锡矿山热液方解石的REE分配模式及其制约因素  

REE Distribution Pattern for the Hydrothermal Cal cites from the Xikuangshan Antimony Deposit and Its Constraining Factors

作　　者：彭建堂[1] 胡瑞忠[1] 漆亮[1] 赵军红[1] 符亚洲[1] 

机构地区：[1]中国科学院地球化学研究所,贵阳550002

出　　处：《地质论评》2004年第1期25-32,共8页Geological Review

基　　金：国家重点基础研究发展规划项目(编号G1999043200);国家杰出青年科学基金(编号49925309);国家攀登计划预选项目(编号95-预-25)的研究成果

摘　　要：锡矿山锑矿床中成矿期热液成因方解石的REE分配模式表现出明显的MREE、HREE 富集,LREE 亏损特征;且早、晚两期方解石的 REE分配模式有所不同,晚期方解石 REE分配曲线相对平缓,REE 系列元素之间的分馏不如早期方解石明显。初步研究表明,早期方解石存在强烈的 REE分馏作用,暗示成矿早期可能有类似独居石的矿物生成;方解石中 REE分配行为与角闪石中的 REE分配行为非常类似,晶体化学因素对其REE 分配模式起着重要的制约作用,REE 在方解石中的这种分配行为与溶液体系中 REE络合物的稳定性无关;方解石中 REE最佳替代位置的离子半径大约为0.091±0.001 nm,明显小于理想的 Ca^(2+);这种最佳置换位置并非由Ca^(2+)自身,而是由方解石晶体结构决定的。The chondrite-normalized REE patterns for the syn-sulfide calcites from the Xikuangshan antimony deposit are unique, being MREE- and HREE-enriched and LREE-depleted. Moreover, there are differences in the REE patterns between the early-stage and late-stage hydrothermal calcites. Compared with the late-stage calcite, the LREE concentrations for the early-stage calcite are obviously lower, and the MREE and HREE contents are relatively higher than the former. There is an abrupt increase between the LREE and MREE for the early calcite, which may result from the coeval precipitation of some LREE-enriched minerals analogous to monazite. The REE distribution behavior in the hydrothermal calcites is similar to that in some igneous minerals such as hornblende. This distribution behavior is predominately constrained by crystallographic factors rather than the stability of REE complex in hydrothermal solutions. The optimum ion radius of substitutional site for the REEs in the hydrothermal calcites from the Xikuangshan deposit is about 0. 091 ± 0. 001 nm obviously smaller than the theoretical value of the ideal Ca2+ ion. This optimum site in the hydrothermal calcites is determined by the crystal structure of calcites rather than by the Ca2 + ion in calcites.

关 键 词：锡矿山 热液方解石 REE分配模式 稀土元素 锡矿山 

分 类 号：P618.6[天文地球—矿床学]