湖南泥盆系成矿金属元素含量背景——兼论湖南泥盆系是否为金属矿源层

THE BACKGROUND OF ORE-FORMING METALS IN THE DEVONIAN IN HUNAN——WITH A DISCUSSION OF WHETHER THE DEVONIAN IN HUNAN IS A SOURCE BED FOR METALS

根据单一地球化学过程产生的单一地质体中元素含量趋向于正态分布的认识,对被认为是“矿源层”的湖南泥盆系中成矿金属元素的分布进行检验,剔除超差样品,求得正态母体平均值可反映沉积成岩时的含量背景,结果表明:湖南泥盆系在沉积成岩过程中没有造成铜、铅、锌、锑、金等元素的显著浓集,局部出现这些元素的高含量是由于后期叠加矿化作用造成。区域地球化学背景和稀土丰度与邻区对比也表明:泥盆纪时,湖南的区域地壳较稳定,少有深部物质卷入上地壳的沉积作用,不可能造成上述金属元素在地层中的明显浓集,不可能形成普遍的矿源层。

Based on the understanding that the element content of a single geologic body formed by a unitary geochemical process tends to be normally distributed, normality tests were made for the ore-forming metals of the Devonian strata considered as a 'source bed' in Hunan, and the odd samples far away from normal distribution were discarded and the mean of the normal population thus obtained can represent the background during diagenesis. The results show that no significant concentration of such elements as Cu, Pb, Zn, Sb and Au was produced in the Devonian in its diagenesis and that the locally occurring high contents of these elements resulted from post-diagenetic superimposition of mineralization. The regional geochemical background and a comparison of its REE abundances with those of the adjacent areas also indicate that as the regional upper continental Crust in Hunan was stable in the Devonian and very little material from the deep levels of the crust was involved in the sedimentation of the upper crust,it was impossible to create significant concentration of the above metals in the strata so as to form a source bed.