Over the next few years, mapping & sampling projects continued & eight 24,000 scale geological maps were completed by Hausel with nearly 3 dozen historical gold mines mapped at either 1:120 or 1:240 scale. Some of these mines had not been entered for many decades as was suggested by an 1800s date written in mud on a mine rib at the Tabor Grand mine. The 8 quadrangles were compiled into one large 1:48:000 scale map (Hausel, 1991). Some detailed 1:24,000 scale maps were published, but 3 remain unpublished even though they were submitted to the WGS editor in the 1980s. While investigating this district >100 gold anomalies were identified and controls on gold mineralization were recognized. At least one major gold deposit was also identified that likely hosts several million ounces of gold.
It became apparent that South Pass was a Archean (>2.5 billion year old) greenstone belt (Hausel, 1985, 1986) and nearly all lode gold in the district was structually controlled by steeply plunging ore shoots known as reefs (Hausel, 1987). This simply meant that the ore shoots had 3 dimensions and one of these (the most important) was overlooked by all previous investigators. On the surface, the two smallest dimensions (width & length) were exposed but the greatest dimension (plunge of the shoot) was overlooked! This third dimension likely continues to depths of 1000 to 10,000 feet but has never been tested. Only at the Carissa mine was this dimension tested to any kind of depth. The mine workings continue down plunge to 400 feet (in high grade gold). Later drilling to 930 feet intersected high-grade gold. How much deeper does this third dimension continue remains unknown.
The best gold deposit in the district is the Carissa according to Hausel. This property was taken from the public by the state legislature without any scientific review. All citizens of Wyoming should demand an investigation. The Carissa is a major gold deposit that is likely a multi-million ounce deposit worth $hundreds of millions if not billions. In addition to missing the significance of the down-plunge dimension, essentially all other researchers overlooked another dimension. The Carissa shear zone was reported by all past researchers as being a few feet wide when in fact, it is as much as 1000 feet wide!
Left - the Carissa shear zone: >1000 feet wide with an ore shoot that is 1000 feet long and at least 930 feet deep. This shoot is open in all three directions. Below, Seve Gyorvary poses at the 350 feet level in the historical mine.
The greenstone belt is located at the south tip of the Wind River Mountains 50 km (30 mi) south of Lander at 7,800 feet elevation. The district encloses two villages: Atlantic City and South Pass City.
South Pass is a classical Archean greenstone belt. Important geological research on this district didn't begin until 1983 & culminated in 1991 with the publication of a treatise of the greenstone belt. Prior to 1983, the district was a significant source for iron ore which was mined for 20 years at the Atlantic City open pit mine. Approximately 90 million tons of iron ore were recovered from the mine prior to its closing. Mapping by Hausel (1991) suggested that at least 400 million tons of iron ore remain in place. In addition to the iron ore resource, a few hundred gold anomalies were detected, several that were significant. A distinct belt of mineralized gold-bearing shears trend through South Pass City, through Atlantic City and further northeast to Miners Delight (Hausel, 1987). At both ends of this structure are significant paleoplacers. Several placers lie downstream from this structure.
Schematic geological map of the South Pass greenstone belt.
The primary shear at the Carissa mine contains high-grade gold in a 1.5 to 80-foot–wide, steeply-plunging cataclastic zone. This high-grade shoot is enclosed in larger (previously unrecognized) major shear that is as much as 1000 feet wide! The shear envelope is untested! A 97-foot composite chip sample taken within this structure on the south side of the high grade shear yielded 0.023 opt Au. Another 30-foot sample taken on the north side of the high-grade shear yielded 0.07 opt Au (Hausel, 1991)! The remainder of this envelope remains untested!
The Carissa is structurally controlled and represents a steeply-plunging saddle reef deposit with high-grade gold localized in fold closures and rehealed fractures similar to the Homestake. Drilling by Consolidated McKinney Resources identified a highly anomalous 80 foot wide zone at depth. Drill core assays from this zone ranged from 0.03 to 2.54 opt Au (the shear envelop was not tested). This mineralized structure was intersected at depths of 930 feet. Earlier, Carissa Gold Inc. made the following reserve estimates using an extraordinary high reserve cutoff grade in the high-grade portion of the shear. They reported 208,000 tons of ore at an average grade of 0.343 opt, and geological reserves of 37,000 tons of ore averaging 0.85 opt! Anaconda Minerals Company drilled the property and all holes interested ore grade material and included a high-grade ore zone over widths of 2.3 to 16.1 feet that yielded 0.11 to 0.36 opt Au at depths 700 feet. Agein the low-grade, giant shear envelope was ignored.
