赣中大王山钨钼多金属矿集区辉钼矿微量元素地球化学特征

GEOCHEMICAL CHARACTERISTICS OF TRACE ELEMENT OF THE MOLYBDENITE IN THE DAWANGSHAN TUNGSTEN MOLYBDENUM POLYMETALLIC ORE CONCENTRATION AREA,CENTRAL JIANGXI PROVINCE

为厘清大王山钨钼多金属矿集区成矿流体性质和成矿物质来源,以矿床(点)中与黑钨矿共生的辉钼矿为研究对象,利用ICP-MS分析方法,展开稀土元素和微量元素地球化学研究。结果显示,辉钼矿中稀土元素含量较低(ΣREE=60.8×10^(-6)~92.19×10^(-6)),轻稀土元素(LREE)富集(LREE/HREE=15.50~36.84,平均为26.53),轻重稀土分异程度较弱((La/Yb)N=1.10~10.37,平均为4.35),辉钼矿稀土元素具有Ce负异常(δCe=0.21~0.44)和强烈的Eu亏损(δEu=0.01~0.03)现象,δSm与δCe呈负相关关系,ΣREE与δCe具有正相关性,指示其成矿条件为较高温的还原环境。微量元素多以非类质同象的机械混合或流体包裹体的形式存在,富集Cu,W,Bi,Pb等,除瑶蓝窝矿点的Nb/La>1外,其他矿床(点)的Nb/La,Hf/Sm,Th/La均<1,表明成矿流体富Cl。通过REE vs La/Yb图解可以看出辉钼矿与赋矿花岗岩投点范围集中,具有壳幔混合的同源性。综合前人对研究区硫化矿硫同位素特征的研究,结合La vs La/Sm图解,暗示中生代辉钼矿可能有一个共同的富集成矿元素的幔源区。大王山钨钼多金属矿集区的岩浆-流体在深部可能经历了两个主要演化过程:(1)幔源成矿物质与赋矿围岩岩浆在深部发生了充分的混合作用;(2)赋矿岩浆在演化后期发生了液态不混溶作用。

ICP-MS analysis is used for the geochemical study of rare earth elements and trace elements of the molybdenite associated with the ore deposit in the Dawangshan Tungsten-Molybdenum polymetallic ore concentration area,so as to clarify the ore-forming fluid properties and oreforming material sources. It shows that the molybdenite is poor in content of rare earth elements （ ∑REE = 60.8 × 10-6 ～92.19× 10 6 ）, rich in light rare earth elements （（La/Yb）N = 1.10～ 10.37, average 4.35）, and the light and heavy rare earth elements are less well differentiated with negative Ce anomaly（δCe=0.21～0.44） and strong depletion of Eu （δEu=0.01～0.03）. There is a negative correlation between δSin and δCe, and a positive correlation between δREE and δCe, a condition of higher temperature and reducing environment. Most of the trace elements exist in the form of mechanical mixing of non-isomorphic or fluid inclusions, enriched in Cu, W, Bi, Pb, etc,Nb/La,Hf/Sm,Th/La〈1 in most of the ore occurrences except Yaolanwo ore occurrence （Nb/La〈1）, indication of enrichment of CI in the ore-forming fluid. REE vs La/Yb diagram shows that the molybdenite and ore-dressing granite have a wide range of plotting points and have the homology of crust-mantle mixing. Based on previous studies on the sulfur isotopic characteristics of sulphide ores in the study area and the combination of the La vs. La/Sm diagrams,it is considered that the Mesozoic molybdenite may have a common mantl-derived region rich in ore-forming elements. The magmatic fluid in the Dawangshan Tungsten-Molybdenum ore district experienced two major evolution processes in the deep. （1） the mantle source metallogenic material and the ore-bearing porphyry magmatism fully mixed in the deep; （2） liquid immiscibility effect occurred in the late stage of magma mineralization evolution.