Briggs Mine

Producer in Inyo county in California, United States with commodities Gold, Silver

Sections on this page

Identification information
Geographic coordinates
Site location context
Geographic areas
Public Land Survey System information
Commodities
Materials information
Alteration
Mineral occurrence model information
Host and associated rocks
Nearby scientific data
Geologic structures
Ore body information
Controls for ore emplacement
Economic information about the deposit and operations
Mining district
Land status
Ownership information
Bibliographic references
General comments
Reporter information

Geologic information

Identification information

Deposit ID	10310699
Record type	Site
Current site name	Briggs Mine
Alternate or previous names	Briggs, C.R. Briggs

Comments on the site identification

This record refers to the modern mining operation at the Briggs deposit.

Geographic coordinates

Geographic coordinates:	-117.185, 35.9375 (WGS84)
Elevation	480
Location accuracy	100(meters)
Relative position	34.3 miles N 51? E of Ridgecrest CA

Site location context

Political divisions (FIPS codes)

Inyo(county)

California(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Manly Fall(quadrangle 1:24,000 scale)

Ridgecrest(quadrangle 1:100,000 scale)

Trona(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Panamint Valley(hydrologic unit)

Northern Mojave(hydrologic accounting unit)

Northern Mojave-Mono Lake(hydrologic subregion)

California(hydrologic region)

Federal lands

Bureau of Land Management(Bureau of Land Management CA)

Bureau of Land Management CA BLM(Type of land area)

BLM(Federal land areas administered by BLM)

Geographic areas

Country	State	County
United States	California	Inyo

Public Land Survey System information

Meridian	Township	Range	Section	Fraction	State
Mount Diablo	023S	044E	11,12,13,14		California

Comments on the location information

The location point selected for longitude and latitude represents the Briggs Mine adit symbol near the head of the alluvial fan at the mouth of Redlands Canyon below Manly Fall shown on the 24K Manly Fall Quadrangle.
The C.R. Briggs Mine is located 58 road miles NE of Ridgecrest, CA, via State Hwy 178 (paved) and Wingate Road (gravel). The route passes through the town of Trona near Searles Lake and ghost town of Ballarat in Panamint Valley. The mine is located 4.3 miles WNW of Manly Peak, at an elevation of approx. 1580 feet (480 meters) along the base and west flank of the Panamint Range in the area north to south of Manly Fall at the mouth of Redlands Canyon. The mine is accessible year-around, but paved and gravel roads, especially those in Panamint Valley, are subject to temporary closures due to flash-flooding and washouts.

Commodities

Commodity	Importance
Gold	Primary
Silver	Primary

Comments on the commodity information

Commodity Info: 2003 average grade of ore mined by open-pit (1.8 millions tons of run-of-mine ore) = 0.036 oz au/ton; 2003 average grade of ore mined underground (89,700 tons) = 0.187 oz au/ton; in area between Gold Tooth and Briggs pits, the best drill intercepts show grades ranging 0.185 oz au/ton -1.4 oz au/ton.
Ore Materials: For the most part, disseminated Au associated with pyrite (oxidized and sulfide ores) occurs in quartz-rich gneiss (metasediments), and amphibolite gneiss (metamorphosed hypabyssal intrusions and/or volcanic flows of mafic to intermediate compositions); to a much lesser extent, gold mineralization is also hosted by deformed volcanic rocks of Tertiary(?) age.
Gangue Materials: Unmineralized host rocks: quartz-rich gneiss and amphibolite gneiss

Materials information

Materials	Type of material
Pyrite	Ore
Amphibolite	Gangue
Gneiss	Gangue

Alteration

(Local) Silica-carbonate-pyrite

Mineral occurrence model information

Model code	129
USGS model code	40a
Deposit model name	Detachment-fault-related polymetallic Cu-Au-Ag-Pb-Zn deposits

Host and associated rocks

Host or associated Host

Rock type Metamorphic Rock > Gneiss

Rock type qualifier Quartz

Stratigraphic age (youngest) Precambrian
Host or associated Host

Rock type

Rock unit name Briggs Mine formation

Stratigraphic age (youngest) Proterozoic
Host or associated Host

Rock type Metamorphic Rock > Gneiss

Rock type qualifier Amphibolite

Stratigraphic age (youngest) Precambrian
Host or associated Host

Rock type Volcanic Rock (Aphanitic)

Stratigraphic age (youngest) Tertiary
Host or associated Associated

Rock type Sedimentary Rock

Rock unit name Pahrump Group

Stratigraphic age (youngest) Neoproterozoic
Host or associated Associated

Rock type Plutonic Rock

Stratigraphic age (youngest) Mesozoic
Host or associated Associated

Rock type Volcanic Rock (Aphanitic)

Stratigraphic age (youngest) Tertiary

Nearby scientific data

(1)	-117.185, 35.9375	ListMap

Economic information

Geologic structures

Type of structure	Regional
Structure description	North- to northwest-striking, west-dipping rangefront faults with both normal and right-lateral components (some active); high-angle faults that strike northwest along the rangefront but generally strike north to northeast within the range (the high-angle north-trending, west-dipping Gold Tooth fault in the Briggs Mine area shows evidence of normal movement but may have originated as a reverse fault that later had dip-slip displacement to the west); north-trending, west-dipping low-angle extensional faults, some of which appear to steepen and merge or transform into rangefront faults; north-trending anticlines and synclines.

