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Imperial Project

Prospect in Imperial county in California, United States with commodities Gold, Silver
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Sections on this page
  1. Identification information
  2. Geographic coordinates
  3. Site location context
  4. Geographic areas
  5. Public Land Survey System information
  6. Commodities
  7. Materials information
  8. Alteration
  9. Mineral occurrence model information
  10. Host and associated rocks
  11. Nearby scientific data
  12. Geologic structures
  13. Ore body information
  14. Controls for ore emplacement
  15. Economic information about the deposit and operations
  16. Mining district
  17. Land status
  18. Ownership information
  19. Bibliographic references
  20. General comments
  21. Reporter information

Geologic information

Identification information

Deposit ID 10310706
Record type Site
Current site name Imperial Project
Alternate or previous names Glamis Imperial Gold Mine, Indian Rose, Ocotillo

Comments on the site identification

  • The Imperial Project is located approximately midway between the historic Mesquite, Picacho, Tumco, and Cargo Muchacho gold mining districts. The Imperial Project includes the Indian Rose and Ocotillo deposits.

Geographic coordinates

Geographic coordinates: -114.78833, 32.97694 (WGS84)
Elevation 240
Location accuracy 100(meters)
Relative position The approximate center of the deposit is about 22 miles north-northwest of Yuma, Arizona, and 46 miles east-northeast of El Centro.

Site location context

Political divisions (FIPS codes)

Imperial(county)

California(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Hedges(quadrangle 1:24,000 scale)

Yuma(quadrangle 1:100,000 scale)

El Centro(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Salton Sea(hydrologic accounting unit)

Southern Mojave-Salton Sea(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 Imperial

Public Land Survey System information

Meridian Township Range Section Fraction State
San Bernardino 013S 021E 31,32,33 California
San Bernardino 014S 021E 4,5,6,7,8 California

Comments on the location information

  • The location selected for latitude and longitude represent a 4-wheel-drive road junction (in NW1/4 Sec. 5, T14S, R21E) near the center of the Imperial Project area. This point on the Hedges, CA, 7.5-minute quadrangle can be reached by traveling west from Yuma, AZ, approx. 13 miles (20.8 km) on Interstate Highway 8 to the junction with County Highway S34; then north 4.8 miles (7.7 km) on S34 to Ogilby. From Ogilby, continue 9.5 miles (15.2 km) north on S34 to Indian Pass Road; travel east 4 miles (6.4 km) on Indian Pass Road to the junction with a 4-wheel drive road, which heads generally east to southeast for approx. 0.5 mile (0.8 km) before turning northeast for approx 1.5 miles (2.4 km) to a 4-wheel-drive road junction at the approx. center of the project area. The condition of the 4-wheel-drive roads in the area is not known to this MRDS reporter.

Commodities

Commodity Importance
Gold Primary
Silver Primary

Comments on the commodity information

  • Ore Materials: Native gold, silver (as electrum?)

  • Gangue Materials: Limonite, hematite, quartz, carbonate, clays

Materials information

Materials Type of material
Gold Ore
Silver Ore
Electrum Ore
Limonite Gangue
Hematite Gangue
Quartz Gangue
Clay Gangue

Alteration

  • (Local) Oxidation; hematitic, limonitic
    Sericitic (weak, from minor hydrothermal alteration)
    Silicic; quartz (minor veining and silicified zones)
    Carbonate;

    Commonly the biotite gneiss has a shatter-breccia texture that is variably cemented by iron oxides, clays, and less commonly quartz or carbonate.

    Depth of mineralization: 400 to 880 feet (oxidized zone).

Mineral occurrence model information

Model code 283
USGS model code 37d
Deposit model name Gneiss-hosted epithermal Au

Host and associated rocks

  • Host or associated Host
    Rock type Metamorphic Rock > Gneiss
    Rock type qualifier Biotite
    Rock unit name Chuckwalla Complex
    Stratigraphic age (youngest) Mesozoic
    Stratigraphic age (oldest) Proterozoic
  • Host or associated Host
    Rock type Metamorphic Rock > Gneiss
    Rock type qualifier Sericite
    Rock unit name Chuckwalla Complex
    Stratigraphic age (youngest) Mesozoic
    Stratigraphic age (oldest) Proterozoic
  • Host or associated Associated
    Rock type Volcanic Rock (Aphanitic) > Intermediate Volcanic Rock > Andesite
    Stratigraphic age (youngest) Tertiary
  • Host or associated Associated
    Rock type Volcanic Rock (Aphanitic) > Mafic Volcanic Rock > Basalt
    Stratigraphic age (youngest) Tertiary

Nearby scientific data

(1) -114.78833, 32.97694
ListMap

Economic information

Geologic structures

Type of structure Regional
Structure description Chocolate Mountains-Orocopia Thrust; San Andreas Fault system; detachment fault features

Ore body information

  • General form Tabular (sub-tabular blocks averaging 200 to 300 feet thick, structurally controlled by the intersection of low-angle and high-angle shear zones, which are localized to the ore body).

Controls for ore emplacement

  • Permeability: faults, fault zone intersections, shear zones, brecciation, stockwork veins associated with faults and fault intersections, gouge zones.

Comments on the geologic information

  • REGIONAL GEOLOGY

    Crystalline Basement Units

    Regionally significant basement lithologies are the Pelona, Orocopia, and Rand Schists of late Mesozoic-early Cenozoic age (collectively referred to as the POR schists) and older Mesozoic-Proterozoic gneisses, schists, and plutonic rocks. The POR schists are units of highly metamorphosed and deformed greywacke, basalt, chert, limestone, and ultramafic rock stretching across southern California into Arizona, whose protoliths are considered to represent Triassic- Jurassic accretionary wedge deposits. The Mesozoic-Proterozoic rocks have been assigned to the Chuckwalla Complex.

