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(1) Geology of Mining Districts.
Prior to 1977, many of the State's metal and precious stones districts were either unmapped or partially mapped
(FIGURE 1). Since that time, many of these districts have
now been mapped. More than 700 mi2 of complex metamorphic and igneous terrain in several districts have been mapped by the
Section since 1977, including the South Pass, Seminoe Mountains, and Rattlesnake Hills greenstone belts; the State Line, Iron
Mountain, and Middle Sybille Creek kimberlite districts; the Leucite Hills lamproite field; and the Cooper Hill, Keystone
and Copper Mountain mining districts. In addition, the Section completed and compiled maps of the Barlow Gap 1:24,000 and
the Rattlesnake Hills 1:100,000, and is currently working on compilation of the Saratoga 1:100,000.
(2) Diamonds.
Wyoming is underlain by a craton of Archean granite and gneiss known as the Wyoming Province, and cratonized Proterozoic
metamorphics of the Colorado Province. At least 20 diamondiferous kimberlites occur in the State Line district in southeastern
Wyoming, one diamondiferous kimberlite has been identified in the Iron Mountain district, and a diamondiferous lamprophyre
blow-dike trend has been identified in the Cedar Mountain area of the Green River Basin. Hundreds of kimberlitic mineral
anomalies have also been identified over very large regions in the Laramie, Medicine Bow, Sierra Madre, Seminoe, and Owl
Creek Mountains and in the Bighorn and Green River Basins. It is apparent that Wyoming has been intruded by a major swarm of
kimberlite, lamproite and lamprophyre!
The Section recently completed a project in the Iron Mountain district 40 miles north of Cheyenne. A summary report,
Geology of the Iron Mountain Kimberlite district and nearby kimberlitic indicator mineral anomalies in southeastern Wyoming
, was published as Report of Investigations 54. Kimberlite and carbonatized kimberlitic dike-blow complexes with strike
lengths up to 3.5 miles, and blows as large as 1,000 feet were mapped in the district. Geochemical studies identified diamond-
stability garnets in samples collected from the majority of the kimberlites suggesting that additional diamond occurrences
will probably be identified. When funding for this project was terminated in 1998, the Section was still finding kimberlite
and geomorphic anomalies to the north and west of the district. Future studies will undoubtedly result in additional
discoveries.
The Section also completed an extensive report on diamond targets in Wyoming and the U.S. The report,Diamonds and mantle
source rocks in the Wyoming craton with a discussion of other U.S. occurrences, indicates that the Wyoming Craton has the
highest potential for the discovery of commercial diamondiferous kimberlites in the U.S. This report was published as Report
of Investigations 53. The report also notes that Wyoming hosts the two largest kimberlite and the largest lamproite district
in the US.
Reconnaissance studies in the Leucite Hills lamproite field in southwestern Wyoming by the Section and others have shown that
these rocks are similar to lamproites in Western Australia. Reports include Kimberlites and Lamproites of Colorado and
Wyoming, USA, 8th International Kimberlite Conference Guidebook, Geological Survey of Canada, and Geology and
geochemistry of the Leucite Hills volcanic field, Rock Springs uplift, Greater Green River Basin, Southwestern Wyoming,
Wyoming Geological Survey Report of Investigations, submitted for publication in May, 2002.
(3) Colored Gemstones.
During the past few years, some gemstones have been discovered and (or) evaluated by the Section. These include gem-quality
olivine (peridot) in the Leucite Hills of western Wyoming, where more than 13,000 carats of peridot were recovered during
reconnaissance. Much of the peridot is high quality gem material.
West of Wheatland, the Section discovered another gemstone known as iolite (cordierite). Iolite is an attractive,
transparent, sapphire-blue mineral with noticeable pleochroism that produces a gemstone, which is violet-blue to grey-blue
when viewed at different angles. The Section Head recovered specimens of gem material weighing more than 3000 carats. In
1998, a field report was made available as Mineral Report MR98-1 (Field reconnaissance of the Palmer Canyon corundum-
kyanite-cordierite deposit, Laramie Mountains, Wyoming). A second report was published in 2002 entitled A new source
of gem-quality cordierite and corundum in the Laramie Range of Southeastern Wyoming: Rocks & Minerals, vol. 76, no. 5,
p. 334-339. In addition to iolite, this same deposit also contains some gem-quality sapphire, ruby, and kyanite. Similar
deposits are believed to occur nearby, and these are currently being investigated.
The Section is evaluating other gemstones including pyrope garnet, chromian diopside, and chromian enstatite. These may
provide value-added commodities to supplement the value of diamond recovered from some kimberlites.
