|Gold recovered from Rock Creek in the South Pass greenstone belt, Wyoming|
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.
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 thatwere 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.
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|
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.
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.
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.
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).
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.
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.
|This was great! I was inducted into the International Order|
of the Ragged Ass Miners in Denver!
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.
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 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.
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|
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|
|Gold from Dickie Springs (photo courtesy of Dr. Dave Love)|
|Recent photo of the author still looking for gold and base metals. Photo taken at the|
Resolution mine, Arizona.