塔西陆内红层盆地中盆地流体类型、砂砾岩型铜铅锌-铀矿床的大规模褪色化围岩蚀变与金属成矿

Types of Basin Fluids,Mechanism of Discolored Alterations and Metal Mineralizations of Glutenite-type Cu-Pb-Zu-U Deposits in Intercontinental Red-bed Basin of the Western Tarim Basin

在塔里木盆地西部—北部地区中—新生代陆内红层盆地中,具有铜铅锌-铀-煤-石油天然气同盆共存富集规律。采用地球化学岩相学和构造岩相学研究方法,对盆地流体类型、褪色化围岩蚀变机制和金属富集成矿关系进行了研究。本区盆地流体可划分为天然气型、油气型、卤水型、热水沉积型、富烃类还原型、富CO2非烃类流体型、构造流体型、岩浆热液型和层间水-承压水型等9种。其热水沉积型、高盐度卤水型、富Fe-Mn-CO_2流体型、岩浆热液型和富烃类还原型等5种成矿流体在盆地后期变形过程与碎裂岩化相之间,发生了强烈的构造-岩相-岩性物性多重耦合作用和大规模水岩耦合反应。在地球化学岩相学机制上,大规模低温围岩蚀变机制为强烈的成矿流体蚀变作用,地球化学岩相学标志为"一黑(沥青化蚀变相)二白(碳酸盐化蚀变相)三褪色(褪色化-绿泥石化蚀变相)"。沥青化蚀变相可划分为黑色强沥青化蚀变带、灰黑色中沥青化蚀变带和灰色弱沥青化-褪色化蚀变带。碳酸盐化蚀变相可划分为强碳酸盐化蚀变带、中碳酸盐化蚀变带和弱碳酸盐化蚀变带。这些围岩蚀变作用将大量Fe^(3+)还原为Fe^(2+),使紫红色铁质碎屑岩类发生了大规模的褪色化-变色化蚀变作用,而且形成了砂砾岩型-砂岩型铜铅锌-铀矿床。在上述多重耦合机制过程中,含烃盐水-液烃-气烃-气相CO_2、含烃盐水-气烃-液烃-气液烃-轻质油-沥青等多相态流体不混溶作用导致矿质沉淀富集。气相CO_2逃逸与热水解作用导致带状碳酸盐化蚀变带形成和矿质沉淀富集。富烃类还原型成矿流体和Ca-Mg-Fe-Mn-CO_3酸性还原型成矿流体、以赤铁矿-铁辉铜矿为标志的地球化学氧化-还原相作用界面导致矿质沉淀。强酸性氧化相Ca-Sr-Ba-SO_4型热水沉积作用形成了含铅锌石膏天青石岩等,为砂砾岩型铜铅锌-铀矿床矿质大规模沉淀富集成矿机制。

Co-enrichment of Cu-Pb-Zn-coal-oil-gas deposits in the basin exhibits in MesozoicCenozoic intercontinental redbed basin of the northwestern Tarim Basin.Based on the methods oftectonic lithofacies and geochemical facies,the relationships among the types of basin fluids,discolored mechanism and metal mineralization were studied.Basin fluids may be classified into the nine types of gas,oil-gas,brine,hydrothermal sedimentary,hydrocarbon-rich with extensive reductibility,CO2-rich nonhydrocarbon fluid,tectonic fluid,magmatic hydrotherm and interlayer to confined-water.Five types of hydrothermal sedimentary,high-salinity brine,Fe-Mn-CO2-rich fluid,magmatic hydrotherm and hydrocarbon-rich with extensive reductibility,undergo the extensive physical coupling among tectonics-lithofacies-lithology during the late cataclastic lithification phase and basin deformations.At the same time,the chemical coupling reactions are taken place.＂Black-first,white-second,and discolored-third＂is named for extensive alterations of the basin fluid in the mechanism of the geochemical lithofacies,resulting in most of Fe^3＋ into Fe^2＋ for the discolored alterations in the amaranthine irony conglomerate.Bituminization alteration facies may be classified into the extensive black bituminization zone,the middle gray-black bituminization zone and the weak bituminization-discolour zone;carbonatization alteration facies may be classified into the extensive,the middle,and the weak carbonatization zones.Nonmiscibility of hydrocarbon-bearing brine,liquid hydrocarbon,gas hydrocarbon and gas-phase CO2,and multiple phases of nonmisciblity for hydrocarbon-bearing brine,gas hydrocarbon,liquid hydrocarbon,gas-liquid hydrocarbon,light oil and asphalt,might have resulted in enrichments and depositing of minerals. The escape of gas-phase CO2 could be pyrohydrolysized in carbonatization alteration facies and enrichments and depositing of minerals.Geochemical redox interfaces resulted in mineralizations may be indicated by hydrocarbon-rich with extensive reductibility,Ca-Mg-Fe-Mn-CO3 acid reducing metallogenic fluid,and intergrowth of hematite and Fe-chalcocite.However,Pb-Zn-bearing gypsum celestine ores might have been formed by CaSr-Ba-SO4-type hydrothermal sediment with strongly acidic and oxidizing. All of these mechanisms of the geochemical lithofacies could be assumed that the discolored alterations at the large-scale are not only for the amaranthine irony conglomerates to sandstones,but also for glutenite-type Cu-Pb-Zn-U and sandstone-type Cu metallogenic belt in Mesozoic-Cenozoic continental red-bed basin of the western Tarim Basin.