Low-K granophyres of the Stillwater Complex, Montana

Small bodies of granophyre occur as a volumetrically insignificant but ubiquitous component of the Banded series of the Stillwater Complex. White to pink granophyre typically occurs as veins, 1-12cm thick and as much as 100m long. A geochemically similar body of coalescing alaskite dikes, associated with an occurrence of Pt-group elements in the Banded series of the complex, crops out approximately 2km south-southeast of Picket Pin Mountain over an area 130 by 210m. Considering host rocks and chemistry, these rocks are comparable to the most siliceous examples of oceanic plagiogranite. The Stillwater granophyres, however, are enriched in Si, Th, U, and LREEs, and depleted in K, Fe, and Eu, relative to oceanic granophyres. -from Authors