The McDougall-Despina Fault Set, Noranda, Quebec: Evidence for Fault-Controlled Volcanism and Hydrothermal Fluid Flo

Abstract 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 750 m, and coincident with post-cauldron volcanism. Feeder dikes cross-cut each other and are typically depleted in Na2O and CaO, and enriched in MgO, K2O, Fe2O3 and MnO relative to fresh ?ows. Economic and subeconomic massive sul?de deposits occur adjacent to the McDougall-Despina fault set at different levels over a stratigraphic thickness of 3000 m. These include the Corbet deposit, the subeconomic D-68 Zone deposits, and the subeconomic stringer zones of South Rusty Hill and Bedford Hill. Numerous copper occurrences and abundant hydrothermal alteration occur in and immediately adjacent to the fault set. The McDougall, Despina, and adjacent, parallel, ancillary faults de?ne a synvolcanic fault set which controlled the location of magmatism, hydrothermal alteration and mineral deposition during the early evolution of the Noranda cauldron. Signi?cant sul?de mineral deposition commonly occurred in proximity to the intersection of the McDougall-Despina fault set with northeast-trending synvolcanic faults. Recognition of synvolcanic faults is therefore a major objective of exploration programs for volcanic-associated massive sul?de deposits.
Keywords: Fault-controlled Volcanism, Hydrothermal fluid flow, Stratisgraphy, synvolcanic faults.
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Summary: 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
depo...
Publication: Exploration & Mining Geology
Author(s): JEFFREY S. LOEN
Keywords: Gold, Gold Characteristics, Placer Gold, Mineralization
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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