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ARIZONA

The Lost Tungsten Mine of the Saucedas

GEOLOGY OF THE AREA

The Sauceda Mountains are part of the vast Basin and Range Province which comprises the southern third of the state of Arizona, plus its western edge. Like most of the mountain ranges in southern Arizona, the Saucedas trend northwest-southeast and are mostly composed of volcanic rocks. Four "pulses" of post-Paleozoic volcanism are recognized in southern Arizona. The earliest occurred during early-Cretaceous times and produced vast amounts of andesitic lava flows, tuffs, and agglomerates. The second pulse occurred during Laramide times and produced silicic to intermediate volcanic rocks and granitic plutons. The third pulse occurred during mid-Tertiary times and produced abundant rhyolites, andesites, and basalts. The final pulse occurred during fairly recent Quaternary times and produced vast amounts of basalt. Most, but not all of the mineralization in southern Arizona is associated with Laramide igneous activity.

 

The Sauceda Mountains are truly volcanic in nature. They are predominantly composed of andesite flows and tuffs. The northwestern half of the range is dominated by older Cretaceous-age rhyolites and andesites while the southeastern half is mostly made up of younger Tertiary andesites. Small exposures of younger still Quaternary-Tertiary basalts occur on the northwestern spur of the range and on the southeastern flanks of the range. The Sauceda Mountains lie in the center of an area dominated by Tertiary volcanic activity. Tertiary andesites comprise half of the Saucedas, all of the nearby Crater Range, almost half of the Sand Tank Mountains (located about 12 miles to the northeast of the Saucedas), most of the small Pozo Redondo mountain range (located just south of the Saucedas), half of the adjacent Sikort Chuapo Range, and almost all of the Ajo Range (located near the Arizona/Mexico border). Few of these areas are highly mineralized.

PROSPECTING POTENTIAL

The northwest portion of the Sauceda Mountains seems to offer the best prospects for mineralization. In particular, the west flank of the range near Hat Mountain should be prospected in detail. Tungsten, like tin, is almost invariably associated with silicic igneous rocks. The northwest portion of the range is made up of older, more silicic rhyolites and andesites - theses rocks may harbor undiscovered tungsten deposits.

 

Twelve tungsten minerals are known to science, but only four of them are rich enough and abundant enough to constitute ore minerals. These are scheelite, wolframite, ferberite, and huebnerite. Scheelite usually fluoresces in short-wave ultraviolet light, giving off a pale-blue glow. In this case, an ultraviolet light source may prove to be a useful prospecting tool. Prospectors should note that the Sauceda Range lies within the Barry M. Goldwater Air Force Range. Permits are required to enter the area.