Some Geochemical Aspects of Precambrian Iron Formation

Abstract

<p>Spectrochemical analyses of rock samples of iron formation from the Archean of Ontario and Melville Peninsula reveal the generally low abundances of (1) the alkali metals (Li, Rb, Cs) in the whole rock; (2) the trace ferrides, Ga, Cu, Al and Mg in the magnetite fractions.</p> <p>In the oxide facies of iron formation there is a slight enrichment of Rb and a significant enrichment of Cs, with respect to K. Much of the Rb and Cs is trapped or adsorbed in the magnetite fraction. Lithium is concentrated in the silicate and clay fractions of the iron formation giving a positive correlation between Li and Al, reflecting the variation in physico-chemical conditions of deposition. Correlation of K/Na ratio with stratigraphic height agrees with the developMent of iron formation, in the Kirkland Lake area, as a late stage of an Archean volcanic cycle.</p> <p>The trace ferrides {Ti, V, Cr, Mn, Co, Ni} and Ga, Cu, Al and Mg are extremely depleted in the magnetite fraction, their ranges of abundances resembling those of volcanic-sedimentary iron deposits.</p>