Gold Deposits at South Pass, Wyoming - A Guide for Gold Prospectors

South Pass is Wyoming's principal gold area & produced nearly all gold mined in the past. But, geologist Dan Hausel (the GemHunter) found supporting evidence for a major gold deposit at the Carissa mine & several significant gold anomalies throughout the South Pass-Atlantic City-Miners Delight and the Lewiston districts. There is also evidence of significant placer gold remaining in Rock Creek & Willow Creek & a giant paleoplacer gold deposit at Dickie Springs.

Monday, December 17, 2018

South Pass gold district - prospecting from the air.

Dan Hausel (GemHunter) stands in front of the
Atlantic City Hilton at South Pass.

I was paid by the Wyoming Geological Survey at the University of Wyoming, along with some federal US Geological Survey grants to live in a tent for 5 summers in the 1980s and map and explore the South Pass greenstone belt. The state supplied me with nourishing instant oatmeal, spam and instant coffee for breakfast, lunch and dinner, while I lived in my personal tent and mapped the 250-square-mile greenstone belt and its gold and iron ore deposits, mines and mineralized trends. Some weekends, I splurged and wandered into the Atlantic City Mercantile to buy a beer and talk to locals to gain insight into their prospects.

Start with a web search on ‘South Pass gold’, then expand the search to ‘South Pass gold prospecting’. Already, you should be finding information on gold deposits, geology, mines, mining districts and towns. Now expand to ‘South Pass gold mines’. As you find mine names, search the web for those mines. It doesn’t take long and you will have a considerable file.

Now examine South Pass on Google Earth. Search “Atlantic City, Wyoming 82520”. This will take you to one of the larger cities in the state at the base of the Wind River Mountains. When I was a ‘snowbird’ resident of Atlantic City living in a tent, the city population sign read “population about 57”. This was probably an exaggeration unless you include pets.

Examine the region at an eye altitude of 50,000 to 10,000 feet on Google Earth and you will see prominent rock lineation that trends roughly E-W to E-NE in hills surrounding Atlantic City. Move your stylus to 42°29’10"N; 108°40’18"W just east of Atlantic City for an excellent aerial view of lineation. The lineation is prominently expressed in the Miners Delight Formation, a thick rock unit formed mostly of meta-graywacke. ‘Meta’ refers to the fact that the graywacke is metamorphosed (recrystallized), and ‘graywacke’ refers to a ‘dirty’ sandstone that has considerable sand, clay and silt that later recrystallized to a mica-cordierite-andalusite quartzite (metagraywacke).

These rocks were abused by tectonic deformation and squeezed into a steeply-dipping and plunging basin 2.8 billion years old such that we now see the edges of the meta-sedimentary (and meta-volcanic) layers. To visualize this, take a book and lay it flat on a table in front of you. Imagine the pages represent layers of rock deposited on top of one another. Now rotate the book 90 degrees and sit it on the binder. As you view each page on end, they will appear similar to lineaments at South Pass, so now you should have some idea of what happened at South Pass. All of that lineation you are looking at on Google Earth is the metamorphosed sedimentary and volcanic rock beds that have been tilted 90 degrees (more or less) and now sitting on end. Try to imagine the force required to do this to this part of the earth’s crust. To make things more complicated, the entire belt was also folded like an accordion and recrystallized.

As you admire some drainages at South Pass on Google Earth such as Big Atlantic Gulch, Rock Creek, Meadow Creek and portions of the Sweetwater River, keep in mind that hundreds of nuggets came from these drainages in the 19th century, and are still being found to this day. Big Atlantic Gulch, Rock Creek and Meadow Creek cut rock foliation, which is good to keep in mind when prospecting for gold placers. Since gold-bearing structures in this region lie parallel to nearly parallel to foliation; thus, any drainage that cuts foliation will sample these gold-bearing structures and the foliation will provide natural riffles at bedrock.

When I mapped South Pass, I came across two prospectors (Buddy Presgrove and Hank Hudspeth) exploring for gold in Smith Gulch (42°31'3"N; 108°42’19"W) with backhoe and trommel. They recovered gold from two pay streaks: one on bed rock, and the other on false bedrock about 4 feet above bedrock. The two recovered about 20 ounces of gold per week in an area that arm chair prospectors claimed had no gold or was all ready mined out.