    During the late Mesozoic, the older gneisses, schists, and plutonic rocks were thrust over the younger POR schists along low-angle the Vincent, Chocolate Mountains, Orocopia, and Rand faults. Regional studies indicate that metamorphism and thrusting were approximately coeval (Drobeck and others, 1986). In the vicinity of the Imperial Project, the Orocopia Schist forms the lower plate (footwall) of the Chocolate Mountains fault (CMF) and the Chuckwalla Complex forms the upper plate (hanging wall). Jacobson and others (2007) have provided the most recent summary of the structural environment of this region.

    The upper plate gneisses and granites host important gold deposits in several locales in the Chocolate Mountains and neighboring Cargo Muchacho Mountains. Besides the Imperial Project, these include the Mesquite, Picacho, American Girl, Padre y Madre, and Oro Cruz (Tumco) mines. At the nearby Mesquite Mine, a biotite gneiss unit within the Chuckwalla Complex hosts the bulk of the ore deposits.

    Suprajacent Rocks

    Suprajacent rocks in the region consist of Tertiary volcanics and sediments unconformably overlain by Cenozoic alluvium, gravels, and lesser amounts of volcanics.

    Tertiary volcanics were deposited on the older granitic and metamorphic rocks on an irregular erosional topography with considerable local relief. The earliest volcanics were basalt flows that erupted into paleovalleys. Basalt caps conspicuous mesas in the Chocolate Mountains. Fanglomerates, alluvial fan deposits, overlie the basalts and are in turn followed by several hundred feet of agglomerates, flows, and breccias of the Oligocene Quechan Volcanics. These volcanics are thought to immediately post-date the initiation of Oligocene extension in the region.

    Deposition of alluvium on low land and pediment surfaces followed a period of extensive erosion. The youngest deposits occupy the washes that have dissected the older alluvium and cut into the older erosion surfaces. Desert pavement is conspicuous on the gently sloping surfaces covered with the older alluvium.

    Regional Structure and Tectonics

    Regionally, the Colorado Desert area has undergone a complex history of metamorphism, intrusion, volcanism and faulting. At least four important tectonic episodes have contributed to the structural complexity of the area: Jurassic-Cretaceous thrusting and metamorphism, Oligocene-Miocene extension with detachment and strike-slip faulting, Miocene-Pliocene Basin and Range normal faulting, and younger dextral strike-slip faulting associated with the evolution of the San Andreas Fault system. Structural ambiguities are many due to overprinting and fault reactivation. Late Cenozoic structural features (high angle normal faults, dextral strike-slip faults) overlap and sometimes obscure earlier Tertiary features (detachment faulting), which in turn overprint Mesozoic features (thrust faulting).

  • REGIONAL GEOLOGY (continued)

    During the late Jurassic or Cretaceous, basement and supracrustal rocks across southern California and southern Arizona were folded and thrusted northward and northeastward during the Cordilleran Orogeny. The Cordilleran Orogen developed as the principal effect of oblique northeastward subduction of the Farallon plate, and to some extent the Kula Plate, along the western continental margin (Atwater, 1989). This produced a large belt of deformation from Canada to Mexico. As the plates converged, allochthonous terranes were scraped from the descending plates and accreted to the continental mass including the Baldy and the Santa Lucia-Orocopia terranes in southern California. Mesozoic-Proterozoic gneisses, schists and intrusive rocks were then emplaced over the Pelona and Orocopia schists along a regional system of mylonitic faults that included the CMF. The exposed trace of the CMF occurs about 3 miles northeast of the nearby Mesquite Mine. Seismic data indicates that the lower plate schists dip at low angles to the southwest, but at moderate angles in proximity of later high angle Tertiary faults (Morris, 1986a) and that the CMF itself deformed into a series of synforms and antiforms by high-angle normal faults and multiple detachment-style faults (Morris, 1986a,b, 1987).

    During the early Tertiary, the Pacific Plate's relative motion slowed and became more northwesterly. Accordingly, convergence gave way to divergent plate motions with widespread volcanism and regional extension. Initial extension occurred along low-angle detachment fault systems, which accommodated much of the Oligocene-Miocene extension with an anatomizing network of low-angle faults throughout much of southern California (Frost and others,1997). Foremost among these were the detachment faults in the Colorado River Extensional Corridor (150 miles north of Mesquite) in which some of the best exposures of detachment faults in the western US occur. Displacement of upper plate rocks has been measured in tens of kilometers. Upper plate rocks are characteristically broken by numerous high angle northeast dipping normal faults and further deformed by rotation along these faults which flatten which with depth before merging with the main detachment fault plane. Important mineralization is associated with these detachment features at the nearby Picacho Mine, about 9 miles to the east. Geophysical studies have indicated that detachment-style extension was regionally pervasive and extended to mid crustal levels.

    Volcanism and normal faulting swept from east to west across the Basin and Range and into southern California. Basin and Range extension continues to this day; however, extensional accommodation shifted from low angle detachment faulting in the Oligocene to high angle block faulting and strike-slip tectonics during the Miocene-Pliocene. By late Pliocene, the regional tectonic environment had became one dominantly of dextral strike-slip motion exemplified in the San Andreas Fault zone southwest of the Imperial Project.

    LOCAL GEOLOGY

    The Imperial Project is located on the southwestern flank of the Chocolate Mountains, and is structurally aligned and approximately equidistant between the Picacho and Mesquite gold deposits. The geology of the Imperial Project consists of Mesozoic-Proterozoic-age gneisses and schists unconformably overlain by Tertiary andesites, basalts, fanglomerates, and Quaternary alluvium.

