Colloform magnetite in a contact metasomatic iron deposit, Vancouver Island, British Columbia

Abstract

Colloform magnetite has recently been found in the magnetite orebodies on the Empire Development property at the northern end of Vancouver Island, British Columbia. Magnetite with colloform habit is very unusual and none, as far as the writers know, has been described from limestone. The colloform magnetite occurs as pockets of nodular masses within pipe-like orebodies of predominately coarsely crystalline magnetite in limestone close to a diorite stock. The magnetite is associated with typical skarn minerals.The colloform magnetite possesses all the textural features ascribed to deposition through colloidal processes, and the deposits appear to have been formed by gel metasomatism of limestone. The writers conclude that the iron for the colloform magnetite was carried in HCl solution, replaced the limestone, and was precipitated as a colloid during an intermediate state of aggregation that existed between the state of ionic solution and the precipitate.