The Luyuangou gold deposit is located in the eastern section of the Xiong’ershan Au-Ag polymetallic district (XESPMD) and consists of a few gold-bearing veins found in the EW-striking faults located in the Archean Taihua and Mesoproterozoic Xiong’er Groups. The gold deposits contain numerous gold-bearing pyrites in thin quartz veins, representing an ideal tool for explaining the enigmatic genesis of gold deposits in the XESPMD. The distributions of trace elements and the sulfur isotopes of gold-bearing pyrite in the Luyuangou gold deposit were investigated to define the origin and evolution of ore-forming fluids. Five generations of pyrite have been identified: coarse-grained euhedral pyrite cores (Py1-1) and margins (Py1-2) in milky quartz veins, fine-grained pyrite (Py2) in quartz veins and host rocks, pyrite (Py3) in quartz + polymetallic sulfide veins, and pyrites (Py4) in quartz calcite veins. The distributions of trace elements indicated that Py2 and Py3 represented the main gold-bearing minerals and contained high concentrations of As, Au, Ag, Pb, Zn, and Cu, and the distributions were controlled by the micro/nanoinclusions. The δ34S values in the five pyrite generations ranged from −19.5 to 3.4‰. Py2 (−15.4 to −6.1‰) and Py3 (−19.5 to −12.4‰) had the lowest δ34S values, indicating that the sulfur originated from an oxidizing fluid. Py1 showed δ34S values (−0.3 to 1.9‰) corresponding to a magmatic origin. Py4 (1.1–3.4‰) displayed the highest δ34S values, indicating that the sulfur originated from the host rock under the action of meteoric water cycles. Analyses of the pyrite’s trace elements and sulfur isotopes, in combination with geological evidence, indicated that magmatic ore-forming fluids contributed to the formation of the Luyuangou gold deposit. The magmatic ore-forming fluids interacted with meteoric water during the main mineralization period. The changing physicochemical conditions of the mineralized fluids caused the precipitation of a large amount of gold and other mineralized elements.
Antimony (Sb) is identified as a critical metal in many countries. The source of hydrothermal Sb-bearing deposits is currently debated in two opposing models (magmatic fluids or country rocks). Some Sb-bearing hydrothermal systems host abundant cadmium (Cd). Due to the close association of Cd and Sb in hydrothermal systems and the distinct Cd isotopic signatures between magmatic and sedimentary rocks, Cd isotopes have the potential to trace the metal origin in Sb-bearing deposits. Here, we conducted Cd isotope analyses of sulfide (jamesonite and sphalerite) collected from the Jianzhupo Zn-Sb deposit, SW China. A narrow range of δ114/110Cd relative to NIST SRM 3108 Cd standard was observed in sphalerites (−0.15‰ to +0.18‰; mean = 0.03‰ ± 0.10‰, one standard deviation [1SD]), identical to that of intermediate igneous rocks (−0.20‰ to +0.15‰); in contrast, pure jamesonites show a large range of δ114/110Cd (−0.42‰ to +0.17‰; mean = −0.22‰ ± 0.20‰, 1SD), differing from those of sphalerite. Different Cd isotope signatures between jamesonite and sphalerite are unlikely to have been triggered by sulfide precipitation, vapor-liquid phase separation, diffusion, and different Cd-S bond strengths. Instead, based on a comparison of δ114/110Cd and Zn/Cd ratio of sulfide and potential source rocks, we propose that a mixing of two ore-forming endmembers, derived from igneous and sedimentary rocks, may better explain the sulfide Cd isotopic signatures. This is supported by the well-defined positive correlation between δ114/110Cd and Zn/Cd ratio in sulfides. This study shows a novel application of Cd isotopes for metallogenetic tracing and demonstrates that Sb-bearing hydrothermal systems can incorporate metals from multiple sources.
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