Location: listed as being from 1 mile north of Mica Tanks, in the Plato Verde Prospect, Van Horn Mountains County: Culberson County, Texas Minerals: assume disseminated Cerargyrite (synonym for Chlorargyrite) from the mine description text below. Chemical Formula: AgCl Crystal system: Isometric (typically clear when fresh with waxy, adamintine luster) Specimen size: 6 x 3 x 1.5 inches Specimen weight: 690 grams Collection Reference: TMM 1310 In the Jackson School of Geosciences Collection, at the University of Texas at Austin. Additional Information: Very specific information on this mine is found on the Supporting Text on the Geologic Quadrangle Map No. 23, Geology of the Van Horn Mountains, By Page C. Twiss, August 1959. "The Plata Verde mine, a mile northwest of the Mica Mine area along the western base of the Van Horn Mountains, contains small quantities of cerargyrite (horn silver). The mine was worked sporadically during the 1930's and 1940's. Most of the production occurred between 1936 and 1939, when 10,800 tons of ore were shipped to the El Paso smelter of American Smelting and Refining Company. The silicious silver chloride ore contained 9 to 26 ounces of silver and 0.23 to 0.46% copper, 68% silica, 13% alumina, 2% ferric iron oxide, 1% lime, 0.1% zinc, and 0.3% sulfur. The most recent exploratory work was done during 1951-1955, when a vertical shaft was sunk at the south end of the old workings (Peter T. Flawn, personal communication). According to Flawn, the mineralization is controlled by at least two major north trending gravity faults which border the shafts and inclines on the east and west. Small blebs of cerargyrite are concentrated along bedding planes and shear zones (parallel to the bedding) in the steeply dipping muscovite sandstone beds of the Permian Powwow conglomerate in the Wolfcamp Series."
Minerals: Sphalerite (green/brown) and Galena - silver/grey (base metal sulfides) Location: identified as from the Bonanza Mine, Quitman Mountains County: Hudspeth County, Texas Chemical Formulas: Sphalerite (Zn, Fe)S and Galena (PbS) Crystal Systems: Sphalerite (Isometric hextetrahedral), Galena (Isometric/cubic) Moh's Hardness: Sphalerite (3.5-4), Galena (2.5-2.75) Specimen Size: 3.5 x 3.25 x 2.5 in Specimen Weight: 1.11 kilograms Collection Reference: TMM 1508 Other information: The Bonanza mine is located in the northern Quitman Mountains in southern Hudspeth County, approximately 130km southeast of El Paso, Tx. The northern Quitman Mountains are a volcanic cauldron that has been superimposed across Laramide-deformed Paleozoic and Mesozoic marine strata of the Chihuahua Trough. The cauldron is expressed as a thick, areally restricted sequence of ash flow tuffs encircled and intruded by a composite granitic ring dike with a stock at its northern end. Separating the ring dike from the volcanic pile on the north and east is an arcuate septum of Cretaceous limestone that has been deformed into an anticline (Murry, D.H., 1980). The Bonanza Mine is located in the northern stock. The Bonanza Mine has four levels: 32 m, 50 m, 69 m and 85 m. All are connected by a main shaft and an exploration shaft, and a ventilation shaft opens to the first level. The main shaft is badly caved, and the others are filled with debris. The lower levels reportedly are flooded (Murry). The 1902 Mineral Survey of Texas lists a Bonanza Mine sample assay with 28 ounces of Silver (Ag) per ton and 61.8% Lead (Pb). A more detailed description of the mineralogy of the Bonanza mine vein was captured by McNulty, W.N et al (1971) in the 5th Annual Field Trip Guidebook of the El Paso Geological Society: "The principal ore minerals are galena and sphalerite. Quartz constitutes most of the gangue; comb structure is common, Pyrite is fairly abundant, and a small amount of wulfenite is present in the upper levels. Silver appears to be tied up with the galena, and the sphalerite contains some cadmium. Gold and uranium occur in trace amounts. Chalcopyrite and oxidized copper minerals (malachite and chrysocolla) are sparsely disseminated through the vein material. The vein also contains appreciable amounts of specular hematite, magnetite, altered feldspars, and clay minerals. In the upper levels galena and sphalerite are present in approximately equal amounts, but the sphalerite content increases with depth. The water table stands 200-300 feet below the surface, depending on the topography. The amount of water is relatively small -- about 2 or 3 gallons per minute in the lower levels. Therefore, water presents no great problem in mining; in fact, the water available is an asset for milling. The quartz monzonite is highly altered (kaolinized) in places and does not stand well--especially in the wet, lower levels. " Remember, this was in 1971, the mine has caved in and deteriorated significantly since.
Tenorite (aka Melaconite) County: El Paso County Chemical formula: CuO Crystal System: Monoclinic Specimen size: 3 x 1.75 x 2 inches Specimen weight: 336 grams Collection reference: TMM 2859 In the Jackson School of Geosciences at the University of Texas at Austin.
