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西秦岭李坝金矿床地质、同位素地球化学及其成因探讨
投稿时间:2020-03-06  修订日期:2020-06-20  点此下载全文
引用本文:
DOI:10.19762/j.cnki.dizhixuebao.2020243
摘要点击次数: 34
全文下载次数: 37
作者单位E-mail
李蓓 西北大学地质学系 15829384406@163.com 
朱赖民 西北大学地质学系 zhulaimin@nwu.edu.cn 
丁乐乐 西北大学地质学系  
马渊博 西北大学地质学系  
熊潇 西北大学地质学系  
杨涛 西北大学地质学系  
王飞 西北大学地质学系  
基金项目:国家自然科学基金项目(编号 41730426,41421002,41272092)及西北大学大陆动力学国家重点实验室科技部专项基金
中文摘要: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示踪,测定了成矿流体的氢-氧同位素组成,并对与矿体相伴产出花岗斑岩脉进行了LA-ICP-MS锆石U-Pb定年。研究表明,李坝金矿床花岗斑岩脉中黄铁矿δ34S值范围为8.19‰~10.06‰,赋矿围岩中金属硫化物δ34S值范围为4.94‰~9.81‰,矿石硫化物的δ34S值范围为4.94‰~10.82‰,矿石硫化物的硫同位素组成与矿区花岗斑岩及赋矿围岩的硫同位素组成相似,暗示成矿流体中的硫源主要来自受改造或变质的地层岩石与岩浆热液硫的混合。不同地质体的铅同位素组成变化范围较小,在Zartman铅构造模式图解中,样品投影点均落于造山带与上地壳演化线附近,矿石铅投影点与赋矿围岩及矿区岩脉的投影点重合,表明矿石中的铅可能来源于赋矿围岩和岩浆作用的混合。氢-氧同位素研究表明,成矿流体可能为变质流体、岩浆流体及地层建造水的混合热流体。矿区花岗斑岩脉与矿体相伴产出,花岗斑岩的LA-ICP-MS锆石U-Pb年龄为223 Ma,与金矿化时间一致,暗示成矿作用与岩浆活动同时发生。李坝金矿床与矿区岩浆岩同为造山作用的产物,并且其矿床地质特征、同位素地球化学特征与造山型金矿床相似,为形成于秦岭造山带由碰撞向伸展转变环境下成矿物质来源复杂的造山型金矿床。
中文关键词:李坝金矿床  多元同位素  锆石U-Pb定年  造山型金矿床  西秦岭
 
Geology, isotope geochemistry and ore genesis of the Liba gold deposit in the western Qinling orogen, China
Author NameAffiliationE-mail
Li Bei Department Of GeologyNorthwest University 15829384406@163.com 
Zhu Laimin Department Of GeologyNorthwest University zhulaimin@nwu.edu.cn 
DING Lele Department Of GeologyNorthwest University  
MA Yuanbo Department Of GeologyNorthwest University  
XIONG Xiao Department Of GeologyNorthwest University  
YANG Tao Department Of GeologyNorthwest University  
WANG Fei Department Of GeologyNorthwest University  
Abstract:The Liba gold deposit is located in the Liming ore cluster of west Qinling orogenic belt, occurs in the epi-metamorphic fine clastic rocks of the Devonian. It is produced in the thermal contact metamorphic belt outside the Zhongchuan intrusion and orebodies in the Liba gold field are controlled by the fracture zone. In detail, this paper analyzed the geological characteristics of the Liba gold deposit, the S isotopes of the host rocks, granite porphyry and ore sulfides by LA-MC-ICPMS and MAT-253 mass spectrometer. The Pb isotope 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 was measured, and LA-ICP-MS zircon U-Pb dating was performed on granite porphyry dykes. The δ34S value of the pyrite ranges from 8.19‰ to 10.06‰ in granite porphyry, the host rocks δ34S value of the sulfides from 4.94‰ to 9.81‰. In contrast, the δ34S value of the ore sulfides from 4.94‰ to 10.82‰, close to the value of granite porphyry and host rocks represent the sulfur source is a mixture of formation rocks and magmatic hydrothermal. Zartman’s plumbotectonic model diagram shows that the data all fall near the orogenic and upper crust Pb evolutionary curve, and the ore lead coincide with the host rocks and dyke in Liba gold deposit. This indicates that a complex source of ore lead, which from the mixture of the host rocks and magmatism. The isotopic hydrogen and oxygen compositions supports a mixed origin of the ore-forming fluids, which compose of metamorphic, magmatic and formation water. Granitic porphyry and ore body are produced together, 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 occur simultaneously. The Liba gold deposit and the magmatic rock are both the 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 the environment from collision to extension in the Qinling orogenic belt.
keywords:Liba gold deposit  multi-isotope geochemistry  zircon U-Pb dating  orogenic gold deposits  western Qinling
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