Molybdenum mineralization genetically linked with magmatism at the Shipingchuan deposit, SE China

Most molybdenum (Mo) deposits are considered to be associated with magmatic systems; however, their genetic link is not clearly resolved when using, for example, bulk sulfur (S) and lead (Pb) isotopes of sul-fides dominated by pyrite separates. Here, we present microtextures and in situ trace -element results of pyrite, in situ S isotopic compositions of molybdenite and pyrite, and Pb isotopes of pyrite and K-feldspar deter-mined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and multicollector (MC) LA-ICP-MS. Com-bined with geochronologic data for both the magmatism and Mo mineralization, these in situ methods allowed the genetic link be-tween Mo mineralization and magmatism to be unraveled at Shipingchuan, SE China. The Shipingchuan deposit is characterized by molybdenite-quartz veins hosted by faults or fractures around a biotite K-feldspar gran-ite. Zircon LA-ICP-MS U-Pb and molybde-nite Re-Os dating results confirm that the biotite K-feldspar granite and mineralization were coeval and formed during the end of the Early Cretaceous (ca. 105 Ma), whereas postmineralization monzogranite porphyry dikes formed at 93.7 Ma. Pyrite shows a close mutual relationship with molybdenite and is characterized by Co-Ni-As-Te-Cu-Pb-Ag-Bi-rich cores (PyI) revealed by LA-ICP-MS data. Co/Ni and calculated (Se/S)fluid ratios for both cores (PyI) and rims (PyII) indicate a magmatic-hydrothermal origin. The in situ S isotopic compositions (634S) of mo-lybdenite are 2.1%0 to 6.8%0, which are iden-tical to those of molybdenite separates. PyI has 634S values of -6.9%0 to 0.8%0, whereas PyII exhibits slightly more negative values of -7.5%0 to -0.2%0. These analyses indicate reliable results for in situ S isotopes in mo-lybdenite, which could be more appropriate to constrain the origin of sulfur in hydrother-mal fluids than results from pyrite analysis. The in situ S isotopic compositions of sulfides confirm a magmatic source for sulfur. The in situ Pb isotopic compositions of pyrite are consistent with those of K-feldspar from the biotite K-feldspar granite, indicating a com-mon source. The heterogeneous As/Ni, As/ Sb, and As/Bi values, as well as the variations of 634S values of both PyI and PyII, indicate progressive oxidization of the hydrothermal fluids. These results illustrate that the metal -rich fluids were released from the granite and migrated along faults and fractures around the granite in an extensional setting. The precipitation of molybdenite-quartz veins at Shipingchuan was triggered by changes in temperatures and redox conditions, which were caused by mixing of magmatic fluids and meteoric water. Results in this study pro-vide an example of tracing the link between Mo mineralization and magmatism using in situ S isotopic compositions of molybdenite and Pb isotopes of pyrite and K-feldspar.