Formula: Fe1-xS Monoclinic
Description: Pyrrhotite is found in a wide range of hydrothermal deposits. It is often associated with mafic intrusive and volcanic rocks. It is found in massive sulfide deposits associated with pyrite, sphalerite, galena and chalcopyrite. At times it is intergrown with rare nickel minerals such as pentlandite.
FLORENCE COUNTY: Pyrrohotite is found associated with pyrite in several horizons in metasedimentary rocks recovered from drill core from the Bass Lake area, T.38N. R.17E.
— Pyrrhotite is found associated with fluorite locally in granite in section 7 T.38N. R.20E. Pyrrhotite is also reported from sec. 19 and 30 T.38N. R.19E. and sec. 27 T.39N. R.18E. (Dutton and Bradley, 1970).
FOREST COUNTY: Anhedral pyrrhotite occurs rarely in the massive sulfide zone and more commonly in the associated graphitic argillites in the Crandon deposit, near Little Sand Lake (Lambe and Rowe, 1989).
IOWA COUNTY: Pyrrhotite was reported with pyrite and sphalerite from the Grey Property near Mineral Point (Heyl et al., 1959).
MARINETTE COUNTY: Pyrrhotite is a major sulfide mineral at the Duval massive sulfide deposit, sec. 2 and 3 T.35N. R.18E. and sec. 28 T.36N. R.18E. Here it occurs intergrown with pyrite, sphalerite and chalcopyrite in a magnetite-grunerite iron formation. An estimated 10 million tons of sulfide ore exist in this deposit (Hollister and Cummings, 1982).
— Pyrrhotite occurs with chalcopyrite in the outcrop at Pine Rapids (AKA “LaSalle Falls”) NW SE sec. 30 T.39N. R.18E. (Schulz and LaBerge, 2003).
OCONTO COUNTY: Massive pyrrhotite is found as vein material within a gabbroic dike near Mountain Post Office (NE sec. 13 T.31N. R.16E.) The pyrrhotite is bronzy, iridescent and strongly magnetic. Analyses show it to be devoid of any nickel minerals. Prospects were dug in a vein, which was traced 8 feet below the surface, where it opened into a zone 41 feet wide. (Bagg, 1913). Lahr (1972) notes the mineralÕs localization along the contact between the basal and middle members of the Waupee Formation. The basal member consists of metamorphosed massive lava flows and volcanoclastic sediments. The middle member is mostly metamorphosed sandstone. Dutton and Bradley (1970) report pyrrhotite as occurring nearby in sec. 6, 11, 12 and 18 T.31N. R.17E.
ONEIDA COUNTY: Pyrrhotite is found in the Pelican massive sulfide deposit east of Rhinelander (sec. 29 T.36N. R.9E.). It is particularly common in the footwall stockwork zone where it is associated with chalcopyrite, pyrite and magnetite. The pyrrhotite apparently formed during the metamorphism of the deposit (Mudrey, 1979).
— Pyrrhotite is common at the Lynn massive sulfide deposit where it occurs with sphalerite, galena, chalcopyrite, silver and gold minerals (Kennedy, 1993).
— Significant pyrrhotite occurs in sec. 30 T.36N. R.11E. (Dutton and Bradley, 1970).
PRICE COUNTY: Pyrrhotite is a major component of the Ritchie Creek massive sulfide deposit (De Matties, 1990).
RUSK COUNTY: Pyrrhotite is a minor component of the massive sulfide ore at the Flambeau Mine, near Ladysmith. (May, 1977). Pyrrhotite is a major component of the Eisenbrey massive sulfide deposit north of Ladysmith ( NW sec. 17 T.35N. R.6W). It occurs intergrown with pyrite, chalcopyrite and sphalerite (May, 1996).
WOOD COUNTY: Small bronzy to silvery magnetic xls. tentatively identified as pyrrhotite occur in vugs in veins cutting granite at the Frederick Schill Quarry, NE of Vesper on the east side of Hwy. 186 (Buchholz, 1999)
— Pyrrhotite occurs masses along as fillings in miarolitic cavities in granite at the Haske Quarry, sec. 25, T24N R2E. (Tom Buchholz, et al., 1998.).