青海祁漫塔格虎头崖铅锌矿床流体包裹体、同位素地球化学及矿床成因

Fluid inclusions,isotopic geochemistry and genesis of the Hutouya Zn-Pb deposit in Qimantag, Qinghai Province

青海虎头崖铅锌矿床位于东昆仑祁漫塔格地区西段,铅锌矿体受蓟县纪狼牙山组控制,矿体多呈层状、似层状产出,部分为透镜状、脉状,成矿分为2个阶段。金属硫化物电子探针分析表明,闪锌矿中Fe含量为2.255%~5.579%,贫Ga、Ge,Zn/Cd值为146~198,方铅矿中Ag含量为0.015%~0.038%,具有岩浆热液有关金属硫化物的特征。方解石内流体包裹体δD值为-92.7‰^-76‰,δ18OH2O值为-11.58‰^-2.27‰,多数位于大气降水范围,但部分位于大气降水和岩浆水之间,且早阶段成矿流体含有CO2、CH4、N2、H2等地幔流体或岩浆流体成分,表明早期成矿流体为岩浆热液,后期不断加入大气降水。早阶段成矿流体具中低温、高盐度、中等密度的特征,晚阶段随着大气降水的不断混入,盐度和密度显著降低。金属硫化物的δ34SV-CDT值为1.6‰~9.9‰,具有岩浆硫与围岩硫混合来源特征;金属硫化物的206Pb/204Pb值为18.533~18.580,207Pb/204Pb值为15.606~15.669,208Pb/204Pb值为38.344~38.522,主要来源于区内深源岩浆活动,有部分地壳铅的混染。综合分析认为,虎头崖铅锌矿床为与印支期岩浆作用有关的层控夕卡岩型铅锌矿床。

The Hutouya Zn-Pb deposit is located in western Qimantag of East Kunlun Mountains, Qinghai Province. The layered, quasi-lamellar, lenticular and veined ore bodies are controlled by the Langyashan Formation of Jixianian Period. Two stages of miner- alization are recognized based on cross-cutting relationships. The late stage is represented by the galena-bearing calcite veins, which cut the banded ores. Sphalerite is characterized by higher content of Fe （2.255%-5.579%）, lower content of Ga, Ge, and Zn/Cd ratios （146-198）, and the content of Ag in galena is lower （0.015%-0.038%）. These data indicate that the metallic minerals were probablyformed in close relation to magrnatic fluid. δD and δ18OH2O values of fluid inclusion water in calcite vary from -92.7‰to -76‰and -11.58‰ to -2.27‰ respectively, and parts of the values are between the range of magmatic water and atmospheric water. The ore- forming fluid of the early stage was magamtic fluid with components of CO2, CH4, N2 and H2. All these data show that the ore-form- ing fluid was mainly magmatic water at the early stage, with the addition of atmospheric water at the late stage. The ore-forming fluid of the early stage was characterized by middle-lower temperature, high salinity and middle density. At the late stage, the salinity and density of ore-forming fluid decreased because of the continuous mixing with atmospheric water. The values of δ34S vary from 1.6‰ to 9.9‰, which indicate that sulfur in sulfides was mainly from the mixing of magma and wall rocks. The sulfides have 206Pb/204pb ra- tios from 18.533 to 18.580, 207Pb/204Pb ratios from 15.606 to 15.669, and 208pb/204pb ratios from 38.344 to 38.522, which suggest that ore-forming metals might have come from deep magmatic activity, with a little crust mixing. In summary, the Hutouya Zn-Pb de- posit may be a layered skarn type deposit related to Indosinian magrnatic activity.