The Superior (Pioneer) district is about 15 miles southwest of Miami and 12 miles northwest of Ray. Most of its gold has been a byproduct from copper ores of the Magma property; however, some gold ore has been mined south of the main copper mines.
The first significant mineral discovery in the Superior district was of nugget silver in 1873 or 1874 at the Silver Queen mine, now known as the Magma mine, and the initial locations were made in 1875. Rich silver ore was mined in the early years and the camp was active until 1893 when a drop in the price of silver halted operations. Several unsuccessful attempts at silver mining were made in later years (Short and others, 1943, p. 59-75, 139-141). Exploration in the old Silver Queen mine by the newly organized Magma Copper Co. in 1912 revealed large bornite-chalcopyrite ore bodies which effected a rejuvenation of the district that was sustained through 1959. Gold is produced from the copper ores and also from auriferous quartz veins in the old Lake Superior and Arizona workings (Gardner, 1934, p. 1-2).
Prior to 1912 the output of gold from the district was small, probably less than 500 ounces. From 1914 through 1959 the recorded production was 397,700 ounces.Rocks of the area range in age from Precambrian through Tertiary. The oldest is the Pinal Schist, unconformably overlain by the Apache Group and Troy Quartzite of late Precambrian age. Thick diabase sills, considered to be of Precambrian age, intrude the foregoing rocks (A. F. Shride, oral commun., 1962). An aggregate thickness of about 2,000 feet of Paleozoic strata, predominantly limestone, overlies the Precambrian rocks. The Paleozoic rocks were faulted and invaded by dikes and stocks of quartz monzonite porphyry and quartz diorite of late Mesozoic or Tertiary age. Parts of the district are covered by conglomerate and thick dacitic flows and tuffs of Tertiary age and by conglomerate of Tertiary and Quaternary age. Additional crustal movement involving tilting and faulting occurred during middle and late Tertiary time (Short and others, 1943, p. 12-15). Small plugs, flows, and dikes of basalt were intruded locally during Pliocene or Pleistocene time.
The Magma deposits are a series of disconnected ore shoots in replaced shattered country rock between two east-trending shear zones. The richest ore bodies are found along the Magma fault, where it intersects diabase. The principal ore minerals are pyrite, bornite, chalcopyrite, and enargite, with subordinate tennantite and hypogene chalcocite. In places sphalerite is the predominant sulfide; small amounts of galena accompany the sphalerite. Most of the ore bodies were enriched by supergene copper sulfides (Short and others, 1943, p. 74-78).
A considerable amount of gold ore has been mined from the Lake Superior and Arizona property and lesser amounts from similar gold lodes in the Belmont-Queen Creek area. The gold occurs in small lenticular ore bodies 10 to 20 feet above the base of the Martin Limestone (Devonian) and adjacent to faults. Gold, malachite, and chrysocolla occur in a gangue of iron and manganese oxides and quartz. Silver is associated with the copper minerals and gold (Short and others, 1943, p. 138).
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