bohemian Massif.
Inside Mining, Vol. 109, July, pp. 32-35. Available pdf
Africa
Microdiamonds - responses
Abstract: The recovery and analysis of microdiamonds helps to predict the presence of commercial-sized diamonds in kimberlites. It is a cost-effective method for prioritising targets for bulk sampling.
Abstract: Analysing the size frequency distributions (SFDs) of both micro diamonds and macro diamonds from primary deposits shows that the distributions are continuous across all sizes and that there are two regions of different character with a transition about 1-2 mm. Using log axes, the frequency curve is linear for the smaller sizes allowing slope and intercept parameters to be determined which are less ambiguous than stone counts and ratios of macro to micro populations that are generally reported. Modelling a diamond population that has undergone removal of a uniform thickness of the outer layer transforms a linear frequency curve into a quadratic form, which is also the form of the frequency curve for macro diamonds. Diamonds grown synthetically also display a linear distribution across a smaller fraction of their size distribution curve.
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: Size frequency distributions are the principal tool for predicting the macro-diamond grade of new kimberlite discoveries, based on micro-diamonds (i.e., diamond ? 0.5 mm) recovered from small exploration samples. Lognormal size frequency distributions – as observed for the Artemisia kimberlite (Slave Craton, Canada) – suggest a common source for micro- and macro-diamonds recovered from single samples, an implication that has never been conclusively tested. We analyzed 209 diamonds between 0.2 and 2 mm in size from the Artemisia kimberlite for their carbon isotopic compositions and nitrogen characteristics to determine the nature of the micro-/macro-diamond relationship.-Despite overall similarity in the ?13C distributions of micro- and macro-diamonds – both are bimodal with peaks in classes ? 5.0 to ? 4.5‰ and ? 3.5 to ? 3.0‰ – rare diamonds with ?13C between ? 14.2 and ? 24.5‰ of presumed eclogitic origin are restricted to macro-diamonds, whereas positive values are only observed for micro-diamonds. In addition, a shift in main mode and median value in ?13C of about +1‰ is observed for micro- relative to macro-diamonds. Fundamental differences between micro- and macro-diamonds at Artemisia were revealed through the analysis of nitrogen concentrations: 68% of micro-diamonds are Type II (“nitrogen free”) versus 21% of macro-diamonds, and only 19% of micro-diamonds have nitrogen contents > 100 atomic ppm versus 43% of macro-diamonds. Similarly, the presence of a detectable hydrogen related peak (at 3107 cm? 1) increases from 40% for micro-diamonds to 94% for macro-diamonds.-Previous studies on diamond populations from individual deposits have documented that single batches of ascending kimberlite or lamproite magma sample multiple diamond subpopulations formed during distinct growth events in compositionally variable sources and at various depth levels. The Artemisia data clearly show that even over a fairly narrow size interval, spanning the micro- to macro-diamond transition, the specific diamond subpopulations present and their relative proportions may vary significantly with diamond size. At Artemisia, we conclude that the observed lognormal size distribution is not a reflection of an entirely common origin of micro- and macro-diamonds.
Kryvoshlyk, 38ppt. Available ppt. Email ikryvoa481 @hotmail.com
Technology
Microdiamonds - responses
Abstract: Diamond grade is the most important parameter of a kimberlite rock. A few hundreds of microprobe analyses of garnets picked randomly from a kimberlite concentrate might be enough to calculate mathematically accurate diamond grade.
Diamond and Related Materials, Vol. 39, pp. 89-97.
Technology
Microdiamonds - responses
Abstract: Geometrical crystallographic features of rare diamond micro-crystals (0.3-0.5 mm in diameter) from kimberlites having different complex flat and smooth faces are described. Such polyhedrons of microdiamonds are typically composed of two or more combinations of seven different crystal forms belonging to hexoctahedral symmetry class: octahedron, cube, rhombic dodecahedron, trisoctahedron, trapezohedron, tetrahexahedron and hexoctahedron. Many of them are not yet known for macro-crystals of this mineral. All these forms are found as small faces on the octahedral crystals. Both flat and smooth faces of octahedron and cube on such crystals have their own growth sectors. Flat faces of rhombic dodecahedron, different trisoctahedrons, trapezohedrons and hexoctahedrons occur as so-called faces of degeneration of octahedral growth planes. Nature of tetrahexahedron flat faces is not clear. An investigation of the complex diamond polyhedrons should give a new idea on crystal morphology of diamond, make more precise its symmetry and be important for the explanation of the nature of diamond on the whole.
Mineralium Deposita, Vol. 38, pp. 496-504. Available pdf
Global
Microdiamonds - responses
Abstract: The economic evaluation of diamond-bearing kimberlites is usually carried out in four stages. Expenditure tends to increase by an order of magnitude at each successive stage. At the end of each stage, the sample results should be critically appraised before deciding to proceed to the next phase. In the first stage, even before individual kimberlite bodies have been discovered, the indicator mineral geochemistry will give a first rough idea of the diamond potential. The relative abundance of harzburgitic pyropes (subcalcic chrome-rich) is often directly correlated with the diamond grade. In the next stage, when the kimberlite body has been discovered, a relatively small sample of a few hundred kilograms will be enough to recover sufficient microdiamonds to allow an extrapolation of the size distribution towards the commercial-sized diamonds and a rough estimate of their grade. If positive, the third stage should be a limited bulk sampling programme (order of 200 tonnes) to determine the commercial-sized diamond grade, expressed as carats per tonne. The aim of the final stage is to obtain a parcel of the order of 1,000 carats to estimate the average commercial value of the diamonds. The robustness and reliability of the grade and value estimates can be verified with extreme value analysis and by obtaining the confidence limits with bootstrapping.
