Some effects of the Precambrian basement on the development of the Sacramento Mountains
Arthur L. Bowsher
High-intensity anomalies of gravity and aeromagnetic maps outline different blocks of Precambrian rocks within the Sacramento Mountains because the relief on the Precambrian basement rocks is generally negligible and Tertiary igneous rocks have negligible magnetism but do have mass. The positive aeromagnetic anomaly within the Sacramento Mountains appears to be the strongest and largest such anomaly within New Mexico. The anomaly is interpreted to be caused by abundant magnetite in the upper portion of a huge, layered, ultramafic Precambrian intrusive body. Late-stage intrusive bodies flanking it are represented by Pajarito Mountain and the gabbro stock drilled near Lincoln. The utramafic stock appears to be intruded along a failed, possibly Proterozoic, rift. Other Precambrian intrusives and metamorphic rocks surround the ultramafic stock. Strong facies changes occur in the overlying Paleozoic rocks of the Sacramento Mountains. Mississippian, Pennsylvanian and Permian reef patterns indicate uplift along the west edge of the basement block. Facies of the San Andres Formation over the anticlines of the Tinnie-Dunken anticlinorium indicate that the Precambrian basement blocks were rising during deposition of the limestones. The Sacramento Mountains began to rise in the early Mesozoic. A set of consequent streams developed on the east-dipping slope of the mountains. Simultaneously the Tinnie-Dunken anticlinorium began to rise. The Rios Hondo, Picacho and Felix, and Bluewater Creek are now antecedent streams that breach the anticlinorium. Molycorp is currently developing a large zirconium and yttrium deposit near Pajarito Mountain. Minerals of the ultramafic stock and related rocks of the Precambrian are buried beneath the San Andres, Yeso and Abo Formations but may become important resources in the future should the United States of America lose its sources of strategic minerals abroad.
- Bowsher, Arthur L., 1991, Some effects of the Precambrian basement on the development of the Sacramento Mountains, in: Geology of the Sierra Blanca, Sacramento and Capitan Ranges, New Mexico, Barker, James M.; Kues, Barry S.; Austin, George S.; Lucas, Spencer, G., New Mexico Geological Society, Guidebook, 42nd Field Conference, pp. 81-89.