AEROMAGNETIC ANOMALIES OF INTRUSIVE ROCKS ASSOCIATED WITH MINERAL DEPOSITS IN SEDIMENTARY ENVIRONMENT OF THE NORTHEASTERN MEXICO

The Consejo de Recursos Minerales magnetic database generated in the Mexican Republic is being extremely useful in the investigation of the mining resources associated with intrusive stocks. One of these applications is when these igneous bodies do not outcrop, but they are located near the surface. In the analysis of the aeromagnetic data, the geophysical responses of these geologic elements are identified, selecting in this way prospective areas with a high mining interest, for the association of the intrusive stocks with the metallic mineral deposits.

The studied region located in between the northeastern Mexico and the borderline with Texas, U.S.A. is shown like an example of the utility of the aeromagnetic database.

Mesozoic sedimentary rocks were intruded by granitoids of laramidic age giving origin to economic skarn type ore deposits, containing Pb, Zn, Cu, Ag and Au in the contact zone; and in minor quantity veins, chimneys, breccias, and mantos. (Megaw, et. al; 1988)

A close correlation is observed between intrusive stocks, skarn type ore deposits and dipolar aeromagnetic anomalies. Apparently the group of Mesozoic and Tertiary intrusive rocks of the northeastern Mexico are emplaced surrounding the Coahuila basement block (Lehmann et. al., 1999), that is could be the cause we have a gap of dipolar aeromagnetic anomalies and intrusive outcrops, in the south-central portion of the Coahuila state.

The E-W elongated aeromagnetic anomalies defined over this gap seem to be part of the igneous and metamorphic rocks of Permian and Triassic age of the Coahuila basement block.

The Concepcion del Oro mining district, in Zacatecas state is a good example of the application of the aeromagnetic database in the exploration of high temperature skarn type ore deposits, most of them are stock and dyke contact-skarn dominated systems, that show multiple stages of intrusive emplacement and skarn development as well as strongly structurally-controlled metal mineralization with the presence of pyrrhotite. (Megaw, 1999)

The Mesozoic and Tertiary intrusive bodies are distributed in groups and only a few have a surface expression that is larger than a square kilometer. Contact zones between the Jurassic limestones and intrusive dipolar aeromagnetic anomalies of the northeastern Mexico; are prospective for Pb, Zn, Cu, Ag and Au.