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The Ruby Mine, Sierra County, California

[Read this article from the California Mining Journal, April 1987]

The Ruby Mine is an underground placer and lode mine located between Downieville and Forest City, in Sierra County, California. It is in the Alleghany-Downieville mining district, a northern extension of the historic Mother Lode system, and situated in the Sierra Nevada foothills south of the Yuba River, approximately 100 miles north of Sacramento and 90 miles west of Reno, NV. The property covers approximately 2,312 acres consisting of the subsurface mineral rights to 2 patented claims comprising 435 acres, and 59 unpatented claims comprising approximately 1,877 acres.

The Ruby is one of California's best-known placer drift mines, and is considered by many to be one of the largest producing channel mines of modern times. It features a system of gold-bearing Tertiary channels that have already produced over 350,000 ounces of gold. The Ruby is also renowned for its production of coarse and jewelers-grade gold, with the largest gold nugget weighing 201 ounces. Gold nuggets from the Ruby are currently on display as the C.L. Best Collection at the Los Angeles County Museum of Natural History.

Location, Access, Physiography, and Climate

The Ruby Mine is located in southwestern Sierra County, in the northern part of the Sierra Nevada Foothills, Northern California. It lies approximately 25 air miles northeast of Grass Valley/Nevada City and is serviced by paved roads. Highway 49 passes through Downieville in the northern part of the area. The Pliocene Ridge road crosses the central part of the area and eventually merges with the Henness Pass road. There are paved spur roads to the town of Alleghany and the village of Forest City. The remaining few miles to the various mine sites are accessed by high quality, well maintained gravel roads.

The property is situated in the Sierra Nevada physiographic province and lies along the western slope of the Sierra Nevada Mountain range, at elevations varying from 2,500 feet in the canyons to more than 6,000 feet on the ridge crests. Regional physiographic conditions generally consist of gently to moderately rolling terrain, and steep sided plateaus with deeply incised streams and rivers.

The annual temperature varies between 10 and 100 degrees Fahrenheit. The annual precipitation varies between 50 and 70 inches, which falls principally as snow during the months of January, February and March.

Regional native vegetation typically includes pine, cedar and fir trees, manzanita, black oak, brush and native grasses. Commercial stands of second growth pine and Douglas Fir are sufficient to satisfy mine timber requirements, and there is ample water available. Rock Creek is the nearest year-round stream and water source to the site, which crosses the northern portion of the property generally east to west. The north fork of Oregon Creek (a seasonal drainage) also crosses the southern portion of the property from northeast to southwest.

Property Description

The Ruby Property covers approximately 2,312 acres, consisting of the subsurface mineral rights of two patented claims totaling approximately 435 acres and 59 unpatented claims containing approximately 1,877 acres. The mine encompasses at least eight distinct underground river channels and five known lode gold veins.

The Ruby property comprises two contiguous claim groups, the Ruby and the Golden Bear (aka Carson Camp), both of which include lode and placer claims. The Ruby claims combine three former producing gold mines; the Ruby, the Bald Mountain Extension, and the Wisconsin. The Golden Bear claims comprise several former producing mines as well, including the Golden Bear, the Ireland, and the Cincinnati. Collectively, the claims have produced in excess of 350,000 ounces of gold in a mining history dating from the 1850's.

The property covers one and one-half miles of strike length along the Eastern Melones Fault, the major structure along which many of the gold deposits of the Mother Lode are localized. The property also encompasses an estimated 4 miles of partially mined and unmined auriferous Tertiary channels. The Ruby is located on the northern extension of the historic Mother Lode system, as evidenced in the map below that shows the location of the Alleghany-Downieville mining district in relation to the overall Mother Lode.

The most recently active mining areas include the Ruby Portal and Lawry Shaft locations. Ruby Development Company maintains a Plan of Operations (effective through December 31, 2018) for its mining operations on public lands in the Tahoe National Forest, administered by the United States Forest Service (USFS). Current access roads to the site include Henness Pass Road, Sierra County Road 401, Forest Service Road 401-2, and Forest Service Road 30, along with a variety of small unimproved dirt connector roads. The site is primarily surrounded by public national forest lands administered by the USFS, with privately owned parcels adjacent to the northwest and northeast property boundaries. The privately owned parcels are designated for use as rural land, timberland, or mineral land.

