Monday, June 15, 2015

The Lewiston Gold Mining District, South Pass, Wyoming

A long, long time ago in my home away from home at South Pass.
As you read this blog about the Lewiston district, be sure to look at a a few of my other sites such as the Gemhunter, Goldhunter, Gold prospecting, Gemhunter Facebook, Amazon books, Wyoming authorsAbout me. I also have many blogs and bloodspots in the Internet - just wish I could find a list of them. Anyway, you might look at a few sites and search the list of blogs (links) such at the one at finding gemstones and Guide to agates and Jasper. Some of you will also be interested in a few of my past newsletters - sorry, I quit writing these newsletters, so don't ask about a mailing list. The Cheyenne Chapter of the GPAA was nice enough to post my past newsletters (thanks guys!).

I spent an entire summer living in the Lewiston gold district in a tent so I could sing at night with the local coyote band and get up early in the morning and walk around on the ancient rocks of the greenstone belt while sketching them, foliations, faults, gold-bearing structures, etc on my maps. In total, I spent about 5 years mapping the South Pass greenstone belt along with eight 7.5-minute quadrangles. It was tough, but someone had to spend time in that fresh air. And I did wear out a few pairs of boots. 

Another pair of field boots suffers through
South Pass - actually, these are the boots I left
on the door at the Wyoming Geological
Survey as I walked out for my last day after
the State Geologist confiscated my field
vehicle, tent, T-paper, underwear, spam & who
knows what else. I was told weekly I
was not capable of communicating with
the public or industry, a poor writer, a poor
field geologist. Sorry, I tried.
The South Pass greenstone belt is a large tightly folded and complexly faulted metamorphosed synformal basin similar to many gold-bearing regions in Australia, Canada and southern Africa. The South Pass greenstone belt encloses several old mining districts that I combined into the (1) Atlantic City-Miners Delight-South Pass City district to the west of the Lewiston district and (2) the Lewiston district. Considerable gold is also found to the south of the greenstone belt in the Dickie Springs-Oregon Buttes area in geologically young gravels, conglomerates and sediments that were eroded from the South Pass greenstone belt. The USGS reported that those eroded conglomerates could contain as much as 28.5 million ounces of gold - in my opinion, all eroded from the South Pass greenstone belt to the north as well as the greenstone belt rocks hidden under the younger Tertiary sedimentary rocks in the area.

Greenstone belts formed in the geological past in deep volcanic and sedimentary basins along the shores of active volcanic coasts. As a result, much of the material deposited in these old oceanic basins consist of volcanic material shed from volcanically active islands as well as sediments from both the eroding continent and islands. A modern analogy would be the Sea of Japan, where much volcanic material in the oceanic basin comes from the Japan islands and submarine hotspots, and much of the sedimentary material is eroded not only from Japan, but also from the Korean coastline.  As a result, many of the rock types seen greenstone belts are pillow basalts and serpentinites that were deposited in the sea. Other volcanics commonly found in greenstone belts include unusual magnesium-rich rocks known as komatiites. Some of these were deposited along the edge of the sea as well as along the coast of the volcanic islands.

pillow basalts
The common types of sedimentary rocks found in greenstone belts include limited pelitic sediments, some banded iron sediments, and more widespread greywackes. The pelites and greywackes eroded primarily from the coastlines, while the banded iron sediments likely were produced from submarine volcanic eruptions.

These sediments and volcanics at South Pass were deposited more than 2.8 billion years ago when the earth was poor in oxygen in what geologists refer to as the Archean Eon. As geological time continued, the volcanic islands continued to move closer and closer to the  continental shore line due to continental drift. This resulted in squeezing and compression of the rocks on the oceanic basic until the forces of compression produced sufficient pressures and temperatures that the sediments in this basin began to lithify and as the pressures and temperatures reached critical levels, the rocks began to recrystallize resulting in what geologists call metamorphic rocks. As these rocks were recrystallizing, they were also complexly folded and faulted and this likely was the time much of the gold was released (leached) from many of the rocks and focused into the faults (referred to as shear zones) and into the tops (peaks) of the folds. I came across a cross section on the Internet that gives a general cartoon of what a slice of a greenstone belt might look like. Along the edges of the greenstone belt are some granites that later intruded the belt about 2.4 to 2.6 billion years ago.

Banded iron formation
At the Hidden Hand mine in the Lewiston district, one will see rocks that are mostly greywackes that have been metamorphosed to produce ‘meta-greywackes’. These were clay-rich sandstones that are now light to dark gray in color and most are standing on edge from folding. The lode gold at the Hidden Hand mine and other mines in the area, was focused along a shear-zone (fault). 

If you look at the Hidden Hand mine on Google Earth, you will see many prospect pits and trenches that were dug along the trend of the shear zone in the search for commercial gold deposits. I was able to follow this shear zone for 2 to 2.3 miles along a 40 degree heading. Where the Hidden hand shear zone intersects Strawberry Creek to the north, the fault (shear zone) is likely offset by a much later fault that controls the location of Strawberry Creek (i.e., Strawberry Creek lies in a fault zone). This gold-bearing shear is offset to the west about 0.25 mile and continues along the same trend on the north bank of the creek for another mile at least. 

Much of the lode gold in the Lewiston district occurs in strike-trending shear-zones that parallel fold limbs in metagreywacke and are thought to have formed during regional folding and metamorphism.  

Cross-cutting shears are poorly mineralized. The strike shears (those that follow the trend of rock foliation and bedding) are weakly mineralized with sporadic rich ore shoots most likely occurring in fold closures. In some of these ore shoots, excellent specimens of native gold in quartz have been found in recent years. The shears were traced a few hundred to >3 miles along strike. It can’t be emphasized enough that significant portions of these shears are hidden under thin soil cover and remain unsampled. Some rich ore shoots are likely hidden under a few inches to a few feet of soil in this area and it would be interesting to expose the entire trend of these shears with a backhoe or dozer. Gold placers occur downstream from the shear structures in Strawberry Creek, Deep Creek, the Sweetwater River and Big Nugget Gulch. Others likely occur with limited volumes of gravel.

This was great! I was inducted into the International Order
of the Ragged Ass Miners in Denver!
Big Nugget (Giblin) Placer (Sections 31, 32 & 33, T29N, R98W). Haff (1944e) reported “five good-size nuggets were found in this placer”. The Wyoming State Journal (March 23, 1932) reported nuggets weighing 5.3 and 5.2 ounces were also found. The Big Nugget placer possibly resides adjacent to the old Lewiston ghost town just southwest of the Mint mine, but several drainages are located near Lewiston that cut gold-bearing shear zones, and anyone could be the Big Nugget placer including Deep Creek to the east. Based on the reports of several nuggets in this placer, the Big Nugget likely sits over or adjacent to, an ore shoot in a shear zone. 

Bullion mine (N/2 section 5, T28N, R98W). The Bullion was developed by a series of open cuts on a strike shear and in eluvium on the north bank of Strawberry Creek adjacent to the former Lewiston town site. The Bullion ore shoot lies at the intersection of N46oE-trending strike shear with N80oE-trending cross-fault in metagreywacke. Gold values were reported to range from 0.3 to 3 opt Au (Barlett and Runner, 1926). Pfaff (1978) reported 21,000 ounces were mined from this site. This may be exaggerated based on the relatively small size of the workings.

Burr mine (N/2 section 8, T28N, R98W). The Burr is located at coalescing shears which produced a zone of intense brecciation. An N49oE-trending shear was intersected by an N73oW-trending cross shear. A few hundred feet west, the Amanda incline was sunk on the intersection of three shears: an N73oW-trending cross shear, N40oE-trending strike shear and an N56oE-trending shear. South of the Burr, a prominent cross fault intersects the shear near the Irish Jew prospect. 

Working on my South Pass in my office at the University of Wyoming. Note
the high-quality computer they gave me.
Rich pockets were mined that yielded 25 to 250 opt Au (Lewiston Gold Miner, 1894). Some rare specimen grade material reportedly contained as much as 1,690 opt Au (Wyoming Industrial Journal, 1901, v.2, no.11, p. 320). One 16-foot wide zone was reported to average 0.5 opt Au.  In 1893, a small pocket of ore was intersected that yielded nearly 2,900 ounces of gold (Engineering and Mining Journal, 1893, v. 56, p. 406). In addition, tungsten was found at this site. Wilson (1951a) reported scheelite was found in stringers, lenses, pods and specks conformable to the gold horizon. Samples yielded 2.5 to 70 % WO3 and averaged 5% WO3

Goodhope mine (SW section 34, T29N, R98W). A shallow shaft was sunk on a 2-foot wide, N45oE-trending, vertical, chloritized shear in metagreywacke. South of the shaft, the shear was trenched for 100 feet exposing sheared quartz lenses with visible gold. A grab sample of quartz assayed 1.18 opt Au. Three 2-foot channel sample dug across the shear assayed 0.11 opt Au, 0.35 opt Au and 0.63 opt Au. As incredible as it sounds, much of the shear remained unexplored when investigated by Hausel (1991a).

Hidden Hand mine (SE section 5, T28N, R98W). The Hidden Hand mine is located about 8 miles east, southeast of Atlantic City along the Lewiston road (also referred to as the Oregon trail road) south of both the Lewiston ghost town site and Strawberry Creek. The mine is on a patented claim. Patented claims are claims filed under the 1872 mining law that had enough value that the government allowed the claimants to purchase the property at a fair market price, which was done in the 19th century to stimulate interest in mining and development of the West. Today, it is impossible to patent claims. Although we never had access problems to this mine because it sits in the middle of BLM ground surrounded by vast, empty, wasteland, it could easily be blocked off. There is a very disturbing trend of people with non-mining interests buying patented claims for cabin sites and then closing off access. Maps that cover this area include the Radium Springs 7.5 minute (1:24,000 scale) topographic and geological maps. 