There are many placers and lodes of potential interest in this area, as there are in most gold districts. Placers that continue to yield nuggets include Rock Creek (42°29'11"N; 108°42’25”W), Spring Gulch (42°31'59"N; 108°40’43"W), Big Atlantic Gulch (42°29'54"N; 108°42’31”W), Meadow Gulch (42°27’49"N; 108°47’9"W) and parts of the Sweetwater River. To obtain information on ownership visit the Fremont County courthouse in Lander and the State BLM office in Cheyenne.

Monday, July 24, 2017

Ode to South Pass

Twas the spring of ’78,

When prospectors tipped beer with squirrelly mates,

At the Mercantile we heard cheers and moans,

Interrupting exaggerations about gold in shear zones.

Along came a geologist named GemHunter Dan,

Twas said to be a hard rock man,

Surrounded himself with rocks of old,

Including amphibolite, a host for gold.

The GemHunter

In the summer, when snow buried his tent,

Off to Laramie is where he went,

He swore he would be back with hammer and map,

And would also bring a miner’s cap.

Atlantic City with population of 40,

Dogs, Barbara, Steve, Tony and Shorty,

Blessed by a geologist with all his maps,

Found gold at a mine face covered with bats.

Down the shaft in stopes so cold,

Then up in a raise he was told,

Is where the yellow metal resides so bright,

In tunnels and chutes lit by a miner’s light.

The Carissa kept its secrets deep,

Until the State took her while we weeped,

A billion in gold, now lay with mold,

So tourists can enjoy a town of old.

There was a Mary Ellen mine and its mill,

With Steve the captain at the wheel,

We descended 240 feet of incline,

Followed the vein while my assistant whined.

He’s claustrophobic at 240 deep,

Carrying him up a ladder that’s way too steep,

So we yelled “Jay” climb to the light,

He made the head-frame before midnight.

Then there was Barbara so bold and old,

Swindled a tourist with jars of fool’s gold,

The pyrite was shiny, brassy and cold,

But the tourist was mad when he was told.

He plugged his whiskey bottle with a cork,

Decided to get even by calling her dork,

And that evening, while she slept on a floor,

Barbara’s Cadillac was ablaze from door to door.

Gold panned out of the Rock Creek dredge tailings

Barbara awoke to whisky and flakes,

We wondered who next she would take,

When into the Mercantile strolled a mark,

Dressed like a dandy at the bar he parked.

Where’s the Mary Ellen he asked so kind,

So Barbara offered him title to a mine,

No thanks said the gentleman from Missouri,

You see, I’m really in a big hurry.

Besides the mine cannot be sold,

After all its my mine he told,

So Barbara drank another shot,

Another swindle and she was caught.

Then there was Shorty with wet pockets and old,

Sat in his trailer to count his gold,

Cut a hole in a single wide on Rock Creek,

To fill his honey pot and make everyone reek.

Atlantic City is the place,

To mine gold and investors with hast,

Dig the gravel and fill a mucker,

A sluice, a pan, or a sucker.

Enough! I said as I headed out with cap,

Grabbed my Brunton and began to map,

Eight quadrangles, 500 square miles, a dozen or so mines completed,

Searched for the yellow stuff and found more Mormons than needed.

Published a paper a book and cried,

Why do bureaucrats have to lie,

Elected a crooked Democrat,

With a State geologist, a two-bit rat.

So long I said to South Pass of old,

You can keep your Democrat and your gold,

Wyoming democrats smell ripe and old,

Just like Shorty’s honey pot I’ve been told.

Mining districts and mineralized terrains of Wyoming

(after Hausel, 1997; and Hausel & Hausel, 2011).

South Pass, what a glorious place! I saw South Pass for my first time in 1978. The vast gold mining region and greenstone belt along Highway 28 at the southern tip of the Wind River Mountains was just south of the town of Lander in western Wyoming. It was love at first site! The geology, the old mines, a couple of tiny towns partially occupied by ghosts - it was a geologist’s paradise.

