MODEL 15a
By Dennis P. Cox and William C. Bagby
APPROXIMATE SYNONYM Quartz-wolframite veins (Kelly and Rye, 1979).
DESCRIPTION Wolframite, molybdenite, and minor base-metal sulfides in quartz veins (see fig. 39).
Figure 39. Maps and sections of W vein deposits illustrating mineral and alteration zoning. A, Chicote Grande deposit, Bolivia. B, Xihuashan deposit, China.
GEOLOGICAL ENVIRONMENT
Rock Types Monzogranite to granite stocks intruding sandstone, shale, and metamorphic equivalents.
Textures Phanerocrystalline igneous rocks, minor pegmatitic bodies, and porphyroaphanitic dikes.
Age Range Paleozoic to late Tertiary.
Depositional Environment Tensional fractures in epizonal granitic plutons and their wallrocks.
Tectonic Setting(s) Belts of granitic plutons derived from remelting of continental crust. Country rocks are metamorphosed to greenschist facies.
Associated Deposit Types Sn-W veins, pegmatites.
DEPOSIT DESCRIPTION
Mineralogy Wolframite, molybdenite, bismuthinite, pyrite, pyrrhotite, arsenopyrite, bornite, chalcopyrite, scheelite, cassiterite, beryl, fluorite; also at Pasto Bueno, tetrahedrite-tennantite, sphalerite, galena, and minor enargite.
Texture/Structure Massive quartz veins with minor vugs, parallel walls, local breccia.
Alteration Deepest zones, pervasive albitization; higher pervasive to vein-selvage pink K-feldspar replacement with minor disseminated REE minerals; upper zones, vein selvages of dark-gray muscovite or zinnwaldite (greisen). Chloritization. Widespread tourmaline alteration at Isla de Pinos.
Ore Controls Swarms of parallel veins cutting granitic rocks or sedimentary rocks near igneous contacts.
Weathering Wolframite persists in soils and stream sediments. Stolzite and tungstite may be weathering products.
Geochemical Signature W, Mo, Sn, Bi, As, Cu, Pb, Zn, Be, F.
EXAMPLES
Pasto Bueno, PERU (Landis and Rye, 1974)
Xihuashan, CINA (Hsu, 1943; Giuliani, 1985; and personal visit)
Isla de Pinos, CUBA (Page and McAllister, 1944)
Hamme District, USNC (Foose and others, 1980)
Round Mountain, USNV (Shawe and others, 1984)
Chicote Grande, BLVA (Personal visit)