中文摘要：

岔路口矿床是迄今为止在中国北方发现的最大规模钼多金属矿床,钼、铅锌和银的储量分别为134万t、37万t和4 200 t。考虑到大规模地质勘查工作仍在进行中,金属储量的增加只是个时间问题。为了进一步查明岔路口矿床的形成时间,笔者对主要钼多金属矿体8件辉钼矿样品进行了铼-锇同位素分析,所获同位素等时线年龄为（146.96±0.79）Ma（2σ）,其MSWD值为1.2。鉴于辉钼矿呈浸染状和团块状分布于花岗斑岩岩株中,并且与部分黄铁矿和黄铜矿呈共生结构关系,可以推测岔路口地区钼多金属矿床及花岗斑岩的形成时间均为晚侏罗世,属燕山中期构造-岩浆活动的产物。岔路口钼多金属矿床形成时代的厘定对于提高该矿床的理论研究水平和指导隐伏金属矿床的找矿勘查工作均具有重要意义。

英文摘要：

Located at the northernmost corner of the Deerbugan metallogenic belt and in the northeastern part of the Mongolian-Hinggan amalgamated massif,the newly found Chalukou ore deposit is the largest molybdenum polymetallic deposit ever discovered in China.It contains 1.34 Mt of Mo（metal）,0.37 Mt of Pb-Zn and 4 200 t of Ag.As a part of the evaluation project of the molybdenum deposit,mineral exploration around Chalukou is still underway.During the Mesozoic Yanshanian orogeny,intense extensional tectonic and igneous activities resulted in the formation of large-scale acid volcanic rocks and granitoid intrusions at Chalukou and its neighboring areas.The Chalukou granite porphyry and quartz porphyry stocks were emplaced in the Jurassic volcano-sedimentary sequence controlled by NE-and NW-trending fault zones.Rock-forming minerals of the two porphyry stocks are mainly quartz,microcline,microperthite and plagioclase associated with minor biotite and sericite.Accessory minerals include magnetite,apatite,zircon,sphene,and allanite.Molybdenum mineralization occurs within the Chalukou porphyry stocks and volcanic rocks as stockworks,veins,veinlets and disseminated blocks. The molybdenum ore consists of pyrite,chalcopyrite,molybdenite,sphalerite,galena,magnetite,pyrrhotite,K-feldspar,fluorite,quartz,sericite and chlorite.As the most important economic molybdenum mineral,molybdenite occurs in the impregnation,radioflake,thin film,aggregated flake and veinlet forms.Re-Os isotopic dating of eight molybdenite separates from the main ore body yielded an isochron age of（146.96±0.79） Ma and model ages ranging from 146.2 Ma to 149.1 Ma with an average value of 147.4 Ma.The Re-Os isochron age is in agreement with field geological evidence,and the molybdenite is coexistent with chalcopyrite and pyrite,suggesting that the Re-Os isochron age represents the ore-forming time of the porphyry Mo mineralization in the Chalukou ore deposit and its neighboring areas.Combined with field geological observations and petrological evidence,th