Diamond and Related Materials, Vol. 40, pp. 24-31.
Technology
Microdiamonds - responses
Abstract: A transmission electron microscopy study of garnet from diamond-grade gneisses of the Betic Cordillera (Spain) has revealed the presence of abundant, previously unrecognized, nanosized carbonaceous grains, coexisting with micrometer-sized graphite and diamond. The nanosized particles occur as multiwall nanotubes, and as polyhedral and quasi-spherical graphite + diamond nanoparticles, whereas larger graphite particles appear as rods and as tabular crystals. The topotactic relationships between graphite in nanoparticles and in micrometer-sized particles and the host garnet suggest that carbon nano- and microparticles precipitated from an originally homogeneous solid solution of carbon in the garnet. Based on orientation relationships and on experimental data it is suggested that the three main types of nanosized particles (nanospheres, polyhedral particles and nanotubes) were the precursor of the three main types of larger carbon phases (diamond, tabular and rod-shaped graphite particles, respectively). It is interpreted, as in the case of diamond-graphite nanocomposites, that diamond formation in the core of the nanoparticles is due to an increase of the cross-links between the layers, and then, to the collapse, at a certain point, of the whole graphite structure into diamond. This finding opens a new door for explaining the origin of some metamorphic diamonds and of coexisting graphite and diamond in ultrahigh pressure rocks.
Proceedings of the 5th. International Kimberlite Conference, Vol. 2, pp. 78-97.
United States, Arkansas
Microdiamonds
Abstract: The first report of diamond in igneous rock in the United States originated at Prairie Creek, Arkansas. We have examined the morphological, carbon isotope, and inclusion characteristics of diamonds from Prairie Creek, and from the Twin Knobs # 1, #2, Black Lick, and American lamproites. White is the most common macrodiamond color at Prairie Creek (62% of total), with 20% brown and 16% yellow. This contrasts with Australian lamproites where brown predominates, and with other North American localities such as the Sloan, Colorado kimberlites where yellow is rare. Lamination lines indicate ductile deformation at mantle conditions. The macrodiamonds are very resorbed; 82% are equiform or distorted tetrahexahedroida and none are octahedra. Low relief surfaces indicate prolonged and/or intense resorption. Microdiamonds differ dramatically, with octahedra and fragn~ents common and tetrahexahedroida abscnL Serrate laminae, knob-like asperities, pointed plates, ribbing, and non-uniform resorption are the most common surface features. Diamonds from the Twin Knobs # 1 lamproite are similar to microdiamonds with respect to size and surface features. Magnetite and olivine (F093) are the only primary inclusions foqnd in the diamonds, although inclusions of peridotitic and eclogitic parageneses have been reported in previous studies. Carbon isotope B13c values for Prairie Creek macrodiamonds peak at-3.0 to -6.2 %o (ave. -4.7 %o for 19 stones) and -10.3 to -10.6 %o (ave. -10.5 %o for 2 stones). The diamonds with magnetite and olivine inclusions have B13c values of -5.1 %o and -4.0 %o respectively. Microdiamonds from Prairie Creek, Twin Knobs #2, American, and Black Lick are similar to Prairie Creek macrodiamonds ( -0.5 to -7 .8; ave. -4.1 %o for 8 stones). A Prairie Creek and a Black Lick microdiamond have B13c values of -26.1 and -25.2%orespectively, and the latter exhibits non-uniform resorption. Lamination lines on macrodiamonds and xenocrystic surface features on microdiamonds imply that both are xenocrysts in lamproite. Carbon isotopes are characteristic of a peridotitic or primordial carbon reservoir. Two 13cdepleted microdiamonds may be from a subducted carbon source. In comparison to macrodiamond populations from most kimberlites, Prairie Creek macrodiamonds are intensely resorbed, and lamproite may be more corrosive than kimberlite \\ ith respect to diamond resorption. Microdiamonds were probably encapsulated in xenolith material ani.! esca•,)ed resorption. The differences in size and color of Prairie Creek macrodiamonds relative to Sloan kimberlitic diamonds are genetic, and may be related to their formation in lithosphere of differing age and tectonic history.
Abstract: The Variscan French Massif Central (FMC) is classically described as a stack of nappes with increasing metamorphism from the bottom (parautochthonous unit) to the top (lower and upper gneiss units). Ultra-high pressure (UHP) metamorphism was already recognized in the uppermost units, with notably coesite-bearing rocks. We report the first finding of metamorphic microdiamonds in the parautochthonous unit, revealing that the UHP event affected the whole stack of nappes and also that the pressures reached are above what was previously expected, since the presence of diamond, according to the peak temperature estimates for this unit, indicates pressures of ca. 3 GPa (i.e. 100 km depth). At the scale of the FMC, this finding adds complexity to the established models. On a broader scale, this adds evidence of similarity between this part of the belt and other UHP Variscan terranes such as the Erzgebirge and the Bohemian Massif.
