安徽宣城茶亭斑岩铜金矿床金的赋存状态及金铜成因联系

Modes of occurrence of gold and genetic connection between gold and copper in the ores from the Chating porphyry copper-gold deposit, Xuancheng City,Anhui Province

安徽宣城茶亭铜金矿床是长江中下游成矿带中新发现的一个大型斑岩型矿床。本文在矿相学观察和研究的基础上,开展了矿石组成矿物的成矿金属元素化学分析和电子探针(EPMA)分析,以了解矿床矿石中金的赋存状态,确定金与铜的成因联系。茶亭铜金矿床的热液成矿期可以划分为4个阶段,应用单矿物火试金法化学分析显示,第2阶段黄铁矿(Py II)和第3阶段黄铁矿(Py III)以及相应阶段的黄铜矿均富含金,各阶段石英及第3阶段硬石膏基本不含金。矿相学观察发现"可见金",金的嵌布形式主要为包裹金、粒间金,少量裂隙金。电子探针分析表明这些"可见金"主要为银金矿,其次为自然金。"不可见金"以不均匀形式分布于黄铜矿、黄铁矿、闪锌矿、斑铜矿等硫化物矿物中,"不可见金"主要为纳米级自然金。金与铜的相关性以及金的赋存状态表明,金与铜具有密切的成因联系。Simon实验研究结果表明高温环境下铜-铁硫化物中Au的溶解度更大,结合矿物共生组合及流体包裹体均一温度测定结果可以推测,茶亭铜金矿床的成矿作用经历了从较高温度到较低温度的演化过程,随着温度的降低部分Au从铜-铁硫化物中出溶并富集为"可见金",而另一部分金仍然以"不可见金"形式分散保存于黄铜矿、黄铁矿、闪锌矿以及其它含铜硫化物矿物中。

The Chating copper-gold deposit in Xuancheng City of Anhui Province is a large porphyry deposit newly discovered in the middle and lower reaches of the Yangtze River metallogenic belt. Based on detailed ore mineragraphic research, the authors carried out the measurement of ore-forming element concentrations of main minerals from the ores by EMPA and chemical analysis, with the purpose of studying the modes of occurrence of gold and the genetic connection between gold and copper in this deposit. The hydrothermal mineralization period of the Chating copper-gold deposit was divided into 4 stages. The fire assay analysis results of single mineral show that the pyrites at the second stage（ Py II）, the pyrites at the third stage（ Py III） and the chalcopyrites at these two stages are rich in gold, whereas the quartzs at all stages and anhydrites at the third stage contain almost no gold. ＂ Visible gold＂was found in the ores and they are mainly embedded as inclusion gold and interparticle gold, with a small amount of fissure gold. The major minerals of the ＂visible gold＂ are electrum, followed by native gold. ＂Invisible gold＂ is distributed unregularly in the sulfide minerals such as chalcopyrite, pyrite, sphalerite and bornite. And the ＂invisible gold＂ exhibits nanoparticle native gold in pyrite. The correlation between gold and copper and the modes of occurrence of gold show that gold and copper have a close genetic connection. Simon＇s experimental study reveals that the solubility of Au in Cu-Fe sulfide is very high at high temperature. The mineralization of the Chating copper-gold deposit underwent the evolution from high temperature to low temperature. As the temperature decreased, part of gold was exsolved from Cu-Fe sulfides and became enriched as ＂visible gold＂; while the other part remained in the form of ＂invisible gold＂ preserved in chalcopyrite, pyrite, sphalerite and other copper-bearing sulfide minerals.