Greenstone belts form geological (structural) basins filled with primitive volcanic flows and sediments that were intruded by dikes, sills and stocks and deposited along the margins of ancient proto-continents. These were later deformed and metamorphosed. To many geologists and prospectors, ‘greenstone belts’ are synonymous with ‘gold belts’ since they provide excellent places to search for gold. Such basins are typically >2 billion years old: the majority of rocks in the South Pass greenstone belt were metamorphosed >2.8 billion years and were likely deposited 3+ billion years ago. Some of the more notable greenstone belts in the world are located in the Slave and Abitibi regions of Canada, the Pilbara and Yilgarn regions in Western Australia, and the Kaapvaal and Barberton regions of Africa – all are well known for significant gold deposits.
When circumstances are right, greenstone belts provide good source beds for lode gold. What is required is hot metamorphic fluids to migrate through the basins and leach enough rock and then focusing the gold-bearing hydrothermal fluids in faults, veins or similar traps to produce ore shoots (enriched pockets) of gold. This happened in several greenstone belts around the world simply because mother earth was brutal to these basins but she provided several opportunities to leach gold from the layered rocks and focus the gold into traps. Such traps include fractures, intersecting fractures and veins, shear zones, stockworks, fold closures and chemically reactive rocks. For the most part, fractures, or zones of lower pressure, were ideal for gold-bearing fluids that were squeezed from the adjacent ductile rocks under great pressure and temperature.
To see how this works, take your hands, place them in front of you. Now touch your finger tips together. The top of each hand would represent the top of the rock unit when it was deposited. Now let your finger tips act as a hinge and bring your palms together: the top of your right hand should be in the opposite direction as your left hand.
|A 34-ounce nugget found in the
Rock Creek drainage during|
dredging prior to World War II. Specimen from the Los
Wyoming has four greenstone belts (Elmer’s Rock, Rattlesnake Hills, Seminoe Mountains and South Pass) and one large metasedimentary belt with similarities to greenstone belts (Copper Mountain). All remained unmapped and only partially explored until the 1980s and 1990s. The author mapped all of them with the exception of Elmer’s Rock, which was mapped by Graff and others (1982). For the most part, greenstone belts are formed of dark to black rocks with some dark green rocks that are difficult to differentiate and only a handful of geologists find great joy in the challenge of unraveling these complex geological puzzles.
|Dark meta-basalt folded into an isoclinal fold in which the fold is so tight that the|
fold limbs parallel one another. Below – fold in banded iron formation displaying very tight folds, almost like an accordion.
In 1861, another group of prospectors began mining along Willow Creek, 15 miles west of Strawberry Creek. This group of 52 prospectors was attacked by Shoshone Indians and driven out. In 1863, another group of prospectors discovered gold in dry placers near Dickie Springs adjacent to the Oregon Buttes along the Overland trail several miles south of Willow Creek and worked the area for 3 months before being attacked by Indians. Most of the prospectors were killed. At this time in history, little could be done to provide security for prospecting groups as the nation was in the grips of civil war.
Over the next several years, hostilities between prospectors and the Shoshone intensified requiring that the Overland Trail be abandoned for a more southerly route (Hausel and Love, 1993). These kinds of hostilities were common in Wyoming and were one of many reasons why Wyoming remained relatively unprospected compared to other territories in the West. Wyoming remained a wilderness that few settlers dared to journey into. Today, instead of Indian hostilities, both the State and Federal Government bureaucrats have taken on hostilities against prospectors and miners.
Another group of prospectors entered South Pass in 1866 to mine gold in Willow Creek. In the following year, this group traced gold up Willow Creek to Carissa Gulch, which was rich in gold. From the mouth of the gulch, the precious metal was traced further up slope to the Carissa lode. Claims were filed on the lode on June 8th, 1867. Within a short time, this group of prospectors was attacked by Indians and three were killed: the surviving members fled, but returned more than a month later on July 28th. During the ensuing winter, more than 400 ounces of gold were recovered using very primitive hand tools and mortars. Four tons of high grade ore was hauled to Springville, Utah and milled yielding an astounding 1,400 ounces of gold! News of the discovery reached the outside world and a rush followed.
|Generalized geological map of
the South Pass-Atlantic City district (from|
Hausel, 1989, 1991)
The district was initially called the Shoshone district. Then it was divided into smaller districts that included an area east of the Carissa near Rock Creek which became known as the California district. Four towns erupted along the pediment at South Pass. South Pass City boasted 5,000 citizens – most living in tents (some reports suggested as many as 10,000 people were in South Pass City). Hamilton City (Miners Delight) grew to 1,500 people and Atlantic City had 500 citizens. Pacific City in the Pacific district to the south near Oregon Buttes claimed 600 people. In 1870, the US Army established Camp Stambaugh a few miles east of Atlantic City and Hamilton City to add stability in the area. The camp was abandoned eight years later.