Ecole Nationale Superieure des Mines de Paris, 207p. Pdf
Global
Microdiamonds
Abstract: This research deals with diamond content estimation in kimberlite based on information obtained from microdiamond sampling. In spite of the abundance of diamonds smaller than 0.5mm square mesh the conventional approach of estimating diamond content is based on information derived from stones in the +0.5mm size fraction. While large samples are required to ensure recovery of sufficient numbers of diamonds for evaluation the largest number is therefore discarded as treatment tailings. As far back as the 1960’s this inspired the approach to lower the bottom screen aperture in order to recover microdiamonds, and was accompanied by the introduction of recovery methodology based on acid dissolution. As a consequence the required sample size is smaller, bringing along many practical advantages. The research deals with estimation of the weight of diamonds (diamond content) in kimberlite, based on information obtained from microdiamond sampling to a bottom screen diameter as low as 0.075 mm square mesh (~0.0000018 carats). Determination of the diamond size distribution has always been a challenge when estimating deposit diamond content. The method proposed in the research is based on the assumption of lognormality, which is in line with experience at all primary deposits. Over the years special techniques of estimating deposit diamond content have been developed and in this research have ‘matured’ into a proper sampling and estimation approach, taking cognizance of the fact that sampling is partially ‘flawed’ due to inevitable losses of diamonds during sample treatment. Some smaller diamonds are lost when they pass through the bottom cut-off screen used during diamond recovery, when according to their weight they should actually be recovered. Other losses of small diamonds occur when they remain locked in host rock particles and are discarded along with non-diamond bearing material. Modelling of diamond content is performed by means of an iterative process of simulating diamonds as distributed in their in situ state, followed by emulating recovery effects to reproduce a representative sample.
Abstract: First predictions of the macrodiamond grade of newly discovered kimberlites are commonly obtained using size frequency distributions of microdiamonds. The success of this approach suggests a common origin of microdiamonds and macrodiamonds, an implication not yet conclusively established or disproved. In contrast to previous comparative studies on microdiamonds and macrodiamonds from single deposits, here all diamonds analyzed originate from the same microdiamond samples (558 diamonds, ranging from 0.212 to 3.35 mm). The diamonds were analyzed for their carbon isotope compositions and nitrogen characteristics, and, based on this dataset, statistical comparisons were conducted across the size range to assess cogenesis. As a whole, the Misery diamond suite shows high nitrogen contents (median = 850 at. ppm), a bimodal distribution in time-averaged mantle residence temperatures (two distinct subpopulations in mantle residence temperatures: ?1,125° and ?1,175°C), a high degree of platelet degradation, and ?13C compositions that are isotopically slightly heavier (median = ?4.4‰) than the global median. Statistical comparisons of the various size classes indicate the presence of subtly different subpopulations at Misery; however, the nature and magnitude of these geochemical differences are very small in the context of the global diamond database and are viewed as petrogenetically insignificant. The general geochemical similarity of diamonds from different size fractions at Misery reinforces the use of size-frequency analysis to predict diamond grade in kimberlite diamond deposits.
Journal of Metamorphic Geology, in press available
Europe, Sweden
Microdiamond
Abstract: Metamorphic diamond in crustal rocks provides important information on the deep subduction of continental crust. Here, we present a new occurrence of diamond within the Seve Nappe Complex (SNC) of the Scandinavian Caledonides, on Åreskutan in Jämtland County, Sweden. Microdiamond is found in situ as single and composite (diamond+carbonate) inclusions within garnet, in kyanite-bearing paragneisses. The rocks preserve the primary peak pressure assemblage of Ca,Mg-rich garnet+phengite+kyanite+rutile, with polycrystalline quartz surrounded by radial cracks indicating breakdown of coesite. Calculated P-T conditions for this stage are 830-840 °C and 4.1-4.2 GPa, in the diamond stability field. The ultrahigh-pressure (UHP) assemblage has been variably overprinted under granulite facies conditions of 850-860 °C and 1.0-1.1 GPa, leading to formation of Ca,Mg-poor garnet+biotite+plagioclase+K-feldspar+sillimanite+ilmenite+quartz. This overprint was the result of nearly isothermal decompression, which is corroborated by Ti-in-quartz thermometry. Chemical Th-U-Pb dating of monazite yields ages between 445 and 435 Ma, which are interpreted to record post-UHP exhumation of the diamond-bearing rocks. The new discovery of microdiamond on Åreskutan, together with other evidence of ultrahigh-pressure metamorphism (UHPM) within gneisses, eclogites and peridotites elsewhere in the SNC, provide compelling arguments for regional (at least 200 km along strike of the unit) UHPM of substantial parts of this far-travelled allochthon. The occurrence of UHPM in both rheologically weak (gneisses) and strong lithologies (eclogites, peridotites) speaks against the presence of large tectonic overpressure during metamorphism.
Abstract: Microdiamonds ?200 ?m in size, occurring in ophiolitic chromitites and peridotites, have been reported in recent years. Owing to their unusual geological formation, there are several debates about their origin. We studied 30 microdiamonds from 3 sources: (1) chromitite ore in Luobusa, Tibet; (2) peridotite in Luobusa, Tibet; and (3) chromitite ore in Ray-Iz, polar Ural Mountains, Russia. They are translucent, yellow to greenish-yellow diamonds with a cubo-octahedral polycrystalline or single crystal with partial cubo-octahedral form. Infrared (IR) spectra revealed that these diamonds are type Ib (i.e., diamonds containing neutrally charged single substitutional nitrogen atoms, Ns0, known as the C center) with unknown broad bands observed in the one-phonon region. They contain fluid inclusions, such as water, carbonates, silicates, hydrocarbons, and solid CO2. We also identified additional microinclusions, such as chromite, magnetite, feldspar (albite), moissanite, hematite, and magnesiochromite, using a Raman microscope. Photoluminescence (PL) spectra measured at liquid nitrogen temperature suggest that these diamonds contain nitrogen-vacancy, nickel, and H2 center defects. We compare them with high-pressure-high-temperature (HPHT) synthetic industrial diamond grits. Although there are similarities between microdiamonds and HPHT synthetic diamonds, major differences in the IR, Raman, and PL spectra confirm that these microdiamonds are of natural origin. Spectral characteristics suggest that their geological formation is different but unique compared to that of natural gem-quality diamonds. Although these microdiamonds are not commercially important, they are geologically important in that they provide an understanding of a new diamond genesis.