    Mineralization occurs primarily in thick quartz-biotite gneissic and sericitic units. The basic rock-ore types are biotite gneiss and sericite gneiss with gradational schistose sequences. The biotite gneiss package occurs across the entire project area while sericite-rich units are more prevalent in the eastern portion of the deposit.

  • LOCAL GEOLOGY

    The Imperial Project is located on the southwestern flank of the Chocolate Mountains, and is structurally aligned and approximately equidistant between the Picacho and Mesquite gold deposits. The geology of the Imperial Project consists of Mesozoic-Proterozoic-age gneisses and schists unconformably overlain by Tertiary andesites, basalts, fanglomerates, and Quaternary alluvium.

    Mineralization occurs primarily in thick quartz-biotite gneissic and sericitic units. The basic rock-ore types are biotite gneiss and sericite gneiss with gradational schistose sequences. The biotite gneiss package occurs across the entire project area while sericite-rich units are more prevalent in the eastern portion of the deposit.

    Major regional structures include the Chocolate Mountains Fault, which placed gneissic rocks over the younger Orocopia Schist, and the nearby San Andreas Fault system. Complicating the geologic setting within the region are detachment fault features identified at the Picacho Mine and American Girl Mine, and intricate strike-slip fault systems identified at the Mesquite Mine (Tosdal and others, 1991).

    The dominant structural feature in the project area is a west-northwest-trending fault, which placed the Mesozoic-Proterozoic gneisses and schists over metamorphic and sedimentary rock units. The structure appears as a network of curved faults (flower faults) that dip approximately 30? to the south. High-angle, east-west-striking normal faults (step faults) drop the stratigraphy down to the south.

    The "stratigraphic" sequence, from bottom to top, consists mainly of a lower unit of hornblende-biotite gneiss, which is overlain by a quartz-biotite gneiss unit, which is capped by a quartz-feldspathic gneiss unit. The lowermost unit that would be exposed during mining is undifferentiated gneiss, which forms the footwall to the orebody. Generally above the undifferentiated gneiss, is biotite gneiss, which has sericitic schist zones that appear to be structurally and/or hydrothermally localized. The biotite gneiss varies from a white quartzofeldspathic rock to dark gray hornblende-biotite gneiss. Commonly, the biotite gneiss has a shatter-breccia texture that is variably cemented by iron oxides, clays, and, less commonly, quartz or carbonate. The sericitic schist is a white, red-to-tan iron-oxide-stained rock composed predominantly of sericite with quartz. The sericite schist is weak and highly foliated.

    Gradational schistose and sericitic units occur predominantly across the northeastern portion of the project. The biotite gneiss package occurs across the entire project area while the muscovite-sericite schist units are prevalent in the East deposit in the area of the proposed East Pit.

    A discontinuous horizon of Tertiary andesite-basalt flows and volcaniclastic mudflows (and/or paleosoil horizons) with basaltic fragments rests unconformably on the Jurassic rocks. This volcanic unit is discontinuous and thin, ranging from zero to 100 feet (30.5 m) in thickness within the project area.

    A Tertiary-age conglomerate overlies the volcanics, or lies directly on the Jurassic metamorphic rocks where the volcanics are absent. The conglomerate is typically a moderately well-indurated, clay/carbonate/iron oxide-cemented material with coarse, sub-angular gneissic fragments in a moderate- to coarse-grained sand matrix with considerable mica component. Zones of finer-grained material, including silty sands and silts are present locally.
  • LOCAL GEOLOGY (continued)

    About 95 percent of the project area consists of Quaternary-age alluvium (in active ephemeral stream channels) and older alluvium (in upland areas). These deposits vary in total thickness from 10 to 700-1000 feet (3 to 213-305 meters) depending on various reports.

    The footwall of the deposit consists of a siliceous breccia unit, which varies from 10 to 170 feet (3 to 152 m) in thickness. This unit appears to parallel the fault planes (fault surfaces) of the low-angle thrust sheet. Apparently, breccia was injected along fault contacts during hydrothermal activity. Both the gneiss and conglomerate units occur below the siliceous breccia. The gneissic footwall rocks below the siliceous breccia unit consist of hornblende-biotite gneiss. The footwall unit tends to be very hard and shows rare, thin, mineralized intercepts. The footwall conglomerate unit is a well-indurated, clay-carbonate-cemented material with coarse, subangular, gneissic fragments and varies from 10 to 200 feet (3 to 61 m) in thickness.
  • Mineralization

    Gold and silver mineralization in the project area occurs in Mesozoic-Proterozoic-age granitic gneiss in the upper plate of the Chocolate Mountains Fault. The fault has an estimated throw of 48 kilometers (30 miles) to the northeast, moving gneiss and intrusive rocks over greenschist facies schists. Analysis of drill information indicates that the geology of the deposit is similar to that observed at the nearby Picacho Mine and Mesquite Mine gold deposits.

    The mineralization occurs in sub-tabular blocks averaging 200 to 300 feet (61 to 91 m) thick and is structurally controlled by the intersection of low-angle and high-angle shear zones, which are localized to the ore body.

    Mineralization is contained within a northwest-trending zone of altered biotite and sericite gneisses. Primary gold mineralization occurs within hematitic and limonitic altered breccias, micro-fractures, and gouge zones developed in the host biotite gneiss and sericite gneiss ore types. Minor quartz veining, very fine-grained pyrite pseudomorphs* and silicified zones are also common. Sporadic mineralization is also noted along the gravel and volcanic contact and in fault structures through the brecciated volcanic units. Low-grade mineralization also occurs within the overlying gravels as thin layers eroded from exposed mineralized gneissic units.

