White mica geochemistry of the Catheart Mountain porphyry copper deposit, Maine

White micas from hydrothermally altered and mineralized zones in the Catheart Mountain Cu-Mo porphyry deposit have regular compositional variations that are generally related to the contents of copper, total iron, and sulfur in the whole rock. Micas in unmineralized rocks exhibit no such relationship. White mica compositions reflect primarily the control imposed by the celadonitic substitution AIIV +Aiv1 =Si+ (Fe, Mg).

The variation in white mica composition in the Catheart Mountain porphyry may be explained by superposition and overprinting of mineral assemblages by ore fluids during mineralization and during the waning stages of hydrothermal alteration. Local bulk compositional differences, changing PHao and fluid compositions during mineralization, and superposition of mineral assemblages along microzoned veins contributed to variation in white mica composition. However, the general relation between white mica composition and base-metal content in the mineralized rocks at Catheart Mountain suggests that identification of this white mica population might be useful as an indicator of mineralization gradients.