内蒙古白音诺尔铅锌矿铅同位素研究

摘要

The Baiyinnuoer Pb-Zn Deposit in Inner Mongolia is the largest one in Da Hinggan Mountains. The ore-bodies in the deposit mainly occur along the contact zone of the granodiorite (or granodiorite porphyry)and marble. In order to determine the source of the ore-forming materials, the sulfides from the ores, and whole rocks from strata and intrusive rocks in Baiyinnuoer Pb-Zn Deposit were analyzed for the Pb isotopic compositions. The results showed that .V(206 Pb)/N(204 Pb) of the sulfides from the ores ranged from 18.266 to 18.372 with an average of 18. 296, N(207Pb)/N(204Pb) ranged from 15. 501 to 15.579 with an average of 15. 536, and N(208 Pb)/N(204Pb) ranged from 38. 016 to 38. 339 with an average of 38. 138. The calibrated Pb isotopes by using the ages of intrusive rocks demonstrated that the Pb isotopic compositions of the sulfides from the ores were similar with those of whole rocks from granodiorite(or granodiorite porphyry)and marble. It was suggested that the ore-forming materials might be dominantly derived from these two types of rocks. This further proved that the ore-forming of Baiyinnuoer Pb-Zn Deposit was related to the granodiorite(or granodiorite porphyry)and marble. Baiyinnuoer Pb-Zn Deposit belonged to the skarn deposit, and the lead isotopic features of which were quite different from the ore-forming materials of the SEDKX and VHMS deposits. Comparing with other Ag polymetallic deposits occurring in the central-southern part of Da Hinggan Mountains, the Pb isotopic compositions of these deposits overlapped, and were very similar. It indicated that Pb of these deposits might be derived from a similar source. It was proposed that a common Ag-richbasement or strata might exist in the region, which could provide the ore-forming materials for these Ag polymetallicdeposits.%内蒙古白音诺尔铅锌矿床是大兴安岭地区储量最大的铅锌矿床,矿体主要沿花岗闪长(斑)岩与大理岩接触带产出.为了查明成矿物质来源,对矿石中的硫化物和矿区内及外围主要侵入岩开展了铅同位素示踪分析.测试结果表明:矿石中硫化物的N(206 Pb)/N(201 Pb)为18.266～18.372,平均值18.296,N(207 Pb)/N(204 Pb)为15.501～15.579,平均值15.536,N(208Pb)/N(204 Pb)为38.016～38.339,平均值38.138.铅同位素年龄校正计算结果表明:矿石中硫化物的Pb同位素比值与大理岩和花岗闪长(斑)岩非常相似,表明矿石中的铅主要来自花岗闪长(斑)岩和大理岩,说明成矿物质也主要来自这两类岩石,进一步证明了白音诺尔铅锌矿床的成矿与花岗闪长(斑)岩和大理岩有关,属于矽卡岩型矿床,与喷流沉积型和火山岩块状硫化物矿床有明显的差别.与区域上其他银多金属矿床对比发现,本区银多金属矿床的Pb同位素组成非常相似,其组成范围多有重叠,暗示这些矿床的矿石铅来源也非常相似,可能表明有一个共同的富银的基底或地层为这些银多金属矿床的形成提供了成矿物质来源.