Frederick Brewster Loomis
Boulder County [Colorado] tungsten ores
Economic Geology and the Bulletin of the Society of Economic Geologists (November 1937), 32(7):952-963

Abstract:
Ferberite, the chief tungsten mineral, occurs in (a), coarse textured, drusy veins; (b), stringers with chalcedony and cryptocrystalline quartz; and (c), breccia fragments. In (a), ferberite coats the walls, and scheelite is in the druses; in (b), ferberite likewise encrusts the walls and quartz crusts rest upon it. The medial parts are cryptocrystalline quartz and chalcedony that contain ferberite largely as mechanical inclusions. Adjacent tabular inclusions have their long axes parallel as in flow structures. These features suggest a viscous rock-silica mixture at least approximating a gel. Bursts of the mixture through the quartz-ferberite zone into the wallrock indicate moderate to high pressure in it. Presence of chalcedony and wurtzite suggests acid conditions at one mineralization stage.The breccia-like deposits have ferberite only as inclusions derived from the preceding types. Opal and minor cryptocrystalline quartz are the only depositions. The fragments include quartz, potash feldspars, and muscovite, but are chiefly sericite and minerals of the montmorillonite-beidellite-nontronite series. These associated minerals and the general structure of the mass suggest that the deposit formed in the upper part of a hot spring channel.