Formula: (Ce, Ca, Y)2Nb2O6(OH,F) Isometric
Description: Pyrochlore is a group of rare minerals found in pegmatitic granites, syenites, and carbonatites.
MARATHON COUNTY: Pyrochlore group mineral can be found as tiny grains in the Stettin Pluton and Nine-Mile Granite in the Wausau area. Numerous locations, many as ephemeral construction sites, are reported in Buchholz, Falster, and Simmons (2009).
— Octahedral ceriopyrochlore crystals up to 3 mm in diameter were found in a pegmatite dike in the SW NW sec. 22 T.29N. R.6E. This material was originally described as “marignacite.” The crystals were light to yellow brown. Associated minerals were lithium-rich mica, quartz, K feldspar, fluorite, rutile, aegirine, riebeckite, and zircon (Weidman and Lenher, 1907). Small yellow ceriopyrochlore crystals still are found in the dumps at the nearby old thorium mine (Buchholz, 1994, personal communication).
— A pyrochlore group mineral is found at the Ladick Quarry (sec. 19 and 20 T. 27N. R.6E) (Buchholz Falster, and Simmons, 2002).
— A pyrochlore group mineral was tentatively identifed at the Koss Pit, a “rotten granite” quarry several miles west of Wausau (SW sec. 2 T27N R.5E) (Buchholz, Falster, and Simmons, 2000).
— A pyrochlore group mineral was identifed at the Red Rock North Pit, a “rotten granite” quarry along Spring Brook road west of Wausau (Buchholz , Falster, and Simmons, 2009).
— Tiny grains of uranpyrochlore have been found at the Wimmer #3 “rotten granite” quarry SW of Rib Mountain (Buchholz, Falster, and Simmons, 2009).
— A material identified as plumbopyrochlore was found as tiny grains intergrown with ferrocolumbite in the Maguire Pit, part of the LaDick East quarry complex east of Wausau. (Buchholz et al. , 2005a)
— Pyrochlore group minerals were found when 2011 road construction in Stettin township revealed several small vuggy pegmatites. Anorthoclase, microcline and albite are the main rock forming minerals. Associated minerals are zircon, columbite-(Fe), Ilmenite, brookite, cassiterite, pyrite, arsenopyrite, and fluorite. ( Buchholz, Falster and Simmons, 2012)