黔西北铅锌成矿区成矿金属来源的铅同位素示踪

The Origin of Ore-forming Metals in Northwestern Guizhou Pb-Zn Metallogenic District Constrained by Pb Isotopes

黔西北铅锌成矿区是川滇黔铅锌成矿省的重要组成部分,已发现中—小型矿床（点）100余处,它们的分布严格受到区域性构造的控制。在系统收集前人资料的基础上,对黔西北铅锌矿床成矿流体中的金属来源进行了深入的探讨。矿石的206Pb/204Pb为18.439~18.729（均值18.563,n=25）,207Pb/204Pb为15.681~15.887（均值15.748,n=25）和208Pb/204Pb为38.885~39.522（均值39.112,n=25）;黄铁矿的206Pb/204Pb为18.280~18.768（均值18.571,n=10）,207Pb/204Pb为15.677~15.920（均值15.737,n=10）和208Pb/204Pb为38.609~39.144（均值38.940,n=10）;闪锌矿的206Pb/204Pb为18.029~18.726（均值18.448,n=34）,207Pb/204Pb为15.505~15.825（均值15.689,n=34）和208Pb/204Pb为38.145~39.455（均值38.772,n=34）;方铅矿的206Pb/204Pb为18.062~19.900（均值18.536,n=83）,207Pb/204Pb为15.440~16.334（均值15.717,n=83）和208Pb/204Pb为38.004~40.695（均值39.022,n=83）。矿石全岩与硫化物单矿物具有相似的Pb同位素组成,表明脉石矿物对矿石全岩没有明显的Pb同位素影响,矿石全岩和金属硫化物Pb同位素所指示的物源信息均能反映成矿流体中金属的来源。经与地壳、地幔和造山带及峨眉山玄武岩、赋矿沉积岩和基底岩石Pb同位素组成特征对比,发现黔西北铅锌矿床成矿流体中的金属具有混合来源特征,主要来自赋矿地层沉积岩和基底岩石。综合分析认为,黔西北铅锌矿床成矿流体中的金属是由循环的盆地卤水活化、淋滤流经地层（包括基底和赋矿地层）岩石所得。

The NW Guizhou Pb-Zn metallogenic district is an important part of the Sichuan-Yunnan-Guizhou Pb-Zn metallogenic province in the western Yangtze Block, southwest China. In this district, more than 100 Pb-Zn deposits（spots） have been found so far. Base on the previous research achievements, this paper deeply discusses the origin of ore-forming metals. The 206Pb/204 Pb, 207Pb/204 Pb and 208Pb/204 Pb ratios of ore whole-rock samples range from 18.439 to 18.729（average 18.563, n=25）, 15.681 to 15.887（average 15.748, n=25） and 38.885 to 39.522（average 39.112, n=25）, respectively; Pyrite samples have 206Pb/204 Pb, 207Pb/204 Pb and 208Pb/204 Pb ratios ranging from 18.280 to 18.768（mean 18.571, n=10）, 15.677 to 15.920（mean 15.737, n=10） and 38.609 to 39.144（mean 38.940, n=10）, respectively; The 206Pb/204 Pb, 207Pb/204 Pb and 208Pb/204 Pb ratios of sphalerite samples range from 18.029 to 18.726（average 18.448, n=34）, 15.505 to 15.825（average 15.689, n=34） and 38.145 to 39.455（average 38.772, n=34）, respectively; and Galena samples have 206Pb/204 Pb rations ranging from 18.062 to 19.900（mean 18.536, n=83）, 207Pb/204 Pb ratios ranging from 15.440 to 16.334（mean 15.717, n=83） and 208Pb/204 Pb ratios ranging from 38.004 to 40.695（mean 39.022, n=83）. The Pb isotopic compositions of ore whole-rock samples are similar to those of sulfide mineral samples, suggesting that the Pb isotopes of gangue minerals don＇t have obviously effect on that of ore whole-rock and all the Pb isotopes of ore whole-rock and sulfide minerals can trace the origin of ore-forming metals. Compared with the Pb isotopes of ore whole-rock and sulfide mineral samples with those of the crust, mantle and orogenic belt, and Emeishan basalts, ore-hosting sedimentary rocks and basement rocks, the ore whole-rock and sulfide mineral samples have similar Pb isotopic compositions to those of the hosting rocks and basements, suggesting that the ore-forming metals have mixed sources. We propose that the ore-forming metals in northwestern Guizhou Pb-Zn metallogenic district were derived from the strata（basements and hosting rocks） that flowed through by the ore-forming fluids.