Field Trip Reports

Jim Paschis lead a DREGs field trip to the Cash Mine in September 2007

Operations Summary of the Cash Mine, Mount Royal Ventures, LLC.
By Jim A. Paschis

Location The mine is in the central part of Sec.12, T1N, R72W, Gold Hill Mining District of Boulder County, Colorado, U.S.A. The town of Gold Hill lies in the western part of the section. Access is by way of County Road 52 (9145 Sunshine Canyon Drive), 9 miles west of Boulder at the Front Range foothills.

Cash Mine Headframe

Discovery history Placer gold was first discovered in the county in 1859 on Gold Run whose watershed includes the Cash Gulch. Gold-silver telluride veins were later discovered and staked in 1872. The lode discovery by B.N. Sanford is the Cash claim, M.S. #62, December 19, 1872. The mill site claim is the Cash No. 2 M.S. #544b by A. McClellan, September 10, 1872.

Mine development Access was by the Cash shaft following the steep northwest dipping vein to the 9th level. The head frame and hoist are in view on travel down to the current development at the 3rd level adit, 7,840 feet above msl. From that portal, 18-gauge track intersects the NNE striking Freiburg vein and extends through a cross-cut to the ENE striking Cash vein. On the Cash drift the secondary escape and ventilation raise collar are east of the Cash shaft. Currently, there are ten stopes in final development phase to provide 50 tons-per-day ore to the Gold Hill Mill near the mine property entry.

Geologic setting The intruding Boulder Creek Granodiorite, a 1.7 byr catazonal pluton, assimilated older Precambrian schist and gneiss in the area leaving only small xenoliths. This imparted a northeasterly biotite and feldspar phenocryst layering to the host rocks. This orientation is cross-cut by the 2nd order northwest trending, Laramide-reactivated Precambrian, Hoosier breccia reef structure, just west of the mine.

The mining district is one of several gold-silver telluride and tungsten districts on this part of the NE-SW trending Colorado Mineral Belt. This trend hosts a very wide variety of hydrothermal ore deposits and is coincident with a series of post-Laramide shallow intrusives along the Precambrian Idaho Springs Ralston shear zone. This shear is part of the 1st order, continental scale, Colorado lineament.

Geologic dating four miles south in the Boulder Falls-Sugar Loaf Mining District is 48 million years bp in a partially mineralized, latite porphyry dike cross cutting a ferberite vein. Tungsten and telluride mineralization is locally coeval and suggests that possible timing for ore at the Cash Mine telluride veins. Emplacement was possibly beneath at least 2,000 feet of pluton topped by the Eocene Flattop peneplain of the Colorado Front Range.

Mineralization Geologic site and mine mapping by Russ McClellan in the 1940’s provides further geologic insight to the many veins on the property. Very important to the property acquisition was the extremely detailed and verified gold and silver assay record provided by McClellan. This record guided stope development as late as the 1960s. Lower grade vein portions peripheral to those stopes are now undergoing re-evaluation and stope development by MRV. The ore-hosting veins are within shears and near aplites suggestive of re-activation of Precambrian structures. Pre-vein fault geometry controls the extent of ore deposition.

Gold is found as fine leaves, rarely as striated, curled horn, and as inclusions in the common silver telluride, hessite, on the 3rd level. The ore has a general ratio of Au : Ag = 1 : 6. Pyrite, galena, sphalerite and chalcopyrite with rare scheelite are associated with the tellurides. Fine-grained quartz, varying from clear to dark gray, locally known as “horn quartz” is the major gangue with subordinate carbonates and clays. Sulfidation of biotite left chlorite and pyrite flanking the veins.

Milling The mill makes a Knelson gravity gold concentrate and a froth flotation circuit produces a sulfide telluride concentrate. XRF analysis revealed that flotation beneficiation of 12 times was essentially identical with fire assay values. The concentrate is shipped off site for pyrometallurgical recovery of silver and gold.

Brittle Structures, Kinematics, and Hydrothermal Alteration in the Central Colorado Rocky Mountain Front Range
A U.S. Geological Survey and Denver Region Exploration Geologists Society Field Trip, June 2, 2007
Jonathan Caine, (U.S. Geological Survey) and John Dreier (DREGS).

