Saturday, November 21, 2009

Gold at South Pass Wyoming

Visible gold in amphibolite from South Pass. 
Reconstructed head frame at the Carissa Mine at South Pass
(Photo taken during field trip in 2010).

Every year for 29 years, one geologist at the Wyoming Geological Survey (W. Dan Hausel) volunteered time to lead free field trips for the public and geological associations to teach them about geology & gold & diamond prospecting methods, gem-hunting and methods used to find new gold deposits. He was in high demand for talks to prospecting groups, mineralogical associations, business organizations and geology federations throughout the country.

In his office in Laramie at the University of Wyoming, he met with hundreds of visitors and prospectors and identified rocks and minerals for the general public and mining companies. Over the years, hundreds of books, documents and maps on geology were published and Hausel was presented national and international awards for research.

Very little modern research was conducted at South Pass, until this geologist (Dan Hausel) mapped the greenstone belt and identified hundreds of gold anomalies and produced eight 1:24:000 scale maps of the geology and 1:48,000 scale summary geological map and several 1:120 and 1:240 geological maps of accessible underground mines.

The South Pass greenstone belt produced nearly all of the known historical gold in Wyoming, yet it remained mostly unmapped until the 1980s and early 1990s, when the entire greenstone belt and all accessible underground mines were mapped and hundreds of samples were collected for assay, geochemistry and mineralogical studies. .This resulted in several publications culminating with a report on the greenstone belt and its mining districts (Hausel, 1991). It was clear that considerable gold remained unmined and very little modern exploration was conducted in this region other than a few, piecemeal drilling and trenching studies due to the investigations by Hausel (1991).

Some mysteries that remained to be resolved was how extensive was the Carissa ore deposit,, which appears to have potential to be a multi-million ounce deposit, how extensive was the Miners Delight, Duncan, Diana, Tabor Grand, Wolf and other significant mines. Additionally, how much placer and eluvial gold have been missed by earlier prospectors. At least one diamond was reportedly found in this belt, thus was there potential for diamonds in this region?

Other problems that remain to be resolved include the sources of the giant Oregon Buttes and McGraw Flats paleoplacers. The Oregon Buttes paleoplacer appears to be mostly eluvial with some reworking into modern placers at Dickie Springs.

The closure of areas by the State and Federal government based on very sketchy data is of great concern. In particular, the closure of the Willow Creek placer, which is likely a major gold deposit, is purportedly filled with mercury from a mysterious source. There are no known natural sources for mercury in this region, and the introduction of so much mercury by mankind is highly unlikely: the environmental data is likely flawed. This placer along with the significant gold mineralization at the Carissa mine was withdrawn by the State of Wyoming and should be made available to the taxpayers rather than kept in government holding.

While exploring the surface and underground workings at the Carissa mine along with drilling by mining companies, it was more than apparent that a major, untapped gold deposit remained. Evidence of commercial gold was found throughout the surface workings over a minimum of 1000 by 980 feet as well as to depths of 970 feet. BUT, the mineralization was open in every direction and undoubtedly continues hundreds of not thousands of feet below the mine workings.
Placer gold from Smith Gulch at South Pass - about 20 ounces recovered
in a week by Buddy Presgrove and Hank Hudspeth. 

On the 350-foot level at the Carissa mine. Steve Gyorvary stands in mined out stope to provide scale of size of the primary shear (look for his mine lamp). All of the open space that Steve is standing in is the former gold-bearing shear structure that was mined out. This structure continues 350 feet to the surface; another 640 feet beneath this level (based on drilling) and likely a few thousand feet deeper.

It also continues along strike (trend) for a minimum of 1,000 feet and is enclosed in a envelope shear that is about 1,000 feet wide. This could have been one of the great gold deposits of Wyoming. But the Wyoming legislature supported its purchase by the state, withdrawal and placed the property within Wyoming's version of a Disneyland at the South Pass City historical site. One should ask why their taxes are being used to purchase economical gold mines and reconstructing historical facilities. This property could have been developed, mined and reclaimed then donated to the South Pass City historical site instead of taking the mine from the public as well as a major gold resource, jobs and a tax base.

