Lithologically controlled invisible gold, Yukon, Canada

MacKenzie, Doug; Craw, Dave; Finnigan, C. S.

doi:10.1007/s00126-014-0532-5

Cited by 17 publications

(5 citation statements)

References 37 publications

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“…Similar substratal supergene enrichment of gold has occurred in Spain, albeit without formation of nuggets (Yesares et al, 2014(Yesares et al, , 2015. In contrast, extensive (locally N200 m deep) unconformity-related oxidation of gold-bearing sulphides in the Yukon goldfield of Canada has not caused significant supergene gold enrichment, although some localised, micron scale, liberation of gold from sulphides has occurred (e.g., MacKenzie et al, 2015). It may be this lack of confounding supergene gold mobilisation in the Yukon goldfield that has enabled linkage of detrital gold with hydrothermal sources (Chapman et al, 2010(Chapman et al, , 2011.…”

Section: Distinguishing Hydrothermal From Supergene Goldmentioning

confidence: 89%

Gold nugget morphology and geochemical environments of nugget formation, southern New Zealand

Craw

Lilly

2016

Ore Geology Reviews

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Section: Distinguishing Hydrothermal From Supergene Goldmentioning

confidence: 89%

Gold nugget morphology and geochemical environments of nugget formation, southern New Zealand

Craw

Lilly

2016

Ore Geology Reviews

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“…2; Wainwright et al 2011;McKenzie et al 2013;MacKenzie et al 2014). These deposits contain elevated As and Mo and also contain stibnite, which is rare in YTT orogenic systems.…”

Section: Cretaceous Au Depositsmentioning

confidence: 91%

“…Because of locally elevated As backgrounds in some host rocks, especially quartzites (up to 100 ppm; cf Fig. 12A), the Sb enrichment can be a more significant indicator of Au mineralization than As in these deposits (MacKenzie et al 2014).…”

Section: Cretaceous Au Depositsmentioning

confidence: 99%

Contrasting geochemistry of orogenic gold deposits in Yukon, Canada and Otago, New Zealand

Craw

Mortensen

MacKenzie

et al. 2015

GEEA

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The YTT and OSB both formed and were mineralized during convergent tectonism that spanned Palaeozoic, Mesozoic and Cenozoic (Fig. 1). Initial Palaeozoic accretion and construction of the basement of both regions were followed by distinct collisional events that produced the main orogenic gold deposits in the Abstract: The Yukon-Tanana Terrane (YTT) of western Yukon Territory in NW Canada and Otago Schist belt (OSB) of South Island, New Zealand share similar geological evolutionary histories as convergent orogenic belts. Both belts host orogenic gold deposits of mainly Jurassic to Early Cretaceous age. Jurassic mineralization in the YTT occurred during convergent orogenesis and stacking of previously-metamorphosed (Palaeozoic) greenschist-amphibolite facies metasediments, metavolcanic rocks, and metagranitoids. Early Cretaceous OSB mineralization occurred in the latter stages of terrane accretion of un-metamorphosed turbidites with minor basaltic rocks. Metamorphism of the OSB turbidites mobilised background levels of Au (0.6-1.3 ppb), As (2-20 ppm), Sb (0.1-1 ppm), and W (< 10 ppm), primarily under greenschist to lower amphibolite facies conditions when diagenetic pyrite (Au c. 0.5-2 ppm; As c. 500-10 000 ppm) transformed to pyrrhotite on a regional scale. In contrast, the previously-metamorphosed YTT rocks had generally low background As contents (1-2 ppm) apart from some As-rich quartzites (up to 100 ppm As). Consequently, there was less As available for orogenic mobilisation, and YTT Au deposits generally have lower concentrations of this pathfinder element compared to the OSB. YTT host rocks, especially metagranitoids, have anomalous levels of Mo (10-300 ppm), and many orogenic deposits contain elevated Mo, locally including molybdenite. OSB turbidites have elevated Mo (2-200 ppm), along with elevated Au and As, in diagenetic pyrite, but this Mo became largely dispersed through the metamorphic pile as metamorphic grade increased and pyrite transformed to pyrrhotite. OSB orogenic deposits have only marginally elevated Mo (c. 1 ppm), no molybdenite, and accessory scheelite in these deposits is distinctly Mo-poor. Only minor mobilisation of base metals occurred in these orogenic belts, and orogenic Au deposits contain sparse base metal sulphides. Orogenic deposits in the YTT and OSB differ in that Au (and other associated elements) in many of the orogenic deposits in the YTT was remobilised from relatively local sources (e.g. pre-existing Cu-Mo-Au porphyry or volcanogenic sulphide mineralization) whereas Au in the OSB was mobilised from larger volumes of homogeneous rock at depth.

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“…This process does not necessarily result in gold of the requisite size to accumulate in fluvial settings to form placers. For example, large scale Au remobilization in the supergene environment resulting in size enhancement from 'invisible' gold to micron size was reported at the Coffee orogenic gold deposit, Yukon (MacKenzie et al 2015).…”

Section: Generic Process Affecting Gold Stability In Weathering Profilesmentioning

confidence: 99%

Evaluation of the contributions of gold derived from hypogene, supergene and surficial processes in the formation of placer gold deposits

Chapman

Craw

Moles

et al. 2021

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Placer gold particles have traditionally been considered as either detrital products of weathering or authigenic minerals growing within placers. Recent advances in understanding of gold chemistry/bio-geochemistry demonstrate that gold growth in specific environments is plausible, but opinions differ on the importance of ‘new’ gold in the overall placer inventory. Here we draw upon visual inspection over 40,000 polished gold particle sections from locations worldwide to evaluate the implications of gold alloy composition and particle heterogeneity in determining the contributions of detrital and authigenic gold to fluvial placers. We conclude i. the detrital model of placer gold formation is widespread and demonstrable, ii. supergene gold may be a locally important constituent of fluvial placers, iii. gold-rich rims on placer gold particles comprise two distinct components: a surface micron-scale addition of pure Au and a tens- of- micron- scale inner rim formed by Ag depletion, iv. the importance to placer inventories of gold particle formation and modification by biogenic processes is considerably overstated.

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Lithologically controlled invisible gold, Yukon, Canada

Cited by 17 publications

References 37 publications

Gold nugget morphology and geochemical environments of nugget formation, southern New Zealand

Gold nugget morphology and geochemical environments of nugget formation, southern New Zealand

Contrasting geochemistry of orogenic gold deposits in Yukon, Canada and Otago, New Zealand

Evaluation of the contributions of gold derived from hypogene, supergene and surficial processes in the formation of placer gold deposits

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