Geochemistry and Genesis of the Murray Brook Precious Metal Gossan Deposit, Bathurst Mining Camp, New Brunswic

Abstract 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 bedrock. The massive sulfide gossan constitutes the main body of economic mineralization and consists of goethite, primary quartz, secondary amorphous silica, K-Fe-Pb-AsSb-Ag hydrated sulfate and oxide minerals (beudantite, plumbojarosite, jarosite, bindheimite, scorodite), trace cinnabar, and cassiterite of primary origin. The order of stability of sulfide minerals during oxidation was pyrite,arsenopyrite, galena, Bi-Sb sulfosalts chalcopyrite, tetrahedrite group, sphalerite.
Two mass balance techniques (isovolumetric and conservative element) indicate elemental depletion in gossan relative to primary ore in the order: S>Cd=Zn>Cu=Mn>Na=Ca>Fe=Al=V> Mg=
K=Se=Hg>Pb>Ti>Ag>Mo=P>Ba; and enrichment in the order Au>As>Sb>Si>Bi. Tin, as cassiterite, is conservative.
Mineralogic and paleomagnetic data suggest that the gossan deposit formed under a warm temperate climate throughout the Pliocene. The rate of oxidation and the compositional nature of the ore
was significantly influenced by: a) the position of the primary sulfide zone in a downward moving
hydrological system, b) primary sulfide composition and zonation that promoted the development of
a strong electrochemical oxidation system, and c) pronounced intercalation of carbonate and sphalerite mineralization in sulfide zones, which promoted rapid development of secondary porosity, permeability and downward flow of oxygenated groundwater. During progressive oxidation and physico-chemical erosion of the gossan zone, Au was transported downward in groundwaters, probably as a Au o colloid complex, to be concentrated in the lower horizons of the gossan profile. The precipitation of Au was greatly increased in the pyrite/arsenopyrite zones. Gold concentration was multi-cyclic with continual dissolution and nucleation of the metal until final concentration in the void structures of the gossan. Leaching experiments and microprobe analyses indicate that Au is present in the gossan as submicron composite sols of Au-Ag-silica.
Keywords: Geochemistry, Genesis, Murray Brook, Precious metal deposit, Gossan deposit, Mineralogy, Metallurgy, Gold concentration
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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 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
Text
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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