内蒙古特拜金矿流体包裹体特征与成矿作用

Fluid Inclusion Features and Mineralization of the Tebai Gold Deposit in Alxa League,Inner Mongolia

华北地台北缘西段是我国重要的金矿成矿区。目前区内已发现了浩尧尔忽洞、朱拉扎嘎、赛乌素、碱泉子、卡修他他等多个规模不等、不同成因的的金矿床,显示出较大的成矿潜力。特拜金矿是近年来在华北地台北缘西段新发现的一个中型金矿。为探索该金矿的成矿机制,本文对特拜金矿开展了矿床地质和流体性质研究。结果表明,特拜金矿赋存于早古生代碳质板岩、碳质千枚岩中。矿体展布受黑色岩系、NW向F2断裂带和NE向F8断裂带的共同控制。矿区周边出露华力西期特拜石英闪长岩和管材陶鲁盖花岗岩等岩浆岩。该金矿从早期成矿阶段到晚期成矿阶段,流体包裹体的均一温度从300℃～350℃逐渐降低到150℃～200℃,盐度从16wt%NaCleqv～20wt%NaCleqv逐渐降低到1wt%NaCleqv～4wt%NaCleqv;流体的气相组成以CH_4-N_2-CO_2为特征,δDV-SMOW为-91. 6‰～-84. 5‰,δ^(18)OH_2O为2. 8‰～3. 5‰,流体相对富集Ba、Pb、Sr等元素,相对亏损Rb、Th、Nb、Zr、Y、Yb等元素。成矿流体主要来源于岩浆期后热液,可能混合了少量的大气降水。成矿流体处于一种还原性、低温的环境下,金在流体中以Au(HS)_2-络合物的形式迁移。流体向上运移过程中,因温度、压力的降低而发生不混溶现象,并导致金的沉淀。

The western part of the northern margin of the North China Craton is one of the most important gold metallogenic provinces in China.Nowadays many gold deposits with different scales and various genetic types have been found in this area,such as the Haoyaoerhudong,the Zhulazhaga,the Saiwusu,the Jianquanzi and the Kaxiutata iron-gold deposit.The Tebai gold deposit is a newly found deposit with a medium scale in this area.Through our study on the geological characteristics and ore-forming fluid of the Tebai gold deposit,it is known that the ore body is located in the Early Paleozoic slates and phyllites containing carbon.The ore body is controlled by the NW trending and NE trending fault zones.The magmatism around the ore body is very strong.The Early Permian Tebai quartz diorite and Early Permian Guancaitaolugai granite intruded into the surrounding formations of the gold deposit.From the early mineralization stage to the late mineralization stage,the homogeneous temperature declines from 300~350℃to 150~200℃gradually,while the salinity declines from 16wt%NaCleqv^20wt%NaCleqv to 1wt%NaCleqv^4wt%NaCleqv gradually.The metallogenic fluid contains CO 2-CH 4-N 2,and theδD V-SMOW varies between-91.6‰^-84.5‰,and theδ18 O H 2O varies between 2.8‰~3.5‰.The fluid is rich of Ba,Pb,Sr and poor of Rb,Th,Nb,Zr,Y,Yb.Based on the actual geological conditions of this deposit,it is concerned that the metallogenic fluid resources from the mixed hydrothermal solution of after magma fluid of the Guancaitaolugai granite porphyry,which was probably mixed with a small amount of meteoric waters.The ore-forming fluid flowed in a reduction environment with low temperature.The gold migrated in the fluid in Au(HS)2-form.Golds were deposited by the unmixing mechanism because of the reducing of the temperature and pressure when the fluid moved upward.