In 1872, the district had 12 operating stamp mills. A few years later, in 1879, another town was established east of South Pass City near the original gold discovery. This town became known as Lewiston (Lewiston, Miners Delight and Pacific City are now ghost towns). In 1884, an engineering project was initiated with the construction of the Granier Ditch. The ditch was built to haul water from Lake Christina 12 miles to the west in the high peaks of the Wind River Mountains to the South Pass area for hydraulic mining. This project was finished in 1890. In the following year, 6,720 ounces of gold were recovered at the hydraulic mine.
|Oregon Buttes on the horizon.
all of the land in the sunlight on the
horizon is part of a giant gold deposit
known as the Dickie Springs-Oregon
Buttes paleoplacer estimaed to
contain >28.5 million ounces of gold
according to the USGS.
|Rock Creek placer with old tailings|
Within the greenstone belt are many significant ore shoots. The richest discovered to date, was that of the Carissa lode near South Pass City. This mine lies a short distance southeast of State Highway 28.
Past gold production from the mine is poorly documented, but available statistics suggest 50,000 to more than 180,000 ounces of gold were produced prior to 1950. The Carissa shaft was sunk to a depth of 350 feet with more than 2,300 feet of drifts on four levels over a strike length of 750 feet. A winze was later sunk to a 5th level at a depth of 400 feet below the surface.
The mine was developed in a shear zone in dark rock known as metagraywacke (a metamorphosed, micaceous sandstone) of the Miners Delight Formation and a mafic dike (metamorphosed igneous rock or gabbro). Essentially, all prospecting efforts concentrated on the primary shear, as it contained ore shoots of high-grade gold. The structure averaged about 6 feet wide, is 2 to 3 feet wide at the surface, but swelled to 50 feet at depth. More importantly, this primary shear lies within a much larger shear that isn’t quite as distinct and was essentially overlooked. This larger structure forms an envelope surrounding the primary shear that is >1,000 feet wide. The envelope is expressed by numerous parallel fractures with numerous quartz veinlets.
In the 1980s, Consolidated McKinney Resources intersected an 80-foot mineralized zone beneath the mine workings that assayed 0.031 to 2.54 ounces per ton gold! In addition, one intercept contained >5 opt over several feet. All of these are verifiable and provide evidence for a significant to major gold deposit at the Carissa. Based on drilling, mining and surface sampling, the Carissa ore shoot has a minimum strike length of 950 feet that is open at either end. This shoot is more than 1000 feet wide and continues to a minimum depth of 970 feet and is open at depth. This shear structure is traced on the surface to the northeast and southwest for several thousand feet and most of it remains unsampled. Such shear zones typically continue to a few thousand feet deep in similar greenstone belts worldwide.
Based on sampling, the Carissa has a distinct mineralized zone that is likely a few thousand feet deep, as much as 1,000 feet wide, and 1,000 feet along strike. However, the mineralized zone is open in all three directions and could be enlarged considerably with additional drilling.
This would suggest, that at an average ore grade of 0.1 opt Au, this zone potentially hosts 3.7 million ounces of unmined gold worth $4.4 billion dollars. This does not include potential resources deeper than 1,000 feet or further along the strike length of the shear. In effect, the Wyoming State legislature and Governor removed (nationalized) a major gold deposit from the public sector that would have created numerous jobs in Fremont County and provided a significant tax base to Wyoming and Fremont County. Instead, in the wisdom we have come to love in government, Wyoming now has a mining Disneyland sitting on a major ore deposit. This Disneyland may produce a few thousand dollars in revenue for the state while at the same time it sucks out a few $hundred thousand for budget and salaries to operate the Wyoming Disneyland park.
The people who operate the South Pass City historic site are very good at what they do and should be respected for their knowledge. But the legislature and governor should have their heads examined. This Disneyland appears to be spreading in a district that could provide many future jobs. Dollars set aside for Federal abandoned mine reclamation programs were used to rebuild the Carissa surface buildings and are being used to rebuild buildings on private land at the Duncan mine, another probable ore body. When will government ever be required to pay for their actions?
Table 1. Chip channel and channel sample analyses in the South Pass greenstone belt (Hausel, 1989a).
SAMPLE DESCRIPTION Au
Carissa Mine (low-grade envelope) (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
Anaconda Minerals Company drilled the property prior to Consolidated McKinney Resources and all of their drill holes interested ore grade material. They intersected a high grade ore zone over widths of 2.3 to 16.1 feet that yielded 0.11 to 0.36 opt Au to depths of 700 feet.
The Wyoming legislature & governor did what the Shoshone Indians of the past could not do. The Wyoming legislature ‘nationalized’ this mine by purchasing private property and incorporating it into the South Pass City historical site without considering geological studies or scientific testimony. This was likely one of the two best gold targets in the state. The other is located within the Rattlesnake Hills where a multi-million ounce gold deposit is currently being drilled.
Other properties of interest at South Pass include Miners Delight and the Wolf mine along with thousands of feet of unexplored shear zones in the South Pass-Atlantic City district, the Lewiston district, and in the Crows nest. The Miners Delight mine has a very attractive shear structure that yielded a 0.68 opt Au channel sample across about 8 feet and the Wolf mine yielded a grab sample that assayed 0.5 opt Au. This shear is poorly exposed by was trenched by one company that showed a shear that was 160 feet wide (Steve Gyorvary, personal communication, 2010).
However, due to the lack of regard for the mining sector and prospectors, the author recommends that companies and prospectors come to Arizona, Nevada or Canada to search for gold.