History of Exploration, Development, and Production

Gold was originally discovered in the Alleghany-Downieville district in 1849, during the early days of the California Gold Rush. Since that time the district has produced at least 2.35 million ounces of lode gold from the vein deposits and at least 440,000 ounces of placer gold from the Tertiary channel deposits (not including an unknown amount of production from placer workings around Alleghany). Much of this production occurred intermittently, during relatively short periods of intense mining activity, separated by longer periods of minimal production when political and/or economic factors were unfavorable.

The history of the Ruby claim area dates from the 1850's, when placer gold occurrences were followed upstream from the North Yuba River to the headwaters of Slug Canyon where rich deposits of gold were discovered in a Tertiary gravel deposit at the site of the present City of Six Mine. By the 1860's several mines were developing the gravels of a buried river system within and adjacent to the boundaries of the present Ruby property at the headwaters of nearby Rock Creek. These mines included the City of Six, the Golden Bear and the Guatemala. The Golden Bear and City of Six mines are estimated to have collectively produced 96,000 ounces of gold.

During the same time period, gold-bearing gravel deposits were mined at Forest City, two miles south of the Ruby Mine. By 1880 it had become apparent that the mines at Forest City and those at Rock Creek were located on the same channel system. The Ruby portal was collared in December, 1880 to access the central portion of this rich river system. Between 1880 and 1889 the Ruby Mine produced 86,500 ounces of gold from three buried river channels.

By the turn of the century, interest in drift mining had waned and attention turned to lode gold prospects In 1916, the Carson Mine, just north of the Ruby Property near the City of Six Mine, was developed by the sinking of the Rippin shaft. The Cincinnati and the Ireland mines were also probably active at this time. During the 1920's and 1930's, over 2,000 feet of development was carried out on the Carson vein, while the Cincinnati vein was developed from the Golden Bear crosscut.

The increase in the price of gold during the early 1930's helped to revive interest in drift mining on the Ruby property. C.L. Best, the co-founder of Caterpillar Tractor, acquired the Ruby Mine, and developed the Black channel. Best Mines produced an estimated 58,000 ounces of gold from the gravels before the government forced closure under War Production Board Order L-208. C.L. Best saved 123 nuggets of $100 value or greater for a personal collection. That collection is presently on display at the Los Angeles County Museum of Natural History.

After the Second World War, the cost of labor and supplies rose rapidly, while the price of gold remained frozen at $35 an ounce. The mine was not re-opened by Best and it was sold after Best's death in 1951. The Ruby Development Company acquired a lease on the Ruby Mine in 1959 and bought the property outright in 1966. Lessees intermittently worked the gravels of the Black channel from the Lawry shaft until the mid-1970's.

In the late 1970's the Ruby Mine was leased to Alhambra Mines of Sparks, Nevada. During that same period, the Golden Lion Mining Corp. rehabilitated the Carson Mine and produced a small quantity of ore from the upper level. The Golden Lion Mining Corp. also attempted to drive a decline to access the Cincinnati channel, which had previously been discovered in the quartz workings of the Cincinnati vein.

The Brush Creek Mining and Development Company, Inc. (“Brush Creek”) acquired the Ruby in 1990. From 1990 through 1995, Brush Creek rehabilitated and re-timbered approximately one and one-quarter miles of horizontal haulage tunnel supports and a 210 foot vertical shaft for access and mine safety, constructed a new wash plant and quartz mill, built underground roads for use by diesel loaders, installed a hoist and constructed a new sixty-foot steel head frame over the Lawry Shaft at the Ruby Mine, installed a complete underground ventilation system and electrical system at the Lawry Shaft, constructed a new waste water treatment system for use at the mill site, and modified and enlarged the structures and ore bins at the mill site. Brush Creek’s total investment in the Ruby was $4,554,575 as of June 30, 1997, including $2,251,714 of development costs, and $1,975,525 of mining equipment, most of which remains intact and in good operating condition. Production during this period was limited. From December 1992 until July 1993 an estimated 7,300 tons of mineralized material was mined, resulting in the recovery of approximately 200 ounces of gold. Brush Creek stated that these preliminary results were too small to be a reliable representative sample of the expected placer grades. In 1994, approximately 400 tons were mined from the Lawry channel, at an average grade of 0.2 ounces per ton. However, by 1995, falling gold prices caused mining operations to be suspended, and except for limited periods of sporadic activity over the next few years, the mine was put on care and maintenance. Brush Creek briefly resumed operations in 1998, driving a development tunnel in the south Lawry Shaft workings. The property was eventually forfeited and returned to the Ruby Development Company, who has maintained the property and permits to the present day.

