江西崇义淘锡坑钨锡矿区基性岩脉的岩石地球化学特征及意义

Geochemical characteristics and significance of basic dyke in Taoxikeng tungsten-tin ore district,Chongyi county,southern Jiangxi

江西省崇义县淘锡坑钨锡矿床地处南岭有色金属成矿带东段崇(义)-(大)余-(上)犹钨锡矿集区。在详细的坑道编录和岩矿鉴定的基础上,对矿区内烂梗子矿组和枫林坑矿组的基性岩脉进行了岩石地球化学分析,结果显示:356 m中段烂梗子矿组Ⅰ、Ⅱ号基性岩脉为辉绿岩,属于富钠准铝质钙碱性基性岩类;056 m中段枫林坑矿组的Ⅲ号基性岩脉为闪辉正煌岩,属于钙碱性钾质煌斑岩。辉绿岩、闪辉正煌岩稀土配分曲线均右倾,重稀土曲线比较平坦,无明显的Eu负异常(δEu=0.74~0.96),轻稀土有一定程度的富集;辉绿岩强烈亏损Nb,亏损Ba、Ti等高场强元素,富集Rb、Th、U、Sr、Zr、Hf等不相容元素和LREE元素;闪辉正煌岩强烈亏损Nb、Ti,亏损Zr、Hf等高场强元素,富集Rb、Ba、Th、U等不相容元素和LREE元素。本区基性岩脉侵入年龄为158.2~159.6 Ma,与九龙脑岩体的成岩成矿作用时间相近,可能是我国东南部晚中生代岩石圈拉张-伸展-减薄地球动力学背景下的产物,为淘锡坑钨锡矿床提供成矿物质来源的可能性不大。

Taoxikeng tungsten-tin deposit in Chongyi county of Jiangxi,is located in Chongyi-Dayu-Shangyou tungsten-tin ore concentration area,which is the eastern segment of Nanling nonferrous metallogenic belt.On the basis of the detailed geological logging of gallery and rock-mineral determination,we have carried out petrogeochemical analysis of the basic dykes in Langengzi ore veins group and Fenglinkeng ore veins group,Taoxikeng tungsten-tin ore district.And the results show that the No.Ⅰ and No.Ⅱ basic dykes of Langengzi ore group in the levels of 356 m are diabase,belonging to meta-aluminous basic rocks in calc-alkaline series with the characteristics of sodium rich;the No.Ⅲ basic dykes of Fenglinkeng ore group in the levels of 056 m is garganite,belonging to potassic calc-alkaline lamporpyres.Moreover,all REE pattern of basic dykes shows the curve with right-dip and flat HREE,low level enrichment of LREE and not obvious negative Eu anomalies(δEu=0.74-0.96).And the MORB normalized multi-element variation diagram of diabase shows strongly depletion in Nb,and obviously depletion in Ba,Ti and other HFSEs,but enrichment in Rb,Th,U,Sr,Zr,Hf and other incompatible trace elements and LREE;the MORB normalized multi-element variation diagram of garganite are strongly depletion in Nb,Ti,and obviously depletion in Zr,Hf and other HFSEs,but enrichment in Rb,Ba,Th,U and other incompatible trace elements and LREE.In addition,the intrusive age of the basic dykes is ranged from 158.2 to 159.6 Ma,similar to or slightly earlier than the diagenesis and mineralization of the Jiulongnao composite granite batholith.As a result,it may be the product of the Late Mesozoic lithospheric stretching-extension-thinning geodynamic setting in the southeastern of China.It is unlikely that the basic dykes could provide ore-forming materials for the Taoxikeng tungsten-tin deposit.