大兴安岭中北段古中公路钼矿床形成时代与矿床成因

古中公路钼矿床含矿岩体为碎裂硅化片麻状二长花岗岩体,蚀变呈带状分布,成矿过程可划分为钾长石+石英、石英+辉钼矿及石英+黄铁矿3个阶段。2件辉钼矿样品的Re-Os同位素模式年龄分别为(142.4±2.9)Ma和(142.3±2.0)Ma,表明矿床为早白垩世构造-岩浆活动的产物;辉钼矿中w(Re)含量分别为11.894×10~(-6)和11.584×10~(-6),暗示成矿物质主要为地壳来源,可能有地幔物质的参与。流体包裹体研究表明:主成矿阶段的石英中主要以气液两相包裹体为主,其次为含子晶三相包裹体,CO_2三相包裹体最少;不同类型包裹体的均一温度范围为196.3℃~450℃,盐度可分为0.18%~12.62%和45.33%~53.26%两个不同区间。因此,成矿流体为中高温、高盐度的Na Cl-H2O-CO2体系,在热液成矿阶段可能发生过流体沸腾作用,且是钼矿的主要形成机制。综合成矿地质条件、矿床地质特征及成矿流体特征认为,该矿床成因上属斑岩型,形成于区域伸展的构造环境。

Mineralization age and ore genesis of Guzhonggonglu molybdenum deposit in central-northern Great Xing'an Range

The ore-hosting intrusion of Guzhonggonglu molybdenum deposit is the fragmented silication gneissic monzogranite, and the alterations are distributed in belt. The metallogenic process can be divided into K-feldspar+quartz, quartz+molybdenite and quartz+pyrite stages. The Re-Os isotope model age of two molybdenite samples are (142.4±2.9)Ma and (142.3±2.0)Ma, respectively, indicating that the deposit was caused by the Early Cretaceous tectonic-magmatic activities. The content of Re in the molybdenite are 11.894×10-6 and 11.584×10-6, respectively, suggesting that the ore-forming materials are mainly derived from the crust, and probably affected by the mantle. The preliminary study of fluid inclusions demonstrates that the fluid inclusions in the quartz are mainly gas-liquid two phase inclusions, secondly gas-liquid-solid three phase inclusions, minor CO2-bearing three phase inclusions. The homogenization temperature of all type of inclusions are of 196.3~>450℃, while the salinities can be divided into two groups: 0.18%~12.62% and 45.33%~>53.26%. Thus, the ore-forming fluid belongs to the medium-high temperature, and high salinity NaCl-H2O-CO2 fluid system, and the fluid boiling might occur during the ore-forming stage and be the major metallogenic mechanism. Combined with the characteristics of ore-forming conditions, ore deposit geology and fluid inclusions, the study indicate that the Guzhonggonglu molybdenum deposit is of porphyry type, and formed under a regional extension tectonic settings.