Circular 57—Preliminary geologic and relief map of the Precambrian rocks of New Mexico

By R. W. Foster and T. F. Stipp, 1961, 37 pp., 1 table, 1 figure, 1 sheet.

This circular contains a list of oil tests that have penetrated rocks of Precambrian age, and the references used in compiling the Precambrian outcrops shown on the accompanying map. The wells are listed by county and assigned a number beginning with 1 in each county. In addition to the map number, the list includes the well name, location, year of completion, well elevation, total depth drilled, depth to Precambrian rocks, elevation of the Precambrian surface, lithology of the Precambrian rocks, and the source of the data presented. The location of the well is given by section, township, and range, followed by the standard letter designation within the section. The depth to Precambrian rocks was determined, where possible, by examination of well samples and electric and radioactive logs. For the remaining wells, the depth was taken from records maintained by the New Mexico Bureau of Mines and Mineral Resources and the U.S. Geological Survey for each oil test drilled in the state.

These records consist of completion reports, drillers logs, production data, and geological reports and maps. In most cases, the data are thoroughly reliable, being supplied generally by trained geologists and engineers. Where the source of the information is not known or is insufficient, an attempt has been made to interpret the material available and remove questionable wells. Because of this, the list may not be entirely complete or may include a few wells that did not reach Precambrian rocks.

The lithology of the Precambrian rocks presented in the list includes data from wells for which cuttings or cores are available in the well-sample library at Socorro, as well as information obtained from published and unpublished reports. Unless otherwise noted, samples from Precambrian rocks were identified with a binocular microscope with maximum magnification of 36x. It is believed that the rock names that have been applied are reasonably accurate; additional mineral determinations by petrographic methods would result in only minor changes of classification. A considerable amount of probably valid information concerning the lithology of the buried Precambrian rocks has not been included in this report because of the unfortunate synonymous usage of granite and Precambrian.

The outcrop distribution and subsurface data of the basement rocks of NM are restricted in this report to rocks of known or probable Precambrian age. Post-Precambrian intrusive rocks, believed to be, for the most part, of Tertiary age, have not been included, because of the generally small area of exposure and because many of these rocks consist of laccoliths, sills, or dikes underlain by unmetamorphosed sedimentary rocks of Paleozoic or Mesozoic age.
Outcrops of Precambrian rocks have been divided into four principal lithologic types on the basis of areal extent. These include granite and related rocks, metamorphic rocks with the exception of quartzite and granite gneiss, quartzite, and intrusive and extrusive rhyolite.