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

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 mineralization 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 probably formed in close relation to magmatic 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-forming 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 ratios 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 deposit may be a layered skarn type deposit related to Indosinian magmatic activity.