Geology, ore-forming fluid and metallogenic age of orogenic gold deposits in the Northern Qaidam

The northern margin of Qaidam Basin is a well-known ultra-high pressure metamorphic belt with abundant mineral resources. The orogenic gold deposits are widely distributed in the northern Qaidam. This paper focuses on the study of the geological characteristics, temperature and isotopes of ore-forming fluids of the gold deposits in northern Qaidam. The results show that the orogenic gold deposits are mainly distributed in the shear zones of the Mesoproterozoic, Cambrian and Ordovician metamorphic rocks, and most ore bodies is related to the NW-trending structures. Besides, the mineralization temperature of most gold deposits is bimodal, and only a few gold deposits exhibit monomodal in temperature, indicating that multi-phase fluids were involved in the mineralization process. The δ¹⁸O_H2O-SMOW (-1.7‰-10.31‰) and δD_V-SMOW(-113.8‰﹣-41.6‰) of the ore-forming fluid indicate that the metamorphic fluid is influenced by magmatic water and atmospheric water. The δ³⁴S of gold-containing sulfides (pyrite and galena) ranges from 0.5‰ to 11‰, mainly in the range of 5‰ to 9‰, ²⁰⁶Pb/²⁰⁴Pb from 18.238 to 19.296, ²⁰⁷Pb/²⁰⁴Pb from 15.547 to 15.773, and ²⁰⁸Pb/²⁰⁴Pb from 37.918 to 38.978, which indicates that the ore-forming materials are derived from the mantle-upper crust, and are affected by magmatism to some extent. The tectonic evolution and metallogenic ages reveal that three gold metallogenic events occurred in the northern Qaidam during 426-376 Ma、357-330 Ma and 288-246 Ma.