云南澜沧老厂隐伏花岗斑岩岩石学、年代学及成因研究

【作者】 陈珲；

【导师】 李峰；

【作者基本信息】 昆明理工大学 ， 地质工程， 2010， 硕士

【摘要】 澜沧老厂矿区于上世纪八十年代末在钻孔中相继揭露到花岗斑岩细脉及矽卡岩带,但直至2008年,因揭露隐伏岩体的工程很少,获得的岩芯有限,对花岗斑岩岩石学、地球化学、年代学及其与矿化关系的研究进展缓慢,相关成果稀少。2007年在危机矿山接替资源找矿专项—云南省澜沧县澜沧铅矿接替资源勘查项目实施中,ZK153101钻孔再次揭露到三段花岗斑岩脉,ZK14824等钻孔中揭露到矽卡岩带及钼矿体,2009年又在ZK14827、ZK14830、ZK15501孔中揭露到多段斑岩脉,终孔处揭露到主岩体。为查明老厂矿区隐伏花岗斑岩特征,本文从花岗斑岩的岩体地质、岩石学、地球化学、年代学及锆石标型特征等方面入手,综合研究其成因类型和形成的构造环境。本区揭露到的隐伏花岗斑岩岩体及与之有关的辉钼矿化、矽卡岩化主要分布在F3断裂以东、F4断裂以西的144线—9线之间,总体沿F1断层分布,出现的标高大致在900-1530m,有西高东低的趋势。岩石学研究表明,该区花岗斑岩呈浅灰、灰白色,斑状结构,块状构造,斑晶主要由正长石、石英、斜长石和黑云母组成,基质由等轴微细粒正长石、石英组成。岩石地球化学研究表明,老厂隐伏花岗斑岩体属偏铝质高钾钙碱性花岗岩；微量元素K、La、Hf、Tb相对富集,Nb、Ta、P、Ti相对亏损,反映了造山带花岗岩及大陆地壳特征；稀土元素总量较小,平均126.56x10-6,(La/Yb)N=12.01-24.85,为轻稀土中等富集；87Sr/86Sr为0.70835-0.71544,平均0.71。锆石SHRIMP U-Pb测年证实,澜沧老厂隐伏花岗斑岩的侵位结晶年龄为44.6±1.1Ma,与滇西地区喜山期陆内造山主碰撞期(65-41 Ma)末相当。而澜沧老厂矿区辉钼矿Re-Os同位素测年结果(43.78±0.78Ma)与花岗斑岩中锆石SHRIMP U-Pb年龄(44.6士1.1Ma)很相近,都为喜山早期(始新世晚期)的产物,且年龄数据略新于岩体年龄,与斑岩热液成矿期总体晚于成岩期的基本规律相吻合。老厂花岗斑岩中的锆石群型简单,有4种主型,20种亚型。锆石晶形主要由{100}、{110}柱面和{101}、{211}锥面构成,其中柱面以{110}最为发育,锥面{]01}和{211}都较发育,但{101}较{211}更为发育,具低温过碱环境锆石特征。锆石标型指示矿区花岗斑岩是以壳源为主的壳幔源混合成因花岗斑岩。综合花岗斑岩地球化学、锆石标型以及同位素特征判断,老厂隐伏花岗斑岩应是以壳源重熔为主,有部分幔源物质参与的混合成因花岗斑岩。该区花岗斑岩形成于青藏高原新生代碰撞造山作用的主碰撞向晚碰撞转化时期,在空间上产于澜沧江断裂西侧的晚古生代裂谷带中,区域动力学环境属碰撞造山环境。更多还原

【Abstract】 The granite porphyry veins and skarm had been exposed by drilling in the 80’s of the last century in Laochang of Lancang, but the research progress for the granite-porphyry Petrology, geochemistry, geochronology and its relationship with mineralization were slow and relevant results were scarcity until 2008, because the projects of exposing concealed rock body were very little and the limited core was obtained. In the implementation of "the special projects of Superseding Resources Prospecting in Crisis Mines-the program of Superseding Resources exploration for Lancang lead ore of Yunnan Province" in 2007, three granite porphyry veins and the skarns belt, the molybdenum had been revealed in the ZK153101 and ZK14824 drillings hole respectively. In 2009, many granite porphyry veins and the final hole of main rock had been exposed in ZK14827, ZK14830 hole. In order to verify the Laochang concealed granite-porphyry characteristic, this article starts with granite-porphyry rock mass geology, petrology, geochemistry, chronology and zircon typomorphic characteristic, and comprehensive study on its genetic type and the formation of tectonic setting.The concealed granite-porphyry and the related molybdenite mineralization, skarn-based that had been revealed in this area mainly distributes between exploration line 145 to 9, east of the F3 break to west of the F4 break, and the overall distribution along the F1 fault, there are approximately elevation of 900-1530m, tendency of high east and low west.The petrology research indicated that this area granite porphyry show light gray, greyish white, the porphyritic texture, massive structure. The phenocrysts are mainly composed of the orthoclase, the quartz, the plagioclase feldspar and the biotite, the matrix are composed of the equiaxed particle-fine orthoclase, quartz. The rock geochemistry studies have shown that the Laochang concealed granite-porphyry body is the meta luminum high-K calc-alkaline granite, trace elements K, La, Hf, Tb is relatively enrichment, Nb, Ta, P, Ti depletion, they has reflected the characteristics of the orogenic granitoids and the continental crust. The total REE is low, with an average of 126.56×10-6, light REE enriched slightly with (La/Yb) N of 12.01 24.85,87Sr/86Sr of 0.70835～0.71544, with an average of 0.71. The SHRIMP zircon U-Pb dating results confirm that the crystallization age of the Laochang granite porphyry is 44.6±1.1 Ma, and equivalent with the main collision terminal stage(65～41Ma) of the Cenozoic intracontinental collision orogenics. The Re-Os age (43.78±0.78Ma) of molybdenites in the Laochang Mining Area is similar to the SHRIMP U-Pb zircon age (44.6±1.1 Ma) of granite porphyry, both are formed in the early Himalayan (late Eocene). The age of molybdenites is lightly new to the rock mass age, it is basically consistent with the Basic Law of porphyry hydrothermal metallogenic period later than diagenesis stages.The zircon crystal forms of the Laochang granite-porphyry are Simple, including four main types and twenty Subtypes. The zircon crystals were composed of cylinder{110},{100}and cone{101},{211}. With{100} cylinder and{101},{211} cone being very well developed, and{101} more developed than{211}. The zircon typomorphic characteristics suggest that the zircon in Laochang granite-porphyry were formed in a low-temperature and too alkaline environment, and the Laochang granite porphyry was formed mainly by crust source petrogenesis with the addition of mantle source composition.A comprehensive analysis of chemical composition, chronology and zircon typomorphic of Laochang granite-porphyry shows that the Laochang granite-porphyry should be formed mainly by crustal remelting with the addition of mantle-derived materials, with mixing genesis. This area granite-porphyry forms in the transition period of the main collision stage to the late collision of the Qinghai-Tibet Plain Cenozoic intracontinental collision orogenics, occurred in a late Paleozoic rift zone in the west of the Lancangjiang fault in Space, the regional dynamics environment was a collision orogeny environment.更多还原