青海三江北段莫海拉亨铅锌矿床地球化学特征及成因分析

Geochemical Characteristics and Genetic Analysis of Lead-zinc Deposits of the Mohailaheng Area in the Northern Section of Lancang River,Nujiang River,Jinsha River,Qinghai

莫海拉亨铅锌矿地处三江北段成矿带北缘的结多弧后前陆盆地,含矿层位主要为下石炭统杂多群碳酸盐岩组,赋矿地层及北西西向断裂为重要的控矿因素,矿石矿物主要为方铅矿、闪锌矿、褐铁矿等;研究区主量元素Mg/Ca值均小于0.6,稀土元素LREE/HREE值平均为5.59,(La/Yb)N平均值为0.73,显示轻重稀土有分馏,且呈HREE弱富集型特征;微量元素Sr、Ba略呈富集型,Rb、Th、Ta、Nb等元素呈轻微亏损型特征,显示矿体与围岩具有相同或相似物质来源。由上所述,研究区铅锌矿产于滨浅海-海陆交互相的沉积环境,矿床成因具有类MVT型矿床特征。

Mohailaheng lead-zinc mineralization is located in Jieduo back-arc foreland basin in the northern margin of metallogenic belt in the northern section of Lancang River, Nujiang River and Jinsha River. It mainly contains carbonate seam of Zaduo group in Lower Carboniferous. Ore-bearing formation and the NWW fracture are important ore-controlling factors in the Mohailaheng area. Ore minerals are mostly galena, sphalerite, limonite, etc. In the studied area, major element Mg/Ca value is less than 0.6, the average LREE/HREE value is 5.59, the （La/Yb）N average is of 0.73, showing that there is LREE/HREE fractionation, and there is a weak HREE enrichment characteristic; Trace elements Sr and Ba are slightly enriched, Rb, Th, Ta, Nb and other elements show a slight loss characteristic. These data indicate that ore body and surrounding rock have the same or similar material sources. In conclusion, lead-zinc deposits originated in shallow shore-paralic depositional environment, and ore deposit genesis possesses the characteristics of the Mississippi Valley-type（MVT） deposit.