Tuesday, April 27, 2010

Gold Discovered in the Rattlesnake Hills, Central Wyoming

In 1981, an application was made to the University of Wyoming MMRRI research center for grant funds at their request. UW Engineering was looking to build a new institute to conduct research on in situ and/or bulk minable mineral deposits. Thus at their request, a grant proposal was made to investigate the Rattlesnake Hills (RSH) in central Wyoming for bulk-minable gold deposits (Hausel and Jones, 1982 a,b). The geology of the RSH appeared to be very favorable for bulk-minable gold mineralization due the the presence of a large Archean greenstone belt intruded by more than 42 alkalic plugs. The area had been investigated for the petrology of the alkalic plug by Pekarek (1977) without any regard to potential mineralization. The belt had an excellent source bed for gold (greenstone belt rocks) and several heat engines necessary to mobilize gold from the greenstone belt (alkalic intrusives) and the Tertiary intrusives potentially provided brecciation and permeability of the intruded rocks.

Thus, in 1982 several significant gold anomalies were discovered in the RSH of central Wyoming during the initial search for disseminated gold mineralization. The access route from the north was so difficult, that the muffler for the State field vehicle was ripped off of the vehicle. In honor of the muffler, the first gold discovery in this complex was named 'Lost Muffler' by Hausel. A grant was provided by the University of Wyoming Mining and Mineral Resource & Research Institute. Based on what was known of the geology at that time, it was predicted that the RSH had high potential for discovery of disseminated gold mineralization & by Hausel and Jones (1982a). In addition to disseminated gold, high-grade gold mineralization was detected in veins and exhalites (Hausel and Jones, 1982b) and gold was also detected in banded iron formation and in a large stockworks in gneiss. The RSH was interpreted as a fragment of a greenstone belt (Hausel, 1996).

Gold Discoveries
This was one of the great discoveries in North America. Gold was predicted in this belt in 1981 and verified in 1982. This was followed by several research studies - all that lead to additional gold discoveries by Hausel at the Wyoming Geological Survey. In addition, other gold anomalies were discovered by John Ray of American Copper and Nickel Company. It was a completely new discovery and unfortunate that others who entered this district more than 20+ years after the initial discoveries have attempted to take credit for discoveries that are well documented in more than a dozen publications and in press releases. But this is a sign of the times.

In 1977, Hausel was employed by the Geological Survey of Wyoming (as it was known at that time) to investigate mineral deposits in Wyoming. His first project was to investigate the Colorado-Wyoming State Line district for diamondiferous kimberlite. A group of kimberlites had been found by Eggler (1968) and McCallum and Mabarak (1975). Hausel's assignment was to produce a geological map to promote Wyoming’s resources by attracting a diamond company to test for commercial mineralization and he was hired by Dr. Daniel N. Miller Jr, director of the WGS.

During mapping, a group of 9 kimberlites were discovered that had been missed by previous investigations (Hausel and others 1979, 1981). Over the years, >600 similar diamond and kimberlite discoveries were made, mostremain untested.

After the first couple of years of focusing on diamonds, Hausel began to look for other mineral deposits and made several hundred gold, silver, platinum-group, base metal and gemstone discoveries. News of these discoveries were published in local newspapers, on the Internet, in books, Wyoming Geological Association newsletters and Guidebooks and in annual reports of the State Geologist and US Bureau of Mines.

Discovery of a Major New Gold District
In 1981, a search for gold the RSH west of Casper began. Based on what was known of the geology, this area had great potential for discovery of low-grade disseminated gold & high-grade gold. Initial research was funded by a grant from the University of Wyoming MMRRI (now defunct) to search for bulk minable gold so that the university could search for a large grant to develop metallurgical recovery systems (Hausel and Jones, 1982a).

In 1977, there was no pragmatic interest in the RSH and only limited academic interest. Pekerek (1977) successfully defended a dissertation on the igneous petrology of Tertiary alkalic rocks; this followed an earlier study by Carey (1954, 1959). Both focused on the genesis of the igneous rocks, but the older Precambrian rocks remained unmapped and unexplored.

Why should this region contain gold? The basement complex (Precambrian) was similar to South Pass & had been disrupted by several volcanic eruptions. Such Precambrian complexes often have rocks with above normal gold content. They are referred to as greenstone belts and in many places in the world, the terms ‘greenstone belt’ and ‘gold belt’ are essentially synonymous.

Auriferous vein in front of Goat Mountain.

So here was an excellent source bed for gold that was intruded by high-temperature heat engines (Tertiary alkalic igneous rocks) that provided heat & fluids to leach gold from Precambrian rocks and focus the precious metals in fractures and replace select minerals in the host rocks.

Thus, armed with these concepts in 1982, field research began. However, the State of Wyoming assay budget was only about $100, thus sampling was selective. Even so, a whole new gold district was identified during this and subsequent investigations - something that rarely happens. The samples assayed yielded as much as 0.25 opt gold and the Lost Muffler vein as exposed on the surface was traced over a strike length of 2.5 miles. In addition to the samples collected in the RSH, a few samples were assayed from the Seminoe Mountains (one assayed 2.87 opt Au) greenstone belt. Both discoveries resulted in gold rushes with dozens of companies, consultants and prospectors running to the hills.

