Chemical and Mineralogical Signatures of Gold Formed in Oxidizing Chloride Hydrothermal Systems and their Significance within Populations of Placer Gold Grains Collected during Reconnaissance

Chapman, Robert J.; Leake, R. C.; Bond, David P.G.; Štědrá, Veronika; Fairgrieve, B.

doi:10.2113/gsecongeo.104.4.563

Cited by 81 publications

(67 citation statements)

References 59 publications

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“…The higher fineness (higher Au/Ag ratios) might be explained by: (1) the higher solubility of silver when compared to that of gold in surface and oxidizing conditions (Boyle 1979;Webster and Mann 1984); (2) gold transport by chloride oxidizing systems, with silver being present as a solid Ag chloride, such as chlorargyrite, and is not available for transport in solution (Chapman et al 2009). …”

Section: Epigenetic Mineralizationmentioning

confidence: 99%

The Paleoproterozoic metaconglomerate-hosted Castelo de Sonhos gold deposit, Tapajós Gold Province, Amazonian Craton: a modified paleoplacer origin

Queiroz¹,

Klein

2018

JGSB

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The Castelo de Sonhos gold deposit (~1.5 Moz Au) is located in the southeastern Tapajós Gold Province and is hosted in variably deformed metaconglomerates and metasandstones of the Castelo dos Sonhos Formation, which was deposited between 2011 and 2050 Ma and considered to be a relic of a major foreland system. Gold is found mainly in the matrix of metaconglomerates and subordinately in fractures of metasandstones. The host rocks are strongly silicified, which was demonstrated to be the result of silica overgrowth during diagenesis, without relationship to hydrothermal alteration. The rocks are also impregnated with secondary iron oxides, which are interpreted to be consequence of weathering of the metasedimentary sequence and total or partial dissolution of iron-bearing minerals and re-precipitation of iron during circulation of oxidized (meteoric and/or magmatic) fluids. The morphology of matrix gold particles indicates that they are not pristine, but only slightly modified and reshaped, which suggests detrital provenance and relatively proximal distance of transport from the original sources. The chemical composition of the particles, with Au grading 94-97%, very high Au/ Ag and lack of other significant metals, suggest single source, or sourcing from a single class (orogenic?) of gold deposits. The gold particles from fractures are platy and show even higher Au/Ag ratios, given by very low Ag contents (<<1%), which are interpreted as epigenetic remobilization of the matrix gold. Oxygen isotope compositions of hydrothermal quartz-sulfide-muscovite veins cutting across the host metasedimentary sequence indicate magmatic origin for the fluids, which might have been produced by granites that intruded the metasedimentary rocks and helped gold remobilization to fractures. As a consequence, Castelo de Sonhos is interpreted as a modified paleoplacer gold deposit.

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Section: Epigenetic Mineralizationmentioning

confidence: 99%

The Paleoproterozoic metaconglomerate-hosted Castelo de Sonhos gold deposit, Tapajós Gold Province, Amazonian Craton: a modified paleoplacer origin

Queiroz¹,

Klein

2018

JGSB

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“…A summary in Chapman et al (2009) drew upon multiple examples from the British and Irish Caledonides, Malaysia and early sampling programs in the North American Cordillera. More recent studies of orogenic gold in British Columbia and Yukon (Chapman et al 2010a, b, 2011, Wrighton 2013 have reinforced the assertion that although the Ag content of gold formed in orogenic settings may vary considerably, the mineral inclusion signature comprises a relatively simple suite of sulfides, sulfarsenides, and more rarely sulfosalts and tellurides.…”

Section: Implications For Explorationmentioning

confidence: 99%

“…The microchemical signature may be applied to evaluate variation within a single style of mineralization in a specific area (e.g., Chapman et al 2010a, b, Chapman and or to investigate a specific signature associated with a particular style of Au mineralization (e.g., Chapman et al 2009). This approach has proved particularly valuable in the study of gold from alkalic porphyry systems in which gold is precipitated in different hydrothermal settings within the evolving system (Chapman et al 2017).…”

