宁芜和庐枞火山岩盆地玢岩铁矿矿床地球化学特征及其成矿动力学背景探讨

Characteristic of Deposit Geochemistry and Discussion with Metallogenic Dynamics Background of Porphyrite Iron in Ningwu and Luzong Volcanic Basins

玢岩铁矿是我国铁矿的一个重要成矿类型,宁芜和庐枞火山岩盆地是长江中下游地区玢岩铁矿的主要矿集区。对宁芜和庐枞盆地的构造分析结果表明,NNE向断裂和NW向断裂控制了区内的岩浆活动,断裂的交汇部位往往是玢岩铁矿产出的有利空间。综合对比了宁芜和庐枞地区玢岩铁矿成矿岩体的主量元素、稀土元素以及铅同位素特征,表明其具有相似的地球化学特征和共同的物质来源。稀土元素特征表明两盆地玢岩铁矿的成矿物质主要来源于地幔或下地壳;Pb同位素特征则进一步说明其与EM-Ⅱ型富集地幔具有密切关系。宁芜和庐枞盆地在燕山期受太平洋板块俯冲作用的影响,成矿作用受岩浆活动所控制。两盆地玢岩铁矿成矿作用的差异,可能是由于其受地壳物质混染程度不同所致。

Porphyrite iron deposit is one of important deposit types in China. Ningwu and Luzong volcanic basins are the main ore districts in the middle and lower reaches of Yangtza River. The structure of Ning- wu and Luzong basins is analyzed separately. It shows that NNE-trending faults and NW-trending faults control magmatism in the area and the intersections of fracture are often the favorable space for porphyrite iron deposits. Comprehensive comparison with major elements, rare earth elements and lead isotopes of ore rock, in Ningwu and Luzong area, shows that they have similar geochemical characteristics and common material source. The characteristics of REE show that the ore-forming materials of porphyrite iron deposits are mainly from lower crust or mantle, Pb isotopic characteristics further illustrate that the ore-forming materials are closely related with EM-Ⅱ mantle. Ningwu and Luzong basins were affected by the subduc- tion of Pacific plate, and mineralization was controlled by magmatic activity. The difference in mineraliza- tion of porphyrite iron may be due to the different levels of contamination by crust.