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Durham University

Department of Earth Sciences

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Publication details for Prof. Dave Selby

Lawley, C.J.M., Yang, X.M., Selby, D., Davis, W., Zhang, S., Petts, D.C. & Jackson, S.E. (2020). Sedimentary basin controls on orogenic gold deposits: New constraints from U-Pb detrital zircon and Re-Os sulphide geochronology, Lynn Lake greenstone belt, Canada. Ore Geology Reviews 126: 103790.

Author(s) from Durham

Abstract

Sedimentary basins that open and close during the last stages of mountain building represent an important exploration criterion for orogenic gold deposits. However, the genetic and/or preservation controls of these synorogenic, or “Timiskaming-type”, sedimentary basins and their controlling fault systems on orogenic gold deposits remain unclear. Herein we address that knowledge gap and report new U-Pb detrital zircon and Re-Os sulphide (arsenopyrite and pyrite) geochronology and sulphide Pb isotope results for the Paleoproterozoic Lynn Lake greenstone belt (LLGB), Manitoba, Canada. The youngest detrital zircon from all six meta-conglomerate and -psammite samples of the synorogenic Sickle Group, and previously reported U-Pb zircon ages for post-Sickle Group intrusions, are used to constrain its depositional timing from 1836 ± 15 to 1831 ± 4 Ma. Replicate analyses of one highly-radiogenic arsenopyrite sample from an auriferous vein at the MacLellan gold deposit yield a weighted average Re-Os model age of 1824 ± 12 Ma, which is identical to previously published in situ U-Pb xenotime ages at the same deposit (1827 ± 8 Ma). Each of these hydrothermal ages demonstrate that early-stage auriferous veins immediately post-date deposition of the Sickle Group and most likely occurred prior to peak metamorphism (1814–1801 Ma). This sequence of events is very similar to the Abitibi greenstone belt, suggesting that a synorogenic phase of extension and rapid burial of auriferous veins by Timiskaming-type Sickle Group sediments may have played an important genetic and/or preservation control on early-stage gold mineralization in the LLGB. However, unlike the Abitibi greenstone belt, none of the known gold deposits within the LLGB are hosted within the Sickle Group. Younger Re-Os model arsenopyrite ages at 1782 ± 16 Ma from the MacLellan gold deposit also post-date synorogenic sedimentary basins by ca. 50 Myr. These late-stage auriferous veins are unrelated to the synorogenic extensional phase and more likely reflect repeated fluid focusing along reactivated structures during a post-peak metamorphic phase of hydrothermal activity. The multi-stage hydrothermal history of orogenic gold deposits in the LLGB also provides a possible explanation for the mixture of depleted mantle-like and highly radiogenic fluid components that are inferred from age-corrected sulphide Pb isotope compositions (µ1.8 Ga = 8.9–10.6). Reworked cratonic margins and their associated greenstone belts thus represent favourable depositional settings for auriferous fluids at multiple stages throughout the lifespan of an orogen.