Ruby schist and gneiss was investigated at the Red Dwarf ruby deposit in the Granite Mountains. In 1997, a description
of this occurrence was prepared and published in the International California Mining Journal, v. 65, no. 8, p. 65-68.
This article was titled: The Tin Cup district, central Wyoming - a rock hound's paradise. A second report was made
available as Mineral Report MR97-1 (Geology of the Red Dwarf corundum (ruby-sapphire) deposit, Graham Ranch, western
Granite Mountains, central Wyoming). During mapping of this deposit, the Section found rubies in 50- to 100-foot-wide,
5,000-foot-long gneiss. Rubies up to 2.5 inches across were found in the rock, and eluvial rubies were also found in the
adjacent soils. Although many of the rubies are translucent and fractured, prospectors have recovered some transparent-
and star-rubies in the past.
These discoveries along with the discovery of diamonds in Wyoming in 1975, illustrate the vast and untapped potential of
mineral resources in the State.
(4) Precious and Base Metal Deposits.
The Section is conducting a statewide evaluation of gold, platinum group, and base metal deposits. This investigation has
led to several discoveries and publications. Summaries are available in the agency's Bulletin 68 (The geology of Wyoming's
precious metal lode and placer deposits), which was published in 1989, and in Bulletin 70 (The geology of Wyoming's
copper, lead, zinc, molybdenum, and associated metal deposits in Wyoming), which was published in 1997.
Recently, several gold, and some platinum discoveries
have been made including a 7.5-ounce gold nugget and many more nuggets found by
prospectors searching mine tailings in the South Pass region. Information on
this important region is available in the following WSGS publication: Economic geology
of the South Pass granite-greenstone belt, Wind River Range, western Wyoming, published
in 1994 as Report of Investigations 44. Another report, Wyoming nuggets, published in
1996 in the International California Mining Journal, v. 66, no. 4, p. 7-12 was written
from prospectors. During mapping of South Pass, the Section identified numerous gold
anomalies, copper, some iron formation, and some beryl.
In 1982, the Section discovered significant gold mineralization in the Rattlesnake Hills. This discovery led to the
identification of several other gold anomalies described in Geology and gold mineralization of the Rattlesnake Hills,
Granite Mountains, which was published in 1995 as the agency's Report of Investigations 52. Later exploration and
drilling activity in this region by American Copper and Nickel, Canyon Resources, and Newmont Gold led to the discovery of a
large disseminated gold deposit. The available information suggests the presence of a partially explored disseminated gold
deposit containing > 1.0 million ounces. Other nearby exhalative, stockworks, and vein deposits suggest this district could
have significant potential.
In 1995, the Section discovered significant copper-platinum-palladium-nickel-cobalt-gold mineralization northwest of
Encampment in the Sierra Madre. This was reported in Mineral Report MR95-2 (Reconnaissance of the Charter Oak mine and
Cu-Ni-Au-Ag-Pt-Pd mineralization associated with the Puzzler Hill layered mafic-ultramafic complex, Encampment district,
Sierra Madre, Wyoming). Currently, the Mullen Creek, Lake Owen, Woods Mountain, Tony Ridge, and other platinum group
targets are being evaluated.
(5) STATE MAP PROJECTS. .
The Cooperative WSGS-USGS mapping initiative has allowed the Metals & Precious Stones Section to compile a group of maps
that are now available for public consumption. Please contact our publications office at (307)766-2286 x 224 for
information on placing orders for these. During the past few years, the Section completed 1:100,000 geologic sheets
for the Rattlesnake Hills, South Pass and Saratoga sheets, and 1:24,000 scale quadrangles for Barlow Gap and Keystone.
We are currently finishing the Sundance 1:100,000. These areas were selected because they have some of the highest gold
potential in the State and well as other mineral resources and some very interesting rocks and minerals.
Rattlesnake Hills: Exploration by W. Dan Hausel in 1981 led to the discovery of a new gold district that is now known as the
Rattlesnake Hills district. Follow-up exploration by American Copper & Nickel Company, Newmont Gold, Canyon Resources, Bald
Mountain Mining and others led to additional discoveries in this district, proving it to be a significant district for gold
mineralization. Because of the importance of this discovery, the WSGS completed a detailed study of the Rattlesnake Hills
district and outlined numerous gold anomalies and identified several others. Company exploration led to the discovery of
several significant exhalative gold anomalies including a discovery of a low-grade disseminated gold deposit with a potential
for a 1.0+ million gold resource (e.g. > $660,000,000+ in gold!). Later work by the WSGS included mapping of theBarlow Gap
1:24,000 quadrangle.
South Pass. The South Pass 1:100,000 sheet was completed due to interest in lode, placer and paleoplacers gold in that area.
