Geology, geochemistry and genesis of the Qianfanling quartz-vein Mo deposit in Songxian County, Western Henan Province, China

The Qianfanling Mo deposit, located in Songxian County, western Henan province, China, is one of the newly discovered quartz-vein type Mo deposits in the East Qinling-Dabie orogenic belt. The deposit consists of molybdenite in quartz veins and disseminated molybdenite in the wall rocks. The alteration types of the wall rocks include silicification, K-feldspar alteration, pyritization, carbonatization, sericitization, epidotization and chloritization. On the basis of field evidence and petrographic analysis, three stages of hydrothermal mineralization could be distinguished: (1) pyrite-barite-quartz stage; (2) molybdenite-quartz stage; (3) quartz-calcite stage. Two types of fluid inclusions, including CO2-bearing fluid inclusions and water-rich fluid inclusions, have been recognized in quartz. Homogenization temperatures of fluid inclusions vary from 133 degrees C to 397 degrees C. Salinity ranges from 1.57 to 31.61 wt.% NaCl eq. There are a large number of daughter mineral-CO2-bearing inclusions, which is the result of fluid immiscibility. The ore-forming fluids are medium-high temperature, low to moderate salinity H2O-NaCl-CO2 system. The delta S-34 values of pyrite, molybdenite, and barite range from -9.3 parts per thousand to -7.3 parts per thousand, -9.7 parts per thousand to -7.3 parts per thousand and 5.9 parts per thousand to 6.8 parts per thousand, respectively. The delta O-18 values of quartz range from 9.8 parts per thousand to 11.1 parts per thousand, with corresponding delta O-18(fluid) values of 1.3 parts per thousand to 4.3 parts per thousand, and delta D-18 values of fluid inclusions of between -81 parts per thousand and -64 parts per thousand. The delta C-13(V-PDB) values of fluid inclusions in quartz and calcite have ranges of -6.7 parts per thousand to -2.9 parts per thousand and -5.7 parts per thousand to -1.8 parts per thousand, respectively. Sulfur, hydrogen, oxygen and carbon isotope compositions show that the sulfur and ore-forming fluids derived from a deep-seated igneous source. During the peak collisional period between the North China Craton and the Yangtze Craton, the ore-forming fluids that derived from a deep igneous source extracted base and precious metals and flowed upwards through the channels that formed during tectonism. Fluid immiscibility and volatile exsolution led to the crystallization of molybdenite and other minerals, and the formation of economic orebodies in the Qianfanling Mo deposit. (C) 2013 Elsevier B.V. All rights reserved.