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.

In the mid-1970’s I spent several field seasons working in the southern San Juan Mountains of Colorado.  One of the more interesting properties examined was in the Cave Basin Mining District located about 25 miles NE of Durango on the Hinsdale-LaPlata County common line. The area is reached from Forest Service gravel and dirt logging roads and a series of jeep trails starting at the NE end of Vallecito Lake. The primary collecting site, known as the Tucker’s Tunnel Prospect, is located on the north side of a prominent, rounded mountain known as Runlett Peak.

Access to this site may be limited. In 1976-77 this was a wilderness study area with an established wilderness about a mile to the north. Access on good gravel road from the north end of Vallicito Lake should take one to within about a mile of the prospect in any case. Elevations in the area range between 10,000 and 11,500 feet and there can be severe weather at any time of year.

This is a spectacular location for unusual micromount specimens.  Not only are there species first described here for Colorado (chonichalcite), but this is the type locality for a new mineral, theisite, first found here and described by contractors with the Bendix Corporation in 1982.

GEOLOGY AND MINERALS

The mountains east of Big Pine are made up of a complex of Paleozoic sedimentary and volcanic rocks that are dramatically displayed along SR168. An interesting side trip to the Bristlecone Pine Preserve near the top of Westgard Pass is an option except during the winter months. Entering the Deep Springs valley from the south the Mesozoic granitic rocks that include Crystal Hill can be seen to the north and northwest. The Crystal Hill intrusive appears to be located near the contact between two types of granitic rocks and it has been intruded by a later phase of more mafic granodiorite. The hill is rich with fractures, veins and intrusive dikes and the upper part in particular has been veined and silicified by late-stage quartz. Crystal Hill has an anomalous E-W trend, again supporting the idea that it has been intruded along a contact between rocks of different intrusive stages.

Quartz is the predominant mineral in the veins and cavities with large amounts of late-stage calcite introduced in some areas. Iron oxides in the form of discoloration in the rocks or as small pseudomorphs after pyrite in pockets are present in the most productive areas.

Masses of a dark, earthy to hard material are found in  many pockets and appear to be associated with the formation of and, perhaps the degradation of calcite. Quartz crystals are simple prisms up to 8 inches long and are clear to milky and smoky colored. As in the photo below, many are stained with hematite.

Larger pockets are filled with interlocking crystals of quartz with terminations in open areas or, in some cases, imbedded in late calcite. Doubly terminated crystals are present but are uncommon. Quartz shards are often terminated in interesting, flat crystals and may have secondary, clear crystals attached. Calcite is rarely found as terminated crystals but large masses can be collected as clean cleavage-rhombs.

The calcite specimen shown here has typical crusted pocket materials attached.

Leaving Reno at about noon we drove to Hawthorne and then to the Candelaria District in Mineral County. I wanted to check a locality for nickel minerals where I had visited a mine briefly many years ago and had found small crystals of annabergite on the dumps. We arrived late in the afternoon and found a small open pit where the mine had been. The pit exposed a variety of altered rocks, including lenses of amphibolite which in the records are noted to be associated with the nickel mineralization. We checked the pit walls to find only greenish crusts and small masses along with some massive sulphide pods of pyrite and a few small calcite crystals.

We enjoyed a great Nevada sunset and headed for Montgomery Pass, the nearest place with some firewood, to find a camping spot. We camped in the sage near an abandoned road bed about a half mile from the highway. At an elevation of near 6,000 feet with some snow on the ground it was cold, in the lower ‘teens, but a lively fire and a mug of coffee helped. Sam did say something about waking up feeling like there was a block of ice on his chest but I just figured that he had had too many hot dogs for supper.

In the morning we did some scouting around the area and then headed east and then south through the Fish Lake Valley to Crystal Hill. The route parallels the east flank of the White Mountains and it is a pretty drive. We arrived at Crystal Hill about 12:00 and enjoyed a good afternoon of digging.

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…

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.

In the mid-1970’s I spent some time working in SW Colorado in the La Plata Mountains near Durango. This area has produced significant gold (the Bessie G mine, for example, was active at that time) and has been investigated for its porphyry copper potential and uranium as well.

The Tomahawk Mine and basin are located above timberline in the western part of the complex. Rocks in the area include a variety of intrusives and metamorphosed sediments that form the high ridges and cliffs around the head of Tomahawk Creek. The Tomahawk mine produced gold in the last century. At the time I worked in the area there was still a very thin, rich vein containing visible gold accessible (if you were a skilled rock climber) on the cliff face at the creek near the mine ruins.

Above: Tomahawk Basin seen from high ridge to SE.

Below: Tomahawk Mine structures in 1975.

What passed for a road ended a few hundred yards west of the mine at a drill site located near a small intrusive complex. Talus from the high cliffs to the south of this intrusive contained scattered vugs that were mineralized with epidote, quartz, K-feldspar and rare fluorite. The fluorite crystals were simple octahedrons of a rich violet color. Their maximum size was about 2 mm.

I have always thought that it would be worthwhile to investigate the area for the source of the fluorite. Perhaps there are larger cavities and better crystals in the larger talus or lower cliff faces a few hundred feet up and to the south of the intrusive. Are there any of you energetic young collectors interested?