Bulletin-15—The Geology and Ore Deposits of Northeastern New Mexico (exclusive of Colfax County)

By G. T. Harley, 1940, 102 pp., 11 figs., 5 plates.

This bulletin consists of three parts; Part I: General features, Part II: Mining districts, and Part III: Productive mines. Northeastern NM has in recent years been an important producer of mineral wealth, almost all of which has come from two properties, the Pecos mine of the American Metal Company, at Tererro in San Miguel County, and the I. J. Stauber mine near Pastura in Guadalupe County. Elsewhere in the region, which also includes Mora, Union, Harding, and Quay Counties, the production, recorded and unrecorded, has been negligible, hardly exceeding a total of $5,000; the deposits here are merely interesting examples of geological processes of mineralization without value as possible future producers of wealth. These unproductive counties are included in this report, therefore, mainly for two reasons: first, their metallic mineral resources are not of sufficient importance to warrant separate descriptions; and second, they contain copper minerals in numerous deposits of the sedimentary type, the outstanding example of which, in the state of NM, is the Stauber mine at Pastura.

The field work for this report was begun July 1, 1934, and during that summer the Pecos mine and vicinity were examined. A great deal of time was devoted, at the mine, to a study of the cores from the Company's diamond drilling operations. During the summer of 1935 a field trip was made covering the remainder of the region described in this bulletin, and a study was made of the literature having a bearing on the work. The summer of 1936 and part of the early fall were devoted to the microscopic study of thin sections of the rocks and of polished sections of the ore specimens from the region. Most of these specimens were from the Pecos mine and vicinity, but many were from the Red Beds copper deposits. A short field trip was made, and the first drafts of maps and manuscript were submitted late in 1938; revision of manuscript and final drafting of maps were completed in the summer of 1940.

This bulletin has been prepared particularly for the use and information of prospectors, owners, and operators of mining property, and as a guide to non-residents who may become interested in the development of the metallic resources of the region. Technical phraseology and the presentation of highly scientific aspects of the geology, and of debatable theories, have been minimized, while the evidence gathered in the field, as shown by surface outcrops and by veins exposed in mine workings, has been emphasized.

With the exception of the Pecos and Stauber mines, most of the mine workings have not been operated for many years and consequently are in a bad state of repair or are obstructed by water and debris. It was not always possible to locate the owners, or men who had worked in these properties when they were fully opened, and consequently only a partial and usually an unsatisfactory account of what had been done underground could be obtained.

It is not contemplated by the state Bureau of Mines that much actual sampling of the veins shall be done by the geologist investigating ore deposits in the state for Bureau publications, and he is constrained to gather the figures as to the value of the ore from whatever sources are available, and to use proper judgement in interpretation. This report has been prepared largely on the evidence found on the surface, secured without regard for property lines, and supplemented by the study of practically all the openings accessible to the writer during his visits to the region.

The first part of the report includes descriptions of the physiography and of the rocks and a review of the geological history of the region. It also contains a brief discussion of the various types of orebodies and their mineralogy, and a brief review of the practical points involved in the search for ore. The second part is given to a detailed description of the individual districts in each county. In part three the Pecos and Stauber mines are described in the detail that their importance warrants. Guadalupe County contains by far the most important sedimentary copper deposit within the state; also, the occurrence of sedimentary copper mineralization is probably more widespread in this region than in any other part of the state, with the possible exception of Otero and Torrance Counties. Much has been written about this type of deposit, and geologists are not yet agreed as to the source of the copper minerals; it is proper, therefore, that this bulletin should include a fairly complete list of the papers in NM and the adjacent territory.

While the material in this bulletin may be regarded as a basis on which to locate and plan future work in the ore deposits of the region, such work should not be prosecuted over long periods of time except under sound technical advice and direction. In the long run it is always the most economical procedure to secure the services of an experienced and reputable mining engineer or mining geologist, at frequent and stated intervals, and to rely upon his judgement and advice regarding the future possibilities of the mine, the quantity and value of the ore blocked out, the best campaign for future development, and the advisability of expenditures for plant and equipment.