兰坪盆地西缘沉积岩容矿脉状Cu-Ag(±Pb-Zn)多金属矿床成矿流体特征

Characteristics of ore-forming fluids of Cu-Ag(±Pb-Zn) polymetallic deposits in western Lanping Basin, Yunan Province

兰坪盆地西部发育大量沉积岩容矿的Cu-Ag-Pb-Zn多金属矿床,矿体的分布受逆冲推覆系统控制。逆冲推覆系统根部带主要发育脉状Cu-Ag（Mo）矿床（包括金满Cu-Ag、连城Cu-Mo及一系列脉状Cu矿床）;前锋带主要发育Pb-Zn-Ag（±Cu）矿床（包括白秧坪Pb-Zn-Ag-Cu多金属矿集区及一系列小型的Pb-Zn矿床）。文章系统分析了盆地西缘Cu-Ag（±Pb-Zn）多金属矿床流体包裹体及C、H、O同位素特征进行了根部带Cu和前锋带Pb-Zn矿床成矿流体的对比研究,探讨了盆地西缘Cu-Ag（±Pb-Zn）多金属矿床成矿流体的性质、来源及演化。研究表明,根部带的CuAg（Mo）多金属矿床成矿流体主要为与围岩充分交换的深循环大气降水,具有富CO2、中高温（集中在280-340℃）、中低盐度w（NaCleq）（1%-4%）的特点;前锋带Pb-Zn-Ag（±Cu）多金属矿床成矿流体则主要为源于大气降水的盆地卤水,具有贫CO2、中低温（集中在160-240℃）、中高盐度w（NaCleq）（集中于22.0%-24.0%）的特点。

The Lanping Basin is a significant Pb-Zn-Cu-Ag mineralization belt of the Sanjiang Tethyan metallogenic province in China. A series of sediments-hosted Himalayan Cu-Ag-Pb-Zn polymetallic deposits have been disco- vered in the western part of the Basin, controlled by a thrust-nappe system. In the thrust-nappe system, the Cu orebodies mainly occur in the western and relatively deep part of the mineralization system （the root zone）, whereas the Pb-Zn-Ag （±Cu） orebodies occur in the eastern and relatively shallow part of the system （the front zone）, both with vein-type mineralization. In this paper the authors present new data, combined with existing data on fluid inclusions, isotopes and geological characteristics of representative deposits, to provide the first study that contrasts mineralizing fluids in the Cu-Ag （Mo） and Pb-Zn-Ag （Cu） polymetallic deposits. Fluid inclusion and isotope studies show that the Cu-Ag （Mo） mineralization in the root zone was derived predominantly from deep crustal fluids, with the addition of basinal brines. The deep crustal fluids are marked by high CO2 content, relatively high temperatures （280℃ to 340℃） and low salinities （1% to 4%）. In comparison, hydrothermal activity associated with the Pb-Zn-Ag （±Cu） deposits in the front zone is characterized by basinal brine, with relatively low temperatures （160℃ to 240℃）, high salinities （22.0% to 24.0%）, and low CO2 concentrations.Although evolved meteoric waters have predominantly been proposed as the source for deep crustal fluids, magmatic and metamorphic components cannot be completely excluded. The basinal brine was predominantly derived from meteoric water.