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 best time for collecting at Crystal Hill is in the late fall through spring. In spite of the elevation, about 5,200 feet, temperatures are too high for most daytime work during the summer.

Camping at the site is permitted but there is no wood or water. Winter temperatures can be severe and access may be barred during periods of heavy snow on the passes to the north and south.

Note that the E-W fence that passes over the crest of the hill appears to separate public from private property. Do not trespass to the North.
The main collecting areas are well defined by the numerous pits and rubble piles left by diggers over the years. The dirt and talus on the slopes of the hill contain many crystals weathered from the upper outcrops that may be recovered by sifting the soil and small rocks. The numerous cavities and pockets along veins contain the best crystals but are hard to find and require a great deal of effort to excavate. Open cavities in the silicified rocks along the base of the upper outcrops under the crest of the hill illustrate the nature of the crystallization.

Tools needed include heavy bars, sledges and wedges with the usual assortment of smaller implements for working pockets. Be sure to bring a whisk broom and a small shovel for moving surface dirt from outcrops. And please, pack it out! This location is very clean with hardly a cigarette butt or gum wrapper noted. Let’s keep it that way.

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 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.

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?

In the early 1980’s development work at the Homestake Mining Company Mclaughlin Mine project at the junction of Napa, Lake and Yolo counties in California turned up some nice stibnite specimens. Drill core from some areas contained scattered stibnite in veins and vugs, and in one case, stout crystals up to 3-8 cm in a wide calcite vein. The best specimens from this period, however, were found when a bulk sample decline was sunk in a near-surface part of the ore body. This work was designed to sample an area of the silicified Knoxville formation mudstone, a significant gold host on the property. Numerous quartz-chalcedony veins in the workings contained stibnite in masses, radiating sprays and in small vugs. The best specimens showed bright, needle-like sprays up to 3 cm in open vugs lined with bright micro quartz.

The muck (bulk sample) piles provided lots of fine samples, sometimes in masses of radiating crystals up to several pounds. The exposed faces in the decline were great for finding vugs, but were dangerous and usually only accessable after a blast when the fumes were sure to cause a nice ‘nitro’ headache. A contract minor was severely injured by rockfall at the working face during this period.

There are still a few of these specimens around; there should have been a lot available from the pit as it progressed, but I only have a few remaining. One is pictured here.