华南黑色岩系铂多金属矿成矿流体地球化学及其矿床成因意义

Geochemistry of Ore-forming Fluid and Its Metallogenetic Significances of PGE-polymetallic Deposits in Lower Cambrian Black Rock Series, Southern China

较系统的流体包裹体观测显示:①华南黑色岩系铂多金属矿中存在两种不同体系的流体包裹体,一为具中低盐度、NaCl-H2O体系者(Ⅰ型);二为具中高盐度、CaCl2-NaCl-H2O体系者(Ⅱ型);其中后者为该类矿床中首次确定;②存在2个不同期次的成矿流体,其中铂多金属矿层和其下伏磷块岩中碳酸盐石英网脉的流体包裹体特征基本一致,可能代表主成矿期流体,其均一温度峰值为170℃左右,而盐度具双峰式特征,峰值分别为27%～31%和4%～6%;矿层之上碳酸盐石英脉中流体包裹体可能代表了晚期成矿流体,其均一温度多为130～170℃左右,盐度峰值在12%～14%;③在早寒武世,接受了巨厚沉积的扬子克拉通南缘加里东冒地槽中的盆地热卤水受挤压而顺层侧向迁移,从地层中汲取Ni、Mo、V和PGE等成矿元素,形成中高盐度的CaCl2-NaCl-H2O体系成矿热液,沿断裂上升并与NaCl-H2O体系海水混合,形成黑色岩系中的铂多金属矿床(点)。

Systematic studies on fluid inclusions in PGE-polymetallic deposits in Lower Cambrian black rock series in Southern China were performed, and the results suggest:① There exist two types of fluid inclusions. Type Ⅰ is of NaCl-H-2O system with a medium to low salinity. Type Ⅱ is of CaCl-2-NaCl-H-2O system with a high-medium salinity. The fluid inclusions of typeⅡ are first discovered in this kind of deposit. ② Two periods of ore-forming fluids can be recognized. Characteristics of fluid inclusions in PGE-polymetallic ores and carbonate-quartz stockworks in the underlay phosphorites are basically identical, which may represent the ore-forming fluid of main metallogenetic stage. The peak value of t \-h in those fluid inclusions is about 170 ℃, while their salinities possess bimodal distribution with two peak values of 27%～31% and 4%～6%. On the contrary, fluid inclusions in the carbonate-quartz veins in the hanging wall may represent the ore forming fluid of the post-metallogenetic stage. The t \-h and its peak value of salinities of the fluid are mostly from 130 to 170 ℃ and 12%～14% respectively.③ In the Early Cambrian, the basinal hot brine trapped in the Caledonian basins, which were distributed along the southern margin of the Yangtze Craton and accumulated giant thick sediments, was expelled and migrated laterally along strata because of the pressure generated by overlying sediments. The basinal hot brine absorbed Ni, Mo, V, PGE from the around rocks and transformed into ore-bearing hydrothermal fluid with CaCl-2-NaCl-H-2O system and medium-high salinity, then ascended along faults and mixed with seawater of NaCl-H-2O system, and finally formed PGE-polymetallic deposits or spots in the black rock series.