Hart Mountain

Short, thick flows and intrusions of pantellerite, up to 1.6 km long and 100 m or so wide, occur on the flanks of Hart Mountain. Commonly the flows are strongly flow banded and locally autobrecciated. The rocks contain abundant phenocrysts of alkali feldspar, rather few of green diopsidic pyroxene with deeper green rims, and rare phenocrysts of quartz and somewhat altered amphibole. The groundmass comprises quartz, alkali feldspar, aegirine, a riebeckitic amphibole and an unidentified pleochroic brown mineral, probably a member of the aenigmatite group. Chemical data, including Sr isotopic ratios, are given by Noble et al. (1974).
Pantellerites also occur at Deep Creek, south east of Crane Mountain, which is some 45 km southwest of Hart Mountain. Petrographically they differ from the Hart Mountain pantellerites in containing sanidine phenocrysts, while quartz, oxyamphibole and aenigmatite are more abundant, whereas diopsidic pyroxene and aegirine are rare or lacking.