Examination of the area on Google Earth shows distinct foliation (closely spaced lines) in the Miners Delight Formation metagreywacke that trend to the northeast. Rocks in this area are folded, faulted and turned on end. Also noticeable is the alignment of the Burr Mine with the Hidden Hand Mine and that this trend parallels regional foliation. A nearly east-west to northeasterly trending line of vegetation is visible southwest of the Hidden Hand that represents a cross-cutting shear zone intersecting the primary shear at the Hidden Hand. There are several prospect pits and a number of backhoe trench scars that were cut perpendicular to the primary shear zone. The results of samples from these trenches are unknown.

The shaft was sunk on a 10- to 30-foot-wide, N40oE-trending, 62oNW-dipping shear in chloritized, hematitic metagreywacke. The shaft was 110-feet deep and the shear was explored by at least 640 feet of drifts prior to 1926 (Henderson, 1926). Ore from the 30-foot level ran as high as 75 opt Au. In 1916, about 1000 tons of ore with an average grade of 4 opt Au were reportedly stockpiled. Some specimen-grade material assayed 3,100 opt Au (since there are only 32,000 ounces in a ton, this indicates that the specimen contained 9.6% gold and the value was likely exaggerated). Samples of altered metagreywacke collected from the dump contained only trace gold (Hausel, 1989). This discrepancy suggests one of a two possibilities: (1) the reported assays were exaggerated or (2) the property developed a reputation for excellent gold specimens and the mine dump was thoroughly picked over by collectors. 

Little information about this mine has been published and the mine workings are inaccessible, thus it is difficult to provide much in the way of conclusions. The exposed structure at the Hidden Hand mine exhibits considerable brittle deformation – something that is more typical of Laramide faulting (post gold mineralization) in this region. It is recommended that the mine working be reopened and explored or that the property be drilled.

Iron Duke (SE section 5, T29N, R98W). North of the Hidden Hand mine, coalescing shears intersect at the Iron Duke shaft (Figure 80). The shaft was sunk on a relatively wide shear in altered metagreywacke: secondary hematite, chlorite, quartz with minor sericite and epidote replace portions of the sheared rock and wallrock. A short distance east of the mine is an unexplored shear with chlorite and hematite alteration. A sample of silicified metagreywacke taken in the Iron duke shear assayed 0.21 opt Au. A 6-foot wide channel sample across the shear yielded 0.036 opt Au (Hausel, 1991a). 

Lewiston iron formation (N/2 NE section 25, T29N, R98W). In many greenstone belts around the world, iron formations are known for localizing both syngenetic (gold deposited during deposition of the host rocks) and epigenetic gold (gold introduced to the rocks at a later time). A sample of hematitic iron formation collected from the outcrop assayed 0.55% Cu, 0.02 opt Au and 0.05 opt Ag (Hausel, 1991a). The rest of the iron formation remains unevaluated but this sample suggests that mineralizing fluids were localized by the iron formation.

Lone Pine mine (SE section 9, T28N, R98W). An adit was driven 470 feet across foliation along an N67oW trend in the north bank of the Sweetwater River. Several narrow shears, faults and breccias zones were intersected in the tunnel. Only one narrow, 1-inch-wide, arsenopyrite-quartz vein was intersected. A sample of the vein assayed 0.61 opt Ag with no detectable gold. The apparent target for this mine was a cross-cut vein 1,200 feet from the portal; however the mine stopped 700 feet short of the structure. A shaft was sunk on this structure, but reclamation obscured all geological relationships. 

A 24 (possibly 34) ounce nugget from Rock Creek at South Pass
In some districts, high gold values often correlate with arsenopyrite, but this does not appear to be the case for South Pass. Prospectors should learn to recognize this important sulfide because of its potential to hold significant gold values hidden within the mineral. Arsenopyrite is mostly found as a massive, silver-gray, metallic sulfide associated with distinct yellow-green arsenic-bearing limonite known as scorodite. When arsenopyrite is struck by a rock hammer, a prospector will notice a distinct garlic odor from the arsenic (Hausel, 2009b).

In 1987, two trenches were dug in a search for a possible ore shoot at the buried shaft. The trench perpendicular to the vein demonstrated the vein pinched out just short of the shaft even though it is traceable for >3,000 feet to the northeast. In the trench perpendicular to the foliation, a hidden, 17-foot-wide chloritized shear zone with quartz stringers was discovered. A channel sample across the width of this shear averaged 0.047 opt Au and 0.8 opt Ag. Composite chip samples were anomalous in gold.

Mint-Gold Leaf mine (SE section 33, T29N, R98W). Two shafts located 500 feet apart were sunk on a N53oE-trending vertical, silicified shear in Miners Delight metagreywacke. This shear is traceable over a distance of 10,000 feet, but has fewer than 2 dozen prospects and shafts along its trend indicating considerable potential for mineralized unexplored ground. At the Mint, the shear is well exposed in a shallow trench with shafts located at both ends of the trench. The southern shaft was reclaimed and the northern shaft was covered. The shear is 2.5 feet wide at the northern end of the trench and about 6-feet-wide at the southern end. Samples containing visible gold were collected from this trench. The Gold Leaf shaft is shallow with little development. It appears to lie a few feet west of the main shear.

Gold nuggets found with metal detector in the Crows Nest at
South Pass by Gary Nunn.
Channel samples were collected across the shear. A 2.5-foot channel sample collected near the northern shaft assayed 1.29 opt Au (Hausel, 1987b). Another 2.5-foot channel sample assayed 3.05 opt Au (J.E. Bond, personal communication, 1986). Knight (1901) collected a sample from the Mint shaft that assayed 0.61 opt Au. This property and much of the shear structure provides an excellent gold target that remains mostly unevaluated. This property should be drilled to see if the gold continues at depth. A sample of quartz in the shear zone was dug out that was filled with visible gold. The sample was not assayed but kept as a specimen and likely would have assayed 10 to 50 opt Au.
Wilson Bar adit (SW section 9, T28N, R98W). A 180-foot long tunnel was driven perpendicular to regional foliation to test a 2- to 3-foot-wide cupriferous quartz vein in metagreywacke. The tunnel cut several narrow shears, fractures and veins and terminated in 15-feet of brittle breccia without intersecting the target. The quartz vein pinched out northeast of the mine face.

Wilson Bar placer (SW section 9, NW section 16, T28N, R98W). The Burr and Hidden Hand lodes drain into Burr Gulch. This gulch continues south into the Sweetwater River. The mouth of Burr Gulch is known as Wilson Bar. During the early history of Lewiston, this placer was reported to be exceptionally rich. The Lewiston Gold Miner (1894) reported the placer was discovered following several samples that yielded 0.2 to 0.9 ounces to the pan. It was also reported that 370 ounces were recovered from a 500-foot strip of gravel. 

Wolf (Ruby) Mine (SE section 22, T29N, R98W). The Wolf mine is located to the northwest of the Atlantic City road. Three shafts (<100 feet deep) were sunk on a 4,500 foot long hematite-stained chloritized shear zone. The shear is not well-exposed but is as much as 160-feet-wide. The structure lies within a subtle linear depression. The width of the structure was determined by trenching and the depression continues to the northeast and southwest from the shafts. 

The footwall on the 78oNW-dipping shear is silicified. One grab sample of gray quartz with altered metagreywacke assayed 0.68 opt Au. Samples collected across this shear assayed >1.0 opt (Steve Gyorvary, personal communication, 2010). The property was examined by U.S. Borax who determined the structure to be mineralized over >100 feet of width. This structure, because of potential size and assays, should be thoroughly investigated and likely represents a significant gold deposit. 

Black sand concentrates from panning
7605 Incline (S/2 section 7, T28N, R98W). An incline was sunk approximately 100 feet deep on an N36oE-trending, 42oNW-dipping shear in metagreywacke. The iron-stained shear is approximately 10-feet wide and has scattered quartz boudins and pods. One grab sample of quartz from the mine dump assayed 0.05 opt Ag with no gold. See Hausel (1991a) for location of this deposit.

SE section 9, T28N, R98W. Two narrow, parallel quartz veins carry considerable arsenopyrite and scorodite. Samples collected from the veins assayed 0.26% and 0.28% Cu, a trace to 0.13 opt Au, and 0.77 to 4.2 opt Ag (Hausel, 1991a). The gold and silver values suggest that this deposit should be examined in greater detail although the veins at the surface appear to be very narrow and quite limited. (Hausel and Hausel, 2011)

Another rock creek nugget
A couple of my publications on South Pass are available as PDFs. You can download them by clicking on the following links:

Gold from Dickie Springs (photo courtesy of Dr. Dave Love)
Hausel and Love, 1992










Recent photo of the author still looking for gold and base metals. Photo taken at the
Resolution mine, Arizona.

Friday, September 5, 2014

Wyoming's Gold Geology and Gold Districts

Gold is now available at Amazon.
Over three decades of research and exploration from 1977 to 2007, hundreds of gold anomalies and a previously unrecognized gold district were identified in Wyoming. Essentially, all of this information is discussed and described in a 365-page book entitled, Gold: Field Guide for Prospectors & Geologists (Wyoming & Adjacent Areas) available at Amazon. The book is rated 5 stars and will tell you about the geology and mining history of hundreds of gold prospects, mines and anomalies.

