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Oatman District (San Francisco District; Union Pass District), Black Mts, Mohave Co., Arizona, USA
‡Ref.: The Resources of Arizona - A Manual of Reliable Information Concerning the Territory, compiled by Patrick Hamilton (1881), Prescott, AZ: 70; Wilson, E.D., et al (1934), Arizona Bureau of Mines Bull. 137: 80-89; Ransome, F.L. (1923), Geology of the Oatman Gold District, Arizona, USGS Bull. 743; Anthony, J.W., et al (1995), Mineralogy of Arizona, 3rd.ed.: 148, 283, 235, 347; Wilson, E.D. (1944), AZ nonmetallics: A summary of past production and present operations, AZ Bur. of Mines Bull. 152; Silliman, B. (1866), On some mining districts of AZ near Rio Colorado, ...., Amer.Jour.Sci.: 41:289-308; Ransome, F.L. (1923), Geol. of the Oatman gold district, AZ, a preliminary report, USGS Bull. 743; Roedder, E., et al (1963), Studies of the Fluid Inclusions III, ..., Econ.Geol.: 58:353-374; Galbraith, F.W. & Brennan (1959), Minerals of AZ: 36, 43, 47, 84, 88.
This is a gold mining area located on the western slopes, southern portion of the Black Mountains, 9 miles East of Hardyville, which is on the Colorado River. The district was discovered in 1863. It lies between 2,000 to 3,200 feet of altitude. The district had a few more obscure names including the Katherine District, the Gold Road District, the Vivian District, and the Boundary Cone District.
The southern portion of the Black Mountains consists of a very ruggedly dissected, gently eastward-dipping block of Tertiary volcanic rocks which rest upon a basement of Pre-Cambrian gneiss and granite. The most important ore-bearing formation is the Oatman Andesite, which Schrader termed the "green chloritic andesite." These formations are cut by numerous faults of prevailingly northwestward strike and steep northeastward dip.
Veins of the Oatman District occur within fissures along which faulting has taken place, as a rule before, during, and after the period of vein formation. In general, no distinctiuon between faults and veins can be made, although some fissures, such as the Military fault, are younger than the veins. The veins are rather widely distributed, and the most productive ones are in the northeastern half of the district.
Vein-filled fissures are particularly abundant in the southern and central parts of the district, especially in the Oatman Andesite and Esperanza Trachyte. The general strike is NW, but the strike of individual fissures may range from nearly north to nearly west. The dip is high as a rule, over 60º, and to the NE. Many of the fissures branch, but there appears to be no recognizable rule in respect to this; some fissures diverge to the NW, and others to the SE. The veins vary in width, but few of them are wider than 50 feet at any point. As a rule the large orebodies of the district have been mined from veins or parts of veins that are not prominent at the surface.
Some of the veins have tabular forms but the larger ones are essentially stringer lodes of complex structure. Compound veins, consisting of two or more veins separated by country rock, with stringer veinlets, are common. Many of the veins are lenticular in all dimensions. A strong vein may pinch out within a few tens of feet, and an insignificant stringer may thicken to considerable width within a distance of 30 feet (10 meters). The veins of the Oatman District are of the epithermal bonanza type characteristic of Tertiary volcanic activity. The ores were deposited by ascending hydrothermal solutions at depths of not more than about 3,000 feet (1,000 meters) before the then existing surface.
The Oatman veins are mineralogically of simple character, consisting mainly of quartz, calcite, and adularia, associated in the oreshoots with free gold. As a rule, only quartz and calcite are recognizable with the naked eye. Generally several generations of quartz and calcite may be discernable. The gold is characteristically fine grained and generally can be seen only in rich ore. The adularia occurts generally in microscopic crystals.
Mineral List
Mineral list contains entries from the region specified including sub-localities44 entries listed. 25 valid minerals.
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New Locality Added: Szén-patak Ceternás-bérc, Gyöngyössolymos, Mátra Mts., Heves Co., HungaryFrom Dávid Szabó, 21st May 2013 17:47:38