For example, the primary shear structure has a average gold grade of 0.15 to 0.3 ounces per ton based on sampling, mining and drilling. For comparison, properties currently being mined in Nevada yield average ore grades of 0.03 to 0.15 ounces per ton. The Carissa shear has one of the highest average gold grades for a gold mine in North America. This primary shear is enclosed by a larger low-grade shear zone that is as much as 1000 feet wide and much of it is unexplored but it yielded gold values of 0.01 to 0.09 ounce per ton where it was sampled.

The development of the Carissa mine would have led to other exploration and likely development of other properties. Unlike other greenstone belts in Canada and Australia, the shear zones at South Pass remain relatively unexplored and it is estimated that only about 5% of the exposed shears have been sampled and tested for gold!
Steve Gyorvary poses on the 350 foot level
of the Carissa mine (photo by W. Dan


In 2004, >100 prospectors, members of the general public, and 8 dogs (considered to be first class rock hounds) toured South Pass. For Hausel, this area has special meaning as he spent 5 field seasons living in a tent in South Pass in order to map the 450 mi2 granite-greenstone belt along with 3 dozen underground mines. While all other state employees received full per diem to cover food and lodging, the WGS allowed Hausel to use his personal tent and refunded the cost of groceries. The last two mapping seasons, he was provided a government tent.

South Pass was Wyoming’s principal gold district, and could potentially produce significant amounts of gold and iron ore again – not to mention the possibility of finding colored gemstones and diamonds. Both aquamarine and a diamond have been reportedly found in the district in the past.

During mapping hundreds of gold anomalies and some iron ore resources were identified and/or discovered. The project resulted in the mapping and sampling of several gold-bearing structures that could potentially host some very large gold deposits – by far the best of these, based on sampling and mapping is the Carissa mine near South Pass City. The Carissa mine could easily represent a Million plus ounce gold deposit.

According to historical records, the first report of gold at South Pass was made on Strawberry Creek as early as 1842 by a trapper from the American Fur Company. Several years later (in 1855), a group of 40 prospectors entered South Pass to follow up on the discovery and reported gold nearly everywhere at South Pass. This expedition was followed by a group of 9 prospectors who returned to the area in 1858 and commenced mining on Strawberry Creek. The decayed remains of their sluices were later found in 1870.

In 1861, another expedition to South Pass included a group of 52 prospectors who began mining on Willow Creek, when they were attacked by Indians and driven out. Two years later (1863), gold was discovered on the Oregon Trail immediately south of South Pass in the vicinity of Oregon Buttes (Oregon Buttes was studied more than a century later by the US Geological Survey, and is now recognized as one of the largest undeveloped gold occurrences in North America - the source of the gold is thought by some to be the South Pass greenstone belt).
Oregon Buttes from South Pass includes a giant gold  paleoplacer and placer. The paleoplacer (the ridge in the
lighted area on the horizon below Oregon Buttes) was  suggested by the US Geological Survey to host >28.5 million
ounces of gold, making it one of the larger undeveloped gold deposits in the US. The source of the gold for Oregon
Buttes has never been identified but in all probability lies at depth beneath the sedimentary cover and eroded from the
greenstone belt hidden under those younger sedimentary rocks. Drilling by Hecla Mining Company verified
the presence of the greenstone belt under the sedimentary rocks;and identified what may be a hidden, gold-bearing sulfide-rich iron formation at depth.

In June 1867, the richest lode in the district was discovered that is currently known as the Carissa. These miners were attacked by Indians, three were killed and the rest were driven out, but returned later in late July. In the winter of that year, 400 ounces of gold were recovered from the lode using very primitive tools. Four 4 tons of ore were shipped to Springfield, Utah a short time later, which yielded an incredible 1,400 ounces of gold!

