The Significance of Eclogite and Cr-poor Megacryst Garnets in Diamond Exploration

Eclogite is an important source of diamond in the upper mantle, but is more localized than peridotite. Using eclogitic minerals in kimberlite and diamond exploration is also more problematic than using the well-known peridotite-derived indicator minerals Cr-pyrope and magnesiochromite. The problems include color similarities between orange garnets from eclogites, Cr-poor megacrysts, and crustal garnets, chemical similarities with Cr-poor megacryst suite garnets (specifically elevated Na2O contents), and low abundance of eclogite garnet xenocrysts in most known kimberlites. Chemical screens must be used carefully to distinguish between varieties of orange garnets in exploration samples. For example, most orange garnets of crustal origin have >22 wt% FeO, with mantle eclogite garnets having lower values. Na2O-bearing garnets from the Cr-poor megacryst suite can be distinguished from Na2O bearing garnets from diamondiferous eclogites by the elevated TiO2 contents of the former. The low abundance of eclogite garnet xenocrysts in kimberlites worldwide, however, may dictate that use of eclogite garnets in diamond exploration in most cases be restricted to advanced stages of kimberlite exploration and evaluation of kimberlite diamond potential. Crpyropes, Mg-ilmenites and Cr-rich chromites are more useful than eclogitic garnets in most stages of diamond exploration. If orange garnet xenocrysts are sought in a kimberlite exploration program, those from the Cr-poor megacryst suite will be more useful than eclogite derived garnets, due to the typical great abundance of the former, although they carry no information of the diamond potential of the host kimberlite.
Keywords: Eclogite, Diamond, Kimberlite exploration, Diamond exploration
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Summary: The Geological Society has its own quarterly journal called Exploration
and Mining Geology, for the publication of Canadian and international papers on
applied aspects of mineral exploration and exploitation, including mineral
deposit geology, geochemistry, and geophysics, mining geology, mineral resource
appraisal and estimation methods, environmental geology, and case histories. The
editor of the journal is Jeremy P. Richards
Publication: Exploration & Mining Geology
Issue: 4
Volume: 6
Year: 1997
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<BODY>The Canadian Shield and its extensions are traversed by an orthogonal
system of northwest and northeast trending arch-style uplifts. These basement
arches were formed by repeated vertical movements along pre-existing structures
during compressional and extensional tectonism...
Publication: Exploration & Mining Geology
Author(s): K.D. CARD: Card and Associates’ Geosearch, 86 Penfield Drive, Kanata, Ontario, Canada, K2K 1M1; B.V. SANFORD: 17 Meadowglade Drive, Nepean, Ontario, Canada, K2G 5J4; G.M. CARD: Card and Associates’ Geosearch, 86 Penfield Drive, Kanata, Ontario, Canada, K2K 1M1
Keywords: Canadian Shield, Uplifts, Basement arches, Techtonism, Magnetism
Issue: 4
Volume: 6
Year: 1997
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Summary: The presence of fine-grained mineral intergrowths, the complex distribution of deleterious minor elements, and the variable base-metal contents in some assemblages commonly pose technical problems for the processing of volcanogenic massive sulfide ores. The beneficiation of most massive sulfide ores from the Iberian Pyrite Belt requires extremely fine grinding to liberation sizes of K80 = 15 µm to 25 µm. For several deposits, mapping of the ore types and metal zoning patterns has shown that...
Publication: Exploration & Mining Geology
Author(s): ORLANDO C. GASPAR: Laboratório do Instituto Geológico e Mineiro, 4465 S. Mamede de Infesta, Portugal
Keywords: Mineral intergrowth, base metal, Volcanogenic massive sulfide ores, Iberian Pyrite Belt
Issue: 4
Volume: 6
Year: 1997
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Summary: The acid rock drainage (ARD) buffering capacity of mine waste is governed by its bulk chemical composition and its mineral assemblage. Conventional acid base accounting (ABA) tests can be used to predict short-term buffering, but should be used with caution to model or predict the long-term ARD buffering capacity of mine waste. ABA data for mine waste samples from four different deposit types: anorthosite-hosted magmatic sulfide nickel, dunite-hosted magmatic sulfide nickel, porphyry...
Publication: Exploration & Mining Geology
Author(s): BRUCE W. DOWNING: Gamah International Limited, Vancouver, British Columbia, Canada; HANS E. MADEISKY: HEMAC Exploration Ltd., Vancouver, British Columbia, Canada
Keywords: Acid rock drainage, ARD, Mine waste, Acid base accounting, ABA
Issue: 4
Volume: 6
Year: 1997
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<BODY>The Red Chris Cu-Au deposit (522.7 Mt at 0.35% Cu and 0.27 g/t Au),
northwestern British Columbia, is one of several pre-accretionary porphyry
systems in the Cordillera of western Canada. It is hosted by an Early Jurassic
hornblende monzonite to quartz monzodiorite porphyry which...
Publication: Exploration & Mining Geology
Author(s): T. BAKER: Mineral Deposit Research Unit, Department of Earth and Ocean Sciences
The University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z4
C.H. ASH: Geological Survey Branch, Ministry of Employment and Investment, Victoria, British Columbia, Canada, V8W 9N3; J.F.H. THOMPSON: Mineral Deposit Research Unit, Department of Earth and Ocean Sciences, The University of British Columbia, Vancouver, British Columbia, Canada, V6R 1Z4
Keywords: Red Chris deposit, Cu-Au deposit, Porphyry, Carbonate
Issue: 4
Volume: 6
Year: 1997
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<BODY>Narrow veins are an important world-wide source of silver, tin, uranium
and particularly gold. To potential financiers, this style of mineralization is
viewed as high risk because of the often relatively small resource involved and
high cost of estimation. In many cases diamond...
Publication: Exploration & Mining Geology
Author(s): SIMON C. DOMINY: Mining Geology Group, School of Earth and Environmental Sciences, University of Greenwich, Chatham Maritime, Kent ME4 4TB, U.K., and
Welsh Gold Plc, Northwood, Middlesex HA6 3LY, U.K.; ALWYN E. ANNELS: Mining Geology Group, School of Earth and Environmental Sciences, University of Greenwich, Chatham Maritime, Kent ME4 4TB, U.K.; Steffen, Robertson & Kirsten (UK) Ltd, Cardiff CF1 3BX, Wales, U.K.; G. SIMON CAMM, PAUL WHEELER: Department of Geology, Camborne School of Mines, Unive
Keywords: Geology, Narrow veins, Silver, Tin, Uranium, Gold, Mineralization, Geological study
Issue: 4
Volume: 6
Year: 1997
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