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.

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.

The Crystal Hill quartz collecting location is in Inyo County near the small community of Deep Springs just west of State Route 168. It is some 25 miles east  from the community of Big Pine which is on Route 395 south of Bishop. The small farming community of Oasis is found about 11 miles to the north. The collecting site is clearly visible on the west side of the road as a relatively small hill with brownish color protruding east from the main mass of granitic rocks in the range of hills. It is about half a mile from the highway. Near the center of this bowl-like valley is a cattle guard with a gate and electric fence on the west. A dirt track follows the south side of the fence line about .3 miles to a fork where the access to the collecting area continues to the right following the fence another .3 miles to a parking area at the base of the hill.

Nearby collecting areas of interest are Crystal Ridge (quartz crystals) northeast of Independence and Gem Valley (amazonite, beryl, quartz) east of Lone Pine. Both are reasonably accessible and, as described, have great potential for an active collector. The writer has not yet visited either site.