内蒙古红岭铅锌多金属矿床辉钼矿Re-Os同位素年龄及其意义

红岭铅锌多金属矿床为大兴安岭南段多金属成矿带的代表性矿床之一.区内发育斑岩型和矽卡岩型2种钼矿化，前者为产于花岗斑岩内呈斑点-浸染状产出的辉钼矿，后者为薄膜状辉钼矿.为确定红岭铅锌多金属矿床的成矿时代，对矿区2种类型的钼矿化进行系统研究和成矿年代测定.5件斑点状辉钼矿样品Re-Os模式年龄介于139.9±2.3 Ma~141.5±3.2 Ma之间，Re-Os等时线年龄为140.3±3.4 Ma(MSWD =0.082)，模式年龄加权平均值为140.10±1.80 Ma，两者在同一误差范围完全一致，代表了该红岭矿区斑岩型钼矿化时代为晚侏罗世.1件薄膜状辉钼矿样品模式年龄为143.7±3.6 Ma，应为铅锌矿化阶段的成矿年代上限；其Re、187Os含量较其他样品高出1个数量级，揭示着2种类型钼矿化具有不同的成因，证实区内存在2期钼成矿作用.6件辉钼矿样品的Re含量特征指示其成矿物质的浅源性，应以壳源为主；极低的Re含量可能与其母岩和共生矿物组合有关.结合前人的研究成果，得出红岭铅锌多金属矿床的成岩、成矿物质均来源于增生地壳，成矿动力学背景为蒙古-鄂霍茨克造山带碰撞造山后陆壳伸展环境的认识. 

Re-Os Radiometric Dating of Molybdenite in Hongling Lead-Zinc Polymetallic Deposit,Inner Mongolia,and Its Significance

Hongling lead-zinc polymetallic deposit share many similarities with others from the southern Daxinganling polymetallic metallogenic belt. There are two types of molybdenum mineralization in the mining area, including porphyry and skarn. The former, displaying spot-disseminated feature, occurs in granite porphyry, whereas the latter, displaying film like feature, occurs in quartz. The metallogenic age of Hongling deposit can be constrained from Re-Os isotopic dating of the two kinds of molybdenite. Five samples of spot-disseminated molybdenite yield model ages varying from 139.9±2.3 Ma to 141.5±3.2 Ma, with an isochron age of 140.3±3.4 Ma (MSWD=0.082), and a weighted average of 140.10±1.80 Ma. The isochron age and weighted average model age are consistent with one another, implying that molybdenum mineralization in Hongling deposit occurred in Late Jurassic. A film-like molybdenite sample yielded a model age of 143.7±3.6 Ma, representing the initial stage of lead-zinc mineralization. The Re-187Os contents of the film-like molybdenite are higher than that of spot-disseminated molybdeniteby one order of magnitude, which hints that they have different origins and there are two phases of molybdenum mineralization. The characteristics of Re content of the 6 molybdenite samples suggest that the ore-forming elements had a shallow source, and was mainly derived from the crust. The extremely low content of Re might be du to the low Re content within its parent magma as well as its paragenetic mineral assemblage. Combined with the results of previous study, it is concluded that (a) both rock- and ore-forming materials of Hongling deposit came from hyperplasia crust; and (b) the deposit formed in a dynamical environment of continental crust extension post Mongolia-Okhotsk collisional orogeny.