Samples collected during this period contained a suite of minerals that included species not described before from Colorado.  Later work by the Bendix Corp, under contract to the Atomic Energy Commission, expanded the list of species found there and included one new species. The new mineral, theisite, is an orthorhombic Cu-Zn(As,Sb) arsenate described as sectile, bluish-green scales to 2mm. This species has since been recognized from a locality in Utah and from a number of localities in Europe. A partial listing of additional species includes:

adamite, austinite, azurite, chalcocite, chonichalcite, covellite, cuprite, digenite kolwezite, malachite, parnauite, partzite, pyrite, tetrahedrite, theisite, uraninite, zeunerite.

This unusual suite of elements and minerals have similarities to uranium vein deposits with complex paragenesis in the Co-Ni arsenide group. These could include nearby deposits in Precambrian rocks as well as  uranium bearing, silver, base metal vein deposits in Europe. The deposit at Tucker’s Tunnel contains significant amounts of As, Cd, Sb, Mo, Ni, Co and Ag as well as large concentrations of Cu, Pb and Zn. A uranium-copper-cobalt-silver-arsenic vein in Precambrian rocks at Elk Park, south of Silverton and a uranium vein deposit high in the Needle Mountains northwest of the Tucker’s Tunnel occurrence are of similar interest.

Like many of the lessor mineralized areas in the San Juan Mountains, these prospects were first discovered and tested in the latter part of the 1800’s and in the early 1900’s. First recorded production is in 1913 and included some 57 tons of ore with 12 ounces of gold, 237 ounces of silver, 2,900 pounds of copper and 1,700 pounds of lead.

In the mid-1950’s, Mr. Reno Montonati, a local prospector interested in the silver in the area, discovered radioactivity at Tuckers Tunnel, did some development/exploration work and promoted the prospects for uranium. An engineer, he actually built his own helicopter and flew it in the area!

The collecting site, named the Tuckers Tunnel prospect, consists of a series of pits, trenches and short adits on an east-west trending structure cutting Paleozoic sedimentary carbonate-rich rocks. All minerals noted here have been found in the dumps at this prospect. The best mineralization was found in small openings in fractures and veins in blocks of angular carbonate-rich breccia with visible secondary copper mineralization. There are, however, many prospects, (the Mary Murphy Mine, for example) scattered in the area to the north that show copper mineralization and associated radioactivity. These prospects, unlike those at Tuckers Tunnel, do not show the variety of mineral species or the breccia that is the host for the minerals described here.

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.