Page 51 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

50 GEOLOGY AND ORE DEPOSITS OF SIERRA CO., N. M. much more widespread and general but of considerable lower
grade.
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The ore deposits of Sierra County may be classified accord- ing to form into (1) veins or lodes, (2) stockworks closely re- lated to veins, (3) replacement deposits or "blankets " and (4) placers. The first two occur principally in igneous rocks, while the third type is common in the limestone areas, but there are exceptions to both rules. A classification of the ore bodies may also be based chiefly upon the genetic features of the ores and their constituent minerals, dividing them into primary deposits
and secondary enrichmant deposits.
The table, in pocket presents an alphabetical list of the ore
and gangue minerals occurring in Sierra County. The min- erals in the list include two distinct groups, differing in mode of origin. In the first class are included not only those minerals of which the country rocks were originally composed before the ore deposits were formed, but those that have been developed from them by the action of surface waters. These minerals are en- tirely independent of ore deposition and are marked by an aster- isk in the table. Where unreplaced blocks of country rock are enclosed within ore bodies, these minerals might be considered as gangue minerals.
The second class of minerals includes (1) those formed by ascending ore-forming solutions (hypogene minerals), and (2) other minerals derived from them by the action of descending waters (supergene minerals). This group has been arranged in the table, in pocket according to the principal metals con- tained and the relative temperature at which they were deposited.
Many of the minerals listed in the above tables were not seen by the writer in the field ; some were examined in specimens from private collections, and many are taken from lists compiled by others who have investigated the area. The accompanying table gives the composition of each mineral found in the county, the locality where found, and in many cases the relative abun- dance of the species.
It is of interest and a matter of great importance to note the manner in which the minerals are grouped in the table, in pocket By far the most important group in variety of min- erals contained is that at the top of the table, containing the oxi- dized minerals that are normally found in the zone of oxidation and leaching at and near the surface. The second largest group in point of variety is that of the primary sulfides, and those that have been found in the county are characteristic and com- mon minerals Of the extreme upper part of the zone of moderate temperature (mesothermal) deposition. It is probable that most
MINERALOGY OF SIERRA COUNTY