ORIGIN OF ULTRAMAFIC-HOSTED VEIN MAGNESITE DEPOSITS

Abstract

Large deposits of magnesite (MgCO3) occur either as carbonated ultramafic rocks or as sedimentary beds. The origins of both sedimentary and ultramafic-hosted deposits remain controversial, as does the relationship between them. Ultramafic-hosted deposits are reviewed herein, with an emphasis on veins rather than massive bodies. Magnesium apparently has been supplied to magnesite veins by their ultramafic host. Uncertainties concerning ultramafic-hosted deposits include the source, state, and mode of transportation of carbon, the cause of its precipitation, and the mineralogy of the initial precipitate.