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Reconnaissance of beryl-bearing pegmatites in the Ruby Mountains, other areas in Nevada, and northwestern Mohave County, Arizona

Trace Elements Investigations 655

Work done on behalf of the Division of Raw Materials, U.S. Atomic Energy Commission.
By:
and
DOI:10.3133/tei655

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Abstract

Pegmatite occurs widely in Nevada and northwestern Arizona, but little mining has been done for such pegmatite minerals as mica, feldspar, beryl, and lepidolite.  Reconnaissance for beryl-bearing pegmatite in Nevada and in part of Mohave County, Ariz., and detailed studies in the Dawley Canyon area, Elko County, Nev., have shown that beryl occurs in at least 11 districts in the region.  Muscovite has been prospected or mined in the Ruby Mountains and the Virgin Mountains, Nevada, and in Mohave County, Ariz.  Feldspar has been mined in the southern part of the region near Kingman, Ariz., and in Clark County, Nev.

The pegmatites in the region range in age from Precambrian to late Mesozoic or Tertiary.  Among the pegmatite minerals found or reported in the districts studied are beryl, chrysoberyl, scheelite, wolframite, garnet, tourmaline, fluorite, apatite, sphene, allanite, samarskite, euxenite, gadolinite, monazite, autunite, columbite-tantalite, lepidolite, molybdenite, and pyrite and other sulfide minerals.

The principal beryl-bearing pegmatites examined are in the Oreana and Lakeview (Humboldt Canyon) areas, Pershing County; the Dawley Canyon area in the Ruby Mountains, Elko County, Nev.; and on the Hummingbird claims in the Virgin Mountains, Mohave County, Ariz. Beryl has also been reported in the Marietta district, Mineral County; the Sylvania district, Esmeralda County; near Crescent Peak and near Searchlight, Clark County, Nev.; and in the Painted Desert area near Hoover Dam, Mohave County, Ariz.

Pegmatites are abundant in the Ruby Mountains, chiefly in the area north of the granite stock at Harrison Pass.  In the Dawley Canyon area of 2.6 square miles at least 350 pegmatite dikes more than a foot thick were mapped and beryl was found in small quantities in at least 100 of these dikes.  Four of these dikes exceed 20 feet in thickness, and one is 55 feet thick.  A few pegmatites were also examined in the Corral Creek, Gilbert Canyon, and Hankins Canyon areas in the Ruby Mountains.

The pegmatite dikes in the Dawley Canyon area intrude granite and metamorphic rocks which consist chiefly of quartzite and schist of probable Early Cambrian age. The granite is of two types: a biotite-muscovite granite that forms the main mass of the stock and muscovite granite that occurs in the metamorphic rocks near the borders of the stock.  The pegmatites were emplaced chiefly along fractures in the granite and along schistosity or bedding planes in the metamorphic rocks.

Many of the Dawley Canyon pegmatite dikes are zoned, having several rock units of contrasting mineralogy or grain size successively from the walls inward.  Aplitic units occur either as zones or in irregular positions in the pegmatite dikes and are a distinctive feature of the Dawley Canyon pegmatites. Some of the aplitic and fine-grained pegmatite units are characterized by thin layers of garnet crystals, forming many parallel bands on outcrop surfaces.  The occurrence of aplitic and pegmatitic textural varieties in the same dike presumably indicates abrupt changes in physical-chemical conditions during crystallization, such as changes in viscosity and in content of volatile constituents.

Concentrations of 0.1 percent or more beryl, locally more than 1 percent, occur in certain zones or parts of zones in the Dawley Canyon pegmatites.   Spectrographic analyses of 23 samples indicate that the BeO content ranges from 0.0017 to 0.003 percent in the muscovite granite, from 0.0013 to 0.039 percent in aplitic zones in pegmatite, from 0.0005 to 0.10 percent in coarse-grained pegmatite, and from less than 0.0001 to 0.0004 percent in massive quartz veins.

The scheelite-beryl deposits at Oreana and in Humboldt Canyon, Pershing County., are rich in beryllium.  Twelve samples from the Humboldt Canyon (Lakeview) deposit range from 0.018 to 0.11 percent BeO, but underground crosscuts have failed to intersect similar rock at depth. Beryl locally constitutes as much as 10 percent of the pegmati tic ore at Oreana.  The beryl was not recovered during tungsten mining at Oreana and is now in the tailings of the mill at Toulon, Nevada, in lower percentages than the Oreana ore because of dilution by tailings from other ores milled at Toulon.

Beryl has been found in numerous pegmatite dikes in the Virgin Mountains.  Both beryl and chrysoberyl occur in dikes in the Hummingbird claims, north of Virgin Peak, in Mohave County, Ariz.  Spectra graphic analyses of five representative samples of the principal dike on the Hummingbird claims range from 0.055 to 0.11 percent BeO.

 

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Additional publication details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Reconnaissance of beryl-bearing pegmatites in the Ruby Mountains, other areas in Nevada, and northwestern Mohave County, Arizona
Series title:
Trace Elements Investigations
Series number:
655
DOI:
10.3133/tei655
Year Published:
1957
Language:
English
Publisher:
U.S. Geological Survey
Publisher location:
Washington, D.C.
Description:
Report: 13 p.; 1 Sheet: 13.85 x 16.54 inches
Country:
United States
State:
Arizona, Nevada
County:
Mohave County
Other Geospatial:
Ruby Mountains
Online Only (Y/N):
Y
Additional Online Files (Y/N):
Y