秦岭凤-太矿田与柞-山矿田成矿条件及环境的对比研究

A COMPARATIVE STUDY OF ORE FORMING ENVIRONMENTS AND CONDITIONS IN FENG TAI AND ZHA SHAN OREFIELDS,QINLING MOUNTAINS

凤－太矿田和柞－山矿田分别位于秦岭泥盆系层状多金属成矿带的中段和东段。凤－太矿田主要容矿岩石为硅质岩，其δ３０Ｓｉ、δ１８Ｏ分别为－０．６‰～－０．３‰；１８．６‰～２１．０‰。矿床的δ３４Ｓ值大部分位于４．９‰～１１．３‰之间。柞－山矿田容矿岩石类型复杂，除硅质岩外尚有钠长石岩、黑云方柱石岩等，Ｎａ、Ｃｌ含量很高。容矿硅质岩的δ３０Ｓｉ、δ１８Ｏ分别为－０．２‰～０．１‰、１９．０‰～１９．６‰。矿床的δ３４Ｓ多为高正值，变化范围大，－３．５‰～３３．７‰。文中指出两个矿田的矿床均由海底喷气作用形成，其中凤－太矿田形成于半封闭－半开放的环境，成矿温度低（约９２℃），矿质堆积速度较慢；而柞－山矿田成矿早中期为一封闭海盆，晚期变为开放；成矿温度、矿质堆积速度相对较高；

Silicon,oxygen and sulfur stable isotope compositions and their variation regularity in Devonian stratiform Pb Zn deposits of Feng Tai and Zha Shan orefields are studied in this paper. δ 30 Si values and δ 18 O values of ore bearing siliceous rocks in the Feng Tai orefield range form-0 6‰ to -0 3‰ and from 18 6‰ to 21 0‰ respectively.Similar to δ 30 Si and δ 18 O of siliceous rocks formed in hot spring and by submarine exhalition, δ 30 Si and δ 18 O of the siliceous rocks in the Feng Tai orefield indicate a submarine exhalation origin. δ 30 Si values of the ore quartz veins are the same as those of ore bearing siliceous rocks,suggesting that the ore quartz veins were formed as a result of remobilization and recrystallization of siliceous rocks. δ 30 Si and δ 18 O of the ore bearing siliceous rocks in the Zha Shan orefield range from -0 2‰ to 0 1‰ and from 19 0‰ to 19 6‰ respectively.The authors consider that the ore deposits in the Zha Shan ore field were also formed by submarine exhalation,with however higher ore forming temperature and deposition speed than those in the Feng Tai orefield. δ 34 S values of the principal orebodies are mostly 10‰～30‰; δ 34 S values of barite in the ore deposit are even higher,ranging 22 3‰～33 7‰.Nevertheless,some small lead orebodies above the principal orebodies have relatively low δ 34 S values(-3 5‰～4 0‰,0 6‰ on the average).It is pointed out in the paper that sulfur in the ore deposits was exclusively derived from sulfates in sea water,and that the Zha Shan basin was turned from an enclosed basin at the early(principal)ore forming stage into an open basin at the late ore forming stage. δ 34 S values of ore deposits in the Feng Tai orefield are somewhat lower(4 9‰～11 3‰),implying a semi open to semi closed basin.