Section: Introductionmentioning

confidence: 99%

A new indicator mineral methodology based on a generic Bi-Pb-Te-S mineral inclusion signature in detrital gold from porphyry and low/intermediate sulfidation epithermal environments in Yukon Territory, Canada

et al. 2017

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Porphyry-epithermal and orogenic gold are two of the most important styles of gold-bearing mineralization within orogenic belts. Populations of detrital gold resulting from bulk erosion of such regions may exhibit a compositional continuum wherein Ag, Cu, and Hg in the gold alloy may vary across the full range exhibited by natural gold. This paper describes a new methodology whereby orogenic and porphyry-epithermal gold may be distinguished according to the mineralogy of microscopic inclusions observed within detrital gold particles. A total of 1459 gold grains from hypogene, eluvial, and placer environments around calcalkaline porphyry deposits in Yukon (Nucleus-Revenue, Casino, Sonora Gulch, and Cyprus-Klaza) have been characterized in terms of their alloy compositions (Au, Ag, Cu, and Hg) and their inclusion mineralogy. Despite differences in the evolution of the different magmatic hydrothermal systems, the gold exhibits a clear Bi-Pb-Te-S mineralogy in the inclusion suite, a signature which is either extremely weak or (most commonly) absent in both Yukon orogenic gold and gold from orogenic settings worldwide. Generic systematic compositional changes in ore mineralogy previously identified across the porphyry-epithermal transition have been identified in the corresponding inclusion suites observed in samples from Yukon. However, the Bi-Te association repeatedly observed in gold from the porphyry mineralization persists into the epithermal environment. Ranges of P-T-X conditions are replicated in the geological environments which define generic styles of mineralization. These parameters influence both gold alloy composition and ore mineralogy, of which inclusion suites are a manifestation. Consequently, we propose that this methodology approach can underpin a widely applicable indicator methodology based on detrital gold.

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“…Continental Devono-Carboniferous rocks, the Old Red Sandstone sensu lato, have received less attention in this respect. However, gold-bearing grains in modern streams cutting through Devonian red beds in Scotland (Chapman et al 2009) and the proven availability of gold to the Devonian surface environment in the Rhynie hot spring system, Scotland (Rice et al 1995) suggest that these red beds merit investigation for evidence of gold concentration. This study reports the low-temperature occurrence of native gold in Devono-Carboniferous red beds in Scotland.…”

mentioning

confidence: 99%

Gold in Devono-Carboniferous red beds of northern Britain

Parnell

Still

Spinks

et al. 2015

JGS

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Authigenic gold occurs in Devono-Carboniferous red beds in northern Britain. Red beds exhibit concentrations of gold and pathfinder elements for gold mineralization including tellurium and mercury, at redox boundaries. Detailed studies of samples from Millport, Isle of Cumbrae, Firth of Clyde, show particles of native gold up to 10 µm size, typically with less than 15 wt% silver. Their context indicates that the gold was concentrated during diagenesis, in rocks that had not experienced regional temperatures above 100°C. These occurrences add to other evidence of a role for red beds in the genesis of gold mineralization.

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Chemical and Mineralogical Signatures of Gold Formed in Oxidizing Chloride Hydrothermal Systems and their Significance within Populations of Placer Gold Grains Collected during Reconnaissance

Cited by 81 publications

References 59 publications

The Paleoproterozoic metaconglomerate-hosted Castelo de Sonhos gold deposit, Tapajós Gold Province, Amazonian Craton: a modified paleoplacer origin

The Paleoproterozoic metaconglomerate-hosted Castelo de Sonhos gold deposit, Tapajós Gold Province, Amazonian Craton: a modified paleoplacer origin

A new indicator mineral methodology based on a generic Bi-Pb-Te-S mineral inclusion signature in detrital gold from porphyry and low/intermediate sulfidation epithermal environments in Yukon Territory, Canada

Gold in Devono-Carboniferous red beds of northern Britain

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