南秦岭十里坪锑矿床成矿时代及成因的初步研究

A Preliminary Study on Age and Genesis of Shiliping Antimony Deposit in South Qinling

十里坪锑矿床受赵川陆缘隆_滑构造的主滑脱拆离带的控制。矿体呈脉状赋存于韧_脆性主滑脱带上部的脆性次级断层_节理中,矿石类型主要为萤石石英辉锑矿型。围岩为太古宙_元古宙变质岩系,围岩蚀变弱。成矿流体属H2O_CO2_NaCl体系,流体包裹体盐度w(NaCleq)为3.6%～11.3%,均一温度为109～232℃,形成压力大致为800×105Pa。硫、铅同位素研究表明,矿质主要来源于变火山岩围岩;氢、氧同位素显示,成矿流体以大气降水为主,初步将该矿床定为变质岩源就地式大气降水热液矿床。矿石中萤石Sm_Nd等时线年龄为(392±24)Ma,与南秦岭北部晚古生代拗陷区热水喷流_沉积成矿时代相一致,它们都形成于秦岭微板块泥盆纪非造山裂解阶段。

Located in Late Palaeozoic uplifted area within the southern part of South Qinling region, the Shiliping antimony deposit is controlled by the main delamination belts of Zhaochun pre_orogenic uplift bedding_delamination structure. The vein orebodies occupy brittle shattered fault zones within the upper part of the main brittle_ductile delamination belts. Its Sb ore types are mostly fluorite_quartz_antimonite veins. The country rocks, altered weakly, are Archaean_Proterozoic metamorphites. The ore_forming fluids, with homogenization temperature from 109℃ to 232℃, salinity w (NaCl eq ) from 3.6% to 11.3% and pressure about 800×10 5Pa, belong to the H 2O_CO 2_NaCl system. Sulfur and lead isotopes reveal that the ore_forming materials are mainly derived from the country metamorphic volcanic rocks, while the hydrogen and oxygen isotopic compositions show that the ore_forming fluids are mainly derived from meteoric water. It is therefore genetically a local metamorphic rock source type meteoric hydrothermal ore deposit. Fluorite Sm_Nd dating has yielded an age of (392±24) Ma, which is identical with the age of exhalative sedimentary mineralization in the late_Palaeozoic depressed area within the northern part of South Qinling region. It is suggested that in Devonian the uplifted area of South Qinling region formed meteoric hydrothermal type ore deposits under the condition of a unified extension tectonic setting of Qinling micro_plate. Meanwhile, the depressed area of South Qinling region formed exhalative sedimentary ore deposits and source beds.