South Pass was initially mapped in detail over several years by the Section which led to several significant gold discoveries.
Based on the geology and gold anomalies, it became apparent that the South Pass-Atlantic City-Miners Delight shear swarm
along the western flank of the district hosts reef-type structurally-controlled gold mineralization with high-grade gold
associated with fold closures, and low-grade gold associated with fold limbs. This district most likely hosts several
million ounces of gold. During mapping and sampling of the Carissa shear structure by W. Dan Hausel, a high grade shear
core was identified that is surrounded by a very large low-grade shear envelope that is as much as 1000 feet wide! Based
on sampling, mapping, and drilling of this property, the Carissa probably hosts a very large undeveloped gold resource,
potentially greater than 1 million ounces. Along the southern edge of South Pass is the Oregon Buttes paleoplacers. These
were estimated by the US Geological Survey to potentially contain 28,500,000 ounces (or a contained resource of $18.8
billion in gold). Other significant gold resources are found in this greenstone terrain other paleoplacers and placers.
Saratoga 1:100,000. The Saratoga sheet North ; South was compiled by the Section and shows bedrock geology for a part of the Medicine Bow
Mountains, Sierra Madre Mountains and also the Saratoga Valley. The region at one time included a major copper district known
as the Encampment mining district that produced copper until prices fell to record lows
(;&dt $0.12/pound). At today’s historical high copper prices (>$3.3 per pound) this district could again become an important
source for copper and zinc as well as gold, palladium, platinum, nickel, rare earths, titanium, chromium and gemstones. The
district also hosts some important gold resources at Douglas Creek, Purgatory Gulch and Keystone. Because of the interest
in gold, the Section compiled a 1:24,000 scale quadrangle of Keystone.
Notable within this 1:100,000 sheet was the discovery of several kimberlitic indicator mineral anomalies as well as some
placer gem-quality diamonds within the past 3 decades. These indicate a potential for the discovery of a major kimberlite
district in the Medicine Bow Mountains and nearby areas. During compilation of the sheet, several distinct vegetation
anomalies were noted by Wayne M. Sutherland and placed on the map. Field reconnaissance by the Section of a couple of
these showed that the circular to elliptical features all need serious follow-up exploration for kimberlite and diamonds.
For instance, work by the Section in a number of locations in the State has shown that Wyoming hosts major
kimberlite-lamproite-lamprophyre fields and could potentially include significant (if not world-class) diamond deposits.
The geology of Wyoming is very favorable for the discovery of major diamond deposits, and to date, 22 in-situ diamond
deposits have been found in Wyoming. This is based on a research budget for the WSGS that is
;&dt 0.01% of that spent in Canada in their search for diamond deposits – and today, Canada is the third largest producer of
gem-quality diamonds in the world.
Think of what the WSGS could find if we only had 1% of the Canada’s research and exploration budget devoted to the search
for diamond deposits.
Sundance 1:100,000. The Sundance 1:100,000 sheet was selected for compilation due to the tremendous potential for the Bear
Lodge Mountains alkalic intrusive to host significant resources of gold, rare earth metals and thorium. The district has
already been recognized by the US Geological Survey as hosting the largest low-grade resource of rare earth metals in the
US. In addition, the district is noted for some significant gold anomalies and fluorite. International Curator explored
one anomaly a few decades ago and identified a small, but significant gold resource. Current company activity in the region
could lead to significant gold and rare earth metal discoveries.
Summary. Our maps have been selected to assist company exploration and prospectors. WE HOPE we have been helpful and have
provided a useful public service unmatched by any other government agency. Please contact us if you need more information.
Sincerely, W. Dan Hausel (Senior Economic Geologist) and Wayne M. Sutherland (Assistant Economic Geologist).
Links
rocks and minerals
Rattlesnake Hills district
Barlow Gap 1:24,000 quadrangle; RI 44
South Pass
Saragota Sheet North ; South
Encampment mining district
copper, zinc
gemstones
Keystone
vegetation anomalies
diamond deposits Pic 1 ; Pic 2
(6) Evaluation of the State's Strategic Mineral Resources.
The Section continues to evaluate the State's strategic mineral resources including rare earth minerals, manganese, silver,
titanium, aluminum, chromium, nickel, vanadium, iron, zinc, lead, cobalt, and others.
(7) Talks & Field Trips.
The Section Head (W. Dan Hausel) continues to be a popular speaker for various rock hound, prospecting, general interest and
professional groups, as well as for various field trips. Typically, Hausel speaks to about 2-dozen groups each year
(FIGURE 2a, 2b, 2c). To see a list of all past talks done by Dan Hausel click here.
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Email: wsgs-info@uwyo.edu