The RSH had excellent potential for significant gold. Over several years, the greenstone belt was sampled & mapped. While mapping, gold was detected in old Archean (~3 billion years old) veins, fractures, exhalites (a vein like deposit), stockworks & in much younger Tertiary (~42 million years old) breccias & igneous rocks. American Copper & Nickel entered the district & made additional discoveries in exhalites (veins). This was followed by Canyon Resources & Newmont Gold. These companies explored breccias & made a million ounce gold discovery (Hausel, 1996; Hausel and others, 2000). As predicted, the RSH had high potential for discovery of a large tonnage disseminated gold deposit associated with Tertiary volcanics (Hausel and Jones, 1982a). More recently, Evolving Gold initiated exploration in 21st century at what was initially named Sandy Mountain (their North Stock) (Hausel, 1996) & intersected major auriferous zones at depth between Sandy Mountain and Oshihan Hill where a large brittle breccia had been mapped by Hausel (1996).

It became apparent that the basement rocks in the RSH represented a fragment of an Archean greenstone belt similar to South Pass and to other rich gold districts in Australia, Africa and Canada (Hausel, 1994, 1995, 1996). The RSH belt continues under Tertiary sediments to the south, east & west. And a large part of the belt is missing. Based on geology, this fragment sits under Tertiary & Paleozoic cover to the north. How much of the belt remains hidden is unknown, but the geology indicates what is hidden is larger than that exposed – so yes, there are likely undiscovered hidden gold deposits in the RSH!

During mapping and sampling of the RSH, gold anomalies were found at several locations (Hausel, 1982, 1989, 1994, 1995, 1996, 1997; Hausel and Jones, 1982a, b). In addition to the Lost Muffler vein, another 4500-foot zone jasperized breccia vein was mapped that was weakly anomalous in gold with sporadic enriched zones. Nearby, iron formation also contained anomalous gold.

A stockwork along the southwestern margin of the RSH was anomalous. This, the breccias and Tertiary plugs at Sandy Mountain & Oshihan Hill were considered significant (Hausel, 1995, 1996; Hausel, personal field notes 1981-1995). Several grab & composite chip samples of brecciated metamorphic rock in the Antelope basin, at Sandy Mountain and at Oshihan Hill contained gold. These were collected over a surface area of one-square-mile suggesting a sizable, disseminated gold deposit!

In the vicinity of 3 Tertiary alkalic plugs (see map below) - Goat Mountain, Sandy Mountain, and Oshihan Hill, the country rock is brecciated & locally gossaniferous supporting the presence of disseminated and replacement gold – which was the original intent of the University of Wyoming grant.

During past drilling in this area by Canyon Resources and Newmont in the 1990s, a large disseminated gold deposit averaging 0.042 opt Au was identified. It is possible that Newmont identified a gold resource of >1 million ounces (Hausel and others, 2000).

But what is exciting is that Evolving Gold intersected a rich gold anomaly at depth. This area mapped by Hausel (1994, 1995, 1996) occurs along the flanks of Sandy Mountain & Oshihan Hill in a low lying area that was recently named Antelope basin. According to Evolving Gold, a high-grade 215-ft thick zone was intersected in a drill hole along the south flank of Sandy Mountain.

Recent drilling by Evolving Gold intersected a large auriferous ore body in sections 24 and 25, T 32N, R88W. This area, mapped by Hausel (1994, 1995, 1996) along the flanks of Sandy Mountain (north stock) & Oshinan Hill (south stock) is significant.Geology. According to Evolving Gold, their targets in this area include the following: (1) Alkalic gold system with potential for a multi-million ounce gold deposit, (2) Multiple porphyry targets, including southeast porphyry zone, (3) Mineralized porphyry dikes – 30.5m at 1.89 gpt Au, including 15.2m at 3.11 gpt Au, (4) Deep stockwork mineralization with grades to 8.2 gpt Au.

The following drill results are reported by Evolving Gold:

North Stock Zone (Sandy Mountain)
RSC-003 146.3 meters @ 2.92 gpt Au
RSC-020 67.1 meters @ 10.80 gpt Au
RSC-089 158.5 meters @ 2.64 gpt A

Antelope Basin (Breccia between Sandy Mountain and Oshihan Hill):
RSC-019 163.1 meters @ 1.25 gpt Au
RSC-042 76.2 meters @ 1.70 gpt Au
RSC-078 76.2 meters @ 1.77 gpt Au

Gold Porphyry Target
RSC-006 14.3 meters @ 2.21 gpt Au
RSC-027 35.1 meters @ 1.74 gpt Au
RSC-027 30.5 meters @ 1.89 gpt Au

RSC-020 lies 464 ft southwest of drill hole RSC-007. RSC-007 was drilled along the eastern flank of Sandy Mountain. RSC-020 intersected a mineralized zone that was 120-ft thick.

