GOLD PROSPECTING FIELD TRIPS

Photo by David Miller from Riverton

From 1977-2007, the GemHunter led public field trips and traveled all over the country to talk to general interest and professional groups about gold, diamonds, other gemstones and geology. Many of these trips were on Hausel's personal time, others were related to work at the university. One of the last field trips to South Pass led by the GemHunter included more than 100 prospectors, rock hounds and 8 dogs on a Saturday in August.

Since Hausel no longer leads field trips, you many want to take your own trip using one of several field trip guides published by the professor. Get a free guide by visiting the GemHunter's website and click on the following PDF (Field trip guide to South Pass). You will also want to take the GemHunter's 97-page book on South Pass with you to the field.

Many of the South Pass field trips included prospectors, general public, and a few legislators who could read and write. These attendees outnumbered the population of all towns in the South Pass greenstone belt (Atlantic City, Lewiston, Miners Delight and South Pass City). Never mind that two of the towns were only occupied by ghosts.

My last field trip to South Pass as a field trip guide. Yes, I loved South Pass
I loved my time at South Pass and all of the prospectors,
geologists, rock hounds and lay-people who took these adventures with me.
The GemHunter at far left corner in white hat, Eric Hausel my son
& geologist, physicist and astronomer stands to the far left, and look for the
Duck Dynasty look alike in the center - my good friend Steve Gyorvary.
Absent was the Colorado whiskey man who organized this field trip.

The South Pass greenstone belt had special meaning for the GemHunter (me). "I spent 5 field seasons living in a tent so I could map the 400 mi2 granite-greenstone belt with 3 dozen underground mines". I could have stayed in a motel in Lander, but the Wyoming Geological Survey director was too cheap to provide much travel money - so I lived in a tent, bathed in Rock Creek, Sweetwater River (it sure wasn't sweet after I had finished bathing) and Strawberry Creek, and lived off of instant coffee and oatmeal".

The GemHunter talks to group at South Pass.

On this and many field trips, the caravan outnumbered the residents of the South Pass greenstone belt by at least 2:1.

South Pass was Wyoming’s principal gold-bearing greenstone belt enclosing a group of gold district. Two other significant greenstone belts included the Rattlesnake Hills and Seminoe Mountains, where the GemHunter also discovered significant gold and started gold rushes to both areas.

During the South Pass mapping project, Hausel (a.k.a GemHunter) identified hundreds of gold anomalies and identified previously unknown iron resources. The project resulted in mapping and sampling of several gold-bearing structures that 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 which was subsequently withdrawn by the State of Wyoming and turned into a circus that now attracts a couple of visitors every year.

The GemHunter to the right looks at camera while his field trip attendees

listen to a history lecture at South Pass city.

HISTORY

According to historical records, the discovery of gold at South Pass was made on Strawberry Creek in the Lewiston area as early as 1842 by a trapper with 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 finding gold nearly everywhere. 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 reportedly found in 1870.

Welcome to Atlantic City (photo by Sharon Hall).

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 south of exposed greenstone belt in the vicinity of Oregon Buttes. (Author’s note: 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).

In June 1867, the richest lode in the district was discovered and named 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, more than 400 ounces of gold were recovered from the lode using primitive tools. Four tons of the ore shipped to Springfield, Utah yielded an incredible 1,400 ounces of gold!

Oregon Buttes seen in the distance from South Pass. This area includes a giant gold paleoplacer and reworked

placers. The paleoplacer (the ridge in the lighted area in the background below Oregon Buttes) was suggested by the US

Geological Survey to host upwards to 28.5 million ounces of gold, making it one of the largest undeveloped gold deposits

in North America, about three-quarters the size of the giant Donlin Creek Alaska deposit. The source of the gold for

Oregon Buttes has not been identified but in all probability is part of the buried South Pass greenstone belt at depth

beneath the sedimentary cover near the buttes (photo by W. Dan Hausel).

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 recruits deserted the Army to search for gold.

The Carissa was Wyoming’s principal gold mine and produced more than 180,000 ounces of gold 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 the GemHunter and drilling by various companies indicates that a sizable gold
resource remains unmined. However, the mine was recently incorporated into the South Pass City historic site, and
possibly will never be mined again. The unmanned deposit potentially includes more than a million ounces and possibly
several million ounces.

By 1872, 12-stamp mills were operating in the district. In 1878, the Army abandoned Camp Stambaugh. Even so, things were still not safe: 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 that would eventually lead to the development of Casinos.

In 1884, 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 ma and pa prospecting operations produce some gold. However, South Pass hosts significant hidden and exposed gold deposits – nearly all are unevaluated. For example, the shear zone structure at the Carissa Mine was shown by Hausel to potentially host a very sizable gold deposit based on geology and limited sampling.

The Carissa shear zone (photo by W. Dan Hausel). The Carissa mine was developed on an intensely folded and faulted
structure known as a shear zone. The primary shear containing high-grade gold is 1.5 to 80 feet wide. This high-grade ore
shoot is enclosed within a major shear envelope identified by Hausel to be mineralized over a width of as much as 1000
feet!!! This envelope is almost completely untested even though samples show potential for a major open-potable and
underground 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! Look for the geologist in the photo.

