Green Monster Mine, Shenandoah Peak (Shenandoah Mountain), Goodsprings District, Spring Mts, Clark Co., Nevada, USA
|Latitude & Longitude (WGS84):||35° 53' 21'' North , 115° 38' 56'' West|
|Latitude & Longitude (decimal):||35.88919,-115.64895|
|Köppen climate type:||BWk : Cold desert climate|
A former Cu-Pb-Ag-U-Zn occurrence/mine located in sec. 1, T24S, R56E, MDM, 13.3 km (8.3 miles) WNW of Shenandoah Peak (coordinates of record), 13 miles NW of Goodsprings, on the western margin of the western spur of the Spring Mountains, E of Black Butte (on the northern border of Mesquite Valley), on Bureau of Land Management administered land. Discovered in 1894. MRDS database stated accuracy for this location is 10 meters.
The ore deposit is irregular in thickness and is localized by a shear zone in the Bullion dolomite member of the Monte Cristo limestone of Mississippian age. Secondary uranium minerals occur in a zone 1 to 2 feet thick on the footwall side of the ore body. Kasolite and an unidentified uranium mineral are associated witk malachite, azurite, cuprite, cerussite, calamine, and limonite in a yellow, earthy ore as replacement deposits in the upper stope. Selected specimens assayed as high as 9 percent uranium.
Most of the uranium is in the upper stope, and the grade decreases rapidly with depth. 0.057 percent uranium is the highest value obtained 80 feet below the upper stope. Reserves are evidently small and only one shipment of 5 tons, containing 1.00 percent U308 had been made by the end of 1951.
Mineralization is a replacement deposit (mineral occurrence model information: Model code: 72; USGS model code: 19a; Deposit model name: polymetallic replacement; Mark3 model number: 47) hosted in Mississippian dolomite. The ore body strikes N60W and dips 50SW. Controls for ore emplacement included a shear contact between the Arrowhead & Bullion members plus minor thrusts and local conduits along tear faults. There are 3 ore shoots that range between 5 and 15 feet thick. Ore from tabular bodies are elongated in the bedding plane, and are predominately a mixture of hydrozincite and hemimorphite in a gangue of white dolomite and ocherous limonite. Smithsonite forms veinlets in fractures crossing the ore zones. Cerussite is in granular masses and galena is in lenses and kernels surrounded by thin rinds of anglesite. Radioactive minerals are dumontite, kasolite, rutherfordine, chrysocolla, and limonite intermixed with the oxidized Pb and Zn minerals. The U ore grade is variable, up to 9%. The U decreases with depth. Local rocks include Mississippian Limestone and minor amounts of dolomite and shale.
Local geologic structures include local homoclinal structure of the beds - part of a SE-plunging syncline; one main thrust fault and several minor ones. Regional structures include a large thrust zone.
Workings include unspecified underground openings with a length of 243.84 meters and an overall depth of 121.92 meters (the topo map reflects 1 shaft symbol labeled "Green Monster Mine" at this point.
Production information: Crude ore contained 15 - 25% combined metals. Pb averaged 1%. At the deepest development, Pb was 10% or more.
28 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
|Quaternary - Miocene|
0 - 23.03 Ma
|Cenozoic sedimentary rocks|
Age: Cenozoic (0 - 23.03 Ma)
Lithology: Sedimentary rocks
Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. 
323.2 - 358.9 Ma
|Carbonate Shelf Sequence - Limestone|
Age: Mississippian (323.2 - 358.9 Ma)
Description: This unit is present in southern Nye, Lincoln, and Clark Counties. Unit includes the Monte Cristo Limestone, and Lower Mississippian rocks referred to as the Joana, Mercury, Bristol Pass, and Rogers Spring Limestones. It generally lies depositionally above Devonian carbonate rocks and beneath Pennsylvanian carbonate and clastic rocks. In the Meadow Valley Mountains in southern Lincoln County it is also shown sitting on a thin horizon of Pilot Shale and overlain by a thin Mississippian clastic unit assigned to unit IPMcl.
Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052.