The metal source and genesis of hydrothermal mercury-rich gold metallogenic systems occurring far away from active continental margins remain puzzling. The Youjiang Basin of South China, where exists numerous Carlin-type gold deposits and some synmineralization hidden intrusions, is a natural laboratory to address this issue due to it was up to 1000 km inward from the active continental margins of South China when mineralization. Here, we use mass-independent fractionation of mercury isotope ratios (reported as ∆199Hg), which is predominantly generated during Hg photochemical reactions on Earth’s surface and has superiority of isotopic inheritance during hydrothermal processes, to address the metal source of the Youjiang Carlin-type gold deposits. Ore-associated sulfides from seven representative deposits display negative to near-zero ∆199Hg values (−0.29‰ to 0.04‰), which fall in between that of the regional Precambrian basement rocks (−0.21‰ to 0.06‰) and deep magmatic-hydrothermal systems (∼0‰), suggesting a binary mixing of Hg from these two sources. An isotope mixing model and mass balance calculations demonstrate that ∼1000 km3 of the basement rocks, which contributed to 86% of Hg budget, were leached and remobilized by magmatic-hydrothermal fluids and deep-circulating crustal fluids to endow the gold reserves of these deposits. Given that traditional S, Pb, C, and O isotopic data yielded indirect and ambiguous constraints on metal source due to their complex evolution processes and isotope fractionation during the fluids ascended. Our results, therefore, highlight the great advantage of using Hg isotope as a new tracer to understand metal sources of hydrothermal deposits.
The metallogenesis of collisional orogen has been a significant research topic for comprehending the linkage between magmatism, metamorphism, hydrothermalism and ore deposition. In Southern Tibet, the Zhaxikang deposit is a super-large Pb-Zn-Sb-Ag polymetallic deposit with metal reserves of 2.367 Mt Zn+Pb (average grade of 6.43%), 0.2552 Mt Sb (average grade of 1.14%), and 2960.6 t Ag (average grade of 101.64 g/t), constituting the largest deposit within North Himalayan Metallogenic Belt. However, the metal sources of the ore-forming material and mineralization process in this deposit remain a subject of controversy due to previous studies primarily relying on a bulk analysis of sulfides, which record the mixed results of multistage mineralization and intergrown minerals of different stages. The objective of this study is to constrain the sources and mineralization process of the Zhaxikang deposit through in-situ analyses of trace elements and sulfur isotopes in sphalerite. Based on ore textures and mineral paragenesis, four mineralization stages and three generations of sphalerite deposited respectively in stage 1 (Sp1), stage 2 (Sp2), and stage 4 (Sp3), were identified. The Pb and Zn mineralization mainly occurred in stage 2, while Sb and Ag were dominantly in stage 4. The trace elements characteristics (Cd, Fe, In, Ga, Ag, Cu, Co, and Mn) observed in sphalerite indicate that the Zhaxikang deposit could be a hydrothermal vein-type deposit associated with magmatism. The δ34S values of sulfides (7.7 to 18.4 ‰) in the deposit generally exhibit a slight elevation compared to those (4.1 to 12.9 ‰) of the Jurassic Ridang Formation slate, indicating that the sulfur of the deposit primarily originated from seawater sulfate in the slate through thermochemical sulfate reduction, although a small amount of contribution from mafic rocks also existed in stage 4. The Pb isotopes in stage 2 range from 19.662 to 19.705, 15.852 to 15.865, and 40.214 to 40.283 for the ratios of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb, respectively, indicating that the metals primarily from the Greater Himalayan Crystalline complex (GHC) with a minor contribution from host rocks. While, the Pb isotopes in stage 4 range from 19.687 to 19.849 for 206Pb/204Pb, from 15.86022 to 15.885 for 207Pb/204Pb, and from 40.261 to 40.414 for 208Pb/204Pb, respectively, indicating that the metals originated from sulfides in the earlier stage as well as the more radiogenic GHC.
The Issues Evidence of abrupt climate change such as Younger Dryas Cold Event and Dansgaard-Oeschger Warm Events comes mainly from ice-core data, especially, of Greenland Ice Cores. Here we report updated results of our investigation of the changes in Taiwan. The Approach In this study, carbon-isotope compositions of samples taken from peat-bog cores of Toushe basin (Fig. 1) were measured to investigate the impact of Younger Drays Cold Event on Taiwan’s climate. Toushe basin is a recently desiccated small lake (Fig. 1).
Major, Trace Element and Sr-Nd Isotope Geochemistry of the Agpaitic Lamprohyres The SiO2 is 46.49%~51.63% and rich in Na2O, FeO, TiO2 and LREE. Na2O is 3.0~4.08%, K2O/Na2O rate is 0.44~0.79, TiO2 is1.75~3.17, ƒEu=1.02~1.06. It is belong to sodium-rich lamprophyre in the classification diagrams of the lamprophyre. The LILE were not rich very obvious, some samples even show K/Sr slightly depleted. Within HFSE, Ta/Nb/Nd/P were enriched slightly and Ti/Zr/Hf were not changed obviously, but Yb, Y were depleted. All the patterns of trace elements show the agpaitic lamprophyres have characteristics of typical oceanic island basalt magma source, which very different from the high K/Ti-low Ti apotassic lamprophyres related with the zone of subduction. Initial Sr/Sr isotope ratio is 0.705332 in average, Initial Nd/Nd isotope ratio is 0.512646 and ΣNd(t)= +3.5~ +3.8, express the slightly depletion mantle source and different with the enriched mantle source of the apotassic lamprophyres.
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