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.
Here was an excellent source bed for gold that was intruded by high-temperature volcanic rocks (Tertiary alkalic igneous rocks) that provided heat & fluids to leach gold from Precambrian & alkalic rocks & focus the precious metals in fractures and replace select minerals in the host rocks.
Thus, armed with these concepts in 1982, I packed my field gear & headed for the field and drove into the RSH from the north side to see if there was evidence for exposed or hidden intrusives or replacement deposits in limestones along the northern flank. My primary interest was to find disseminated gold associated with the alkalic Tertiary intrusives that invaded the greenstone belt. Access from the north is not recommended & was the source of the name of one of the first gold prospects found in the area. In honor of my muffler which gave up its life for this investigation, the first gold discovery in the RSH was named the Lost Muffler Prospect. But with a WGS assay budget of only about $100/year, sampling had to be very selective (MMRRI did not provide much additional funding for sampling). And this occurred about the same time as my discovery of high-grade visible gold at the Seminoe Mountains.
A whole new gold district was identified during this & subsequent investigations - something that rarely happens in a person's life. At the Lost Muffler, samples assayed as high as 0.3 opt gold and the vein exposed on the surface was traced over a strike length of 2.5 miles. Gold was also found associated with veins, exhalites, stockworks, banded iron formation, alkalic intrusives and adjacent, widespread breccia pipes. I recommended that the UW Engineering Department focus on the breccias for a low-graded disseminated deposit and drill these areas, but by this time, the Engineering Department had lost interest. I also tried to get the state to provide funding for mapping & detailed sampling, but was unable to gain support. Composite chip samples of the breccia adjacent to the Tertiary plug at Sandy Mountain 37 ppm to 0.14% Cu, trace to 0.03 opt Au & 25 ppm to 1.65% As. Samples of a breccia vein in the disrupted section of the metagraywackes along the flank yielded 92 ppb to 0.01 opt Au and composite chip samples of phonolite at Sandy Mountain assayed 44 ppb to 0.012 opt Au. Nearby stockworks assayed 0.01 opt Au and banded iron formation assayed none to 0.16 opt Au.
The RSH had excellent potential for significant gold. Over several years, I mapped this belt. 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. I attracted companies into this region. Because of having no budget to speak of, mining companies provided the best opportunity to make major gold discoveries at depth. American Copper & Nickel entered the district & made additional discoveries in exhalites (veins). This was followed by Bald Mountain Mining who was able to attract Canyon Resources & Newmont Gold. These companies explored breccias & made a million ounce+ gold discovery by drilling at the Sandy Mountain breccia pipe (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). Evolving Gold later explored Sandy Mountain & intersected major auriferous zones at depth between Sandy Mountain & Oshihan Hill in what has been referred to as Antelope basin. Drill intersepts by this company are extraordinary & their comparison the Cripple Creek demonstrates how promising this region is.
It became apparent that the basement rocks in the RSH represent a fragment of an Archean greenstone belt similar to South Pass and to other rich gold districts in Australia, Africa and Canada (Hausel, 1989, 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.
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 and the breccias and Tertiary plugs at Sandy Mountain & Oshihan Hill were considered significant (Hausel, 1995, 1996; Hausel, personal field notes 1981-1995). 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 a nearly one-square-mile breccia suggesting a sizable, disseminated gold deposit! But support by the State continued to be nearly non-existant.
breccia suggesting a sizable, disseminated gold deposit! But support by the State continued to be nearly non-existant.
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 (Hausel and others, 2000). Follow-up work by Evolving Gold intersected a rich gold anomaly at depth.
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. According to Evolving Gold, a high-grade 215-ft thick ore zone was intersected in drill hole RSC-020 along the south flank of Sandy Mountain that averaged 0.315 opt 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 averaging 0.492 opt Au. Within this 120-ft zone is a 40-ft zone that yielded an average gold content of 1.147 opt Au and a 5-ft zone of 4.526 opt Au. The composite of these mineralized zones includes 610 ft of 0.125 opt Au.
At RSC-007, 464 ft to the northeast, 430 ft of mineralized rock yielded an average of 0.083 opt Au. At RSC-003 located 670 ft north of RSC-007, 480 ft of mineralization was intersected that averaged 0.085 opt Au.
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.
Left - Looking at Goat Mountain from explosed gossaniferous vein. Below - one of several Tertiary breccias mapped by Hausel in the vicinity of Oshihan Hill
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 and an excellent geologist. 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 politicscomparable 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.
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.