The evolution of the Colorado Rocky Mountain Front Range (FR) is intimately associated with pervasive brittle deformation, fluid flow, economic mineral deposition and hydrothermal alteration. Regional to local structural control of the major mining districts and hydrothermal mineral deposits has long been recognized in the Colorado Mineral Belt (CMB). However, the controls on strength, permeability, and rheology of various geological structures in relation to mineral deposit formation are poorly documented and understood. As part of ongoing USGS research, structures resulting from protracted brittle deformation in the Front Range are being examined in detail using an integrative approach to better understand this complex system. The field trip objectives were to show participants key localities that exemplify the details of structures, show preliminary data and conceptual models, and foster dialogue.

Topics discussed included:
1) the structural history of the central FR.
2) evolution and localization of the metal-bearing hydrothermal systems in the CMB.
3) the effects of brittle structures on ground water.

Use the above map to locate the location of the photos below.

Stop 1 - Clear Creek Quarry fault core, bordered
by “damage zone.”

Stop 2. Sheeted veins at left.

Stop 3. Blackhawk. “Slickenlines and shear sense indicators on this fault vein are an example of the many such structures that Bob Moench and others used to infer Laramide shortening directions associated with the formation of these mineral deposits. Caine took this one step further and used these data to model the paleostresses and show that permeability was controlled by the development of new fractures and the opening of preexisting fractures that were optimally oriented in the Laramide stress field. The model ENE shortening direction adds confirmation of the early work and new work along the eastern flank of the Front Range uplift,” (Caine, 2007).

Stop 4. Coal Creek Canyon. (Left) Laramide fault reactivation. (right) Clay-rich alteration at contact.

Stop 5. “Reef structures” (Magnolia Road)

Stop 6. Maxwell Reef

Field Trip to SM-18 Mine September 23, 2005

Jim Pachis led a DREGS field trip to the SM-18 Mine September 23, 2005. A group of 13 were given an underground tour of Cotter's SM-18 Mine near Uravan. Geologists Dick White and Jane Zimmerman gave us a great tour of the mine.

The mine is located in southwest Colorado on the Colorado Plateau. It is found within the Uravan Mineral Belt, which resembles an arcuate lobe that extends from Polar Mesa in Utah, southeast into Colorado, and then bends to the south, and terminates along the southern boundary of San Miguel County (See Map). The SM-18 Mine is located at Uravan, in Montrose County, Colorado, along the San Miguel River.

History

The southern Utah - Colorado border area is known for uranium mainly in continental sandstones of the Salt Wash Member of the Upper Jurassic Morrison Formation. In 1898 uranium was first identified from the southwestern Colorado area but the deposits were sought primarily for their radium content. Early research was done be Pierre Curie and Marie Sklodowska Curie using radium concentrates from these ores for their work in France. Ores found later in the Congo (Shinklobwe Mine and others, about 1912) were characterized as being higher grade than Colorado ores, which caused the industry in Colorado to slacken. The recognition of the accompanying ferroalloy metal vanadium in the uranium ores led to a reopening of the mines. Tailings were located on a small island in the middle of the San Miguel River near the later town of Uravan after the metallurgical processing and recovery of vanadium.

Present day Uravan and the San Miguel River as seen from SM-18 (note the islands). © Doug Piper 2005

Note from Doug Piper: It is interesting to compare the above photo with my memories from a visit to Uravan in the late 60's. In the late 60's, Uravan was s small town covered everywhere with yellow dust - most memorable was the yellow dust. For more information on the history of Uravan including photos go to www.uravan.com/uravan.

In 1942 the intensely focused Manhattan Project sought uranium from all sources and the first available were the milled vanadium tailings - containing uranium. With the Hiroshima and Nagaski bombings ending WWII, the Cold War was on, and uranium prospecting and mining boom in the area regulated by the Atomic Energy Commission (AEC) continued until 1968. Uranium demand continued until the Three Mile Island and later Chernobyl incidents slowed nuclear plant development. Finally in the beginning years into this century, uranium prices bottomed out with the release of nuclear weapons stockpiles. With the consumption of these sources, present day prices are on the rebound to about 75% of the peak highs of 1980.

