摘要
古今海底热液流体系统是人们关注的重要科学问题,正确识别流体系统中不同来源的流体端员及其混合-分离过程,是深刻理解海底流体系统及火山成因块状硫化物(VMS)矿床成因的关键。本文选择了我国境内两个典型的VMS矿床:甘肃白银厂矿床和四川呷村矿床,分别对上部块状矿带和下部脉状-网脉状矿带进行了系统的流体包裹体研究。研究表明,海底热液成矿流体系统是一个富集CO_2和CH_4的NaCl-H_2O流体系统。在此系统中,至少已鉴别出5种端员流体,即(1)低温 (<150℃)高盐度(>12wt％NaCl)卤水;(2)高温(>320℃)高盐度(>14.5wt％NaCl)流体和(3)高温(>350℃)中盐度(10～16wt％Nacl)富气流体,以及(4)低温(～100℃)低盐度(2～5wt％NaCl)流体和(5)中温低盐度流体,它们构成了3个相互分离的温度-盐度演变趋势或混合途径。)低温高盐度卤水封存于卤水池中,在呷村矿床,卤水池发育在海底凹陷盆地热液区内,在白银厂矿床,卤水池则发育在海底之下的多孔火山碎屑岩单元及穿透性断裂破碎带内。高温高盐度流体和高温中盐度富气流体均来自矿区下部浅位岩浆房,前者以液态富金属H_2O流体为主,通常与冷海水发生混合;后者以富CO_2和CH_4的气体为主,高温(>450℃)下呈相对独立的气流存在,至到250～260℃才作为液相混入成矿热液流体中。
Distinguishing of the end-member of fluids with various sources and recognizing the mixing-separation processes in hydrothermal fluids are key to understand the nature of the submarine hydrothermal systems and genesis of volcanogenic massive sulfide deposits. Two typical VMS deposits, the Baiyinchang in Gansu and Gacun in Sichuan, were choice for the study of fluid inclusions in both the upper massive ores and the underlying stringer-stockwork zones. Available fluid inclusion data indicate that the hot fluid in submarine hydrothermal system was a CO2- and CH4-rich, NaCl-H2O solution. At least, five end-members of fluids have been recognized in the hydrothermal system. They are: (1)low temperature (<150degreesC) and high-salinity brine; (2) high temperature (>320degreesC), high-salinity (>14.5wt% NaCl) fluid; (3) high temperature (> 350degreesC), middlesalinity(10similar to 16wt%Nacl) gas-rich fluid; (4) low temperature(similar to100degreesC), low-salinity (2-5 wt % NaCl) fluids; and (5) middle temperature low-salinity fluid. These end-member fluid data lead to three different arrays, e. g., mixing paths, on the homogeneous temperature versus salinity diagram. The low-temperature and high-salinity brine probably was enclosed in the brine pool, which developed within the seafloor depression at Cacun, whereas within the sub-seafloor porous volcanoclastic units and fracture zone at Baiyinchang. The high-temperature high-salinity fluid and the high-temperature middle-salinity fluid were derived from a felsic magma chamber emplaced beneath the districts. The former is mainly metals-rich H2O, usually mixed with cold sea-water; the latter is dominated by CO2- and CH4-rich gases, occurred as an isolated gas phase at temperatures of >450degreesC, and then input to the ore-forming hydrothermal fluids at 250similar to260degreesC. The low-temperature low-salinity fluid, with salinity similar to seawater, had mixed with magma-derived fluid in various proportions. The middle-temperature low-salinity fluid has similar salinities
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2003年第2期221-234,共14页
Acta Petrologica Sinica
基金
"九五"攀登项目(95-预-39)
自然科学基金(49773177)
