豫西太平镇轻稀土矿床矿化特征及矿床成因

摘要

In western Henan Province, the rare earth ore deposit in Taiping Town is a newly-found medium-sized light rare earth deposit. Four orebodies were delineated in the three rare earth veins. The average thickness of the orebodies is 1.77 m, the average grade is 2.23 percent, the preliminary estimation of the amount of the resources is up to 100000 tons. Rare earth orebodies occur in the Mesoproterozoic plagiogranite and Erlangping Group, north of Taiping Town-Banshanping anticline, and are strictly controlled by NW-trending structures. The ∑LREO accounts for 83.23%-99.35%, The ∑HREO accounts for 16.77%-0.65%, and the distribution ratio of CeO2+La2O3+Nd2O3 is 79.56%-94.15%. Rare earth mineral mainly is bastnaesite.The major rare earth minerals belong to the strongly selective partition pattern which is rich in LREE with feature of Ce>La>Nd. The rare earth ore reveals a depletion of light rare earth and enrichment of heavy one, with a weak positive Eu and indistinct Ce anomaly as well as distinct fractionation processes. The average ratio of Eu/Sm is 0.38;the ratio of Th/U is high, the indictation of magmatic origin is similar to bariterare earth distribution pattern. The veined light rare earth ores fill in the fault structures which formed in Yanshanian and were superimposed upon the Erlangping Group and Zhangjiazhuang rock mass. So the ore-forming epoch is not earlier than(108±1)Ma. The origin of the deposit belongs to the quartz vein and altered rock type, controlled by the crust-mantle mixed source and faulted structure. Exploration indicators include the filling materials composed of quartz vein and fluoritization baratization pyritization, altered rock, weak Th radioactive anomalies and low content of U. The results obtained by the authors are very important for theoretical research on rare earth minerals as well as prospecting and work deployment in Henan Province.%豫西太平镇稀土矿床是新发现的中型轻稀土矿床.3条稀土矿脉共圈定4个矿体.矿体平均厚度1.77 m,平均品位ω(∑REO)为2.23%,初步估算资源量达10万t.稀土矿体严格受北西向断裂构造控制,赋存于太平镇—板山坪背斜北翼的中元古代斜长花岗岩和二郎坪群中.∑LREO占83.23%~99.35%,∑HREO占16.77%~0.65%,CeO2+La2O3+Nd2O3在总量中分配比为79.56%~94.15%.稀土矿物以氟碳铈矿为主,矿石中主要稀土矿物的REE配分属Ce>La>Nd富LREE强选择配分型.矿石稀土轻稀土富集,重稀土亏损,轻重稀土分馏明显,LREO/HREO比值大,铕为弱的正异常,不明显铈异常,Eu/Sm平均值0.38;Th/U比值大,与岩浆成因的重晶石稀土元素分配模式类似,显示岩浆成因.燕山期断裂构造叠加在早古生代二郎坪群及张家庄岩体内,沿断裂充填形成的成矿时代不早于(108±1)Ma的脉型轻稀土矿床.矿床成因为壳幔混源、受断裂构造控制的石英脉-蚀变岩型.主要找矿标志:在断裂构造中充填物为石英脉及萤石化、重晶石化、黄铁矿化等蚀变岩,以及弱的Th放射性异常,较低的U含量.