Western Mining History : Reliving the Industrial Revolution of the West

The most productive ore zone lies south of the Dividend fault and the ore bodies are arranged in a semicircle around the stock on Sacramento Hill. The copper ore occurs in irregular replacement bodies in the Paleozoic limestones, in the contact breccia, and as disseminated sulfides in the granite porphyry (Tenney, in Ransome and others, 1932, p. 56-57; C. Trischka, in Arizona Bureau of Mines, 1938, p. 38-40). A few deposits are at some distance from Sacramento Hill and are associated with small porphyry bodies (J. B. Tenney, in International Geological Congress, 1935, p. 228).

The oxidized ores consist of a blanket of copper carbonates, cuprite, copper, limonite, and local chalcocite that extends from the surface to depths of several hundred feet, and in one place to more than 2,000 feet (Tenney, in Ransome and others, 1932, p. 61). The zone of secondary sulfide enrichment contains bornite, chalcopyrite, chalcocite, and a little sphalerite and galena. The disseminated primary ore contains quartz, pyrite, chalcopyrite, and bornite. Most of the gold recovered in current mining operations is very fine grained and is probably allied with the sulfides. Ransome (1904, p. 121) reported concentrations of native gold in the Cretaceous Glance Conglomerate and Morita Formation as well as in Recent placers derived from weathering of these formations. The main ore deposit at Sacramento Hill forms an inclined blanket which is enriched toward the bottom, where the contact with the sparsely mineralized, sericitized porphyry is sharp (J. B. Tenney, in International Geological Congress, 1935, p. 228).

DOS CABEZAS DISTRICT
The Dos Cabezas district is 18 miles southeast of Wilcox in the Dos Cabezas Mountains.

Gold deposits discovered before the Civil War were worked intermittently after the 1870's and yielded about $182,000 (8,835 ounces) through 1932 (Wilson and others, 1934, p. 117). The first workings were probably in the Teviston placers on the north side of the mountains, though most of the gold came from lodes rich in copper, silver, and lead near the village of Dos Cabezas. The district was most active during 1914-20 and 1931-36. No production was reported for 1956-59. Total gold production was at least 15,000 ounces.

In the Dos Cabezas Mountains a complexly folded and faulted section of Precambrian granite and gneiss and Paleozoic and Cretaceous sedimentary rocks is cut by granitic intrusives of Late Cretaceous or Tertiary age (Cooper and others, 1959). The ore deposits occur in veins in the Precambrian granite and Cretaceous sedimentary rocks and are apparently related to rhyolite porphyry and diabase dikes of Tertiary age. Vein minerals are galena, pyrite, sphalerite, and chalcopyrite in a gangue of coarse-textured, white to grayish-white quartz. Most of the gold is in the galena.