Lawry Headframe

Plant, Equipment, Permits, and Site Infrastructure

Site inspections conducted during June and July, 2010 by C. Gary Clifton, a certified professional geologist (P.Geo.) retained by the Company as an independent consulting geologist to inspect and assess the Ruby Mine, and by management in September, 2010, confirmed that the Ruby is in excellent condition, and has been well maintained despite having not been operation since 1998. The equipment currently on-site at the Ruby was mostly purchased in the period between 1990 and 1995 when the mine was last in production, and is therefore between 15 and 20 years old. The equipment, including the wash plant and mill facilities, has been confirmed to be in good working order, though some minor upgrades are expected to be needed once operations resume.

The equipment, fixed assets, and infrastructure in place have been valued at an estimated $3.5 million, and include a 1,000 yard per day placer wash plant, 50-ton per day quartz mill, 6,000 feet of tracked haulage, and related support equipment needed for underground mining operations. A second exit, the Lawry Shaft, almost 2 miles from the main portal, can provide natural ventilation for much of the underground workings. Surface buildings and facilities include a lumber mill, machine shops, offices, and accommodations. The property also features an excellent system of roads, is accessible via paved highway from Reno or Sacramento, has abundant water and timber available for mining purposes, and has PG&E power available on-site.

Interior of quartz mill. Ball mill (toothed edge) in rear,
concentrating tables at left.

Permits in place include a Plan of Operations, a Phase I Environmental Site Assessment, a Water Order, and a Reclamation Plan secured by $171,000 in Reclamation Bonds. The current Plan of Operations was approved by the US Forest Service in February, 2011, and is effective through December 31, 2018. The Waste Discharge Order must be reviewed and approved by the Water Quality Control Board prior to the commencement of mining operations, and the Annual Fee for Waste Discharge Requirements for 2013 has been paid and is up-to-date. The Reclamation Permit has been renewed through April 2018, and a Reclamation Bond of $171,000 is in place.

Skilled underground hard-rock and placer miners with considerable experience in the local ground conditions reside in the area and will provide a valuable resource in the present and future development of the Ruby.

Recent Geological Assessment Work

The Ruby Mine is an underground mine that is known to have produced over 350,000 ounces of gold since the 1850’s, but which currently has no known estimates of proven reserves.

Geological assessment work carried out by Mr. Gary Clifton, P.Geo., during the summer of 2010, including extensive research to evaluate the resource maps and data from Brush Creek Mining’s operations in the 1990’s and Alhambra Mines in the early 1980’s, has identified 3.03 miles of unmined channel and 0.95 miles of partially mined channel available for mining using the existing infrastructure. The following table provides the estimates of each channel surveyed by Mr. Clifton in July, 2010. In compiling the data, the Pilot Channel is considered the northern extension of the Black Channel and the Mt. Vernon Channel is a tributary. In addition, the stretch of Black Channel between the Big Bend and the Lawry Shaft is designated as partially mined, as is one-half of the stretch of the same channel between the Lawry Shaft and the mined portion of the Pilot Channel at the northern property boundary. All measurements are in feet.

Channel Mined Partially Mined Unmined Total
Bald Mtn 7,500 -- -- 7,500
Deep Rock Creek 5,500 -- 2,000 7,500
Cincinnati -- 1,500 4,500 6,000
Black and Pilot 2,000 3,500 3,250 8,750
Mt. Vernon -- -- 3,000 3,000
Bald Mtn Extension 2,750 -- 3,250 6,000
Totals (miles) 3.36 0.95 3.03 7.34

An estimate of unmined gold was obtained by extrapolating the known average mining width and height of 200 by 6 feet, and an average historical grade of 0.164 ounce per cubic yard (27 cubic feet). It is further assumed that partially mined channels contain 50% less gold. From these calculations, it is currently estimated that 134,844 ounces of gold are available for near-term recovery from these channels using the existing Ruby infrastructure.