    Density of fractures, extent of the red-brown to yellow hematitic/limonitic coatings, and pyrite pseudomorphs* within the host units are notable mineralized features. Logging of core and drill-hole cuttings indicates no fresh pyrite or sulfide mineralization is present, due to the oxidized state exhibited throughout the deposit. [*Pyrite pseudomorphs" the term used in Glamis' June 1988, report on Geology and Ore Reserves, appears to refer to "oxidized remnants of pyrite" seen in some drill cuttings (as reported in the Draft EIS/EIR (http://www.blm.gov/ca/imperial/c3.html).]

    Minor hydrothermal alteration is present as a weak form of sericitization. Oxidation extends to depths in excess of 1500 feet below ground surface, and no pyrite or other sulfide minerals have been observed in the ore or waste rock, other than oxidized remnants of pyrite in some drill cuttings.

    The mineralized gneissic and schistose rock units have been separated into biotite gneiss and sericite gneiss ore types, based on differences in physical characteristics utilized for general mine design parameters. Approximately 30% of the ore consists of the sericite gneiss type, and 70% consists of the biotite gneiss type. Depth of mining is determined by economics relating to grade and stripping ratio.

    Structural patterns within the project area, identified by exploration drilling, generally consist of west-northwest- to northwest-trending faults cut by northeast-trending high-angle faults. A south-southwest-dipping low-angle fault bounds the orebody at its base and along the north side. These structural features appear to have acted as conduits, forming the geologic setting for Imperial Project mineralization.

    No other economically recoverable mineral resources are known within the project area.

Economic information about the deposit and operations

Operation type Surface
Development status Prospect
Commodity type Metallic
Deposit size Medium
Significant Yes
Discovery year 1988

Mining district

District name Imperial District

Land status

Ownership category BLM Administrative Area
Area name BLM El Centro Field Office

Ownership information

  • Type Operator
    Owner Goldcorp Inc.
    Year 2007

Comments on the workings information

  • None at present. Three open pits are proposed.

Comments on other economic factors

  • There is no known production from this site.

    Reserves (Northern Miner, v. 887, no. 39, Nov 19-25, 2001):

    Proven and probable: 95.1 million short tons (86.3 million metric tons) ore grading 0.55 gram (0.0177 troy ounce) gold per metric ton (0.016 troy ounce gold per short ton)

    Run-of-mine heap-leach (no crushing) operation that would process oxidized ore over a period of 10 years.

    Average annual production estimate: 120,000 troy ounces gold.

    Recovery estimate: 73%

    Initial capital investment estimate: US$57 million.

    Total cash cost per troy ounce estimate: less than US$200 per troy ounce.

    Stripping ratio: 2.7:1 (Indian Rose deposit) to 4:1 (Ocotillo deposit); combined stripping ratio: 2.64:1.

    Ore Grade:
    81,623,700 short tons (74 metric tons) of proven reserves grading 0.016 troy ounces per short ton, and 13,504,500 short tons (12.3 metric tons) of probable reserves grading 0.014 troy ounces of gold per short ton (based on a 73% recovery rate, a cut-off grade of 0.007 troy ounces of gold per short ton, and a gold price of US$350 per ounce). This amounts to a total of, yielding approximately 1.5 million troy ounces (46.4 metric tons) gold.

Comments on development

  • The project to date includes exploration drilling and surface sampling only.

    Proposed Operation: Run-of-mine heap-leach (no crushing) operation that would process 120,000 to 130,000 short tons per day (on average) of oxidized ore over a period of 10 years.

    OVERVIEW

    Glamis Gold's Imperial Project is located in southeastern California within the Colorado Desert portion of the Basin and Range physiographic province. The project is situated along the southwestern flank of the Chocolate Mountains in eastern Imperial County, on public lands administered by the U.S. Bureau of Land Management (BLM), El Centro Resource Area Office, California Desert District. The project site is approximately 45 miles (72 km) northeast of El Centro, California, and 20 miles (32 km) northwest of Yuma, Arizona. The site lies east of Ogilby Road along Indian Pass Road.

    The project comprises approximately 1650 acres of unpatented mining claims, and includes the mine and process area containing the proposed open pits, waste rock stockpiles, soil stockpiles, diversion channels, office and maintenance facilities, heap leach facility, precious metal recovery plant, an electric substation, and internal roads and electrical distribution lines. The project ancillary area includes ground water production wells, a buried water pipeline, and a new electrical transmission line, and two relocated portions of Indian Pass Road. In addition, the Imperial Irrigation District would overbuild an existing electric transmission line to provide electrical power for the project.

    Although the Proposed Action incorporates measures to reduce the level and significance of impacts to the environment, the BLM concluded that, even with the application of additional proposed mitigation measures, the project would result in significant adverse effects to prehistoric cultural resources, Native American traditional cultural uses and values, and visual resources.

    Operations were projected to commence in 1998 and terminate around the year 2017. Reclamation activities were expected to continue beyond this date.

    The project anticipated generating up to 120 local jobs, and would require approximately US$48 million in initial capital expenditures, US$1.7 million per year in continuing capital expenditures, and US$26 million per year in non-capital expenditures including payroll.

    In November 1998 the area surrounding, and including, the Imperial Project was "segregated" from mineral entry by the Federal Government, for the protection of cultural artifacts, subject to valid existing rights. Following segregation, the BLM began the process of examining the validity of the mining claims within the Imperial Project area. In December 1999 a legal opinion issued by John Leshy, Chief solicitor for the Department of the Interior, concluded that BLM has the "discretionary authority" to deny the Imperial Project because of alleged impacts on the historic, cultural or religious values of the Quechan Indians. Although the Imperial project is not on tribal lands, the solicitor concluded that because it lies in a much larger traditional and cultural area (covering much of southern California, western Arizona and southern Nevada), a mine would introduce activities and intrusions "incompatible with the historic area." In April 2000, as a result of the Leshy opinion, Glamis Gold filed suit against U.S. Secretary Bruce Babbitt, U.S. Department of the Interior, Bureau of Land Management. In January 2001, the U.S. Department of the Interior denied the Imperial Project permits in accordance with a Clinton administration directive that substantially changed the rules governing mineral development on public lands.

