For a fairly complete list of minerals from the “Dexter Group” of claims see Bullock, Kenneth C., “Minerals and Mineral Localities of Utah” Utah Dept. of Natural Resources Bulletin 117, 1981. Of primary interest are sulphates that occur in micro to small thumbnail sizes such as coquimbite, roemerite, voltaite and others in association with alunogen, halotrichite, jarosite and a mix of massive, soluble, crystalline sulphates. Uranium minerals are present but were not seen as ‘collectible’ specimens.

For picture of some of these species see location references in the MINDAT database at www.mindat.org

Workings at the Dexter No. 7 mine include short drifts and slopes largely open to the surface of the cliff face. Other than the access road the only other evidence of the operation remaining in the late 80’s was a cable, part of a tram system from the portal area to the base of the mesa, and remnants of shacks and trash dumps. While the literature describes coquimbite specimens from parts of the underground workings, there was nothing significant found underground.

The Dexter No. 7 mine on Calf Mesa is located about 12 miles north of Interstate (70) on the crest of the San Rafael Swell some 25 miles west of Green River, Emery County,Utah. Access is good in dry weather but it is a remote area so plan accordingly. A 4wd road to the mine was passable in the late 1980’s but there may have been ‘reclamation’ on the property since. With the present interest in uranium there could be exploration activity as well.

The uranium workings at the south end of Calf Mesa in Emery County, Utah (the Dexter Group of claims)  have produced some of the more unusual and attractive sulphates known from the Western U.S.  Workings develop uranium mineralization in sandy units in the Chinle Formation of Triassic Age. While specimen production during actual development of the properties in the 1950’s thought to have been minor, abundant specimens were found as secondary accumulations in waste rock at the mines in the late 1980’s. There has been more recent collecting of specimens there but the extent of that activity is unknown. Because many of the minerals of interest at the Dexter Group are formed in waste rock and ores exposed to weathering there may be a continuing opportunity for collecting good specimens there for some time.

The southern part of the Black Rock Desert is a nice day trip from Reno and includes a variety of geologic environments, mines, trails and historic sites along with the flora and fauna typical of the Basin and Range. Leaving Reno at 05:30 we drove around the south end of Pyramid Lake and turned north. It was just full light when we passed the tiny community of Empire, five miles south of Gerlach, where a large deposit of gypsum has been mined and processed for decades.

Gerlach means Bruno’s, the only place to eat and one that serves meals definitely not for sissys. It is located at the west end of the Black Rock and is the last outpost of civilization for nearly a hundred miles in any direction.

We breakfasted and then turned south for a few miles to pick up the road along the south edge of the Black Rock. This is a gravel and mud track that parallels the railroad between Gerlach and Winnemucca some 100 miles to the east. The only activity in this area is around the Hycroft Mine at Sulphur, about halfway between the two towns. We proceeded to drive east enjoying stunning views of the Chocolate Mountains, the Black Rock to the north and local points of interest. These included a rather cold pine gopher (bull) snake and the markers indicating the passing of the emigrants along the Applegate Trail in the 1840’s. Tracks are still visible in the alkali at the edges of the Black Rock where wagons passed more than 150 years ago.

Approaching Sulphur the large and colorful waste piles and leach pads of the mining operation are visible from 15 miles away. This property produced gold and silver and then sulphur and aulunite in the past but more recently, since the 1980’s, has produced gold and silver from low-grade ore bodies associated with hydrothermal activity along Basin and Range faulting.

The alteration along the structures has produced a rich range of colors in the rocks that include reds, ocher and stark white with many shades of browns and grays. Current operators are expanding the known ore zones and will resume mining operations in the near future. All ores are processed by heap-leaching, the most efficient method of extracting gold from the low-grade ores. The old town site of Sulphur is adjacent to the railroad tracks about a mile west of the Hycroft Mine. Only a few foundations and building and equipment remnants remain.