I told the greenstone belt, "I will be back to map you". And, I did get back and accumulated fond memories during the five summers in a tent while mapping the 450 to 500-square mile granite-greenstone belt and more than two dozen gold mines.

South Pass is a gold prospector's paradise. At least it use to be. The geology forms a tightly folded, granite-greenstone belt, a geological basin, with banded iron ore deposits along the western and eastern limbs of the belt. If you are unfamiliar with this kind of geology, I recommend searching the Internet for a summary on ‘greenstone belts’. Archean age ‘greenstone belts’ and ‘gold belts’ are often synonymous terms to geologists who work in Archean (older than 2.5 billion years) rocks.

Schematic map of the South Pass granite-greenstone belt

showing location of the South Pass-Atlantic City and Lewiston

districts, and McGraw Flats and Oregon Gulch paleoplacers (after Hausel, 1991)

Decades ago, iron ore was mined at US Steel’s Atlantic City mine; a mine that was a show-case for the company. But, the once majestic mine closed and is now a lake (42°32'26"N; 108°44'44"W) sitting along Highway 28.

The iron ore occurs in a rock known as banded iron formation (BIF), or taconite. It consists of alternating layers of magnetite and quartz. BIF is a good source for iron, and some are also sources for gold, particularly where quartz veins and sulfides such as pyrite, chalcopyrite or arsenopyrite occur in the rock. Take the Homestake mine as an example: nearly 40 million ounces of gold were mined at Homestake over a century, and it was classified as iron formation. Other examples of gold in iron formation occur at the Lupin mine in the Northwest Territories, Detour Lake in Ontario, Mt. Morgans in Western Australia, and others in Zimbabwe, India and Brazil.

Folded BIF from the Atlantic City iron ore mine, Wyoming, with
quartz veinlets,

The BIF at South Pass lies in a meta-sedimentary unit known as the Goldman Meadows Formation that includes mica schist and quartzite resting on older rock of the Diamond Springs Formation. The average iron content of the BIF is upwards to 40%. US Steel operated the mine and recovered more than 90 million tons of iron ore prior to closing the mine in 1983. The geology of the Goldman Meadows formation indicates these rocks were originally deposited in a shallow sea on a stable platform possibly 3 billion years ago.

Copper-stained BIF from the Seminoe Mountains greenstone belt,
Wyoming, with both black and white quartz veinlets
mixed with dark gray magnetite.

When the Atlantic City mine closed, the BIF was unsampled for gold until I asked about archived gold assays. The company was so focused on iron, they didn’t consider the possibility of gold. I got permission to visit the mine, but my annual assay budget at the Wyoming Geological Survey was a pitiful $100 per year (at that time, $100 would cover 3 to 5 assays), so I was unable to test the rock for gold since I had already spent my annual assay budget. Even so, I found quartz veinlets cutting the BIF with pyrite and chalcopyrite as well as other veinlets that penetrated the rock foliation - good signs for gold. Even so, I was unable to prove the rock had any gold. But when the beer started flowing at the Atlantic City Mercantile and I brought up the subject, former iron miners swore they had seen visible gold in the open pit. In 1981, I had found highly anomalous and localized gold in BIF in the Seminoe Mountains greenstone belt east of South Pass, but we still don't know if there is any gold in the BIF at South Pass.

The Diamond Springs Formation, the lowermost mappable rock unit at South Pass includes primitive, metamorphosed, igneous rock known as amphibolite (metamorphosed basalt) and serpentinite (metamorphosed komatiite). Samples of this material contain 18 to 38% MgO, a trace to 1.0% chromium; and trace to 0.26% nickel. Based on chemistry and rock mineralogy, I interpreted these ancient and altered rocks to originally be basalts and komatiites deposited on the earth’s surface 3 billion years ago. Komatiites are rare volcanic rocks often found in greenstone belts and are essentially restricted to Archean age (older than 2.5 billion years).

