A Zn-Pb-Ag-Cu-Au-Mn (F-Ba-alunite) mining area located in T.22-23S., R.15-16E, in the northeastern Patagonia Mountains, about 70 miles SE of Tucson. This district adjoins the Wrightson District and Redrock District on the south. It is about 5 miles wide and extends from Sonoita Creek at Patagonia 9 miles southeastward to a point 3 miles beyond Harshaw. Harshaw Creek marks the northeast boundary, Meadow Valley Flat the east boundary, and east-west line passing just south of the American Mine the south boundary, separating it from the Patagonia District, and the main ridge of the Patagonia Mountains to the west of Alum and Flux Gulches the west boundary, separating it from the Palmetto District (per USGS Bulletin 582).

The topography is rough and much of it in the western part, which lies in the Patagonia Mountains, and rises to elevations of more than 6,000 feet, is rugged.

The bedrock of the district comprises five or more formations, which, named in ascending order, are the Paleozoic limestones, quartz diorite, granite porphyry, rhyolite, and andesite. The most important of the formations with reference to the mineral deposits are the diorite, granite porphyry, and rhyolite.

The Paleozoic limestones occupy only a small east-west belt along the middle part of the southern border of the district, but this belt is part of the limestone area around Mowry on the south.

The quartz diorite and granite porphyry belong with the group of Mesozoic intrusive rocks and the rhyolite and andesite with the Tertiary volcanic rocks.

The quartz diorite occupies an irregular belt about ¾ mile wide and nearly 3 miles long, extending from a point about 1 mile SE of Harshaw northwestward to the World's Fair ine and Alum Canyon.

The granite porphyry occupies a belt about ½ mile wide along the western border of the district, where it seems to underlie the rhyolite. This belt is but the eastern part of the much larger area in the Palmetto District, on the west.

The most extensive formation is the rhyolite, which, besides occurring in a north-south belt near the west border of the district, occupies a belt 2 miles wide extending across the north-central part and includes practically the whole of Red Mountain. It is coarsely porphyritic, tridymite-bearing rock profusely impregnated with pyrite, chalcopyrite, and chalcocite disseminated in crystals and grains and at a number of places contains promising copper prospects. The oxidation of the iron content of these minerals colors the entire mountain a brilliant red. In Alum Canyon, on the southwest, the weathered surface of the rock and the alluvial gravels derived from it are coated with efflorescences and incrustations of alum, some of whose constituents seem to be derived from the pyritic content of the rock through oxidation.

The next most abundant rock is the andesite, which occurs in flows and tuffs filling chiefly the valleys and low places. It overlies the rhyolite and other older rocks. Besides occupying an irregular circular area about 2½ miles in diameter in the south-central part of the district, north of Harshaw. It also occurs in a belt about 1 mile wide extending northward along the Patagonia road for about 3 miles.

Some syenitic rocks occur locally in the western part of Alum Canyon.

Quaternary gravels occupy two belts, each about 1½ miles in width, across the northeast and southwest ends of the district and more or less deeply cover the bedrock formations.

Mineralization is varied: (1) Irregular and lensing lodes and veins of argentiferous lead minerals with varying zinc, copper and minor gold along fault fissures and in breccia zones in Jurassic-Triassic, Cretaceous, and Laramide andesitic and rhyolite volcanics, probably intruded below by a Laramide granitic body. Some replacement of interbedded limestone in the volcanics. Silver enrichment near the surface; (2) Disseminations and fracture fillings of copper mineralization, with varying lead and zinc, in brecciated zones in Cretaceous andesite; (3) Irregular mantos, lenses and pods of manganese-silver ore as replacements in silicified, altered and brecciated Paleozoic limestone and Jurassic-Triassic volcanics and agglomerate; and, (4) Small, spotty, and generally low grade gold placer deposits.

Workings include shaft, tunnel, adit and open pit operations. Developed and mined from about the 1850's to the middle 1960's. Total production would be some 1,300,000 tons of ore containing about 86,000 tons of zinc, 72,000 tons of lead, 9,200,000 oz. of silver, 3,100 tons of copper and 4,300 oz. of gold. An estimated 10,000 long tons of manganese ores of variable grade were also produced, much of it as argentiferous smelter flux. Placer gold output is unknown but probably minor.

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References