GOLD PRODUCTION IN WYOMING

Available production records for metals for Wyoming are far from accurate. In the past, few records were archived and production from the Wyoming territory was often incorporated into totals of neighboring territories, states and mining districts. However, based on the scattered reports, it appears that sufficient quantities of metals were recovered from Wyoming during past years to warrant further exploration in the State (Table 1). In fact, geological evidence for major gold and base metal deposits suggest there are likely several undiscovered and/or undeveloped deposits in Wyoming.
Gold 
(oz)
Silver 
(oz)
Platinum
(oz)
Palladium 
 (oz)
Lead   
(lbs)
Copper   (lbs)
Iron   
(tons)
385,000
157,000
900
16,900
29,000
63,850,000
135,000,000

Table 1. Historic production of selected metals for Wyoming (from Hausel, 1989a)
A 24-ounce gold nugget from Rock Creek in the South Pass district.
Based on the reported production for Wyoming, compared to the surrounding regions (Colorado, Utah, Idaho, South Dakota, Montana) it is apparent that Wyoming has greatly underproduced compared to the adjacent states suggesting that some major gold deposits remain to be found (Hausel and Hausel, 2011). Metal deposits are scattered throughout the stratigraphic record in Wyoming; however, the greatest concentrations are found in rocks of Precambrian and Tertiary age. The very ancient Archean (>2.5 Ga = more than 2.5 years old) rocks have a number of significant metal and semi-precious stone deposits and anomalies. These rocks are folded and metamorphosed sedimentary, volcanic, and plutonic rocks exposed in the core of mountain ranges. Keep in mind that folds are very important in focusing gold deposits in places like South Pass

Archean rocks of interest include sheared rock, quartz veins, along with nearby banded iron formation,  massive hematite, localized veinlet and disseminated scheelite, vein nephrite (jade), ruby and sapphire schist, podiform and veinlet chromite, metagraywacke and amphibolite. Granitic rocks include copper deposits, some rare earth deposits (REE), tantalite, and beryl pegmatites.  Rare aquamarine beryl and green tourmaline have been reported in some pegmatites. In addition, some of the largest colored gemstone deposits in the world were discovered in metapelite near the Elmers Rock Greenstone belt. These deposits are mostly iolite gemstones (some gems my thousands of carats in weight) found in quartzofeldspathic gneiss adjacent to sillimanite gneiss, kyanite schist and ruby- and sapphire-vermiculite schist.
Mineralized terranes and districts in Wyoming (after Hausel, 1997).
In southeastern Wyoming, thick Proterozoic (<2.5 Ga) metasedimentary rock successions crop out as miogeosynclinal wedges unconformably lying on top of the Archean basement. These include quartzite-hosted Cu-Ag-Au (copper-silver-gold) deposits, Au-Ag veins, and radioactive Witwatersrand-type metaconglomerates (metamorphosed conglomerates) with isolated Au anomalies and a few diamonds. This miogeoclinal terrane is separated from a predominantly metavolcanic terrane to the south by a major Precambrian suture, or shear zone, known as the Mullen Creek-Nash Fork shear zone. The suture includes scattered Cu-Au-Ag and some Pt-Pd (platinum-palladium) bearing cataclastics. In fact, the first deposit commercially mined for palladium and platinum (with value-added copper, gold and silver) in north America was the New Rambler mine in the Medicine Bow Mountains. This mine was located along a shear zone at the edge of a layered mafic complex suggesting there is likely a cumulate (lode) source for the platinum and palladium along with vanadium, titanium and chromium in this area in what is known as the Mullen Creek and Lake Owen layered mafic complexes. But these areas were strategically withdrawn by the US Forest Service.
Gold in black sands from Douglas Creek placer district, Medicine Bow
Mountains, Wyoming.
South of the suture, a Proterozoic metavolcanic terrane (1.8 to 1.6 billion years old) includes volcanogenic (derived from volcanic activity) Zn-Cu-Ag (zinc-copper-silver) massive sulfide deposits similar to the massive sulfides at the United Verde Mine in Jerome, at least one Cu-Au porphyry, and two large layered mafic complexes (1.8 billion years old). The northern edge of one of these intrusives yielded some Pt and Pd with Cu, Au, and Ag at the beginning of the 20th century. A 350 mi2 anorthosite batholith (1.4-1.5 billion years old) in the Laramie Mountains has long been considered as a possible source of low-grade aluminum ore as well as extensive disseminated and massive Ti-Fe-V (titanium-iron-vanadium) deposits. At one point along the margin of the batholith is a Cu-Au-Ag-W-Mo (copper-gold-silver-tungsten-molybdenum) lode with anomalous nickel (Ni). And in this area may be one the largest colored gemstone deposit found on earth, the Sherman Mountains iolite deposit that was briefly investigated by Wyoming Geological Survey geologist Dan Hausel and suggested it could potentially host more than a trillion carats of iolite gems based on past cordierite resource investigation in 1949. In addition to these gems, large resources of spectrolite (labradorite) are found and some kimberlites intrude the anorthosite near Grant Creek suggesting a possibility for diamonds and other gemstones.
A close look at this small nugget from Douglas Creek shows it is rounded suggesting that it traveled some district from
its source. 
Mineralizing events for much of the Phanerozoic (rocks from about 541 million years old to the present) was not widespread, although there were several spatial events in various parts of the State. Phanerozoic rocks can be separated into the Paleozoic, Mesozoic and Cenozoic. Within Paleozoic rocks (those deposited 541 to 252 million years ago), Au-REE (gold-rare earth elements) anomalies are described in Cambrian conglomerates, diamonds are found in some Cambrian- and Devonian-age kimberlites at Iron Mountain in the Laramie Range and in the Colorado-Wyoming State Line district south of Laramie. Another diamond-bearing kimberlite was described at Grassrange, Montana (Tertiary age) and possibly in one of the kimberlites in Riley County Kansas (Cretaceous age). These are surrounded by hundreds of cryptovolcanic structures of unknown origin that need to be prospected. While consulting for Echo Bay, Dan Hausel highly recommended the company consider the Grassrange intrusives as diamond prospects prior to discovery of diamonds at the Homestead kimberlite at Grassrange.
Early Jurassic prospectors searching for gold (colored pencil sketch by Dan
Hausel). Original sketch donated to the University of Wyoming Geology
Museum.

There are several Pennsylvanian and Mississippian Cu-Ag and Mn (manganese) carbonate-hosted occurrences in Wyoming that appear to have limited extent. Permian phosphatic shales and black shales are reported to contain a number of unusual metal anomalies in western Wyoming. Ag-Cu-Zn (silver-copper-zinc) stratabound deposits are found in bleached Jurassic redbeds in western Wyoming, and the broad Wyoming basins include some enigmatic gold occurrences and anomalies that can only partially be explained by detrital transport in fluvial systems. Rocks of Late Cretaceous age along the flanks of some uplifts have scattered black titaniferous sandstone deposits that represent ancient beach deposits. These include detrital heavy minerals with anomalous Ti (titanium), Zr (zirconium), REE (rare earth elements), and in some cases Au (gold).  
Folded schist in the Medicine Bow Mountains of Wyoming.
Note that these rocks provide evidence of two episodes of
folding. The primary folds are isoclinal folds in that the fold
limbs are parallel and indicated intense folding.
Tertiary rocks host important ore deposits, occurrences, and anomalies. These also provide examples of extreme global warming with widespread swamps depositing giant resources of coal, particularly in the Powder River Basin. It is interesting this (and many other climate change events) was a natural event and like all previous global warming events, the planet naturally recovered. Some events were possibly due to increased volcanism, impacts, mountain building, plate tectonic movements and sunspot activity.

Some of the largest ore deposits and areas of mineralization in the state are associated with the Cu-Ag porphyries in the Absaroka Mountains of northwestern Wyoming. These are similar to the great copper-porphyry deposits of Arizona, Butte Montana, Santa Rita New Mexico, and Bingham Utah. This deeply incised volcanic plateau includes several Tertiary age composite stocks with zoned hydrothermal alteration and mineralization. Usually thought of as copper deposits, such porphyries contain significant Cu (copper), Ag (silver), Pb (lead), Zn (zinc), Au (gold), Ti (titanium), Mo (molybdenum) and sometimes REE (rare earth elements). But ALL of these giant deposits were piecemeal withdrawn from exploration and mining by the US Forest Service. To the north of this region, the Crown Butte gold mine in the New World mining district, was located on private property but was forced to terminate development during the Clinton Administration likely in response to UN agenda 21. There was no evidence that any mining activity would have affected Yellowstone National Park, as the mine was northeast of the park. Yellowstone is a caldera and provides one of the most caustic environments on the surface of the earth.
In the Black Hills of northeastern Wyoming, Au-Th-REE (gold-thorium-rare earth elements) mineralization and large fluorite deposits are associated with Tertiary alkalic intrusives. In addition, some Pb-Zn-Ag replacement mineralization and Sn (tin) pegmatites are found in this region. Significant gold and silver, in particular, we detected by Hausel (1997) at Mineral Hill in this area. The Rattlesnake Hills in central Wyoming were intruded by similar Tertiary igneous rocks that intrude an Archean greenstone belt, implying this terrain to have the high potential for major gold deposits similar to Cripple Creek. Gold was discovered in this area in 1981 by W.D. Hausel of the Wyoming Geological Survey. 
Isoclinally folded metagabbro at the Duncan gold mine,
South Pass. Some of these folds in shear zones likely
control ore shoots as the plunge into the earth to unknown
depths to form saddle reef-type gold deposits. 
The Tertiary of Wyoming was not only a time of volcanism, but was also an important time of paleoplacer development. Paleoplacers are nothing more than fossilized placers where stream and river sediments were deposited in the geological past. In many cases, the original source rock for the sediments was removed over time leaving a paleoplacer high and dry with no obvious source. Most of these deposits were buried under thick overburden that sufficiently compressed and solidified the otherwise detrital sediments to produce hard rock. These hard rocks contain valuable gold (about 50% of the gold mined in the world was from paleoplacers in the Witwatersrand of South Africa), uranium and some diamonds. 
Consolidated gold-bearing paleoplacer with distinct, rounded
stream worn pebbles in a limonite-stained sandstone matrix.

