浙赣皖相邻区燕山期花岗质岩类含矿性及其氧逸度特征

The Ore-bearing Potential and Oxygen Fugacity of the Yanshanian Granites in the Intersection Area of Zhejiang,Jiangxi,and Anhui Provinces,SE China

对浙赣皖相邻区燕山期两类花岗岩的岩石学、地球化学及成矿元素研究发现,燕山早期岩体主要岩石类型为花岗闪长岩,岩石偏中性,成矿元素方面更富含Au、Ag、Cu、Mo、Ni等深源元素,研究区大部分铜金钼矿床都与其有关;燕山晚期岩体主要岩石类型是花岗(斑)岩,岩石偏酸性,成矿元素相对缺乏Au、Ag、Cu、Mo、Ni等深源元素,与之伴生的铜金钼矿床罕见。可见,花岗质侵入体与研究区的金、铜、钼等成矿作用密切相关。通过锆石Ce异常计算出的岩浆氧逸度结果显示,早期花岗质侵入体的氧逸度范围介于FMQ(铁橄榄石-磁铁矿-石英缓冲对)和MH(磁铁矿-赤铁矿缓冲对)之间,平均值为FMQ+2.7,氧逸度较高;晚期氧逸度小于FMQ,平均值为FMQ-1.1。因此,氧逸度对部分元素(如铜、金、钼)的成矿有重要影响,氧逸度高,更有利于形成铜、金、钼等矿床。由于锆石成分分析的普及,获得锆石中的稀土微量元素含量越来越便利,利用锆石成分来计算岩浆的氧逸度具有非常广阔的应用前景。

Two intense tectonic-magmatic activities during the Yanshanian have been identified in the adjacent area of Zhejiang, Jiangxi, and Anhui provinces （the WZG region）. Correspondingly, there are two entirely different kinds of granites. The early Yanshanian granites are composed of granodiorite, and the rock is nearly neutral, enriched in Au, Ag, Cu, Mo, and Ni elements. The late Yanshanian granites are composed of granite porphyry, and the rock is acidic, depleted in these metallogenic elements. Therefore, the Cu, Au, Mo mineralization in the study region is related to these Yanshanian plutons. The oxygen fugacity （foE） of the magma calculated by zircon Ce anomalies and Ti-in-zircon temperatures shows that the average magmatic fo2 for the early Yanshanian granites in the study area is fayalite-magne- tite-quartz （FMQ） ＋ 2. 7, much higher than that of the late Yanshanian granites （ FMQ - 1.1 ）. Thus, the high oxygen fugacity contributes to the formation of Cu, Au, and Mo deposits. With the popularity of the zircon analysis, it is much easier to obtain the content of rare earth elements in zircon. Using zircon trace element to calculate the oxygen fugacity tends to have a broad prospect.