New Mexico Mineral Symposium — Abstracts

The Iron Hill district is located on the west flank of the low hills in the southwestern Robledo Mountains in Dona Ana County. The district is approximately 3 mi southwest of Robledo Mountain, and is in the NW ¹/₄ sec. 16 T22S R1W. The latitude and longitude of the center of the district is 32° 23' 51"N, 106° 57 00"W. Adits and prospect pits of the Iron Hill district are readily visible on the Leasburg, New Mexico quadrangle.

The district is not directly accessible by any roads or trails. It is best reached by taking Interstate 10 to Road C 9 and a dirt road that exits Road C 9 to the north, which parallels the north-south trend of the Robledo Mountains. The mines are approximately 2 mi east of the dirt road. A hike over relatively flat ground with arroyos is required to get to the mines.

The geology of the district was summarized by Dunham (1935). Hematite is present in dark-red botryoidal masses with radiating fibers and minor quartz and gypsum. Many of the botryoidal masses are aggregates of rough spheres of hematite that have grown together and often resemble bunches of small grapes. The rough spheres range in size from less than a millimeter to a few centimeters. The botryoidal character is similar to that of manganese oxide deposits near Socorro and Deming, but no significant manganese mineralization is apparent in the Iron Hill district.

The hematite bodies replace sections of Pennsylvanian limestone of the Magdalena series, which dip to the southeast approximately 20°. The orebodies are lenticular and appear to be related to fissure zones that cut across the bedding of the limestone in various directions. Sixteen bodies of hematite have been opened up, and many other outcrops have not been explored. The dimension of the bodies varies, from small masses to large bodies as much as 200 ft long, 120 ft wide, and of unknown vertical extent. Dunham indicated that a moderate resource of iron was available, but the remoteness of the deposits and their distance to markets made them uneconomic to mine.

The deposits are reported to be mineralogically similar to the hematite deposits of West Cumberland and the Forest of Dean, England, which are known for "kidney ore" hematite. Like these deposits in England, the Iron Hill district formed in Carboniferous limestones that were formerly overlain by a great thickness of "red bed" deposits. The red beds may have provided hematite cement that leached and subsequently precipitated into the underlying limestones.

Fourteen short tunnels are reported in the hills, and there are many shallow shafts. The dumps are loaded with excellent specimens of botryoidal hematite, and collecting is easy once you get to the mines. The mines are easily spotted on the hillsides because the dumps are a distinct dark red against the outcrops of light-gray limestone.

References:

1. Dunham, K. C., 1935, reprinted 1980, The geology of the Organ Mountains; part III???the mines and mineral resources of Dona Ana County: New Mexico Bureau of Mines and Mineral Resources, Bulletin 11, pp. 248-249.