Geological, geochemical and isotopic characteristics of the Lincoln County porphyry belt, New Mexico: Implications for regional tectonics and mineral deposits
Michael S. Allen and Eugene E. Foord
The Lincoln County porphyry belt (LCPB) is composed of alkalic and silica-oversaturated Tertiary intrusive and volcanic igneous centers in east-central New Mexico. The LCPB alkalic rocks belong to the Rocky Mountain alkalic province (RMAP), which comprises magmas generated during post-Laramide time along the Rocky Mountain front from Canada into Mexico, to the east of a more voluminous continental calc-alkalic magmatic arc. Igneous activity in the LCPB occurred in two pulses. An early (38.2-36.5 Ma) pulse, coinciding with waning subduction, was concentrated along the north-trending Pedemal arch and consisted of alkalic complexes emplaced along northeast-trending faults. The later (30-26.5 Ma) pulse, coinciding with early rifting, consisted of bimodal, mafic, alkalic dikes and granite plutons intruded along the east-trending Capitan lineament, and granitic plugs intruded into the older Sierra Blanca alkalic complex. Geochemical data indicate that the mafic alkalic magmas were derived from metasomatized mantle, whereas the granitic magmas of the younger pulse were derived from the lower crust. Fractional crystallization of mafic alkalic magma and crustal contamination produced the compositional variation present in some LCPB complexes. Certain mineral deposit types are related to igneous rocks belonging to either magma suite. Gold deposits are hosted by LCPB alkalic complexes, and are similar to deposits elsewhere in the RMAP (e.g., Cripple Creek, Colorado; Ortiz, New Mexico). Molybdenum porphyry deposits and thorium vein deposits are hosted by evolved granites. Iron skarn deposits and REE deposits are associated with rocks of both magma types.
- Allen, Michael S.; Foord, Eugene E., 1991, Geological, geochemical and isotopic characteristics of the Lincoln County porphyry belt, New Mexico: Implications for regional tectonics and mineral deposits, 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. 97-113.