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UNITED STATES MINERAL RESOURCES 



pitching along the intersections of favorable beds 

 with the intrusive. In some places, as at Tern Piute, 

 Nev., ore-bearing tactite having no exposed contact 

 with igneous rock has formed in layers parallel to a 

 contact but is separated from it by several hundred 

 feet of barren strata. Irregularities in igneous con- 

 tacts and premineralization faults provide traps as 

 well as channelways for mineralizing solutions that 

 result in major local enlargements of tactite bodies. 

 At the Pine Creek mine, Calif., and at the Nevada 

 Scheelite mine. Mineral County, Nev., overhangs of 

 the granite contact are associated with enlarged and 

 enriched ore bodies. Also at the Pine Creek mine, as 

 at the Riley mine in the Osgood Range, Humboldt 

 County, Nev., plunging troughlike curvatures of the 

 intrusive contact are occupied by enlarged ore shoots. 

 Roof pendants and inclusions of calcareous sedi- 

 mentary rocks in plutonic rocks may be converted to 

 tactite bodies that range in size from only a few feet 

 in all dimensions to others that measure hundreds 

 of feet. Large pendants like the one at Pine Creek, 

 Calif., which is 7 miles long and nearly a mile wide, 

 contain a variety of rock types, only some of which 

 are replaced by tactite. 



Scheelite is seldom uniformly distributed in tac- 

 tite, and many tactite bodies, perhaps most, contain 

 none at all. In many mines, scheelite occurs in fairly 

 well defined shoots or is more concentrated along 

 certain bands in the tactite than in others. The verti- 

 cal range may be as great as that of the tactite it- 

 self or may be restricted by such factors as perme- 

 ability, fracturing, channeling of the ore-bearing 

 solutions, and other local controls. 



Scheelite-bearing tactite deposits range in size 

 from small isolated pods scattered along a contact to 

 massive bodies which may comprise millions of tons. 

 The content of WO3 in tactite deposits is generally 

 low. Parts of the Humboldt ore body at Mill City, 

 Nev., contained 10 percent WO., but the entire body 

 averaged about 1 percent. A few smaller mines in 

 California and Nevada yielded ore averaging between 

 1 and 2 percent, but these are the exception. Most 

 productive mines contain between 0.5 and 1.0 per- 

 cent and a few properties, during periods of high 

 prices and under conditions of inexpensive mining, 

 produced concentrates from tactite containing as 

 little as 0.3 percent WO3. 



Major production of tungsten from tactite deposits 

 in the United States has come from the Pine Creek 

 mine, Inyo County, Calif. (Bateman, 1965 ; Gray and 

 others, 1968) ; the Mill City district, Pershing Coun- 

 ty, Nev. ; various deposits in the Osgood Range, Hum- 

 boldt County, Nev. (Hobbs and Clabaugh, 1946 ; Hotz 

 and Willden, 1964) ; and the Brownes Lakes and 



Calvert Creek deposits in Beaverhead County, Mont. 

 Numerous other deposits, particularly in the Sierra 

 Nevada of California and in western Nevada, have 

 produced lesser but cumulatively very significant 

 amounts of concentrates. 



Major occurrences of tungsten-producing tactite 

 outside the United States occur at the Flat River 

 area in the Northwest Territories, Canada, on King 

 Island, Tasmania, and in South Korea. 



TUNGSTEN-BEARING VEIN DEPOSITS 



Tungsten-bearing quartz veins are widely dis- 

 tributed and account for more than three-fourths of 

 the known world reserves of the metal. The great 

 bulk of these reserves, however, are concentrated in 

 the extensive tungsten province of southeastern 

 China. As with the tactite deposits, most of the pro- 

 ductive veins are associated spatially and probably 

 genetically with plutonic rocks of granitic composi- 

 tion and usually occur near their contacts — either 

 within border zones of the plutons or, more gener- 

 ally, in the adjacent intruded terrane. In contrast 

 with environments favorable for tactites, however, 

 the host rock associated with such veins generally 

 contains little, if any, carbonate. Shale, siltstone, 

 and quartzite or their metamorphic equivalents, as 

 well as igneous rocks, either older than the parent 

 intrusive or forming the border zones of the parent 

 intrusive itself, are favorable hosts for the deposi- 

 tion of tungsten in quartz veins. Exceptions to this 

 general rule are the quartz-scheelite veins cutting 

 carbonate beds in the Minerva district, Nevada, and 

 calcite-scheelite veins and stockworks in the Cherry 

 Creek district and the Snake Range, Nev. 



Most tungsten veins are mineralogically simple 

 and consist of quartz with scheelite and (or) one of 

 the wolframite series and minor amounts of other 

 minerals. Scheelite is the only ore mineral in the 

 quartz-calcite veins at Atolia, Calif., which occur in 

 quartz monzonite, and at the Minerva district, 

 Nevada, where veins cut carbonate beds. Ferberite 

 is the predominant mineral in veins of the famous 

 Boulder tungsten district, Colorado, which carry 

 only minor amounts of scheelite. Huebnerite is the 

 dominant mineral at the Ima mine, Idaho, and at 

 the Hamme district, North Carolina, although some 

 scheelite occurs in both places. In some veins both 

 scheelite and wolframite occur in nearly equal 

 amounts. Other minerals such as sphalerite, galena, 

 chalcopyrite, tetrahedrite, and arsenopyrite occur 

 in large enough amounts in some deposits to be 

 recovered as byproducts. Pyrite, pyrrhotite, molyb- 

 denite, fluorite, rhodochrosite and some feldspar 

 may be present as gangue minerals. In many dis- 



