Abstract:

The Wangjiazhuang iron deposit in Shanxi Province is a typical case of banded iron formation in the Wutaishan area. The orebearing rock is magnetitequartzite, with wall rocks mainly being amphibolite, amphibolemetadolerite and quartz schist. Through the restoration of the metamorphic rocks, we conclude that the protolith are principally volcanic rocks. The volcanic rocks in the area evolved from the tholeiite series to the calcalkaline series, along with some terrestrial clastics. The negative anomalies of HFSE, high contents of LILE and a low ratio of Y/Nb show that this area was in an islandarc and active continental margin tectonic setting. REE patterns of the magnetitequartzite demonstrate a right inclined curve with slightly LREE enrichment. Eu shows a slightly positive anomaly and Ce shows a slightly negative anomaly. This REE characteristics show that BIF was formed in a typical marine environment. It is predicted that hightemperature hydrothermal fluids created during oceanic crust subduction in the Neoarchean played a considerable role in the formation of BIF. The slightly Eu positive anomaly suggests that the volcanic activity of the area was weak, so hightemperature hydrothermal fluids in the bottom of the ocean played a minor role. The correlatability between BIF and its wall rocks in the primitive mantlenormalized incompatible element spider diagrams suggests that they have the same or similar material source and diagenetic environment, as well as belonging to a same depositional basin, but with different deposition processes and conditions, respectively.

Key words: banded iron formation, Wangjiazhuang iron deposit, trace element, rare earth element, metavolcanite, Shanxi