  • OVERVIEW (continued)

    In October 2001, under the Bush administration, the U.S. Department of the Interior reversed a legal opinion issued by the Clinton administration that effectively blocked development of the Imperial Project. During December 2002-April 2003, amendments to the California Surface Mining and Reclamation Act of 1975 (designed to block the Glamis Imperial Project) compelled all new open-pit metal mines in the state to restore original land contours (including back-filling of pits) as part of mine rehabilitation.

    In December 2003, Glamis Gold, Ltd., a publicly-held Canadian corporation, submitted a US$50 million claim (Glamis Gold Ltd. vs. United States of America) to arbitration on behalf of its subsidiaries, Glamis Gold, Inc. and Glamis Imperial Corporation. Glamis claimed that certain Federal Government actions and California measures with respect to open-pit mining operations breached the United State's obligations under Chapter 11 of the North American Free Trade Agreement. As of August 2007, no settlement has been agreed upon, and no mining has been initiated at the Imperial Project.


    DETAILS OF EXPLORATION AND DEVELOPMENT

    As reported in the Glamis Gold March 26, 1998, Amended Annual Report (Glamis Gold Ltd. 12/98 Annual Report: http://sec.edgar-online.com/1998/03/26/14/0000891020-98-000417/Section4.asp): approximately 185,750 feet of reverse circulation and 4240 feet of core drilling had been completed over several areas on the Imperial Project. Additional exploration included geologic mapping and geochemical and geophysical surveys. As of December 31, 1997, drilling, geological interpretation, and mine evaluation studies had resulted in the delineation of a proven and probable mineable ore resource within preliminary pit outlines having a combined stripping ratio of 2.64:1. This resource consisted of 81,623,700 short tons (74 metric tons) of proven reserves grading 0.016 troy ounces per short ton, and 13,504,500 short tons (12.3 metric tons) of probable reserves grading 0.014 troy ounces of gold per short ton (based on a 73% recovery rate, a cut-off grade of 0.007 troy ounces of gold per short ton, and a gold price of US$350 per ounce). This amounts to a total of 95.1 million short tons (86.3 million metric tons) ore and approximately 1.5 million troy ounces (46.4 metric tons) gold.

    As reported by the Northern Miner (Volume 87, Number 39, November 19, 2001), the Imperial Project is a run-of-mine (no crushing) heap-leach operation that would process simple, oxidized ores over a 10-year period, with an initial capital investment of US$57 million, resulting in average production of about 120,000 troy ounces gold at a total cash cost of less than US$200 per ounce. The deposit reportedly hosts proven and probable reserves of 86 million metric tons (95.1 million short tons) grading 0.55 gram (0.0177 troy ounce) gold per metric ton (0.016 troy ounce gold per short ton).

    As reported in the Imperial Project EIS/EIR (November 1997) prepared by Environmental Associates, Inc., up to 150 million short tons of ore would be mined and leached, and 300 million short tons of waste rock mined and deposited at proposed waste rock stockpiles or the mined-out portions of three open pits (East Pit, Singer Pit, West Pit). The daily mining rate was reported to be 130,000 short tons per day on average, and range between zero and 200,000 short tons per day.

    Geochemistry from U.S. BLM, Imperial EIS, Geology and Mineral Resources at http://www.blm.gov/ca/eis/imperial/c2.html:

  • DETAILS OF EXPLORATION AND DEVELOPMENT

    As reported in the Glamis Gold March 26, 1998, Amended Annual Report (Glamis Gold Ltd. 12/98 Annual Report: http://sec.edgar-online.com/1998/03/26/14/0000891020-98-000417/Section4.asp): approximately 185,750 feet of reverse circulation and 4240 feet of core drilling had been completed over several areas on the Imperial Project. Additional exploration included geologic mapping and geochemical and geophysical surveys. As of December 31, 1997, drilling, geological interpretation, and mine evaluation studies had resulted in the delineation of a proven and probable mineable ore resource within preliminary pit outlines having a combined stripping ratio of 2.64:1. This resource consisted of 81,623,700 short tons (74 metric tons) of proven reserves grading 0.016 troy ounces per short ton, and 13,504,500 short tons (12.3 metric tons) of probable reserves grading 0.014 troy ounces of gold per short ton (based on a 73% recovery rate, a cut-off grade of 0.007 troy ounces of gold per short ton, and a gold price of US$350 per ounce). This amounts to a total of 95.1 million short tons (86.3 million metric tons) ore and approximately 1.5 million troy ounces (46.4 metric tons) gold.

    As reported by the Northern Miner (Volume 87, Number 39, November 19, 2001), the Imperial Project is a run-of-mine (no crushing) heap-leach operation that would process simple, oxidized ores over a 10-year period, with an initial capital investment of US$57 million, resulting in average production of about 120,000 troy ounces gold at a total cash cost of less than US$200 per ounce. The deposit reportedly hosts proven and probable reserves of 86 million metric tons (95.1 million short tons) grading 0.55 gram (0.0177 troy ounce) gold per metric ton (0.016 troy ounce gold per short ton).

    As reported in the Imperial Project EIS/EIR (November 1997) prepared by Environmental Associates, Inc., up to 150 million short tons of ore would be mined and leached, and 300 million short tons of waste rock mined and deposited at proposed waste rock stockpiles or the mined-out portions of three open pits (East Pit, Singer Pit, West Pit). The daily mining rate was reported to be 130,000 short tons per day on average, and range between zero and 200,000 short tons per day.