Partially mined channels: (200 x 6 x 5,000 x 0.164 x 0.5)/27.0 = 18,222 ounces
Unmined channels: (200 x 6 x 16,000 x 0.164 x 1.0)/27.0 = 116,622 ounces
Total (inferred) unmined ounces: = 134,844 ounces

Additional channels as well as lode deposits in quartz veins are known to exist on the property. These will require additional development and no attempt has been made as of yet to estimate the amount of gold they may contain.

During the 2010 summer program, 35 samples were collected by Mr. Clifton from the Lawry Shaft workings and sent to American Assay Laboratories Inc. in Sparks, NV for fire assay analysis. The samples, each weighing approximately 1 kilogram, were collected at 10-foot intervals at the gravel-bedrock interface at 5 locations (A through E) within tunnels and crosscuts. At location C, samples C9 through C12 returned several high values, including 45.5 grams (1.45 ounces) and 15.05 grams (0.48 ounces) per metric ton (tonne) gold, as per the table below. This represents a 30-foot wide zone of placer gold-enriched sediments in which 3 of the 4 samples are highly anomalous. This zone is considered mining width. Having delineated a 30-foot wide zone with a limited 35-sample set, we believe this indicates that gold-rich gravels are relatively abundant, easily identified, and present in existing workings ready to be exploited. .

SAMPLES lbs ppb
A1 1 4
A2 2 4
A3 1 3
A4 2 11
B1 2 12
B2 2 8
B3 2 14
B4 1 72
B5 2 61
B6 2 9
B7 2 4
C1 3 5
C2 2 3
C3 2 3
C4 2 4
C5 3 7
C6 2 20
C7 2 7
C8 2 14
C9 2 15050
C10 2 18
C11 2 45500
C12 2 785
D1 2 453
D2 3 6
D3 3 49
D4 3 12
D5 3 12
E1 3 23
E2 2 12
E3 3 8
E4 2 8
E5 3 15
E6 3 10
E7 3 25

Typical channel gravel on bedrock (white), glove for scale.
Note irregular but smooth surface of base of channel and irregular size
of river gravels. All rocks are well rounded and polished, indicating
long transport. Placer gold must be more local in origin.

Regional Geology

The geology of the region consists of Mesozoic and Paleozoic metavolcanic rock, Paleozoic Calaveras Formation rocks (phyllite, schist, with thin beds of metachert), and Silurian slate with subordinate chert, conglomerate and sandstone. The Mesozoic era occurred between approximately 65 and 248 million years before present (MYBP). The Paleozoic era occurred between approximately 248 and 543 MYBP. The Silurian period was part of the Paleozoic era, and occurred between 417 and 443 MYBP.

Local Geology

The Alleghany-Downieville gold mining district is situated in the northern pan of the Sierra Foothills Metamorphic Belt, to the west of the Sierra Nevada Batholith. The district forms the northern continuation of the Mother Lode System, a major, north-northwesterly trending metallogenic province that extends for a distance of 160 miles and has produced over 125 million ounces of gold.

Most of the gold mines within the Mother Lode System are localized along the Melones Fault, a steep, easterly dipping crustal-scale suture that extends from Mariposa County in the south to Plumas County in the north. This structure marks the boundary between several tectonic terrains. In the northern part of the foothills belt, the structure defines the contact of continentally derived sediments of the Paleozoic Shoo Fly Complex to the east, with generally younger oceanic and volcanic island arc rocks of the Western Assemblage to the west. In the south, the structure marks the boundary between the Calaveras Complex, an Upper Paleozoic sedimentary sequence of deep water, oceanic affinity to the east with rocks of the Western Assemblage to the west.

Geology of the Ruby Property

The Ruby Property covers one and one-half miles of strike length along the Eastern Melones Fault, the major structure along which many of the gold deposits of the Mother Lode are localized. The property also encompasses an estimated 4 miles of unmined auriferous Tertiary channels. The Ruby is considered part of the northern extension of the historic Mother Lode system.

