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ARIZONA

The Lost Duppa Mine

GEOLOGY OF THE AREA


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The Bradshaw Mountains are part of the Central Highlands Province of Arizona. This physiographic province forms a transition zone between the massive sedimentary formations of the high Colorado Plateau to the north and the desert mountains of the Basin and Range Province to the south. This tectonically-active belt of rugged mountains has undergone several episodes of folding, faulting, and uplift. Uplift has been quite dramatic. In fact, so dramatic that the thick blanket of Paleozoic and Mesozoic sedimentary rocks that once rested upon the ancient Precambrian core has been completely stripped away. Consequently, many mountain ranges in the Central Highlands Province consist of an exposed core of Precambrian igneous and metamorphic rocks. The Bradshaw

Mountains are such a range. The Bradshaws consist almost entirely of ancient Precambrian schist intruded by younger Precambrian granites, granodiorites, and diorites. The granitic intrusions are batholithic in size; indeed, most of the southern half of the Bradshaws is composed of granite. A belt of schist crops out along the eastern flank of the range. Although this belt is only two to three miles wide in the southern part of the Bradshaws, it comprises much of the northern portion. South of Cleator, these dark-colored schists form the wall rock of Black Canyon (which was named for these ancient black schists).

Small exposures of Tertiary basalt occur in the northern portion of the range. The two largest are located on the northeast flank of the Bradshaws, between Mayer and Cordes Junction and in the north-central part of the range, just east of Mount Union. But again, these are minor occurrences. The northern half of the Bradshaws is dominated by Precambrian crystalline rocks.

PROSPECTING POTENTIAL

The Bradshaw Mountains have been a miner's delight for 150 years. The rugged peaks and canyons of the Bradshaws have been blessed with a number of rich mineral deposits, most of which have been found. The eastern flanks of the range are scored by many deep canyons and ravines. It is entirely conceivable that one of these canyons

harbors a hidden silver ledge. Prospectors may want to concentrate on the canyons that lie between the crest of the northern Bradshaws and the Agua Fria River to the east. A metal-detector may be of some use in the search for silver-bearing float in the lower reaches of each canyon. Careful mapping and tracing of the float may prove to be fruitful.