Page 119 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

118 GEOLOGY AND ORE DEPOSITS OF SIERRA CO., N. M.
highest return from the smelters. For the mining that has been done in the district, the following costs are reported as being average; mining $1.75 per ton of ore, hauling $0.50 per ton, and milling $1.50 per ton, making a total operating cost of $3.75 per ton of ore. It cost $7.00 per ton of concentrates for freighting to Engle, the nearest railroad point, and $5.00 per ton to haul freight back to the mine.
MINE DESCRIPTIONS
IRON MOUNTAIN DEPOSITS
North of Fairview about 12 miles are the Iron Mountain
contact-metamorphic deposits of iron ore. They are in the north- ern end of the Sierra Cuchillo and for the most part in Socorro County, although part of the main occurrence and several small detached deposits are in Sierra County. The deposits in Socorro County have been described briefly by S. G. Lasky. 45
These deposits occur in the Magdalena (Pennsylvanian) limestone and are genetically related to the great sill of monzon- ite porphyry which is a prominent feature of the Sierra Cuchillo faulted block. This sill separates the Magdalena limestone into an upper and a lower portion, and has slightly arched the over- lying beds in a large area. The intrusion has also caused numer- ous slight folds and much cross fracturing, particularly along the crests of the minor folds. Considerable contact-metamorphism has occurred along these fractures in the tops of the eastward- trending minor folds. The ore minerals are magnetite and hema- tite, while garnet and partly altered limestone are the gangue minerals. The limestone overlying the ore is altered in places to nearly pure garnet. In places within the ore and occasionally within the overlying garnetized beds, a small amount of copper staining, probably malachite, was noted.
Aside from a few pits and short tunnels, no development work has been done in these deposits, and hence the extension of the ore bodies in depth could not be ascertained. Contact-meta- morphic action has been confined largely to the roof of the sill, however, and it is believed with some confidence that the bottoms of the deposits will be confined to the base of the limestone lying above the porphyry intrusion and that it will follow for consider- able distances down the general dip of the sedimentary rocks, which here is about 20° NE. As exposed on the surface the main bodies are lens shaped, average 1,200 feet in length, and are 60 to 250 feet wide. The average grade of the ore is reported to be about 45 per cent iron.
VINDICATOR AND WEST CONTACT GROUPS
These claims, about 33 in number, are located for a distance
of 7,000 feet along the contact of the porphyry and the overlying limestone northwest of the Black Knife claims, and reach to the
45The or- deposi's of Socorro County, N. Mex.: N. Mex. Sch. of Mines, State Bur. of Mines and Min. Res. Bull. 8, pp. 138, 139, 1932.