Pima/Pinal County, AZ
The water supply of this placer area is chiefly from wells and from the intermittent flow of Canada Del Oro Creek. The mean annual rainfall at Oracle, which is 4,500 feet above sea level, amounts to about 19.44 inches. On the Santa Catalina Mountains, which attain 9,150.feet above sea level at Mt. Lemmon, less than 10 miles southeast of the placer area, much heavier summer rains and winter snows obtain. Hence the large canyons may carry torrential floods during summer and a steady, small flow from melting snow in the spring.
The Canada Del Oro placers are presumed to have been discovered by Spaniards, during the early days of Tucson. Numerous old pits, trenches, and tunnels indicate considerable early placer mining, the yield from which is unknown.
During the 1932-33 season, approximately thirty men intermittently carried on small scale rocking and panning in the Canada Del Oro region, chiefly on the northern side of the creek. Although one $25 nugget and a few $5 nuggets were reported, the average daily returns per man were seldom more than 50 cents.
The Santa Catalina Mountains are made up principally of pre-Cambrian gneiss, schist, and granite; Paleozoic beds, post- Carboniferous granite, granite phophyry, diabase, and diorite; and Tertiary sedimentary rocks and lavas. Gold-bearing quartz veins, such as occur in the vicinity of the Copeland, Kerr, Matas, and other prospects in the upper reaches of Canada del Oro, were the probable source of the placer gold.
Based upon information from Capt. J. D. Burgess, Heikes describes the placers occurring in T. 10 S, R. 14 E., Gila and Salt River Meridian as having apparently been deposited at intervals by floods from the Santa Catalina Mountains so as to form a deposit of nearly equal value from surface to bedrock, there being no pronounced accumulation of heavy gold at bedrock except in the stream, Canada Del Oro Creek, which passes through the region. The bed of dry gravel is from six feet deep at the creek side to 475 feet at the summit, with an average thickness of about 150 feet. The deposit is in general a loose gravel, un-cemented. There are, however, alternating strata of deep-red, clayey material. These strata are of nearly uniform thickness of three to four inches and probably were formerly surfaces existing between floods, each being covered by a later flow of gravel from rainfall-eroded veins farther up the mountain. Shafts sunk on the hill sides from 27 to 50 feet in depth show values from 10 to 42 cents per cubic yard. The average is difficult to determine, as the gold is not equally distributed. All the gold is found in well-rounded nuggets ranging from a few cents to $5 in value. There is a tradition of a lump weighing 16 pounds with probably 40 per cent quartz, whose discoverers were found murdered in their camp 16 miles north of Tucson. The nugget had disappeared. In fineness the gold averages about 905. Generally the placer material is dug, screened, and hauled to the creek, and there worked by rockers, or sluiced when there is enough water. Many dry-washers have been tried, but most of the gold lies in the red clayey seams which apparently acted as bedrock for each period of deposition. Pulverizing this adherent material gives good results with the common bellows type of 'dry washer.' A boiler and pump were once used to throw water against the creek bank, but the water at that time proved insufficient for extensive operations.
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