Geological map of the Rattlesnake Hills gold district (by Hausel, 1996).

At RSC-007, 464 ft to the northeast, 430 ft of mineralized rock was intersected. At RSC-003 located 670 ft north of RSC-007, 480 ft of mineralization was intersected.

Drilling to date has identified a mineralized body that has a 1440 ft strike length that is 640 ft wide and 1760 ft deep. The average grade of mineralized zones are 0.03 opt Au. The data supports a central high grade mineralized zone surrounded by a low grade gold halo producing a large tonnage gold deposit that will likely be minable by open pit and underground mining.

Breccia found at Sandy Mountain during mapping project by Hausel.

So will there be a gold mine in the RSH? In 1981 & 1982, this greenstone belt was considered to have high potential for commercial gold deposits. RSH also has the added attraction of disrupted zones associated with Tertiary intrusives. The area is located in the middle of nowhere with no active streams & no population to speak of.

However, there is an old saying in the mining industry - "mines are not found, they are made". Whether Evolving Gold can make a mine out if this property remains to be seen. There are many factors involved in any company and its investors and the involvement of government interference and environmental groups who look to stop all human progress. EV has a good property that was considered highly prospective >25 years ago. If they can make a mine out of this property, it will result in other gold mines in Wyoming. Problems seen by the industry with Wyoming has been its reputation for gothic politics that is only comparable to Louisiana and an incorrect perception that the state is poorly mineralized. Even so, the latter has been proven wrong (Hausel, 1989, 1997, 1998, 2000, 2009; Hausel and Sutherland, 2000).

Drill data by EV supports a central high grade mineralized zone surrounded by a low grade gold halo in a large tonnage gold deposit. This is a significant deposit that was initially mapped by Hausel as a large breccia zone nearly a mile long! This discovery will result in increased activity in Wyoming and notable increases in Mineral Hill, Black Butte, Bear Lodge Mountains, South Pass, Seminoe Mountains, Granite Mountains & Sierra Madre in Wyoming as well as in the Tobacco Root and other supracrustal terrains in Montana.

Pillow basalts in the Rattlesnake Hills.

Granite Mountains
The RSH are part of the Granite Mountains. The Granite Mountains are actually hills and probably should be called the Granite Hills. These hills form a belt of Archean rocks immersed in a sea of Cenozoic sediments. The Precambrian terrain is divided into two general units: (1) a complex belt of amphibolite-grade metamorphic rocks exposed along the northwestern and northern margins of the Granite Mountains at Tin Cup and the Rattlesnake Hills-Barlow Gap areas, & (2) 2.6 Ga (billion year old) granites in the center of the uplift. These are intruded by later tholeiitic dikes that cut the granite & metamorphic rocks (Stuckless and Peterman, 1977). Along the northern edge of the hills, Tertiary (40 to 44 Ma – million year old) alkalic phonolites & latites cut the Precambrian rocks (Pekerek, 1977).

The schists in the hills are metavolcanic schists and gneisses that were metamorphosed to amphibolite grade at 2.9 Ga. However, Sr87/Sr86 ratios are unusually high for rocks of this age. To explain such high ratios, these rocks likely formed as much as 3.2 to 3.3 Ga ago (Peterman and Hildreth, 1978).

The metamorphics have steep, southerly dipping, northeasterly to easterly foliation trends (Hausel, 1995, 1996). These include quartzofeldspathic gneiss, augen gneiss, epidote gneiss, biotite gneiss, metagreywacke, amphibolite, metabasalt, minor serpentinite & banded iron formation (Peterman and Hildreth, 1978; Hausel, 1996). At Barlow Gap, both oxide- and silicate-facies BIF are reported (Bickford, 1977). In the Tin Cup belt, massive sulfides are found in hematitic iron formation along with scattered copper, gold & iron anomalies & exotic ornamental stones & gemstones including agates, jade, sapphires & rubies (Love, 1970; Hausel and Sutherland, 2000; Hausel, 2009). Diamonds were also reportedly found in this area by a prospector from Laramie - Eugene Clark.

The RSH is a newly discovered gold district that remained overlooked until several gold discoveries were made in 1982. This was followed by additional discoveries from 1982 to 1995 (Hausel, 1996) along with discoveries made by John Ray of ACNC. In the 21st century, Evolving Gold and others entered the district and interested gold anomalies by drilling, more than 20 years after initial gold discoveries made by Hausel and Ray in the 1980s. With an assay budget of $100/year, the Wyoming Geological Survey was unable to drill, but predicted where gold would be found and verified the presence of anomalous gold with a very minimal assay budget. It is very exciting to see the extraordinary gold intercepts from recent drilling in the area proposed by Hausel as a bulk minable target in 1982. The exploration and work that has been conducted by Evolving Gold in recent years is extraordinary and we are all hoping to see Wyoming's first gold mine in nearly a century.

How to Prospect for Gold