中文摘要：

与多数产于岩浆弧环境中的斑岩铜矿不同,西藏冈底斯带斑岩铜矿形成于碰撞造山环境,查明其形成过程有助于理解非岩浆弧环境中斑岩铜矿床的成因。为此,选择冈底斯带最大的斑岩铜矿——驱龙斑岩铜矿进行解剖,通过对矿床岩浆-热液过程形成的各类脉体详细的流体包裹体研究,以及不同蚀变阶段蚀变矿物的H-O同位素研究发现：引起矿床早期蚀变（钾硅酸盐化）与矿化的流体并非通常认为的高盐度岩浆热液,而是直接从岩浆房出溶的中等盐度（约9%NaCl）、近临界密度的高温（550～650℃）气相;气相近临界密度的特征表明,早期蚀变与矿化形成于较高的压力（105±15～90±20MPa）条件下,用静岩压力估算,对应的古深度在4.2±0.6～3.6±0.8km之间,成矿后（约16Ma）矿区发生了至少3～3.5km的剥蚀;与高盐度流体相比,中等盐度气相与熔体密度差较大,很难在斑岩体顶部聚集并集中释放,而连续释放则直接导致矿床含矿斑岩体与Cu、Mo矿体时空关系的解耦,并造就了矿床早期蚀变范围大、但强度弱,矿化范围大、但品位低的矿床地质特征;成矿物质的沉淀并非温度降低的结果,而是因压力降低及气相中S大量减少所致。总之,驱龙斑岩铜矿是一类成矿与低密度气相有关的斑岩铜矿类型,其蚀变-矿化特征及成矿过程与高盐度流体引发的斑岩矿床类型有所不同,意识到斑岩矿床蚀变及矿化特征与矿床成因的密切关系,对矿床勘查将具有重要的现实意义。

英文摘要：

Porphyry Cu deposits are usually thought to form in magmatic arc settings,although some porphyry deposits also occur in collisional orogen settings,such as Gangdese Porphyry Cu Belt（GPCB） in south Tibet. Genesis of these deposits remain poorly understood. Here we report detailed fluid inclusions and H-O isotopes data on Qulong,the most giant deposit in GPCB. The results indicate：①Fluid that induced K-silicate alteration and Cu-Mo mineralization at Qulong,are not dominated by generally-accepted high-salinity brine,whereas they are prevailed by magmatic vapor exsolving from magma chamber with near critical density,moderate salinity（～9% NaCl） and high temperature（550～650℃） . ②Early-stage alteration and mineralization in the deposit should occur at a relatively high pressure condition（105±15～90±20 MPa） that the vapor-like fluids trapped at that condition were in the one phase field,which correspond to a paleodepths between 4.2±0.6 km and 3.6±0.8 km based on lithostatic pressure. So at least 3～3.5 km-thick rock formation above the deposit were denudated after formation of the deposit（～16 Ma） . ③Greater density contrast between moderate-salinity vapor-like fluids and melt would have led to more continuous separation of the fluid from magma chamber during exsolution,resulting in pervasive but poor K-silicate alteration,large-scale but low-grade Cu-Mo mineralization,and the less direct relationships between individual porphyry intrusions and mineralization at Qulong. ④Cu（-Mo） precipitation in the deposit are induced by decrease of pressure and reduce of S in the vapor-like fluids,and are not caused by decrease of temperature,which is the generally accepted mechanism for metal precipitation in porphyry Cu system. In summary,Qulong is a kind of porphyry Cu deposit（PCD） formed by low-density vapor-like fluids,and show very different characteristics of alteration and mineralization with the PCDs formed by high-salinity brine.