Type of structure

Regional

Structure description

North- to northwest-striking, west-dipping rangefront faults with both normal and right-lateral components (some active); high-angle faults that strike northwest along the rangefront but generally strike north to northeast within the range (the high-angle north-trending, west-dipping Gold Tooth fault in the Briggs Mine area shows evidence of normal movement but may have originated as a reverse fault that later had dip-slip displacement to the west); north-trending, west-dipping low-angle extensional faults, some of which appear to steepen and merge or transform into rangefront faults; north-trending anticlines and synclines.

Ore body information

General form Lens (multiple stacking of sub-horizontal to steeply dipping lenses; near-vertical lenses along steeply dipping faults)

General form	Lens (multiple stacking of sub-horizontal to steeply dipping lenses; near-vertical lenses along steeply dipping faults)

Controls for ore emplacement

The gold occurrences at the Briggs Mine area and throughout the Panamint Range are strongly controlled by several parallel vertical to near-vertical faults, including the regionally persistent Goldtooth fault, and low-angle gravity slide (extensional) faults. The vertical faults have acted as the feeder conduits to the disseminated Briggs mineralization and to the mineralization that made its way into the permeable plumbing zones represented by the low-angle faults (at the North Briggs and Cecil R deposits).

Comments on the geologic information

REGIONAL GEOLOGY

(Modified from Lang, Dennis, May 22, 2004: Information handed out to field trip participants): the Panamint Range is a north-trending mountain range approximately 80 miles long and 16 miles wide with about 5800 feet of topographic relief in the vicinity of the Briggs deposit. The range is isolated from other bedrock exposures by broad valleys with centrally located saline playas that have numerous marginal freshwater seeps. These seeps emanate from small alluvial fans along the western edge of the Panamint Range. Depth to bedrock below the alluvial fans has only been tested in a few areas, but it appears that bedrock is within 200 to 500 feet of the surface within 1000 feet or more of the rangefront. Within the Briggs claim block this zone of potentially thin alluvial cover extends over a strike length of about 12 miles.

The mineral deposits and prospects within the Panamint District are located in an area of complex structural intrusive relationships. Precambrian metamorphic host rocks crop out for a distance of about 10 miles along a north trend. Within the Precambrian sequence most of the gold mineralization in the claim block, as well as the Briggs Mine, is hosted by a distinct rock assemblage. This assemblage is probably the oldest Precambrian suite in the Panamint Range, informally referred to in this referenced report as the Briggs Mine formation because it hosts the gold mineralization at the Briggs Mine. To a much lesser extent, gold mineralization is also hosted by deformed volcanic rocks of Tertiary(?) age.

The Briggs Mine formation is composed of two distinct rock types. The predominant rock type is quartz-rich gneiss, composed of quartz, feldspar, and muscovite, interpreted to be part of a thick package of clastic sediments. A second rock type consists of dark-colored lenses and bands of mafic to intermediate material, informally described as amphibolite gneiss. In most instances the origin of the amphibolite layers is unknown, but the mineralogy and rare relict textures are consistent with that of intercalated hypabysal intrusions and/or volcanic flows of mafic to intermediate compositions; some of the amphibolite lenses also may represent volcanic detritus. Emplacement of this igneous component may have occurred during or soon after deposition of the clastic sediments. Later the entire sequence was strongly metamorphosed during multiple episodes of deformation and recrystallization. Andrew (1998) has recognized at least six distinct deformational events in the Panamint Range. The oldest event is older than a 148 Ma quartz diorite.

The approximate age of the Briggs Mine formation was established in the Telescope Peak area as middle Proterozoic based on an isotopic age of about ~1750 Ma (Lanphere et al., 1964). No isotopic age dates have been determined for Precambrian rocks in the Briggs Mine area proper.

Less deformed upper Proterozoic sedimentary rocks, formally designated the Pahrump Group, overlie the Briggs Mine formation. Substantial variation in the thickness and lithologies of these rocks suggest their accumulation spanned several periods of tectonic activity within trough-like depressions in a near shore marine environment. Locally, the Radcliff schist, a facies of the Kingston Peak Formation of the Pahrump Group, is a host to gold mineralization. The upper contact of the Pahrump Group and an overlying section of late Precambrian marine sediments is marked by an angular unconformity. The rocks of this overlying stratigraphic sequence are not hosts for gold mineralization.
REGIONAL GEOLOGY (continued)

