江西武山铜矿黑云母的化学成分特征:地质与成矿意义

Chemical composition of biotite from Wushan copper deposit,Jiangxi Province:Geology and metallogenic significances

华南燕山期岩浆活动频繁,出露有大量的斑岩侵入体,形成了许多与斑岩侵入体有关的铜多金属矿床。对九瑞矿集区与铜矿有关的武山岩体黑云母矿物进行了详细的镜下观察和电子探针分析。依据镜下岩相学特征可以将研究的黑云母分为斑晶黑云母和基质黑云母两类,两类黑云母成分上均为镁质黑云母,并且大部分斑晶黑云母受到热液蚀变的影响,已经具有蚀变黑云母的特征。黑云母Ti温度计显示斑晶黑云母的核部结晶温度平均值为744℃,边部温度平均值为742℃,基质黑云母结晶温度平均值为732℃。黑云母压力计显示斑晶黑云母的侵位深度平均值为3.3 km,基质黑云母的侵位深度平均值为2.6 km。利用黑云母成分反映出的岩浆为高氧逸度岩浆,有利于成矿。研究表明,大多数武山岩体的斑晶黑云母受到热液作用的影响,其TFeO、Na_(2)O、MnO和TiO_(2)等含量显著降低。这些黑云母在成分上更可能反映的是浅部岩浆房受到来自深部的中基性岩浆注入、脱水,并诱发中酸性岩浆上侵形成斑岩的作用过程。利用黑云母成分特征,可以大致判断武山铜矿的剥蚀程度。

Yanshanian magmatic activity was widespread in South China,and a large number of Yanshanian-aged porphyry intrusions are exposed in the Jiurui region,with many polymetallic copper deposits related to these porphyry intrusions.This paper presents the detailed mineral composition of biotite from the Wushan copper deposit in the Jiurui ore concentration area.According to their microscopic petrographic characteristics,the biotites of the Wushan copper deposit can be divided into two types:biotite phenocrysts and matrix biotite.Detailed EPMA analyses of the two types show they are all magnesium biotite,with most phenocrysts exhibiting hydrothermal alteration.The biotite Ti thermometer returned average crystallization temperatures of 744℃for the phenocryst cores,742℃for the phenocryst rims,and 732℃for matrix biotite.The biotite phenocrysts yielded an average emplacement depth of 3.3 km,and the matrix biotite had an average depth of 2.6 km.The biotite composition indicates that the source magma likely had high oxygen fugacity,which is conducive to porphyry mineralization.The biotites in the Wushan copper deposit have been affected by hydrothermal fluids,resulting in a significant decrease in TFeO,Na_(2)O,MnO,and TiO_(2).The composition of biotite phenocrysts records the magmatic processes that formed the Wushan intrusion.A shallow magma chamber was dehydrated by the intrusion of intermediate-basic magma,following which the magma upwelled and intruded into the shallow crust to form a porphyry.The approximate degree of denudation of the Wushan copper deposit can be determined based on the biotite composition.