Laramide uplifts were nearly leveled by erosion over time, which resulted in deposition of large volumes of fluvial conglomerate and fanglomerate along the flanks of the uplifts. Where these conglomerates were eroded from mineralized terranes such as greenstone belts, they often contained gold. Today most commercial placers worldwide are mined for gold, although some cassiterite, native platinum, scheelite, monazite, diamond, chromitetantalite and various gemstones may be recovered with the gold.
VERY OLD MINERAL DEPOSITS (Archean)
The ancient geology of Wyoming has been compared to some of the richest precious metal regions of the world including South Africa, Western Australia, and the Superior Province of Canada. These areas are all underlain by ancient Archean cratons with some of the oldest rocks on the surface of the earth. But unlike these other cratons, the Wyoming craton (termed the Wyoming Province) has been greatly modified by Laramide tectonics which thrust slices of the ancient craton through much younger Phanerozoic sedimentary rocks. Due to the unfortunate nature of the Laramide tectonics, vast regions of the Wyoming craton remain at the bottom of the Tertiary basins unavailable for direct observation, but the exposed slices exposed in the mountain cores contain some of the best exposures of Archean rock in the world.  Even so, there are several gold districts in this region.
Stretched pebble conglomerate from the Medicine Bow
Mountains Wyoming showing white, lens-shaped quartz
pebbles compressed by more than 2 billion years of deep
burial under thick overburden.
The Wyoming Province is not confined to the State of Wyoming, but extends into northern Utah, extreme northeastern Nevada, the eastern edge of Idaho, portions of Montana, and the northwestern corner of South Dakota.  And according to Condie (1976), the Wyoming craton may have once been connected to the Superior Province (crayon) of Canada. 
Similar to other cratons of the world, the Wyoming craton is also highly mineralized. Mineral resources include those of the Stillwater complex (platinum, palladium, chromium) in Montana, the Jardine gold district in Montana, the Homestake gold mine in South Dakota, the South Pass gold and iron ore district, the Seminoe Mountains gold and iron district, the Rattlesnake Hills gold district, the Hartville iron district, and the central Laramie Range gemstone district in Wyoming. 
The Wyoming Province is formed of a vast region of high-grade gneiss and migmatite intruded by granite and granodiorite plutons with scattered blocks, fragments, and belts of supracrustal terrains that include greenstone belts, eugeoclinal successions, layered mafic complexes, and high-grade metamorphosed supracrustal belts.  Mineral occurrences in the granite-gneiss terrane are uncommon, but the supracrustal belts have hundreds of gold, base metal, and related mineral deposits and prospects.
Greenstone Belts
Robert Houston in 1983 noted that the Wyoming Province contained supracrustal successions (layered metamorphic rock)  of low-rank metamorphosed rock in the southern part of the craton (South Pass, Rattlesnake Hills, Elmers Rock and Seminoe Mountains) that exhibited similarities to greenstone belts in other cratons of the world.  However, in the northern region of the craton, the rank of the supracrustal belts generally increases, and the belts are lithologically distinct in that they are formed of intercalated amphibolite and gneiss with subordinate successions of meta-sedimentary rocks that include quartzite, metapelite, BIF (banded iron formation), amphibolite, and minor metacarbonate.  Exceptions occur, such as the Jardine belt of the Snowy Range block of the Beartooth Mountains in the northern portion of the Wyoming craton, which was reported by Thurston (1986) to exhibit similarities to the South Pass greenstone belt in the Wind River Mountains in the south. But it was Houston's contention, that the greenstone belts represented the greatest potential for mineralization compared to any other part of the Province. These belts host several known gold deposits.
In general, the Wyoming greenstone belts form tripartite successions of low-rank metamorphosed (upper greenschist to middle amphibolite facies) sedimentary, volcanic, and plutonic rock, folded into a regional synclinorium. Bedding and most structural features (i.e., foliation, isoclinal fold axes, gold-bearing shear zones) parallel the axis of the synclinorium. Although amphibolite facies metamorphism presides in these terranes, the overall metamorphism is relatively low resulting in the preservation of some primary textures. Pillow structures, and porphyritic, amygdaloidal, spinifex, and cumulus textures are preserved in some igneous rocks. Graded bedding, quartz pebbles, cross-bedding, and cut and fill channels occur in some metasedimentary rocks.  
The lower portions of the greenstone belts are formed of ultramafic to mafic metavolcanics that may include hornblende amphibolite (orthoamphibolite), serpentinite, tremolite-talc-chlorite schist and metabasalt. These rocks have compositions that suggest they represent the metamorphosed remains of  high-magnesian basalts and tuffs, and komatiitic basalts and peridotites. The majority of these rocks have high in magnesium and low in silica suggesting that the erupted directly from the earths upper mantle.
Pillow basalts (basalts deposited in water)
The character of the greenstone successions changed through time, and  the underlying successions were replaced by more calcium and iron rich calc-alkaline metavolcanics (meta-andesite, metadacite, felsic schist), high-iron tholeiitic basalts (amphibolite, greenstone, and metabasalt), and metakomatiite (actinolite schist, hornblende-plagioclase amphibolite, tremolite-talc-chlorite schist, and minor serpentinite).  Metasedimentary rocks are prominent in the upper succession and include metagreywacke, BIF, with lesser quartzite, graphitic schist, metaconglomerate, and metapelite.
Spinifex textured komatiite from the Hannas Lake
Serpentinite, Australia.
Several greenstone belts and fragments are recognized in Wyoming and include South Pass in the Wind River Mountains, Barlow Gap and Tin Cup in the Granite Mountains, the Seminoe Mountains, Casper Mountain, Sellers Mountain, Esterbrook, and Elmers Rock in the Laramie Range, as well as other fragments in the Laramie, Medicine Bow, and Sierra Madre ranges (Condie, 1967; Houston, 1983). 
South Pass greenstone belt & mining districts
The South Pass greenstone belt in the southern Wind River Mountains encloses the Anderson Ridge pegmatites, the South Pass-Atlantic City district, the Miners Delight district, the Lewiston district and the Crows Nest. The northern edge of the greenstone belt is overlain by placers and Tertiary paleoplacers of McGraw Flats-Twin Creek and the southern margin of the greenstone belt projects under younger sedimentary cover and also under the Dickie Springs-Oregon Buttes placers and paleoplacers. Much of this gold-rich area was incorporated into the Sweetwater Mining district in the 19th century.

The greenstone belt crops out over an area of roughly 250 square miles, and a large portion of the belt continues under a thin (<1 foot to > 2,000 feet thick) blanket of Tertiary arkosic sandstone, siltstone, and conglomerate. The extension of the greenstone belt as far south as to the base of Oregon Buttes was confirmed by both drilling and aerial geophysics by Hecla Mining in the 1980s. During the past, this region received only minor exploration interest for lode, paleoplacer, and placer gold, yet the region offers the greatest potential of all of the greenstone belts in the Wyoming craton for discovery of significant mineralization. Precious and base metal deposits in the belt include auriferous shear zones and veins, associated Tertiary paleoplacers and modern placers, restricted Ag- and Au-bearing cupriferous veins, and cupriferous stockworks. 
The South Pass greenstone belt (after Hausel, 1991).
Shear zones in the greenstone belt are narrow, foliation-parallel, cataclastic zones, that exhibit both brittle and ductile deformation and have strike lengths of dozens of feet to more than 11,000 feet (Hausel and Hull, 1990).  Widths are typically between 2 to 15 feet, although greater widths occur at several mines. For the most part, these structures are weakly mineralized along much of their trend with localized ore shoots that may plunge to depths of more than a thousand feet. The shoots occur at pinches, swells, fold closures, attitude changes, and at intersections of structures.
Historic reports indicate the gold tenor of the ore shoots ranged from a trace to as much as 3,100 opt Au.  Average mine grades varied from 2.06 ppm (0.06 opt) to 68.6 ppm (2.0 opt) Au with minor silver (Hausel, 1989a). The continuation of these structures downdip has not been fully tested since the deepest gold mine is only 400 feet deep, and drilling penetrated the mineralized structures to depths of only 930 feet below the surface (deQuadros, 1989). It is likely that these shoots continue to the base of the greenstone belt (a few thousand feet or more?).
Many of the shears and veins are localized in metagreywacke and hornblendic amphibolite with fewer in graphitic schist, meta-andesite, greenstone, greenschist, metatonalite, and tremolite/actinolite schist. A large proportion of these gold-bearing structures are found along or adjacent to lithologic contacts of rocks with contrasting competency (Bayley, 1968; Hausel, 1987), such as the metamorphosed graywackes and graphitic schist as opposed to the more competent metamorphosed gabbros (metagabbros) and basalts (amphibolites).
The source of the gold found in the shear zones was suggested by Bow (1986) to have been rocks of komatiite affinity. But recent stable isotope and fluid inclusion studies by Spry and McGowan (1989) are redolent of a greywacke source. Hausel (1991), however, was impressed by the ubiquitous occurrence of structurally controlled gold anomalies throughout the greenstone belt independent of rock type and proposed the gold was derived by metamorphic secretion during a 2.8 billion year old regional metamorphic event, and the shears served to focus the auriferous fluids.