    Geochemistry from U.S. BLM, Imperial EIS, Geology and Mineral Resources at http://www.blm.gov/ca/eis/imperial/c2.html:

    Metal analyses, using total metal and acidic rain water extraction methodologies (the latter using the U.S. Environmental Protection Agency Synthetic Precipitation Leaching Procedure (SPLP) (Method 1312)), were conducted on samples of waste rock and ore material. The SPLP is designed to simulate the concentrations of metals and other compounds which could be leached from waste materials exposed to acidic rainfall. Ore samples were first subjected to leaching by dilute cyanide solution to remove precious metals, then neutralized, to be representative of the leached ore material which would remain on the heaps following completion of Project activities.

    None of the total extracted metal concentrations from the samples exceeded the State of California Total Threshold Concentration Limits (TTLCs) for characteristically toxic hazardous waste for any constituents tested, and most metal concentrations were an order of magnitude or more below the respective TTLC values. Metal concentrations detected in the solution extracted from samples using the SPLP method were all consistently very low.

  • HISTORY

    1780: the first gold mining in the region is attributed to early Spanish communities in the Cargo Muchacho Mountains (Clark, 1970).

    1848 - 1849: Mining interest in the region increased soon after the Mexican War in 1848 and the advent of the California Gold Rush in 1849.

    1870 - 1930: Mining interest peaked in the region. Production from the mines at Picacho, Tumco, and American Girl peaked in the early 1900s, producing a cumulative total of approximately 500,000 troy ounces of gold. Scattered, small-scale dry wash placer operations were attempted throughout the region and many small tailings piles from these operations are still visible.

    1970s: Increasing gold prices and bulk tonnage leaching technology developed in the 1970s led to exploration and subsequent development of open pits at the Picacho Mine in 1979, and the Mesquite an American Girl mines in 1980.

    1982 - 1985: Little mining history exists for the Imperial Project site. Bedrock exposed in limited locations on the north side of the Project was first prospected by Dick and Alice Singer during 1982-1985 (personal communication, Steve Baumann, Chemgold, 1995). Between 1982 and 1985, Gold Fields Mining Corporation conducted a regional exploration program comprised of aeromagnetic, gravity, and resistivity surveys and stream-wash geochemical studies. Gravity anomalies, low-grade mineralization in exposed bedrock, and a very limited drilling program led to the discovery of minor mineralization in the fringe areas of the current Imperial Project area.

    1987: Glamis Gold Exploration, Inc. acquired the mining claims and began exploration drilling through a joint venture agreement with a third party, Imperial Gold, a wholly owned subsidiary of Arizona Star Resources. This program led a "discovery" which became the Imperial Gold Project (Glamis Gold, Ltd. History: http://www.fundinguniverse.com/company-histories/Glamis-Gold-Ltd-Company-History.html).

    1992: Glamis and Arizona Star Resources completed a new reserve study that increased proven, possible, and probable reserves in two main zones of the Imperial Project (Indian Rose and Ocotillo deposits) to approx. 44.2 million short tons grading 0.024 troy ounces gold per short ton with a cutoff grade of 0.012 troy ounces per short ton. Stripping ratios for the Indian Rose and Ocotillo deposits are 2.7:1 and 4:1 (Northern Miner, v. 78, no. 39, Nov. 30, 1992; v. 78, no. 13, June 1, 1992; Northern Miner, v. 77, no. 35, Nov. 4, 1991).

    1994: Glamis acquired the remaining 35% interest in the Imperial Project from Arizona Star Resources (Amir Mines). Glamis thus became the sole owner and operator of the claims and initiated an accelerated development drilling and pre-feasibility program. This program culminated in the delineation of three ore bodies designated by the proposed East Pit, Singer Pit, and West Pit.

  • HISTORY (continued)
    April 1996: the final feasibility study for the Imperial Project was completed.

    May 2, 1996: Glamis Board of Directors approved the Imperial Project and directed the company to proceed with permitting, detailed engineering and procurement.

    1997: All of the Imperial Project claims were assigned to "Glamis Imperial Corporation."

    November 28, 1997: the second DEIS was published in the Federal Register; the comment period ended April 13, 1998.

    November 2, 1998: the area surrounding, and including, the Imperial Project was "segregated" from mineral entry by the Federal Government, for the protection of cultural artifacts, subject to valid existing rights. Following segregation, the BLM began the process of examining the validity of the mining claims within the Imperial Project area.

    December 1999: A legal opinion issued by John Leshy, Chief solicitor for the Department of Interior, concluded that BLM has the "discretionary authority" to deny the Imperial Project because of alleged impacts on the historic, cultural or religious values of the Quechan Indians. Although the Imperial project is not on tribal lands, the solicitor concluded that because it lies in a much larger traditional and cultural area (covering much of southern California, western Arizona and southern Nevada), a mine would introduce activities and intrusions "incompatible with the historic area." (Northern Miner, v. 86, no. 49, Jan. 29, 2001; v. 86, no. 9, Apr. 24, 2000)

    April 2000: As a result of the Leshy opinion, Glamis Gold filed suit against Bruce Babbitt, Secretary of the Interior, U.S. Department of the Interior, Bureau of Land Management.

    January 2001: the U.S. Department of the Interior denied the Imperial Project permits in accordance with a Clinton administration directive that substantially changed the rules governing mineral development on public lands (Northern Miner, v. 87, no. 37, Nov. 5, 2001).

    October 2001: Under the Bush administration, the U.S. Department of the Interior reversed a legal opinion issued by the Clinton administration that effectively blocked development of the Imperial Project (Northern Miner, v. 87, no. 35, Oct. 26, 2001).

    December 2002 - April 2003: Amendments to the California Surface Mining and Reclamation Act of 1975 (designed to block the Glamis Imperial Project) compel all new open-pit metal mines in the state to restore original land contours (including back-filling of pits) as part of mine rehabilitation.