The Panamint Range underwent a broad period of intrusive activity and regional metamorphism in the mid- to late-Mesozoic. Radiometric age determinations (Hall, 1983) of intrusive rocks have yielded a range of ages of ~145 and ~137 Ma from the Manly Peak stock. These rocks and ~170 to 150 Ma granites in the nearby Argus Range represent a regional suite of shallow-level intrusives with relatively narrow thermal aureoles. A few miles north of the Briggs claim block, the Hall Canyon stock (~70 Ma) crops out in the Telescope Peak area (Crossland, 1995; Mahood et al., 1996). An intrusive body (South Park Canyon pluton) between Redland Canyon (Briggs Mine Area) and South Park Canyon has been dated at ~107 Ma (Chickanski, 1995). Superimposed on the above intrusive events was a period of regional metamorphism centered in the Telescope Peak area which Labotka et al. (1990) feels was related to post-intrusive folding, which produced a large north-northwest-trending fold system composed of anticlines and domes. Commonly, the anticlines are asymmetric with steepest dips on the western limbs. Undated deformed latites, dacites, and rhyodacites in the vicinity of Jackpot Canyon are believed to be about 11 Ma based on structural relationships (Andrew, 1999). Narrow dike- to sill-like bodies of lamphrophyre are common throughout the Panamint District. These igneous bodies show no signs of deformation and appear to be the youngest intrusive rocks in the district. A lamphrophyre outcrop south of the Briggs Mine was dated a 5Ma (Luddington, 1992).

The tectonic fabrics in the Panamint Range were overprinted by a Cenozoic extensional regime characterized by regional development of low-angle, north-trending, west-dipping extensional faults. Much of this overprinting was the result of reactivation of older structures (Andrew, 1998). Detailed work by Labotka and Albee (1988) and Harding (1988) shows that the low-angle faults in the Panamint Range formed during a period of mid-Miocene crustal thinning. Burchfiel et al (1987) document, through palinspastic reconstruction, the tectonic development of the northern Panamint Valley/Saline Valley, about 60 miles north of the Briggs deposit. Their work suggests that this portion of the Panamint Valley is a pull-apart basin that opened during an episode of extensional deformation along a low-angle fault within the last 3 Ma. These studies help establish the age of the low-angle faults associated with the occurrence of gold in the Panamint claim block. At the Briggs Mine and at the Jackson prospect, it appears that low-angle faults rapidly steepen at the valley margin and transform into rangefront faults. These observations appear to validate the model proposed by Burchfiel et al, and therefore, indicate a mid-Miocene or younger age for the low-angle fault at Briggs, Jackson, and presumably throughout the claim block.

Regional linear structures that are prominent within the Panamint claim block include high-angle faults, anticlines and synclines. Strike orientations of high-angle faults are northwest-southeast along the rangefront, but generally trend north-south to northeast-southwest in the range proper. As pointed out above, rangefront faults appear to be related in some instances to transformation of low-angle faults. In addition, common features expressed in the gravel cover along the rangefront are fault scarps. These faults may occur in sets forming grabens, such as in the Ballarat to Happy Canyon area, or they may form half grabens with one side being the rangefront, as seen at the Briggs Mine.
REGIONAL GEOLOGY (continued)

Among the most important of the high-angle faults is the north-trending, west-dipping Gold Tooth Fault. The Gold Tooth Fault can be traced for a distance of over five miles from the area of abandoned Gold Tooth mine workings south of the Briggs Mine northward to South Park Canyon. Shears and complicated rock contacts suggest continuation of the Gold Tooth Fault from South Park Canyon to Happy Canyon, a distance of about five miles more. Although the drag orientation in its hanging wall would indicate that the Gold Tooth Fault is a normal fault, it may have originated as a reverse fault that later had dip-slip displacement to the west. At the location where Redlands Canyon crosses the trace of the Gold Tooth Fault, a regional low-angle fault (Goldslud Fault described in the Briggs Mine Section) displaces the Gold Tooth Fault. The age of this displacement can only be determined to be younger than the youngest rock it displaces which is the ~170 Ma South Park pluton, but regional studies cited above suggest that it is Miocene in age. Abandoned mine workings, and the occurrence of gold mineralization along the trace of the Gold Tooth Fault, indicate the importance of this fault as a regional control for gold mineralization.

Speculative, or not well understood, is the possible structural control of major east-west-trending canyons that cut across the range. East-west faulting within the canyons is not obvious, and regional mapping by prior workers has not identified major east-west structures. This ease-west structural regime may be reflected in refolding of northerly-trending anticlines and domes along east-west axes. Labotka (1990) placed this refolding event at about the time of the intrusion of the Hall Canyon pluton (~70 Ma). Interpretation of airborne geophysical data (Aerodat, Inc., 1997; Anzman, 1997) observed interruptions and discontinuities in north-south magnetic trends consistent with crosscutting east-west fault structure. The work by Aerodat and Anzman identifies an association of interpreted east-west fault structures within mapped prospect occurrences. An explanation may be that stress orientations changed near the end of the Mesozoic long enough to impart a new tectonic fabric to Panamint Range rocks. Subsequent vertical readjustment during differential uplift of the Panamint Range may have reactivated axial plane cleavage and joint surfaces in the east-west folds, which served as conduits for gold-bearing hydrothermal fluids, and leading eventually to formation of the present day east-west canyon system.
Deposit Size:
Medium; 550,000 oz gold (15.6 metric tons gold produced); engineering estimate of remaining gold around existing pits: 264,000 oz (7.5 metric tons); drilling has defined 2.2 million tons of mineralized rock containing 84,000 oz gold at the Jackson-Cecil R area two mines north of the Briggs Mine.

