德兴铜厂斑岩铜(钼金)矿床蚀变-矿化系统流体演化:H-O同位素制约

江西铜厂斑岩铜(钼金)矿床是德兴斑岩矿集区最大的矿床.文章根据铜厂矿床发育的钾硅酸盐化、绢英岩化、青磐岩化蚀变组合特征,和已厘定的铜厂矿床脉体类型,选取代表不同蚀变矿化阶段的石英、黑云母、绢云母及绿泥石等,进行单矿物的H、O同位素测试.石英和黑云母单矿物O同位素,与石英、黑云母平衡流体的δ 18O 值和δD值联合示踪结果显示,铜厂矿床早期A脉(不规则疙瘩状A1脉、石英-黑云母A2脉和石英-磁铁矿A4脉)和中期B脉(矿物组合为石英-黄铁矿+黄铜矿±辉钼矿±斑铜矿)形成时,成矿热液均为岩浆流体来源,但B脉可能混入了少量大气降水;晚期低温D脉和碳酸岩脉(180～200℃)的成矿热液全部为大气降水来源.斑晶黑云母平衡水的δ 18O和δD值变化范围较大表明,黑云母形成时的热液系统主要为岩浆水,局部受区域变质水和大气降水的混染,也可能与少量黑云母斑晶受到后期绿泥石化、水云母化蚀变有关.绿泥石蚀变主要由岩浆流体作用形成,但混入了一些大气降水,导致其δ 18O值少量降低.绢云母平衡的水的δ18O值和δD值(4.6‰和-19.4‰)表明,绢云母是大气降水与千枚岩共同作用的结果.总体来说,铜厂矿床钾硅酸盐化、绿泥石化蚀变,以及钾硅酸盐化阶段形成的A脉和B脉,均由岩浆流体作用引起,大气降水在绿泥石化阶段进入蚀变-矿化系统,而绢云母化、晚期低温D脉和碳酸盐脉均是大气降水作用的产物.

Restriction of H-O isotopes for alteration and mineralization system of Tongchang Cu (-Mo-Au) porphyric deposit, Jiangxi Province

Tongchang is the biggest porphyry Cu(Mo,Au) deposit in the Dexing metallogenic ore concentation area.For tracing the origin of ore-forming fluid during complicated mineralization and alteration process of the Tongchang porphyry Cu(-Mo-Au) deposit,the work has been mostly devoted to oxygen isotopes of rocks or spatial anomaly delineation of oxygen isotopes of whole rock,whereas researches on combined hydrogen and oxygen isotopes of single minerals including altered minerals and gauge minerals are very insufficient.According to detailed classification of different alteration and mineralization assemblages,the authors analyzed H and O isotopes of quartz,biotite,chlorite and sericite of different stages in Tongchang porphyry Cu(Mo,Au) deposit to evaluate the source and evolution of the ore-forming fluid.δ18O and δD values of water balanced with quartz and biotite from regular barren quartz veins in phyllite(A1),quartz-biotite veins(A2),quartz-magnetite veins(A4) and quartz-pyrite±chalcopyrite veins(B) show that all the ore-forming fluids were derived from magma except for partial contamination of B-veins by a little meteoric water.δ18O and δD values of quartz from the last low-temperature D-veins and carbonate veins lying at the end of the meteoric water-granodiorite porphyry line indicate that the ore-forming fluid during the last low-temperature stages(180～200℃) were totally derived from meteoric water.Considerable variations of δ18O and δD values of biotite phenocrysts from fresh and chloridie-hydromicazation porphyry suggest that minor amounts of meteoric water and regional metamorphic water were partially involved in the magmatic water during biotite phenocryst crystallization,or late weak chloritization-hydromicazation had already altered granodiorite porphyry.Chloritization was caused by magmatic water besides minor meteoric water,while the sericitization was triggered by the reaction of meteoric water with phyllite.In general,potassium-silicate alteration,chloritization,A-veins and B-veins were formed by the action of magmatic fluid,and meteoric water entered the alteration-mineralization system during chloritization.However,sericitiztion,late low-temperature D-veins and carbonate veins of the Tongchang deposit were formed by meteoric water.