Tonnes and Tonnes of Jasper - A Rockhounds' Treasure Trove!

 

Never seen so much jasper! Tonnes and tonnes of jasper in the Tin Cup district, yet much 
of the area remains to be prospected. Some jasper was exposed in old prospect pits, while
considerable jasper trends along strike lying under inches of soil. All of this on public land 
administered by the BLM (Bureau of Land Management). 

You can follow  these dike-like occurrences of massive jasper for hundreds of feet. In the
same area, are low-quality nephrite jade, some rare jade pseudomorphs after quartz,
rubies, sapphires, agate, and pyrite. These deposits in central Wyoming, lie north of the Jeffrey
City almost ghost town.

JASPER - Some things you should know about jasper: (1) Do you know how many different varieties of jasper are recognized? (2) What rock formations in America contain chert (agate, jasper, flint, chalcedony, etc)? (3) Where is jasper found? (4) Do you know how many times jasper is mentioned in the Holy Bible? (5) Everything you need to know about jasper; (6) Pick a state in the US where jasper is found; (7) GemHunter's guide to Agate and Jasper.

TIN CUP DISTRICT - Just how much jasper is in the Tin Cup district? Don't know, but suspect it may be one of the larger deposits in North America! When you visit scatter prospects in the district, it is clear most are likely interconnected. When you walk over the ground in-between prospects, you will find thin soil cover with periodic chips, fragments and pieces of the lapidary mineral in the dirt. SO, potentially, there could be considerable tonnage buried under just inches to a few feet of soil. 

The GemHunter, former research geologist for the Wyoming
Geological Survey at the University of Wyoming, holds cobbles
of jasper in hands from the Tin cup district, Wyoming, while
Wayne Sutherland takes photo.

During initial reconnaissance of the district some years ago, I was intrigued by the impressive gold assays reported by Henry C. Beeler, geologist, in his 1907 publication (see below). Beeler's report suggested possibilities for significant gold occurrences, but samples I later collected for assay, did not detect any anomalous gold! Even so, the area should be sampled in detail, as there are many small prospects, several shear zones, and a few large  shear zones (Tin Cup Mountain shear, and Sweetwater shear) that are readily visible on aerial photography. There are also numerous tight and isoclinal fold closures in these rocks (42°38'57"N; 107°53'15"W) that are outlined by white granitic dikes and pegmatites in dark schist. The fold noses are potential sites for mineral enrichment, if any mineralizing fluids were released during regional metamorphism of the Granite Mountains. The district is also extensively faulted and fractured with a number of interesting minerals found nearby. While exploring for jade and corundum in this area, examples of distinct hydrothermal alteration was recognized with most in-situ jade deposits. So, there is potential for hydrothermal and metamorphogenic gold in the Granite Mountains, and there still is a lot of geology to examine in the region! 

Photo by Wayne Sutherland showing massive to brecciated
jasper in the wall of the prospect, with geologist for scale. 

The nearby Sweetwater shear zone (42°37'5"N; 107°54'16"W) forms a N65oE-trending shear structure that can be traced for 3 miles on trend. Locally, it is as much as 0.25 to 0.5 mile wide with numerous shear fractures, foliation, and rock cleavage. These all potentially provide permeable pathways for mineral fluids mobilized during regional metamorphism (2.8 Ga) of the Granite Mountains.

Another shear structure is visible in a granitic inselberg west of Tin Cup Mountain, where the N55oW-trending, Tin Cup shear (42°39'13"N; 107°55'42"W) is visible on aerial photography. The region has potential, but is mostly unexplored even to this day.

JADE - Other interesting minerals in the region include nephrite-jade pseudomorphs after quartz. Nephrite is a calcium-, magnesium-, iron-rich silicate (amphibole) of the formula: Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂ that forms masses while crystallizing in the monoclinic crystal system. While exploring this region, specimens of nephrite jade with interesting crystal habits were collected. These include jade specimens with quartz (a hexagonal mineral).

Emerald green nephrite jade (monoclinic) with hexagonal quartz crystals in matrix. Tin Cup
district, Wyoming.

Grass-green nephrite jade with pyramidal (hexagonal) quartz,
Tin Cup district, Wyoming

These include rare specimens of nephrite jade (verified by XRD by Robert Gregory at the Wyoming Geological Survey) that exhibit, distinct, hexagonal crystal habit. Since primary jade does not have hexagonal habit, it is apparent these specimens are pseudomorphs of original, hexagonal quartz crystals replaced by jade. During the regional metamorphic event (dramatic changes in pressure and temperature) in the Granite Mountains in the Archean, some quartz was replaced by nephrite which inherited the original quartz crystal habit. These secondary crystals generally do not have high-quality nephrite like those found further south in the Crooks Gap and Green Mountain uranium district by jade prospectors during the 1930s through the 1960s. The jade pseudomorphs in the Tin Cup region have grass-green, light-green to white colors. Still, these specimens are rare.

Hexagonal jade pseudomorph after quartz, Granite Mountains,
Wyoming.

Crystals of nephrite jade mimicking crystal habit of quartz. These hexagonal specimens
likely formed by nephrite replacing a vug of quartz crystals (Tin Cup district, Wyoming).