1. Age of Mineralization: mid- to late-Miocene, contemporaneous with crustal thinning and associated extensional tectonics and low-angle detachment faulting; at the Briggs Mine low-angle faults steepen at the valley margin and appear to transform into rangefront faults. Undated deformed latites, dacites, and rhyodacites in the vicinity of Jackpot Canyon are believed to be about 11 Ma based on structural relationships (Andrew, 1999). Narrow dike- to sill-like bodies of lamphrophyre, common throughout the Panamint District, show no signs of deformation and appear to be the youngest intrusive rocks in the district. A lamphrophyre outcrop south of the Briggs Mine was dated a 5 Ma (Luddington, 1992).

Host Rock Type:
1. The principal host rocks are an assemblage of rocks that comprise what are probably the oldest Precambrian rocks in the Panamint Range; this assemblage is composed of two distinct rock types informally referred to as the Briggs Mine formation by mine geologists:
a. The predominant rock type is quartz-rich gneiss, composed of quartz, feldspar, and muscovite, interpreted to be part of a thick package of clastic sediments.
b. The second rock type consists of dark-colored lenses and bands of mafic to intermediate rocks, informally described as amphibolite gneiss. In most instances the origin of the amphibolite layers is unknown, but the mineralogy and rare relict textures are consistent with that of intercalated hypabysal intrusions and/or volcanic flows of mafic to intermediate compositions; some of the amphibolite lenses also may represent volcanic detritus. Emplacement of this igneous component may have occurred during or soon after deposition of the clastic sediments.

2. To a much lesser extent, gold mineralization is also hosted by deformed volcanic rocks of Tertiary(?) age.
Host Rock Age:
The approximate age of the Briggs Mine formation (Precambrian) was established in the Telescope Peak area as middle Proterozoic based on an isotopic age of about ~1750 Ma (Lanphere et al., 1964). No isotopic age dates have been determined for Precambrian rocks in the Briggs Mine area proper.

Associated Rock Types:
2. Less deformed upper Proterozoic sedimentary rocks, formally designated the Pahrump Group, overlie the Briggs Mine formation. Substantial variation in the thickness and lithologies of these rocks suggest their accumulation spanned several periods of tectonic activity within trough-like depressions in a near shore marine environment. Locally, the Radcliff schist, a facies of the Kingston Peak Formation of the Pahrump Group, is a host to gold mineralization. The upper contact of the Pahrump Group and an overlying section of late Precambrian marine sediments is marked by an angular unconformity. The rocks of this overlying stratigraphic sequence are not hosts for gold mineralization.

3. The Panamint Range underwent a broad period of intrusive activity and regional metamorphism in the mid- to late-Mesozoic. Radiometric age determinations (Hall, 1983) of intrusive rocks have yielded a range of ages of ~145 and ~137 Ma from the Manly Peak stock. These rocks and ~170 to 150 Ma granites in the nearby Argus Range represent a regional suite of shallow-level intrusives with relatively narrow thermal aureoles. A few miles north of the Briggs claim block, the Hall Canyon stock (~70 Ma) crops out in the Telescope Peak area (Crossland, 1995; Mahood et al., 1996). An intrusive body (South Park Canyon pluton) between Redland Canyon (Briggs Mine Area) and South Park Canyon has been dated at ~107 Ma (Chickanski, 1995).

4. Undated deformed latites, dacites, and rhyodacites in the vicinity of Jackpot Canyon are believed to be about 11 Ma based on structural relationships (Andrew, 1999). Narrow dike- to sill-like bodies of lamphrophyre are common throughout the Panamint District. These igneous bodies show no signs of deformation and appear to be the youngest intrusive rocks in the district. A lamphrophyre outcrop south of the Briggs Mine was dated a 5 Ma (Luddington, 1992).

Associated Rock Age: Upper Proterozoic sedimentary rocks; mid- to late-Mesozoic intrusive rocks; undated latites, dacites, rhyodacites believed to be about 11 Ma based on structural relationships; lamphrophyre dated at 5 Ma.

Host Rock Unit: Briggs Mine formation (local mine nomenclature)

Host Rock Unit Age: Middle Proterozoic; within the Precambrian sequence most of the gold mineralization in the claim block, as well as the Briggs Mine, is hosted by a distinct rock assemblage, which is probably the oldest Precambrian suite in the Panamint Range. The approximate age of the Briggs Mine formation was established in the Telescope Peak area as middle Proterozoic based on an isotopic age of about ~1750 Ma (Lanphere et al., 1964). No isotopic age dates have been determined for Precambrian rocks in the Briggs Mine area proper.

