Basin and Range Proterozoic W veins and replacements

Region West, Southwest
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area All tungsten occurrences from all sources were first plotted. Those locations were compared with mapped distribution of Early and Mid-Proterozoic intrusive rock based on knowledge of the Boriana and Black Pearl mines, Arizona. Additional members of the class were then selected based on proximity and examination of records. Small clusters of relatively important past-producer mines then enclosed into 4 small-district-sized groups, particularly if there was record of any ore left in place when mines closed.
Identified resources Identified resources and historical production of copper, gold, silver, and tungsten.
Production Boriana mine: 120,413 short ton units (stu) WO3 (Conway and others, 1990), mostly between 1929 and 1943, with about 98% coming from wolframite- and scheelite-bearing quartz veins in fine-grained muscovite schist (Dale, 1961, p. 73; Hobbs, 1944, p. 149). About 2 tons of 18% Cu concentrate from dump material was produced per month. Black Pearl mine: produced 62,100 lbs concentrate (70% WO3) from 1951-56 : 6,312 short ton units of WO3 (Dale, 1961, p. 44-45). Tens of additional small mines, including Williams mine, Tungstona mine, Rose mine, and the North Star group produced minor tonnages particularly during times of government price supports for tungsten in WWI and WWII.
Status Past mining.
Estimated resources Boriana mine resources: Indicated 8,800 metric tons at 2% WO3, Measured 2,200 metric tons at 1.75% WO3, Inferred 40,000 metric tons at 1% WO3. Titley and Anthony (1989) report a resource of 239,000 t at 0.085% Cu, 1.79 g/t Ag, 0.01 g/t Au, and 0.49% WO3 from the Boriana mine. Perhaps 10,000 to 20,000 stu of WO3 in ore of grade around 1.0% WO3 was left in levels 7, 8, and 9 (of 9) of the Boriana mine, toward the northeast, but swelling of the phyllite in the mine ribs has made access impossible through any existing workings. Tens of additional small mines that closed after WWII have very small resources at a variety of grades.
Geologic maps Wilson and others (1959), scale 1:375,000; Hobbs (1944, plates 43 and 45), scale 1:9,600 and unknown, respectively; Schmitz and Burt (1990, figure 2), scale 1:25,700.
Geophysical data Adequate Rank 2 aeromagnetics and aeroradiometric coverage (NURE 1-mile spaced lines).
Favorable rocks and structures Yavapai Supergroup granites and granites of about 1400 Ma in western Basin and Range terrane in Arizona are cut by wolframite- and scheelite-bearing quartz veins. With overprinted basin-and-range style extension, these geologic targets are complex and require careful mapping of large areas.
Deposits Boriana mine (MRDS dep_id: 10008548; USMIN Site_ID: AZ00039), Bull Canyon Group (MRDS dep_id: 10102536), Tungstite mine (MRDS dep_id: 10027706), Midway prospect (MRDS dep_id: 10102542), Black Pearl mine (MRDS dep_ids: 10161782, 10027556), Williams mine (MRDS dep_id: 10102533), Tungstona mine (MRDS dep_id: 10026938), Rose mine (MRDS dep_id: 10046310), North Star group (MRDS dep_id: 10027578).
Evidence from mineral occurrences MRDS; USMIN.
Geochemical evidence Data available for selected districts; see Conway and others (1990). The W minerals at the Boriana mine are wolframite and scheelite, contained in quartz veins that follow the foliation of the phyllite. These veins also contain chalcopyrite; other sulfides (pyrite, arsenopyrite, and molybdenite) and fluorite occur locally. Tungstona mine samples (in 1952): 0.16 and 0.13% WO3 with some higher grade ore samples, up to 0.3% WO3; Black Pearl mine samples: average 0.922 and 0,784% WO3.
Geophysical evidence No publicly available data.
Evidence from other sources Unknown.
Comments Boriana, Black Pearl, and Williams mines are each fairly exemplary of medium- to small-sized quartz-wolframite vein systems, the first two with evidence for greisenization and Black Pearl also having a well-developed stock-scheider pegmatitic layer (Hobbs, 1944; Schmitz and Burt, 1990). Boriana had scheelite in the veins, as well, replacing wolframite; with about equal values from the wolframite and scheelite, Proterozoic Yavapai Supergroup schists have widespread occurrences of relatively large tonnages of rock with mostly low-grade epidote-quartz-scheelite mineralization developed near pegmatitic intrusions, such as the North Star deposit and deposits of the White Picacho district, including Scheelite Reef, Climax, and Starlight (Dale and others, 1960, p. 36-38). Some worthwhile new research would be to confirm the age of the various dateable rocks at and near Boriana which would assumedly demonstrate an age near 1700 Ma. Vein ores contained molybdenite. Vein scheelite also contains molybdenum (solid solution toward powellite). It might be possible to use the Re-Os system to obtain a mineralization date. Boriana veins had a rather well defined ore shoot that dipped about 35 degrees to the northeast along the vein system. That dip probably records tilting due to basin-and-range faulting, a now common theme for ore deposits in the province. The ore shoot was probably originally nearly vertical. The ore shoot dipped towards a small cupola of granite at Bull Canyon mine that is greisenized, and, into which, the Boriana veins are actually rooted. Uranium-Pb ages on zircons from the cupola granite as well as 40Ar/39Ar dating on greisenization muscovite would be ages well worth comparing with the Re/Os age of vein molybdenite (facts in the above on Boriana are from Hobbs, 1944; interpretations are from T. Hayes, USGS).
Cover thickness and description Some veins exposed at the surface; the Boriana mine reached a depth of ~ 300 m. Cover thickness can be highly variable, with basins having cover perhaps as great as 14,200 feet (in the Higley Basin east and south of Phoenix). The Middle Proterozoic rocks crop out in a number of ranges scattered across both the Higley Basin and areas of Arizona and New Mexico.
Authors Timothy S. Hayes, Lukas Zurcher, Carson A. Richardson, David A. Ponce, Nora K. Foley, Jane M. Hammarstrom.
New data needs Detailed geologic mapping, geophysics. Isotopic age dating (Re-Os on vein molybdenite; U-Pb on cupola granite zircon; 40Ar/39Ar on greisenization muscovite) to test the supposition of Mid-Proterozoic age at Boriana. If Boriana proves to be Mid-Proterozoic, larger quartz-wolframite systems could be worth targeting in the Yavapai Supergroup terranes of western Arizona Basin and Range terrane.
Geologic mapping and modeling needs Detailed geologic mapping.
Geophysical survey and modeling needs High resolution, Rank 1 aeromagnetic and aeroradiometric coverage.
Digital elevation data needs Lidar inadequate.