Geology in the Resource and Reserve Estimation of Narrow Vein Deposits





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 core drilling will not enable
resource estimation beyond the inferred and indicated categories. Exploratory
underground development is required to define measured resources. The definition
of geological and grade continuity are major factors in narrow vein assessment.
A measured resource must be based on strong geological and grade continuities.
Narrow veins, generally less than 3 m wide, are complex geological phenomena,
which commonly display unpredictable geometry and grade distribution. Variations
in structural continuity, dip, strike, width, mineralogy and specific gravity
are common. Veins may be composite, with ore-grade mineralization restricted to
a specific structural domain. Branches, intersections and braided zones are
common features. Potentially high-grade zones are often localized within ore
shoots, which are surrounded by barren/low-grade regions. Resources must be
determined as closely as possible to reality and reflect the distribution of the
commodity in the rock. Estimation has three main requirements: (1) geological
study to determine orebody nature; (2) estimation of tonnage and grade, and (3)
the presentation of this information using a classification that is clear,
unambiguous and bankable. Estimation methods employed are either classical or
geostatistical; however, classical methods are often used because of the
difficulties in applying geostatistics. Grades generally show a strong
positively skewed distribution testifying the presence of high-grade values.
Problems exist in the applicability of cutting outlier values risking over- or
underestimation of grade. It is generally believed that where resource estimates
are in error, poor geological control is usually the cause. Overestimation can
lead to the closure of a mine through lost revenue and capital. An understated
estimate can result in an opportunity missed for profit and/or greater economies
of scale. Definition of reserves involves the consideration of economic and
engineering data, to decide which part of the resource is economically mineable.
Geology plays a similarly important role at this stage in the assessment of
likely mining method, dilution, recovery etc. Throughout resource/reserve
estimation, it is crucial that the amount and quality of the data and the
geologist’s experience are relevant. The impact of geological understanding on
estimation is often undervalued or assumed to be of lesser importance than
finding grades and tonnages. This paper discusses the geology of narrow vein
deposits and the importance of geology in their evaluation.
Keywords: Geology, Narrow veins, Silver, Tin, Uranium, Gold, Mineralization, Geological study
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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: 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...
Publication: Exploration & Mining Geology
Author(s): DANIEL J. SCHULZE: Department of Geology, University of Toronto, Erindale College
Mississauga, Ontario, Canada L5L 1C6
Keywords: Eclogite, Diamond, Kimberlite exploration, Diamond exploration
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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Summary: <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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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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