| 紫金山地区斑岩-浅成热液成矿系统的成矿流体演化 |
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| 引用本文：张德全,丰成友,李大新,佘宏全,董英君.2005.紫金山地区斑岩-浅成热液成矿系统的成矿流体演化[J].地球学报,26(2):127-136. |
| DOI：10.3975/cagsb.2005.02.05 |
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| 基金项目:国家重点基础研究项目“大规模成矿作用与大型矿集区预测”(编号 :G1999043209) |
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| 中文摘要:本文从流体包裹体和热液矿物的年代学方面追踪了紫金山地区的斑岩-浅成热液成矿系统中成矿流体的演化过程和演化轨迹。研究表明，汇聚到岩体顶部的岩浆流体在104．5Ma左右、650～550℃温度区间减压沸腾，形成的不混溶流体导致了钾硅酸盐化蚀变及初始Cu(Mo)矿化。其后流体继续向花岗闪长斑岩的外接触带上升运移和降温，在102．5Ma左右、420～380℃区间，再次减压沸腾，分离出的富液相H2O-NaCl流体进一步与对流循环中的大气降水混合，导致体系的温度和盐度逐步降低，演化出绢英岩化蚀变及含铜-硫化物矿化的流体。流体进一步向花岗闪长斑岩外接触带汇聚，在不同构造部位、不同时期分别氧化形成两种不同的流体：其一是在100Ma左右，流体到达花岗闪长斑岩顶面之上800～2000m的火山岩穹部位，温度降至280～250℃时又一次减压沸腾和不混溶，不混溶流体进一步与对流循环中的大气降水混合，使之冷却、稀释和酸化．演化成酸性硫酸盐型浅成热液蚀变和Cu—Au矿化的流体；其二是在94．7Ma左右，形成绢英岩化后的流体侧向扩散到远离花岗闪长斑岩的大型低平火山洼地中，由于大气降水的大量注入，使其演化成为低盐度、较低的温度的H2o-NaCl体系，其沿不整合面附件的断裂-裂隙系统充填，形成冰长石-石英细-网脉及Ag-Au矿化。 |
| 中文关键词:成矿系统 流体演化 沸腾和混合 福建紫金山 |
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| The Evolution of Ore-forming Fluids in the Porphyry-Epithermal Metallogenic System of Zijinshan Area |
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| Abstract:The sericite-adularia type epithermal Ag-Au deposit, acid-sulfate type Cu-Au epithermal deposit and porphyry type Cu (Mo) deposit constitute an intrusion-centered metallogenic system in Zijinshan area. This paper traced the evolutionary process and pathway of the ore-forming fluids in the system on the basis of fluid inclusion data and 40 Ar- 39 Ar dating of hydrothermal minerals. At 105 Ma of Early Cretaceous, calc-alkalicand intermediate-felsic magma intruded into the intersections of regional NE-trending faults with regional NW-trending faults and formed granodiorite porphyry. Having ascended and converged to the top of the granodiorite porphyry body, magmatic fluids of the H 2O-NaCl system boiled due to decompression of dense fissures and formed immiscible fluids at the temperature range of 650～550 ℃ and 104.5 Ma, resulting in potassic alteration and copper (molybeenum) mineralization. With the further ascent of fluids to the exocontact zone of granodiorite porphyry and the decrease of temperature, fluids boiled once again and formed immiscible fluids at 420～380 ℃ and 102.5 Ma. The liquid-rich phase of the immiscible H 2O-NaCl fluid system was mixed with meteoric water in the convection celland hence resulted in gradual decrease of temperature and salinity of the system, which was responsible for phyllic alteration and copper-bearing sulfide mineralization. Later, further migration and convergence of fluids to the exocontact zone led to the formation of two styles of fluids at different structural positions. When the fluids converged at the volcanic dome 800～2 000 m above the top ofgranodiorite porphyry at 100 Ma, they boiled and were unmixed with liquid-rich,gas-rich and CO 2-bearing phases at the temperature of 280～250 ℃. The unmixed fluids were further mixed with meteoric water in the convection cell, which resulted in cooling (up to 120 ℃) and dilution (up to 0.9wt%NaCl) of fluids and the formation of ore-forming fluids that were responsible for acid-sulfate type epithermal Cu-Au mineralization and alteration. When the fluids migrated laterally into the large volcanic rent far away from granodiorite porphyry at 94.7 Ma, they evolved into ore-forming fluids of low salinity ( 0.9%～ 5.0% NaCl) and lower temperature (260～120 ℃) due to the participation of large quantities of meteoric water. The evolved fluids were filled along the fault-fissure system around the plane of unconformity,producing adularia-quartz-stockworks and Ag-Au mineralization. |
| keywords:metallogenic system evolution of fluid boiling and mixing Zijinshan Fujian Province |
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