The source of gold in the Yata Carlin-type deposit, southwest China: constraints from pyrite chemistry and sulfur isotope

Although the Youjiang basin in southwest China is the second-largest Carlin-type gold district worldwide, the sources of the gold in this district remain considerably debated. This study, using laser ablation-inductively coupled plasma-mass spectrometry and secondary ion mass spectrometry, investigated the trace element and sulfur isotope compositions of the pre-ore and ore pyrite in the Yata gold deposit. In this deposit, pre-ore pyrite occurs as nodules (Sed-Py0) in the carbonaceous sedimentary rocks, or as a core (Ore-Py1) characterized by irregularly shaped porous aggregates (locally as framboids) in ores, both of which are considered to be sedimentary and/or diagenetic in origin. Ore pyrite consists of an irregular As-rich mantle (Ore-Py2) and an As-poor rim (Ore-Py3) with subhedral crystals. Trace element analysis indicates that the above pyrite generations contain average concentrations of gold of 0.2 ppm for Sed-Py0, 8.9 ppm for Ore-Py1, 30.7 ppm for Ore-Py2, and 391.2 ppm for Ore-Py3. The latter three generations of ore pyrite yield δ 34 S values ranging from +3.7 ‰ to +7.4 ‰, +4.9 ‰ to +9.0 ‰, and +6.1 ‰ to +9.2 ‰, respectively. Pre-enrichment of Au, as well as As, and Sb in sedimentary/diagenetic pyrite, combined with the indistinguishable sulfur isotopes between pre-ore and ore pyrite, collectively supports a sedimentary rock origin of gold that accounts for the Yata Carlin-type gold deposit in the Youjiang basin.