The phosphate, volcanic and carbonate rocks of Christmas Island (Indian Ocean)

Abstract

Abstract Christmas Island consists of an interbedded sequence of volcanic and carbonate rocks, mainly of Eocene and Miocene age. The volcanic rocks are successively more basic, varying from andesite to limburgite. The carbonate rocks are limestones and dolomites and are mainly of the reef‐wall and lagoonal facies. The phosphate deposits consist of three main mineral groups: apatite, barrandite and crandallite‐millisite. They are essentially superficial. Apatite occurs on irregular karrenfelder of carbonate rock and as secondary replacement deposits. Barrandite has formed by the supergene replacement of volcanic rocks. Crandallite and millisite occur in the lateritic profiles derived from apatite and barrandite and the weathering, in the presence of phosphate, of the carbonate and volcanic rocks.