SM-18 Mine

This mine was acquired under the AEC lease program. It had originally been patented in 1926 for the contained vanadium as the Wright Mine. The ores mined are in the uppermost of three essentially flat-lying sandstone beds. The sandstones total about 300 feet thickness separated by mudstones.

The original uranium source is believed to be volcanic ash. The ash, erupted from volcanics to the north, was transported as airfall, and was deposited on continental sand and muds. Uranium, mobilized during the devtitrification of the glass, was by circulated by meteoric water and reduced by organic detritus.

The ratio of U:V at this mine is about 1:5. Farther south vanadium content increases the ratio to as high as 1:20. Uranium grades in the mine range from 0.2 to 0.25 per cent U3O8 and vanadium grades are approximately 1.3% V2O5. The mine has between 20,000 to 300,000 tons of reserves. Reserves in the mine are based on core drilling from the top side of Spring Creek Mesa (abbreviated as SM, and incorporated into the current mine name - SM-18). Several of these vertical core and rotary drill holes could be seen in the stope faces examined.

Primary minerals identified here are uraninite, pitchblende, and montroseite in addition to minor sulfides of galena, sphalerite, and chalcopyrite. Upon contact with moist mine air visible yellow carnotite, a secondary mineral, forms as a crust on the primary black mineralization. Locally grades are as high as 2 percent U3O8. Uranium appears to be localized by organic detritus which act as reductants to precipitate uraniferous minerals at short travel distance laterally, coincident with soft sediment dewatering prior to lithification. This is a rather different orogenesis than the hydrologic models developed for the oxidation - reduction interface mineralization concepts developed in the Wyoming sedimentary formation basins.

Exploration

Cotter Corporation, which is now a General Atomics subsidiary, has drilled to as deep as 650 feet from surface in previous years. Ore delineation drilling was on 100-foot centers looking for thicker sands with reduced appearance. Most of the surface drilling was by rotory air. Drilling was followed up by truck mounted borehole gamma probes. Drill hole spacing at 100 -foot centers is not tight enough to fully delineate significant orebodies, and consequently ore horizons are followed underground along stratigraphic markers. Exploratory drifts are developed to further delineate the extent of subsurface mineralization.

Production

Cotter Corporation has a total of four producing mines in the Uravan Mineral Belt. In addition to the SM-18 Mine at Uravan, they have three underground mines to the south on the Monogram Mesa which are the JD-6, JD-8 and JD-9 Mines. The SM-18 Mine produces 150 tons/day and the remaining three active mines produce approximately 350 tons/day. The ores are trucked about 300 miles to the Canon City Mill for processing. Currently, Cotter Corporation is driving a 1,380-foot decline in the Slick Rock District on the south end of the Uravan Mineral Belt near Egnar. This mine, SR-11, may be in production in the later part of 2006.

DREGS Field Trip to the MolyCorp.'s Questa Mine, New Mexico

Jim Paschis led a group of 10 DREGS members on the 2006 DREGS field trip to Molycorp's Questa Mine. The field trip took place on Monday, February 26th. The Questa Mine, located in the Sangre de Cristo Mountains, is about 20 miles south of the Colorado - New Mexico border. It lies 5 miles east of the small town of Questa, and 6 miles west of the Ski Resort at Red River. The trip was a 4.5 hour drive from Denver, and the weather for our field trip was unseasonable warm, in the low 60s.

Molycorp was a subsidiary of Unocal until Chevron acquired Unocal last year. After the acquisition, Molycorp became a subsidiary of Pittsburg & Midway Coal Mining Co. (P&M) which is a subsidiary of Chevron.. Molycorp operates the Questa Mine and Mill in New Mexico, and owns the Mountain Pass Rare Earth Mine in California. Molycorp.'s Chief Geologist, Bruce Walker and its Senior Geologist, David Jacobs led the mine tour. In the morning Bruce and David gave an impressive presentation to our group. The material presented was instructive, and gave us an appreciation of the geology and mining, and environmental aspects at Questa. The afternoon was dedicated to a surface tour, which an overview of the surface geology, open pit mine workings, and important environmental features.

Here are a few photos from the field trip. A more detailed account of the field trip is forthcoming