摘要
膏盐层是富含石膏/硬石膏的蒸发沉积岩建造。膏盐层除SO_(4)^(2-)外还富含Cl^(-)、CO_(3)^(2-)、Na^(+)、K^(+)等盐类物质和H_(2)O,且在自然界广泛存在。膏盐层可以向成矿系统提供氧化剂(SO_(4)^(2-))、矿化剂(Cl^(-)、CO_(3)^(2-)、Na^(+)、K^(+)等)、还原硫(S^(2-))和H_(2)O等挥发分,使金属成矿物质迁移或沉淀,是玢岩型铁矿(IOA)、矽卡岩型铁矿、MVT型铅锌矿、岩浆型Ni-Cu-PGE硫化物矿和部分热液铀矿成矿的关键因素。但膏盐层在内生金属矿床成矿中的作用一直没有得到应有重视,制约了相关成矿理论的发展,影响了找矿效率的提升。与膏盐层有关的内生金属矿床空间分布明显受膏盐层控制,矿床中普遍发育石膏等硫酸盐矿物,硫酸盐和硫化物的δ^(34)S值及磁铁矿等铁氧化物的δ^(18)O值异常高。膏盐层的加入可大幅提高成矿岩浆系统的氧逸度,使铁氧化物在熔体固结线之上大量提前形成,是岩浆发生液态不混熔,形成矿浆型富铁矿的重要条件。膏盐层向岩浆-热液成矿系统提供氧化剂(SO_(4)^(2-)),将熔/流体中Fe^(2+)氧化成Fe^(3+),富集形成铁矿床的同时,SO_(4)^(2-)自身被还原为S^(2-),S^(2-)与Fe^(2+)结合富集形成硫化物矿床,因此膏盐层-玢岩/矽卡岩铁矿-硫铁矿三者紧密共生,互为找矿标志。在MVT铅锌多金属成矿系统,膏盐层中SO_(4)^(2-)被炭质/有机质/甲烷等还原形成H_(2)S,与沿逆冲推覆构造上升的富含Pb^(2+)、Zn^(2+)的氧化性成矿溶液混合,S^(2-)与Pb^(2+)、Zn^(2+)等结合富集形成铅锌多金属矿床。膏盐层-有机质-铅锌矿三位一体,紧密共生。
The evaporite layer is evaporated sedimentary rock rich in gypsum/anhydrite.In addition to SO_(4)^(2-),the evaporite layer is also rich in Cl^(-),CO_(3)^(2-),Na^(+),K^(+),and other kinds of salts with H_(2)O,which exist widely in nature.The evaporite layer can provide volatiles such as oxidizing agent(SO_(4)^(2-)),mineralizing agent(Cl^(-),CO_(3)^(2-),Na^(+),K^(+),etc.),reduced sulfur(S^(2-)),and H_(2)O to the metallogenic system to migrate or precipitate ore-forming materials.It is the key factor for the mineralization of iron-oxide apatite ores(IOA),skarn-type iron ores,MVT-type Pb-Zn ores,magmatic Ni-Cu-PGE sulfide ores,and some hydrothermal uranium ores.However,the role of the evaporite layer in the mineralization of endogenetic metal deposits has not been focused on,which restricts the understanding of related metallogenic theories and affects the improvement of prospecting efficiency.The evaporite layer controls the spatial distribution of endogenic metal deposits related to the evaporite layer.The sulfate miner⁃als such as gypsum are generally developed in these deposits,with abnormally high δ^(34)S values of sulfate and sulfide and the δ^(18)O values of iron oxides such as magnetite.The addition of evaporite layers can greatly increase the oxygen fugacity of the ore-forming system and make the iron oxide formed in advance on the consolidation line of the melt,which is an important condition for the liquid immiscible melting of the magma and the formation of pulp type rich iron ores.The evaporite layer provides oxidants(SO_(4)^(2-))to the magmatic-hydrothermal mineralization system,oxidizing Fe^(2+)to Fe^(3+)and enriching it to form an iron deposit.Meanwhile,SO_(4)^(2-)is reduced to S^(2-),which combines with Fe^(2+)to enhance and form sulfide deposits.Therefore,the evaporite layer,IOA/skarn iron ores,and pyrite ores coexist closely and provide mineral exploration indicators.In the MVT Pb-Zn polymetallic mineralization system,SO_(4)^(2-) in the evaporite layer would be reduced by carbon,organic,and met
作者
李延河
段超
范昌福
胡斌
侯可军
朱乔乔
王倩
郭东伟
LI Yanhe;DUAN Chao;FAN Changfu;HU Bin;HOU Kejun;ZHU Qiaoqiao;WANG Qian;GUO Dongwei(MNR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China)
出处
《矿产勘查》
2024年第8期1391-1408,共18页
Mineral Exploration
基金
国家重点研发计划项目(2022YFC2903701)
国家自然科学基金项目(41473014、41402078)
公益行业科研院所基本科研业务费项目(KK2015、K1307)联合资助。