In addition to narrow mineralized structures,  the possibility exists for large-tonnage, low-grade, precious metal deposits in this greenstone belt. Four mines suggested as possible large tonnage deposits by Hausel (1991) included the Carissa, Duncan, Lone Pine, Wolf, and Tabor Grand. 
The gold-bearing Carissa shear zone hosts a major, unmined gold deposit.
At the Carissa mine in the South Pass-Atlantic City district along the northern flank of the greenstone belt, the principal shear is a narrow 5 to 50 foot wide structure enveloped by a broad, 300 to 1,000 foot zone of weakly mineralized wallrock with rehealed fractures. A 1.5 foot channel sample taken across the shear assayed 5.2 ppm (0.15 opt) Au (Hausel, 1989a), and Beeler (1908) reported the average ore ran 10.29 ppm (0.3 opt) Au. Composite chip samples collected in the adjacent wallrock also yielded anomalous gold over a 97 foot width (Hausel, 1989a). The mineralized structure was appears to have a with of nearly 1000 feet with considerable strike: significant gold was intercepted at depth in the deepest drill holes drilled in the area to a depth of 970 feet. Based on geology, the gold bearing ore shoot is believed to continue to much greater depth (Hausel and Hausel, 2011).
At the Duncan mine, the foliation-parallel shear is folded and splayed. The splay has a aggregate width of more than 40 feet adjacent to the shaft, and is mineralized across its entire width.  But within the fold closure, the gold values are enhanced, and the nose of the steeply plunging drag fold averages nearly ten times the amount of gold in the fold limbs.
General location map of the South Pass, Atlantic City, and Miners Delight
mining districts showing locations of principal mines, faults and streams.
In the Tabor Grand mine, a 1 to 5 foot wide shear cuts hornblendic amphibolite.  Samples of the shear yielded 0.06 to 58.0 ppm Au (0.002 to 1.87 opt) over a 350 foot length. During mapping of the mine, a second shear parallel to the first was discovered 20 feet south of the primary shear.  Two samples taken in this shear yielded 1.7 and 7.0 ppm Au. Surface mapping extended the length of the shear another 800 feet to the east where an 8 ft channel sample assayed 3.8 ppm Au (Hausel, 1991).
At the Lone Pine mine in the Lewiston district along the southeastern margin of the greenstone belt, a hidden shear was discovered hidden under a thin veneer of Tertiary South Pass Formation.  The discovery trench exposed a 17 foot wide shear which yielded gold values of 0.47 to 3.5 ppm. The maximum mineralized width and strike length of this structure have not been determined. At another mine in the same district known as the Wolf mine, representative samples yielded 23.3 ppm (0.68 opt) Au (Hausel, 1989a). This property was later examined by U.S. Borax, and it was determined the shear was mineralized over a width of more than 100 feet.
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Chip channel and channel sample analyses in the South Pass greenstone belt (Hausel,1989a).
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SAMPLE DESCRIPTION
Au
Ag
Carissa Mine
(ppm)
(ppm)
0 to 10 ft north of shear
0.4
--
10 to 20 ft north of shear
1.05
--
20 to 37 ft north of shear
2.5
--
0 to 10 ft south of shear
0.65
--
10 to 20 ft south of shear
0.25
--
20 to 30 ft south of shear
0.30
--
30 to 60 ft south of shear
0.35
--
30 ft composite north of shear
2.4
--
Duncan Mine


0 to 2 ft west of fold closure in shear
3.0
2.2
2 ft channel across fold closure
33.0
6.0
0 to 5 ft east of closure
1.8
1.8
5  to 15 ft east of closure
6.6
2.7
15 to 25 ft east of closure
0.71
7.4
25 to 35 ft east of closure
0.53
1.0
Lone Pine Mine


0 to 4 ft (E to W) in shear
0.47
2.5
4 to 7 ft (E to W) in shear
0.69
1.9
7 to 11 ft (E to W) in shear
3.5
4.3
11 to 17 ft (E to W) in shear
1.6
2.9

_________________________________________________________________________________
In addition to the gold-bearing shear zones (lodes), cupriferous veins with Au and Ag values are found at several locations in the belt. These veins have little economic value because of the lack of tonnage. They are seldom greater than 2 feet wide and pinch and swell over short distances along strike. However, one Cu-Ag stockwork discovered along the northwestern flank of the belt may be of interest. The extent of the stockwork is unknown since it lies under soil in a large aspen grove. Grab samples of the mineralized rock yielded 3.23 % Cu, 3.2 ppm Ag, and 0.16 ppm Au (Hausel, 1991).
The South Pass greenstone belt also has extensive iron deposits in the limbs of the South Pass synclinorium. The BIF along the northern flank of the belt was structurally thickened fourfold by internal folding and plication and by repetition along faults. This deposit was reported by Bayley (1968) to have indicated reserves of 300 million tons of 30% Fe. From 1962 to 1983, U.S. Steel Corp. mined more than 90 million tons of iron ore from this BIF. Recent mapping by Hausel (1990a), indicates a sizable resource is available.
The possibility of gold in the iron formation apparently was not considered during the 20 year operating lifetime of the mine.  However, samples collected a short distance southwest in the BIF by the Wyoming Geological Survey, yielded gold anomalies (maximum of 1.3 ppm).  Other anomalies were detected in BIF along the southeastern margin of the greenstone belt.  Only a small number of sulfide-bearing oxide facies BIF were collected by the Survey in the open pit mine before it was flooded in 1983.  None of the samples contained detectable gold (minimum detection limit 0.02 opt).

If you would like to make your own gold discovery in this district, there are many opportunities. Connect the dots - i.e., draw lines between a groups of mines and prospects and in-between all of these will be a hidden, gold-bearing shear zone that likely has never been prospected. As an example, use Google Earth to find the Carissa Gold Mine (42°28'29.15"N; 108°47'42.65"W) and then look to the east-north east along a 250o trend (N80oE) and you will see many holes dug in a search for the Carissa Lode. In between all of these prospect pits and mines are places that have not been prospected - anyone of those localities could be hiding an overlooked ore shoot. Remember, the prospectors who searched this area before you had no magic powers, and they overlooked many things. This is true throughout the mining district and greenstone belt.

Now examine Willow Creek downstream from the Carissa mine. Only small patches of this gold placer were ever mined for gold such as at the tailings at 42°27'48.64"N; 108°47'9.45"W. This drainage sampled the Carissa lode and other lodes; thus the gravels are likely very rich. Try similar investigations in the Lewiston district. There are reports of several gold nuggets recovered in that area. Search for the shear zones by using published geological maps (Hausel, 1991) and then look anywhere downstream from those shears. Look for drainages with both water and without water as the dry drainages are also likely to have some coarse gold. You are going to have to do some work and research, but there is considerable gold left in the South Pass area.
The Seminoe Mountains greenstone belt includes a distinct, large
altered zone surrounding gold-bearing veins at the Penn mines.
Seminoe Mountains mining district
The Seminoe Mountains greenstone belt is in south-central Wyoming.  This belt is ~2.7 Ga (billion years old), whereas South Pass is a minimum of 2.8 Ga.  The Seminoe Mountains have similar rock types as South Pass, but in different proportions (also, it is easy to predict that based on the rocks, considerable greenstone belt rocks lie under the basins to the north and south of Bradley Peak). The relative volume of metagreywacke in the Seminoe Mountains is less than South Pass, BIF is abundant, and the belt includes a thick section of aphyric and spinifex-textured basaltic komatiite and cumulate-textured serpentinite and metaperidotite (Klein, 1981; Snyder and others, 1989).
Gold is concentrated in a 1/4 mile diameter zone of altered  metagabbro and metabasalt near the western margin of the belt (Klein, 1981; Hausel, 1989b). Samples of quartz recently collected in this region were highly anomalous and have yielded gold values as high as 98.4 ppm (2.87 opt).  BIF is also locally anomalous in Au and Ag.  Amphibolites in the altered zone have been overprinted by chlorite, carbonate, quartz, and sulfide alteration assemblages (Klein, 1981). The zone is transected by narrow quartz-calcite veins and stockworks containing minor pyrite and chalcopyrite.  Ore shoots often yield visible gold and exhibit control by folding.        
Folded BIF in the Seminoe Mountains.
The Seminoe Mountains greenstone belt contains ubiquitous BIF. The BIF is interlayered with metabasalt and metasediments, and is predominantly oxide facies.  Harrer (1966) outlined a 100 million ton deposit of BIF, which varied from 28% to 68.7% Fe. 
Copper deposits are sporadic and appear to be unimportant in the greenstone belt.  Some samples with anomalous Zn and Pb were detected in a shear zone near some gold mineralization (Hausel, 1990b), and follow-up studies on this shear is currently in progress.  The Seminoe Mountains were explored by Kerr McGee Corp. and Timberline Minerals in the 1980s. Hausel recovered a large number of G10 pyrope garnets from the northern flank of the greenstone belt near the Miracle Mile. The source of the diamond-stability pyrope garnets has not been identified, but this area may be of interest to gold prospectors. The Tertiary gravels sitting high and dry in the flats surrounding the North Platte river in what is known as the Kortes Placer, contain gold and likely have diamonds.

