Paragenesis of clinohumite and associated minerals from Wolf Creek, Montana¹

The Wolf Creek ultramafic pluton, in the southern Ruby Mountains in southwestern Montana, intrudes Prebeltian metamorphic rocks and is itself late Prebeltian in age. It consists chiefly of coarse-grained harzburgite which has been partly altered, chiefly to serpentinite, anthophyllite rock, actinolite rock and clmohumite-bearing rock. Along the contacts the wall rocks have undergone extensive exomorphic changes that include various recrystallizations and the formation of metasomatic actinolite and anthophyllite.

The sequence of replacement minerals involves progressive linkage of SiO₄ tetrahedra in the series: clinohumite, anthophyllite, actinolite and chlorite, serpentine and laic. It is concluded that crystallization of the peridotite was accompanied and closely followed by the two types of wall-rock changes and that the solutions producing the wall-rock metasomatism effected similar reactions locally within the peridotite itself.