Reported jade localities in Wyoming. Jade is found primarily within the Granite Mountains where
detrital rocks were shed in alluvial fans south of the Granite Mountains during erosional events in the
geological past. Other jade localities reported in Wyoming have not been verified, and some are likely
serpentinite or chlorite schist mistaken for jade, such as those in the Big Sandy Opening in the Wind
 River Mountains, and those found near Deer Creek in the northern Laramie Mountains.

Tin Cup jasper

REFERENCES:

Beeler, H.C., 1907, Prospecting in the Black Canyon-Long Creek vicinity near the Sweetwater River, Fremont County, Wyoming: Wyoming State Geologist Report, Cheyenne, Wyoming, 12 p.

Hausel, W.D., 2014, A Guide to Finding Gemstones, Gold, Minerals and Rocks: GemHunter Publications, 368 p.

Hausel, W.D., and Hausel, E.J., 2011, Gold - A Field Guide for Prospectors and Geologists (Wyoming Examples), GemHunter Publications, 366 p.

Love, J.D., 1970, Cenozoic Geology of the Granite Mountains area, Central Wyoming: US Geological Survey Professional Paper 495-C, 154 p.

Tin Cup Hilton. Don't know if anyone else experienced
strangers in the night in Wyoming? While camping and 
mapping in the Granite Mountains, Seminoe Mountains, and
South Pass, my tent was periodically visited at night by a 
very fast critter that would run around my tent much faster than
any coyote could run. Each time I stepped out my front 
door with my flashlight and gun in hand, there was never anything
to find? Still don't know what it was to this day.

The Tin Cup district in the Sweetwater Rocks, Granite Mountains, Wyoming

The author near old Sutherland
mine shaft

The Tin Cup district (a.k.a. Black Rock-Long Creek district) is in the western part of the Granite Mountains (T30 and 31N, R92 and 93W). Find this district 42^o38’53”N; 107^o53’00”W on GoogleEarth (you can search for Tin Cup Mountain on Google Earth). From high altitude, you should see a large, triangular-shaped, fragment of dark Archean supracrustal rocks with nearby, linear, dark-colored northeasterly-trending mafic (basaltic) dikes. This entire area is complexly deformed and metamorphosed and likely hosts additional undiscovered jasper, massive sulfide, ruby, sapphire, diamond and other gemstone deposits. If you study the area with aerial photos, many white pegmatites (coarse-grain granites) and gneissic dikes are present in the darker country rock. These help to outline many of the complex folds: both open and isoclinal folds are evident. Along with helping to identify cross-cutting faults. The foliation parallel shears and faults are more difficult to pick out on aerial photography, but where prospects line up, there are usually shear zones.

Copper-stained quartzite, Tin Cup

The district includes northeasterly-trending, parallel, shear zones and impressive amounts of jasper, agate, and jasperoid, and some massive sulfides. 

By following these on the ground, it will become apparent there is a lot of barren ground in-between the jasper-rich prospect pits. This area has extensive, hidden (or blind), pockets of additional jasper. These jasper deposits are some of the more spectacular jaspers and agates in the State and locally exhibit impressive tight to isoclinal folds. Sizable cobbles and boulders of jasper should be investigated as countertop and lapidary material. Some would make extraordinary counter tops and provide a new resource for Wyoming. Beeler (1907a) and Love (1970) suggested this area also had significant gold anomalies; however, these cannot be duplicated by the author. However, I only collected scattered samples from prospects and these contained mostly no detectable gold. At the southern edge of this district, is a chlorite-biotite schist and gneiss with some spectacular rubies. One of the ruby deposits was examined by the Dr. Love and the author at different times, and sometime later, Robert Odell (RIP), a Casper Consultant, staked claims on the ruby deposit and named it the Red Dwarf.

Zoisite after ruby from the Red Dwarf schist. Some of the
original ruby is preserved in this specimen.

The Red Dwarf yielded several, large rubies including many zoisite pseudomorphs after ruby that indicate some very large rubies were present in this deposit prior to retrograde metamorphism. One, poor-quality ruby measured 2.5 inches across. Another stone, collected from the Red Dwarf was 90% replaced by zoisite. The original ruby was more than 5 inches in length and about 2 to 3 inches wide,  and retained some high-quality, pigeon’s blood, red corundum in the large pseudomorph (Hausel and Sutherland, 2000). It is possible that this deposit hosts some of the largest rubies on earth. Excavation of this deposit and a search of nearby drainages might produce of some impressive rubies. However, the Red Dwarf has only been examined at the surface. The district also hosts large resources of jasper, other ruby deposits, and some, low-quality, blue and white sapphire, as well as some low-quality jade. Reports of detrital diamonds of 2 to 5 carats, are intriguing, but remain unverified (Eugene Clark, personal communication, 1980). The stones in question were examined by Dr. McCallum at CSU and, according to him, the crystals in question could have been diamonds, but the prospector (Clark) would not let him touch or examine them. Some Cryptovolcanic depressions occur in this region provides additional intrigue along with drainages with names like Diamond Springs Draw.

