NBMG Sample Site 2611, Potosi Mining District, Osgood Mountains, Humboldt County, Nevada, USAi

Regional Level Types
NBMG Sample Site 2611	Occurrence
Potosi Mining District	Mining District
Osgood Mountains	Mountain Range
Humboldt County	County
Nevada	State
USA	Country

Structure: Reg.Struct: Getchell Fault System Fault Along Range-Front; Ne-Trending Offset Fault

Alteration: Silicification, Bleaching

Deposit: Largest of the 3 tactite ore zones is the eastern one, a continuation of the riley tactite. The middle and western zones are thinner tactite bands formed in limestone units which lie down-section (west) of the riley limestone. The middle orebody was discovered underground and does not crop out at the surface. The western orebody was mined from the surface. The limestones dip 40-50e and the granodiorite contact is generally conformable to the strike and dip of the sediments. Pre-intrusive folding of the limestone into gentle, asymmetrical folds has resulted in a "scalloped" contact configuration, and the richest ore has formed where synclinal troughs intersect the contact forming embayments shaped like cone segments. To the east, down dip, the contact steepens and passes into hornfels which lies below the limestone, limiting the extent of the tactite to the east. One of the earliest tungsten properties developed in the area was riley. Getchell mine inc.'s underground mining, here at riley extension began in 1951; open pit on west orebody later. 3 tactite bodies. The eastern most of which is the northward continuation of the riley mine orebody. Riley and riley extension mines comprise the largest single tactite deposit in the district. Recent exploration (geologic mapping and drilling) defines areas containing approximately 186,000 tons of tungsten ore in the riley extension area. ; info.src : 1 pub lit; 2 unpub rept; 3 field observ

Deposit type: W skarn

Development: Recent work defines 186,000 tons ore in this area

Geology: 3 tactite zones; the east vein extends along the granodiorite contact for about 1600 ft, mined on both riley and riley extension properties. The main orebody was a tabular mass of tactite mined for approx. 800 ft. Down dip, averaging 10 ft. Thick. Preble formation limestone lenses in hornfels; most important is the 200-ft thick riley limestone, thin-bedded, with shaley partings.

Rock formation(s): Osgood Mtns Stock
Preble Formation;Preble Formation;Riley Limestone


Ore(s): 3 Tactite Zones Near Granodiorite Contact Pre-Stock, Ne-Trending Structure May Have Influenced Emplacement And Guided Mineralizing Fluids Of Reactive Limestones

Other Databases

Link to USGS MRDS:	10104002

Other Regions, Features and Areas containing this locality

References