The locus of the Melones Fault coincides with a discontinuous zone of intensely sheared and variably altered serpentinite, commonly associated with more massive gabbroic rocks. These rocks are believed to represent part of an ophiolite suite. At the latitude of the Alleghany-Downieville district, the Melones Fault zone is up to 4 miles wide. At this location, the fault zone is occupied by a serpentinite-hosted melange of ophiolitic rocks, blueschist to greenschist-grade oceanic sediments and mafic volcanics, as well as complexly deformed, amphibolite-grade Paleozoic rocks

Mineralization and Deposit Type

The primary mineralization at the Ruby is gold. The primary deposit type consists of gold-bearing Tertiary-age channels, as exemplified by the Bald Mountain and Bald Mountain Extension channels, both of which have been among the most prolific gold producers in the Alleghany-Downieville district. Younger intervolcanic channels also formed rich placer gold deposits where the younger river system eroded and redeposited the auriferous gravels of the older channels. Examples of this type of younger channel include the Black channel in the vicinity of the Big Bend in the Ruby Mine and the Deep Rock Creek channel, which reworked extensive stretches of the Bald Mountain channel.

Distinct concentrations of placer gold have also been associated with the existence of quartz gold deposits. Some of the most productive quartz gold deposits in this area were discovered in the bedrocks while mining the placer channels. The quartz veins in this region typically extend to thousands of feet in depth, and are noted for rich ore shoots often containing spectacular pockets of Gold-in-Quartz. The Ruby is known to contain quartz vein deposits, as exemplified by the Wolf Vein near the Bald Mountain Channel.

Another photo of base of channel in Lawry workings.
Large boulder at top left is approximately one foot in diameter.
Again, very irregular mix of large and small boulders.
Gold is in the sand that binds the rocks and within the cracks in the basement rocks (white to gray).

Ruby Mine Mining Plan

The Ruby mining plan anticipates that much of the first season will be engaged in determining the exact locations of the targeted channels identified by our geologist from historical resource maps and recent geological surveys, with exploration drifting (tunneling) and establishing mining headings in these channels.

Prior to the start of mining operations, the initial startup work has concentrated on rehabilitating the Ruby tunnel, renovating the Ruby Mill, improving the infrastructure, and getting the Ruby facilities and equipment into good working order. The Company began rehabilitation of the Ruby tunnel in October, 2011. The initial phase of this work was completed in the third quarter of 2013 with the restoration of natural air flow throughout the extent of the Ruby tunnel and the reopening of the tunnel for a full mile to restore access to the Black Channel and the Big Bend mining targets. Mill renovation has been completed, and the wash plant is fully operational as of the date of this prospectus.

The Pilot and Mount Vernon Channel targets are projected to lie in the near vicinity of the existing Lawry Shaft workings. Active exploration tunneling (“drifting”) with air-powered slushers and trackless loaders (“LHD's”) is expected to be underway shortly after mining operations begin and the Lawry Shaft section of the mine is fully rehabilitated.

Construction of the 1,500 foot Deep Rock Creek Project access tunnel can also begin once full mining operations commence. This tunnel will be a tracked haulageway. The rate of progress will be determined by the amount of time required to complete the maintenance program in the Ruby tunnel beyond the “Daylight Turn” where the Deep Rock Creek Access Tunnel begins. This maintenance will also be required prior to constructing the Big Bend Bypass Raise to the Black Channel workings. This maintenance work was completed in the third quarter of 2013. Construction of the Big Bend Bypass Raise is currently in progress as of the date of this prospectus. The Company has commenced test mining (bulk sampling) operations in the White Channel section of the Ruby tunnel, which as of the date of this prospectus has been suspended pending further evaluation.

The mining plan anticipates a “herring bone” drift pattern for exploitation of the channels. A central tunnel (known as a “drift”) will be driven following the gut (deepest part) of the channel. This drift will be continued until the end of the channel is reached and the length of the resource has been defined. Regularly spaced crosscuts (known as “crosscut drifts”) will be driven out on each side of the central drift to determine the width of the channel.

