THE METALLOGENESIS AND MAGMATIC DIFFERENTIATION OF SUZHOU A-TYPE GRANITE
苏州A型花岗岩的岩浆分异与成矿作用

Suzhou A-type granite shows distinct mineralogical and geochemical zonations. Meanwhile, two different types of ore deposits could be found along its marginal areas. If the granite body, as it is in direct contact with pelitic-arenaceous strata, shows such a zonatin: the inner phase is composed of K-feldspar granite, then it is gradually transformed outward through Ab-rich granite to niobitized biotite-rich granite at its outermost part. As it is in contact with limestone, the outer biotite-rich granite phase can no longer be found, instead of it, a zinc, iron (tin, fluorite) ore deposit of skarn type is formed in the outer contact zone. According to the studies of mineralogy, petrology, geochemistry and the investigations of melt inclusions of the zircon crystal of the granite, these zonations were caused by vigorous magmatic differentiation (liquid and crystalline fractionation). During the processes of magmatic differentiation, the ore forming materials are steadily migrating toward the marginal area and then concentrated there. As a good protective layer the pelitic-arenaceous rock formation will prevent the diffusion of the ore-bearing melts(fluids), thus they will be enriched inside the intrusive body to form niobite deposit of magmatic type, while those in contact with limestone, the Zn, Fe(Sn, fluorite) deposit of skarn type will be produced along the outer contact through the process of contact-infiltration metasomatism.