Locally, some of the serpentinites have cross-fiber asbestos veinlets that were prospected in the early 20^th century for asbestos, while other outcrops are massive, and a few have cumulate texture. Cumulates are magnesium-rich metamorphosed volcanic flows that erupted directly from the earth’s mantle and when they began to cool, tiny olivine grains crystallized in the lava, sank, and accumulated at the bottom of the flow producing a sandstone-like, cumulate texture.

Rock foliation and bedding of dark gray to black meta-greywacke

of the Miners Delight Formation is nearly perpendicular to Rock

Creek with its dredge tailings in the foreground. In other words, the

bottom of rock creek is lined with many natural riffles to trap gold.

By the way, the name ‘Miners Delight’ would be better applied to a beer.

Magnesium-rich volcanics are good rocks to prospect for nickel, chromium, platinum-group metals and gold: none of which I detected in anonymous amounts at South Pass. Elsewhere in Wyoming, I found anomalous nickel and palladium in another magnesium-rich rock at Puzzler Hill in the Sierra Madre Mountains, and chromite was found nearly a century ago in serpentinite in the Laramie Mountains near Douglas. Nickel anomalies are also reported in the Laramie Mountains anorthosite complex, where a king’s ransom in labradorite (spectrolite) and iolite gemstones occur.

As a rock hound or prospector, any time you see the term 'anorthosite', it usually means it's a good place to search for labradorite. And if you are interested in iolite - that is a little more complicated. Look in areas where the rocks have been metamorphosed and have high alumina. Or, simply look for the term 'cordierite' applied to metamorphic rocks. Cordierite is the geologist's designation, and few geologists know what gemstones look like. Often they mention the mineralogical term but completely overlook the fact that the mineral may be gem quality. But remember, there is a lot of cordierite out there that is very poor quality.

At one location north of Laramie based on the few samples I collected on a county road, and based on historical estimates of the amount of cordierite exposed in trenches, there could be a deposit with more than a trillion carats of iolite. Nearby, I found some extraordinary deposits of iolite at Palmer Canyon and Grizzly Creek. Iolite is a low-value gem.

Miners Delight mine was developed on a 3 to 16 foot wide shear zone that has been traced over 2500 feet on the surface. Gravels in nearby Spring Gulch draining this shear zone produced 1500 ounces of gold including several 1 & 2 ounce nuggets, a 6 ounce 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 the author assayed from 0.01 to 0.36 ounce per ton gold. A historic prospectus reported there were 2,400 feet of drifts accessed from a 250 foot deep shaft and the mine produced 60,000 ounces. The gold tenor ranged from 0.3 to 110 ounces per ton of gold. It is likely that this property still has considerable ore at depth.

Some gemstones are also found in serpentinites - for instance, my good friend Robert Odell (RIP) found hundreds of tiny, blue sapphires in alumina-rich serpentinite near the Red Dwarf ruby deposit in the Granite Mountains of central Wyoming northwest of Jeffrey City. While exploring northern California for diamonds, I came across chromian diopside in serpentinite. Chromian diopside is considered to be a kimberlitic (diamond) indicator mineral and some specimens yield spectacular emerald-green gems. In central California, east of Sacramento, I also found gem-quality benitoite in the river adjacent to a serpentinized breccia pipe I examined for diamonds. The benitoite was flawless and likely eroded from nearby aluminum-rich serpentinite. I was hoping to get back to that area some day and search for the source for those gemstones, but never did. Even though some serpentinites contain gemstones, the South Pass serpentinites lack anything of value, other than for a few crooked jade dealers who sell it as jade.

The base of the South Pass greenstone belt is interleaved with gneiss. Similar gneiss found elsewhere in the Wind River Mountains is dated from 2.8 to as much as 3.8 billion years old. Age dates in the South Pass granite-greenstone belt include the Louis Lake granitic batholith (which intrudes the greenstone belt) and is dated at 2.6 billion years old. Some poor quality helidor (yellow-green beryl) and rare aquamarine beryl occurs in granite pegmatite associated with this batholith. A 2.8 billion year age (isochron) was determined for the Miners Delight Formation metamorphic event that recrystallized all of the rocks of the greenstone belt. A similar age was determined for a vein at the Snowbird mine located in the Miners Delight Formation, suggesting that a temporal connection exists between metamorphism (rock recrystallization) and gold mineralization. It is likely much of the primary gold at South Pass leached out of the rock during metamorphism and migrated to zones of lower pressure (i.e., fractures), such as shear zones that lie parallel to near-parallel to regional rock foliation. Thus, when prospecting at South Pass, it is important to learn as much as possible about these shear zones.