This property has produced interesting specimens of sulphur, cinnabar, stibnite, opalized and silicified rocks, calcite and some more uncommon minerals in isolated occurrences. At the north end of the property is an occurrence of silicified reeds near a ‘fossil’ hot spring.

To be continued…

Leaving the Sulphur area we drove a few miles to Rosebud Canyon and the Rabbit Hole Springs. Rosebud Canyon was placered by early prospectors and there is a small, currently inactive underground silver mine (Rosebud Mine) as well.  This mine has produced some excellent specimens of barite and a variety of silver minerals. Again, there are a number of trail markers with information from the journals of travelers in the wagon trains. Rabbit Hole Spring at the west end of the canyon was a welcome stop for the weary emigrants as they prepared to start the trek north across the Black Rock Desert.

Following the path of the emigrant trail from Rabbit Hole Spring to the Gerlach-Winnemucca road we turned west, stopping for a look at an area with reported trilobite fossils.  Directions were vague and we didn’t have time for prospecting so a bit of research will be needed before returning for another try. We hiked around the base of a granite intrusive, checking out some prominent veins of feldspar and quartz. They were barren with no associated openings or loose areas where one might find crystals.

Trego Hot Springs is near the road about 20 miles east of Gerlach. It consists of a series of pools and ‘tanks’ surrounded by cottonwood, willow and tamarisk trees with lush grasses and cattails in the wetter areas. It is truly an oasis in the desert and it attracts wildlife of all kinds. It is a popular spot for campers and bathers; one should be careful to not surprise anyone who has “forgotten” their bathing suit. The source of the warm water here is a series of wells drilled into artisian, geothermally heated groundwaters.                 

The crystal-clear pool pictured is about 85 degrees warm and has an 8 inch pipe in the center running about 20-30 gallons per minute.
The last stop of the day was at a small tungsten prospect high on the mountain overlooking the western Black Rock. The workings are in a fairly thin carbonate unit near the contact with a granite intrusive. The beds are very steeply dipping to overturned and show a typical development of garnet-diopside and marble skarn. There are a few boulders or outcrops showing rather large (to 10 inches) crystal sprays of clinozoisite but they are uncollecteble on the massive, tough blocks of skarn. Garnet is common in the skarn although crystals are indistinct.

As we headed down the trail to our truck we could see rain and snow showers to the north in the Granite Range. A brisk wind and cold sprinkles hurried us along as a train passed headed for the West Coast.

In the mid-1970’s I spent a good deal of time working on projects in Central and Southwestern Colorado. Among several areas of interest in the Gunnison area was an exploration project that incorporated much of the Italian Mountain intrusive complex, an area some 15 miles NE of Gunnison. This is one of the premier mineral collecting spots in the western US, one that has been recognized for the unusually fine specimens found there since it was first described by geologists in the 1870’s.

Later discovery of perhaps the only commercially significant North American deposit of gem-grade lazulite adds considerable interest. It is a place of sublime beauty that is seldom visited by mineral collectors because of it’s remoteness, elevation and lack of access for motorized vehicles.

Italian Mountain complex looking west from Italian Creek drainage

This writing will just introduce the reader to the area and the interesting geology and mineralogy there. There is a variety of literature available concerning the general area and the Italian Mountain complex itself. From the collectors point of view, the best reference is a fine article in The Mineralogical Record by Henry Truebe, (March-April, 1984).

Henry spent some time over a period of several years doing thesis work, mining specimens and evaluating the commercial potential for specimens in the area. He identifies and locates all of the significant species found there.

Italian Mountain is located between the Taylor River and Cement Creek drainages and is best approached from the east from a jeep trail that, starting just north of Taylor Reservoir, follows North Italian Creek to the area of the Star Mine in Star Basin. Several mines in this area produced small amounts of lead, zinc and silver from replacement ore bodies in limestone. The ponds in Star Basin are large enough to produce some fine trout for those interested in fishing. From Star Basin the trail turns south, rounding the east end of the long east-west trending ridge that separates Star Basin on the north from Stewart Basin to the south.