Because of the continual hostilities between the Whites and Indians, the US Army established Camp Stambaugh near the towns of Atlantic City and Miners Delight in 1870. However, many of the recruits deserted to search for gold.
View of the primary, high-grade gold-bearing shear zone at the Carissa mine.
Note the geologist (Jon King) for scale. 

The Carissa mine (see photo to left) was Wyoming’s principal gold mine & produced more than 180,000 ounces of gold (worth about $300 million at today's gold prices) based on incomplete production records. Missing production records over a period of several years suggest that the gold production could have been considerably more. Mapping by Hausel and drilling by various companies indicates that a sizable gold resource remains unmined. However, the mine was incorporated into the South Pass City historic site.

By 1872, 12 stamp mills were operating in the district. In 1878, the Army abandoned Camp Stambaugh, even so, the Oregon Trail had to be abandoned for a safer route to the south due to increased hostilities. South Pass continued to be a battle ground until 1882 following the signing of the Treaty of Five Nations.

In 1884, significant placer operations were proposed and the Granier ditch was constructed to haul water from Christina Lake (12 miles away) to South Pass. Start up of the hydraulic operation did not occur until 1890. In 1891, 6,720 ounces were recovered from the operation. Today, scattered and sporadic prospecting operations continue to produce minor amounts of gold. However, the South Pass district hosts significant hidden and exposed gold deposits – nearly all are unevaluated. For example, the shear zone structure at the Carissa Mine may host a very sizable gold deposit based on geology and sampling. The Carissa shear zone. The Carissa mine was developed into an intensely folded and faulted structure known as a shear zone. The primary shear structure containing high-grade gold is 1.5 to 80 feet wide. This high-grade ore shoot is enclosed in a major shear envelope that is as much as 1000 feet wide!!! This envelope is almost completely untested even though samples show potential for a major gold deposit! A 97-foot composite chip sample taken on the south side of the high-grade shear yielded 0.023 ounces per ton. Another 30-foot sample taken on the north side of the high-grade shear yielded 0.07 ounces per ton of gold! Thus the remainder of this envelope (about 850 to 900 feet) remains untested!.

The Carissa ore deposit is structurally controlled and appears to represent a saddle reef deposit where high-grade gold is localized in fold closures and rehealed fractures similar to the Homestake mine. Thus geological evidence suggests that the Carissa ore body undoubtedly continues to great depths. Support for the presence of a major ore deposit includes drilling that tested the mineralized shear below the mine workings. Drilling by Consolidated McKinney Resources identified a highly anomalous zone that was up to 80 feet wide. Assays of drill core from this zone ranged from 0.03 to 2.54 ounces per ton gold (the shear envelop was not tested). This mineralized structure was intersected at depths up to 930 feet. Based on similar deposits in other greenstone terrains around the world, it is likely that the deposit continues to depths of 2,000 to 10,000 feet. In addition, Carissa Gold Inc. made the following reserve estimates on the property using an extraordinary high reserve cutoff grade. They reported 208,000 tons of ore that had an average grade of 0.343 ounces per ton and a geological reserve of 37,000 tons of ore averaging 0.85 ounces per ton!

Anaconda Minerals Company also drilled the property and all of their reported drill holes interested ore grade material. They intersected a high grade ore zone over widths of 2.3 to 16.1 feet that yielded 0.11 to 0.36 ounces per ton gold at depths up to 700 feet. There are many unknowns about this mine, but it is clear that the Carissa is a viable exploration target for gold that could potentially host a very sizable, untapped gold deposit!


The attendees of the field trip learned that South Pass is a fragment of a larger greenstone belt. Greenstone belts are found at a number of places worldwide including Canada, Australia, and Africa where a very large percentage of the world’s gold is produced.

