Use of Placer Gold Characteristics to Locate Bedrock Gold Mineralizatio

Abstract The size, morphology, surface texture, per cent mineral inclusions, and bulk chemistry
(Ag and trace elements) of placer gold particles vary systematically according to transport distance from source rocks, as indicated by a case study from the Pioneer district in Montana, and data from the literature.
Placer gold samples show a rapid decrease in mean and maximum particle length, and a gradual
increase in ?atness index (F.I. = length + breadth/2 thickness) from about F.I. = 2 in bedrock
deposits, to as much as F.I. = 45 over transport distances of several tens of kilometers. Primary mineral inclusions (mainly quartz, sul?de minerals, and iron oxides) are mostly lost within 10 km to 20 km of ?uvial transport; this loss of quartz and trace metals causes a major change in bulk chemistry of placer gold samples. Following the loss of inclusions and the development of ?akes, edges of ?akes are folded and the mean number of folded edges in a sample increases with distance. When viewed under the electron microscope, surface textures of placer gold particles also become progressively more pitted with distance. Analysis of placer gold particles can be used to help evaluate placer source-area problems (placers with no known hard-rock gold deposits). For example, coarse placer gold containing abundant inclusions indicates a proximal source. On the other hand, an abundance of thin ?akes is evidence of a long transport distance and possible reworking from older gravels. Placer gold characteristics can therefore provide information on distance to mineralized source rocks
Keywords: Gold, Gold Characteristics, Placer Gold, Mineralization
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Summary: The McDougall-Despina fault set in the Noranda district of northwestern Quebec de?nes the eastern margin of the Despina cauldron, nested within the district-scale Noranda cauldron. The faults are stratabound in that they displace stratigraphy of the cauldron ?ll, but do not offset the cauldron cover. The faults are occupied by dikes that acted as eruptive centers to volcanic members of the cauldron-?lling sequence. Measurable displacement across the McDougall-Despina fault set is greater than...
Publication: Exploration & Mining Geology
Author(s): Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada, N6A 5B7, H.L. GIBSON, Mineral Exploration Research Centre, Laurentian University, Sudbury, Ontario, Canada, P3E 2C6, J.J. WATKINS P.O. Box 3127, Courtenay, British Colu
Keywords: Fault-controlled Volcanism, Hydrothermal fluid flow, Stratisgraphy, synvolcanic faults.
Issue: 4
Volume: 4
Year: 1995
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Summary: The Murray Brook precious metal (Au, Ag) gossan deposit is one of nine supergene mineral deposits that have developed over polymetallic massive sulfide deposits in the Bathurst Camp of New Brunswick. Reserves consist of 1.9 Mt of gossan containing 1.53 g/t Au and 65.9 g/t Ag. The supergene zone at Murray Brook consists of six distinct units: a) altered massive sulfide, b)
pyrite-quartz sand, c) massive sulfide gossan, d) disseminated sulfide gossan, e) ferruginized wallrock, and f) leached...
Publication: Exploration & Mining Geology
Author(s): D.R. Boyle
Keywords: Geochemistry, Genesis, Murray Brook, Precious metal deposit, Gossan deposit, Mineralogy, Metallurgy, Gold concentration
Issue: 4
Volume: 4
Year: 1995
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Summary: Norm calculation procedures originally designed principally for igneous rocks are very rigid in their application and, in general, do not utilize important alteration minerals. For instance,
volatile components are essential constituents of many metasomatic rocks but either are not used or are not used effectively in determining normative minerals by the CIPW norm or Niggli-Barth norm procedures. Our approach to determining norms for metasomatic rocks allots all major, minor and volatile...
Publication: Exploration & Mining Geology
Author(s): XIAOLIN CHENG, A.J. SINCLAIR
Keywords: Hydrothermal alteration systems, Igneous rocks, metasomatic rocks, Petrography.
Issue: 4
Volume: 4
Year: 1995
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