Stewart Basin with South Italian Mountain on left and Central Italian Mountain to right.
Vehicle is near the base of the trail that follows the east ridge to summit area.

American Flag Mountain forms a high North-South trending escarpment east of Stewart Basin. A foot trail from the south side of this ridge provides access from the ridge on the east flank of the main peak to the primary collecting area in a saddle at a contact zone just north of and below the 4,078 meter (13,380 foot) summit.

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Author on east ridge. Note colorful brown alteration of sedimentary rocks near summit and the lighter intrusive quartz monzonite porphry to the right.

Access from the head of Cement Creek follows a trail on the ridge northwest of the North Italian Mountain where the lazulite is found and skirts the peak of North Italian Mountain and approaches the summit of (Central) Italian mountain from the north across a talus slope. This is by far the most difficult access and the trail from the east is recommended. Note that the lazulite deposit is located on patented claims and is off limits to collecting without permission from the owners. Truebe located lazulite in several small occurrences around the main peak of Italian Mountain, but none proved to be of commercial interest.
The three peaks of the Italian Mountain intrusive complex are related to three intrusive ingneous stocks, the youngest of which is about 34 million years old and is usually described as a quartz-monzonite-porphyry (QMP). These rocks intrude Paleozoic sedimentary rocks that intrude limestones, dolomites, shales and quartzite. In these reactive rocks adjacent to the contacts with the QMP main stock and related intrusive dikes are developed skarn zones that contain the primary minerals of interest.

Steeply dipping beds of Leadville Limestone northeast of North Italian Mountain at the head of Cement Creek. The lazulite deposit is below and on a ridge to the left.

Italian Mountain summit from saddle to north. Note sedimentary beds and light-colored intrusive dikes and contact.

Looking north from peak to saddle collecting area. Note digging. Light-colored QMP talus and upper Cement Creek in background.

While there are some 80 mineral species described from the area, the most important and accessible to collectors are found in a relatively small area near the summit of Italian Mountain. These include vesuvianite (idocrase), garnet var. grossular, prenite, clinozoisite, epidote, diopside, chabazite and heulandite. Several pits have been opened on contact zones where these minerals have formed in skarns associated with intrusives and shaley sedimentary rocks of the Beldon formation. My favorite spot is in the saddle north of the main peak. Here the the west slope drops sharply some 500 meters to the Cement Creek valley and to the east is a near vertical drop of some 100 meters to a talus slope above Star Basin.

Ponds in Star Basin from saddle area north of main peak of Italian Mountain

In the 1970’s there were some remnant cables attached to the vertical cliffs below this area. Presumably they were used by some of Truebe’s crew to evaluate the contact zones on the cliff face. There are fine vesuvianite crystals here, up to 5-6 cm, although the best are those up to about 2.5 cm both on matrix and as floaters in collapsed pockets.

Vesuvianite, about 1cm, on grossularite-skarn matrix

Larger crystals, particularly those found near the east edge of the saddle area, tend to be corroded and may show unusual silky, fibrous vesuvianite surfaces. In addition, this is an area where there are gemmy grossularite crystals up to (rarely) 2cm.

Heulandite crystals to 3mm from saddle area.

A nice mineral collecting day trip from the Reno area is to the Nightingale Mining District, an area with many mines and interesting geology, flora and fauna. The area produced mostly tungsten with some by-products but has not been significantly active since the demand for the metal declined after the Korean War. There are a number of major mines with associated ruins as well as hundreds of smaller prospects. As with all such areas, approach any mining area with caution. Do not enter mine openings and remember that not all shafts and pits are fenced.

We approached Nightingale from the southwest from the south end of Pyramid Lake and the town of Nixon. Pyramid Lake is one of the largest and deepest desert lakes in the Great Basin; is is one of the remnants of the huge Lake Lahontan that covered thousands of square miles in northwestern Nevada several thousand years ago. From Nixon a gravel road trends north and east crossing a divide to the basin of Winnemucca (dry) Lake. This lake bed is long and narrow and parallels the Nightingale Mountains on the west. Our goal was the MGL mine, some 7 miles north of the main access road and a mile or two up into the mountains.

