Mineralization Characteristics and Ore Genesis of the Zaozigou Gold Deposit,Gansu Province

The Zaozigou gold deposit is tectonically located in a transitional area of the western Qinling Orogenic belt and the Songpan-Ganzi terrane.Gold mineralization is hosted in calcareous and siliceous slates of the Middle Triassic Gulangdi Formation and diorite dike swarms.Ore bodies are strictly structurally controlled by the NE-,NW-,and roughly SN-striking faults,with the NE-oriented ore bodies being the most important in terms of ore reserves.The Zaozigou gold deposit consists of three types of gold ores in alterated slates,alterated dikes,and quartz-stibnite veins,respectively.Pyrite,asenopyrite,and stibnite are the main metallic minerals,whereas quartz,calcite and sericite dominate the nonmetallic minerals.Hydrothermal alteration is well developed,and gold-related alterations include silicification,sericitization,carbonatization,pyritization,and asenopyritization.Gold is present predominantly as invisible gold,occurring in sulfide minerals.However,visible native gold is also locally noticed,mostly distributed in the microfractures of quartz and sulfides.A synthesis of the host rocks,alteration characteristics,mineral assemblages,geochemical association,and occurrence of gold suggests that the Zaozigou gold deposit can be considered as a Carlin-type gold deposit.Petrographic observation,combined with previous data,indicates that sulfidation of Fe-bearing minerals in the host rocks has been an important mechanism of gold mineralization at Zaozigou.Zircon U-Pb dating of mineralized diorite dikes and a synthesis of regional geological data suggest that the Zaozigou gold deposit formed in the Middle-Late Triassic,under a tectonic transition from compressional to extensional regime of the Qinling orogen.