西藏甲玛铜多金属矿二长花岗斑岩岩浆-热液过渡特征及成矿意义

Characteristics and Significance of Magmatic-Hydrothermal Transition in Jiama(Gyama) Monzonite Granite-porphyry,Tibet

以原始地质资料为基础,结合电子探针数据和岩石地球化学分析,从岩石学、岩相学和地球化学的角度分析了甲玛矿区二长花岗斑岩岩浆-热液过渡的特征及成矿作用。甲玛二长花岗斑岩岩浆热液过渡以电气石-钠/钙硅酸盐化、似伟晶细晶岩壳(脉)和具"冰长石"结构特征的钾长石、蠕状石及显微晶洞(或空腔)构造为特征;地球化学上表现为Na、K的反消长和挥发分含量的涨落,并伴随着Cu、Mo、Au等成矿物质从晚期岩浆的逃逸。甲玛二长花岗斑岩的岩浆热液过渡过程可划分为以超临界流体为代表的液相不混溶阶段和超临界流体逃逸为特征的气液分馏阶段。其中前者决定了岩浆晚期的矿质分馏程度,而后者控制了含矿蒸汽和成矿热液流体的形成,进而分别形成浸染状矿化和脉状矿化。

Based on basic geological data, this paper summed up the characteristics and metallogenesis of the magmatic-hydrothermal transition in the Jiama（Gyama） monzonite granite-porphyry with the help of the electron microprobe analytical data and rock geochemical data in the aspects of petrology, petrography and geochemistry. The characteristics of the magmatic-hydrothermal transition in the Jiama（Gyama） monzonite granite-porphyry is manifested as tourmalinization-sodium/calcium silicate, like pegmatite-aplite shell （pulse）, ＂adularia-habit＂ K-feldspar crystals, myrmekite, miarolitic cavities, while the geochemical characteristics are expressed as the growth and decrease of Na/K and the fluctuatation of the volatiles with the separation of the ore-forming materials such as Cu, Mo, Au. The development of the magmatic-hydrothermal transition can be divided into liquid immiscibility and volatile-liquid fractionation, the former dominated the mineral fractionation in the later magma, while the latter controlled the formation of ore solution and ore-forming hydrothermal fluids, forming disseminated mineralization and stockwork mineralization respectively.