Canadian Institute of Mining and Metallurgy, Vol. 7, 4, pp. 216-239.
Global
microdiamonds
Abstract: Concerns around the use of micro-diamonds for resource estimation have been raised by some workers because: 1) multiple diamond populations are present in many parts of the mantle source region, 2) small diamonds in kimberlite could be exposed to proportionately greater levels of resorption and modification, and 3) euhedral micro-diamonds could crystallize immediately prior to kimberlite eruption. This paper addresses these concerns and discusses the geology of the mantle and the principal diamond host rocks, the impact of mantle processes, compares micro- and macro-diamond properties and features, and outlines several steps that can be undertaken to identify and mitigate the risk of resorption of diamond and its impact on the diamond grade size relationship.
South African Institute of Mining and Metallurgy, Vol. 116, 8, pp. 737-745.
Technology
microdiamond
Abstract: Estimating the size frequency distribution of the macrodiamonds on a new deposit is important for both economic reasons and for the design of the processing plant. Millions of dollars can be lost due to incorrectly sized comminution circuits. This report analyses an alternative methodology for macrodiamond grade estimation using the cumulative results from small parcels of microdiamonds and plotting them on a log-log scale. The method was first evaluated mathematically for diamond populations to assess the confidence for data extrapolation. Macrodiamond size distributions and grades were predicted using microdiamond data from three kimberlites, and the actual macrodiamond grades compared to the the predicted grades. The predicted grades were found to replicate the actual grades closely, showing that a high degree of confidence can be ascribed to the results from this method of analysis. This analysis can be used both for resource estimates and for predicting the diamond size distribution information needed for designing a new operation.
Journal of Metamorphic Geology, Vol. 35, 5, pp. 541-564.
Europe, Scandinavia
microdiamond
Abstract: Metamorphic diamond in crustal rocks provides important information on the deep subduction of continental crust. Here, we present a new occurrence of diamond within the Seve Nappe Complex (SNC) of the Scandinavian Caledonides, on Åreskutan in Jämtland County, Sweden. Microdiamond is found in situ as single and composite (diamond+carbonate) inclusions within garnet, in kyanite-bearing paragneisses. The rocks preserve the primary peak pressure assemblage of Ca,Mg-rich garnet+phengite+kyanite+rutile, with polycrystalline quartz surrounded by radial cracks indicating breakdown of coesite. Calculated P–T conditions for this stage are 830–840 °C and 4.1–4.2 GPa, in the diamond stability field. The ultrahigh-pressure (UHP) assemblage has been variably overprinted under granulite facies conditions of 850–860 °C and 1.0–1.1 GPa, leading to formation of Ca,Mg-poor garnet+biotite+plagioclase+K-feldspar+sillimanite+ilmenite+quartz. This overprint was the result of nearly isothermal decompression, which is corroborated by Ti-in-quartz thermometry. Chemical Th–U–Pb dating of monazite yields ages between 445 and 435 Ma, which are interpreted to record post-UHP exhumation of the diamond-bearing rocks. The new discovery of microdiamond on Åreskutan, together with other evidence of ultrahigh-pressure metamorphism (UHPM) within gneisses, eclogites and peridotites elsewhere in the SNC, provide compelling arguments for regional (at least 200 km along strike of the unit) UHPM of substantial parts of this far-travelled allochthon. The occurrence of UHPM in both rheologically weak (gneisses) and strong lithologies (eclogites, peridotites) speaks against the presence of large tectonic overpressure during metamorphism.
Anais da Academia Brasileira de Ciencas, Vol. 79, pp. 321-332.
South America, Brazil
microdiamonds
Abstract: The origin of diamonds from Serra do Espinhaço in Diamantina region (State of Minas Gerais) and in Chapada Diamantina, Lençóis region (State of Bahia) remains uncertain, even taking into account the ample research carried out during the last decades. The lack of typical satellite minerals in both districts makes a kimberlitic source for these diamonds uncertain. In mid 18th century the occurrence of a metamorphosed igneous rock composed of martite, sericite and tourmaline was described in Diamantina region and named hematitic phyllite, considered by some researchers as a possible diamond source. Similar rocks were found in Lençóis and examined petrographically and their heavy mineral concentration was investigated by means of scanning electron microscopy (SEM). Petrographic analyses indicated an igneous origin for these rocks and SEM analyses showed the discovery of microdiamonds. Geochronological studies using the Ar/Ar technique in muscovites yielded minimum ages of 1515+/-3 Ma, which may correlate with 1710+/-12 Ma from U-Pb method in igneous zircons from the hematitic phyllites. Both rock types also have the same mineral and chemical composition which leads to the conclusion that the intrusive rocks were protolith of the hematitic phyllites. This first discovery of microdiamonds in intrusive rocks opens the possibility of new investigation models for diamond mineralization in Brazilian Proterozoic terrains.