The Duncan mine northeast of the Carissa mine, has a significant gold anomaly enclosed in a fold. A 2.5-foot channel sample yielded 0.96 opt Au in the steeply plunging fold adjacent to the shaft! Is this another major gold deposit?
Several historical mines along the Carissa-Duncan-Miners Delight belt yield gold anomalies. These include the Mary Ellen, Tabor Grand, St. Louis, Diana and Caribou mines. At several locations, one can find specimens with visible gold. All drainages downstream of the shear trend have yielded anomalous placer gold.
Another parallel shear zone belt occurs in the Lewiston district to the east (Hausel, 1986). Secondary rock alteration was also found in the Crows Nest area between these two mineralized belts that is characteristic of gold mineralization and probably represents hidden shear zones in that area. The Crows Nest area remains unevaluated.
The greenstone belt continues under Tertiary sedimentary rock of the South Pass and Wasatch Formations to the northeast and to the south. It is notable that both of these regions are overlain by giant unconsolidated gold paleoplacers (McGraw Flats-Twin Creek to the north, and Oregon Buttes-Dickie Springs to the south) suggesting the presence of at least two major hidden gold deposits (Hausel and Love, 1991).
Geophysical exploration and drilling by Hecla mining identified greenstone belt rocks to continue under Tertiary sedimentary rock for at least 6 miles to the south of South Pass City. Visible gold in banded iron formation was found in this area by Hecla!
Gold geochemistry reported by the US Geological Survey show Au/Ag ratios are high & Au/Cu ratios are low (Love and others, 1977; Antweiler and others, 1980). Trace metal contents (Bi, Pb, As, Sb, V, Mo, W, B, Nb, Zn, Cr, Co, Ni) are typical of hypothermal veins in other greenstones worldwide. Stable isotopes and fluid inclusion studies support that the South Pass gold is similar to that of a hypothermal vein system. The carbon and oxygen isotopes in shear zones along with hydrogen isotopes from fluid inclusions support that the much of the gold solutions were derived from the dewatering of the Mineral Delight Formation during compaction.
Structurally, some gold systems at South Pass are located adjacent to a distinct group of metagabbos, metatholeiites, and actinolite schists (metakomatiites) that trend from South Pass City to Miners Delight. The localization of gold in this region is believed to be due to competency contrasts between the metagabbros and adjacent Miners Delight metagraywackes. During folding, it is thought that these were favorable for the development of numerous fractures and faults. Much of the ore is found in these shear structures contain enriched ore shoots developed in folds suggestive of a reef-type structural control. Placers downstream from the shear structures are highly enriched in gold.
Some placers contain coarse gold. XL Dredging mined portions of Big Atlantic Gulch south of Miners Delight in 1910 and recovered nuggets weighing 0.07 to 1 ounce. The ET Fisher Company dredged Rock Creek near the Duncan mine from 1933 to 1941 and produced 11,000 to 30,000 ounces: 75% of the gold was found within 1 m (3 ft) of bedrock. Some of the gold was coarse and several nuggets were recovered. Nuggets included many small specimens and some large nuggets. A boulder with as much as 630 ounces of gold was also reported.
A 34-ounce gold nugget (left) recovered from South Pass.
Gold paleoplacers cover large areas of South Pass (Love and others, 1978). These are found in and on the edge of the greenstone belt.
Testing at Fritag alluvial placer at Oregon Gulch near Dickie Springs yielded values as high as 1.0 ounce/yd3 (Dave Fritag, personal communication, 2004).
The Oregon Buttes paleoplacers (the ridge in sunlight in the background) are suggested to host 28.5 million ounces of gold by the USGS. The source of the gold has never been identified but likely lies at depth beneath the sedimentary cover near the buttes. A similar paleoplacer (McGraw Flats-Twin Creek) (with 5 million ounces) along the northern edge of the belt has a projected source near the historical Miners Delight mine and defunct Atlantic City iron ore mine.
IN summary, several properties in the greenstone belt need to be explored with a detailed geochemical sampling program in the Carissa-Duncan-Miners Delight shear structure to search for saddle reefs. Several gold deposits of note lie along this trend that include the Carissa, Miners Delight, Duncan, Caribou, St. Louis, Tabor Grand, Mary Ellen, Diana, Caribou and more. A parallel structure to the east includes several interesting deposits including the Wolf, Hidden Hand, Bullion, Mint and Two-Johns gulch. In order to complete such a regional sampling program, one must rely on the Wyoming Geological Survey as companies can not afford to conduct this kind of research. In order to do this, one must have an active Survey - which is not going to happen with the current group and administration. At least 90% of the survey should be replaced and director eliminated.
Placer gold from Dickie Springs-Oregon Gulch paleoplacer (photo from J.D. Love).