| 安徽铜陵老鸦岭层状铜矿床的成矿地球化学研究 |
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| 引用本文： | 杨学明,顾炳忠.安徽铜陵老鸦岭层状铜矿床的成矿地球化学研究[J].大地构造与成矿学,1997,21(4):347-361. |
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| 作者姓名： | 杨学明 顾炳忠 |
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| 作者单位： | [1]中国科学院技术大学地球与空间科学系 [2]合肥工业大学资源与环境科学系 |
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| 摘 要： | 安徽铜陵老鸦岭铜矿床是长江中下游地区的一个典型的层状矿床，以远离侵入岩体和赋存于二叠系钙质－硅质岩中为特征，其矿石矿物组合简单，近矿围岩蚀变较弱，为绢云母化、高岭石化、碳酸盐化和绿泥石化等，且分带性不明显。按照矿物形成的时间序列，矿床矿物可分为四个共生组合：（1）磁黄铁矿＋黄铁矿组合；（2）黄铜矿＋黄铁矿＋闪锌矿＋磁黄铁矿组合；（3）石英＋黄铜矿组合；（4）方解石＋黄铜矿组合。矿物包裹体以气液两相为主，气液比从早到晚逐渐减小直至成为单一的液相。均一法测温表明，组合1的均一温度为290～320℃，组合2为240～265℃，组合3为180～220℃，和组合4为110～116℃。矿物包裹体液相成分属于NaCl－H_2O体系，并含有F~－和，盐度小于10wt％。根据热力学计算，圈定了矿物共生组合的物理化学场，从组合1到4，成矿热液的fo_2、fs_2及∑S浓度依次降低，pH值变化不大，但还原性降低，氧化性增强。矿床硫同位素组成δ~34S_∑S为：组合1是＋0．5％。，组合2为1‰～3‰，组合3大于＋5‰和组合4大于＋6‰。这证实成矿热液中硫来源于岩浆，并随着时间的演化有地层硫的加入。氧和氢同位素研究说明参与成矿作用的热液除岩浆源之外，还有相当多的大气水或地下水的加入。矿石普通铅同位素为异常
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| 关 键 词： | 液成矿作用 矿物共生组合 矿物气液包裹体 热力学计算 同位素组成 矿床成因 老鸦岭 |
METALLOGENIC GEOCHEMISTRY OF THE LAOYALING STRATIFORM COPPER DEPOSIT, TONGLING, ANHUI PROVINCE, P. R. C. |
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| Abstract: | The Laoyaling copper ore deposit is a typical stratiform ore deposit in the mid-lowerarea of Changjiang (Yangtze) River, Tongling, Anhui Province, which is characterized bythat it is far away from plutonic rocks and hosted in Permian calcareous-silicalites. The oredeposit has relatively simple mineral assemblages and weak wall-rock alteration such ascarbonation, chloritization, kaolinization and sericitization, and those alterations show nozonation. In light of time sequence the minerals within the deposit could be grouped into fourparagenetic assemblages: (1) pyrrhotite + pyrite assemblage; (2) chalcopyrite + pyrite +sphalerite+pyrrhotite assemblage; (3) quartz+chalcopyrite assemblage; and (4) calcite+pyriteassemblage. Fluid inclusions in minerals from the deposit are mainly composed of gas andliquid phases, the size of which are 4 to 15 μm and ratio of gas to liquid phase decreasegradually from the early to late stage till become single liquid one. Homogenizationtemperature measurement on the inclusions show that from assemblage one to four their temperatureare 290- 320 ℃, 240- 265℃, 180- 220℃ and 110- 160 ℃, respectively, Liquidcompositions of inclusions belong to NaCl-H_2O system which contains F~- and . The salinity isless than 10%. According to thermodynamic calculation, the physic-chemical fields of eachassemblage are assigned. From assemblage one to four, four ,fo_2 , fs_2, and ∑S contents ofmineralizing hydrothermal solution decrease successively and its pH value changes little. However,the redox potentials of the solution increase from assemblage one to four. Sulphur isotopesδ~34S values of sulphides in the ores range from - 0. 54 to + 3. 73‰, whose distribution showsa tower effect. The total sulpur isotopic composition δ~34S of hydrothermal solutionequilibrating with each assemblage are calculated. From assemblage one to four δ~34 values are +0. 5, 1-3, ≥+5 and ≥+6‰, respectively. This fact verifies that sulphur in themineralizing solution derived from magma and heavy sulphur hosted in strata was increasingly addedto the hydrothermal fluid during mineralization. Oxygen and hydrogen isotopic compositionsof the solution are 3. 21 and - 58. 65‰, (SMOW), respectively. This implies that besidesmagmatic hydrothermal solution there was contribution of meteoric or underground water inmineralization. Lead isotopic composition of ores are ~206Pb/~204Pb= 17. 70- 18. 23,~207Pb/~204Ph = 15. 15- 15. 54,~208Pb/~204Pb = 36. 42 - 38. 31, which are abnormal lead and reflect thatlead in ores had complicated evolution. According to multi-component mixture model lead inores could be the result of mixture of deep source lead from the lower crust or the uppermantle with that from younger and older strata. The features of trace elements in pyrite etc.are also discussed in this paper. The formation mechanisms of the Laoyaling stratiformcopper deposit could be summarized as follows: (1) In Permian period source-bed ofcalcareous silicalite type, which contained Cu-bearing pyrite, was formed. (2) Yanshanian dioritemagma was emplaced, around and in the vicinity of which a circulating system of meteoricwaterhydrothermal solution was formed. Mineralizing hydrothermal solution was produced by thecirculating solution reacted with diorite and the source-bed. With cooling of the pluton themineralizing solution gradually escaped from the circulating system and transfered along afracture zone in the calcareous-silicalite of Dalong group (P_2d) and the lower part of Yinkenggroup (T_1y). The fracture zone was closed by argillite, pelitic siltstone and shale. Duringtransfering it continued to react with wall-rock. On one hand the physic-chemical conditionsof the mineralizing solution changed. One the other hand it leached mineralizing materialsfrom wall-rock. At last the deposit was formed in a favourable position at the nucleus ofQingshan anticline that is far from igneous pluton. |
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| Keywords: | hydrothermal mineralization mineral paragenetic assemblage fluid inclusion in minerals thermodynamic calculation isotope composition genesis of ore deposit Laoyaling |
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