The material mined from these drifts will be washed in the placer plant. Careful records of the gold recovery will also provide a grade for the material “blocked out” in this process, thereby developing a proven resource to be mined in the production phase of the mining plan.

The Ruby Mine typically experiences considerable snow fall, and a decrease in activity is planned for during the winter months of Year 1. It is expected that the Ruby will operate year-round once the operation is well established.

We are currently building a raise from the end of the Ruby Tunnel into the Big Bend and the Black Channel section of the mine. The Big Bend and the Black Channel were the areas of the mine where CL Best produced over 58,000 ounces of gold in the period just before WWII, and represents an important mining target. We expect this work to be completed by the end of May, 2014. Once completed, it will then be determined if mining can commence at that time, or if further work is required to rehabilitate the Black Channel prior to the start of mining that area.

We are also currently engaged in drilling newly identified mining targets closer to the Ruby Portal. These targets are the result of geological mapping by our geologist as well as a recent-completed gravity survey that identified the location of these new targets that deserve further exploration and investigation. If this drilling produces positive results in any of these new targets, a raise will be built into the new location and mining can begin fairly quickly.

Q2 2014 drill targets currently underway

Quartz Gold Potential

This mining plan is built on exploiting the Ruby Mine's well-known placer gold potential. The Ruby also hosts known quartz veins which have produced gold, such as the Wolf Vein (1,625 ounces), and which offer the possibility for production of quartz gold. The Ruby Property contains many untested quartz veins exposed in old workings that are excellent targets for exploration and development.

"Lines of Coarse Gold" were noted by the miners who worked the channels in the Ruby, and such distinctive concentrations of gold have been associated with the existence of quartz gold deposits. Some of the most productive quartz gold veins in the Alleghany District -- including hundred-thousand-ounce producers such as the famous Sixteen-to-One, Oriental, Rainbow, and Plumbago-- were discovered in the bedrock while mining the placer channels.

The quartz veins in this region typically extend to thousands of feet in depth and are noted for rich ore shoots often containing spectacular pockets of Gold-in-Quartz running hundreds or thousands of ounces per ton. Considering the large size and coarse nature of the Ruby’s nuggets, and the fact that both the Melones Fault structure and the probable northern continuation of the 16-to-l vein system pass directly through the Ruby Mine Property, the Ruby Mine has an excellent potential for long-term quartz gold production in addition to the Ruby's famous placer nuggets.

Operational Considerations

The southern working area, the Deep Rock Creek Project, is accessible by the Ruby Tunnel, which is equipped with 30 lb. rail and 4" Victaulic steel compressed air pipe. The northern area, the Lawry Shaft Project, will be mined by LHD's from the existing tunnel system.

On the north end, entry to the mine is through the Lawry Shaft which has a steel headframe and a complete hoist house and hoisting facilities for men, ore and materials. There are two LHD's with 1 yd. buckets underground. There is a 40 hp. fan and a secondary ventilation fan with fan line as well as water and compressed air lines and electrical service underground. Electricity in this area is provided by PG&E and a 150 kw diesel generator providing backup power. A 250 cfm electric compressor located on the surface provides compressed air.

The south end of the mine is accessible by a portal. Electricity is provided by 250 kw and 55 kw diesel generators and compressed air by a 750 cfm diesel compressor. There is a 40 hp. ventilation fan located underground, electric and diesel trammers, and ore cars and flat cars. The site has a shop with an electric overhead hoist on a track and various tools, mill buildings, a 4,500 gallon diesel tank with containment basin under cover, a 1,000 yard-per-day placer gravel recovery plant and a 50 ton hard rock quartz recovery plant.

The north and south ends of the mine are connected underground, which facilitates ventilation and provides an exit at both ends.

The north end has a 2 story bunkhouse which can provide accommodations, a trailer which can also be used for accommodations, and an office. The adjacent cook shack will accommodate several more people. There is a 40' by 70' steel shop building on a concrete slab, a 10,000 gallon double-walled diesel tank, and other buildings. Electricity in this area is provided by PG&E.

The property contains Douglas fir trees which can be used for mine timber. The Forest Service has marked trees for cutting, and there is a bandsaw lumber mill on the property. Several thousand board feet of milled mine timbers are currently onsite.

