南秦岭旬阳盆地下古生界铅锌成矿作用

Mineralization of Pb-Zn deposits in Lower Paleozoic in Xunyang basin,South Qinling

近年来,南秦岭旬阳盆地志留系铅锌矿集区铅锌矿床勘查取得重大突破,备受关注。旬阳盆地下古生界中的铅锌矿床主要赋存于志留系梅子垭组和双河镇组,受地层控制明显,矿体形态简单,主要为层状和似层状,矿石结构简单,矿物成分单一,围岩蚀变弱且不对称;闪锌矿δ34S组成平均为6.83‰,方铅矿δ34S组成平均为5.95‰,黄铁矿矿石δ34S为1.1‰,志留系泥质岩石中黄铁矿的δ34S平均为15.64‰,硫主要来源于海水硫酸盐;208Pb/204Pb为37.93%～38.95%,207Pb/204Pb为15.55%～15.69%,反映铅的来源为上地壳。成矿温度为135～297oC,属于中低温,成矿流体成分主要以K+、Na+、Ca2+、Mg2+、F-、Cl-、SO42-为主,Na+/K+值小于1,F-/Cl-值很小,主要来自于海水。因此,热水沉积成矿作用是旬阳盆地下古生界铅锌矿床形成的主要原因。

Recently, significant achievements has been obtained in the exploration of lead-zinc deposits in mineralized zones in the Silurian system in Xunyang basin of Shaanxi province. These deposits in Xunyang basin mainly locate in middle Meiziya Group and Shuanghezhen Group of Silurian, and it is controlled by stratum. The ore body is simple in shape. It is mainly layer and stratiform-like; the structure of ore is simple, with few components; alteration weak and asymmetry. The average δ34S of sphalerite is 6.83%o; average δ34S of galena is 5.95‰; the δ34S of pyrite is 1.1‰; but average δ34S of pyrite located in the mudstone of Silurian is 15.64‰. The sulfur is mainly from seawater. The isotopic ratio of 208Pb/204pb are 37.93%-38. 95%,207pb/204Pb are 15.55%- 15.69%. It indicates the Pb from up earth＇s crust. The temperature of mineralization was from 135 ℃to 297℃. The components of ore-forming fluid mainly are K^＋, Na^＋, Ca^2＋, Mg^2＋. F/6-, Cl^-, SO4^2-. TheNa^＋/K^＋ ratio is less than 1; F^-/Cl^-is very low. That means ore-forming fluid comes from seawater. To sum up, the major genesis of Pb-Zn deposits in Lower Paleozoic in Xunyang basin is hydrothermal sedimentary mineralization.