内蒙古敖仑花斑岩型钼铜矿床地质特征及成因探讨

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

敖仑花钼铜矿床是近年来新发现的大型斑岩型钼铜矿床,该矿床钼铜矿化多产于敖仑花岩体内及外接触带的角岩中,矿化类型主要为细脉浸染状。矿石矿物为辉钼矿、黄铜矿、黄铁矿、闪锌矿、方铅矿等。敖仑花岩体为中酸性的花岗闪长斑岩体,岩石SiO2、Al2O3、K、Na含量较高,Na2O/K2O比值在1.1～2.1之间,σ值在3～3.7之间,A/CNK值小于1,0.68～0.82,属于偏钠质的高钾钙碱性Ⅰ型花岗岩。矿床的围岩蚀变类型从中心向外依次为石英-钾硅酸化、石英-绢云母化、角岩化,其中钾硅酸盐化和绢云母化叠加带与钼矿化空间分布关系密切;据包裹体测温结果显示,该矿床成矿温度和盐度较高,属于中高温热液斑岩型钼矿床。矿区硫化物的δ34S值变化范围较小,介于-1.2‰～3.5‰,平均为1.78‰,结合岩浆岩演化等特征表明,成矿作用与中酸性含矿斑岩关系密切,并可能受幔源岩浆混合作用的影响。

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.