内蒙古东北部得耳布尔铅锌银矿床闪锌矿Rb-Sr年龄及地质意义

得耳布尔铅锌银矿床产出于内蒙古东北部额尔古纳地块中部,得尔布干断裂西北侧。矿石呈角砾状、团块状产出,尤以闪锌矿粗大集合体与方铅矿伴生为特征。本次研究在对矿石开展矿相学研究基础上,选取成矿早阶段未遭受构造活动影响的8件闪锌矿样品进行Rb-Sr同位素分析,结果显示,8件样品~(87)Rb/~(86)Sr和~(87)Sr/~(86)Sr同位素比值分别在0.0824~8.957和0.712 902~0.730 753之间,二者之间具线性关系,8件样品构成等时线年龄为(144±13)Ma,剔除2件偏离等时线较远样品数据后,获得等时线年龄为(141.6±1.9)Ma(MSWD=1.8)。矿床形成于早白垩世,与额尔古纳地块内其他铅锌银矿床时代基本一致。额尔古纳地块中生代成矿作用直接受控于蒙古-鄂霍茨克造山过程,造山带后碰撞阶段局部拉伸环境引发晚侏罗世—早白垩世浅成岩浆侵入活动,得耳布尔铅锌银矿床的形成与之相关。

Rb-Sr isochron age of De'rbur Pb-Zn-Ag deposit in Erguna massif of northeast Inner Mongolia and its geological significance

The De''rbur Pb-Zn-Ag deposit is located in the middle of the Erguna massif, northeast Inner Mongolia. Brecciated and massive ores, especially sphalerite and galena coarse aggregations, constitute the main ore structures in the deposit. Eight integral sphalerite samples were chosen to conduct further Rb-Sr isotopic analysis after petrographic observitions under microscope. The results show good linear relationship between (⁸⁷Rb/⁸⁶Sr) and (⁸⁷Sr/⁸⁶Sr), being in the range of 0.0824~8.957 and 0.712 902~0.730 753, respectively. An isochron age of (144±13) Ma from all eight samples was obtained, and further result of (141.6±1.9) Ma (MSWD=1.8) was obtained after elimination of two deviated samples. The De''rbuer Pb-Zn-Ag deposit was formed in Early Cretaceous by this study, in agreement with the achivements on the Pb-Zn-Ag deposits in the Erguna massif by previous researchers. The Mongol-Okhotsk orogenic process in the E''rguna massif affected the Mesozoic mineralization, and the late-orogenic stage triggered Late Jurassic to Early Cretaceous hypabyssal magmatic intrusions in the region. The deposition of ore-forming materials in the De''rbur deposit was related to the comprehensive magmatic intrusion activities in the region.