吉林临江地区草山花岗岩体中黑云母成分特征及其成岩成矿意义

Compositional characteristics and petrogenetic and metallogenic significance of biotites from Caoshan granite rock mass in Linjiang area,Jilin Province

草山花岗岩为八里沟金矿成矿岩体。笔者利用电子探针对草山花岗岩体中黑云母化学成分进行研究,以此来探讨岩浆成因及成矿潜力。研究表明草山花岗岩中的黑云母为岩浆成因的镁质黑云母,具有富Al、K、Mg、Ti,低Na、Ca的特征。以22个氧原子为基础计算了黑云母的阳离子数及相关参数,其全铝(~TAl)、镁质率(Mg~#)较高。利用黑云母化学成分对岩体固结的温度、压力、侵位深度及氧逸度进行了估算。岩石固结时的温度为750℃~780℃,固结压力范围为131.77~143.89 MPa,侵位深度为5.0~5.4 km,氧逸度f(O_2)=10^(-13)~10^(-14);由此得出其为中等深度、高温、高氧逸度岩体。黑云母化学成分特征暗示岩石为I型花岗岩,岩浆是在太平洋板块向华北板块俯冲、地壳加厚的背景下,由壳、幔物质混熔而形成。草山花岗岩固结时温度、氧逸度较高,有利于Au进入岩浆期后成矿流体中,表明八里沟金矿潜力较大。

Caoshan granite is the ore-forming rock mass of Baligou gold deposit.The authors studied the chemical composition of Caoshan biotites in the rock mass by electron microprobe,to understand the magma genesis and metallogenic potential.Results show that biotites from the Caoshan granite mass are magmatic magnesian biotites with high contents of Al,K,Mg and Ti,but low contents of Na and Ca.Based on 22 oxygen atoms,the number of cation and relevant parameters of the biotites are calculated,demonstrating high total aluminum（^TAl）and magnesian rate（Mg^#）.The temperature,pressure,emplacement depth and oxygen fugacity of rock mass consolidation are estimated according to the chemical composition of biotites.Solidification temperature of rock is 750℃～780℃,solidification pressure is 131.77～143.89 MPa,depth of emplacement is 5.0～5.4 km,and oxygen fugacity f（O2）is 10^-13～10^-14,indicating that the rock mass formed under medium depth,high temperature,and high oxygen fugacity.The chemical characteristics of biotites indicate that the rock is a type I granite.The magma is formed by the fusion of the crust and mantle material under the background that the Pacific Plate subducted toward the North China Plate and the crust was thickened.The high solidification temperature and oxygen fugacity of Caoshan granite are favorable for the Au element to get into post-magmatic ore-forming fluid,indicating good mineralization potential in the Baligou gold deposit.