The term greenstone belt is often considered to be synonymous with the phrase Gold Belt. This is because most greenstone belts are important sources for significant amounts of gold as well as other metals including iron and nickel, and gold anomalies have been detected over very large areas of the South Pass greenstone belt. In particular in a distinct belt running from South Pass City, through the Carissa mine, through Atlantic City and to the Miners Delight mine over a belt of more than 6 miles in length.

At the Miners Delight mine a 3 to 16 foot wide shear zone was traced over 2500 feet on the surface. Gravels in Spring Gulch draining this shear zone produced 1500 ounces of gold including several 1 ounce, >2 ounce nuggets, a 6 oz nugget, and a sample of auriferous quartz described as “the size of a water bucket that was filled with gold”. Samples collected across the shear zone by Hausel ranged from 0.01 to 0.36 ounce per ton gold. A historic prospectus reported that there were 2,400 feet of drifts accessed from a 250 foot deep shaft and that the mine produced 60,000 ounces and that the gold tenor ranged from 0.3 to 110 ounces per ton of gold. Little is known about the mine.

View of the Duncan mine - Gold was detected in
a fold nose by the author. A 2.5 foot channel
sample assayed 0.96 opt Au. Such a sample likely
had some visible gold.
Several mines along this belt contain anomalous gold. The Duncan, Mary Ellen, Tabor Grand, St. Louis, and Diana are some of the better known mineralized properties and mines. Common specimens containing visible gold attest to their potential.

All of the drainages downstream from this belt have produced significant placer gold. Another parallel belt (about 4 miles in length) occurs in the Lewiston area. During geological mapping of the greenstone belt, Hausel also identified rock significant alteration that is characteristic of gold mineralization in the Crows Nest area between these two mineralized belts. In addition, the greenstone belt continues under rock to the northeast as well 6 miles to the south of South Pass City. It is notable that both of these regions are overlain by giant gold paleoplacers (McGraw Flats-Twin Creek to the north, and Oregon Buttes to the south) suggesting the presence of at least two major hidden gold deposits.

The rocks at South Pass are old! South Pass is an Archean (older than 2.5 billion years) greenstone belt. Gneiss in the early crystalline complex of the Wind River Mountains yields Rb-Sr dates of 2.8-3.8 Ga (billion years old), and granitic rocks of the Louis Lake Batholith (which intrude the greenstone belt) yield dates of 2.6 Ga. A Rb-Sr isochron for the Miners Delight Formation within the greenstone belt yielded a 2.8 Ga date. This latter age may represent a prograde metamorphic event, and the rocks could be older. One model lead date from the Snowbird vein at the Snowbird mine of 2.8 Ga, may suggest a temporal connection between metamorphism and mineralization.


The Mary Ellen mine (1989
Nearly everything that is known about the geology of the South Pass greenstone belt is due to the work of Hausel over a period of several years. Mapping showed that only a portion of the South Pass greenstone belt synform is preserved at the surface. Geophysical exploration and drilling by Hecla mining to the south supported that the greenstone belt continues under young sedimentary rocks to the south for at least 6 miles.

At the base of the South Pass synform (basin) gneiss referred to as an S-type gneiss complex, or the basement of South Pass, is interleaved with the Diamond Springs Formation, the oldest member of the South Pass greenstone belt. The Diamond Springs Formation consists primarily of primitive metamorphosed igneous rocks that include distinct peridotites with MgO contents ranging from 18 to 38%; chromium from 600-10,000 ppm (parts per million); and nickel from 160-2600 ppm. The CaO/Al2O3 ratios for these rocks are low (0.06-2.8) and they posses flat REE (rare earth element) patterns similar to komatiites. Thus these rocks are thought to represent primitive mafic and ultramafic basalts and komatiites (in other words, very high magnesium volcanic rocks).

