安徽金寨银山钼-铅-锌多金属矿床Re-Os和有关岩浆岩^(40)Ar-^(39)Ar年龄测定

Re-Os ages of molybdenum-lead-zinc polymetallic deposits and ^(40)Ar-^(39)Ar ages of related magmatic rocks in Yinshan area, Jinzhai, Anhui Province

近年,在安徽金寨银山地区,发现了钼-铅-锌多金属矿床,赋矿岩石为中酸性岩浆岩。岩浆岩中的黑云母和角闪石单矿物的40Ar-39Ar同位素地质年龄测定表明,矿区内的中粒二长花岗岩、细粒二长花岗岩和细晶闪长岩脉分别形成于(136.8±1.6)Ma、(130.4±1.2)Ma和(125.4±1.0)Ma,为燕山晚期早白垩世侵入岩。根据岩体产状和接触关系,赋矿石英正长(斑)岩和爆发角砾岩的形成晚于二长花岗岩和细晶闪长岩脉。矿区内,钼矿体和铅锌矿体主要呈脉状产于不同岩性的岩浆岩体中,钼矿体主要发育于爆发角砾岩中心附近的石英正长斑岩中,铅锌矿体则主要赋存在二长花岗岩体中。钼矿床中辉钼矿的Re-Os同位素模式年龄为(112.6±1.3)Ma和(113.5±1.3)Ma。根据矿体与岩浆岩的相互关系以及同位素地质年龄测定,矿区内的钼-铅-锌多金属矿床与石英正长斑岩的形成时间接近,成矿与浅成-超浅成偏碱性岩浆的侵入和相关的热液作用有关,属于斑岩-隐爆角砾岩型矿床。结合前人的研究成果,笔者认为:该区的岩浆岩和钼-多金属矿床形成于中国东部大规模岩石圈减薄、拆沉和热侵蚀的地球动力学背景,大别造山带应力场由挤压转化至伸展阶段以后;区内的钼-多金属矿床归属东秦岭-大别钼成矿带的东延部分,是中国东部EW向大规模成矿带的组成部分。

In recent years, molybdenum-lead-zinc polymetallic deposits were discovered in Yinshan area, Jinzhai, Anhui Province. The ore bodies are hosted mainly in Yanshanian magmatic rocks. Dating results of 40Ar/39Ar isotopic ages of biotite and hornblende in magmatic rocks show that medium-grained adamellite, fine-grained adamellite and fine-granined diorite in the ore district were formed respectively in （136.8±1.6） Ma, （130.4±1.2） Ma and （125.4±1.0） Ma, suggesting that they are Early Cretaceous products formed during late Yanshanian movement. According to their attitudes and relationship, quartz-syenite （porphyry） and explosion-breccia were formed later than adamellite and diorite. Regional magmatism evolved from high potassium calc-alkaline to alkaline. Molybdenum and lead-zinc deposits occur in the veined form in different lithologic magmatic rocks, and molybdenum deposits mainly occur in quartz syenite （porphyry） distributed in the center of explosion-breccia. The Re-Os isotopic model ages of molybdenite in molybdenum deposits are （112.6±1.3） Ma and （113.5±1.3） Ma, which are considered to be the ages of regional molybdenum deposits. Geological characteristics and isotopic ages show that the molybdenum-lead-zinc polymetallic deposits may genetically related to the emplacement and hydrothermal activities of the late stage quartz syenite （porphyry）. These deposits should thus belong to shallow-seated or ultra-shallow-seated porphyry-explosion-breccia deposits. In combination with the achievements made by previous researchers, the authors hold that the molybdenum-lead-zinc polymetallic deposits and related magmatic rocks were formed in a geodynamic setting of regional large-scale lithospheric thinning, delamination and thermal erosion in East China, and also in a regional stress field formed during the conversion of the Dabie orogenic belt to the extension stage. The molybdenum polymetallic deposits are controlled by the EW-trending structures, and belong to the East Qinling-Dabie molybdenum belt, a part of the larger EW-trending metallogenic belt in eastern China.