NEW STRUCTURAL AND METALLOGENETIC INSIGHTS FOR THE CENTRAL PART OF MEXICO FROM FIELD AND LANDSAT THEMATIC MAPPER DATA

The excellent exposure of the mesozoic pre-cretaceous volcanic-sedimentary basement, early-cretaceous limestones reefs and the tertiary volcanic and intrusive rocks and their inaccessibility made the use of Landsat Thematic Mapper TM7 data desirable in this study. Landsat TM7 data were used to create a spectral ratio image of bands 3/4, 4 and 1, displayed as red, green and blue, respectively, and a principal component analysis images of bands 741 and 457 (RGB). These images were interpreted in the context of available geologic maps, field work, lithostratigraphic and new age data. They were used to create a coherent geological map of the area and cross sections that document intrusive bodies as well as the rhyolitic domes, several tectonic and stratigraphic units and provide a new and more detailed metallogenetic evolution for the region.

Ore deposits locations were visited and mapped, there are Au-Ag, Pb-Zn, and fluorite mineralizations, all of them related with igneous rocks from 43.6 to 29.2 My. Three metallogenetic belts were recognized: skarn-Pb-Zn-Ag, Hydrothermal Au-Ag and Hydrothermal fluorite deposits.

The application of multispectral imaging to remote regions such as central and northern Sierra Gorda-Querétaro makes the construction of detailed geologic maps possible and economical. The Landsat TM7 satellite combines good spatial and spectral resolution and allows geologic mapping directly on an image with the aid of ERMapper and Arcview-GIS-Image software. The application of band rationing and principal component analysis allows structural and lithologic data to be extrapolated from limited ground truth. The NW-SE structures inherited of the upper cretaceous, played an important control in the distribution of the intrusives, a second set of NE-SW structures control the form of ore bodies and their distribution.