Research On Geochemistry Of Intermediate-acidic Instrusive Rocks In The Saishitang Copper Deposit, Qinghai Province, China: Implications For Their Origin

Through the detailed studies of petrochemistry, rock-forming, chronology, trace elemental and isotopic geochemistry of intermediate-acidic instrusive rocks, This thesis tried to investigate the genesis and magamatic evolution of it. The time of the large-scale calc-alkaline magma instrusion events were preliminarily determined, and the models of partial melting and crystallization fractionation were used to determine the property of source magma and its evolution process with the following conclusions:The intermediate-acidic instrusive rocks in the Saishitang copper deposit mainly include intermediate to acidic quartz diorite (quartz dioritic porphyrite), then diorite (dioritic porphyrite),granodiorite and quartz porphyry, formed in about 220Ma, as a result of the large-scale calc-alkaline magmatic activities of early Indosinian epoch. The intermediate-acidic instrusive rocks in Shaishitang copper deposit was shown to be hypogene syntexis-type with the parent magma formed by 63% partial melting degree from 63.75% of the lower crust content with 36.25% of the upper mantle material. And the magma experienced crystallization fractionation from low REE magma to REE-rich magma. Quantitative modeling calculations show that high REE granitoid rocks in Shaishitang copper deposit are products crystallized from the low REE intermediate-acidic instrusive rocks with a relatively high degree of crystallization fractionation (59%). Geochemical characteristics of the rock-forming minerals and whole rock petrochemistry show that the regional source being heterogeneous.