South Mountain is approximately 30 miles northeast of Albuquerque in the southern end of the San Pedro-Ortiz porphyry belt. It is a Tertiary monzonite laccolith that intrudes the Permian Abo and Yeso Formations and, in places, the Permian Glori eta Sandstone. The base of the laceolith lies on the Abo except in the southeastern part where it overlies the Mes eta Blanca Member of the Yeso. The incompetence of the Yeso appears to nave allowed the monzonitic magma to spread laterally throughout the stratigraphic interval up to the Glorieta Sandstone which was more resistant and broken only locally by the intrusion. The Yeso was apparently shoved aside by magmatic forces and, at the same time, added to the doming of overlying sediments caused by the intrusion. The Abo and widerlying formations were folded into a basin apparently by the intrusion. In the southwestern part of the laccolith a small circular quartz monzonite stock intruded the monzonite with little shattering or brecciation along the contact. This seems to indicate that crystallization of the monzonite had not been completed. Northwest of South Mountain a latite-andesite porphyry laccolith intruded the Pennsylvanian Sandia Formation. It overlies a conglomerate at the base of the Sandia Formation and is overlain by massive lime- stone of the Madera Limestone.
North of South Mountain a series of rhyolite sills intrude the Madera Limestone. The sills can be traced to the San Pedro Mountains. The feeder for the sills appears to be a dike around which there is zoning of mineral deposits.
There appear to be at least two periods of faulting: 1) contemporaneous with intrusion, and 2) post-intrusion. The dominant trend of faulting is to the northeast while minor trends are northwesterly and easterly. Most of the faults belong to the Tijeras fault system which is of regional extent.
Mineral deposits include: 1) a small contact-metasomatic magnetite deposit, 2) many small supergene iron deposits, 3) a fissure vein of magnetite-specularite, and 4) a fissure vein of galena, sphalerite, chalcopyrite, and pyrite. These deposits are small and not economically important. Ground water is usually available in the Madera Limestone or in Quaternary alluvium at a depth no greater than 200 feet.
Earth and Planetary Sciences
Level of Degree
Department of Earth and Planetary Sciences
First Committee Member (Chair)
Vincent Cooper Kelley
Second Committee Member
J. Paul Fitzsimmons
Third Committee Member
Wolfgang Eugene Elston
Thompson, Tommy B.. "The Geology of the South Mountain Area, Bernalillo, Sandoval, and Santa Fe Counties, New Mexico." (1963). https://digitalrepository.unm.edu/eps_etds/221