Genesis of Chambishi Copper Deposit in Copperbelt Province of Zambia: Evidence from Fluid Inclusions and H-O-S Isotope Geochemisty
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摘要: 为揭示谦比希铜矿床的成矿流体性质、成矿物质来源及其演化特征，对其矿石和脉石矿物展开了流体包裹体和H-O-S同位素地球化学研究.结果显示，热液型脉状矿化石英流体包裹体均一温度变化于100~350 ℃，盐度变化于11%~19%NaCleqv；δDV-SMOW值为-64.0‰~-52.6‰，δ18OH2O值为1.57‰~2.97‰.热液型脉状和沉积型层状铜矿体δ34SCDT值分别变化于5.5‰~12.1‰和6.0‰~21.0‰.分析表明，热液型成矿流体属Cl-Na-Ca型水溶液，属中低密度流体；成矿流体受幔源和壳源岩浆混合，导致铜发生沉淀.沉积型层状矿化硫主要来自成岩硫化物和海水硫酸盐，硫酸盐以热化学还原为主，导致SO42-较彻底的变为H2S.整体看来，谦比希铜矿床热液型脉状矿化与新元古代中期岩浆活动密切相关，沉积型层状矿化主要与新元古代晚期大规模造山运动和区域变质作用有关.Abstract: Fluid inclusions study and H-O-S isotopic geochemical analysis of ore and vein minerals were carried out in this study in order to reveal the characteristics of ore-forming fluid and material of the Chambishi copper deposit. The results of microscopic measurement of temperature show that the homogenization temperature and salinity of the fluid inclusions from hydrothermal fluid filling deposit mainly range from 100 to 350 ℃ and 11% to 19% NaCleqv, respectively. Analyses of H-O isotopic composition of the hydrothermal fluid filling deposit show that the values of δDV-SMOW and δ18OH2O are -64.0‰ to -52.6‰ and 1.57‰ to 2.97‰, respectively. Analyses of S isotopic composition show that the values of δ34SCDT from hydrothermal fluid filling orebodies and depositional orebodies are 5.5‰ to 12.1‰ and 6.0‰ to 21.0‰, respectively. The above data indicate that the ore-forming fluid of the hydrothermal fluid filling deposit is of medium-low temperature, low-middle salinity and density, and belongs to Cl-Na-Ca-type aqueous solution. The fluid is a mix of mantle and crust-derived magmas. Fluid mixing is the main reason for copper precipitation. Sulfur of the hydrothermal fluid filling deposit is similar to those of mantle-derived sulfur, whereas the sulfur of the depositional ore deposit is mainly sourced from diagenetic sulphide and seawater sulfate. The mechanism of sulfate reduction for both deposits is thermochemical reduction which resulted in the change of sulfur from SO42- to H2S. The mixed sources of ore-forming fluid and material indicate that mineralization of the hydrothermal fluid filling deposit is closely related to the middle Neoproterozoic magmatism, whereas mineralization of the depositional ore deposit is mainly related to the strong Late Neoproterozoic orogenesis and regional metamorphism.
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Key words:
- fluid inclusion /
- H-O-S isotope /
- ore-forming fluid /
- Chambishi copper deposit /
- Zambia /
- ore deposit
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图 1 赞比亚铜带省构造纲要图
Fig. 1. Simplified tectonic map of the copperbelt province, Zambia
图 4 谦比希铜矿床矿石、矿化石英脉照片
a.含黄铜矿化的石英脉；b.含辉钼矿化、斑铜矿化的石英脉；c.顺层产出的层状黄铜矿；d.浸染状黄铜矿；e.网脉状斑铜矿；f.层纹状黄铜矿.Qtz.石英；Ccp.黄铜矿；Mo.辉钼矿；Bn.斑铜矿
Fig. 4. Field photos of the orebodies and veins of the Chambishi copper deposit
图 5 谦比希铜矿床岩矿石显微镜下照片
