Latitude: 33°21'57"N
Longitude: 110°58'33"W
A former surface Mo-Ag-Au-Cu-Pb deposit/mine located on 18 claims south-central sec. 6, T1S, R14E (Pinal Ranch 7.5 minute topo map), just N of Top of the World, in the NW part of the Pinal quadrangle, 1¾ miles NE of Pinal Ranch. The property was worked in the 1890's as a high-grade Cu, Ag, Au mine. In 1942, the owner claimed a 12 foot vein in which 7 feet carried 1.04% Mo. Owned by Mr. Frederick Weise (circa WWI). Claims extend into sec. 7.
Mineralization is a replacement deposit. Several mineralizaed veins/fractures that crop out in Schultze granite near the western edge of the stock. They were formed by replacement of the granite. The mineral assemblage of these veins is unlike that of any of the other deposits of the district, but it has characteristics that suggest a relationship to the quartz-muscovite veinlets that occur throughout the most prominent set of joints of the Schultze granite, and they are like the Swede and Clark deposits except that no tungsten minerals have been recognized and molybdenite is present in greater abundance. The veins are widest and most strongly mineralized at the bottom of the canyon, suggesting that the outcrops are near the upper limits of mineralization. Ore occurs in stringers to 3 feet wide zones.
The vein fractures strike NE and dip 60 to 80SE, approximately parallel to the general strike of the muscovite-bearing joints, but they are perhaps a little stronger and more persistent than most joints of the set. The veins are exposed in a deep rugged canyon tributary to Pinto Creek, which is about 4,000 feet to the NE. The outcrop of one vein can be followed for about 1,000 feet, but the others cannot be traced for more than 100 to 200 feet. The veins range in size from stringers and inch or two wide to irregular, partly replaced zones as much as 3 feet wide. They are widest and most strongly mineralized near the bottom of the canyon.
The granite wallrock of the fractures is replaced mainly by quartz and muscovite. Where mineralization was strongest, the middle part of each vein is mostly quartz intergrown with coarse muscovite and containing small masses and scattered grains of pyrite and chalcopyrite. Outward from the middle part the vein commonly grades into loose, porous aggregates of coarse muscovite containing occasional grains and small masses of purple or colorless fluorite. Clots and thin sheaves of molybdenite flakes are abundant in the transition zone between the middle part of the vein and the muscovite envelope. In some places, muscovite aggregates form lenticular masses 2 or 3 feet thick that commonly contain narrow, vug-like masses of quartz intergrown with muscovite and molybdenite and with euhedral quartz filling the central part. The molybdenite is generally associated with quartz; but in some places, coarse flakes of molybdenite are intergrown with flakes of muscovite several inches from the quartz masses.
In the oreshoot that was mined molybdenite occurs as irregular foliated masses as much as 2 inches (5 cm) across in the outer parts of the central quartz core, as coarse flakes in the inner parts of the greisen envelope, and as selvages along many quartz veinlets traversing the less completely replaced granite on the hanging wall side of the quartz core.
The Bronx deposits crop out well within the granite stock and therefore probably were formed in a higher temperature zone than the wolframite veins at the edges of the mass.
Workings include 3 tunnels, one of which was caved in 1939. Production was some 50 tons of high-grade molybdenite ore from one oreshoot during the early days of WWI, consigned to the German government, but never shipped since the stockpile was swept away by a flash flood. Claimed to have produced $60,000 in Au (period values - $35.00 per Troy oz.).
1935 assay data: $11.20 Au $27.80 Ag, $11.70 Cu (6.5%) (period values) Another sample had 1.77-5% Mo.
References
Peterson, N.P. (1962), Geology and ore deposits of the Globe-Miami District, Arizona, USGS PP 342: 71, 73, 77, 78, 133-134.
Peterson, N.P. (1963), Geology of the Pinal Ranch quadrangle, USGS Bull. 1141-H: H16-H17.
USGS & Arizona Bureau of Mines, and U.S. Bureau of Reclamation (1969) Mineral and Water Resources of Arizona, Arizona Bureau of Mines Bull. 180: 234.
Hicks, Clifford J. (1979) Molybdenum Occurrences in Arizona, Arizona Department of Mineral Resources: 15.
Niemuth, N.J. & K.A. Phillips (1992), Copper Oxide Resources, AZ Dept. Mines & Min. Resources Open File Rept. 92-10: 7 (Table 1).
USGS Pinal Ranch Quadrangle map.
Arizona Department of Mineral Resources Bronx Copper Mine file.
MRDS database Dep. ID #10027088, MRDS ID #M001974; and Dep. ID #10160962, MAS ID #0040070203.
Mineral List
8 entries listed. 8 valid minerals.
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