桂北地区甲龙锡多金属矿床锡石的微量元素地球化学意义

Geochemical significance of trace elements in cassiterite of jialong tin polymetallic deposit in northern Guangxi

甲龙锡多金属矿床位于江南造山带西段九万大山-元宝山的北东端,矿体产于新元古代元宝山花岗岩岩体东北部的外接触带与四荣韧性剪切带的叠加部位,明显受层间构造控制,由于矿床规模较小,工作程度较低。本文使用EPMA、LA-ICP-MS原位微区分析技术对甲龙锡多金属矿床的锡石进行了分析,结果显示锡石发生了明显的破碎、溶蚀和再生长现象,元素分布具有明显的环带结构,高FeO(0.23%~1.36%),相对富集Pb(0~2.90ppm)和Sb(4.98ppm~93.94ppm)等低温元素,强烈亏损Sc(2.81ppm~22.9ppm)、Nb(8.94ppm~1046ppm)、Ta(0.063ppm~74.0ppm)和Ti(81.1ppm~1952ppm)等高场强元素,(La/Lu)_(N)比值较高(1.51~58.52),指示了甲龙锡多金属矿床可能形成于中低温成矿流体,而与岩浆热液并无明显的成因联系。甲龙锡多金属矿床中的锡很大可能来源于新元古代富锡地层,后期构造活动使地层活化,锡等金属元素从地层中萃取出来,并沿韧性剪切带运移至次级断裂带中富集成矿。

Jialong tin-polymetallic deposit is located in the northeast of Jiuwandashan-Yuanbaoshan,western section of Jiangnan orogenic belt.The orebody hosts in the superposition of the outer contact zone of the northeastern Yuanbaoshan granite body and Sirong ductile shear zone,which is obviously controlled by the interlayer structure.Due to the small size of the deposit,the research work is relatively low.In this paper,EPMA and LA-ICP-MS in-situ microanalysis techniques have been used to analyze cassiterite from Jialong tin polymetallic deposit.The results show that cassiterite has obvious fragmentation,dissolution and regrowth phenomenon,with an obvious ring structure in element distribution.The samples have high FeO(0.23%~1.36%),relatively enriched in low temperature elements,such as Pb(0~2.90ppm)and Sb(4.98ppm~93.94 ppm),strongly depletion of high field strength elements,such as Sc(2.81ppm~22.9 ppm),Nb(8.94ppm~1046ppm),Ta(0.063ppm~74.0ppm)and Ti(81.1ppm~1952ppm),and the ratio of(La/Lu)_(N) was higher(1.51~58.52).It indicates that Jialong tin polymetallic deposit may be formed in medium and low temperature ore-forming fluid,but there is no obvious genetic relationship with magmatic hydrothermal.The Sn in Jialong tin polymetallic deposit probably originated from the Neoproterozoic tin rich strata,which were activated by later tectonic activities.Sn and other metal elements were extracted,and then migrated along the ductile shear zone to the secondary fault zone for enrichment and mineralization.