The road north passes some spectacular volcanic geology and excellent examples of ancient shorelines with associated tufa mounds. in several areas old beach deposits consist of hard, cemented gravels made up of black eroded igneous rocks that flank the basin in the area.

At the lower end of the canyon where the MGL Mine is located is the cement foundation of the processing plant where tungsten ores were concentrated. The ores were crushed and the heavier minerals containing tungsten were separated and concentrated during several stages of processing as they traveled down through the mill. Concentrates were hauled by truck to a railroad for transport to refining plants outside the area.

The road up the canyon required a bit of careful driving and would not be passable in wet weather. The ore chute or dump is located below the main mining operations. Open cuts in the tungsten bearing rocks can be seen above it. There are several adits (horizontal tunnels) that access the ore zones and allow the ores to be moved down and out to be loaded on trucks for the trip down-canyon to the mill.

The dumps around the ore chute and along the access roads contain many of the minerals that can be found in the open pits and tunnels. The MGL Mine is known for particularly fine specimens of large, brown andradite garnets as well as clinozoisite. Some of the best examples can be etched from calcite that fills some veins and pockets, protecting the crystals. Other minerals include pyrite, quartz, tremolite, copper secondary minerals and rare molybdenite.

Although the area is dry this time of year there are a variety of flowers and lots of lizards. Desert plume, Stanleya pinnata, is one of the more spectacular. Lizards like the black-collared, the western whiptail and the sagebrush lizard abound. It must have been a productive spring for them, because there were little lizards everywhere. It is amusing to see a 3-inch lizard on a 6-inch rock, protecting his territory with all of his bravado. The bigger lizards get to protect bigger rocks, and even graduate to a boulder if they are really assertive. And they run like the wind! Even the littlest ones will raise a small plume of dust as they dash down the road.

Returning to the main access road we again went northeast over a pass of about 6,000 feet in elevation to the site of the Nightingale Mines. Here are cement foundations and a metal stack and a large water tank that provided water for the milling operation. Most of the metal structures have been riddled by bullet holes and there is considerable trash left by campers. I have never thought of a water tank as a challenging target, but it must be.

The mining here was concentrated in a steeply-dipping sedimentary unit some 15 to 20 feet thick that has been metamorphosed by nearby and included granitic intrusives. The mining covers some half-mile of strike and has left large, open cuts and overhangs. Dumps contain a similar assortment of minerals as seen at the MGL Mine, but the rock is ‘tighter’ with less opportunity for good specimens where we checked.

Returning over Nightingale Pass we stopped at some smaller workings known as the Jay Bird Mine but found nothing of interest. The rest of the trip was uneventful. Pyramid Lake was calm and some the local white pelicans were having a meeting on the beach as we passed by. All in all a very good day.

The Leadville Mine northeast of Gerlach in Washoe County, Nevada, has produced a variety of metals from ores associated with porphyritic dikes in andesite. There is a mention in the literature that there were large fluorite crystals associated with the deposits, although there are no real details describing the occurance. It was worth a trip to see this area and some new country and to check out some geode areas on the north side of the Blackrock.

We left Reno early and had breakfast at Bruno’s in Gerlach, the iconic restaurant on the Black Rock-Smoke Creek junction. We traveled by paved and then gravel roads about 35 miles NE to the turn into the Leadville District. A good jeep trail leads to the mine site. It was a very windy and cold day with showers at the 6,000 plus foot elevation, but the flowers were out and a lone antelope and several groups of mustangs didn’t seem to mind the weather. We spent several hours climbing over mine dumps and looking at prospect pits on the main structure and to the southeast on several parallel dikes. The dumps produced several specimens of massive galena, one of sphalerite and numerous samples of sulfide-rich waste rock. There was no recognizable fluorite on the dumps or on the mineralized structure on a single exposure on the drainage south of the main workings.

