McMahon Ridge, Goldfield Mining District, Esmeralda County, Nevada, USAi

Regional Level Types
McMahon Ridge	Ridge
Goldfield Mining District	Mining District
Esmeralda County	County
Nevada	State
USA	Country

Structure: The most productive mines in Goldfield form an arcuate belt that trends generally north from the Goldfield Main District, then northeast through the Adams and Conqueror mines area, and then easterly through McMahon Ridge and Black Butte. This belt of gold deposits coincides with the western and northern limits of an inferred intrusive-related, ring-fracture system and is host to nearly all of the most productive gold ore bodies known in the District. Tertiary deposits are domed and faulted by steeply dipping post Miocene: N-S and E-W faults.

Alteration: Large envelopes of intense argillic alteration surround most of the ore zones with silicification of core ore zones.

Tectonics: volcanic center, Basin and Range

Commodity: Ore Materials: gold Gangue Materials: quartz, alunite, barite, gypsum, limonite, kaolin

Deposit: The drill-defined part of the McMahon Ridge mineralized area has the following dimensions: 4,800 ft long and open, 800 ft down dip and open, and average 100 ft thick. The mineralized area at McMahon Ridge is formed by a series of east-west trending and northeast trending veins and breccia zones hosted by Milltown andesite. Almost all of the precious and base metal production recorded from the Goldfield mining district has come from rich epithermal bonanza ore bodies in the area northeast of the Goldfield town site. These ore bodies occur within silicified hydrothermal alteration zones. Mineralization in the argillized wall rock envelopes appears to be leakage zones emanating from core silicified zones. Ore zones are commonly associated with silicification and/or free quartz surrounded by large envelopes of intense argillic alteration. In the main district, gold-copper ores were found in a series of pipe-like shoots referred to locally as ledges, the most productive of which occurred where the east-west striking Goldfield structural trend intersects a mile-long arcuate section of inferred intrusive-related ring-fracture zone. Although the major ore bodies are hosted in a complex intersecting set of faults and fracture zones, the ore-bearing structures are generally north-south trending and sub-parallel to the strike of the ring-fracture zone in that location.

Deposit type: Epithermal quartz-alunite Au

Development: At McMahon Ridge, Metallic Ventures was running a 25,000-foot drilling program in 2004 and was planning to implement a feasibility study of the Gemfield and McMahon Ridge deposits by the third quarter of 2004. In April 2004, high-grade gold was intersected during infill drilling at McMahon Ridge and along structures in the main district at its Goldfield Project in Nevada. Highlights of the McMahon infill drilling include RC drill hole MCM-333 intersecting 30 ft grading 15.04 g/t Au including 5 ft grading 68.72 g/t Au, MCM-343 intersecting 115 ft grading 4.11 g/t Au including 5 ft grading 22.29 g/t Au, and MCM-344 intersecting 115 ft grading 15.09 g/t Au including 15 ft grading 98.4 g/t Au. The McMahon Ridge drill hole data base will be taken into a prefeasibility study whereby minable ounces of gold will be calculated in 2004.

Geology: The Goldfield mining district is located at the site of a complex and long-lived igneous intrusive and volcanic center that is defined by eruptive vents and curviplanar faults. The local volcanic stratigraphy, a moderately well-defined ring-fracture zone, concentric structural doming, high sulfidation-style quartz-alunite hydrothermal alteration, and widespread copper-gold mineralization are all genetically related to the emplacement of a large dominantly andesitic igneous complex and the most significant components of which are late Oligocene to early Miocene in age.

Ore(s): The ore-bearing structures are generally north-south trending and sub-parallel to the strike of the ring-fracture zone.

References

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Link to USGS MRDS:	10310418

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