甘肃西成铅锌矿田铅同位素地球化学成矿信息

METALLOGENETIC INFORMATION ON THE LEAD ISOTOPICGEOCHEMISTRY OF THE XICHENG LEAD-ZINCOREFIELD, GANSU PROVINCE

甘肃西成铅锌矿田含有沉积—变质热液弱改造型和沉积—动力构造分异热液强改造型两类泥盆系层控铅锌矿床。对该矿田系统的铅同位素地球化学研究结果表明:(1)两类主要矿床的铅同位素组成有所不同。例如,沉积—变质热液弱改造型矿床的铅同位素组成变化相对较稳定;(2)矿床的铅平均单阶段模式年龄均不代表成矿年龄,而只反映铅质源区岩石的形成时代;(3)成矿金属物质主要取自下伏区域基底地层,而与含矿层和岩体无关;(4)成矿物质源区构造环境主要为造山带(岛弧),这种地质构造环境有利于富含金属热卤水的活动和成矿物质的富集成矿。

: The Devonian stratabound lead-zinc deposits can be genetically divided into metamorphic hy-drothermal weakly reworked and dynamo-differential hydrothermal strongly reworked sedimentary stratabound deposits in the Xicheng lead-zinc orefield, Gansu. Through the systematically geochemi-cal studies of the lead isotopic compositions of this orefield, the following conclusions have been reached: (1) There are some differences in the lead isotopic composition of the two kinds deposits. For example, the compositions of the metamorphic hydrothermal weakly reworked sedimentary deposits are more stable than those of the another kind of deposits. (2)The average single-stage model ages of the both kinds of deposits reflect only that of the forming source-rocks but not that of the metallogenic ages. (3)The ore-forming metals are mainly derived from the areal basement strata and they are unrelated with the ore-bearing strata and the intrusive rocks. (4)The tectonic environment of the source material showing by the isotopic field was mainly of the orogenic (island) environment which would be favourable for the activities of heavy metal-rich brines and the concentration of ore-forming materials.