四川米易海塔地区混合岩化与铀成矿作用
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摘要
米易海塔地区晋宁期发生大规模的区域性混合岩化作用,形成一套中-深变质岩相的岩石组合,并且在混合岩中发育了较好的铀矿化。但是,混合岩化与铀成矿的关系,以及混合岩形成以后是否有后期热液叠加成矿,前人一直没有进行过研究。笔者通过对该区混合岩开展脉体的锆石UPb测年、矿化岩石的晶质铀矿测年,以及与铀矿化共生的辉钼矿Re-Os同位素测年,探讨了混合岩化与铀成矿作用的关系。研究发现,混合岩脉体的锆石U-Pb加权平均年龄为801±38 Ma,晶质铀矿表观年龄为701.8 Ma,辉钼矿的Re-Os同位素加权平均年龄为754±10.7 Ma,三者的形成时间大体一致,均属晋宁期,说明混合岩化的同时铀得到了富集,局部形成高品位的铀矿化。同时,区内发育后期热液叠加成矿作用,铀矿化年龄为228.6、 225.9、 210.5 Ma,属印支晚期矿化。这与矿化体附近细粒花岗岩脉测得的锆石U-Pb年龄(219±14Ma)基本一致,暗示铀矿化可能与印支晚期的花岗岩浆活动有关,花岗岩脉侵位及其带来的热液活动,导致混合岩脉体中铀的叠加富集成矿。
There was a large regional migmatization of Jinning period in Haita area of Miyi, which produced a set of intermediate-deep metamorphic lithofacies, and favorable uranium mineralization was found in the migmatized rocks. However, the relationship between the uranium mineralization and migmatization and the post-hydrothermal metallogenesis was not studied. In this paper, migmatization lithology and uranium metallogenesis were discussed with U-Pb dating of zircon in dyke rocks. The dating of uraninite in the mineralized rocks and the Re-Os isotopic dating of molybdenite associated with uranium mineralization. The chronology study found that the weighted average zircon U-Pb age for the migmatized rock was 801 ±38 Ma, the apparent age of the uraninite was 701.8 Ma, and Re-Os isotope dating of molybdenite obtained a weighted mean age of 754 ±10.7 Ma. The three age is generally in the same period which fall in Jinning period and indicating that uranium was enriched at the same time as migmatization and formed local highgrade uranium Mineralization. At the same time, the hydrothermal action was developed and brought superimposed mineralization in the area with the ages of 228.6 Ma, 225.9 Ma, and 210.5 Ma, which belongs to the late Indosinian period and the zircon U-Pb dating of fine-grained granite near uranium mineralization was measured at 219 ±14 Ma. The two ages were basically the same suggesting that the uranium mineralization in the late Indosinian may be related to the granite activity during this period. The intrusion of granite veins resulted in the superimposition and enrichment of uranium mineralization in the migmatized dyke.
There was a large regional migmatization of Jinning period in Haita area of Miyi, which produced a set of intermediate-deep metamorphic lithofacies, and favorable uranium mineralization was found in the migmatized rocks. However, the relationship between the uranium mineralization and migmatization and the post-hydrothermal metallogenesis was not studied. In this paper, migmatization lithology and uranium metallogenesis were discussed with U-Pb dating of zircon in dyke rocks. The dating of uraninite in the mineralized rocks and the Re-Os isotopic dating of molybdenite associated with uranium mineralization. The chronology study found that the weighted average zircon U-Pb age for the migmatized rock was 801 ±38 Ma, the apparent age of the uraninite was 701.8 Ma, and Re-Os isotope dating of molybdenite obtained a weighted mean age of 754 ±10.7 Ma. The three age is generally in the same period which fall in Jinning period and indicating that uranium was enriched at the same time as migmatization and formed local highgrade uranium Mineralization. At the same time, the hydrothermal action was developed and brought superimposed mineralization in the area with the ages of 228.6 Ma, 225.9 Ma, and 210.5 Ma, which belongs to the late Indosinian period and the zircon U-Pb dating of fine-grained granite near uranium mineralization was measured at 219 ±14 Ma. The two ages were basically the same suggesting that the uranium mineralization in the late Indosinian may be related to the granite activity during this period. The intrusion of granite veins resulted in the superimposition and enrichment of uranium mineralization in the migmatized dyke.
引文
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[3]李文贤,李巨初,姚建,等.米易-攀枝花地区铀多金属成矿条件研究[R].核工业二八〇研究所,2014.
[4]胥德恩.康滇地轴前寒武纪地壳演化特征及铀成矿远景研究[R].核工业二八〇研究所,1990.
[5]赵建波,姚建,黎丕林.四川省攀枝花市大田505铀矿点混合岩型铀矿化成因初探[C].中国核学会论文集,2011.
[6]邓尚贤,王江海,常向阳,等.鄂东北大别杂岩中混合岩的形成时代研究[J].地质学报,1997,18:68-70.
[7]张秋生.混合岩化成矿作用的几个问题[J].地质学报,1962,1:73-78.