Copper Basin placers, Copper Basin Wash, Kirkland area, Copper Basin District, Sierra Prieta Mts, Yavapai Co., Arizona, USA
|Latitude & Longitude (WGS84):||34° 27' 23'' North , 112° 35' 53'' West|
|Latitude & Longitude (decimal):||34.45639,-112.59806|
|Köppen climate type:||BSk : Cold semi-arid (steppe) climate|
A placer gold deposit area located North of Copper Basin Wash, between Skull Valley and the Sierra Prieta. Started about the 1880's. Reactivated about 1929. Placers were located all along Copper Basin Wash in the early 1930's.
A plain slopes southwestward from an elevation of 5,500 feet at the base of the Sierra Prieta to 4,000 feet at the junction of Skull Valley and Copper Basin Washes. Most of this plain is floored with extensive deposits of gravel, sand, and clay, locally interbedded and mantles with volcanic tuffs and flows, but its easternmost one to three miles of width is a pediment that has been carved on granite. The whole area is dissected by many southwestward-trending gulches which are tributary to Skull Valley Wash.
The bedrock of the placers generally consists of cemented gravels, but, in certain areas relatively far from the mountains, it is hard clay. The gold-bearing gravels are made up largely of granitic sand together with various amounts of boulders and clay. The gold-bearing gravels form a relatively thin mantle on the ridges, but range in thickness from 3 or 4 feet up to 15, or more, feet in the gulches. The richest streaks are generally near bedrock. The gold is 925 to 950 fine.
3 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
1600 - 1800 Ma
|Early Proterozoic granitic rocks|
Age: Statherian (1600 - 1800 Ma)
Description: Wide variety of granitic rocks, including granite, granodiorite, tonalite, quartz diorite, diorite, and gabbro. These rocks commonly are characterized by steep, northeast-striking foliation. (1600-1800 Ma)
Comments: ~ 1.6 - 1.8 Ga
Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. 
1600 - 2500 Ma
|Government Canyon Tonalite|
Age: Proterozoic (1600 - 2500 Ma)
Description: Medium-grained, equigranular hornblende-biotite stock (Krieger, 1965) having average composition of tonalite. Exposed from east of Granite Mountain to south of Wilhoit. Redescribed herein to tonalite, based on chemical composition. Undeformed in many eastern outcrops, but strongly deformed west of Copper Basin and mildly deformed in central Bradshaw Mountains. Ranges in composition from alkali-calcic gabbro-diorite to calc-alkalic granodiorite. Very sodic to average and very Mg rich to Mg rich. Age, from U-Pb zircon analyses, is about 1,740 Ma (Anderson and others, 1971)
Reference: DeWitt, E., V. Langenheim, E. Force, R.K. Vance, P.A. Lindberg, R.L. Driscoll. Geologic map of the Prescott National Forest and the headwaters of the Verde River, Yavapai and Coconino Counties, Arizona. Scientific Investigations Map SIM-2996. 
Wilson, E.D. (1961) Gold Placers and Placering in Arizona. Arizona Bureau of Mines Bulletin 168 (revised 1978): 46-48.
USGS Wilhoit quadrangle topo map.
USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10137856, MRDS ID #M001103.
U.S. Bureau of Mines, Minerals Availability System (MAS) file ID #0040250552.