Bulletin  10—The geology and ore deposits of Sierra County, New Mexico

By G. T. Harley, 1934, reprinted 1975, 1989, 220 pp., 19 figs., 11 plates, 1 index.

Discusses geology and metallic resources of Sierra County, third largest producer of mineral wealth in New Mexico. Sierra County, one of the smaller counties of NM, has been its third largest producer of mineral wealth. All of the ore bodies so far exploited have been of small to moderate size, although some of them have been phenomenally rich. To those who are interested in seeking out and operating small mining properties, the potential mineral wealth of this area is still a matter of great interest.

The field work for this report was begun July 1, 1931. During July and August a general survey was made of the county, and most of the mining districts were examined in such detail as time and the condition of the mines permitted. A topographic map of the Hillsboro district was made and the areal geology worked out. It was planned to complete the preparation of the report during the winter months and to have it ready for the printer in the summer of 1932. In the meantime, however, due to depressed conditions in the metal market, many of the larger base-metal mines in the southwestern US greatly curtailed production or suspended operations completely. This encouraged many individuals and small operating units to take up in an energetic manner the search for placer and lode gold deposits, or to attempt to find base-metal deposits containing gold in sufficient quantity to make operation profitable in spite of existing low prices. The result was that many of the mines in the county that were inaccessible in 1931 had been or were being sampled or prepared for operating in the spring of 1932. It was necessary, therefore, during July 1932, and on several occasions thereafter, to revisit the different mining camps in the county and to include much additional material with that already gathered.

This bulletin has been prepared primarily for the use and information of prospectors, owners and operators of mining property in Sierra County, and as a guide to those non-residents of the county who are seeking an outlet for funds through the development of the metallic resources of the region. To this end technical phraseology and the presentation of the highly scientific aspects of the geology of the county have been minimized, and the evidence gathered in the field, as shown by surface outcrops and the portions of veins exposed underground, has been emphasized.

Throughout Sierra County, most of the small properties and many of the larger ones have been inactive for many years, and their workings have caved and have become inaccessible. Many of the owners, as well as others who were once familiar with these old workings, are no longer in the county, and the claims have declined until claim and location monuments, and the notices that were once in them, can no longer be found in the field. Where old records of production are still available or reports by reputable engineers have been read, it has been possible in a measure to picture the conditions that existed in the veins when these old mines were active, but on the whole, the details of production and the value of the ore shipped have become clouded and in many instances are quite out of line with the evidence obtainable at surface. 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 source is available, and to use proper judgement in utilizing them.

In those camps now active, most of the smaller holdings have operated in the past two or three years under a whole series of new claim and company names, and the original and often historical names have been lost completely. Only the more important properties, as the Rattlesnake, Bonanza, Lady Franklin, Silver Monument, US Treasury, and several others, have held to their original names. The report has been prepared very largely on the evidence found on surface, secured without regard for property lines, and supplemented by the study of practically all of the openings accessible to the writer during his several visits to the county.

The first part of the report includes a description of the rocks and the geological history of the county, a discussion of the ore bodies and their mineralogy, and a brief review of practical points involved in the search for ore and the economical exploitation of this mineral wealth. The second part is given to a detailed description of the vein systems and other modes of occurrence of the ore in each of the mining districts within the county, and to the descriptions of most of the mines that were open at the time of visit, and which contributed something to the store of knowledge regarding these veins.

While the material of 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 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.