Diamond & Related Materials, Vol. 81, pp. 161-167.
Technology
microdiamonds
Abstract: Polylactic acid (PLA)-based composites filled with 20 or 50 ?m-diameter microdiamond are synthesized by hot pressing. Through improving the interface compatibility between the filler and the matrix enabled by octadecylamine (ODA) coating on the microdiamond particles, the maximum thermal conductivity of the composites is 2.22 Wm? 1 K? 1, which is a ~ 10-fold increase in comparison with that of pure PLA. According to the analysis on the glass transmission of the composites and the surface chemistry of the fillers using DSC, FI-IR, and Raman microscopy, it is found out that ODA is connected with the -OH group on the microdiamond surface through hydrogen bonding and an interfacial structure of PLA/ODA/microdiamond is formed. Thus, the interfacial thermal transport between PLA and microdiamond is significantly improved, leading to the enhancement of the thermal conductivity of the composites. Our work presents a simple method to modify the surface chemistry of microdiamond and to improve the interface compatibility between microdiamond and PLA. The microdiamond/PLA composites with large thermal conductivity are promising thermal management materials used for modern electronic products.
Mineralogy and Petrology, doi.org/10.1007/ s00710-018-0566-y 12p.
Global
microdiamonds
Abstract: Microdiamonds offer several advantages as a resource estimation tool, such as access to deeper parts of a deposit which may be beyond the reach of large diameter drilling (LDD) techniques, the recovery of the total diamond content in the kimberlite, and a cost benefit due to the cheaper treatment cost compared to large diameter samples. In this paper we take the first step towards local estimation by showing that micro-diamond samples can be treated as a regionalised variable suitable for use in geostatistical applications and we show examples of such output. Examples of microdiamond variograms are presented, the variance-support relationship for microdiamonds is demonstrated and consistency of the diamond size frequency distribution (SFD) is shown with the aid of real datasets. The focus therefore is on why local microdiamond estimation should be possible, not how to generate such estimates. Data from our case studies and examples demonstrate a positive correlation between micro- and macrodiamond sample grades as well as block estimates. This relationship can be demonstrated repeatedly across multiple mining operations. The smaller sample support size for microdiamond samples is a key difference between micro- and macrodiamond estimates and this aspect must be taken into account during the estimation process. We discuss three methods which can be used to validate or reconcile the estimates against macrodiamond data, either as estimates or in the form of production grades: (i) reconcilliation using production data, (ii) by comparing LDD-based grade estimates against microdiamond-based estimates and (iii) using simulation techniques.
Using diamond characterization to refine micro and macro diamond processing and recovery.
Vancouver Kimberlite , Jan. 31, 1p. Abstract
Global
microdiamonds
Abstract: Bulk samples for both micro and macro diamond recovery are very costly, and typically only a small amount of quantitative data is collected, this is particularly the case for micro diamonds. Standard practise is to only provide information on the number of diamonds, their sizes, and weight. However, a large amount of quantitative data can be collected for both micro and macro diamonds to understand their unique characteristics. This data can be used to enhance diamond recovery through optimization of standard processes or introduction of appropriate processing equipment. The more information that can be collected in the prefeasibility stage, the more streamlined the diamond recovery circuit can be made, and the less diamond loss will occur. This presentation will provide an overview of standard recovery methods for micro and macro diamonds as well as other test work that can be applied to the parcels. The resulting data can provide information on the unique properties for that parcel in order to customize process flows and optimize recovery. Caustic fusion is a widely accepted method for micro diamond recovery. Thanks to its high liberation efficiency by dissolution, caustic fusion can also be an effective tool for auditing process streams. Any additional diamonds recovered through these audits can be studied to determine if crusher gap or pressure settings are appropriate for optimal liberation or if there are any other properties the diamonds may have that inhibits proper recovery, such as unique fluorescence characteristics, abundant inclusions, coats, etc. Dense media separation (DMS) is currently the most common method of concentration for the recovery of macro diamonds. Process flows can be modified in attempts to optimize plant performance but there can often be sacrifices. Diamond breakage can be assessed to give insight on the type of damage occurring and if the source is mechanical or related to the properties of the diamonds themselves. By considering the diamond breakage, updated size frequency distribution plots can be made, and predictions on the largest diamond expected for the kimberlite tonnage can be made. This information can also be used when determining parameters such as crusher gap settings. In addition, densiometric analyses can provide a useful profile of the predominant mineral background in the DMS process material to determine the appropriate cut point. Once diamonds are recovered, the resulting parcels can have a story to tell in addition to the diamond value. Magnetic susceptibility investigations can provide information on included diamonds and how magnetics could be incorporated into a flow sheet for pre-recovery concentration. Diamond Typing based on their nitrogen content and aggregation states can identify populations of stones that could make recovery less effective. Type II diamonds are commonly known for being large and high value, however, they also exhibit low to no luminescence under conventional x-ray recovery equipment. Luminescence profiles can be measured and provide feedback on the appropriate x-ray thresholds for the recovery equipment. Being able to predict the characteristics of the diamond populations which will be mined can provide information to design a primary ore recovery circuit to recover these stones. There is a wide array of process equipment available for diamond recovery, some very old, and some very new, however there are ways to provide data on what combination will work best.
Geochimica et Cosmochimica Acta, in press available, 43p.
