与铜、金矿化有关的富碱侵入岩矿物化学研究

MINERAL CHEMISTRY STUDIES OF Cu-AND Au-MINERALIZED ALKALINE INTRUSIONS

以哀牢山-金沙江富碱侵入岩带内与金矿化有关的姚安正长斑岩和与铜矿化有关的马厂箐花岗斑岩为研究对象，开展了系统的矿物化学研究。结果表明，姚安岩体形成的温压条件为（818±50）℃和0.9×10^8，1．3×10^8Pa。马厂箐岩体形成的温压条件为（729±50）℃和2．2×10^8～2．8×10^8Pa，两岩体的氧逸度均高于地幔石英．橄榄岩．磁铁矿出溶线，相对于马厂箐岩体而言，姚安岩体结晶时的氧逸度更高。两岩体矿化作用的差异与岩浆的分异程度有密切的关系。相对于铜矿化而言，氧逸度较高的岩浆有利于金矿化。

The Yao＇ an and Maehangqing alkaline intrusions belong to the Jinshajiang-Red River alkaline intrusive suite, located in southwestern China. The Yao＇ an syenite porphyry is associated with Au mineralization and the Maehangqing granite porphyry with Cu mineralization. Study of the mineral chemistry of dominant silicate minerals from evolved granitic rocks from these two intrusions provides insight into the overall petrogenesis of the Ailaoshan-Jinshajiang alkaline intrusive uite. The temporature and pressure derived from amphibole-plagioclase and perthite-plagioclase geothermometry, and Al in mphibele baroraetry suggest that the syenite porphyry in the Yao＇ an intrusion crystallized around 818±50℃ and 0.9-1.3 kbar, whereas the granite porphyry in the Machangqing intrusion crystallized around 729±50℃, 2.2-2.8 kbar.The two intrusions formed under imposed oxygen fugacities far above the quartz fayalite-magnetite buffer. Oxygen fugacity stimates suggest that the syenite porphyry in the Yao＇ an intrusion crystallized under more oxidizing conditions than the qachangging. The similar tectonic setting, emplacement age, magma source region and the only slightly different bulk heroical compositions of the intrusions suggest that the difference in mineralization （ Cu vs. Au） of these two intrusions may ave been related to the differences in t, p, or f（O2） during crystallization. The results show that a high f（O2） and realdy fractionated magma favored Au enrichment relative to Cu in the Jinshajiang-Red River alkaline zone.