False bedrock on Rock Creek (42°29'10"N; 108°42'22"W). Layers of false

bedrock can lead placer miners to give up after they recover gold from a

pay-streak thinking they are on bedrock. The handle of the shovel rests

against the massive clay layer (claystone) that acts as a barrier to gold.

Siting above this layer, cobbles and pebbles in the overlying conglomerate

are characteristic of stream gravel and this material carries gold which

is enriched at the interface between the conglomerate and the claystone.

Below the claystone, more gold-bearing steam gravel is visible. As one

digs further down into the placer on Rock Creek, similar false bed rock

layers will likely be found. On Smith Gulch (42°31'3"N; 108°42'19"W),

two placer miners (Hank Hudspeth and Buddy Presgrove) found a similar

false bedrock layer with considerable gold sitting on false bedrock and

found additional gold below the layer on actual bedrock.

Sitting on the Goldman Meadows Formation is the Roundtop Mountain Greenstone Formation - a belt of metamorphosed pillow basalts deposited in an ancient sea. Some pillow basalts are so well preserved that I was able to use them the tell which way was up in this part of the stratigraphic section. This is helpful when mapping rocks in greenstone belts, because most greenstone belts were compressed and squeezed like an accordion during tectonic stress, and many rock units can be overturned.

If you are not familiar with pillow basalt but familiar with the Black Cat snake fireworks made from sodium bicarbonate and sugar, you have a good idea of what pillow basalts look like. Pillow basalts erupt under water expanding like snakes. Where they rest on a rock layer, they tend to sag until they completely solidify and look like a pillow. Since they sag, one can determine which way was up at the time of deposition. The pillow basalts at South Pass are now tilted nearly 90^o.

The Roundtop Mountain Greenstone is overlain by the Miners Delight Formation, which is estimated to be 5,000 to 20,000 feet thick and seen throughout much of the exposed greenstone belt. Determination of the thickness of this unit is complicated by folding and faulting, and in most places it has been tilted nearly 90^o and many places it is overturned. This formation consists primarily of dark gray to brownish black meta-greywacke. Greywacke (or meta-greywacke) is nothing more than dirty sandstone deposited along the edge of an ancient continent.

Non-mineralized rocks of the Miners Delight Formation contain a trace to 0.051 ppm Au (gold) (compared to a worldwide average of 0.002 ppm. Essentially all of the rock units at South Pass exhibit above average gold content and these were deposited in a shallow to moderately deep oceanic basin by volcanic activity and erosion of an adjacent continental shelf. All of the old Archean rocks were intruded by a belt of gabbroic rocks along a rift. These intrusive rocks are now classified as amphibolite but were originally gabbro, diabase, andesite and komatiite.

As the entire belt was compressed and folded along the edge of the subduction zone 2.8 billion years ago, shear zones formed along the contact between the Miners Delight meta-greywacke and the amphibolites due to the competency contrast between the two rock types. This is a very important concept for gold prospectors. Wherever you find shear zones at South Pass, you usually find quartz stringers, quartz lenses, fractures, limited hydrothermal rock alteration and gold! So, take a look at Google Earth and scan from South Pass City (42°28'7"N; 108°48'10"W), to Atlantic City (42°29'46"N; 108°43'49"W), to the Miners Delight ghost town (42°31'60"N; 108°40'51"W) and place pins (placemarks) on mines, trenches and prospect pits. Not only will your fingers wear out placing pins in prospect pits, but soon you will visualize the trend of the shear zones. They form a northeasterly belt running along the western limb of the greenstone belt. If you do the same for the Lewiston district 11 miles to the east, you will see a similar pattern emerge.

