Ore-Forming Fluid Controlling Mineralization in Qulong Super-Large Porphyry Copper Deposit, Tibet
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摘要: 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.Abstract: 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.
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Key words:
- Qulong /
- super-large porphyry copper deposit /
- ore-forming fluid /
- ore-controlling /
- necessary condition
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图 1 西藏驱龙铜(钼) 矿床主要流体包裹体显微照片
a.含矿石英脉中的富液包裹体(Ⅱ类); b.含矿石英脉中的含子矿物多相包裹体(Ⅴ类); c.含矿硬石膏中的纯液包裹体(Ⅰ类)、富气包裹体(Ⅲ类) 和纯气包裹体(Ⅳ类) 共存; d.含矿石英脉中富液包裹体(Ⅱ类)、富气包裹体(Ⅲ类) 和含子矿物多相包裹体(Ⅴ类) 共存
Fig. 1. Micro-photos of fluid inclusions in Qulong porphyry Cu (Mo) deposit
图 2 驱龙矿床流体包裹体均一温度直方图(据28件样品691个数据成图)
a.按包裹体类型; b.按主矿物; 1.富液包裹体; 2.富气包裹体; 3.含子矿物多相包裹体; 4.含矿石英脉; 5.含矿硬石膏; 6.石英斑晶
Fig. 2. Homogenization temperature histogram of the fluid inclusion in Qulong deposit
图 3 驱龙矿床流体包裹体温度、盐度及密度关系图(据68个数据成图)
Fig. 3. Homogenization temperature, salinity and density of the fluid inclusions in Qulong deposit
表 1 驱龙斑岩铜(钼) 矿床流体包裹体群体成分分析结果
Table 1. Analytical results of colony composition for fluid inclusion in Qulong porphyry Cu (Mo) deposit
表 2 驱龙斑岩铜(钼) 矿床单矿物微量元素含量
Table 2. Analytical results of trace elements of single mineral in Qulong porphyry Cu (Mo) deposit
表 3 驱龙矿床成矿流体物理化学参数
Table 3. Physical-chemical parameter of ore-forming in Qulong deposit
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[1] Wang, Z. G., Zhang, Z. X., 1991. Calculation code of physical and chemical parameters of composition in fluid inclusion in minerals. Geology and Prospecting, 27 (7): 22-27 (in Chinese with English abstract). [2] Zheng, Y. Y., Xue, Y. X., Cheng, L. J., etal., 2004. Finding, characteristics and significances of Qulong superlarge porphyry copper (molybdenum) deposit, Tibet. Earth Science—Journal of China University of Geosciences, 29 (1): 103-108 (in Chinese with English abstract). [3] Zhu, H. P., Wang, L. J., 2001. Quadrupole mass spectrometer analy sis of gases fluid inclusion. Science in China (Series D), 31 (7): 586-590 (inChinese). [4] 王真光, 张姿旭, 1991. 矿物包裹体成分物理化学参数的计算程序. 地质与勘探, 27 (7): 22-27. https://www.cnki.com.cn/Article/CJFDTOTAL-DZKT199107004.htm [5] 郑有业, 薛迎喜, 程力军, 等, 2004. 西藏驱龙超大型斑岩铜(钼) 矿床: 发现、特征及意义. 地球科学———中国地质大学学报, 29 (1): 103-108. https://www.cnki.com.cn/Article/CJFDTOTAL-DQKX200401018.htm [6] 朱和平, 王莉娟, 2001. 四极质谱测定流体包裹体中的气相. 中国科学(D辑), 31 (7): 586-590. https://www.cnki.com.cn/Article/CJFDTOTAL-JDXK200107007.htm -
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