Global
microdiamonds
Abstract: The origin of micro-diamonds is controversial and although the application to determine the grade and value of macro-diamonds in kimberlite/lamproite bodies continues to receive widespread usage there are several outstanding factors generally not considered, the most important of which is genesis. The issue is addressed in this study in the context that two classes of small diamonds (generally <0.5?mm and rarely <1?mm) are recognized. Micro-diamonds sensu-stricto (MDS) are typically sharp-edged octahedra, free of mineral inclusions and surface etching or corrosion, increase exponentially with decreasing size and are in overwhelming larger concentrations, by orders of magnitude, relative to macro-diamonds (>0.5?mm). The second class of small diamonds (SD <0.5?mm), used in industrial applications, may have modified solution-growth morphologies (e.g. dodecahedra, tetrahexahedra and related forms), and include loosely bonded polycrystalline diamonds (framesite), boart, fibrous cubes and broken fragments. There are large differences in volume to surface-area ratios between MDS and SD, demonstrating unequivocally that pristine and solution-modified forms could not have co-existed in equilibrium under the same P-T-t-fO2 conditions in the mantle. From detailed studies of N and C in diamond, and experimental results on the redox-partitioning of N in the presence of metallic Fe, it is concluded that MDS are plume-related from the D? core-mantle boundary, and are melt-derived in lower mantle proto-kimberlite. The lower mantle is expectedly saturated in metallic Fe, and is highly depleted in N which is siderophile under very low f O2 conditions, a setting in which excessively large (?100 to 3000 ct), but rare Type II mega-diamonds (but also MDS) are inferred to have originated. These diamonds (Type II, Ib, IaA) are distinct from the majority of N-rich Type Ia upper mantle macro-diamonds that grew slowly by metasomatic processes and annealed over long periods. Two crystal growth laws are possibly applicable to the size-distribution of diamonds encountered in kimberlites/lamproites. Gibrat’s Law of proportionate, short-term crystal growth in open systems by advection is applicable to magmatic MDS, whereas macro-diamonds bear some relation to McCabe’s Law of long-term, relatively constant crystal growth, by diffusion metasomatism. The range from small to large diamonds (SFD size-frequency-distribution) is lognormal but is composed of two segments: the smaller size (<0.5?mm) fraction has an overall linear distribution, whereas macro-diamonds (>0.5?mm) are quadratic. The two distributions meet or overlap in a marked discontinuity, implying but not proving distinct origins. The power law governing SFD lognormal distributions is fundamental and is widespread across an enormous number of disciplines (from biology to economics), and may be universal (e.g. it is applicable to planetary scale meteorite impact craters, and to the SFD of cosmic-diamonds from supernovae explosions). Industry applications in resource predictions are from mixtures of diamonds (MDS and SD), and extrapolation to larger stones is valid because the fundamental law is independent of origins.
Abstract: The results of geochemical studies of the diamondiferous suevites of the Kara astrobleme (Pay-Khoy) using a new approach based on “area” microprobe analysis of suevite matrix and consolidated impact melt aggregates with subsequent data processing by multivariate statistic methods are described for the first time. At least three suevite varieties that differ essentially in geomorphology, mineralogy, petrography, and geochemical features have been recognized. The predominant protoliths of the rocks of the target are proposed for these suevite varieties on the basis of integrated data analysis.
Abstract: We report new ?13C ?values data and N?content and N?aggregation state values for microdiamonds recovered from peridotites and chromitites of the Luobusa ophiolite (Tibet) and chromitites of the Ray?Iz ophiolite in the Polar Urals (Russia). All analyzed microdiamonds contain significant nitrogen contents (from 108 up to 589 ± 20% atomic ppm) with a consistently low aggregation state, show identical IR spectra dominated by strong absorption between 1130 cm?1 and 1344 cm?1, and hence characterize Type Ib diamond. Microdiamonds from the Luobusa peridotites have ?13C ?PDB?values ranging from ?28.7‰ to ?16.9‰, and N?contents from 151 to 589 atomic ppm. The ?13C and N?content values for diamonds from the Luobusa chromitites are ?29‰ to ?15.5‰ and 152 to 428 atomic ppm, respectively. Microdiamonds from the Ray?Iz chromitites show values varying from ?27.6 ‰ to ?21.6 ‰ in ?13C and from 108 to 499 atomic ppm in N. The carbon isotopes values bear similar features with previously analyzed metamorphic diamonds from other worldwide localities, but the samples are characterized by lower N?contents. In every respect, they are different from diamonds occurring in kimberlites and impact craters. Our samples also differ from the few synthetic diamonds; we also analyzed showing enhanced ?13C ?variability and less advanced aggregation state than synthetic diamonds. Our newly obtained N?aggregation state and N?content data are consistent with diamond formation over a narrow and rather cold temperature range (i.e. <950°C), and in a short residence time (i.e. within several million years) at high temperatures in the deep mantle.
