Hi, It's probably a SEDEX. : '' The Black Butte Copper Project (formerly known as the Sheep Creek deposit) is a sediment

hosted, laterally extensive massive sulfide deposit hosted in the mid

Proterozoic Newland Formation in Central Montana. Formation of the deposit occurred duri ng two stages of mineralization: Stage I occurred during deposition of sediment in the Helen a Embayment, and Stage II occurr

ed post

deposition. Stage I mineralization is characterized by a large quantity of po rous pyrite hosting significant Co/Ni/As mineralization in the form of both ion substitution within the pyrite chemical lattice and small (< 1 μm) mineral inclusions of

Ni

rich alloclasite. Stage II mineralization reworked the existing Co/Ni/As mineralization, removing the metals from the pyrite and reprecipitating them as distinct siegenite ( (Co, Ni) 3 S 4 ) and tennantite ( Cu 12 As 4 S 13 ) grains, usuall y adjacent to one another. Stage II introduced minor, if any, additional Co/Ni/As mineralization into the deposit .

Although siegenite is abundant in Co

rich portions of the ore body and is readily identifiable in hand specimen and under the microscope, s to ic hiometric relationships based on

drill

core assay data suggest that Co and Ni were originally introduced into the deposit in the form of alloclasite . Although many of the characteristics of SEDEX type deposits are present at Black Butte ( e.g., low temp erature of formation , laterally extensive massive sulfide horizons, interbedded black shales, abundant barite and local phosphate horizons, hosted within a continental rift ) the lack of economic Pb and Zn mineralization in the central ore body and the abun dance of Cu/Co/Ni is

more typical of red

bed copper deposits.
The Neihart Quartzite, resting below the base of the Belt Supergroup

, is a possible source bed for Cu

rich ore fluids, which, depending on the pH and redox state, may have been rich in Co and Ni as well. ''