东昆仑拉陵灶火钼多金属矿床地质特征及辉钼矿Re-Os同位素定年

摘要

The Lalingzaohuo molybdenum polymetallic deposit in the Qimantag metallogenic belt of Qinghai Province is a newly discovered skarn-porphyry type deposit.Eleven samples and four repetition samples for Re-Os isotopic dating were analyzed,and the model ages show two segments:214.1～223.9 Ma and 235.7～240.8Ma with 107Re-107Os isochron ages of (214.5±4.9) Ma and (240.8±4.0) Ma and the weighted average model ages of (217.6±3.5) Ma and (238.4±1.2) Ma,respectively.The age dating indicates that there are two metallogenicepochs:Middle Triassic and Late Triassic.The rhenium content of the molybdenite ranges from 17.40 × 10-6 to 149.52 × 10-6,with the great majority concentrated in a dozen micrograms to tens of micrograms,indicating a crust-mande mixed mineral source.Combined with previous studies,the authors hold that the two ore-forming events in Triassic were associated with the breakoff of the subducting slab in Middle Triassic and lithospheric delamination in Late Triassic.%拉陵灶火钼多金属矿床是青海祁漫塔格成矿带新发现的矽卡岩-斑岩型矿床.利用辉钼矿Re-Os同位素定年技术,11件样品和4件重复样品的模式年龄显示2个分段:214.1～223.9 Ma与235.7～240.8 Ma,187Re-187Os等时线年龄分别为(214.5±4.9)Ma和(240.8±4.0)Ma,模式年龄的加权平均值分别为(217.6±3.5)Ma和(238.4±1.2)Ma,等时线年龄与模式年龄加权平均值在误差范围内一致,表明矿床存在2期成矿作用:中三叠世和晚三叠世.辉钼矿样品中铼含量为17.40×10-6～149.52×10-6,绝大多数集中在十几至几十微克,指示其成矿物质来源为壳幔混合源.结合前人及本次研究成果表明,两次成矿作用分别与中三叠世东昆仑地区俯冲结束与碰撞开始时的板片断离作用和晚三叠世岩石圈拆沉作用有关.