Dr. A. Moore, Ph D, Rhodes University (RSA)

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Framesites are polycrystalline diamonds of enigmatic origin, which differ in numerous respects from mono-crystalline diamond varieties. Their textures suggest rapid crystallization, while the low N-aggregation state of some stones, and zoning in some garnet inclusions, point to a short mantle residence time and formation broadly coeval with the host kimberlite. This differs from the much older (Archean to Proterozoic) ages of peridotitic and most eclogitic diamonds. The most common inclusions in framesites are garnets, which have previously been assigned to a websteritic paragenesis. However, websteritic garnet compositions show a strong overlap with those of the megacryst suite, and several observations argue that framesites are rather linked to the latter paragenesis. Crystallization of megacrysts, like framesites, was broadly coeval with eruption of the host kimberlite, and some megacryst nodules are characterized by quench textures. Megacrysts are grouped into relatively Cr-rich and Cr-poor sub-populations that may occur within a single hand specimen. Likewise, relatively Cr-rich and Cr-poor garnet inclusions are reported in framesites, occasionally even within the same diamond host. Framesites from individual localities are characterized by closely similar, highly diagnostic C-isotopic signatures, with a majority enriched in ¹²C (modal δ¹³C ^o/_oo of -18 to -19) relative to peridotitic and eclogitic diamonds. This highly diagnostic C-isotopic signature is also a characteristic of CLIPPIR Type II diamonds from Cullinan and Letseng, pointing to common paragenesis, and thus also linking CLIPPIR Type II diamonds to the megacryst suite. The large size (> 10mm) of many of the CLIPPIR Type II stones is consistent with such a linkage, as is the evidence that crystallization of CLIPPIR Type II diamonds was broadly coeval with emplacement of the host kimberlite. Following the model proposed by Harte and Gurney (1981), megacrysts are envisaged as forming in a pegmatitic vein network within the thermal aureole surrounding a pooled magma body in the lithosphere. Framesite and CLIPPIR Type II diamonds crystallized as low temperature megacryst phases. This provides the basis for developing a proxy for predicting the presence of CLIPPIR stones when evaluating the economic potential of kimberlites, analogous to the use of G10 garnets for estimating the abundance of peridotitic diamonds. Late-stage megacryst magmas would be Ca- and carbonate rich, providing a chemical environment favourable for the crystallization of breyite under lithospheric P-T conditions.

John Kaiser,  Kaiser Research Online

Why have investors lost confidence in diamond exploration and what will it take to bring them back?

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When Dia Met and BHP announced the discovery of diamonds in the Canadian Arctic in late 1991 it unleashed a tremendous exploration boom, not just in Canada but elsewhere in the world. Three decades later less than a dozen juniors still explore for diamonds. Intensive exploration using geophysical and indicator mineral tools had reduced the likelihood that any large and high grade diamond deposits not hidden under post emplacement cover remained to be found. The acquisition of the Chidliak field by De Beers at sunk exploration cost told investors that small but high grade is not good enough. However, the discussion around large, high value CLIPPIR type diamonds has raised the question if they represent populations with a genesis distinct from the diamonds with an ecologitic or peridotitic paragenesis that make up the bulk of a deposit's grade. This opens the idea that reasonably large but apparent low grade deposits should be revisited with bulk sampling to assess the presence of high value large diamonds that make mining viable. Scientific research into the origin of diamonds and the identification of pathfinders may be the key to a revival of diamond exploration by junior companies.

Lucy Hunt, PhD, Saskatchewan Research Council

Advancements in the capabilities and services of the Saskatchewan Research Council's Diamond Laboratory, and future innovations

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The Geoanalytical Laboratories Diamond Services (GLDS) facility at the Saskatchewan Research Council (SRC) is comprised of three key business lines: Indicator mineral analyses; the micro diamond recovery circuit; and the macro diamond mini bulk sample plant and recovery circuit. The facility is focused on developing new services intended to provide detailed information on the recovered indicator grains, and micro and macro diamonds. With the ever-increasing supply and demand gap in the diamond industry, focus is shifting to prioritize deposits that contain diamonds with unique properties, such as colour, size, and quality to help balance the difficult economics. Nitrogen is the main impurity in diamonds, and SRC can Type the nitrogen to identify higher value populations, and help in grade estimations, resource modelling and target prioritization. Nitrogen can give the diamonds a high value “fancy” yellow colour. Whereas the lack of nitrogen classifies the diamonds as Type II, and these stones can have the top D colour classification and may indicate the potential of courser size frequency distributions (SFD). Identifying populations of potentially higher value stones in a deposit might provide the information needed to advance a project or prioritize deposits.Diamond breakage assessments on macro diamond parcels indicate the proportion of freshly broken stones. Understanding the breakage of an exploration parcel is vital in understanding the SFD. For breakage assessments on Run-of-Mine production the type of damage is important to recognize, and whether changes need to be made in the processing plant. For micro diamond parcels, if there is a large proportion of fragments then this should be taken into consideration when estimating the grade.When it comes to understanding a diamond deposit, one of the key factors is the recoverability of the diamonds. The two main techniques to recover diamonds are X-Ray Luminescence (XRL) and X-Ray Transmission (XRT). By studying the luminescence properties of a parcel of diamonds SRC can determine the proportion of diamonds that would be recoverable by standard XRL technology and compare that with data from the final recovery XRT sorter. This will also indicate if any additional recovery methods would be beneficial such as laser or grease. Finally, SRC can provide full parcel grading and valuation by a qualified diamond grader. Being in the unique position of having recovered the diamonds, and often still having them broken out into recovery method and/or geologic unit, an additional layer of context is given to the graded diamond parcel, which can help with future evaluation and understanding of the deposit. Future developments will be focused on the indicator mineral circuit. Traditionally, indicator minerals have been identified and picked by highly skilled observers. However, the industry is changing, and automated mineralogy has become the new tool in understanding mineral deposits. By collecting data on hundreds of thousands of grains we will be able to employ machine learning to look for trends or patterns and enhance throughput.

 M. Thurston, A. Davy

A big challenge in diamond mine development: diamond price estimation