The Goldman Meadows Formation overlies the Diamond Springs Formation. These rocks include thick banded iron formations along with mica schists and quartzite. The average iron content for the iron formations is upwards to 40%, and a sizable resource is still present. In the past, US Steel Corporation operated a large open pit mine (Atlantic City mine) and recovered more than 90 million tons of iron ore prior to the closing of the mine in 1983. Even so, mapping suggests that at least 300 to 400 million tons of iron ore remain in place. The geology of the Goldman Meadows formation suggests that it was deposited in shallow water on a stable platform and was shed from a nearby shelf.

A 7.5 ounce nugget found on Rock Creek
The Goldman Meadows Formation is overlain by the Roundtop Mountain Greenstone. The Roundtop Mountain Greenstone consists primarily of thoeiitic oceanic basalts that in places have well preserved pillow structures. One of the more popular stops on the South Pass field trips is overlooking the iron ore mine where some excellent pillow basalts are preserved under the power line.

The Roundtop Mountain Greenstone is overlain by the Miners Delight Formation, which is estimated to be 5,000 to 20,000 feet thick. Determination of the thickness of this unit is complicated because the entire belt has been intricately folded and faulted almost like an accordion. This formation consists primarily of metagraywacke that contains a trace to 0.051 ppm Au (gold) (compared to average of 0.002 ppm). Essentially all of the rock units at South Pass exhibit above average gold content and are interpreted to have been deposited in a moderately deep oceanic basin. However, the spatial association of proximal facies metagraywacke with meta-andesites near Miners Delight suggests that there was also a contribution from an Archean age island arc. Portions of the South Pass greenstone belt are overlain by Tertiary age, gold-bearing conglomerates in the Wasatch, White River, Arikaree, and South Pass Formations. It is obvious that South Pass is highly anomalous in gold!


The gold geochemistry was studied by the US Geological Survey. The Au/Ag ratios are high & Au/Cu ratios are low for some of the gold at South Pass. The trace metal contents (Bi, Pb, As, Sb, V, Mo, W, B, Nb, Zn, Cr, Co, Ni) are typical of hypothermal veins in other greenstones worldwide. Stable isotopes and fluid inclusion studies support that the South Pass gold is similar to that of a hypothermal vein system. The carbon and oxygen isotopes in shear zones along with hydrogen isotopes from fluid inclusions support that the much of the gold solutions were derived from the dewatering of the Mineral Delight Formation during compaction.

Structurally, the major gold systems at South Pass are located adjacent to a distinct group of metagabbos, metatholeiites, and actinolite schists (metakomatiites) that trend from South Pass City to Miners Delight. The localization of gold in this region is believed to be due to competency contrasts between the metagabbros and adjacent Miners Delight metagraywackes. During folding, it is thought that these were favorable for the development of numerous fractures and faults. Much of the ore is found in these shear structures contain enriched ore shoots developed in folds suggestive of a reef-type structural control. Placers downstream from the shear structures are highly enriched in gold.


Nuggets recovered from the Crows Nest at South Pass by Gary Nunn. Above photo is visible gold in quartz found by
Steve Gyorvary
Gold from dredge tailings on Rock Creek from Gerald Stout 
(photo by Hausel). It is interesting to note that the last dredge 
that operated in Rock Creek terminated operations 
because of world war II, not because they ran out of gold. 
If the placer was commercial at $35/ounce of gold - one 
would anticipate that it is still commercial at $1900/ounce. 
And what about the parallel Willow Creek that drains 
off of the Carissa mine to the south of Rock Creek? 
It has much less gravel, but possibly is much richer in gold. 
It remains unmined due to state withdrawal. Based on today's gold
price, the Rock Creek placer produced more than $115 million

Some of the placers at South Pass contain significant coarse gold. For example, XL Dredging mined portions of Big Atlantic Gulch about 1910 and recovered nuggets weighing 0.07 to 1 ounce. The ET Fisher Company dredged Rock Creek from 1933 to 1941 and produced 11,000 to 30,000 ounces: 75% of the gold was found within 3 feet of bedrock. Some of the gold was coarse and several nuggets were recovered. Nuggets recovered from Rock Creek include many small nuggets and some large nuggets.