Economic information about the deposit and operations

Operation type	Surface-Underground
Development status	Producer
Commodity type	Metallic
Deposit size	Medium
Significant	Yes
Discovery year	1970

Mining district

District name	Panamint District

Land status

Ownership category	BLM Administrative Area
Area name	BLM Ridgecrest Field Office

Ownership information

Type Owner-Operator

Owner Canyon Resources Corporation

Interest 100

Home office 14142 Denver West Parkway, Suite 250\nGolden, CO 8040

Year 2007

Type	Owner-Operator
Owner	Canyon Resources Corporation
Interest	100
Home office	14142 Denver West Parkway, Suite 250\nGolden, CO 8040
Year	2007

Comments on the workings information

Workings Type:
1. Pre- early 1970s: small underground operations with several adits and shafts developed by C.R. Briggs and possibly by others prior to C.R. Briggs.

2. Early 1990s to April 2004: Canyon Resources Corp. acquired the property and commenced open-pit, heap-leach mining, with supplementary underground mining of high-grade ore.

Description of Mine Workings:
From south to north: Goldtooth, Briggs, and North Briggs deposits and open pits.

Comments on other economic factors

Total gold production approx. 550,000 oz.
Annual gold production averaged approx. 68,750 oz.

From 1996 to October 2003, approx. 71 million tons of rock were mined, including approx. 23 million tons of ore (19 million tons crushed ore and 4 million tons run-of-mine open-pit ore), and 48 million tons of waste.
The grade of ore from the three main pits at the Briggs Mine was: 0.037oz gold per ton, 0.03 oz gold per ton; and 0.052 oz gold per ton.

Au/Ag averages about 4/1.
Some high-grade ore mined underground ran 0.25 ounces gold per ton.
Ore is 70% oxide, 30% sulfide.
The gold occurs in association with pyrite.
Recovery averaged approx. 72%.
Operating costs averaged $446.00 per ounce.
Post cessation of mining costs average $180.00-$200.00 per ounce.

July 2006: Canyon Resources Corporation website, http://www.canyonresources.com/projects/briggs.php:

"Recent engineering estimates indicate that remaining gold mineralization around the existing pits totals 11.0 million tons at a grade of 0.024 ounces per ton. Infill and step out drilling operations are nearly completed and have produced positive results, indicating the potential for expanding mineralization around the existing Briggs pits and also indicate the potential for continuity of mineralization between the existing Goldtooth and Briggs pits. Over 16,547 feet in 49 RC holes have been drilled in our recent development drilling program. The best intercepts include: 15 feet (4.5 meters) of 0.206 oz Au/ton (5.8 g/t Au) in Hole R-3, 15 feet (4.5 meters) of 0.229 oz Au/ton (6.5 g/t Au) in Hole R-4, and 10 feet (3.0 meters) of 0.202 oz/ton Au (5.7 g/t Au) in Hole R-11. 10 feet (3.0 meters) of 1.4 oz/ton Au (47.9 g/t Au) in Hole R-16, 20 feet (6.1 meters) of 0.22 oz/ton Au (7.6 g/t Au) in Hole R-25, 25 feet (7.6 meters) of 0.281 oz/ton Au (9.6 g/t Au) in Hole R-29 and 20 feet (6.1 meters) of 0.185 oz/ton Au (6.34 g/t Au).

Re-starting the Briggs Mine in light of today's gold market is Canyon's top priority. The mine is fully permitted with existing plants, infrastructure, and mobile equipment."

2007 Reserves:
Drilling established a revised reserve estimate and discovery of a major underground extension.

Proven & Probable Reserves Grade Gold
(short tons) (troy ounces (troy (metric
Au per ton) ounces) tons)

Open-pit 4,160,000 0.026 108,500 3.37
Underground 183,000 0.118 21,500 0.67
Total Proven & Probable 4,343,000 0.030 130,000 4.04
An additional 100,500 short tons of mineralized rock at a grade of 0.116 troy ounces gold per ton (not included in proven and probable reserve estimates) is contained within designed underground excavations and could be extracted without additional capital development of infrastructure requirements.

Comments on development

The deposit was discovered in the early 1970?s as a potential economic, low-grade, disseminated gold deposit.
1. 1960s: property owned by C.R. Briggs;
2. Early 1970s: drilling program begun by Addwest Gold;
3. Drilling/exploration continued until 1989 (950 reverse circulation holes on 125- to 150-foot centers);
4. Permitting took place in early 1990s; the mine was permitted in 1993 at a cost of approx. $4 million;
5. 1996: Canyon Resources' open-pit, heap leach operation was constructed at a cost of approx. $38 million for mine startup;
6. April 12, 2004: mining ceased; rinsing of the leach pads began and continues as of July 2006; over 550,000 oz (total) gold produced.
7. Feasibility studies for both open-pit and underground operations were completed in early 2007.

