| 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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| 关键词:metallogenic system evolution of fluid boiling and mixing Zijinshan Fujian Province |
| 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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| The Evolution of Ore-forming Fluids in the Porphyry-Epithermal Metallogenic System of Zijinshan Area |
| 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. |
| ZHANG De-quan,FENG Cheng-you,LI Da-xin,SHE Hong-quan,DONG Ying-jun.2005.The Evolution of Ore-forming Fluids in the Porphyry-Epithermal Metallogenic System of Zijinshan Area[J].Acta Geoscientica Sinica,26(2):127-136. |
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