New production in the Idaho Cobalt Belt: A unique metallogenic province

Abstract

The Idaho Cobalt Belt (ICB) is a unique example of sea-floor hydrothermal brines that vented along an ancient rift within a deep-water setting, providing for an interesting and distinctive geochemistry. The ICB is a northwest-trending zone of Co-Cu-Au occurrences, at least 64 km long and up to 10 km wide, centred on the Blackbird mine. It is an exceptional metallogenic province in which cobalt occurs in sufficiently high concentrations to make it the primary metal in the deposits. The deposits are mostly strata-bound and appear to have formed during a mafic volcanogenic-exhalative mineralizing event on a palaeo-sea-floor ca 1600 m.y. ago. Regional metamorphic events have remobilized Cu and, to a lesser extent, Co in varying degrees throughout the belt. The deposits are unusually rich in Co, Cu, Fe, As, Au, B, Bi and light rare earths, but low in Ni (relative to Co), Ag, Pb, and Zn. The synsedimentary controls, mineralogy and geochemistry are unusual among ore deposits, though similar features in some other deposits are known. Sediment-hosted deposits are major ore producers in the world, but most tend to be Pb- and Zn-rich. Some sediment-hosted deposits that contain Cu also contain Co—notably, the deposits of the Zambian Copperbelt. Significant differences exist between deposits in the Zambian Copperbelt and the ICB, whereas many intriguing similarities are found between ICB deposits and Sullivan, Canada, and Mount Isa and Broken Hill, Australia.

The ICB is currently known to host 18 Co-Cu deposits within eight sequences of metamorphosed, mafic volcaniclastic rocks. Additional exploration is expected to discover more deposits as only a small portion of the belt has undergone systematic exploration. Formation Capital's Idaho cobalt project encircles the inactive Blackbird mine and encompasses the Ram and Sunshine deposits as well as more than 30 prospects and six deposits. The project's total resource base exceeds 5 000 000 t in four deposits, all of which remain open in at least two directions. To date, only two of the deposits have been included in pre-feasibility studies—Ram and Sunshine. The project is in the final feasibility, permitting and pre-development phase.

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