The Duncan mine and mill, 1989

Parts of the South Pass greenstone belt are overlain by geologically young sedimentary rocks of Tertiary age (65 to 2.6 million years old) that include gold-bearing conglomerates in the Wasatch, White River, Arikaree, and South Pass Formations. When you prospect at South Pass, you will periodically see lenses of younger rocks scattered high and dry away from any known drainages - if they look like they have pebbles, cobbles, and boulders, dry pan them for gold. On past gold prospecting and geology field trips, I often stopped at one or two of these sites (42°28'45"N; 108°42’58"W) so prospectors could see another type of gold deposit found in the greenstone belt that has been overlooked.

The more I mapped South Pass, the more it was clear that only a portion of the greenstone belt was visible at the surface and large parts of the complex continued under younger sedimentary rocks to the north and south. Geophysical exploration and drilling by Hecla Mining Company discovered greenstone belt rocks under a thick layer of sedimentary rocks, 6 miles south of South Pass City. Hecla had an excellent gold target at that location that their geologist (Foster Howland) interpreted as a buried, sulfide-rich iron formation, but the drilling project was cut short due to a recession.

The Carissa mine was developed in an intensely folded and faulted structure known as a shear zone. The primary high-grade gold-

bearing shear structure is 1.5 to 80 feet wide. This high-grade zone is enclosed by a much larger, completely unmined, low-grade shear envelope that is as much as 1000 feet wide! The envelope is almost completely untested even though samples show potential for a major gold deposit! A 97-foot composite chip sample that I collected on the south side of the high-grade shear within this low-grade zone yielded 0.023 ounces per ton. Another 30-foot sample on the north side of the high-grade shear yielded 0.07 ounces per ton of gold! The remainder of the 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. Geological evidence suggests the Carissa orebody continues to great 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 a very high reserve cutoff grade. They reported the mine had 208,000 tons of ore with 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 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. Again, they also ignored the shear envelop, which likely contains considerable gold that is minable at today’s gold prices.

In this region near Oregon Buttes (42°15'19"N; 108°51'21"W) and Dickie Springs (42°18'30"N; 108°51'48"W), Wasatch Formation conglomerates are estimated to be 1,300 feet thick and cover 8 mi². Some gold-bearing oil well cuttings were recovered from depths of 6,500 to 7,000 feet just north of the Continental Fault to the north of Oregon Buttes. This vast gold-bearing paleoplacer has been mostly ignored for decades, except at the Dave Freeman prospect, where Dave has been recovering gold from the dry placer.

Erosion over millions of years left behind extensive Eocene paleoplacers along the north and south ends of the greenstone belt. One estimate by the US Geological Survey suggested the paleoplacers south at Dickie Springs and Oregon Gulch could contain 28.5 million ounces of gold! But the gold is distributed throughout a very large volume of conglomerate, and little to no standing water is available except at Dickie Springs. So, one either brings water to the conglomerate or vise versa. But just like any placer, these paleoplacers have pay streaks associated with black sands that contain magnetite, so a search using magnetic surveys may assist in identifying pay streaks.

Remains of the E.T. Fisher washing plant on Rock Creek. This mine operated from the 1933 to 1941. How good are your eyes?

Can you see the beginning of World War 2 in this photo? It's pretty obvious. When WW2 broke out, all non-essential mines were

ordered closed by the War Miners board - which included all gold mines. This placer operation on Rock Creek was still recovering

commercial amounts of gold, when it was ordered to close. The mine (like many gold mines at that time) never reopened. Gold

prices were $35.5 per ounce in 1941 as compared to $1,250 per ounce today. Few people have ever tried to reopen these old

placer and lode gold mines that were ordered to close, even though they are almost guaranteed to be commercial.

Learn as much as you can about shear zones: this is where the primary gold will be found. And, all of the good placer gold deposits are found a short distance downstream from shear zones. As you dig for placer gold in the drainages, keep in mind you will likely find pay streaks on false bed rock surfaces, with additional pay streaks on bedrock.

