NOBLE METALS IN RECENT AND ANCIENT PHOSPHORITES

Abstract

Noble metals (except Ag) in phosphorites are less studied than many other rare and trace elements. High Ag contents (4 g/t) were first reported from Missourian (Carboniferous) phosphorites in Alaska. Subsequently, different contents of Au (<0.4–7 g/t) were detected in many of the world’s Precambrian–Miocene phosphorite deposits, including Russia and the CIS. For example, the Ag content is 1 g/t in Precambrian Tomalyk phosphorites and ~2 g/t in Cretaceous–Paleogene phosphorites of the Ukraine [4]. Generalization of data on 15 regions of the world showed that the average Ag content in phosphorites is 2 g/t, which is approximately 30 times higher than the average content in sedimentary rocks.