The distribution of rare earth elements in iron-formations

Abstract

Many of the common iron-rich oxide, silicate, carbonate and sulphide lithological facies of iron-formation and stratafer sediments distributed throughout the geological records are interbedded or associated with facies containing economically significant amounts of Fe, Mn, Cu, Zn, Pb, Ni, Au, Ag, Sn, W, Ba, and REE. They formed in tectonic and geothermal settings conducive to prolific hydrothermal effusive activity. Analytical data from more than 2000 samples demonstrate the typical erratic distribution of more than 50 minor elements commonly found in these cherty hydrolithic sediments. Their distribution and consistent patterns in interelement relationships as shown by the correlation coefficient data for element pairs are attributed to the composition of primary constituents derived from hydrothermal sources and to hydrogenous factors in their depositional environments. Chondrite normalized analytical data for REE from more than 400 samles of oxide facies iron-formation ranging in age from Early Archean (+3 b. y.) to Recent including Proterozoic, Paleozoic, and Mesozoic units consistently show relative enrichment of the light REE and positive anomalies for Eu, features considered to be indicative of hydrothermal input to their depositional environments. The Bayan Obo iron-formation in Inner Mongolia has an exceptionally high content of REE and other hydrothermal constituents but exhibits similar interelement relationships and correlation coefficient patterns to those found in Lake Superior type iron-formations in Labrador and Quebec, and in Algoma type iron-formations from other parts of Canada.