早前寒武纪硫铁矿矿床Fe同位素特征及其地质意义——以山东石河庄和河北大川为例

Fe isotope characteristics of early Precambrian pyrite deposits and their geological significance:examples from Shandong and Hebei Provinces

报道了山东石河庄和河北大川地区前寒武纪层状硫化物矿床中黄铁矿单矿物的Fe同位素组成。相对于标准物质IRMM-014,大川黄铁矿的ε57Fe为-38.8^-13.1,石河庄黄铁矿的5ε7Fe为-39.4^-15.1,表明形成这两个层状硫化物矿床的新元古代海水富集Fe的轻同位素。世界不同地区新太古代黑色页岩中的黄铁矿的Fe同位素组成与华北两个硫铁矿矿床的Fe同位素特征基本一致,暗示新太古代海洋富集Fe的轻同位素可能是全球现象。导致早前寒武纪海洋富集Fe轻同位素的原因是海水中大量的Fe被氧化形成了富集Fe重同位素的磁铁矿和赤铁矿。

Reported in this paper are Fe isotope compositions of pyrites from Neo-Archean stratiform sulfide deposits, North China. Relative to IRMM-014, all pyrites analysed show light Fe isotope enrichment, with variations of -38.8～-13.1 ε^57Fe units for those from Hebei, and -39.4～-15.1 ε^57Fe units for those from Shandong. The results suggest that the Neo-Archean seawater where these sulfides originated are enriched in light Fe isotopes. As pyrites from Archean black shales worldwide show similar Fe iso- tope features to those from the two Chinese sulfide deposits, the enrichment of light Fe isotopes in early Precambrian ocean is likely to be regional, or even global. This is resulted from the prolonged and large-scale precipitation of iron oxides which show light Fe isotope depletion.