Location
Northeast and southwest flanks of the Sierra Prieta, Tps. 13 and 14 N., Rs. 3 and 4 W.
Topographic Maps
Kirkland 15-minute quadrangle (covers only E 1/2 of quadrangle); Iron Springs 15-minute quadrangle; Congress 30- minute quadrangle; Prescott 2-degree sheet, Army Map Service.
Geologic Maps
Krieger, 1967, Reconnaissance geologic map of the Iron Springs quadrangle, Yavapai County. Arizona, scale 1:62,500.
Arizona Bureau of Mines, 1958, Geologic map of Yavapai County, scale 1:375,000.
Access
From Prescott, about 12 miles southwest on light-duty road paralleling Aspen Creek to Copper Basin; a light-duty road leads north across the crest of the Sierra Prieta to Miller Creek and Thumb Butte.
Extent
Placers in the Copper Basin district are found in gulches that dissect the pediment slope on the southwest flank of the Sierra Prieta and in the gravel-floored plain between this pediment and Skull Valley. A small amount of placer gold was recovered between 1933 and 1940 near Thumb Butte on the northeast slope of the mountains.
In the immediate vicinity of Copper Basin (sees. 20 and 21, T. 13 N., R. 3 W., Kirkland quadrangle) placers have been mined from terrace gravels and stream gravels in and near Copper Basin Wash and tributary gulches; tht terrace gravels contain oxidized copper deposits and some gold placers. These deposits contain gold fragments that are wiry to angular and noticeably coarser than the placers away from the mountains. Oxidized copper minerals are common in placers in the upper part of the Copper Basin Wash.
Other placers near the mountains include deposits in Mexican Gulch, Copper Creek, and Spruce Canyon. Mexican Gulch is not located on the topographic maps, but Wilson (1961, p. 47) states that it is 2 1/2 miles from Skull Valley and probably near the low hills at the east edge of T. 14 N., R. 4 W. The deposit in Mexican Gulch had an over burden of 10-15 feet of soil and sand on top of pay gravel 2 feet thick that contained appreciable amounts of clay.
The gold recovered from this gulch was commonly the size of mustard seed to $3 nuggets, but some $15 nuggets were found (valued at $20.67 per oz) .
Spruce Canyon is on the northwest slope of the Sierra Prieta, about 5 miles northeast of Skull Valley (T. 14 N., R. 4 W., Iron Springs quadrangle); results of sampling in 1933 indicated values of 56 cents to $2.12 per yard. Copper Creek, a tributary to the Hassayampa River, is southeast of Copper Basin (Tps. 12 1/2 and 13 N., R. 3 W., Kirkland quadrangle), but the exact location of the placers is unknown.
Apparently, the richest placers are on the gravel-floored plain west and south of Copper Basin (T. 13 N., R. 4 W.); most of this area is shown only on the Congress 30-minute quadrangle, which does not show the details necessary for accurate location of the placers. The gravels in this area are characterized by small boulders and more clay than the gravels near the mountains.
The gold in these gravels occurs as particles worth less than 25 cents; larger nuggets are rare. The placers contain small particles of cinnabar and natural amalgam probably derived from cinnabar veins in the Copper Basin area.
Production History
The placers in the Copper Basin district were worked intermittently until 1931. At that time a few companies started placer mining on a large scale in various localities in Copper Basin. The Aztec placer claim (and other unlocated claims) was active in 1931. The Aztec deposit in Copper Basin Wash (sec. 21, T. 13 N., R. 3 W.) is in terrace gravels cemented by copper carbonate and oxide minerals.
Most of the large-scale placer mining was apparently concentrated in the southwestern part of the placer field; during the early 1930's the Forbach and Easton Co., the Skull Valley Corp., and the Gold Star Placer Co. worked these deposits. Unfortunately, lack of detailed maps precludes location of any of these claims.
Source
The source of the placer gold in Copper Basin is reported to be gold-bearing tourmaline-quartz veins of Precambrian age (Johnston and Lowell, 1961).
Literature
Engineering and Mining Journal, 1933a: Results of sampling placer ground in Spruce Canyon.
Gardner and Johnson, 1935: Depth of gravel; type of bedrock; accessory minerals in placer gravels; size of nuggets; placer operations.
Girand, 1932: Describes gravels in Mexican Gulch.
Johnston and Lowell, 1961: General bedrock geology; source of placer gold.
Mining Journal, 1932a: Reports recovery of nugget weighing 6 ounces from Chase placer.
U.S. Bureau of Mines, 1929, 1931: Names placer-bearing creeks and placer claims.
1934-35: Names placer creeks; placer-mining operations.
Wilson, 1961: Location; extent and character of gold-bearing gravels; size of gold particles; accessory minerals in placers; placer-mining activity during the period 1932-33.
