| 四川冕宁牦牛坪碱性花岗岩锆石铀-铅同位素年龄及其地质意义 |
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| 引用本文：.1993.U-Pb isotopic age of zircon from the Maoniuplng alkali granite, Sichuan province and its geological significance[J].Mineral Deposits,12(2):189~192,147 |
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| 基金项目:地矿部定向科研项目（直科定92-25） |
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| 中文摘要:对四川冕宁牦牛坪富稀土碱性花岗岩锆石的铀-铅同位素年龄研究，得出一致线上交点年龄为(249±43)×106a，下交点年龄为(12±2)×106a。前者相当于岩体中残余锆石的形成年龄，可能代表碱性花岗岩母体岩石的年龄，后者应是碱性花岗岩及新生锆石的形成年龄。(12±2)×106a 的年龄值是攀西裂斧带内，甚至整个扬子准地台内最年轻的花岗岩年龄值。新的喜马拉雅期成岩成矿年龄数据的得出，对于认识区域构造-岩浆活动历史，了解稀土元素矿床的时间-空间分布，有重要意义。 |
| 中文关键词:牦牛坪碱性花岗岩 碱性花岗岩型稀土矿床 锆石铀一铅同位素年龄 喜马拉雅期成岩成矿 |
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| U-Pb isotopic age of zircon from the Maoniuplng alkali granite, Sichuan province and its geological significance |
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| Abstract:A study of the U-Pb isotopic age of zircon from the Maoniuning alkalidies are controlled by NE-trending faulted structures, and its host rocks are volcano-sedimentary rocks of the Middle Proterozoic Shuangqiaoshan Group. Intrusive activity is weak, with merely small intermediate-basic pre-ore dikes observed in the ore district. The orebodies take the veinlike form, and the ore composition is complex. There are ma ny(more than 30 kinds)of silver minerals, belonging to S-Sb-Cu-Ag and S-Sb-Pb-Ag series. The ore-forming process could be divided into two phases: hydrothermal filling phase and supergene oxidation phase. The former phase includes four mineralization stages, namely quartz-carbonate stage, quartz-sulfide stage with silver minerals deposited at the end, carbonate stage and silver sulfosalt stage. Wall rock alterations are silicification and carbonatization. The upper limit of the mineralization age (the single stage Pb model age) of the deposit is 497.9940 Ma (pyrite) and 499.7953 Ma(galena). Isotope compositions are as follows: 37Sr/86Sr=0.71483±0.00013 and 0.71403±0.00009 (rhodochrosite); 206Pb/204Pb=17.937 and 17.920, 207Pb/204Pb=15.594 and 15.582, 208Pb/204Pb=38.314 and 38.271(galena and pyrite respectively); δ34S‰(CTD)=-0.6～+3.3(sulfides); δ13C‰(PDB)=-6.1～8.0(carbonate); δ18O‰(SMOW)=+15.8～+18.7(carbonate); δD‰(SMOW)=-74.4(dolomite)and -58.7 (quartz)．The REE content of the ore varies from 9.61 to 20.56×10-6, and the REE content of the host rock is between 154.27 and 194.75×10-6. The strontium, lead, sulfur, carbon, oxygen, hydrogen isotope compositions and the chondrite-normalized REE patterns of the ore and host rocks suggest that both the ore-forming substance and the mineralizing solution came from the basal Middle Proterozoic Shuangqiaoshan Group. The Hujiajian silver-gold deposit seems to be a metamorphogenic mesothermal-epithermal filling-metasomatic type ore deposit． |
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