闽中丁家山铅锌矿床同位素地球化学及其地质意义

Isotope geochemistry of Dingjiashan Pb-Zn deposit in central Fujian Province and its geological significance

通过铅、硫、铷、锶同位素地球化学特征的系统分析,对闽中丁家山铅锌矿床的成矿物质来源、成矿时代及矿床成因进行了深入研究。围岩全岩及矿石内方铅矿的Pb同位素变化范围较宽,方铅矿的^206Pb/^204Pb比值在18.182-18.605之间,^207Pb/^204Pb比值在15.010-15.932之间,^208Pb/^204Pb比值在38.331-39.666之间,具有明显的壳-幔混合来源特征,可能由龙北溪组地层和燕山期重熔型花岗岩共同提供。黄铁矿、磁黄铁矿、闪锌矿、方铅矿的δ34S组成为-1.7‰-5.6‰,平均值为2.7‰,具有向正值偏移的塔式分布特征;系统δ34S初始值为3.97‰,深源硫特征明显,说明硫由燕山期重熔型花岗岩提供。成矿期的石英铷-锶等时线年龄为（146.15±3.95）Ma,成矿时间属燕山早期第三阶段。以上结果进一步证实,丁家山铅锌矿床为马面山群龙北溪组上段经区域变质的富钙质沉积岩与燕山期重熔型花岗岩发生接触交代作用,形成的矽卡岩型矿床。

Based on a systematic study of Pb,S,Rb and Sr isotope geochemistry,this paper deals with the sources of ore-forming materials,metallogenic epoch and genetic type of the Dingjiashan Pb-Zn ore district in Fujian Province.The ^206Pb/204Pb,^207Pb/^204Pb and^208Pb/^204Pb ratios are 18.182-18.605,15.010-15.932,and 38.331-39.666 respectively.The wide ranges of Pb isotopes indicate that Pb was derived from the mantle and the crust.Neoproterozoic Mamianshan Formation of Longbeixi Group and Yanshanian remelted granite might have jointly served as the sources.Theδ34S values of pyrite,pyrrhotite,sphalerite,galena are-1.7‰ - 5.6‰,2.7‰on average,characterized by tower-shaped distribution shifting to the positive value.Theδ34S initial value of the metallogenic system is 3.97‰,obviously suggesting deep-sourced sulfur characteristics. These data imply that sulfur was supplied by Yanshanian remelted granite.Rb-Sr isochron of quartz reveals that the ore-forming processoccurred at（146.15±3.95）Ma,in late Jurassic period,belonging to the third stage ofearly Yanshanian.It is thus held that the Dingjiashan Pb-Zn ore district is a skarn ore deposit resulting from the contact metasomatism between the Yanshanian remelted granite and the regional metamorphosed calcareous rock in Longbeixi Formation of Mamianshan Group.