Pima County Arizona Gold Production
The oxidized zone ranges from 20 to 190 feet in thickness and its base terminates sharply at a horizontal plane. In this zone are abundant malachite, and small amounts of azurite, cuprite, tenorite, chrysocolla, hematite, and limonite (Gilluly, 1956, p. 2). Considerable supergene chalcocite has accumulated just below the oxidized zone.
Gold has not been seen in the sulfide ore. However, the close relationship of the ratios of recovered gold to total gold and recovered copper to total copper led Gilluly (1956, p. 87) to conclude that the gold in the ores is associated with copper sul-fides rather than pyrite.
The oldest formation in the vicinity of the mineralized area is the Cardigan Gneiss, of Precambrian (?) age. It is bounded on the east along north-trending Gibson fault by the Concentrator Volcanics of Cretaceous (?) age. The Cornelia Quartz Monzonite of Tertiary age is a stock that occupies much of the northern part of the district and crosscuts the older rocks. The Locomotive Fanglomerate of Tertiary age overlies parts of the eroded surface of Cornelia Quartz Monzonite. The rocks were faulted several times during Tertiary time (Gilluly, 1956, p. 57-58, 105-106). The ore body consists of chalcopyrite, bornite, and a little pyrite in veinlets and scattered grains in the quartz monzonite. Less abundant minerals are tennantite, sphalerite, molybdenite, magnetite, and specularite. The richest ore occurs where the rock is impregnated with orthoclase.The oxidized zone ranges from 20 to 190 feet in thickness and its base terminates sharply at a horizontal plane. In this zone are abundant malachite, and small amounts of azurite, cuprite, tenorite, chrysocolla, hematite, and limonite (Gilluly, 1956, p. 2). Considerable supergene chalcocite has accumulated just below the oxidized zone.
Gold has not been seen in the sulfide ore. However, the close relationship of the ratios of recovered gold to total gold and recovered copper to total copper led Gilluly (1956, p. 87) to conclude that the gold in the ores is associated with copper sul-fides rather than pyrite.
GREATERVILLE DISTRICT
The Greaterville district is in southeastern Pima County, about 34 airline miles southeast of Tucson. It is chiefly a placer district, though for many years preceding the Civil War, silver and copper lodes were worked successfully in the Patagonia and Santa Rita Mountains south of the district. In 1874 silver and lead lode deposits were discovered in Hughes Gulch in the Greaterville district, and later in the year placer gold was found which started a rush, during which most of the richer placers were mined out. By 1886 the district was practically dormant (Hill, 1910b, p. 11-12). From 1900 through 1959 there was only desultory activity and very small production. According to Hill (1910b, p. 12), the placers yielded about $7 million in gold before 1900; however, Elsing and Heineman (1936, p. 98) estimated the total production was worth $650,000. From 1903 through 1959 only 4,146 ounces of gold was mined in the district.
The placer deposits occupy a triangular area of about 8 square miles on the lower east slope of the Santa Rita Mountains. The richest gravels are those along present stream courses, although placers are also in older gravels on benches and tops of ridges. The source of the gold was probably the auriferous pyritic-quartz veins of nearby Granite Mountain or the veins in Tertiary andesite that once covered the district (Schrader, 1915, p. 161-165).