西藏驱龙超大型斑岩铜矿床成矿流体对成矿的控制

驱龙斑岩铜矿是冈底斯成矿带新发现的规模最大的超大型矿床, 形成于中新世.原生流体包裹体有5种类型, 主成矿阶段均一温度集中于240~650℃之间, 盐度变化于0.18%~52.04%之间, 明显分为高盐度高密度、低盐度低密度2类.可见含子矿物、液相、气相等包裹体共存现象, 且均一温度相近, 盐度相差很大, 表明成矿流体经历了沸腾过程; 氢氧同位素及单矿物微量稀土元素研究表明, 成矿物质主要来源于斑岩岩浆体系, 而成矿流体主要来源于岩浆水、天然热卤水有关的混合水, 且天然热卤水占优势, 属NaCl (F) -KCl (F) -C₂H₆-HCO₃-CaSO₄型流体.成矿流体总体显示出高温、高盐度、高矿化度、高氧逸度的还原性酸性流体特征, 并且富集Na+、K+、F-、Cl-、SO₄2-、CO₂等成分, 以富F-为特征(F-/Cl- > 1, 平均为5.66), 这种特殊性质的流体特别有利于Fe2+、Cu2+等元素的迁移, 并最终在岩浆期后热液期富集成矿, 它是形成驱龙超大型斑岩铜矿床的必要条件; 流体减压沸腾及不同性质流体混合作用是促使金属离子沉淀富集的主要机制.对该矿床成矿深度(0.5~2km) 进行了探讨, 可作为该矿床勘查评价的依据. 

Ore-Forming Fluid Controlling Mineralization in Qulong Super-Large Porphyry Copper Deposit, Tibet

The Qulong porphyry copper deposit is the largest recently found in the Gangdise metallogenic belt. It was formed in the Miocene. The original fluid inclusions can be divided into five types according to the compositions of liquid, gas and single minerals The temperature of the main ore-forming phase ranges from 240 to 650 ℃ and the salinity is about 0.18wt.%-52.04wt.%. The fluids can be classified into two types including high salinity and high density, low salinity and low density. Daughter mineral inclusions, liquid and gas inclusions are coexistent and their homogeneous temperature is approximate, however salinity is quite different, showing that the fluid underwent the process of boiling. A study of the H and O isotopes and trace and rare elements of a single mineral indicates that the mineralization substance comes from the system of porphyry magma and fluid belonging to the NaCl (F) -KCl (F) -C₂H₆-HCO₃-CaSO₄ type fluid, which comes from magma and natural hot-brine. The fluid is characteristically reducing and acid, with high temperature, high salinity, high mineralization degree, and high oxygen fugacity.The fluid has high concentrations of Na+, K+, Cl-, SO₄2-, CO₂ etc., with high F-(F-/Cl- > 1, average 5.66), which was good for the transfer of Fe2+ and Cu2+, finally concentrated and formed the deposit, and is the necessary condition for the Qulong super-large porphyry copper deposit to form. Decompression and the mixing of different quality fluids is the main mechanism for the depositing of metalions. The mineralizated depth is also discussed and could be regarded as the prospecting base of mineral deposit.