Microchemical Studies of Placer and Lode Gold in the Klondike District, Yukon, Canada: 1. Evidence for a Small, Gold-Rich, Orogenic Hydrothermal System in the Bonanza and Eldorado Creek Area

Chapman, Robert J.; Mortensen, J. K.; Crawford, Evan Cameron; LeBarge, W.

doi:10.2113/econgeo.105.8.1369

Cited by 54 publications

(31 citation statements)

References 37 publications

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“…Quantitative compositional characterization of the gold particles was carried at UBC using a Cameca SX50 Chapman et al (2010a) reported that the data sets produced using the two analytical facilities are comparable, although the use of the Jeol 8230 Superprobe lowered the limit of detection (LOD) for Hg from 0.3 to 0.06 wt%. The data presented in Table 3 applies the appropriate LOD value to each sample according to their analytical history.…”

Section: Methodsmentioning

confidence: 99%

“…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. Where tellurides are observed, they are usually present as hessite, and in all studies in orogenic areas, only a tiny number of gold particles containing bismuth telluride have been reported.…”

Section: Implications For Explorationmentioning

confidence: 97%

“…Secondly, sample populations of detrital grains may contain particles derived from different sources. Chapman and Mortensen (2016) noted that gold grains collected from allochthonous placer deposits may be derived from multiple sources, whereas autochthonous placers are typically associated with smaller catchments and are more likely to contain gold from a single source (e.g., Chapman et al 2010a). Location maps indicating the sampling sites at Casino, Klaza and Nucleus-Revenue are provided in the Online Resources 1-4.…”

Section: General Approachmentioning

confidence: 99%

“…However, as discussed previously in relation to the Ag content of gold alloy, metal speciation within hydrothermal regimes at different localities is not always clear, which may result in different compositional trends within the evolving porphyry mineralisation (e.g., at Cerro Casale, Palacios et al 2001 andSanto Tomas II, Tarkian andKoopmann 1995). While it is at least possible to speculate on the factors affecting the Cu content of Au-Ag alloys, controls on Hg content remain poorly understood (see discussion in Chapman et al 2010a).…”

Section: Evolution Of the Microchemical Signatures Of Gold In The Pormentioning

confidence: 99%

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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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Section: Methodsmentioning

confidence: 99%

Section: Implications For Explorationmentioning

confidence: 97%

Section: General Approachmentioning

confidence: 99%

Section: Evolution Of the Microchemical Signatures Of Gold In The Pormentioning

confidence: 99%

See 2 more Smart Citations

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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“…Sigmoidal profiles of shallow gradient are typical of orogenic Au (e.g. Chapman et al 2010b) but may be generated in any mineralizing system where the chemical conditions of Au precipitation are stable. There are some differences between areas within the Mournes: Au from the Leitrim River has a larger proportion of Ag-poor Au than elsewhere, and Ballincurry River Au has a higher proportion of Ag-rich Au (Fig.…”

Section: Microchemical Signaturementioning

confidence: 99%

The significance of copper concentrations in natural gold alloy for reconnaissance exploration and understanding gold-depositing hydrothermal systems

Moles

Chapman

Warner³

2013

GEEA

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Analytical studies of placer (detrital) gold grains, intended to track bedrock sources and styles of mineralization, mainly consider alloy Ag content and inclusion mineralogy to generate 'microchemical signatures'. Occasionally Hg and Pd help discriminate gold from different sources; Cu infrequently because electron microprobes seldom detect the low concentrations. Reporting of Cu has been largely confined to gold from porphyry-epithermal environments, and this has biased subsequent interpretations of observed Cu-bearing gold alloys.This study focuses on placer gold in the Mourne Mountains, Northern Ireland, where auriferous bedrock remains undiscovered and the complex geology is consistent with either orogenic or intrusion-related mineralization. Over 500 gold grains analysed average 0.17% Cu ranging to >1% Cu and show a wide variation in Ag content. Inclusion mineralogy mainly matches that of orogenic gold elsewhere in the host terrane; however, some signatures are suggestive of zonation within an orogenic hydrothermal mineralizing system, or possibly metamorphic-hydrothermal remobilized gold associated with subsequent intrusive activity. One locality in the study area has placer gold of a distinctive Cu-rich alloy composition containing Cu sulphide inclusions, an association noted elsewhere in gold derived from alkali Cu-Au porphyries.Consideration of Cu-bearing gold alloys worldwide indicates that previously proposed compositional correlations with deposit type are of limited value. We show that Cu contents to at least 0.8% are permissible within orogenic gold -the first time that such compositions have been clearly ascribed to orogenic mineralization. The result is particularly important considering on-going exploration in northern Canada which employs gold grain analysis to help define exploration targets.

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Mineral chemistry, bulk rock geochemistry, and S‐isotope signature of lode‐gold mineralization in the Bétaré Oya gold district, south‐east Cameroon

et al. 2017

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Lode‐gold mineralization in the Bétaré Oya gold district is related to a series of quartz–sulphide veins that define a steeply dipping NNE–SSW‐trending brittle–ductile shear zone. The veins transect metasedimentary sequences in the vicinity of small granitic intrusions. Quartz veins range from barren (massive quartz) to mineralized with textures that vary from foliated, sheared, vuggy, fractured, and sugary to brecciated with inclusions of altered wall rock. They contain gold, pyrite, and galena in addition to chalcopyrite and both hypogene and supergene haematite and covellite. Parameters that consistently define primary gold mineralization in the area include silicification, sulphidation, sericitization, K‐feldspar alteration, haematitization, and carbonatization. Gold grains recovered from heavy mineral concentrate and grains that occur as inclusions in pyrite were characterized by microchemical methods. The gold grains are zoned and exhibit a simple internal structure of partly deformed and leached rims and high‐purity intragranular veinlets. Gold is alloyed with Ag; gold fineness varies between 859 and 877 in the core and from 958 to 997 in the leached rims. Inclusions of gold in pyrite cluster between 875 and 900. Pyrite has up to 0.59 wt% Au, and other trace elements occur in low quantities but for Pb (0.13 wt%), Ag (1.36 wt%), and Sb (1.63 wt%). The bulk trace element signature of the veins is characterized by Au, Ag, As, Bi, Ba, Cr, Cu, Mn, Pb, Sb, Sr, V, W, Zn, and Zr. This depicts a geochemical association of Au ± Cu ± Bi ± As ± Pb. The occurrence of Au as well as elevated Pb and Zn could suggest a granitic source for the ore‐bearing fluid. The auriferous quartz veins are characterized by a widespread in δ34S from 2.8 to 14.9‰ pointing to multiple sources of sulphur in the system, perhaps a mixture of sulphur from the metasedimentary and the granitic rocks.

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Microchemical Studies of Placer and Lode Gold in the Klondike District, Yukon, Canada: 1. Evidence for a Small, Gold-Rich, Orogenic Hydrothermal System in the Bonanza and Eldorado Creek Area

Cited by 54 publications

References 37 publications

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

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

The significance of copper concentrations in natural gold alloy for reconnaissance exploration and understanding gold-depositing hydrothermal systems

Mineral chemistry, bulk rock geochemistry, and S‐isotope signature of lode‐gold mineralization in the Bétaré Oya gold district, south‐east Cameroon

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