湖南沃溪金-锑-钨矿床成因的稀土元素地球化学证据

REE geochemical evidence for the genesis of the Woxi Au-Sb-W deposit, Hunan Province

沃溪金-锑-钨矿床的稀土元素地球化学组成良好地反映了成矿作用的条件和过程,并为示踪矿床成因提供了有用的信息。以流体包裹体为代表的成矿溶液,以较高的稀土总量、显著的轻稀土富集和缺乏明显的铕异常为特征,代表了一种通过在碎屑沉积物柱中循环而萃取矿质的演化的海水热液。矿石相对于成矿流体(母液)富集重稀土而轻微亏损铕,反映了矿石沉淀过程中来自于海水的稀土元素掺合。同一矿层内由下往上,重稀土相对富集的程度逐渐增大而稀土总量则逐渐降低,表明随着热液化学沉淀作用的进行,海水掺合的影响逐渐增强。矿石的稀土元素组成,无论在分布模式还是在轻重稀土之间的分馏程度上,均与其他许多Sedex型多金属矿床十分相似,暗示了这些矿床具有相似的成因机制。稀土元素地球化学特征支持矿床同生沉积成因的观点。

The REE geochemical compositions of the Woxi Au-Sb-W deposit well reflect the conditions and processes of the hydrothermal mineralization and provide some useful information for tracing the genesis of the deposit. The ore-forming hydrothermal fluids, as demonstrated by fluid inclusions, are characterized by relatively high total REE contents, marked LREE enrichment and no significant Eu-anomalies. They were mostprobably derived from evolved seawater that acquired ore-forming materials by circulating in the clastic sediment pile. The bulk ores are enriched in HREE and slightly depleted in Eu relative to their parent fluids, indicating the influence of seawater. Within a single ore layer, the degree of HREE enrichment tends to increase upward, while the total REE contents decrease, reflecting greater influence and dilution of seawater with time. There is a broad similarity in chondrite-normalized REE patterns and the amount of REE fractionation of the ores in this study and exhalites from many other Sedex-type polymetallic ore deposits, suggesting a similar genesis for these deposits. The REE geochemistry supports a syngenetic model for the Woxi deposit.