张家口梁家沟铅锌银多金属矿床同位素特征及矿床成因

摘要

Lead, zinc and silver polymetallic deposits are intimately associated with the hypabyssal acidic rock mass in northern Zhangjiakou area. Middle-Upper Proterozoic carbonate strata are widely distributed in southern Zhangjiakou. Some polymetallic ore deposits (ore spots) have been found in carbonate strata, such as Liangjiagou, Huoshigou and Changzhuangzi. Dolomite formation of Gaoyuzhuang Group and Wumisan Group of Jixian System constitute the major ore-host rocks. Contrary to polymetallic deposits located in northern Zhangjiakou area, polymetallic deposit lies in the dolomite strata where intermediate-acid intrusive masses are not developed in the mining area. In addition, the orebody characteristics, ore fabric and ore deposit geochemistry have significant difference from the polymetallic deposits related to the hypabyssal acidic rock mass in northern Zhangjiakou area. Taking the Liangjiagou polymetallic deposit as an example, based on the field observation of the geological characteristics of ore deposit and ore, and taking into consideration various isotope test results for such elements as Pb, S, Rb, Sr, the authors have reached the conclusion that the sources of ore-forming material might have come from dolomite strata or substrata, the formation of the deposit was related to the large-scale overthrust nappe tectonic system, and the genetic type of ore deposit belongs to the Mississippi valley type (MVT) ore deposit.%提张家口北部已发现的铅锌银多金属矿床在成因上多与浅成中酸性侵入岩关系密切。张家口南部中上元古界碳酸盐岩地层分布广泛，目前已在其中发现了梁家沟、火石沟、常庄子等多处铅锌银多金属矿床(点)。赋矿围岩以蓟县纪高于庄组、雾迷山组白云岩为主。与张家口北部已发现的多金属矿床相比，赋存于白云岩中的多金属矿床在矿区范围内浅成中酸性侵入岩体不发育。此外，在矿体形态、矿石组构、矿床地球化学等方面均与已发现的与浅成酸性岩体有关的多金属矿床存在较大差异。文章以梁家沟多金属矿床为例，在矿床和矿石宏观地质特征的基础上，结合矿石Pb、S、Rb、Sr等同位素测试结果，认为成矿物质来源以白云岩围岩和下覆地层为主，矿床的形成与区内大规模逆冲推覆构造有关，矿床成因属密西西比河谷型(MVT)矿床。