西秦岭李坝金矿床地质、同位素地球化学及其成因探讨

李坝金矿床位于西秦岭造山带中的礼-岷矿集区内,赋矿围岩为泥盆系浅变质细碎屑岩,矿床产于中川岩体的外侧热接触变质带内,矿体主要受断裂破碎带控制.本文在李坝金矿床地质特征研究的基础上,对赋矿围岩、花岗斑岩岩脉、矿石硫化物进行了LA-MC-ICPMS原位微区硫同位素测试及化学溶样法分析,对不同地质体的铅同位素进行了系统测定与...

Geology, isotope geochemistry, and ore genesis of the Liba gold deposit in the western Qinling orogen, China

The Liba gold deposit is located in the Liming ore cluster of the west Qinling orogenic belt in the epi-metamorphic fine clastic rocks of the Devonian.It was produced in the thermal contact metamorphic belt outside the Zhongchuan intrusion.Orebodies in the Liba gold field are controlled by the fracture zone.This paper analyzes the geological characteristics of the Liba gold deposit in detail using the S isotopes of the host rocks,granite porphyry,and ore sulfides by LA-MC-ICPMS and MAT-253 mass spectrometer.The Pb isotopes of different geological bodies were measured by Nu Plasma HR MC-ICPMS.At the same time,the isotopic hydrogen and oxygen compositions of the ore-forming fluid were measured,and LA-ICP-MS zircon U-Pb dating was performed on granite porphyry dykes.Theδ34S value of the pyrite ranges from 8.19‰to 10.06‰in granite porphyry,and the host rocksδ34S value of the sulfides range from 4.94‰to 9.81‰.However,theδ34S value of the ore sulfides varies between 4.94‰to 10.82‰,closer to the value of granite porphyry and host rocks suggesting that the sulfur source is a mixture of formation rocks and magmatic hydrothermal.Zartman’s plumbotectonic model diagram shows that all data fall near the orogenic and upper crust Pb evolutionary curve,and the ore lead coincides with the host rocks and dyke in Liba gold deposit.This indicates a complex source of ore lead that was derived from a mixture of the host rocks and magmatism.The hydrogen and oxygen isotopic data support a mixed origin of the ore-forming fluids,which composed of metamorphic,magmatic and formation waters.Granitic porphyry and ore body were produced together.The U-Pb age determination of zircon indicates that the granite porphyry intruded at 264.4±1.3 Ma which is consistent with gold mineralization time,suggesting that mineralization and magmatic activities occurred simultaneously.The Liba gold deposit and the magmatic rock are both products of orogeny.The geological and isotopic geochemical characteristics of the deposit are similar to orogenic gold deposits.It shows that the Liba gold deposit is an orogenic gold deposit formed with a complex source of ore-forming materials under a changing environment ranging from collision to extension in the Qinling orogenic belt.