The Rattlesnake Hills supracrustal belt is located in the northern Granite Mountains. Within this belt, a 500 ft long, mineralized vein (metachert), was discovered in 1981, and named the Lost Muffler prospect.  Composite chip samples 3.6 ft in length were taken in the vein, and assayed 7.5 and 4.5 ppm Au (Hausel, 1989a).  Later exploration in this area by American Copper and Nickel intersected auriferous BIF and gold-bearing Tertiary alkalic igneous rock.  Drill intercepts included 10 ft of 10.3 ppm Au in BIF and 250 ft of 2.1 ppm in the Tertiary volcanics. Additional sampling by Hausel identified anomalous gold in nearby breccias and Tertiary alkalics and drilling to depth by recent companies on these breccias intersected some very impressive gold deposits (Hausel and Hausel, 2011).
Other Supracrustal Belts.
 In addition to greenstone terranes, the Wyoming Province encloses medium to high-rank metamorphosed supracrustal belts.  These belts occur in the Tobacco Root Mountains, the Ruby and Gravelly Ranges of Montana, and the Copper Mountain district of the Owl Creek Mountains, Wyoming.  Also in Wyoming is the Hartville uplift in the southeastern corner of the Province.  This terrane consists of relatively low-rank metamorphosed eugeoclinal sedimentary and volcanic rocks.
Copper Mountain district, Owl Creek Mountains
The Copper Mountain district in the eastern Owl Creek Mountains is interpreted as a high-grade supracrustal belt (Hausel and others, 1985). It is intensely metamorphosed and isoclinally folded such that all primary textures have been essentially destroyed or overprinted by foliation. Two mappable units in the belt are similar in appearance and consist of intercalated amphibolite and quartzofeldspathic gneiss. A third unit is formed of gneiss, amphibolite, BIF, metapelite, and quartzite.
Scattered mineral deposits in the Copper Mountain district include stratiform scheelite, vein Cu and Au, and REE-Ta pegmatites.  One relatively significant development (the DePass mine) lies along the eastern edge of the district in a 50 ft wide Proterozoic mafic dike emplaced in Archean granite.  This mine was driven into the dike and produced a minimum of 568,000 lbs of mill concentrates in the early 1900s with receipts for Cu, Au, and Ag.  The mine has more than 11,000 feet of workings.
Hartville district 
The Hartville uplift in southeastern Wyoming has yielded more than 5 million pounds of copper and 45 million tons of iron from Archean schists and overlying Phanerozoic rocks. Mineral deposits in the region include the McCann Pass pyritiferous massive sulfide deposit, scattered Cu-Ag-Au-U (copper-silver-gold-uranium) unconformity deposits and several gemstone and lapidary minerals of potential interest including onyx, copper minerals, specularite, garnet and aquamarine (Hausel, 2009, 2014, Hausel and Hausel, 2011). The Silver Cliff mine in the northern portion of the uplift was initially developed for gold and silver in the 1870s and later mined for uranium in the early and mid 1900s (Hausel, 1989a). Mineralization at the Silver Cliff is localized in fault gouge and along a Precambrian-Cambrian unconformity.    
Onyx, Hartville uplift
The Hartville uplift is principally known for its massive hematite. Hematite was mined by C.F.&I. Corporation for many decades from hematite schist until 1981.  Total recorded production amounted to more than 45 million tons of ore with some by-product copper.  The hematite is secondary in origin and interpreted to have been derived by groundwater oxidation and enrichment of originally ferruginous beds (Bayley and James, 1973; Snyder and others, 1989).  These deposits often contain copper as well as anomalous gold.  For instance, the Michigan mine in the central portion of the uplift encloses two hematite pods.  The northern ore body contains 75 million tons of 25% Fe, and the southern deposit contains 41 million tons of 24% Fe (Wilson, undated).  The upper segment of these deposits are copper stained and anomalous in gold (Woodfill, 1987). 
Unconformity deposits also occur in the belt.  In the northern Hartville uplift, the Silver Cliff shaft was developed on a Precambrian-Phanerozoic unconformity and mineralized reverse fault.   Available assay reports indicate the ore contained none to 10.88 % Cu, none to 15.04 opt Ag, 0.001 to 3.39% U3O8, and anomalous gold (Wilmarth and Johnson, 1954).  In the southern portion of the uplift, Kerr McGee explored a copper-stained Precambrian-Paleozoic unconformity recovering samples with cerargyrite, unmangite, electrum, and native gold (Kerr McGee Corp., 1988).
Malachite in specularite, Hartville uplift, Wyoming
South of the Silver Cliff mine, a contact between hanging wall dolomite and footwall schist is mineralized over a 1 to 15 ft thickness.  Lenses from the Copper Belt Group assayed 2 to 8 % Cu and the adjacent altered iron-stained schist contained 0.05 to 0.58 opt Au and 2 to 5 opt Ag (Ball, 1907).     
In the southern portion of the uplift, an extensive gossan at "gossan hill" along the McCann Pass fault was prospected by Mine Finders in the 1970s, and more recently by Exxon Minerals.  Outcrop and shallow drill holes recovered samples with elevated Cu, As, and Zn.  Deeper drilling intersected thick zones of anomalous mineralization including 10 ft of 0.8% Zn, and 2 ft of 1.2 % Zn and 0.08 opt Au (Woodfill, 1987).
OLD, BUT NOT QUITE AS OLD OF MINERAL DEPOSITS (PROTEROZOIC AGE MINERALIZATION)
Nearly all of the Proterozoic rocks in Wyoming are restricted to the southeastern corner of the state in the Laramie, Medicine Bow, and Sierra Madre Mountains. The Sierra Madre and Medicine Bow Mountains are bisected by a prominent Precambrian suture known as the Mullen Creek-Nash Fork shear zone. This shear is projected into the Laramie Range where it is intruded by a 350 mi2 anorthosite batholith. To the south of the suture are volcanogenic schists and metasediments of the Green Mountain terrane that represent a Proterozoic island arc accreted to the craton nearly 1.7 Ga ago. Archean basement rocks are absent from this region, thus the oldest basement rocks in this area are Proterozoic in age (2.5 billion to 600 million years old). To the north, however, Proterozoic miogeosynclinal metasedimentary rocks form a thick wedge lying on the Archean basement. The Proterozoic rocks of the Green Mountain Terrane are similar to those found in the Jerome district of Arizona. These enclose several volcanogenic massive sulfide deposits rich in copper, zinc, lead, silver and gold; layered mafic complexes and ultramafic massifs containing platinum, nickel, palladium, gold, silver, titanium, chromium and copper; copper-gold-silver veins, gold veins, copper-gold shear zones, copper-REE pegmatites, gold and diamond placers and more. However, the region was piecemeal withdrawn one deposit after another by the US Forest Service making the once area of multiple use into limited and very restricted use.
Green Mountain terrane
Precious and base metals south of the shear zone occur in quartz veins, massive sulfides, a porphyry, and in layered mafic intrusions. In the Keystone district of the Medicine Bow Mountains, N60°W-trending shears are loci for narrow veins. These veins are gold- and copper-bearing, pyritic, quartz-carbonate veins in tensional faults subsidiary to the Mullen Creek-Nash Fork shear zone (Currey, 1965). Mineralization is accompanied by silicification in the form of small, irregular quartz veinlets and the wallrock is enriched in epidote.
At the Keystone mine, gold was found in quartz, and in pyrite and pyrrhotite masses in mylonite selvages adjacent to the vein. The vein lies in sheared diabase that intrudes quartz-biotite gneiss country rock (Currey, 1965). The shear is 2 to 6 feet wide, locally splays to 300 feet, and continues 4,500 feet to the southeast to the Florence mine. Available information indicates the Keystone ore averaged 41 ppm Au. When the mine ceased operations in 1893, 100,000 tons of reserves were reported in site. Eight samples collected from the mine dump by Loucks (1976) yielded 6.5 ppm to 300 ppm (0.19 to 8.75 opt) Au and averaged 117 ppm (3.41 opt) Au. 
At the the southeastern end of the Keystone trend, the Florence mine was developed in quartz diorite.  The ore occurred as 'kidneys' of auriferous pyrite which assayed from 257 ppm to 1,656 ppm (7.5 to 48 opt) Au (Currey, 1965).  Samples collected from the mine dump by Loucks (1976) yielded values ranging from 2.06 ppm to 799 ppm (0.06 to 23.3 opt) Au. One sample collected by the author in 1990, consisted of limonite boxwork after pyrite with abundant visible gold.  Both the Florence and Keystone patented claims are currently for sale, and were recently examined by Homestake.
Volcanogenic massive sulfide deposits occur in the Green Mountain Formation of the southern Sierra Madre. This unit consists of relatively low-grade metamorphosed calc-alkaline metavolcanics and associated metasedimentary rocks and volcaniclastics.  The massive sulfides are copper or zinc dominated with silver and traces of gold.  Between 1979 and 1982, Conoco Minerals Company explored this region for massive sulfides (Conoco Minerals Company, 1982).  Mineralized exhalites were discovered in metarhyolite and meta-andesite, and colloform-textured, pyrite-chalcopyrite was found associated with volcaniclastics (mill rock) (Hausel, 1986).  Currently, BHP-Utah International is exploring to the south in Colorado for Ag-Zn. But true to nature, the US Forest Service followed all of the massive sulfide discoveries with massive withdrawals of land to limit any mining.
At least one deposit in the Laramie Range south of the shear zone has been classified as a Au-Cu porphyry.  The Copper King mine in the Silver Crown district west of Cheyenne (Klein, 1974), was developed in weakly foliated and hydrothermally altered quartz monzonite and granodiorite. A shaft sunk in a potassium-silicate altered zone is surrounded by propylitically altered rock. 
Geology of the Silver Crown district, Wyoming
The Copper King was initially drilled by the U.S. Bureau of Mines in the 1950s, later by Asarco, and more recently by Caledonia Resources, Ltd., Royal Gold, and Saratoga Gold. Drilling outlined a 35-million ton open pitable, ore body averaging 0.755 ppm Au and 0.21 % Cu (Nevin, 1973). Recently, Caledonia Resources outlined a higher grade zone consisting of 4.5 million tons averaging 1.5 ppm Au. The Copper King porphyry is mineralized along a 600 to 700 ft strike length, and a 300 ft width that is open at depth (Stockwatch, 1987). Saratoga Gold and Strathmore Resources reported that a low-grade, 2 million ounce equivalent Au-Cu deposit sat at the site. Consultant Dan Hausel examined the Copper King fault along the east of the ore body and found the ore deposit was offset to the east in an area that has not been drilled suggesting that the deposit is larger than has been reported. Additionally, Hausel and Terry Klein each identified similar hydrothermal alteration zones nearby suggesting additional porphyry deposits are located in the area along I-80. Hausel also suggested that erosion of the porphyry likely produced gold placers in nearby drainages leading from the Silver Crown district to Cheyenne, Wyoming. The discovery of many nearby cryptovolcanic structures by Hausel while at DiamonEx Ltd, suggests the drainages could potentially also have placer diamonds. The area is immediately east of the State Line district where more than 130,000 diamonds were mined in the past. 
