Primary, Bedded, Structureless Phosphorite of the Khubsugul Basin, Mongolia

Abstract

ABSTRACT A phosphatic series of Upper Vendian (Proterozoic) to Lower Cambrian age occurs in the Khubsugul Basin, Mongolia. Unweathered, bedded, aphanitic, structureless phosphorite (microsphorite) is relatively abundant in these phosphorites. Its orthochemical precipitation in shallow water on the inner portion of the Siberian continental shelf of latest Precambrian to Early Cambrian time is established from stratigraphic and petrographic considerations. The microsphorite was the parent material for other petrographic types of phosphorite, which formed both by disintegration of the microsphorite to give intraformational conglomerate and breccia and by granulation of the microsphorite to give granular and pelletal phosphoritc. Although disintegration and granulation were due to a higher energy nvironment, little transportation of grains occurred. Dolomitization of matrix apatite was a significant part of the process of granulation. These various types of phosphorite are intimately interbedded in the lower of two phosphate units.