Year of Discovery: Early 1970s as a potential economic, low-grade, disseminated gold deposit.

Nature of Discovery: Exploration sampling/assaying followed by exploration and development drilling, and geologic mapping in the area of a small, historic underground gold mine with several adits and shafts spatially developed along a zone of detachment faulting.

Canyon Resources holds 3,500 acres of mining claims in the Panamint Range of southeastern California adjacent to the operating Briggs gold mine. Several gold occurrences on this claim block have yielded gold mineralization encountered in multiple drill holes. Canyon Resources had planned to systematically explore the entire claim block with the objective of the development of several mines on the Panamint Range Property. However, mining was impeded by passage, in early 2003, of State of California regulations, which require backfilling of any new mine that produces metals and is developed by open-pit methods.

From 1997 through 2001, the ore was crushed in three stages to a minus ? inch size and was conveyor stacked on the leach pad. In January 2002, crushing was terminated and, since then, run-of-mine ore was placed directly on the leach pad without crushing, and the crushing plant and conveyor system were sold. However, from April through August 2003, higher-grade oxide and sulfide ores from the Goldtooth deposit were crushed by a contractor.

Gold is recovered from leach solutions in a carbon adsorption plant and refined into dore bars on site. The Company increased the initial design production rate to approximately 85,000 ounces per year in 1999, produced 80,000 to 87,000 ounces of gold and 22,000 to 24,000 ounces of silver each year from 1998 through 2000, and achieved production of 96,141 ounces of gold and 28,177 ounces of silver in 2001.

During 2002, a total of 8.9 million tons of waste and run-of-mine ore was open pit mined from the Briggs, North Briggs and Goldtooth deposits. Run-of-mine ore totaled 1.8 million tons at an average grade of 0.036 ounces per ton gold. In addition, 89,700 tons of ore from the North Briggs underground workings were contract mined with an average grade of 0.187 ounces per ton gold. The Briggs Mine produced 57,058 ounces of gold and 14,914 ounces of silver in 2002.

By early 2003, mining had been completed in the Main Briggs and first phase of the North Briggs pits. Ore was mined from the Goldtooth pit through August 2003, when that pit was fully mined. Removal of waste in the layback of the highwall at North Briggs pit, to gain access to an eastern extension of the North Briggs deposit, was the principal mining activity from August through December 2003. Total gold production in 2003 was expected to be approximately 38,000 ounces.

The Company mined remaining ore from the North Briggs layback in the first four months of 2004. Mining reportedly ceased on April 12, 2004, and gold production continued from leaching of ores on the leach pad for a period about eight months. Gold production in 2004 was expected to be approximately 35,000 ounces (Denny Lang, Senior Mine Geologist, personal communication, May 22, 2004).
Residual gold production from leach pads was ongoing as of July 2006.

Canyon Resources website, July 2007: Feasibility studies designed to develop an accelerated approach to putting the mine back into operation were for both open pit and underground operations were completed in early 2007. Drilling established a revised reserve estimate and discovery of a major underground extension. Combined open-pit and underground operations would produce 30,000 ounces gold in the first year of operation, 45,000 ounces in year two, 33,000 ounces in year three, and 4,500 ounces in year four. Operating costs for mining and offsite operations is estimated at $430 per ounce of gold produced. Total capital cost is $8.25 million to initiate open-pit gold production spent over a five month period. An additional $4.6 million will be required in the next year to develop and initiate underground mining. Open-pit and underground reserves were calculated with a cut-off grade of 0.08 troy ounces gold per ton for underground stopes and 0.013 for open pit.

Proven & Probable Reserves Grade Gold
(short tons) (troy ounces (troy (metric
Au per ton) ounces) tons)

Open-pit 4,160,000 0.026 108,500 3.37
Underground 183,000 0.118 21,500 0.67
Total Proven & Probable 4,343,000 0.030 130,000 4.04

An additional 100,500 short tons of mineralized rock at a grade of 0.116 troy ounces gold per ton (not included in proven and probable reserve estimates) is contained within designed underground excavations and could be extracted without additional capital development of infrastructure requirements.

The Briggs Mine is going back into operation, presumably in 2007.

Reclamation at Briggs has progressed with near completion of offsite reclamation, partial backfilling of the Main Briggs pit, and commencement of re-contouring and capping with growth media from the south non-ore rock pile.

