内蒙拜仁达坝银铅锌多金属矿床成矿条件

Ore-Forming Conditions of Bairendaba Ag-Pb-Zn Polymetallic Ore Deposit,Inner Mongolia

内蒙拜仁达坝银铅锌多金属矿床是受断裂构造控制的中温热液脉状矿床。矿床主要受东西向压扭性断裂控制,矿体富集在断裂产状变缓地段。矿体的赋矿围岩主要为海西期石英闪长岩,海西期基性脉岩为成矿提供物源,燕山期霏细岩脉为成矿提供了主要的热源。流体包裹体研究表明,成矿流体具有低盐度(w(NaCl)为5.0%～7.8%)、低密度(0.66～0.95g/cm3)的特点,成矿以中温(280～300℃)为主,成矿压力为76～80MPa,成矿深度为6.8～7.2km。矿石中黄铁矿单矿物硫同位素分析结果表明,δ34S值变化范围为-0.99‰～0.36‰,平均值为-0.315‰,为幔源硫来源。根据地质特征分析,推测在矿区中部的山谷内存在一条北西向成矿后断裂,它将矿床分为南北两个矿段,使北矿段被抬升,剥蚀程度较大,矿体埋藏较浅;南矿段剥蚀则较弱,矿体埋深较深,深部仍存在较大的找矿潜力。

Bairendaba Ag-Pb-Zn polymetallic ore deposit, Inner Mongolia, belongs to a mesothermal vein-type deposit controlled by fractures, which are mainly E - W trending eompresso-shearing faults with the relative flat-dipping other than steep-dipping parts being the favorable ore-hosting locations. The wall rocks of the ore bodies are mainly Hercynian quartz diorite. It is suggested that the Hercynian mafic rocks are the source for ore-forming materials while Yanshanian felsites might provide the heat driving meteoric water cycling. Based on fluid inclusion study, it has been recognized that the oreforming hydrothermal fluid has the features like low salinity（5.0%-7.8% NaC1）, low density（0.66 - 0.95 g/cm^3）, intermediate temperature（280- 300℃）. The ore-forming pressures are from 76 to 80 MPa, which reflect the mineralising depth ranges from 6.8 to 7.2 kin. The sulfur isotope of the ore pyrites varies from -0.99‰ to 0.36‰ with an average value of -0. 315‰, which is similar to mantle sulfur value. According to geological study, it is suggested that there exists a post-ore fault that extends along the NW-striked valley in the district, which dissects the ore district into two parts, i.e. north and south sections, and causes the former uplifted with bigger denudation and the latter relatively down. Therefore, the ore bodies are shallower within the north section than in the south section while the latter still has good potentiality for further ore prospecting.