摘要
滇西马厂箐铜钼多金属矿床位于三江特提斯成矿域,是一个与喜马拉雅期富碱斑岩侵入有关的多金属矿床。前人研究表明,马厂箐铜钼多金属矿床形成于斑岩-矽卡岩成矿系统,但由于缺乏系统矿物学研究,目前对矽卡岩矿化过程和成矿效应仍不清楚,限制了对该矿床成矿过程的全面认识。因此,本文以马厂箐矿床矽卡岩型矿化中的石榴子石为研究对象,利用H-O同位素、电子探针(EPMA)以及LA-ICP-MS原位微区技术开展了同位素及成分分析,限定成矿流体来源以及反演成矿流体演化过程。石榴子石可分为早期自形石榴子石(Grt I)和晚期他形石榴子石(Grt II)。Grt I与辉石共生,并伴有黄铁矿、黄铜矿等金属矿物组合,属于钙铝-钙铁榴石固溶体(And_(49.37~99.58)Gro_(0~49.79));Grt II更富Fe,属钙铁榴石系列(And_(67.50~99.85)Gro_(0~31.84))。两期石榴子石均富含Th、U、Nd,亏损Ba、Sr、Hf、Nb,富轻稀土。基于石榴子石矿物化学特征认为,Grt I可能是在弱酸性、氧化、低水岩比(W/R)条件下形成的,而Grt II可能是在酸性、氧化和高W/R条件下形成的。另外,两期石榴子石δDV-SMOW值为-122.6‰~-98.6‰,δ18O流体值为5.95‰~8.25‰,暗示成矿流体主要来自岩浆水。综合研究认为,在矽卡岩化过程中,成矿流体的氧逸度、温度整体呈现降低趋势,流体pH逐渐由酸性向弱酸性—中性演化,这一转变可能是触发马厂箐矿床矽卡岩型矿化铜钼硫化物沉淀的主要机制。
The Machangqing Cu-Mo deposit,located in the Sanjiang Tethyan metallogenic belt,is a polymetallic deposit related to the intrusion of alkaline porphyry in the Himalayan period.Previous studies have shown that the Machangqing Cu-Mo polymetallic deposit was formed in a porphyry-skarn metallogenic system.However,due to the lack of systematic mineralogical research,a mineralization process and metallogenic effects of skarn are still unclear,limiting a comprehensive understanding of the mineralization process of this deposit.Herein,this paper considers garnet in skarn mineralization in Machangqing deposit as the research object,and uses H-O isotope,electron probe(EPMA)and LA-ICP-MS in-situ microregion technology to carry out isotope and composition analysis to define the source of ore-forming fluids and invert the evolution process of ore-forming fluids.The garnets can be divided into early euhedral garnets(Grt I)and late anhedral type(Grt II).The Grt I,coexisting with the pyroxene,pyrite and chalcopyrite,belongs to the grossular-andradite garnet solid solution(And_(49.37~99.58)Gro_(0~49.79)).The Grt II has elevated Fe compared to Grt I,and mainly consists of andradite(And_(67.5~99.85)Gro_(0~31.84)).Both the types of garnets are enriched in Th,U,LREEs and Nd,depleted in Ba,Sr,Hf and Nb.Based on the chemical compositions of garnet,the Grt I may have formed under mildly acidic,oxidized and low W/R conditions,whereas the Grt II may have formed under acidic,oxidation,and high W/R conditions.In addition,theδD_(V-SMOW)values andδ~(18)O_(fluid)values of these garnets range from-122.6‰to-98.6‰and 5.95‰to 8.25‰,respectively,implying that the hydrothermal ore-forming fluid originated from magma-derived fluid.A comprehensive consideration of data indicated that the oxygen fugacity and temperature of the ore-forming fluid presented a decreasing trend during the skarn mineralization process,and the pH of the fluid gradually changes from acid to weak acid neutral.This process may have been the main mechanism to trigger the precipitation of skarn type mineralized copper molybdenum sulfide in the Machangqing deposit.
作者
吉彦冰
杜丽娟
陈军
黄智龙
李波
李鑫正
刘林林
杨再风
JI Yanbing;DU Lijuan;CHEN Jun;HUANG Zhilong;LI Bo;LI Xinzheng;LIU Linlin;YANG Zaifeng(College of Resources and Environmental Engineering,Guizhou University,Guiyang,Guizhou 550025,China;Key Laboratory of Karst Georesources and Environment,Guizhou University,Ministry of Education,Guiyang,Guizhou 550025,China;State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang,Guizhou 550002,China;Faculty of Land and Resource Engineering,Kunming University of Science and Technology,Kunming,Yunnan 650093,China)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2023年第4期1140-1156,共17页
Acta Geologica Sinica
基金
国家自然科学基金项目(编号41902085)
中国科学院地球化学研究所矿床地球化学国家重点实验室开放基金(编号202210,201905)
贵州大学培育项目(编号贵大培育[2020]7)联合资助的成果。
关键词
石榴子石
H-O同位素
微量元素
成矿流体
马厂箐铜钼矿床
garnet
H-O isotopes
trace elements
ore-forming fluids
Machangqing Cu-Mo polymetallic deposit
