皖南侏罗-白垩纪两类花岗岩的岩石成因、氧逸度特征及成矿意义

Petrogenesis, oxygen fugacity characteristics and mineralization significance of two kinds of Jurassic-Cretaceous granites in southern Anhui,SE China

皖南地区北接长江中下游铜铁金成矿带,南临赣东北德兴铜、金矿集区,成矿潜力巨大。迄今已在区域内发现多个大中型W、Mo、Cu、Au矿床。本次研究选取多个可能与成矿有关的小型花岗岩体进行岩石成因、氧逸度高低及其成矿潜力分析。研究发现：皖南侏罗-白垩纪发育两期花岗岩,早期花岗岩主要形成于160~140±5Ma,岩性多为花岗闪长岩等偏中性岩石,岩石成因与中晚侏罗世的板块俯冲挤压有关。晚期花岗岩主要形成于140±5~120Ma,岩性以花岗岩、正长花岗岩以及碱性花岗岩为主,岩石的成因与构造体制转换之后的伸展环境有关。利用锆石中稀土微量元素的含量计算出皖南及相邻地区早期（160~140±5Ma）花岗岩普遍具有比较高的Ce4＋/Ce3＋值,即岩浆具有高氧逸度;而晚期（140±5~120Ma）花岗岩的Ce4＋/Ce3＋值普遍偏低,指示了岩浆具有较低的氧逸度。通过对氧逸度与成矿关系的分析,认为皖南燕山早期发育的花岗质岩类具有良好的铜、金、钼找矿潜力。

Southern Anhui lies between the Cu-Au-Fe metallogenic belt along the Middle and Lower Reaches of the Yangtze River in the north and the Dexing Cu-Au ore-concentrated areas of northeastern Jiangxi in the south. Many large and medium-sized W,Mo,Cu,Au deposits have been found in this region so far. So metallogenic potential of southern Anhui is tremendous. This study aims to analyze the granitic petrogenesis,oxygen fugacity,and mineralization potential by selecting multiple small granites in study area.Results showed that there are two-episodic granites with entirely different features： the one formed in the 160 ~ 140 ± 5Ma is mainly composed of granodiorite,and maybe related to northwestward subduction of oceanic plate during Late Jurassic; the other formed in the140 ± 5 ~ 120 Ma is mainly composed of granite,syenogranite,alkali granite,and formed in a within-plate extensional setting during the Early Cretaceous. The content of trace elements in zircon showed that the granites formed during 160 ~ 140 ± 5Ma generally have higher Ce4 ＋/ Ce3 ＋value,namely the granitic magma have high oxygen fugacity; whereas the granites formed during 140 ± 5 ~ 120 Ma generally have lower Ce4 ＋/ Ce3 ＋value,indicating the magma with low oxygen fugacity. By analyzing the relationships between oxygen fugacity and mineralization,we believed that the granites formed during 160 ~ 140 ± 5Ma in southern Anhui have a good copper,gold,molybdenum prospecting potential.