    December 2003 (Glamis Gold Ltd. vs. United States of America): Glamis Gold Ltd., a publicly-held Canadian corporation submitted a claim (US$50 million) to arbitration in December, 2003 on behalf of its subsidiaries, Glamis Gold, Inc. and Glamis Imperial Corporation for alleged injuries relating to the Imperial Project in Imperial County, California. Glamis claimed that certain Federal Government actions and California measures with respect to open-pit mining operations breached the United State's obligations under Chapter 11 of the North American Free Trade Agreement.

    August 31, 2006: Canadian Goldcorp Inc., Vancouver, B.C., announced a merger (buy-out) of Glamis Gold Inc., Reno, Nevada, a subsidiary of Glamis Gold Ltd., Vancouver, B.C.

    July 2007: Arbitration with respect to the Imperial Project (Glamis Gold Ltd. vs. United States of America) was on-going as of July 9, 2007.

    Current Land Status: the Imperial Project area is administered by the U.S. Bureau of Land Management; the status of unpatented mining claims in the project area is not known to this MRDS reporter.

Comments on the environmental information

  • The proposed Imperial Project is situated in the eastern Colorado Desert in southeastern Imperial County. The project area is on a broad south- and west-facing alluvial plain southwest of Indian Pass, between the Cargo Muchacho Mountains [located approximately four miles (6.4 km) south] and Black Mountain [located approximately five miles (8.0 km) north]. The elevation over the project area ranges from about 760 feet (232 m) to 925 (282) feet above mean sea level with the lower, and nearly flat, elevations in the south and southwest. Elevations gradually increase to the north and northeast with topography characterized by a series of gently rolling ridges separated by interconnecting drainages generally trending from northeast to southwest.

    About 95 percent of the project area consists of Quaternary-age alluvium in active ephemeral stream channels, and older alluvium in upland areas. The Quaternary deposits vary in thickness from 10 to 1000 feet (3 to 305 meters) and overlie Tertiary andesite and basalt units that, in turn, unconformably overlie Jurassic schist and gneiss.

    Soils within the project area are dominated by desert pavement in the upland areas with gravel-based alluvial soil in the major drainages and the west-central portion of the project area. Soils of the upland landscape support very little vegetation.

    There are no springs, seeps, permanently wet areas, wetlands, nor standing surface water within the project area. Three primary, sub-parallel, ephemeral, stream channels traverse the project area.
    Precipitation in the Colorado Desert tends to occur in short, intense events, and average annual precipitation in the project area is approximately 3.6 inches (9.1 cm). The infrequent rain events result in temporary flow in the channels across the project area which quickly infiltrates in the sandy and gravelly wash bottoms, providing some residual moisture to the wash vegetation between storm events.

    The principal through-going stream channels (washes) within the project area appear to be currently in balance -- not dominated by either erosion or deposition, but both processes occurring at approximately the same rate. The majority of the project area has been subject to very slow erosional deflation by wind, which has produced a well-developed desert pavement. Wash bottoms have a veneer of recently deposited gravelly rock with sand and gravel along the banks. Surface runoff from this region, which comprises a portion of the Chocolate Mountains basin area drains into individual isolated areas along the eastern edge of the Algodones Sand Dunes, providing moisture to pockets of microphyll vegetation.

    The project area is located within the BLM's California Desert Conservation Area (CDCA) and is subject to the applicable plans and goals of the CDCA Plan. Two wilderness areas, Indian Pass Wilderness Area and Picacho Peak Wilderness Area, are located within 1.5 and 0.5 miles (2.4 km and 0.8 km) of the project area, respectively.

    The nearest desert tortoise critical habitat to the project area is the Chuckwalla Unit, located at its closest approximately 2 miles (3.2 km) northwest of the project area.

    Vegetation within the project area is characterized by: tree/shrub vegetation in and adjacent to the ephemeral stream channels; and shrub/scrub vegetation on the upland areas between the stream channels. Dominant species within the wash channels include ironwood, and palo verde, with a diverse plant association containing cat's-claw, purple heather, desert lavender, Anderson thornbush, and yellow felt-plant. Dominant desert scrub species include creosote bush, burrobush, ocotillo, and brittlebush. Several sparsely populated cactus species are found within this habitat, including Bigelow cholla, cottontop cactus, beavertail cactus, diamond cactus, and California barrel cactus.

  • A quantitative, site-specific, baseline vegetation survey of the project and process areas and a buffer zone (approx. 1,700 acres) was conducted in June, 1995, and a quantitative wash vegetation and habitat survey was conducted in May, 1997. Vegetation within the project area and project ancillary area are categorically creosote shrub type. For the purposes of the survey, the vegetation was subdivided into shrub/scrub vegetation observed on the open, drier alluvial flats and slopes; and tree/shrub vegetation observed on the sides of washes and drainages. Approximately 95 percent of the project mine and process area and the project ancillary area are the shrub/scrub type with an almost non-existent (5%) vegetative ground cover. These upland areas were further subdivided into three (3) topographic subtypes: desert pavement, alluvial flats and slopes, and rock outcrop/thin soil.

    No perennial streams, riparian habitat, or wetland areas exist on or adjacent to the project area, and no star dunes, sheet dunes, wind-accumulated sand deposits or other aeolian sand deposits exist within the project area.
    Of the 22 federal- or state-listed or proposed threatened/endangered plant species; U.S. Fish and Wildlife Service special status species; and BLM sensitive plant species which are known to occur in the general vicinity of the area of the Proposed Action, 11 of these plant species do not have potential habitat within the area of the Proposed Action.

