The Diagenesis And Mineralization Of Adakite-Like Rock Form

JiaMa copper polymetallic deposits of Tibet which is a hornfels-skarn type deposit locates at the eastern of Gangdese metallogenic belt. It is adjacent to the QuLong porphyry copper deposit. The stratums of deposit are mainly Limbuzong group of the lower Cretaceous and duodigou group of the upper Jurassic. The Ore body is located between the two stratums as like-layered. The mineralized center have NNE trend arranged in echelon-type The wall rock alteration of deposit is developed, whit the similar horizontal and vertical alteration zoningThe main types of medium-acid porphyry in Jiama deposit are granite porphyry, granodiorite porphyry, monzogranite porphyry and (quartz) diorite porphyry. The granite porphyry arranged in EW are mainly distributed in the southern. The rock is charactered as muscovite, classified as strongly peraluminous S-type granite, also as high-K calc-alkaline series rocks. The other porphyry arranged in NS as echelon-type, classified as metaluminous I-type granite, also as medium-high-K calc-alkaline and C-type adakites.Jiama adakites show the evolutionary trend of from adakites to calc-alkaline rock, that is the fractionation of Fe, Mg mineral. With the crystallization differentiation, all the main elements content reduce except the w(K2O), consistent with the normal magma evolution sequence. In the process of evolution ,there are three magma mingling processes between JiaMa adakites and basic magma, corresponding to the three Cu,Mo mineralization.The formation of the Jama adakite-like rock is under the "post-collision" orogeny between the Asian and the Indian plates, which is the concentrated expression of the tectonics, the magmatism and the mineralization during that period. The source shows that the ignerous and metamorphic rock in the deep arc is amphibolite face through partial remelting , and mixed by the enriched mantle (EMâ…¡).The formation process can be described like this : around 14Ma, with the large-scale asthenospheric upwelling and the rapid thinning of the crust Gangdese, the nearly N-S normal faults and the rift basin system formed. Under the heating of the underplating basaltic magma chamber, the upper crust (the island-arc magma of amphibolite face partially melted, and finally there resulted in the formation of the adakite-like rock. With the emplacement of underplating basaltic magma, there were different degrees of magma mixing between the adakite-like rock and the basic magma, which leading to the extraction and enrichment of the mineral. With the the mixed magma crystallization and differentiation continuing, the mineral separated from the magma affluxed into the fuild system, and precipitated and mineralized in the nearly N-S tensile frature zones .