We left Leadville and drove north to check an area where Sam Knipmeyer, my digging partner, had prospected with his dad in the 80’s. There is a nice display of petrified logs next to the road, protected from passing rock hammers by a sturdy fence. We returned to the north edge of the Black Rock Desert and turned NE again on Soldier Meadow road. We decided not to drive on the playa as it had showered much of the day and might have turned the track to mud. We passed an opal mine (formerly, Little Joe) and proceeded to the Mud Meadows Reservoir and turned south along the west flank of the Black Rock Range. This track follows the approximate route of the 49er’s as they treked to the Highrock Canyon and the Northwest. We passed the site of Hardin City, history unknown. Ruins consist of two eroded piles of cut ash fall tuff blocks that were buildings near a boggy spring.

Top, Hardin City Ruins – Bottom, Double Hot Springs

Some 5 miles to the south is Double Hot Springs, a series of pools with temperatures in the dangerous range. It was to late for a bath, so we turned back north a mile or so to a flat dry camping spot. It was windy and rainy all night but the area was surprisingly dry in the morning.

After breakfast and packing up camp, we re-traced our route to the north and found a track into the hills to the east. The area is reported to have a variety of chalcedony geodes weathering from basalt. We did find a number of specimens, nothing spectacular, and a lot of chips from sites along the flanks of the valley. Some were of a very pretty red jasper and had clearly been shaped as scrapers. The highlight, actually, was at the end of a small box canyon in one of the basalt layers where we found a nesting pair of prairie falcons. They were very upset with our visit but calmed down quickly as we left.

Seeing rain to the south and fearing a muddy track on the playa, we again headed south to Double Hot Springs. We took pictures and reflected on the marker with a quote from a log dated August, 1849, in which the writer remarked on the springs and the fact that they had rested and “boiled beans” (in the springs) as they passed, on the way up the trail. We then headed SW to the track across the Black Rock where for 35-40 miles one can drive in nearly a straight line at 50-60 miles per hour. The dust plume was spectacular!

In the early and mid 1970’s I spent several months working on the uranium potential of the Denver Basin and, in particular, the area east and southeast of Colorado Springs and Trinidad. We were evaluating mostly Lower Cretaceous rocks but spent some time checking surface and sub-surface anomalies based on areal and ground water sampling programs. Surface rocks in much of this area consist of Upper Cretaceous shales containing multiple horizons with large concretions.

On a late afternoon in 1972, returning to our base of operations in La Junta from the area near Timpas, we stopped to check a shale unit along the highway and found several promising concretions. We excavated one, about 4′ in diameter, and found what may have been the first reported clear barite in what was later called the “La Junta” barite area. These barites are often water-clear and display a variety habits some of which are remeniscent of those found in concretions near Grand Junction.

The specimen pictured was displayed at the Denver Gem and Mineral show in, I believe, 1976 in a Self-Collected Minerals case. The blocky crystal is about 2.3 cm on an edge. It generated a bit of interest and the location was given to several people, including Don Knowles who reported little success after at least one trip to the area. Some years later I received an inquiry from Dan Kyle about the location and sent maps of the area to him. As most collectors in the Denver area know, Dan has found some very fine specimens there.

While much has been said about the clear barites there are two additional locations that I have always wanted to re-visit. One, not far from the original barite discovery, was near a well where we collected a water sample. Weathered concretions on the surface nearby contained lovely rosettes of white, flattened calcite rhombs up to 3 inches across displayed on a matrix coated with orange-brown lichens. Another, some miles to the east, was a somewhat obscure zone of smaller concretions, up to about 2.5-3 feet in size, with tabular blue to blue-gray and yellow zoned barites up to 2 inches on a calcite-crystal matrix. We spent less than 20 minutes walking contour on this concretion zone and found one weathered open, with the crystals described above and several others that looked promising but we did no digging.