Composition and Geochemical Characteristics of Pyrite and Quartz: Constraints on the Origin of the Xinjiazui Gold Deposit, Northwestern Margin of the Yangtze Block, China

The Xinjiazui gold deposit, a newly discovered deposit, is situated in the northwestern margin of the Yangtze Block, China. The source and genesis of gold mineralization are poorly understood. It is urgent to use the H-O isotopic composition of quartz and geochemistry of pyrite to evaluate the origins of the Au and ore-forming fluids of this deposit. Three types of pyrite were identified, including synsedimentary framboidal pyrites (Py0), the directional arrangement of pyrites in pre-mineralization stage (Py1), and euhedral coarse-grain pyrites in the quartz-sulfide veins of the mineralization stage (Py2). The As content in Py2 is relatively higher than Py0 and Py1, indicating that the ore-forming fluids are strongly enriched in As. The delta S-34 values of Py2 (+5.50-+13.34 parts per thousand) overlap with the S1-2M phyllite (+7.25 parts per thousand-+8.70 parts per thousand). This result is consistent with the Pb isotopic composition of Py2, showing that the source of ore-forming materials was derived from the S1-2M phyllite. Meanwhile, the variations in quartz's H and O isotopic composition suggest that the ore-forming fluids were derived originally from metamorphic fluid. Additionally, the Au mineralization is strictly controlled by the shear zone. Above all, we would like to classify the Xinjiazui deposit as an orogenic gold deposit.