云南白牛厂矿区古生代沉积盆地的成矿流体系统

白牛厂矿区发育在多旋回演化的裂谷盆地之中 ,超大型银多金属矿床由中寒武世海底喷溢沉积作用形成。海底热液来源于裂谷盆地沉积物中超高压流体 ,热液属于富含 K+、SO2 -4的卤水 ,w ( Zn) /w ( Zn+Pb) <0 .7,与世界超大型 SEDEX矿床特征相似。滇东南下寒武统可能为重要的矿源层 ,该区具有良好的找矿前景

MINERALIZATION FLUID SYSTEM OF PALAEOZOIC SEDIMENTARY BASIN AT BAINIUCHANG,YUNNAN PROVINCE

Located in the western flank on Nanlin Metallogenic Zone,the Bainiuchang superlarge silver polymetallic deposit was formed mainly by submarine exhalative sedimentary during Middle Cambrian.The Bainiuchang ore bearing basin is a fault controlled depression of the slop zone of an aulacogen.The ore bearing fluid in the main orebody was formed by compaction fluid in the depression.The temperatures of the fluid range from 160℃ to 320℃,and the contents of salts range from 11 5% to 17 1%.Ore bearing fluid is characterized by low contents of Na +,Cl - and high contents of K +,SO 2- 4.The values of pH range from 4 7 to 6 3,The values of Eh range from -0 85 to 0 35.The ratio of w (Zn)/ w (Zn+Pb) is 0 57 in the ore similar to those of some well known superlarge exhalative deposits such as Broken Hill,Mount Isa and Sullivan.Results of the numerical modeling show that the pressure of 56 GPa of excess fluid potentials was formed by compacting in the shales which is dominated in the Diandongnan basin.Because the basin was overpressured,it is great possible for large amount of compaction fluid to errupt suddenly during compaction period.The chemical composition in the fluid,the isotopic constitution of sulfides and lead and REE compositions show that the source of the metallogenic elements is from the fine grained clastic formation of the Lower Cambrian in the basin.