New Mexico Geological Society Annual Spring Meeting — Abstracts

More than 50,000 troy ounces of gold and 5 million troy ounces of silver have been produced from Socorro County, New Mexico between 1863 and 1981. Rosedale district is one of the more important gold producing districts in Socorro County. Gold was discovered in 1882 and, because of the rich Au content of the deposit, it created a rush to the area. An estimated total value of metals (Au and Ag) produced from Rosedale district between 1882 to 1981, amounted to about $500,000 generated from 28,000 oz of gold and 10,000 oz of silver mined from 7 levels underground. However, exploration within the district has shown that there is still potential for volcanic-epithermal gold and silver deposits. Exploration work conducted in 1976 by Perry, Knox and Kaufman, Inc. estimated 1.5 to 2 million tons of 0.3 oz/short ton Au remained in the district. Rosedale lies in a tectonically active and structurally complex area and is part of the Mogollon-Datil volcanic field, which is a late Eocene-Oligocene volcanic province that extends from west-central New Mexico southward into Chihuahua, Mexico. Rosedale lies on the northeastern slope of the San Mateo Mountains, about 25 miles south of Magdalena and about 30 miles north of San Marcial. Main rock types associated with mineralization are brecciated and sheared rhyolite, partly cemented by banded bluish-white quartz. These rocks have been fractured, and recemented with glassy vein quartz. The walls have been silicified, and the outcrop stands out clearly. The vein carries free-milling gold. There is limonite throughout, and manganese oxides occur in stringers and as coatings on the fracture surfaces. Manganese appears to be associated with the higher grades of ore. Sulfide mineralization appears to exist above the water level, which is at 725 ft depth. Some of the quartz in the oxidized ore above water level contains cavities formerly occupied by other minerals. Changes in the primary ore values within the veins have been observed and the origin of this can be established by actual examination of the paragenesis of the veins in the district. Comparatively rich shoots are present, and are probably very irregular in form. These observations indicate the potential of gold mineralization is part of an epithermal vein system.