Geochemistry of Yaochang iron deposit in Henan Province and its geological implications

The Yaochang iron deposit is located in Lushan area of Henan Province and geotectonically on the southern margin of the North China Platform. Systematic chemical analyses of wall rocks and ores indicate that the banded ferrosilicic formation might have been related to marine volcanic-sedimentary volcanic rocks, and the ore deposit probably belongs to the Precambrian volcanic-sedimentary metamorphic iron deposit. The banded ferrosilicic formation can be further classified as the volcanic-intermediate acid graywacke-ferrosilicic sedimentary formation. The homogenization temperatures of fluid inclusions show a peak at 220～340 ℃ for the wall rock and 220～300 ℃ for the ore, and the ore-forming fluids have low salinity(0.88%～11.34%)and low density (0.66～0.99 g/cm3). The gas and liquid components of fluid inclusions are dominated by H2O and also characterized by the presence of some characteristic peaks of such reducing substances as H2S and CH4, suggesting a reducing environment. It is thus held that the Yaochang iron deposit underwent the ferrosilicic sedimentary deposition stage followed by further enrichment during the late regional metamorphic process. In the late stage, the metamorphic fluids from the original homogeneous metamorphic ore-forming solution resulted in immiscibility and hence the enrichment of ore-forming elements.