摘要
酸性蚀变岩帽是岩浆热液流体和围岩在近地表相互作用的产物,是斑岩-浅成低温热液成矿系统的重要指标。发育在长江中下游成矿带庐枞盆地内的矾山酸性蚀变岩帽产出面积较大(>20km2)。前人对该酸性蚀变岩帽中的明矾石矿床的地质和地化特征进行了相关研究,但详细的年代学研究工作尚未开展。为精确厘定矾山酸性蚀变岩帽的形成时代,本文开展了明矾石40Ar-39Ar法和金红石原位U-Pb法定年。矾山酸性蚀变岩帽中明矾石共有三种类型:ⅠA型明矾石主要呈交代蚀变发生在热液蚀变早阶段,与石英、粒状黄铁矿或赤铁矿、少量金红石共生;ⅠB型明矾石形成于热液蚀变晚阶段,主要呈叶片状集合体充填在开放空间中,与石英、星点状赤铁矿、粒状金红石集合体共生,少量金红石和赤铁矿沿明矾石解理裂隙分布;Ⅱ型明矾石是表生明矾石,主要呈细粒集合体沿裂隙分布,与赤铁矿、高岭石、地开石共生。三类明矾石形成于不同环境下:ⅠA和ⅠB型明矾石形成于岩浆热液环境下,是大矾山明矾石矿区的主要产物;Ⅱ型细粒明矾石分布在矾山酸性蚀变岩帽的非明矾石矿区,是表生环境下的产物。ⅠA型明矾石的40Ar-39Ar定年的坪年龄为131±6Ma,代表了矾山酸性蚀变岩帽的形成时代。与Ⅱ型明矾石密切共生的金红石U-Pb定年结果为32.7±4Ma,在该期间,整个盆地内无岩浆活动发生,该年龄反映了矾山酸性蚀变岩帽经历表生氧化作用的时间。明矾石和金红石定年结果分别对应岩浆热液和表生明矾石的形成时代。在利用明矾石进行找矿工作时需先明确明矾石成因,矾山酸性蚀变岩帽中深成明矾石是下一阶段的找矿研究的基础。
A lithocap is the product of interaction between the magmatic-hydrothermal fluid and wall rocks near surface,which in turn is an important pathfinder for porphyry-epithermal deposits. Fanshan lithocap is a large-scale( > 20 km2) one,which developed in the Luzong Basin of the Middle and Lower Yangtze River Metallogenic Belt. Previous studies have been carried out about the geological and geochemical characteristics of the alunite deposits within the lithocap,but the detailed geochronological work is not conducted. In order to determine the formation time of Fanshan lithocap accurately,alunite 40Ar-^39Ar dating and in-situ rutile LA-ICP-MS U-Pb dating have been conducted. There are three types of alunite in Fanshan lithocap. Type IA alunite occurs in the early stage of hydrothermal alteration as replacement,coexisting with quartz,granular pyrite or hematite,and minor rutile. Type IB alunite occurs in the late stage of hydrothermal alteration,in forms of bladed-like aggregates filling in open space,coexisting with quartz,star-like hematite and granular aggregate rutile,while small amount of rutile and hematite are distributed along the alunite cleavages. Type Ⅱ is supergene alunite,mainly in forms of fine-grained aggregates filling in fissures,coexisting with hematite,kaolinite and dickite. These three types of alunite have different formation environments. IA and IB types of alunite were formed in the magmatic hydrothermal environment,which consisted of the main production of the Dafanshan mine. Type Ⅱ fine-grained alunite is the product of the supergene process,which is limitedly distributed in the non-mining areas. The plateau age of 40Ar-39Ar dating of IA alunite is 131 ± 6 Ma,representing the formation age of Fanshan lithocap. The rutile U-Pb dating with type Ⅱ alunite is 32. 7 ± 4 Ma,during which no magmatic activity occurs in Luzong Basin,therefore this age reflects timing of supergene oxidation of Fanshan lithocap. The genetic of alunite needs to be carefully examined before using as a tool for explo
作者
李旋旋
周涛发
刘一男
陈静
张乐骏
WHITE Noel C
谢杰
LI XuanXuan;ZHOU TaoFa;LIU YiNan;CHEN Jing;ZHANG Lejun;WHITE Noel C;XIE Jie(School of Resources and Environmental Engineering,Ore Deposit and Exploration Centre(ODEC),Hefei University of Technology,Hefei 230009,China;Anhui Province Engineering Research Center for Mineral Resources and Mine Environments,Hefei 230009,China;Centre of Ore Deposit and Earth Science(CODES),University of Tasmania,Private Bag 79,Hobart,Australia;No.327 Geological Party,Anhui Bureau of Geology and Mineral Resources,Hefei 230011,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2019年第12期3782-3796,共15页
Acta Petrologica Sinica
基金
国家自然科学基金项目(41672081)
国家重点研发计划项目(2016YFC0600206)
安徽省国土资源科技项目(2015-K-03)
中央高校基本科研业务费专项资金(PA2019GDZC0093)联合资助