Abstract: Diamonds have been discovered in mantle peridotites and chromitites of six ophiolitic massifs along the 1300 km?long Yarlung?Zangbo suture (Bai et al., 1993; Yang et al., 2014; Xu et al., 2015), and in the Dongqiao and Dingqing mantle peridotites of the Bangong?Nujiang suture in the eastern Tethyan zone (Robinson et al., 2004; Xiong et al., 2018). Recently, in?situ diamond, coesite and other UHP mineral have also been reported in the Nidar ophiolite of the western Yarlung?Zangbo suture (Das et al., 2015, 2017). The above?mentioned diamond?bearing ophiolites represent remnants of the eastern Mesozoic Tethyan oceanic lithosphere. New publications show that diamonds also occur in chromitites in the Pozanti?Karsanti ophiolite of Turkey, and in the Mirdita ophiolite of Albania in the western Tethyan zone (Lian et al., 2017; Xiong et al., 2017; Wu et al., 2018). Similar diamonds and associated minerals have also reported from Paleozoic ophiolitic chromitites of Central Asian Orogenic Belt of China and the Ray?Iz ophiolite in the Polar Urals, Russia (Yang et al., 2015a, b; Tian et al., 2015; Huang et al, 2015). Importantly, in?situ diamonds have been recovered in chromitites of both the Luobusa ophiolite in Tbet and the Ray?Iz ophiolite in Russia (Yang et al., 2014, 2015a). The extensive occurrences of such ultra?high pressure (UHP) minerals in many ophiolites suggest formation by similar geological events in different oceans and orogenic belts of different ages. Compared to diamonds from kimberlites and UHP metamorphic belts, micro?diamonds from ophiolites present a new occurrence of diamond that requires significantly different physical and chemical conditions of formation in Earth's mantle. The forms of chromite and qingsongites (BN) indicate that ophiolitic chromitite may form at depths of >150?380 km or even deeper in the mantle (Yang et al., 2007; Dobrthinetskaya et al., 2009). The very light C isotope composition (?13C ?18 to ?28‰) of these ophiolitic diamonds and their Mn?bearing mineral inclusions, as well as coesite and clinopyroxene lamallae in chromite grains all indicate recycling of ancient continental or oceanic crustal materials into the deep mantle (>300 km) or down to the mantle transition zone via subduction (Yang et al., 2014, 2015a; Robinson et al., 2015; Moe et al., 2018). These new observations and new data strongly suggest that micro?diamonds and their host podiform chromitite may have formed near the transition zone in the deep mantle, and that they were then transported upward into shallow mantle depths by convection processes. The in?situ occurrence of micro?diamonds has been well?demonstrated by different groups of international researchers, along with other UHP minerals in podiform chromitites and ophiolitic peridotites clearly indicate their deep mantle origin and effectively address questions of possible contamination during sample processing and analytical work. The widespread occurrence of ophiolite?hosted diamonds and associated UHP mineral groups suggests that they may be a common feature of in?situ oceanic mantle. The fundamental scientific question to address here is how and where these micro?diamonds and UHP minerals first crystallized, how they were incorporated into ophiolitic chromitites and peridotites and how they were preserved during transport to the surface. Thus, diamonds and UHP minerals in ophiolites have raised new scientific problems and opened a new window for geologists to study recycling from crust to deep mantle and back to the surface.
Abstract: Recent findings of diamonds in ophiolitic peridotites and chromitites challenge our traditional notion of Earth mantle dynamics. Models attempting to explain these findings involve incorporation of diamonds into chromite near the mantle transition zone. However, the occurrence of metastable diamonds in this context has not been considered. Here, we report for the first time in situ microdiamonds in chromite from ophiolitic chromitite pods hosted in the Tehuitzingo serpentinite (southern Mexico). Here, diamonds occur as fracture-filling inclusions along with quartz, clinochlore, serpentine, and amorphous carbon, thus indicating a secondary origin during the shallow hydration of chromitite. Chromite chemical variations across the diamond-bearing healed fractures indicate formation during the retrograde evolution of chromitite at temperatures between 670 °C and 515 °C. During this stage, diamond precipitated metastably at low pressure from reduced C-O-H fluids that infiltrated from the host peridotite at the onset of serpentinization processes. Diamond was preserved as a result of fracture healing at the same temperature interval in which the chromite alteration began. These mechanisms of diamond formation challenge the idea that the occurrence of diamond in ophiolitic rocks constitutes an unequivocal indicator of ultrahigh-pressure conditions.
Geochimica et Cosmochimica Acta, Vol. 266, pp. 184-196.
Global
microdiamonds
Abstract: The origin of micro-diamonds is controversial and although the application to determine the grade and value of macro-diamonds in kimberlite/lamproite bodies continues to receive widespread usage there are several outstanding factors generally not considered, the most important of which is genesis. The issue is addressed in this study in the context that two classes of small diamonds (generally <0.5?mm and rarely <1?mm) are recognized. Micro-diamonds sensu-stricto (MDS) are typically sharp-edged octahedra, free of mineral inclusions and surface etching or corrosion, increase exponentially with decreasing size and are in overwhelming larger concentrations, by orders of magnitude, relative to macro-diamonds (>0.5?mm). The second class of small diamonds (SD <0.5?mm), used in industrial applications, may have modified solution-growth morphologies (e.g. dodecahedra, tetrahexahedra and related forms), and include loosely bonded polycrystalline diamonds (framesite), boart, fibrous cubes and broken fragments. There are large differences in volume to surface-area ratios between MDS and SD, demonstrating unequivocally that pristine and solution-modified forms could not have co-existed in equilibrium under the same P-T-t-fO2 conditions in the mantle. From detailed studies of N and C in diamond, and experimental results on the redox-partitioning of N in the presence of metallic Fe, it is concluded that MDS are plume-related from the D? core-mantle boundary, and are melt-derived in lower mantle proto-kimberlite. The lower mantle is expectedly saturated in metallic Fe, and is highly depleted in N which is siderophile under very low f O2 conditions, a setting in which excessively large (?100 to 3000 ct), but rare Type II mega-diamonds (but also MDS) are inferred to have originated. These diamonds (Type II, Ib, IaA) are distinct from the majority of N-rich Type Ia upper mantle macro-diamonds that grew slowly by metasomatic processes and annealed over long periods. Two crystal growth laws are possibly applicable to the size-distribution of diamonds encountered in kimberlites/lamproites. Gibrat’s Law of proportionate, short-term crystal growth in open systems by advection is applicable to magmatic MDS, whereas macro-diamonds bear some relation to McCabe’s Law of long-term, relatively constant crystal growth, by diffusion metasomatism. The range from small to large diamonds (SFD size-frequency-distribution) is lognormal but is composed of two segments: the smaller size (<0.5?mm) fraction has an overall linear distribution, whereas macro-diamonds (>0.5?mm) are quadratic. The two distributions meet or overlap in a marked discontinuity, implying but not proving distinct origins. The power law governing SFD lognormal distributions is fundamental and is widespread across an enormous number of disciplines (from biology to economics), and may be universal (e.g. it is applicable to planetary scale meteorite impact craters, and to the SFD of cosmic-diamonds from supernovae explosions). Industry applications in resource predictions are from mixtures of diamonds (MDS and SD), and extrapolation to larger stones is valid because the fundamental law is independent of origins.