Reference information

Bibliographic references

Deposit

Aerodat, Inc., 1997, Unpublished report regarding interpretation of airborne geophysical data.
Deposit

Andrew, 1998, 1999, referenced in Lang, Dennis, Senior Geologist, Canyon Resources Corp.; May 22, 2004; Field trip to the C.R. Briggs Mine, sponsored by Canyon Resources Corp. and Southern California Section, Society for Mining, Metallurgy, and Exploration: personal communication and unpublished text.
Deposit

Anzman, 1990, 1997, referenced in Lang, Dennis, Senior Geologist, Canyon Resources Corp.; May 22, 2004; Field trip to the C.R. Briggs Mine, sponsored by Canyon Resources Corp. and Southern California Section, Society for Mining, Metallurgy, and Exploration: personal communication and unpublished text.
Deposit

Burchfiel, B.C., Hodges, K.V., and Royden, L.H., 1987, Geology of Panamint Valley-Saline Valley pull-apart system, California: Palinspastic evidence for low-angle geometry of Neogene range-bounding fault: Journal of Geophysical Research, v. 92, no. B10, p. 10,422-10,426.
Deposit

Canyon Resources Corporation Website (accessed various times between May 2004 and July 2006).
Deposit

Canyon Resources Website, 7/9/2007: http://www.canyonresources.com/projects/briggs.php
Deposit

CGS Minefile Folder No. 322-5671
Deposit

Chickanski, M., 1995, referenced in Lang, Dennis, Senior Geologist, Canyon Resources Corp.; May 22, 2004; Field trip to the C.R. Briggs Mine, sponsored by Canyon Resources Corp. and Southern California Section, Society for Mining, Metallurgy, and Exploration: personal communication and unpublished text.
Deposit

Chickanski, M., 2000, Low-angle, range-flank faults in the Panamint, Inyo, and Slate ranges, California: Implications for recent tectonics of the Death Valley region, Geological Society of America Bulletin 112, p. 871-883.
Deposit

Crossland, 1995, referenced in Lang, Dennis, Senior Geologist, Canyon Resources Corp.; May 22, 2004; Field trip to the C.R. Briggs Mine, sponsored by Canyon Resources Corp. and Southern California Section, Society for Mining, Metallurgy, and Exploration: personal communication and unpublished text.
Deposit

Hall, 1983, referenced in Lang, Dennis, Senior Geologist, Canyon Resources Corp.; May 22, 2004; Field trip to the C.R. Briggs Mine, sponsored by Canyon Resources Corp. and Southern California Section, Society for Mining, Metallurgy, and Exploration: personal communication and unpublished text.
Deposit

Harding, 1988, referenced in Lang, Dennis, Senior Geologist, Canyon Resources Corp.; May 22, 2004; Field trip to the C.R. Briggs Mine, sponsored by Canyon Resources Corp. and Southern California Section, Society for Mining, Metallurgy, and Exploration: personal communication and unpublished text.
Deposit

Labotka, 1990, referenced in Lang, Dennis, Senior Geologist, Canyon Resources Corp.; May 22, 2004; Field trip to the C.R. Briggs Mine, sponsored by Canyon Resources Corp. and Southern California Section, Society for Mining, Metallurgy, and Exploration: personal communication and unpublished text.
Deposit

Labotka, T.C., 1988, Geology of the Telescope Peak Quadrangle, Central Panamint Mountains, California. in Gregory, J.L., and Baldwin, E.J., eds., Geology of the Death Valley Region: South Coast Geological Society Annual Field Trip Guidebook #16, p. 103-109.
Deposit

Labotka, T.C., 1988, Mesozoic thermal history of the Panamint Mountains, Death Valley area, California: Geological Society of America 1988, Abstracts with Programs, v. 20, p. 17.
Deposit

Labotka, T.C., Albee, A.L. and Ernst, W.G., 1988, Metamorphism and tectonics of the Death Valley region, California and Nevada, in Ernst, W.G., Editor, Metamorphism and crustal evolution of the Western United States: Rubey colloquium on Metamorphism and crustal evolution of the Western United States, v. 7, p. 714-736.
Deposit

Labotka, T.C., Albee, A.L. and Wernicke, B.P., 1990, Uplift and exposure of the Panamint metamorphic complex, California: Basin and Range extensional tectonics near the latitude of Las Vegas, Nevada: Geological Society of America, Memoir 176, p. 345-362.
Deposit

Labotka, T.C., Albee, A.L., Lanphere, M.A., and McDowell, S.D., 1980, Stratigraphy, structure and metamorphism in the central Panamint Mountains (Telescope Peak quadrangle), Death Valley area, California: Geological Society of America Bulletin, v. 91, Part I, p. 125-129, Part II, no. 3, p. 843-933.
Deposit

Labotka, T.C., and Albee, A.L, 1990, Uplift and exposure of the Panamint metamorphic complex, California, in Basin and Range extensional tectonics near the latitude of Las Vegas, Nevada, Geological Society of America, Geological Society of America Memoir 176, 511 pages.
Deposit

Labotka, T.C., and Albee, A.L., 1977, Late Precambrian depositional environment of the Pahrump Group, Panamint Mountains, California, in Short contributions to California geology, California Division of Mines and Geology, California Division of Mines and Geology Special Report 129, 106 p.
Deposit

Labotka, T.C., and Albee, A.L., 1978, Contrast in metamorphic facies in the Panamint and Funeral mountains, Death Valley area, California: Geological Society of America, Cordilleran Section, 74th annual meeting, Abstracts with Programs, v. 10, p. 112-113.
Deposit