a.粗中粒斑铜矿‒黄铜矿共生；b.他形粒状黄铜矿；c.他形粒状斑铜矿；d.他形粒状斑铜矿；e.含硬石膏粒状黑云母钾长片麻岩；f.辉钼矿化粒状‒鳞片状矿石.Bn.斑铜矿；Ccp.黄铜矿；Cc.辉铜矿；Mo.辉钼矿；Sp.闪锌矿；Hem.赤铁矿；Anh.硬石膏；Qtz.石英；Cal.方解石；Bi.黑云母；Mc.微斜长石；Or.正长石；Pl.斜长石
Fig. 5. Microscopic photos of rock and ore of the Chambishi copper deposit
图 6 谦比希铜矿床热液型含矿石英脉流体包裹体显微照片
a.Ⅰ型: 富液相、气液两相原生流体包裹体；b、c、d.Ⅱ型: 含CO2三相包裹体：LH2O代表液体
Fig. 6. Microscopic photos of fluid inclusions from the Chambishi copper deposit
图 7 谦比希铜矿床热液型石英流体包裹体均一温度和盐度频数直方图
Fig. 7. Histograms of homogenization temperature and salinity of hydrothermal fluid inclusions from the Chambishi copper deposit
图 8 谦比希铜矿床热液型石英流体包裹体均一温度和盐度关系图
底图据Bodnar(1983)
Fig. 8. Plot of homogenization temperature and salinity of hydrothermal fluid inclusions from the Chambishi copper deposit
图 9 谦比希铜矿床与区带矿床硫同位素数据对比图
Fig. 9. Comparison of sulfur isotope data among the Chambishi copper deposit and other deposits in the region
图 10 谦比希铜矿床石英流体包裹体的氢氧关系图
底图据Taylor(1974)
Fig. 10. Plot of δ18OH2O versus δD of fluid inclusions from the Chambishi copper deposit
表 1 谦比希铜矿床热液型石英流体包裹体主要类型及特征
Table 1. Major types of hydrothermal fluid inclusions from the Chambishi copper deposit
类型 相态 含量 形态 大小(μm) 主要特征 Ⅰ型 富液相、气液两相原生流体包裹体（LH2O+ LCO2） > 75% 以扁圆状和椭圆状为主，少量呈似六边形负晶或不规则状 10~25 呈孤立状随机分布，或呈群状、带状分布在矿物的生长环带中 Ⅱ型 含CO2三相包裹体（LH2O+LCO2+VCO2） < 10% 以椭圆形为主 10~15 呈孤立状产出，液相CO2相体积约占包裹体总体积的15%~25%.在均一化过程中，部分CO2包裹体发生爆裂 Ⅲ型 含子矿物多相包裹体（S+LH2O+LCO2+VCO2） < 5% 以六边形负晶和椭圆形为主 15 单个包裹体中可见一个子晶，且子晶的种类有石盐、钾盐等.石盐子晶颗粒大，晶形好，呈立方体；钾盐子晶颗粒小，呈浑圆状 注：LH2O代表液体相水；LCO2代表液体相二氧化碳；VCO2代表气体相二氧化碳；S代表子晶矿物. 
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表 2 谦比希铜矿床热液型石英包裹体氢氧同位素测试结果
Table 2. Hydrogen and oxygen isotopic compositions of hydrothermal fluid inclusions from the Chambishi copper deposit
样品号 矿物 δDV-SMOW(‰) δ18OV-SMOW(‰) δ18OH2O(‰) QES560-01 石英 -52.6 12.0 2.07 QES560-02 石英 -57.7 12.3 2.37 QES680-01 石英 -58.6 12.9 2.97 QES680-02 石英 -53.0 12.4 2.47 ES680C8-1 石英 -63.5 12.6 2.67 ES680C8-2 石英 -60.5 12.5 2.57 QES560-03 石英 -60.0 12.7 2.77 QES560-04 石英 -58.5 12.8 2.87 QES680-03 石英 -58.4 12.6 2.67 QES680-04 石英 -58.6 13.4 3.47 ES680C8-3 石英 -64.0 11.5 1.57
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表 3 谦比希铜矿床硫同位素测试结果
Table 3. Sulfur isotopic compositions of chalcopyrite and bornite from the Chambishi copper deposit
样品号 样品描述 测试矿物 δ34SCDT(‰) w232m6-1 层状铜矿体 黄铜矿 10.4 w232m6-2-H 层状铜矿体 黄铜矿 8.9 w232m6-2-B 层状铜矿体 斑铜矿 8.2 w184m4-1-H 层状铜矿体 黄铜矿 7.0 w184m4-1-B 层状铜矿体 斑铜矿 6.8 w184m3-2-H 层状铜矿体 黄铜矿 7.3 w184m3-2-B 层状铜矿体 斑铜矿 7.4 w184m4-2 层状铜矿体 黄铜矿 7.2 w184m3-2-1 层状铜矿体 黄铜矿 6.6 w184m4-h7-B 层状铜矿体 斑铜矿 6.0 se980-9-H 层状铜矿体 黄铜矿 19.2 se980-9-B 层状铜矿体 斑铜矿 21.0 se980-16 层状铜矿体 黄铜矿 11.5 se980-10-H 层状铜矿体 黄铜矿 13.8 se980-10-B 层状铜矿体 斑铜矿 14.1 es98004-4 层状铜矿体 黄铜矿 12.3 es98004-5 层状铜矿体 黄铜矿 12.1 es98004-3 层状铜矿体 黄铜矿 11.9 w184m4-h7-H 脉状铜‒钼矿体 黄铜矿 6.1 mob-1-H 脉状铜‒钼矿体 黄铜矿 8.4 mob-1-B 脉状铜‒钼矿体 斑铜矿 12.1 mob-2 脉状铜‒钼矿体 黄铜矿 6.1 mob-3-H 脉状铜‒钼矿体 黄铜矿 5.6 mob-3-B 脉状铜‒钼矿体 斑铜矿 5.5 mob-4 脉状铜‒钼矿体 黄铜矿 5.7
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