浙江萤石矿床的稀土元素地球化学特征

REE GEOCHEMISTRY OF FLUORITE DEPOSITS IN ZHEJIANG PROVINCE

文章根据浙江14个萤石矿床(点)的94个萤石和49个赋矿岩石样品的稀土元素分布特征,将萤石矿床分为两种类型:即轻稀土富集型(萤石的∑REE=30×10^(-6)～80×10^(-6),Y=10×10^(-6)～50×10^(-6),∑Ce/∑Y≥1,La/Yb>6);重稀土富集型(萤石的∑REE=40×10^(-6)～70×10^(-6),Y=30×10^(-6)～110×10^(-6),∑Ce/∑Y<1,La/Yb<3)。前者从早阶段到晚阶段,萤石的∑REE及Y含量趋于减小,LREE/HREE及La/Yb值增大;后者从早期到晚期,萤石的∑REE和Y含量以及LREE/HREE和La/Yb比值变化则相反。轻稀土富集型萤石的矿床规模越大,萤石与未蚀变围岩的REE含量差值越大;重稀土富集型萤石的矿床规模越大,萤石与未蚀变围岩的REE含量差值越小。

Presented in this paper are REE data of 94 fluorite and 49 host rock samples from 14 fluorite deposits or ore spots in Zhejiang Province. In terms of REE geochemistry, the fluorite deposits might be assigned to two types: (1) LREE-enriched type with fluorite characterized by ∑REE=30×10^(-6)～80×10^(-6), y=10×10^(-6)～50×10^(-6), ∑Ce/∑Y≥1 and La/Yb>6,as exemplified by Yangjia and Hushan deposits; (2) HREE-enriched type whose fluorite is noted for ∑REE=110×10^(-6), ∑Ce/∑Y<1 and La/Yb<3, represented by the Yucun deposit. From early to late stage, fluorite in the former type tends to decrease in ∑REE and Y content but increase in LREE/HREE and La/Yb ratios, whereas things seem to be just opposite for fluorite in the latter type. The LREE-enriched type fluorite deposits, distributed mainly within or near the Cretaceous fault basins in Mesozoic volcanic areas of the Central Zhejiang upwarping zone, have been proved to be genetically products of deep circulation, leaching and drawing of Late Cretaceous geothermal water; the larger the size of the ore deposit, the greater the difference in REE content between fluorite and unaltered wall rocks. The HREE-enriched type fluorite deposits, mostly seen at the contact zone of the Yanshanian granite or neighboring faults in the western Zhejiang downwarping area, are shalIow circulation, leaching and drawing of Late Cretaceous geothermal water in origin; the larger the size of the ore deposit, the smaller the difference in REE content between fluorite and unaltered wall rocks.