Study on In-Situ Sulfur Isotope Compositions of Sulfides: Implication for the Source of Pb-Zn Mineralized Body of Niutoushan in the Xiangshan Area

In recent years, the Pb-Zn mineralization was discovered in the Niutoushan area in the west part of the Xiangshan volcanic basin. The genetic mechanism of Pb-Zn mineralization is still unclear. In order to reveal the source of the Pb-Zn mineralization, in-situ sulfur isotope analysis using laser altered-inductively coupled plasma spectra(LA-MC-ICP-MS)of sulfides is carried out. Paragenetic and crosscutting relationship between sulfide minerals formed by the hydrothermal fluids suggest that the earliest precipitated mineral was pyrite, followed by galena and sphalerite, and the chalcopyrite in fine vein shape was formed at the latest stage of the hydrothermal fluids. The analytical results of this study indicate that the δ³⁴S values of metal sulfide minerals (pyrite, sphalerite, galena and fine-vine chalcopyrite) range from -4.8‰~+5.4‰. In term of sulfur isotopes, not all the sulfide minerals are in completely isotope equilibrium. The δ³⁴S_ΣS(total sulfur isotope) value of the mineralized fluid calculated from the δ³⁴S values of pyrite at its formation temperature is +3.7‰, which is basically consistent with hydrothermal δ³⁴S_ΣSvalue obtained from the δ³⁴S values of the paragenetic mineral pair (sphalerite-galena).Therefore, the δ³⁴S_ΣSvalue of the mineralization fluid(+3.7‰) in the Niutoushan Pb-Zn mineralization indicates that the mineralization fluid was magmatic in origin. Combined with the published dating data of the magmatic rocks of the Xiangshan volcanic basin, the sulfur isotope data of this study suggest that hydrothermal fluid of the Pb-Zn mineralization may have been mainly derived from the subvolcanic magma of the granitic porphyry. The sulfur isotope values of the sphalerite minerals were higher than those of the paragenetic galena in the mineralized bodies, indicating sulfur isotope equilibrium between these two minerals. The temperatures calculated by using the sulfur isotopic compositions of these two minerals are between 197℃ and 476℃, which is consistent with the published temperatures from fluid inclusions. The metallogenic conditions and sources of ore-forming materials of the Niutoushan Pb-Zn mineralization in the Xiangshan volcanic basin are similar to those of Pb-Zn ore deposits in the Huanggangshan and Lizikeng volcanic basins in Northern Wuyi area, which hints promising prospects for Pb-Zn deposit prospecting in the Xiangshan volcanic basin.