STUDY ON THE FLUID INCLUSION PHYSICOCHEMICAL CONDITIONS OF BOLONG PORPHYRY COPPER-GOLD DEPOSIT IN TIBET
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摘要: 应用英国Linkam THNSG600型冷热台测试和前人的经验公式，对西藏波龙斑岩铜金矿床在岩浆晚期、磁铁矿-辉钼矿阶段、黄铜矿-黄铁矿阶段和硬石膏-黄铁矿阶段等4个成矿阶段利于主成矿元素Cu迁移的流体包裹体的一般特征及物理化学条件进行研究。研究结果表明，该矿床流体包裹体类型以含石盐和硫化物子矿物的三相包裹体为主，为高温（232~549 ℃）、低压（1.40×105~234.41×105 Pa）、高盐度（NaCl质量分数28.65%~52.16%）、中—高密度（1.0683~1.1598 g/cm3）的流体；随着成矿进程的发展，各阶段流体逸度和活度均逐渐降低，pH值和Eh值逐渐升高，铜主要以Cu（H2S）（HS）2-形式存在，说明Cu在高温酸性流体中易成矿。Abstract: Using Linkam THNSG600 dating and calculating by experience formulas, this paper discusses the fluid inclusion characteristics of Bolong porthyry copper-gold deposit in Tibet, which is beneficial to the migration of the main ore-forming element Cu, and the metallogenic process includes four periods: magma-advanced stage, magnetite-molybdenite period, chalcopyrite-pyrite period and anhydrite-pyrite period. It shows that the type of fluid inclusion is mainly the three-phases inclusion including NaCl and metal sulfide daughter minerals. The ore-forming fluid forms in high temperature (232~549 ℃) and low pressure (1.40×105~234.41×105 Pa), with high salinity (28.65~52.16wt% NaCl) and middle-high density (1.0683~1.1598 g/cm3). Along with the metallogenic process, the fluid fugacity and activity gradually reduce in each stages, while the values of pH and Eh increase. The element Cu mainly exits in the form of Cu(H2S)(HS)2-, which shows that Cu is easier to mineralization in high tempreture and acidic fluids.
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Key words:
- fluid inclusion /
- physicochemistry conditions /
- porphyry copper-gold deposit /
- Bolong
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图 1 多龙矿集区构造背景简图(a)、地质简图(b)和波龙矿床地质简图(c)[4]
Figure 1. Tectonic and geological maps of Duolong metallogenic district and geological map of Bolong porphyry Cu-Au deposit
表 1 波龙铜金矿床流体包裹体均一温度、盐度、密度及压力测定结果
Table 1. Homogenization temperature, salinity, density and pressure of fluid inclusions in Bolong Cu-Au deposit
成矿阶段 主矿物 均一温度/℃ 盐度/% 密度/(g·cm-3) 压力/105Pa 变化范围 平均 变化范围 平均 变化范围 平均 变化范围 平均 岩浆晚期 斑晶石英 334~549 467 38.24~52.16 41.86 1.0683~1.1067 1.0761 58.76~234.41 102.47 磁铁矿-辉钼矿 石英 312~533 429 34.56~50.49 42.34 1.0683~1.0975 1.0771 26.72~212.69 109.59 黄铜矿-黄铁矿 石英 262~502 388 29.47~40.79 35.01 1.0683~1.1494 1.0930 3.14~86.81 33.54 硬石膏-黄铁矿 硬石膏石英 232~471 332 28.65~36.90 32.48 1.0765~1.1598 1.1153 1.40~45.74 17.68 
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表 2 波龙铜金矿床流体逸度
Table 2. Fugacity of fluid inclusion in Bolong Cu-Au deposit, Tibet
样号 lgfO2 lgfCO2 lgfS2 阶段 BL002 -27.280 1.851 -3.284 磁铁矿-辉钼矿 BL019 -28.778 1.295 -3.865 黄铜矿-黄铁矿 BL045 -30.167 1.177 -4.323 BL058 -29.946 1.254 -4.227
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表 3 波龙铜金矿床流体pH和Eh值
Table 3. The values of pH and Eh of the fluid inclusions in Bolong Cu-Au deposit, Tibet
样号 pH Eh 阶段 BL002 5.149 0.009 磁铁矿-辉钼矿 BL019 5.427 0.013 黄铜矿-黄铁矿 BL045 5.486 0.018 BL058 5.448 0.016
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表 4 波龙铜金矿床总硫、总碳活度计算结果
Table 4. Activity of total sulphur and total carbon in Bolong Cu-Au deposit, Tibet
mol/L 样品编号 lgfS2 lgfO2 lgaH2S lgaHS- lgaS2- lgaHSO4- lgaSO42- lgaΣS aΣS lgfCO2 lgaCO2 lgaH2CO3 lgaHCO3- lgaCO32- lga∑C aΣC 阶段 BL002 -3.284 -26.714 -0.785 -4.636 -11.587 1.135 -0.596 1.148 14.067 1.851 0.151 0.231 -3.530 -10.811 0.494 3.121 磁铁矿-辉钼矿 BL019 -3.865 -28.152 -0.357 -3.930 -10.603 -1.033 -2.486 -0.271 0.536 1.295 -0.405 -0.325 -3.808 -10.811 -0.062 0.867 黄铜矿-黄铁矿 BL045 -4.323 -29.691 0.184 -3.330 -9.944 -3.512 -4.906 0.184 1.529 1.177 -0.523 -0.443 -3.867 -10.811 -0.180 0.660 BL058 -4.227 -29.513 0.143 -3.409 -10.062 -3.235 -4.667 0.143 1.391 1.254 -0.446 -0.366 -3.829 -10.811 -0.103 0.788
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表 5 铜络离子活度及铜的总溶解度
Table 5. Activity of Cu complex ion and total solubility
样品编号 lgaCu(HS)2- lgaCu(H2S)(HS)2- lgaCu+ lgaCuCl0 lgaCuCl2- lgaCuCl32- lgaCu2+ lgaCuCl+ lgaCuCl20 lgaCuCl3- lgaCuCl42- lgaΣCu 阶段 BL002 -6.674 -7.148 -6.428 -14.607 -20.786 -30.765 -13.955 -18.834 -29.214 -40.093 -51.372 -6.183 磁铁矿-辉钼矿 BL019 -5.753 -5.800 -7.065 -21.923 -34.780 -51.438 -15.230 -26.788 -43.845 -61.403 -79.361 -5.464 黄铜矿-黄铁矿 BL045 -4.883 -4.389 -7.509 -12.438 -15.366 -22.095 -16.117 -17.746 -24.875 -32.504 -40.533 -4.268 BL058 -4.983 -4.530 -7.426 -13.964 -18.502 -26.841 -15.951 -19.190 -27.928 -37.167 -46.805 -4.398
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