There are undoubtedly pay streaks downstream from many shear zones in the South Pass-Atlantic City-Miners Delight district and in the Lewiston district to the east. If I were to look for nuggets, I would examine places like Hermit Gulch (42°28'29"N; 108°47'23"W) since it is down slope from many good gold-bearing shear zones near the Carissa mine. Then there is Little Beaver Creek (42°29'26"N; 108°45'5"W) downstream from the Duncan, Mary Ellen and other mines. Spring Gulch lies downstream from the Miners Delight mine (42°31'55"N; 108°40’57”W) where many nuggets were found in the past and in the Lewiston district, there are several, small, immature, dry drainages downstream from shear zones. Most do not have much dirt, but that dirt likely has some gold. Some of these lie near a couple of shear zones that host the Goodhope (42°26'32"N; 108°32'22"W), Mint (42°26'32"N; 108°32’45”W), Gold Leaf and other mines that produced some excellent gold specimens in the 1980s and likely in the 1800s and early 1900s. The more you look around these shear zones, the more targets you will spot.

In the past, some of the better placer gold was collected on Rock Creek (I’ve seen over a hundred nuggets from the area) and Big Atlantic Gulch, and the better gold-bearing rock samples were collected at the Carissa mine (42°28'29"N; 108°47'42"W). So common was visible gold at the Carissa mine, that every field trip I led to the area, at least one person found a very attractive gold specimen on the mine dump. And I’m sure there were many I never heard about.

Hematite-stained quartz breccia with considerable visible gold in vugs
found at the Carissa mine. This became a common occurrence over
the years. Essentially every field trip the author led to South Pass
someone found specimens with visible gold. Most were found at
the Carissa mine. Other localities where visible gold in quartz was
found included the Duncan, Miners Delight, Mary Ellen,
Good Hope, Mint and others

Based on assay samples taken at the Carissa mine (42°28'29"N; 108°47'42"W) by past mining companies and myself, a significant gold deposit continues along the Carissa-Duncan-Mary Ellen trend and down-dip for at least a thousand feet. At the Carissa, the mineralized shear zone is as much as a thousand feet wide. Past miners focused only on the high-grade gold in the narrow, prominent, shear structure, and completely ignored a very large envelope of low-grade gold. Past drilling showed the gold-bearing structure was mineralized to depths of 930 feet. This was the deepest any drill hole penetrated the gold structure - so, it could easily continue another 30 feet, 300 feet, 3,000 feet, or 30,000 feet. We don’t know. So, all of that gold-bearing rock from depths of 400 to 930 feet was never penetrated by the Carissa mine tunnels. And the low-grade envelope was left completely untouched from the surface to 930 feet. This same shear structure continues along strike for at least 1,000 feet before it narrows. Even so, the shear can be traced 8.5 miles from Willow Creek (42°27'49"N; 108°47'9"W) through the Carissa mine, and all the way to the northern edge of the greenstone belt near Meadow Gulch (42°32'4"N; 108°38'58"W) where it is buried by younger sedimentary rock.

In the mid-1980s, I applied for grants to map South Pass. The entire greenstone belt was wide open with no fences (except around the iron ore mine), and I often went for days, weeks and in some cases, an entire summer without seeing another person. But now there are more man-made structures and fences appearing in the belt. There is even a place called Rock Creek Hollow (42°26'25"N; 108°37'25"W) that didn’t exist when I mapped the greenstone belt. The Hollow has amphitheaters, fire pits, and even a parking lot with a bus turnaround. Near the end of my project, I was actually ran off the road by buses and a flatbed truck filled with portable outhouses. at this area. A barren hillside near this parade, sat a lemonade stand manned by women dressed like pioneers. It is clear that South Pass was changing, and my hope is that the area remains a gold-mining district and some of these people can learn to be friendly and share the road.

The Duncan gold mine and mill as it appeared to me when I first visited South Pass in 1978. I later detected significant gold in a

distinct fold near the old glory hole. A 2.5 foot long channel sample yielded 0.96 ounce per ton gold!

During my project, I took one Saturday afternoon off to drive to the Mercantile in Atlantic City to have a beer and find out if the world still existed. I met a prospector who was looking for a place to pan for gold: I sent him to Strawberry Creek (42°26'1"N; 108°29'49"W) where he used a man-powered sluice with a hand shovel and managed to stay out of site of the BLM for a month. He was soon chased out of the area even though it was public land. In the fall, he stopped by my office at the University of Wyoming to tell me he had essentially filled his pockets with gold before being chased off of public land. These federal bureaucrats also need to learn to work with people and quit overstepping their bounds. After all, they work for us, not themselves.

