Kun-Feng Qiu:Giant Mesozoic gold ores derived from subducted oceanic slab and overlying sediments【GCA,2023】
Apr 20, 2023 Views:95

Orogenic gold deposits account for more than 30 % of the global gold resources. To understand the genesis of orogenic gold deposits and ultimately target new orogenic gold deposits, it is important to determine the origin of gold. However, there has been a continuing debate surrounding gold source reservoirs. The Jiaodong gold province, comprising ore hosted within Mesozoic granitoids that intruded Archean metamorphic rocks, together with other gold occurrences in the North China block, collectively constitute the only Mesozoic world-class gold resource in a Precambrian basement. This geological setting, with young deposits in ancient rocks, offers a great opportunity to better determine the gold source because it allows us to fingerprint the isotopically distinct reservoirs. Specifically, it is possible to determine whether the mass-independent isotopic fractionation sulfur (MIF-S)-bearing Archean supracrustal rocks that form the lower crust are a permissive source. We present multiple sulfur isotope (δ34S and Δ33S) measurements of pyrite grains (n = 161) from 18 gold deposits in the six main districts of the Mesozoic Jiaodong gold province. Gold-associated pyrite grains yield non-MIF-S signatures (Δ33S = 0 ‰), indicating that Archean metasedimentary rocks are not a source reservoir of sulfur and gold. The isotopically heavy S (average δ34S = +9.0 ± 3.7 ‰, 2SD) demonstrates a sulfur contribution from a subducted oceanic slab and, in particular, its overlying sediments while excluding mantle and magmatic sources. The subduction-related metamorphism released appreciable gold and sulfur from the top of the downgoing slab into aqueous-carbonic fluids that ascended into the upper plate along crustal structures traversing a tectonically thinned crust. Here, we demonstrate that these giant Mesozoic orogenic gold deposits sourced gold and sulfur during subduction-related devolatilization reactions.

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