RARE-EARTH ELEMENT GEOCHEMISTRY OF BANDED IRON FORMATIONS AND ASSOCIATED AMPHIBOLITE FROM THE SARGUR BELTS, SOUTH-INDIA

Major and rare-earth elements (REE) of banded iron formations (BIFs) a nd associated amphibolite from the Sargur belts, the oldest schist bel ts in the Dharwar craton, were determined by X-ray fluorescence and in ductively coupled plasma mass spectrometry (ICP-MS). The chondrite-nor malized REE patterns of BIFs are light REE-enriched with a striking po sitive Eu anomaly, resembling those of modern hydrothermal solutions f rom the mid-oceanic ridge. Amphibolite is hat and chondritic in the RE E plot. The Al2O3/TiO2 ratio of BIFs is about the same as that of amph ibolite and is different from that of terrigenous clastics. These fact s suggest that the BIFs were of hydrothermal origin and had a genetic relation to amphibolite, which may have originated from the Archaean m id-oceanic ridge basalt. Subtle negative or no Ce anomaly of BIFs indi cates that contemporary seawater was less oxic than today. Copyright ( C) 1996 Elsevier Science Ltd