Formula: MoS2 Hexagonal
Description: Molybdenite is a relatively common hydrothermal mineral. It is most often found in vein complexes associated with granitic igneous rocks and related skarns that form at medium to high temperatures. It is economically important as the most common mineral containing molybdenum. Several small deposits, all at present uneconomic, are known from Wisconsin.
ASHLAND COUNTY: Reported in “limestone” near Mellen, (Greensburg, 1983 referring to a 1940 report by Morris). Greenberg speculates that this could be a skarn deposit.
— Clots of molybdenite up to 2 cm. in diameter occur with other sulfides in shear zones in quarry on Quarry Road, NW NW Sec. 4 T.44N R.3W, west of Mellen (W. S. Cordua field notes).
FLORENCE COUNTY: Molybdenite occurs at the Payant-Chrissman prospect in Sec. 33 T.38N R.19E. The prospect consists of a series of 8 pits along Fisher Creek, about 4 miles south of Aurora. The molybdenite occurs as flakes up to 2.5 cm. in diameter in a granitic pegmatite and as smaller flakes in cross-cutting quartz veins. The surrounding rock is a potassium feldspar-rich schist (Fisher, 1965). Greenberg (1983) also describes this deposit, noting associated quartz, muscovite, k feldspar, biotite, garnet, tourmaline, pyrite, chalcopyrite, hematite and ferrimolybdite. The granite surrounding the veins is locally hydrothermally altered with secondary pyrite, sericite, k feldspar and quartz-lined vugs.
MARATHON COUNTY: Reported as a rare component of the pegmatites in the Wausau syenite (Morris, 1940 as reported by Greenberg, 1983).
— Found in veins cutting syenite in a roadcut behind a grocery store in Wausau in the NE 1/4 SE 1/4 Sec. 27 T.29N R.7E (LaBerge and Myers, 1983).
— Molybdenote occurs in a vein with quartz, fluorite, pyrite, cassiterite, pseudobrookite and other rare minerals cutting Nine Mile granite at the Ladick Quarry near the junction of Hwy 107 nd 153, west of Mosinee. (Buchholz, Falster, Simmons, 2007 b and c)
MARINETTE COUNTY: Molybdenite is the most important mineral found at the Camp Five Deposit in SW 1/4 NW 1/4 Sec. 18 T.33n R.20E. The deposit is approximately 4 miles NW of Middle Islet and is marked by several pits along Plumador Creek, which were worked in the late 1930’s and early 1940’s. The molybdenite occurs in quartz veins and the surrounding granitic country rock (Fisher, 1965). Greenberg (1983) describes the deposit in detail, noting that the quartz veins are nearly vertical, may be up to 4 meters wide, and trend E-NE. Molybdenite may make up 20% of the veins, associated with fluorite, pyrite and ferrimolybdite. The surrounding host granite is hydrothermal altered with secondary cataclasis and the development of secondary sericite, chlorite, epidote and calcite.
— Molybdenite is reported as coarsely crystalline material in a pegmatite found in a granite quarry near Amberg in the NW 1/4 SE 1/4 Sec. 10 T.35N R.21E (Greenberg, 1983).
WAUPACA COUNTY: Molybdenite occurs in road cuts in pegmatite cutting granite along County G near Keller Lake, NE of Big Falls. Associated minerals include euxenite-(Y), biotite, fluorite, K feldspar, bastnaesite group minerals, allanite and various sulfides (Tom Buchholz, 2002, personal communication).
WOOD COUNTY: Molybdenite occurs as masses and crude xls. up to several cm. across in granite with other sulfides at the Haske Quarry, Cary Bluffs, sec. 25, T.24N. R.2E. (Buchholz, 1999)
— Small xls. and massive molybdenite occur in granite and quartz veins in the Tork and Haeselly quarries near Wisconsin Rapids (Tom Buchholz, personal communication)
— Crystals and masses occur in granophyric granite at the Frederick Schill Quarry, near Arpin. (Tom Buchholz, personal communication)