Exploration in the southern Medicine Bow Mountains was recently undertaken by American Copper & Nickel, Chevron Resources, International Platinum, and Vanderbilt Gold.  The target was two large layered mafic complexes dated at about 1.8 Ga based on field relationships. The 60 mi2 Mullen Creek mafic complex abuts against, and is sheared by, the Mullen Creek-Nash Fork shear zone.  This complex is highly deformed and metamorphosed.  Along the northeastern corner of the complex is the historic New Rambler mine.  The New Rambler shaft was collared in sheared and hydrothermally altered mafic rock and was sporadically operated from 1900 to 1918 producing 6,100 tons of copper ore with values in Au, Ag, Pt, and Pd (Hausel, 1989a). The source of the platinoids has not been determined, although one possibility suggested by McCallum and Orback (1968) is hydrothermal remobilization from a platinum reef hidden at depth.
Six miles east of the Mullen Creek mafic complex is a second layered intrusive known as the Lake Owen complex.  This intrusive is of similar size, but is essentially unmetamorphosed.   Exploration activities in the past few years have isolated some significant Pt, Au, and Pd anomalies in the complex. In this same region, Hausel discovered Cu-Au-Ag-Ni-Pd at the Puzzler Hill pyroxenite complex.
The Mullen Creek-Nash Fork shear zone is a major Precambrian suture formed of mylonite, shear cataclastics, and breccia that separates the Archean craton to the north from the Proterozoic basement to the south. Several mineral deposits in the Medicine Bow Mountains occur in this zone.  For example, the New Rambler shaft, as well as several Au-Pt mines in the Centennial Ridge district, were sunk in shear zone cataclastics.
Migeoclinal terrane.  North of the shear, precious metals occur in narrow veins and in thick quartzites with copper.  Gold has also been detected in quartz pebble conglomerate and in shear zones. Vein deposits in the Gold Hill district of the Medicine Bow Mountains, occur as narrow, rich, quartz veins with common visible gold. Specimen samples taken out of the district each year testify to the richness of the veins. Historic reports claim some specimen grade material taken from the Acme mine at Gold Hill assayed 72,000 ppm (2,100 opt) Au. Unfortunately, these veins are narrow (0.5-2 ft wide) and spotty.  One shear recently examined by the Wyoming Geological Survey and the U.S. Forest Service in the Lewis Lake area of the Medicine Bow Moutains, is greater than 100 ft wide and traceable for 2,000 ft.  The shear occurs in limonitic quartz-mica schist.  Samples of pyritized schist yielded 4.1 ppm (0.12 opt) Au (Dersch, 1990).
Mineralized quartzites occur at several localities in the Sierra Madre. Gossans in quartzites were prospected in the late 1800s and led to the development of some important copper mines. Two prominent mines were the Ferris-Haggerty and the Doane-Rambler.  The Ferris-Haggerty is interpreted as a remobilized stratabound deposit  (Hausel, 1986).  During its operation (1902 to 1908) the Ferris-Haggerty was an internationally prominent mine. The massive chalcocite minor chalcopyrite ore was found filling irregular quartzite breccias along the contact between hanging wall schist and the underlying quartzite (Spencer, 1904) of the Magnolia Formation.  Ore shoots greater than 20 ft thick were high-graded for the rich (30-40 % Cu) ore, and much of the lower grade material was left as waste. These shoots averaged 6 to 8 % Cu and carried some Au and Ag (Beeler, 1905; Spencer, 1904).  Beeler (1905) reported the ore contained 3.4 to 15 ppm (0.1-0.44 opt) Au.  The mine was mapped during World War II, and according to Ralph E. Platt (pers. comm., 1988), the steeply dipping quartzite flattens out in the lower mine workings and large blocks of "low grade" ore (6-8% Cu) remain in place.  The property was explored for stratiform Cu-Au-Ag mineralization by Exxon Minerals in the early to mid 1980s.
Proterozoic age quartz pebble conglomerate occurs in the thick miogeoclinal wedge in the northern Medicine Bow Mountains and Sierra Madre.  These conglomerates were of considerable interest in the late 1970s after they were discovered to be radioactive (Houston and Karlstrom, 1979). During the mapping of these conglomerates some samples were tested for precious metal content. Gold values as high as 10 ppm were detected from a conglomerate near Dexter Peak in the Sierra Madre. Even though similarities to the Witwatersrand conglomerates have been noted (e.g. Karlstrom and others, 1981), these rocks still have received only minor attention for gold.  Exxon explored and drilled some of the conglomerates in the late 1970s in search of U and Th.  In the early 1980s, Superior Minerals initiated a project to prospect for Au.
            EVEN YOUNGER MINERALIZATION IN WYOMING'S ROCKS (PHANEROZOIC)
Gold anomalies are scattered throughout the Phanerozoic (600 million years old to the present) record in the State. Many of these anomalies are enigmatic with no definite source terrane.  In Paleozoic and Mesozoic rocks, gold deposits and anomalies are much less common than in the Cenozoic.  Whereas, in the Cenozoic, there is a significant increase in anomalies compared to the earlier Eras. The increase in gold anomalies is partially due to the Cenozoic section being better preserved, but also because the Cenozoic Era represented a period of gold redistribution from Precambrian sources and an influx from volcanic sources.
Paleozoic Mineralization The Paleozoic record is not well preserved in Wyoming. However, thick limestones and dolominte crop out along the flanks of the uplifted mountain ranges, and in southeastern Wyoming and northern Colorado are more than 100 kimberlite intrusives (Devonian), more than a dozen of which are diamondiferous. Gold-bearing Cambrian Flathead Formation (Deadwood-equivalent) conglomerates occur at a few localities in the state. The better known of these is the "Deadwood conglomerate" (basal Flathead conglomerate) at Bald Mountain west of Burgess Junction in the northern Bighorn Mountains.
During the Bald Mountain gold rush near the turn of the century, more than 1,500 miners occupied the short-lived town of Bald Mountain and mined the conglomerate and associated modern placers.  However, grades were too low to sustain commercial operations and the district was deserted.  The gold was reported as flat fine-grained flakes with jagged edges. 
In addition to gold, the conglomerate contains black sands with ilmenite, magnetite, zircon, and monazite (Wilson, 1951; Mckinney and Horst, 1953; King and Harris, 1987). Interest in the monazite resulted in a U.S. Bureau of Mines drilling project which outlined a 20 million ton low-grade resource averaging 2.5 lbs/ton of monazite with a higher-grade resource of 675,000 tons averaging 13.2 lbs/ton (Borrowman and Rosenbaum, 1962).
During testing of the Bald Mountain conglomerate, the Bureau of Mines ran assays on material recovered from six drill holes in the better-grade monazite areas. The assays showed gold contents from 0.034 ppm to 0.172 ppm, averaging 0.103 ppm (McKinney and Horst, 1953).  However, Darton (1906) reported gold assays to run as high as 3.43 ppm (0.1 opt).  Darton's samples may have been from reworked Recent placers, rather than from the Cambrian conglomerate.
Precious metal anomalies are also reported in black shales and phosphorites of the Phosphoria Formation (Permian) in the Overthrust Belt of western Wyoming.  These rocks host anomalous Ag, Au, Cr, Zn, Cu, and V (Love, 1984). The U.S. Bureau of Mines and the U.S. Geological Survey report rocks from the Phosphoria Formation to have high silver values (as much as 2,600 ppm) and anomalous gold (0.2 ppm) (Allsman and others, 1949; Love, 1984).
Mesozoic Mineralization Several argentiferous Cu-Zn redbed deposits occur in Mesozoic rocks in the Overthrust Belt.  The majority of these are in the Nugget Sandstone (Jurassic).  Similar mineralization has been identified in the Beckwith(?) or Twin Creek Limestone(?), and in the Wells Formation Sandstone (Permo-Pennsylvanian) (Hausel, 1989a).
he better known of these deposits are located in the Lake Alice district in Wyoming near the Idaho-Wyoming border.  The Lake Alice deposits are localized in an anticline formed of bleached redbeds of the Nugget Sandstone capped by the Gypsum Spring Member of the Twin Creek Limestone.  The Lake Alice deposits were drilled by Bear Creek Exploration in the 1970s.
The Griggs mine in the northern part of the district, the mineralized sandstone is at least 300 feet thick. Samples collected by Love and Antweiler (1973) ranged from 0.02 to 6.7% Cu, a trace to 0.5% Pb, a trace to 3.2 % Zn, and a trace to 1,200 ppm (35 opt) Ag.  The average mine ore contained 3.5 % Cu and 254 ppm (7.4 opt) Ag (Allen, 1942). The mineralizing fluids are interpreted as interformational or derived from a similar low temperature source and were structurally trapped (in anticlines and faults) during thrusting and folding of the Overthrust Belt (Boberg,1986; Loose and Boberg, 1987).
Cenozoic Mineralization The Cenozoic of Wyoming includes many poorly studied and unexplored gold and silver deposits and anomalies. Only a few are discussed here and the reader is referred to Albert (1986) and Hausel (1989a) for a treatise on these and other occurrences and anomalies.
In northwestern Wyoming, paleoplacers and associated reworked modern placers cover an extensive region. These auriferous quartzitic conglomerates and sandstones range in age from Late Cretaceous to Miocene and include associated Quaternary placers. The average gold content is anomalous but low, and the gold is very fine grained (Antweiler and Love, 1967).  Most past prospecting activities have been confined to reworked alluvial and bench placers primarily along the Hoback and Snake Rivers.
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Stratigraphic unit
Average Au (ppb)
Maximum assay (ppb)
Quaternary alluvium
103
2,000
Miocene(?) conglomerate
65
290
Pass Peak Fm(Eocene)
47
250
Wind River Fm(Eocene)
222
2,000
Early? Eocene conglomerate
94
400
PinyonConglomerate(Paleocene)
86
6,000
Ft Union Fm (Paleocene)
35
300
Harebell (Late Cretaceous)
65
1,000