Boulders containing as much as 630 ounces of gold were also reported in the historical record. Much of this coarse gold was found during dredging of various drainages.


A 34 ounce gold nugget from Rock Creek!
Gold paleoplacers (old dry placers) cover large areas at South Pass. The paleoplacers have been studied primarily by the US Geological Survey. These are found within and on the edge of the greenstone belt. For example, one paleoplacer sits immediately south of Atlantic City in the South Pass Formation. This gold-bearing paleoplacer remains unevaluated.

At Oregon Buttes, the Wasatch Formation conglomerates are estimated to be 1300 feet thick and cover 8 mi2 and to host a major gold resource estimated to be as high as 28.5 million ounces (US$30 billion). Some gold-bearing oil well cuttings were recovered from depths of 6500-7000 feet just 0.5 mile north of the Continental Fault adjacent (north) of Oregon Buttes indicating the presence of a buried auriferous shear zone at that location. Geophysical exploration in this area by Hecla Mining Company identified what appears to be a iron formation (at depth). Hecla interpreted this to be a gold-bearing iron formation. The paleoplacers at Oregon Buttes have been reworked producing some enriched dry placers.


All of the field trip attendees had a good time in the sun and learned about the mining history and methods used to find gold. Many of them also became aware of the tremendous gold potential of this district and the possibilities that some mines and some high-paying jobs could result from exploration and development in this region. One should note that this district is still only in its infancy for exploration and it is estimated that only about 5 to 10% of the shear structures have been sampled. This means that dozens of rich ore shoots are likely hidden under a few inches to a few feet of dirt and eluvium.

Hausel (right) talks about gold at the Carissa shear zone. Based on sampling, mapping, and drilling, the Carissa property is probably one of the better gold targets in Wyoming and potentially in the West. Hausel is the author of more than 50 professional papers, books and maps on South Pass.
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• Hausel, W.D., 1989, The geology of Wyoming's precious metal lode and placer deposits: Geological Survey of Wyoming Bulletin 68, 248 p.

• Hausel, W.D., 1991, Economic geology of the South Pass granite-greenstone belt, Wind River Mountains, western Wyoming: Geological Survey of Wyoming Report of Investigations 44, 129 p.

• Hausel, W.D., 1993, Mining history and geology of some of Wyoming's metal and gemstone districts: Wyoming Geological Association Jubilee Anniversary Field Conference Guidebook, p. 39-63.

• Hausel, W.D., and Hull, J., 1990, Guide to gold mineralization and Archean geology of the South Pass greenstone belt, Wind River Range, Wyoming, in Roberts, S., Geologic field trips to western Wyoming: Geological Survey of Wyoming Public Information 29, p. 178-191.

• Hausel, W.D., 1994, Mining history of Wyoming's gold, copper, iron, and diamond districts: Mining History Association 1994 Annual, Reno, Nevada, p. 27-44.

• Hausel, W.D., and Love, J.D., 1991, Guide to the geology and mineralization of the South Pass area, in S. Roberts, editor, Mineral Resources of Wyoming: Wyoming Geological Association 42nd Annual Field Conference Guidebook, p. 181-200.

• Hausel, W.D., and Love, J.D., 1991, Guide to the geology and mineralization of the South Pass area: Wyoming State Geological Survey Reprint 49, 20 p.

• Snyder, G.L., Hausel, W.D., Klein, T.L., Houston, R.S., and Graff, P.J., 1989, Precambrian rocks and mineralization, Wyoming Province: 28th International Geological Congress guide to field trip T-332, July 19-25, 48 p.

Also, see our websites at: GOLD


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Look what our trammel dredged up! The GemHunter stands in the middle