Map of the Tin Cup district (from
Hausel, 1997).

The district is underlain by amphibolite-grade gneiss, schist and amphibolite metamorphosed at 2,860 Ma. The supracrustal complex was intruded by granite at 2,550 Ma and was followed by intrusion of diabase dikes a short time later (Peterman and Hildreth, 1978). The principal prospect development in the district was the Sutherland (Red Boy) mine. The Sutherland contains massive pyrite (Hausel, 1989). Beeler (1907a) reported several gold prospects and one copper prospect was identified in the district that yielded gold values of 0.08 to 3.5 opt, and as much as 15% Cu. These reported values could not be verified by the author; but, mineralization was reported in schist, diorite, quartz veins and jasper. And there are numerous prospects pits and some trenches in the area, and the author recommends all of these be sampled to try to verify the report by Beeler (1907a).

The author collected some cursory samples of hematite-stained quartz, cupriferous schist, low-grade banded iron formation and limonite-stained quartz breccia. These limited samples yielded 188 ppm to >2.0% Cu, none to 551 ppm Pb, 20 to 253 ppm Zn, 5 to 14 ppm Mo, 20 to 342 ppm As, 0.6 to 14 ppm Sb, none to 0.351 ppm Hg, none to 0.9 ppm Ag, and none to 10 ppb Au (Hausel, personal field notes, 1994).

Reported occurrences

Anderson Mine (SE SE section 13, T31N, R93W). One mile north of Tin Cup Springs. Gold was detected in N80^oE-trending, south-dipping quartz veins in schist (Love, 1970).

Wayne Sutherland point to shear zone
exposed in shaft wall. In background is
a prospect in red jasper

Cedar Rim prospect Location unknown; however, Beeler (1907a) reported a mineralized diorite assayed from 0.01 to 0.02 opt Au.

King Solomon Claim (Section 36, T31N, R92W). Limonite and malachite-stained veins trend northeasterly. Assays of the vein material were reported at 0.1 to 0.88 opt Au (Beeler, 1907a).

Lone Tree claims. Located east of the Queen Sheba claims. A shallow shaft cut a wide ledge of oxidized iron and quartz. Both copper and iron sulfides were noted in the 20- to 30-foot-wide ledge. One sample assayed 15% Cu and 3.5 opt Au (Beeler, 1907a).

Queen Sheba claims. Beeler (1907a) reported this property to lie somewhere on the west end of the district. A shallow shaft was sunk on a huge copper- and iron-stained quartz ledge.

Prospect Pit TC19-95 (NW section 36, T31N, R93W). This prospect lies along a prominent northeast-trending fault in Archean gneiss that was traced on the surface for 5,500 feet (W.D. Hausel, personal field notes). To the northeast, this same structure contains jasperoid and massive sulfides at the Sutherland shaft. Copper mineralization is uncommon along the structure, although weakly copper-stained jasper in the prospect pit contains minor malachite, azurite, tenorite and uncommon chalcocite. A select sample yielded 1.71% Cu, 3.6 ppm Ag, 7 ppb Au, 74 ppm Zn and 10 ppm Pb (Hausel, 1996a).

Some of the extraordinary banded jasper at Tin Cup.
Specimens weighing several hundred pounds were found
in prospect pits and mines in the district.

Prospect Pit TC27-95 (NE section 26, T31N, R93W). Samples of fault breccia from this prospect pit contain goethite, limonite, trace azurite and minor jasper with calc-silicate veinlets. A sample of the breccia assayed 0.48% Cu, 0.5 ppm Ag, and a trace of lead and zinc (Hausel, 1996a).

Prospect Pit TC28-95 (NE section 26, T31N, R93W). A short distance to the west of TC27-95, minor copper stains were found in breccia. A select sample yielded 0.29% Cu and a trace of lead and zinc (Hausel, 1996a).

Prospect Pit TC41-95 (NW section 19, T31N, R92W). Butterscotch and red jasper has vugs filled with botroyoidal quartz in graphitic schist. A sample of schist with jasper yielded 0.13% Cu, 694 ppm Zn, 43 ppm Pb, 11 ppm Mo and 86 ppm As (Hausel, 1996a).

Prospect Shaft TC42-95 (NW section 19, T31N, R92W). One thousand feet to the northeast of TC41-95 is a shallow 8-foot deep prospect that exposed granular quartz in an iron-stained schist. A sample of the schist yielded 0.22% Cu, 336 ppm Zn, 26 ppm Pb, 38 ppm Mo and 65 ppm As (Hausel, 1996a).

Red Boy (Sutherland) Mine (Section 36, T31N, R93W). Massive pyrite is found in hematitic iron formation that was exposed in a shaft. According to the Prosepctus of the Emigrant Mining Company (June 12, 1938) samples from this mine assayed 0.04 to 0.46 opt Au. Samples collected from the bottom of the shaft contained 0.4 opt Au and 23 opt Ag (Love, 1970). Several samples of the massive pyrite were collected to verify these results, in 1983, but none contained detectable gold suggesting that the earlier assays may be questionable (W.D. Hausel, personal field notes).

Mining Districts and Mineralized Terrains (after Hausel, 1997).