Mineralizing Mechanism And Continental Geodynamics Of Typical Pegmatite Deposits In Western Sichuan, China

Western Sichuan is an importan pegamatite province in China. There are manypegmatite type deposits in the region, such as: Jiajika rare metal deposit with thelargest lithium reserve in China, Ke'eryin large-medium scale rare metal deposit, andDanba large scale muscovite deposit. The three deposits locate in Songpan-GanziOrogenic Zone, mineralize in Mesozoic, and have different commodity, andmineralizing scale. Thus, they are the ideal objects to study the mineralizions andtheir backgrounds.But, the location of Chuanxi is remote, and geolocial study degree is very low. Inorder to get the first hand data, the project group have worked in field there morethan one month. Furthermore, much testing work have been done,such as: ①Becauseof lacking precise dating data, 7 40Ar/39Ar dating experiments have been done;②Inorder to tracing the evolving process of mineralizing fluid, I have worked about 50days to measure the homogeneous temperature of about 1500 fluid inclusions, andfluid component, C, H, O isotope were also been measured;③Petrochemistry studyon pegmatites and granites have been done, by which mineralizing process can bededuced;④the components of Muscovite were analyzed, too, which can prove thereseach result by other means;⑤Great deal of geological data were been colected.By these work, several inclusion were got, such as:1. The mineralization of Jiajika, Ke'eryin and Danba deposits respectivelybelong to "magma liquid immiscibility", "magma fractional crystallization" and"magmatism+metamorphism".2. The difference of magma evolving process is the key reason for the differentmineralizing scale between Jiajika and Ke'eryin deposit. Comparing to magmafractional crystallization, magma liquid immiscibility can separate an highly richvolatile melt, wich can enrichment rare metal greatly. So magma liquid immiscibilitycan forming large scale ore deposits more impossible than magma fractionalcrystallization..3. There are close relation among orogeny, magmation and mineralization ofpegmatite in Songpan-Ganzi Orogenic Zone. Jiajika deposit formed in outer place ofmain part in Songpan-Ganzi orogenic zone. Thus Jiajika area underwent one directiontectonic stress, and located a close environment. These provide possibility for magmaliquid immiscibility. Ke'eryin formed in the interior of main part in Songpan-Ganziorogenic zone, and underwent two direction tetonic sterss, Thus, the regionunderwent several phase tectonic movements. In this condition, Ke'eryin depositformed by magma fractional crystallization in multi-period and multi-phaes. Danbadeposit formed in the center of eastern main part in Songpan-Ganzi orogenic zone.The region is the place of two direciton tectonic stress. Thus in Chuanxi, thelithosphere of Danba region is the thickest, and tectonic stress is weak. Therefore thedeep magma is not able to invade, and metamorphism play an importan role in theprocess of mineralization.