Labotka, T.C., and Albee, A.L., 1988, Metamorphism and tectonics of the Death Valley region, California and Nevada, in Ernst, W.G., ed., Metamorphism and crustal evolution of the western United States: Rubey Volume VII, New Jersey, Prentice-Hall, Englewood Cliffs, p. 714-736.
Deposit

Labotka, T.C., and Albee, A.L., 1990. Uplift and exposure of the Panamint metamorphic complex, California, In Basin and Range Extensional Tectonics Near the Latitude of Las Vegas, Nevada, B.P. Wernicke, ed., Geological Society of America Memoir 176, p. 345-362.
Deposit

Lang, Dennis, Senior Geologist, Canyon Resources Corp.; May 22, 2004; Field trip to the C.R. Briggs Mine, sponsored by Canyon Resources Corp. and Southern California Section, Society for Mining, Metallurgy, and Exploration: personal communication and unpublished text.
Deposit

Lanphere, J.A., Wasserburg, G.J.F., Albee, A.L., and Tilton, G.R., 1964, Redistribution of Sr and Rb isotopes during metamorphism, World Beater Complex, Panamint Range, California, in Craig, H., Miller, S.L., and Wasserburg, G.J.F., eds., Isotopic and Cosmic Chemistry: Amsterdam, Holland, North Holland Publishing Company, p. 258-320.
Deposit

Luddington, 1992, referenced in Lang, Dennis, Senior Geologist, Canyon Resources Corp.; May 22, 2004; Field trip to the C.R. Briggs Mine, sponsored by Canyon Resources Corp. and Southern California Section, Society for Mining, Metallurgy, and Exploration: personal communication and unpublished text.
Deposit

Mahood, G.A., Nibler, G.E. and Halliday, A.N., 1996, Zoning patterns and petrologic processes in peraluminous magma chambers, Hall Canyon Pluton, Panamint Mountains, California: Geological Society of America Bulletin, v, 108, p. 437-453.
Deposit

Published(?) or unpublished(?) sources:

General comments

Subject category	Comment text
Deposit	The Briggs deposit formed in mid to late Miocene, contemporaneous with crustal thinning and associated extensional tectonics and low-angle detachment faulting. The principal host rocks comprise two distinct rock types informally referred to as the Briggs Mine formation by mine geologists. The predominant rock type is quartz-rich gneiss, composed of quartz, feldspar, and muscovite, interpreted to be part of a thick package of clastic sediments. The second rock type consists of dark-colored lenses and bands of mafic to intermediate rocks, informally described as amphibolite gneiss. In most instances the origin of the amphibolite layers is unknown, but the mineralogy and rare relict textures are consistent with that of intercalated hypabysal intrusions and/or volcanic flows of mafic to intermediate compositions; some of the amphibolite lenses also may represent volcanic detritus. To a much lesser extent, gold mineralization is also hosted by deformed volcanic rocks of Tertiary(?) age. Precious metals were deposited from hydrothermal fluids migrating within zones of increased host rock permeability associated with vertical to near-vertical faults and low-angle gravity faults (ground preparation), which are spatially related, but may not be temporally related with regard to when they were active. The vertical faults acted as the feeder conduits to the disseminated mineralization and to the mineralization that made its way into the permeable zones associated with the low-angle faults.

Subject category

Comment text

Deposit

The Briggs deposit formed in mid to late Miocene, contemporaneous with crustal thinning and associated extensional tectonics and low-angle detachment faulting. The principal host rocks comprise two distinct rock types informally referred to as the Briggs Mine formation by mine geologists. The predominant rock type is quartz-rich gneiss, composed of quartz, feldspar, and muscovite, interpreted to be part of a thick package of clastic sediments. The second rock type consists of dark-colored lenses and bands of mafic to intermediate rocks, informally described as amphibolite gneiss. In most instances the origin of the amphibolite layers is unknown, but the mineralogy and rare relict textures are consistent with that of intercalated hypabysal intrusions and/or volcanic flows of mafic to intermediate compositions; some of the amphibolite lenses also may represent volcanic detritus. To a much lesser extent, gold mineralization is also hosted by deformed volcanic rocks of Tertiary(?) age.

Precious metals were deposited from hydrothermal fluids migrating within zones of increased host rock permeability associated with vertical to near-vertical faults and low-angle gravity faults (ground preparation), which are spatially related, but may not be temporally related with regard to when they were active. The vertical faults acted as the feeder conduits to the disseminated mineralization and to the mineralization that made its way into the permeable zones associated with the low-angle faults.

Reporter information

Type	Date	Name	Affiliation	Comment
Reporter	20-JUL-2006	Hill, Robert L.	California Geological Survey CGS (Formerly CDMG)
Editor	20-FEB-2008	Schruben, Paul G.	U.S. Geological Survey	Converted from S&A FileMaker format to Oracle. Edit checks on rocks, units, and ages with Geolex search, and other fields.

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