银山多金属矿床成矿流体稀土元素地球化学

对江西银山矿床规模不同的矿体、蚀变围岩及其原岩的稀土元素特征进行了对比研究。结果表明 ,成矿流体的稀土元素以轻稀土富集型 ,无Ce异常 ,强烈的Eu正异常而显著地区别于赋矿围岩。热液蚀变作用造成围岩的稀土总量升高 12 .1%～ 5 2 .4%,轻重稀土比值降低 ,但紧邻矿体的稀土含量则低于原岩。导致围岩稀土总量升高有两个因素 :(1)通过热液蚀变作用带入了稀土元素 ;(2 )体系主元素 (Si)质量迁移而造成稀土元素出现表观浓缩。其中以前者为主导因素。矿体的接触带及其紧邻处的蚀变围岩的REE含量明显偏低 ,主要因出现大量石英或石英 +硫化物等矿物的显微脉体 (脉幅 3～ 8μm)而被稀释 ,是一种表观亏损现象。研究结果表明 ,矿体越大 ,其围岩REE被“稀释”越明显 ,涉及的范围越大 ,REE特征可能是一种潜在有效的找矿勘探地球化学指标。

GEOCHEMICAL BEHAVIOR OF REE DURING HYDROTHERMAL ALTERATION RELATED TO ORE-FORMING PROCESSES IN YINSHAN POLYMETALL IC DEPOSIT, NORTHEASTERN JIANGXI PROVINCE, CHINA

Rare-earth elements and other trace elements in altered phyllite, unaltered phyllite, and ores were determined in order to examine the behavior of REE in hydrothermal alteration associated with ore-forming processes of the Yinshan polymetallic ore deposit. It is demonstrated that the behavior of REE during alteration was extremely complicated. The REE characteristics are as follows: (1) Instead of being leached, REE contents were higher in the altered phyllite in a magnitude range from 9% to 45% than those in their fresh counterparts, except that samples on the contact showed lower REE concentrations. 9%～45% increment of REE contents was caused by the "condensed" effect of mass transfer of major elements such as Si, Na, Mg, etc. removed from the rock, 55%～91% should be responsible for the addition of REE into the rock from hydrothermal fluid that caused rock alteration. Significant lower content of REE in samples on the contacts of intrusion and ore bodies was ascribed to the dilution caused by much higher contents of REE barren-minerals such as quartz, pyrite and sphalerite in the rock. (2) The acting hydrothermal fluid was characterized by low LREE/HREE ratio and in a reductive state, resulting in a less partition between LREE and HREE in altered phyllite and evident loss of Eu caused by reduction of Eu 3+ to more mobile Eu 2+ and its removal from phyllite. Preliminary data suggest that the degree of REE loss increases with the size of ore bodies. Thus, REE loss is a potentially useful method of distinguishing between small and large ore bodies in exploration in the neighboring area. However, this suggestion requires further testing.