The carbonatites and fenites of Chipman Lake, Ontario

Abstract

Simple and composite dikes of dolomitic and ankeritic carbonatite, up to one meter thick, cut and fenitize Archean country rocks around Chipman Lake, Ontario. The carbonate compositions define a complete series from dolomite to ankerite, and coexist with calcite. Cathodoluminescence studies indicate an early dolomitic phase brecciated by later ankeritic carbonate. DropJike inclusions of burbankite within the dolomite are taken as evidence for an early Na-rich fluid or immiscible liquid. Compositional data are given for burbankite and other phases in the carbonatite, including synchysite, parisite, bastnasite, norsethite, barytocalcite (alstonite?), strontianite, apatite, strontian apatite, monazite and F-rich phlogopite. The fenites comprise Na- and K-rich feldspars, magnesio-arfvedsonite and aegirine, with phlogopite particularly concentrated along carbonatite contacts. The evolution of the carbonatite liquid from magnesian to more iron-rich compositions paralleled a decrease in the Na:K ratio, which was responsible for early fenitization of a predominantly sodic character changing later to potassium fenitization.