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ARIZONA

The Lost Four Peaks Gold Mine

GEOLOGY OF THE AREA


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Bounded by the Mogollon Rim to the north and the arid mountains of the Basin and Range Province to the south, the Central Highlands Province is an uplifted, folded and faulted belt of igneous, metamorphic, and sedimentary rocks. The Central Highlands Province is basically a "disturbed belt" or transition zone between the stable platform of the Colorado Plateau and the tensional environment of the Basin and Range Province. In most cases, uplift has been so dramatic that erosion has stripped away the overlying mantle of sedimentary rocks, exposing the ancient Precambrian cores of the mountains. This tectonically-active region has a rich mining history and contains many of Arizona's famous mining districts. These include Jerome, Globe/Miami, Clifton/Morenci, and the Bradshaw Mountains. The Mazatzal Mountains are the largest range in the Central Highlands Province. This uplifted block of ancient Precambrian igneous and metamorphic rocks forms the western wall of the Tonto Basin, extending some 50 miles in a northwest-southeast direction. South of the Mazatzals lie the Tertiary dacites and welded tuffs of the Superstition Mountains. These felsic volcanics emanated from several calderas during the mid-Tertiary, some 15 to 35 million years ago. Several pulses of volcanism produced vast amounts of silicic lavas and pyroclastics.

The Mazatzal Mountains are mostly composed of Precambrian schist, volcanic rocks, and granites. Granitic rocks comprise most of the southern half of the Mazatzals; the exception is a large "roof pendant" of older Precambrian metamorphic country rock preserved in the Four Peaks area. The northern half of the range is underlain by a variety of ancient Precambrian metamorphic and igneous rocks. A belt of Precambrian pyroxenites, schists, rhyolite lava flows, and quartzites extends from Mount Ord northward to Deadman Creek, a distance of about 16 miles. Precambrian granite bounds this belt of older basement rock to the north and northwest. The contact is fault-bounded and trends northeast-southwest. Ancient Precambrian "greenstones" are exposed north of the granitic mass mentioned above; these rocks form the northern terminus of the Mazatzal Mountains. Greenstone belts are prominent features of Archean terranes on all continents. They consist of columns of ancient metamorphosed volcanic rocks. In most greenstone belts, highly mafic metavolcanic rocks are found at the bottom of the sequence with increasingly more felsic rocks piled on top. The entire greenstone belt is often surrounded and intruded by granites. Occasionally, banded iron formations are associated with greenstone belts. Greenstone belts are also known to harbor rich gold deposits - this association has been noted the world over!

The Mazatzals are not highly mineralized but mercury-mining operations have been carried out in the rugged country near Mount Ord.

PROSPECTING POTENTIAL

The Mazatzal Mountains have proven to be relatively barren of mineral deposits. Except for a few isolated occurrences of placer gold, cinnabar, and amethyst, the mountains contain no major mineral deposits. The northern portion of the range near Mount Ord appears to be weakly mineralized. Small mercury mines occur just to the northeast of the peak. In 1911, a small amount of placer gold was recovered near Mount Ord and the Reno Pass area. An air of mystery pervades the area near Mount Ord. In 1870, the skeletons of five prospectors were found on the northern slope of the mountain.

Precambrian "greenstones" are exposed in the northernmost part of the Mazatzal Mountains. Gold deposits have been found in nearly every greenstone belt in the world. A careful search for ironstone beds within the greenstone sequence may prove to be rewarding.


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Prospectors may also want to focus on the western flanks of the Four Peaks, as this area is specifically mentioned in at least two accounts of the story. A careful search for gold-bearing float in the canyons and arroyos of this rugged country may turn up something.