浙江安吉港口多金属矿床铅物质来源初探——铅同位素证据

位于浙西北安吉港口的铅锌银(钼)多金属矿床,是新近在钦杭成矿带东北缘发现的一个产于大陆环境且具较好前景的矿床.文章通过对矿区坞山关杂岩体三套岩性单元、细粒花岗岩和方铅矿铅同位素的全面对比研究,探讨了矿床的铅物源岩浆岩.矿区中的方铅矿为含较高放射性成因铅的J-型铅,在铅同位素的V1-V2和△γ-Δβ图解中,本次研究的样品分别落入华南和岩浆作用上地壳混合地幔铅范围,显示出方铅矿与华南地球化学省壳幔混合岩浆作用的密切关系.矿区铅锌矿体的方铅矿铅同位素比值显示其具有共同的物质来源,并基本保持了细粒花岗岩206Pb/204Pb值的特征,而207Pb/204Pb值具有坞山关杂岩体和细粒花岗岩混合的特征,208Pb/204Pb和208Pb/206Pb值则仅显示出与细粒花岗岩最相近.方铅矿铅同位素比值特征和比值等值线分布形式显示,铅主要来源于细粒花岗岩,杂岩体对铅成矿贡献了少量的206Pb和207Pb,矿区地层对铅成矿贡献了一定的208Pb.安吉矿区进一步针对铅的找矿工作围绕细粒花岗岩展开,取得成果的可能性更大.

A preliminary study of source of lead in Gangkou polymetallic deposit, Anji, Zhejiang Province: Lead isotope evidence

Lying in northwest Zhejiang Province,the Gangkou Pb-Zn-Ag(-Mo) polymetallic deposit in Anji is a recently discovered deposit at the northeast edge of the Qinzhou-Hangzhou metallogenic belt.Lead isotope compositions of galena grains from the deposit are all rich in radiogenic J-type lead.In V1-V2 diagram and Δγ-Δβ diagram,all the samples fall in South China geochemical province and upper crust mixed with mantle lead related to magmatism respectively.The lead isotope composition of galena has 208Pb/206Pb ratios for the fine-grained granite,208Pb/206Pb ratios for the mixing of fine-grained granite and Wushanguan complex,and the 208Pb/204Pb and 208Pb/206Pb ratios approximately for the fine-grained granite.The contour lines of lead isotope suggest that the fine-grained granite probably provided most of the lead source for galena,whereas part of 207Pb and 206Pb was from Wushanguan complex and part of 208Pb was from Cambrian Formation in the ore district.Exploration around the fine-grained granite at Gangkou in Anji might lead to further achievements.