Map of the Wyoming province showing locations
of Greenstone belts including South Pass.

As I mapped, I periodically took samples along various shear zones. I noted in between mines, outcrops and prospect pits, most of the shear zone structures were buried under a few inches to possibly a few feet of dirt. Potentially, more than 90% of the gold-bearing structures are hidden. If only I had a way to see through that dirt. Of course there was a possibility of using geophysics, but it would tell me what I already knew - there were miles of gold-bearing shear zones. But, I identified more than a hundred gold anomalies along these structures, and if I could have seen the buried structures, who knows what I would have found? This should give some prospectors some ideas on other placers to search for gold.

A couple of years ago I consulted on a gold placer project at Rock Creek, and it was clear that the 1930s dredging operation did a poor job, missed many areas, and lost a significant part of the gold where it mined. The operation was poorly designed, and even today, one can still find considerable gold (both fine and nuggets) in the dredge tailings.

While mapping, I found chips of rock with alteration characteristic of gold mineralization associated with shear zones elsewhere. These chips were found in the Crows Nest area (42°29'17"N; 108°36’43"W) of the greenstone belt. A short time later, a prospector (Gary Nunn) found several, nice, jewelry grade gold nuggets in the area using a metal detector. So, the Crows Nest also contains hidden shear zones that remain mostly untouched.

Then there is Willow Creek - likely a very rich placer. But, the state government closed much of this creek to prospecting because it is reportedly filled with mercury! But, there is no known natural source for mercury in the belt; and if there is mercury in the stream, it was accidentally dumped by 19th century mining operations at the Carissa mine, and by now much of it would have worked its way to bed rock and be out of reach of most placer miners. Even more important, if there really is much mercury, it is a finite source that would soon be cleaned up by placer miners. Most of Willow Creek is unprospected and has limited dredge tailings (42°27'49"N; 108°47’9"W).

Many field trips to South Pass were led by the GemHunter to educate the public

on gold prospecting. These trips were free to the public

Some placers at South Pass contain significant coarse gold. XL Dredging mined portions of Big Atlantic Gulch in 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 many nuggets were recovered. Nuggets recovered from Rock Creek include many small nuggets and some large nuggets as well as a boulder that reportedly had 630 ounces of gold.

After five years of mapping, I produced eight 1:24,000 scale geological maps - these should still be available at the Wyoming Geological Survey. I also produced a regional 1:50,000 scale geological map for the pocket of my 129-page book on South Pass published in 1991. This book should be available at the Wyoming Geological Survey. Along with these, I published dozens of books, papers, abstracts and tour guides on South Pass to assist mining companies and prospectors on where to find gold in this region (a partial list of my bibliography is available on my website at http://GemHunter.webs.com), and I wore out a tent, two pairs of field boots, and nearly a dozen tires. It was a dream come true and I feel blessed that I was able to spend so much time at South Pass, meet so many interesting prospectors and few scam artists.

One of the locals at South Pass

REFERENCES

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., 1997, The Geology of Wyoming's Copper, Lead, Zinc, Molybdenum and Associated Metal Deposits: Geological Survey of Wyoming Bulletin 70, 224 p.

Hausel, W.D., 2014, A Guide to Finding Gemstones, Gold, Minerals and Rocks: GemHunter’s Books, Amazon, 368 p.

Hausel, W.D., and Hausel, E.J., 2011, Gold - A Field Guide for Prospectors and Geologists (Wyoming Examples), Self Published, Amazon, 366 p.

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.

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.

A portion of the Radium Springs Quadrangle by the author, showing rocks, mines, veins,
Laramide faults, and shear zones.

Simplified map of the Lewiston gold district

Simplified geological map of the South Pass-Atlantic City district.

Tailings along Rock Creek, Wyoming

Sunday, August 23, 2015

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.

The Gerald Stout placer operation on Rock Creek.