The property is serviced throughout by a system of good dirt roads and oiled roads, with paved roads to the property from Highway 49. The property has a great deal of flat and useable areas available, and there is ample working room around the shops and other buildings.

The mine has rock drills, slushers and tuggers, additional fans and pumps, both air and electric powered, and much miscellaneous equipment, tools, and supplies. The mine also has a Peterbilt water truck, International flatbed truck, Oshkosh 4x4 dump truck, and Hyster equipment trailer. There is a large dump facility as well as ponds for water storage and ample process water that exits from the Ruby Tunnel.

Description of Mining Process

Although the grades encountered in the ancient river channels of the Alleghany District are extremely high relative to most placer deposits elsewhere in the world, underground mining costs are also much higher than the cost of open pit or dredge methods employed in most present-day placer operations. This cost reality, together with the erratic distribution of the gold, requires that selective mining methods based on strict grade control be utilized in order to achieve a profitable operation. We currently estimate that our cost of mining will be approximately $500-600 per ounce, though the cost could be higher, depending on the average grade of gold per yard mined and milled.

A cost effective underground mining operation is accomplished by a two-phase process:

(a) Development occurs on the advance by drifting upstream or downstream along the axis of the channel, with crosscuts driven every fifty to one hundred feet. The muck from these workings is slushed to ore passes that lead to the main haulage level within the bedrock below the channels. This production is accompanied by face and rib sampling and by bulk testing of the muck from the development headings. Each round is quantitatively analyzed to map out the grade distribution of the gold. This work is followed by;

(b) Selective mining--termed breasting-- during the retreat, using the drift as the main haulage-way and leaving pillars of sub-ore grade material. This is facilitated by careful mine planning based on the geometry of the channel and the grade distribution ascertained from the development phase.

Interior of ore car station. One cubic yard cars in front and electric locomotive.

Description of the Recovery Process

The mined gravel (muck) is transported from the mine along the tracked haulageway to the mill and dumped into the ore bin directly above the gravity separation washing plant. The wash plant is a closed-circuit system which recycles the wash water. The gravel is scraped onto a feed belt which elevates and dumps the material into the scrubber (trommel -- a large, inclined metal cylinder). Water is added and the scrubber is rotated in a clockwise direction at twelve revolutions per minute to thoroughly wash the gravel. Retaining rings inside the scrubber catch the larger gold nuggets. The washed gravel is discharged through slots in the final section of the scrubber that serve as a sizing screen. All plus 3/4 inch material is rejected to the coarse material belt which moves the reject gravel to the stacker belt for transport.

Trommel on placer gold circuit. Fines dropped through slits on
bottom end and are diverted to a sluicing screen and trap.

The remaining minus 3/4 inch material and excess water falls onto the walking bottom sluice box. This sluice box is a gravity separation device which utilizes Hungarian riffles mounted on a moving rubber belt to trap all high specific gravity material. The riffle bed rotates up the grade through the sized material and water, cycling completely every twenty minutes while continually dumping the heavy concentrate into the live bottom sluice box.

All lighter material not trapped in the Hungarian riffles is washed off the discharge end of the walking bottom sluice box and over a 1/8 inch vibrating dewatering screen. The dry plus 1/8 inch, minus 3/4 inch material is vibrated onto a skid plate that loads directly onto the stacker belt for transport to the waste dump. The minus 1/8 inch material and water is discharged into the dewatering sand screw.

The live bottom sluice box utilizes a cam-operated jigging action within its bed to further concentrate, grade and separate all gold and other high specific gravity material. The trapped gold and heavy concentrate is cleaned from the box once a day and transported to the gold room for final cleanup.

The lighter material not concentrated within the bed is washed out of the live bottom sluice box with the excess water and discharged into the dewatering sand screw. The coarser material is dried by the dewatering sand screw and dumped onto the stacker belt. The finer waste material is discharged with the wash water to the primary settling pond. The wash water continues to the second settling pond from which it is pumped back to the scrubber at the head of the system. Water discharging from the tunnel is piped to the head of the system by gravity as needed for make up water.

A backhoe is used as required to bail the fine settled material from the primary settling pond to dry before transport to the waste dump.

Ruby Mill in operation