Reported gold content of conglomerates in northwestern Wyoming (Antweiler and Love, 1967).
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The Tertiary of Wyoming was a time of intense erosion, and large volumes of fanglomerate and conglomerate were shed from the mountain ranges into the adjacent valleys.  Where the source terrane included greenstone belts and other mineralized regions, the alluvial fans and fluvial sedimentary rocks often carry detrital gold. For example, the Twin Creek paleoplacer on the northeastern margin of the South Pass greenstone belt is estimated to exceed more than one billion cubic yards of gold-bearing gravel (Antweiler and others, 1980).  The Oregon Buttes paleoplacer along the southern margin of the greenstone belt is estimated to contain more than 28.5 million ounces of gold (Love and others, 1978). Other significant paleoplacers occur in and along the margins of the greenstone belt, but for the most part remain unexplored.   However, in the late 1980s, spurred on by the recovery of auriferous core from an oil well along the southern edge of the South Pass greenstone belt, Hecla Mining drilled and flew airborne magnetic and IP surveys over the buried southern edge of the belt.
Gold-bearing conglomerates and terrace gravels in the Wind River Basin have gold over large regions.  In 1910, gold was discovered along the Wind River, Little Wind River, and Popo Agie River in the basin.  The metal was found in terrace gravels capping benches and buttes and in the nearby plains, mesas, and uplands for thousands of feet to a few miles from the present drainages.  The deposits were reported to average 12 to 14 feet thick over widths of 3 to 4 miles.
The gold is very fine tablet-like particles smaller than a pinhead. In 1913, gravels were tested and varied from none to 0.016 oz/yd3 and averaged less than 0.0025 oz/yd3 Au. Two dredges operated in the Wind River. The Neble Dredge operated in a pay zone that ranged from 0.007 to 0.016 oz/yd3 and averaged 0.014 oz/yd3.  The gold-bearing gravels averaged about 22 feet thick. The Clark Dredge, a few miles west of the Neble Dredge, treated gravels that averaged 0.038 oz/yd3 (Schrader, 1913). The demise of the district was the gold was too fine to be recovered efficiently.
The Black Hills of Wyoming
During the Tertiary, Wyoming was affected both directly and indirectly by volcanism.  In northwestern Wyoming, the Yellowstone and Absaroka regions were inundated by calc-alkaline flows, flow breccias, and ash falls generated from nearby composite volcanoes.  In the Black Hills of northeastern Wyoming, several alkalic volcanic centers erupted.  Local alkalic volcanoes erupted in the Rattlesnake Hills of central Wyoming, and basalts erupted from cinder cones in the Baggs area in southern Wyoming. In southwestern Wyoming, volcanoes ejected rare leucite- and olivine-lamproites with chemical and mineralogical similarities to the Kimberly diamondiferous lamproites in northwestern Australia. The Tertiary record also records Wyoming was buried numerous times by thick ash falls erupted from the west.
Mineral deposits are associated with the Black Hills alkalics,  the Absaroka volcanics, and with the thick ash falls in the Wyoming basins. In the Black Hills, mineralization is reported in the Tertiary alkalic complexes of the Bear Lodge Mountains, Mineral Hill district, and Black Buttes.  In recent years, this area has been explored by Hecla Mining, Molycorp, FMC Gold, and International Curator to name a few.   In the Bear Lodge Mountains, gold has been reported in fluorite veins, pegmatites, and in feldspathic breccia.  Recent exploration in the area led to the discovery of an elongate intrusive breccia (120 by 2,000 ft) containing disseminated gold in values varying from 0.34 to 1.7 ppm.  The deposit averages 0.72 ppm (International Curator Resources Ltd, 1988 Ann. Rept.). This region also includes one of the largest, low-grade rare earth and thorium deposits in the United States (Staatz, 1983).
The Mineral Hill district to the east has a history of placer gold and tin production.  Preliminary work by the Wyoming Geological Survey in cooperation with TRYCCO identified two horizontal pyritiferous quartz veins at the Treadwell open cut that yielded maximum gold values of 130 ppm (3.79 opt) and silver values as high as 330 ppm (9.62 opt).  Previous work in the district by Welch (1974) identified several gold anomalies including a jasperoid that assayed 5 ppm Au and 7 ppm Ag (Hausel and Hausel, 2011).
Black Buttes lies 8 miles west of Mineral Hill and is formed of Tertiary phonolites and trachytes intruded into Paleozoic limestone. Contact replacement mineralization (Zn, Pb, Ag, Mo, F) occurs in the Pahasapa Limestone (Mississippian), but the surface exposures are limited (Hausel, 1989a). Hausel identified both gem-quality fluorite and wulfenite at one deposit at Black Buttes (Hausel, 2009).
Location of gold-silver-copper porphyry deposits in the
Absaroka Mountains, Wyoming
The Absaroka Mountains in northwestern Wyoming include several Cu-Ag porphyry complexes, several of which are located within wilderness designated land.  However, the two largest porphyries--Kirwin and Sunlight Basin lie outside of wilderness within the National Forest.  These two porphyries contain anomalous Cu, Mo, Pb, Zn, Ag, Au, and Ti, and includes disseminated, stockwork, and vein mineralization (Hausel, 1982).  
 The Kirwin porphyry was explored by AMAX for several years, and plans to develop an open pit in 1980 died because of the poor copper market.  However, in recent years interest in Kirwin (as well as the Sunlight porphyry) has increased.  Currently, the U.S. Forest Service is negotiating with AMAX to purchase the property for $3.2 million.   If acquired, the porphyry will be considered for withdrawal from mineral entry.  Published reports indicate the porphyry hosts a minimum of 1.23 billion lbs of Cu, 13,500 lbs of Mo, 121,000 oz of Au, and 5.6 million ounces of Ag (Paydirt, 1985).  The contained metals are worth a minimum of $1.5 billion at 1989 prices.
Throughout Wyoming, many enigmatic gold anomalies have been reported. These include gold associated with coal in the Black Hills, gold anomalies in uranium roll fronts (Gordon Marlatt, pers. comm., 1989), and scattered geochem anomalies in many Wyoming basins (Albert,1986). For example, dozens of NURE geochem anomalies yielding from 0.2 ppm to 6.55 ppm Au were reported by Albert (1986) in the Wyoming basins.  Several of these anomalies have been reexamined and verified.  For example, Marlatt investigated a 200 mi2 anomaly in the Green River Basin in the vicinity of Farson (south of South Pass) and recovered one sample with visible gold. The gold occurred as a irregular-shaped microscopic sliver. Many of these anomalies are possibly due to detrital gold eroded from nearby gold districts.  But others are not easily explained by detrital transportation but instead may represent geochemically transported gold leached from Tertiary ash falls (Gordon Marlatt, pers. comm., 1988).
 Most commercial modern placers in the State have been principally mined for gold, although the Douglas Creek placers in southeastern Wyoming also possess platinum and palladium, the Clarks Camp placers in the northern Wind River Range contain anomalous monazite in addition to gold, and the Mineral Hill placers in northeastern Wyoming also have tin, tantalite, and magnetite (Figure 2).  Monazite placers also occur in the Shirley Basin in southeastern Wyoming (J.D. Love, pers. comm., 1990).  Statistics on gold nuggets are incomplete, although walnut-size nuggets have been recovered from the Mineral Hill district, the Douglas Creek district, and the South Pass greenstone belt.  The largest nugget found in Wyoming may have been a 24 ounce nugget from Rock Creek in the South Pass greenstone belt.  History also records a boulder with nearly 40 pounds of gold was found in the same area prior to 1905 (Hausel, 1989a).  This region also has several potentially rich, but unexplored placers (Hausel, 1991).
Within the State boundaries are numerous gold deposits and anomalies scattered throughout the geologic record.  Many examples occur in rocks ranging in age from Archean to Tertiary, and in Quaternary to Recent unconsolidated gravels and sands.  Yet, relatively few of these deposits and anomalies have been explored and only a handful have been drilled.
Being that much of Wyoming is underlain by an Archean craton similar to the Superior Province of Canada, the eastern and southern African craton, and to the Pilbara and Yilgarn blocks of Western Australia, one would expect Wyoming to also have significant mineralization.