Geochemical constraints on the source of metallogenic fluids and materials in the Jiama polymetallic Cu deposit, Tibet

Located in central eastern Gangdise metallogenic belt, the Jiama polymetallic copper deposit is a giant porphyry-skarn type deposit characterized by the highest level of exploration and complex ore- forming elements and ore body types. Previous researchers have already completed a lot of research work, which includes rock and ore- controlling structure, deposit geology, geochemistry, model of the deposit and some other aspects; nevertheless, researches on metallogenic mechanism of the deposit remain very insufficient. The source of fluid materials lacks systematic study and the information lacks comprehensive rearrangement. Based on reading lots of research reports and summarizing the data obtained by previous studies, the authors carried out the oxygen isotope mapping and collected necessary additional samples of sulfur isotope along No. 16 exploration line which served as the typical cross section. A comprehensive study reveals that there existed magmatic fluid exsolution in the deep-seated porphyry concealed under the Jiama ore district, and hydrogen and oxygen isotopic combination suggests that from the early stage to the late stage of mineralization, fluid evolved gradually from the magmatic water to the atmospheric water. In addition, the oxygen isotope mapping and the distribution of uniform temperature plane of fluid inclusions demonstrate that the source of oreforming fluids was located around drill hole zk1616~zk3216 in this ore district. S, Si isotopic combination implies that the materials were mainly derived from the ore- forming magmatic rocks, and the study of lead isotope further indicates that the metallogenic materials came from the collision environment in Gangdise; the crustal thinning and the crust-mantle upwelling led to the mixture of the crust and the mantle. Based on the study of geochemistry, the authors probed into the source of fluid and metallogenic materials, and the results obtained have laid a solid foundation for the study of the genesis and the metallogenic mechanism of the Jiama ore deposit.