Palmetto District, Patagonia Mts, Santa Cruz Co., Arizona, USA

‡Ref.: Schrader, F.C. (1913), Alunite in Patagonia, Arizona, and Bovard, Nevada, Economic Geology: 8: 752-767.

Schrader, F.C. & J.M. Hill (1915), Mineral deposits of the Santa Rita and Patagonia Mountains, Arizona, USGS Bull. 582: 279-292.

Schrader, F.C. (1917), The geologic distribution and genesis of the metals in the Santa Rita-Patagonia Mountains, Arizona, Economic Geology: 12: 237-269.

Galbraith, F.W. & D.J. Brennan (1959), Minerals of Arizona: 80.

Moger, S.R. (1970) Geology of the west central portion of the Patagonia Mountains, Santa Cruz County, Arizona: Davis, University of California, M.S. thesis, 60 p.

Simons, F.S. (1974) Geologic map and sections of the Nogales and Lochiel quadrangles, Santa Cruz County, Arizona: U.S. Geological Survey Miscellaneous Investigations Series Map I-762, 9 p., 1 sheet, scale 1:48,000.

Keith, Stanton B. (1975), Arizona Bureau of Mines Bull. 191, Index of Mining Properties in Santa Cruz County Arizona: 73 (Table 4).

Anthony, J.W., et al (1995), Mineralogy of Arizona, 3rd. ed.: 117, 426.

Arizona Bureau of Mines file data.

A Cu-Pb-Ag-Au-Zn-Mn-Mo-alunite mining area located in T.22-23S., R.15E., on the western slope of the Patagonia Mountains between Sonoita Creek to the North and Cañada de la Paloma to the South. It adjoins the Harshaw District on the west, lying between the Tyndall District and the Patagonia District and extending from Sonoita Creek southward for 6 miles to the divide north of Paloma Canyon, It is about 4 miles wide, being bounded on the west by a north-south line crossing Estrada's Ranch.

The topography is rough. The western ¾ of the district is a deeply scored plain sloping from an elevation of 4,500 feet at the base of the Patagonia Mountains on the east to 4,000 feet on the west. The closely spaced arroyos, intrenched from 20 to 60 feet below the general level, trend a little south of west. The highest part of the district is the main ridge of the Patagonia Mountains, which extends along its eastern border.

The oldest rocks are seemingly hornfels and quartzites which occur in a small area in the northeastern part of the district, ¼ mile east of the Gray camp. These rocks dip steeply to the west. They are apparently cut off on the north and west by faults and on the east by an acidic intrusive rock which is probably a phase of the granite porphyry. They are dull gray and brown in color, are thinly bedded, and are cut by numerous east-west and north-south joints or shear lines. Except these sediments and a small body of Tertiary rhyolite in the NE corner, and of andesite in the NW corner, both of which belong to larger areas of similar rocks in the Tyndall District on the north, the hard rocks of this district consist principally of Mesozoic granular intrusives occurring in teh SE part and containing practically all the deposits. Beginning with the oldest, these rocks are quartz monzonite, diorite, and granite porphyry.

The quartz monzonite, which occupies almost the whole of the SE part of the district, is a coarse-granular rock composed of orthoclase, plagioclase, quartz, and biotite, locally with some hornblende. In composition it ranges from a rock near syenite to granodiorite.

The diorite occurs in a narrow, tongue-like belt about 2 miles long north of the quartz monzonite, which it intrudes as dikes, sills, and larger masses. It is a dark, granular rock composed of andesine and hornblende, with very minor amounts of quartz.

Granite porphyry occurs in a lens 3 miles wide occupying the middle-eastern part of the border, which is high and rugged and culminates in Three R Mountain. It belongs to the larger area of this rock in the Harshaw District, on the east. It is seemingly intrusive into both the quartz monzonite and the diorite. It is sliced by a sheeting which dips 40º NW. In generakl it is light gray or whitish, medium- to coarse-grained rock, with phenocrysts of greasy-lustered quartz and whitish kaolinized orthoclase resting in a finer-grained groundmass composed mainly of the same minerals. It contains a little pyrite and chalcopyrite widely disseminated in both the feldspar and the quartz, also as accessory minerals considerable apatite and a little zircon. The feldspar is highly altered to muscovite.

Mineralization is varied: (1) Irregular, tabular, and lensing orebody of ozidized copper mineralization along an fault zone cutting altered and locally mineralized Jurassic granite; (2) Narrow, lensing, quartz-fissure veins of argentiferous lead ore in the contact zone of Jurassic granitic intrusive and Precambrian metamorphic rocks; (3) Disseminated and extensivfely oxidized, pyrite-chalcopyrite mineralization in shear zones cutting Jurassic granitic intrusive and in intruded Precambrian metamorphic rocks; and, (4) Minor gold placers in stream gravel.

Workings include numerous, but mostly small and shallow, operations. Prospected and mined since the mid-1800's. Total estimated and recorded production would be some 132,000 tons of ore containing about 5,500 tons of copper, 225 tons of lead, 75,000 oz. of silver, 240 oz. of gold, and one ton of zinc. Only a few oz. of gold came from placer workings.