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 in South Dakota (Hausel and Hausel, 2011). Geological evidence also supports that the Carissa ore body continues to depth. 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. 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!

And if you thought Atlantic City was big. Now this is my kind of town!

Anaconda Minerals also drilled the property and all of their reported drill holes interested ore grade material: they intersected a high grade 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 the Carissa is a viable exploration target that could potentially host a very sizable, untapped gold deposit! It is sad that the Wyoming Legislature purchased this property and withdrew it from mining without even seeking input by the Wyoming Geological Survey!

GREENSTONE BELT GEOCHRONOLGY

The attendees of various South Pass field trips learned that the region is a fragment of a much 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.

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.

Miners Delight mine (Photo by W. Dan Hausel). This mine was developed on a 3 to 16 foot wide shear zone that has been
traced over 2500 feet on the surface. Gravels in Spring Gulch draining this shear zone produced 1500 ounces of gold
including several 1 & 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 the WSGS 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.

All drainages downstream from this belt have produced placer gold. Another parallel belt (about 4 miles in length) occurs in the Lewiston area. During mapping of the greenstone belt, the GemHunter also noted 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 younger rock to the northeast as well 6 miles to the south of South Pass City. It is notable that both regions where the belt continues under younger sediments 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. To the south, Hecla Mining had found specimens of sulfide-bearing iron formation with visible gold in detrital rock. Geophysical surveys in the region identified an IP anomaly associated with a magnetic high suggesting the presence of a buried sulfide rich iron formation similar to that seen at the Atlantic City iron ore mine (Phil Howland, pers. communication). Unfortunately, Hecla pulled the plug on the project a short time later. Of the core samples that the GemHunter was asked to examine for the company, the chemistry of the metabasalts were typical of the Roundtop Mountain Greenstone Formation indicating that they were near their target of searching for banded iron formation within the underlying Goldman Meadows Formation.

View of the Duncan mine and mill. Significant gold was detected enclosed in a distinct

fold at this mine by the GemHunter. A 2.5 channel sample yielded 0.96 ounce per ton gold!

The rocks at South Pass are old! South Pass is an Archean (>2.5 billion years old) 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.

STRATIGRAPHY OF THE GREENSTONE BELT

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).

A pot of gold at the end

of the rainbow at the Duncan mine

(photo by W. Dan Hausel).

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 sizeable 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.

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 metagreywacke 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!

GOLD GEOCHEMISTRY

Iron Formation from South Pass showing open fold.

Banded iron formation from the former Atlantic City

iron ore mine showing many folds

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. 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. Others suggest that the gold was introduced but the intrusion of the Louis Lake batholith. Either way, the South Pass greenstone belt likely hosts some significant discovered (Carissa) and undiscovered gold deposits.

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 zones provided favorable 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 (plunging folded gold ore shoots). Placers downstream from the shear structures are highly enriched in gold.

PLACERS

Figure 10. Visible gold in sample from the Carissa mine dump.

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 within 3 feet of bedrock. Some of the gold was coarse and several nuggets were recovered. Nuggets recovered from Rock Creek include many small 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.

The Fisher dredging operation was not efficient in gold recovery and it is clear that it rejected many coarse gold nuggets, as nugget hunters in the past have found more than a hundred "reported" nuggets with metal detectors searching the mined tailings. Who knows how many unreported nuggets were recovered. In addition, the plant for the dredge likely was not effective in fine gold recovery and much of that gold likely was also lost to the tailings. It was not uncommon for placer miners in the 19th and 20th centuries to ignore fine gold recovery. The placer operation continued mining gold until ordered closed at the beginning of World War II to force domestic production to focus on the war effort. Gold was not considered a strategic metal at the time. After the war, a very large portion of the commercial gold mines did not resume operations as many of the men associated with the mines had been displaced, died, or lost interest in mining. In addition, the country was rebuilding and many metal structures in these gold mines had been scrapped for the war effort. So, even though the Rock Creek mine was considered commercial, it did not resume after the war.

Rock Creek showing areas that remain unmined.

PALEOPLACERS

Gold from the Gerald Stout placer operation on Rock Creek at South Pass.

Gold paleoplacers (old dry placers) cover large areas at South Pass. The paleoplacers have been studied by the US Geological Survey. Isolated islands of the paleoplacer are found within the greenstone belt as well as 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.

A 7.5 ounce nugget recovered from the E.T. Fisher dredge

tailings by a prospector from Rock Springs.

At Oregon Buttes, the Wasatch Formation conglomerates are estimated to be 1300 feet thick and cover 8 mi2 and host a gold anomaly estimated to contain as much as 28.5 million ounces. Some gold-bearing oil well cuttings were recovered from depths of 6,500-7,000 feet just 0.5 mile north of the Continental Fault adjacent (north) of Oregon Buttes indicating the presence of a buried auriferous shear zone. 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.

SUMMARY

Another field trip group at South Pass with the GemHunter

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.