接触交代型夕卡岩金矿床形成机理的实验研究

Experimental study on the formation mechanism of the corctact metasomatic skarn gold deposits

在深入研究安徽铜陵狮子山接触交代型白芒山和包村夕卡岩金矿床野外工作的基础上 (实验以前者为主 ) ,总结出实验地质依据。采用矿区未蚀变的辉石闪长岩和南陵湖组灰岩 ,石英闪长岩分别和南陵湖组灰岩、塔山组条带灰岩及泥灰岩作为试料 ,模拟配制 p H=5.0、 6.0、 7.0和 8.0的0 .8M Na Cl+ 0 .2 M KF+ 0 .0 5M Au Cl3水溶液作为含金热液 ,两者在高压釜中持续了 96小时的交代作用。实验结果表明 :在温度 2 65～ 650℃和 2 0 0× 1 0 5～ 80 0× 1 0 5Pa压力下的弱氧化—弱还原环境中形成了与矿区基本上相吻合的三组夕卡岩矿物共生组合 ,而金在 3 50～ 2 50℃范围内以自然金状态沉淀 ,在 3 50～ 60 0℃时 ,以少量的银金矿形式产出 ,在 60 0℃以上未见金呈独立矿物出现。

The geological basis of the experiments come from the intensive field study of the Baimangshan and Baocun skarn gold deposit of contact metasomatic type in Tongling Shizishan, Anhui. Using unaltered augite diorite with Nanlinghu Formation limestone, quartz diorite separately with Nanlinghu Formation limestone and Tashan Formation streaked limestone, marl in the mine as starting, and the solutions of 0 8 M NaCl+0 2 M KF+0 0 5M AuCl 3 with pH=5 0, 6 0, 7 0 and 8 0 as gold bearing fluids. The metasomatic reaction of them were performed in the pressure vessels for 96 hours. Experimental results show that three groups skarn mineral associations which are in accord with the associations found in the mine are formed in the slight oxidizing slight reducing environments at 265～650℃ and 200×10 5～800×10 5 Pa, and native gold is precipitated at 350～250℃ and little electrum is come out at 350～600℃, while gold is not existed as any independent minerals at more than 600℃.