Abstract
The Newania carbonatitic rocks (NCB), exposed as NW-trending, isolated linear bodies within Archean granitoids, are comprised mainly of Mg- and Fe-carbonate phases and volumetrically negligible Ca carbonate. The magmatic Mg-carbonatite shows partial metasomatic replacement by iron-rich solutions channelized along fractures. The C- and 0-isotopic compositions further document the magmatic lineage of the Mg-carbonatite (δ13CPDB = −4.0 to −5.9% and δ18 OSMOW = + 8.2 to 11.5%, barring one sample characterized by a high value of +25.6%). In contrast, the presumed ankeritic (Fe) and sovitic (Ca) carbonatites appear to be the result of metasomatism and hydrothermal activity, as indicated by corresponding enrichment in the heavier isotopes. The “atypical carbonatites” of Nayaphala, occurring as NW-trending dikes and veins of variable width (south of and colinear with the Newania trend), are nonmagmatic, and can be described as tectonic breccias. A nonmagmatic source for Nayaphala carbonates also is supported by the corresponding enrichment in the heavier C and O isotopes.
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