摘要
宝树尖铜多金属矿床位于长江中下游成矿带安庆-贵池矿集区,是一个新发现的矽卡岩型矿床。本文主要通过岩石地球化学和年代学方法来解释矿床的成因。锆石U-Pb年代学研究表明,宝树尖岩体形成于148.6±3.2Ma,是长江中下游燕山晚期的产物,为长江中下游成矿带内发现的一个较早的中酸性含矿侵入体。对于该成矿岩体及矿床的深入研究,将为区内燕山期岩浆活动及成矿提供一个不可多得的范例。岩石属于高钾钙碱性、钙碱性系列,地球化学特征显示为埃达克质岩;矿区矿石金属硫化物以方铅矿、闪锌矿、黄铜矿和黄铁矿为主,非金属矿物有透辉石、石榴石、透闪石、石英、钠长石、方解石、绿泥石和绿帘石等。矿区侵入岩主要由闪长岩和闪长玢岩组成,总体上具有高的全碱含量,低的Al2O3、TiO 2、Fe2O3^T和P2O5含量,富集大离子亲石元素(U、Rb、Sr)和高场强元素(Nb、Ta、Ti),轻稀土富集、重稀土亏损。岩石具有高的La/Yb、Sr/Y比值,低的Yb、Y含量,属于埃达克质岩。锆石稀土元素配分图显示典型的轻稀土亏损、重稀土富集。锆石Ti温度计表明岩石形成的平均温度为674.3℃。全岩Sr-Nd-Pb同位素特征表明岩石起源于俯冲洋壳的部分熔融。矿石黄铁矿δ34 S变化范围为7.6‰~9.6‰,表明成矿物质来源于岩浆热液和地层。锆石Eu异常特征和Ce^4+/Ce^3+比值表明形成岩石的岩浆具有高氧逸度,这有利于Cu、Au、Zn等成矿物质的迁移。结合区域地质背景,我们认为宝树尖矽卡岩型矿床的形成过程是:燕山期太平洋板块向中国东部俯冲,导致板片部分熔融产生埃达克质岩浆,最后经埃达克质岩浆分异形成的含矿气水热液在地壳浅部与上覆寒武系灰岩发生接触交代作用。
The Middle-Lower Yangtze River Valley Metallogenic Belt(MLYB)is one of the most important metallogenic belts in China.It has long been a hot area for research.The Baoshujian Cu-polymetal deposit,as a newly discovered skarn-type deposit,is located in Anqing-Guichi ore-cluster area,Middle-Lower Yangtze River Metallogenic Belt.It has not been taken research.This paper focuses on petrogeochemistry and geochronology to explain the geneses of igneous intrusion and related Cu-Au polymetallic deposit.Results of the zircon U-Pb geochronology show that the Baoshujian intrusion was formed at ca.148.6±3.2Ma,which is one of the earliest intermediate-acid ore-bearing intrusions in MLYB.The further study of this metallogenic intrusion and ore deposit will provide a rare example for magmatic activity and mineralization in Yanshanian Period in MLYB.Sulfides of ores in Baoshujian are mainly composed of galena,sphalerite,chalcopyrite and pyrite respectively.Non-metallic minerals include diopside,garnet,tremolite,quartz,albite,calcite,chlorite and epidote.The regional igneous intrusions are mainly composed of diorite and diorite porphyrite.Chemical affinity of the Baoshujian intrusion has high total K2O+Na 2 O contents,low Al2O3,TiO 2,Fe2O3^T,P2O5 contents,with enrichments of large ion lithophile elements(U,Rb,Sr),high field strength elements(Nb,Ta,Ti)and light rare earths,and depletion in heavy rare earths.The intrusion has high La/Yb and Sr/Y ratios with low Yb and Y contents,belonging to adakitic affinity.All REE distribution patterns of zircon show a typical light rare earth depletion and heavy rare earth enrichment.The zircon Ti thermometer indicates that the average temperature of rock formation was 674.3℃.The Sr-Nd-Pb isotopic characteristics of the whole rock indicate that intrusions originated from partial melting of the subducting oceanic crust,related to the far stress field of the Paleo-Pacific plate subduction.The δ^34 S values pyrite in ore range from 7.6‰~9.6‰,indicating that the ore-forming materials are derived from magmatic hydrothermal fluids mixed with strata.Their interaction led to the formation of minerals.The Eu anomaly characteristics and Ce^4+/Ce^3+ratios of zircon indicate that the magma forming rock had high oxygen fugacity,which was beneficial to the migration of ore-forming materials such as Cu,Au and Zn,and eventually form the deposit.Conjectured from regional geological background,we suggest that the genesis of the Baoshujian intrusion was formed during the subduction of the Pacific plate,resulting in the enriched Cu-polymetal adakitic magmas.The hydrothermal fluids produced by the adakitic magmas through differentiation had metasomatism with the overlying Cambrian limestone in the shallow crust,finally formed this typical Cu-polymetal skarn deposit.
作者
汪海
赵壮
杨晓勇
古黄玲
郑荥
NGUYEN Tuan Anh
WANG Hai;ZHAO Zhuang;YANG XiaoYong;GU HuangLing;ZHENG Ying;NGUYEN Tuan Anh(School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China;Hunan University of Technology,Zhuzhou 412007,China;The 324 Geological Team,Anhui Bureau of Geology and Mineral Exploration,Chizhou 247100,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2020年第1期184-204,共21页
Acta Petrologica Sinica
基金
科技部深地开采专项研究计划(2016YFC0600404)
国家自然科学基金项目(41673040、41611540339)联合资助
