湘南癞子岭花岗岩 分异演化和成岩成矿

摘要

The Laiziling granite stock was emplaced in the Early Yanshanian period. Its zircon U-Pb age is dated at (154-155) Ma. This granite pluton is characterized by enrichment in Li, Rb, Sn, W, Nb, Ta etc. Rare metal elements, Pb, Zn etc. Base metal elements and H20, F etc. Volatiles. A vertical zonation is well developed within a vertical distance of (450~500) m. From the deeper level upwards to the top of the Laiziling Mountain peak, the following zones are successively observed: protolithionite granite zone, leucogranite (two-mica granite and Li-muscovite granite) zone, albite granite zone, greisen zone, massive quartz and pegmatoid stockscheider. Along this direction, the major and trace elements concentrations of rocks are regularly changed. Well developed magmatic fractionation and magmatic-hydrothermal evolution are responsible for high-degree enrichment of rare-metal elements, base metal elements and volatiles in the rocks and further mineralization.Although most samples of the Laiziling granite stock exhibit peraluminous feature, the protolithionite granite at deeper levelhas high contents of Zr, REE, Y, Nh, Th, U etc. High field strength elements. Furthermore, relatively higher eHf values (from -5.9 to -1.9, averaging -4.2) and relatively lower Hf model ages (/DM values from 1.32 Ga to 1.58 Ga, averaging 1.47 Ga) indicate an evident involvement of mantle materials. We propose that the primary magma source of the Laiziling granite might be derived from the A-type Qitianling batholith, or a fractionated deeper magmatic chamber similar to the Qitianling granite.%湘南癞子岭花岗岩岩株侵位于燕山早期,其锆石U-Pb年龄为154～155 Ma,以富含Li,Rb,Sn,W,Nb,Ta等稀有金属元素,Pb,Zn等贱金属元素以及H2O,F等挥发份为主要特征,具有明显的垂直分带.自下而上,在450～500m的垂直距离范围内,从黑鳞云母花岗岩带,经浅色花岗岩(二云母花岗岩和锂白云母花岗岩)带、钠长石花岗岩带、云英岩带、到块状石英和黄玉伟晶岩带,各带岩石的常量元素和微量元素组成都发生有规律的变化.高度发育的岩浆分异和热液演化,是稀有金属和贱金属元素及挥发份逐步富集并成矿的关键机制.虽然大多数癞子岭花岗岩的样品都具有过铝的特征,但由于该岩体特别是其较深部位的黑鳞云母花岗岩中Zr,REE,Y,Nb,Th,U等高场强元素含量高,锆石的εHf值偏高(在-5.9和-1.9之间,平均--4.2),Hf模式年龄tDM值偏低(在1.32 Ga～l.58 Ga之间,平均1.47 Ga),都显示有地幔物质的明显参与,推测癞子岭花岗岩的原始岩浆,可能来源于深部铝质A型骑田岭花岗岩基,或者是与骑出岭岩基相类似的铝质A型花岗质岩浆体的分离结晶作用.