Evidence of fluid evolution of Baoshan Cu-Pb-Zn polymetallic deposit: Constraints from in-situ sulfur isotope and trace element compositions of pyrite
(1. Key Laboratory of Metallogenic Prediction of Nonferrous Metals, Ministry of Education, Central South University, Changsha 410083, China;
2. School of Geosciences and Info-Physics, Central South University, Changsha 410083, China)
2. School of Geosciences and Info-Physics, Central South University, Changsha 410083, China)
Abstract: In-situ LA-ICP-MS and S isotopes of pyrite from the Baoshan Cu polymetallic deposit were conducted to investigate the ore-forming process and the enrichment mechanism of elements. Three generations of pyrite (Py I, Py II, and Py III) in the skarn-type ores and pyrite in the carbonate-hosted sulfide ores from central, western, and northern (C_Py, W_Py, and N_Py) mining districts are selected for comparison. Compared with Py I and Py III, the contents of most elements in Py II are apparently higher. The As and Se contents are high within a wide range and are decoupled in the growth band of the C_Py. The highest As, Se, and Pb contents were found in W_Py and N_Py. These results indicate the drastic changes in the temperature and fluid mixing during the mineralization. The occurrence of fluctuation and change in temperature and f(O2) was triggered by intermittent pulses of magmatic-hydrothermal fluids, mixing with meteoric water, and water-rock interactions. The sulfur isotopes of all species of pyrite indicated the magmatic source. The change in the f(O2) conditions caused slight differences in the sulfur isotope compositions. Consequently, a metallogenic model was proposed to explain the ore-forming processes.
Key words: pyrite; trace element; in-situ S isotope; hydraulic fracturing; fluid mixing