对甘肃宕昌县代家庄铅锌矿床成因的认识

GENESIS OF THE DAIJIAZHUANG PB-ZN DEPOSIT IN TANCHANG, GANSU

甘肃省宕昌县代家庄铅锌矿床的发现是近年来西秦岭地区铅锌找矿的重大进展。其类型为以菱锌矿、白铅矿为主的碳酸盐型铅锌矿，成为西成矿田西延地段发现新的成矿类型。区内圈定铅锌矿体6条，产于泥盆系龙鳞桥组第2岩性段与第3岩性段的过渡带和东沟组中，受NW—SE向压扭性断裂破碎带控制。断裂是成矿最主要的控制因素，不仅控制着铅锌多金属矿体的沉积就位，而且在成矿后期对矿体的改造起主导作用。矿区内未见岩浆岩及典型的热液蚀变现象。文章分析了成矿地质背景和矿床地质特征，铅同位素显示变化范围小，说明铅来源比较单一，硫同位素结果说明硫质来源于沉积地层中。闪锌矿中流体包裹体均一温度分别为80％-120℃和120％-160℃，说明成矿温度总体比较低。初步认为其成因沉积改造型铅锌矿床。

The discovery of Daijiazhuang Pb-Zn deposit in Tanchang, Gansu is a huge progress of the Pb-Zn deposit exploration west Qinling. Daijiazhuang Pb-Zn deposit is of carbonate type with major ore minerals of smithsonite and cerusite, which is a new ore-forming type in the west region of Xicheng ore field where six Pb- Zn ore bodies have been found. They are occurred in the Devonian Donggou group and in the transition zone between the second and third members in Devonian Linqiao group, controlled by the NW-SE trending compressshear fault systems. Fault systems have been recognized as the most important factor governing the sedimentation of Zn-Pb multi-element deposit and later ore-body reformation. Magmatic rocks and typical hydrothermal alteration are absent in the mining area. This paper analyzes the geological setting of ore-forming processes and the geological characteristics of deposits. The analyzing results give a limited range of Pb isotopes and thus a single Pb origin. S isotopes show a sedimentary stratum origin. The homogenization temperature of the fluid inclusions in blende shows general low metallogenic temperatures, ranging from 80℃-120℃ and 120℃-160℃ respectively. Therefore, we preliminarily think the Daijiazhuang Pb-Zn deposit is of sedimentation-reformation origin.