Geological features and genesis of the Qingyangou molybdenum-nickel deposit in Heilongkou, Shaanxi Province

Abstract： It is for the first time that a molybdenum–nickel sulfide deposit was discovered in the black rock series of the Qinling orogenic belt. The ore deposit has relatively abundant Mo-Ni-Ti-Cu-Pb-Zn-P in carbonaceous marl series, i.e., black rock series of lower Ordovician Miaowan Formation in North Qinling. The tectonic setting of the ore deposit is a deep water sedimentary environment of the back-arc rift basin along Shang-Dan fault zone in North Qinling, and the ore deposit is strictly controlled by the ductile-brittle tectonic contact zone between carbonaceous phyllite and fine-grained marble. The ore bodies assume the forms of tectonic lenses and pods. The alteration types include relatively strong molybdenitization, pyrrhotitization, pyritization and sphaleritization, associated with graphitization, silicification, ankeritization and calcitization. Nickel sulfides and molybdenum sulfides are associated with each other in the ore deposit. The ore types can be classified into carbonaceous phyllite type, dolomite type and fine-grained marble type in accordance with ore rocks, and into Ni-Mo type, molybdenum- graphite type and nickel polymetallic type in accordance with metal elements. The ore deposit is genetically of epigenetic stratabound high-medium-low temperature hydrothermal type. The ore-forming process experienced such stages as initial enrichment of useful components in black rock series, metamorphic activation migration of useful components, ductile-brittle structural transformation and hydrothermal ore enrichment.