Nishiyama, T., Ohfuji, H., Fukuba, K., Terauchi, M., Nishi, U., Harada, K., Unoki, K., Moribe, Y., Yoshiasa, A., Ishimaru, S., Mori, Y., Shigeno, M., Arai, S.
Nature Scientific Reports, Vol. 10, 11645 11p. Pdf
Asia, Japan
microdiamond
Abstract: Microdiamonds in metamorphic rocks are a signature of ultrahigh-pressure (UHP) metamorphism that occurs mostly at continental collision zones. Most UHP minerals, except coesite and microdiamond, have been partially or completely retrogressed during exhumation; therefore, the discovery of coesite and microdiamond is crucial to identify UHP metamorphism and to understand the tectonic history of metamorphic rocks. Microdiamonds typically occur as inclusions in minerals such as garnet. Here we report the discovery of microdiamond aggregates in the matrix of a metapelite from the Nishisonogi unit, Nagasaki Metamorphic Complex, western Kyushu, Japan. The Nishisonogi unit represents a Cretaceous subduction complex which has been considered as an epidote-blueschist subfacies metamorphic unit, and the metapelite is a member of a serpentinite mélange in the Nishisonogi unit. The temperature condition for the Nishisonogi unit is 450 °C, based on the Raman micro-spectroscopy of graphite. The coexistence of microdiamond and Mg-carbonates suggests the precipitation of microdiamond from C-O-H fluid under pressures higher than 2.8 GPa. This is the first report of metamorphic microdiamond from Japan, which reveals the hidden UHP history of the Nishisonogi unit. The tectonic evolution of Kyushu in the Japanese Archipelago should be reconsidered based on this finding.
Abstract: Microdiamonds in metamorphic rocks are a signature of ultrahigh-pressure (UHP) metamorphism that occurs mostly at continental collision zones. Most UHP minerals, except coesite and microdiamond, have been partially or completely retrogressed during exhumation; therefore, the discovery of coesite and microdiamond is crucial to identify UHP metamorphism and to understand the tectonic history of metamorphic rocks. Microdiamonds typically occur as inclusions in minerals such as garnet. Here we report the discovery of microdiamond aggregates in the matrix of a metapelite from the Nishisonogi unit, Nagasaki Metamorphic Complex, western Kyushu, Japan. The Nishisonogi unit represents a Cretaceous subduction complex which has been considered as an epidote-blueschist subfacies metamorphic unit, and the metapelite is a member of a serpentinite mélange in the Nishisonogi unit. The temperature condition for the Nishisonogi unit is 450 °C, based on the Raman micro-spectroscopy of graphite. The coexistence of microdiamond and Mg-carbonates suggests the precipitation of microdiamond from C-O-H fluid under pressures higher than 2.8 GPa. This is the first report of metamorphic microdiamond from Japan, which reveals the hidden UHP history of the Nishisonogi unit. The tectonic evolution of Kyushu in the Japanese Archipelago should be reconsidered based on this finding.
Abstract: The evaluation of advanced stage diamond projects is materially constrained by the time and cost involved in bulk sampling (or trial mining) campaigns that serve to demonstrate the grade and value of (macro)diamonds in a deposit. However, comparatively inexpensive assay data for (micro)diamonds may also be used to estimate (macro)diamond grade, by way of geostatistical extrapolation or modelling of total diamond content curves and diamond size frequency distributions. Geoscientists at SRK (Canada) Inc. compiled publicly available technical disclosure related to micro/macrodiamond sampling campaigns completed since early-2004 and developed a model-independent benchmarking approach to estimate in-situ (macro)diamond grades based on microdiamond assay results - a one-page summary of that work is available here: here Our ongoing investigation of microdiamond data has developed a focus on the occurrence of "low-count" and "high-count" microdiamond assay results. In this VKC talk we contrast "normal"-count with "low"-count results (Snap Lake vs FALC and others) and appeal to diamond-bearing mantle xenoliths to explain occasional "high"-count results. Real-world examples are used to cover topics like microdiamond sample sizes and (attained) resolution thresholds in the range 1 part in 1010 to 1012. The talk closes out with an examination of the microdiamond dataset for the Tuwawi pipe (northern Baffin Island).
