Geological Characteristics and Genesis of the Aolunhua Porphyry Mo-Cu Deposit,Inner Mongolia

The Aolunhua mine is a large-scale porphyry Mo-Cu deposit newly discovered in recent years.The molybdenum mineralization of this deposit occurs primarily within the Aolunhua porphyritic granitoid stock and hornfelsed in the outer contact zone,which are veins,veinlets and disseminated blocks.The ore mineral consists of molybdenite,chalcopyrite,pyrite,sphalerite,and galena.The major elements of the Aolunhua rock show high SiO2、Al2O3、K、Na contents,with ratio of Na2O/K2O between 1.1～2.1,the value of σ between 3～3.7,and the ratio of A/CNK less than 1(0.68～0.82).The lithology of Aolunhua rock is granodiorite-porphyry,belongs to Na-rich and K-high calc-alkaline rock series.Hydrothermal alterations in Aolunhua roughly shows zonation of quartz-K feldspathization,quartz-sericite,hornfelsed.Of these alterations,the overprinting zone of quartz-K feldspathization and quartz-sericite are well developed and have intimate relationship with molybdenum mineralization.Fluid inclusion study shows that the ore-forming fluid has high mineralization temperature and salinity.The variation range of δ34S from sulphide in the deposit is small,between-1.2‰～3.5‰ and average value is 1.78‰.Characteristics of mineral deposit geochemistry,field geological observations and petrological evidence suggest that the Aolunhua deposit is a porphyry type hypothermal-mesothermal molybdenum deposit.Evolution of magmatic and sulfur isotope show that mineralization is closely related to acidic porphyry and affected by mantle-derived magma mixing.