    Systematic pedestrian botanical surveys of the entire project area (including the project area, the project ancillary area, and alternate transmission line corridors, including buffer zones) were conducted in July, August, and September 1994 and in February, April, and May 1995. In addition, incidental observations of sensitive botanical species were made during the pedestrian biological survey of the overbuilt 92 kV/34.5 kV transmission line corridor in August and September of 1995. The biological survey report indicates that no state or federal listed, proposed, or special status species were observed on the surveyed lands. No state or federal listed, proposed, or special status species have been reported to exist within the area of the Proposed Action. A single sensitive plant species, the fairy duster, was observed within the project area. One CNPS List 4 (i.e., "watch" list) species, winged cryptantha, was found in larger stream channels throughout the project area.

    Wildlife found within the vicinity of the area of the Proposed Action is characteristic of the Eastern Colorado Desert. The following common species inhabit or occasionally visit the area of the Proposed Action: reptiles (zebra-tailed lizard, side-blotched lizard, western whiptail, and desert iguana); birds (mourning doves, Gambel's quail, Say's phoebes, black-tailed gnatcatchers, black-throated sparrow, loggerhead shrike, and cactus wren); raptors (multiple raptor species would be expected to periodically forage or migrate through the area, including: golden eagle, red-tailed hawk, sharp-shinned hawk, American kestrel, prairie falcon, northern harrier, western screech-owl, great horned owl, and turkey vulture); mammals (antelope ground squirrel, Merriam kangaroo rat, desert woodrat, black-tailed jackrabbit, deer, kit fox, coyote, American badger, and wild burro.
    The Imperial property contains part of the Trail of Dreams, which historically has been used by the local Quechan Indians for traveling between the Colorado River and the desert interior, and which has spiritual significance for the Quechans. The property also contains the Running Man site, also an area of spiritual significance to the Quechan Indians (Northern Miner, v 89, no 9, Apr 21-27, 2003).

  • In November 1998, the area surrounding, and including, the Imperial Project was "segregated" from mineral entry by the Federal Government, for the protection of cultural artifacts, subject to valid existing rights. Following segregation, the BLM began the process of examining the validity of the mining claims within the Imperial Project area. In 1999, a legal opinion issued by John Leshy, Chief solicitor for the Department of Interior, concluded that BLM has the "discretionary authority" to deny the Imperial Project because of alleged impacts on the historic, cultural or religious values of the Quechan Indians. Although the Imperial Project is not on tribal lands, the solicitor concluded that because it lies in a much larger traditional and cultural area (covering much of southern California, western Arizona and southern Nevada), a mine would introduce activities and intrusions "incompatible with the historic area." (Northern Miner, v. 86, no. 49, Jan. 29, 2001; v. 86, no. 9, Apr. 24, 2000).

    In April 2000, as a result of the Leshy opinion, Glamis Gold filed suit against Bruce Babbitt, Secretary of the Interior, U.S. Department of the Interior, Bureau of Land Management. In January 2001, the U.S. Department of the Interior denied the Imperial Project permits in accordance with a Clinton administration directive that substantially changed the rules governing mineral development on public lands (Northern Miner, v. 87, no. 37, Nov. 5, 2001).

    In October 2001, under the Bush administration, the U.S. Department of the Interior reversed a legal opinion issued by the Clinton administration that effectively blocked development of the Imperial Project (Northern Miner, v. 87, no. 35, Oct. 26, 2001). From December 2002 - April 2003, amendments to the California Surface Mining and Reclamation Act of 1975 (designed to block the Glamis Imperial Project) compelled all new open-pit metal mines in the state to restore original land contours (including back-filling of pits) as part of mine rehabilitation.

    In December 2003 (Glamis Gold Ltd. vs. United States of America), Glamis Gold Ltd., a publicly-held Canadian corporation, submitted a claim (US$50 million) to arbitration on behalf of its Glamis Gold, Inc. and Glamis Imperial Corporation for alleged injuries relating to the Imperial Project. Glamis claimed that certain Federal Government actions and California measures with respect to open-pit mining operations breached the United State's obligations under Chapter 11 of the North American Free Trade Agreement.

    As of July 9, 2007, arbitration with respect to the Imperial Project (Glamis Gold Ltd. vs. United States of America) was on-going.

Reference information

Bibliographic references

General comments

Subject category Comment text
Deposit This deposit is reportedly similar in character to the nearby gold deposits at the Mesquite Mine and Picacho Mine; the deposit lies along the same structural trend in the Chocolate Mountains. Mineralization is contained within a northwest-trending zone of altered biotite gneiss and sericite gneiss. Primary gold mineralization occurs within hematitic and limonitic altered breccias, micro-fractures, and gouge zones developed in the host biotite gneiss and sericite gneiss ore types. Minor quartz veining, very fine-grained pyrite pseudomorphs and silicified zones are also common. Density of fractures, extent of the red-brown to yellow hematitic/limonitic coatings, and pyrite pseudomorphs within the host rock units are notable mineralized features.

Minor hydrothermal alteration is present as a weak form of sericitization. Oxidation extends to depths in excess of 1500 feet below ground surface, and no pyrite or other sulfide minerals have been observed in the ore or waste rock, other than oxidized remnants of pyrite in some drill cuttings.

The mineralized gneissic and schistose rock units have been separated into biotite gneiss and sericite gneiss ore types, based on differences in physical characteristics utilized for general mine design parameters. Approximately 30% of the ore consists of the sericite-gneiss type, and 70% consists of the biotite-gneiss type. Depth of mining is determined by economics relating to grade and stripping ratio.

Structural patterns within the project area, identified by exploration drilling, generally consist of west-northwest- to northwest-trending faults cut by northeast-trending high-angle faults. A south-southwest-dipping low-angle fault bounds the orebody at its base and along the north side. These structural features appear to have acted as conduits, forming the geologic setting for Imperial Project mineralization.

Reporter information

Type Date Name Affiliation Comment
Reporter 31-AUG-2007 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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