The Bagdad-Chase Mine is a gold, silver, and copper mine located in San Bernardino county, California at an elevation of 2,395 feet.
About the MRDS Data:
All mine locations were obtained from the USGS Mineral Resources Data System. The locations and other information in this database have not been verified for accuracy. It should be assumed that all mines are on private property.
Mine Info
Elevation: 2,395 Feet (730 Meters)
Commodity: Gold, Silver, Copper
Lat, Long: 34.62694, -116.16750
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Bagdad-Chase Mine MRDS details
Site Name
Primary: Bagdad-Chase Mine
Secondary: Pacific
Commodity
Primary: Gold
Primary: Silver
Primary: Copper
Secondary: Lead
Secondary: Zinc
Location
State: California
County: San Bernardino
District: Stedman (Ludlow, Rochester, Buckeye) District
Land Status
Land ownership: Private
Note: the land ownership field only identifies whether the area the mine is in is generally on public lands like Forest Service or BLM land, or if it is in an area that is generally private property. It does not definitively identify property status, nor does it indicate claim status or whether an area is open to prospecting. Always respect private property.
Administrative Organization: San Bernardino County Planning Department
Holdings
Not available
Workings
Not available
Ownership
Owner Name: Bagdad Chase, Inc.
Info Year: 2007
Production
Not available
Deposit
Record Type: District
Operation Category: Past Producer
Deposit Type: Hydrothermal breccia-filling
Operation Type: Surface-Underground
Discovery Year: 1880
Years of Production:
Organization:
Significant: Y
Deposit Size: M
Physiography
Not available
Mineral Deposit Model
Model Name: Detachment-fault-related polymetallic Cu-Au-Ag-Pb-Zn deposits
Orebody
Form: Blanket
Structure
Type: R
Description: Mojave Extensional Belt; Trans Mojave-Sierran shear zone; Eastern California shear zone
Alterations
Alteration Type: L
Alteration Text: Propylitic Potassic Argillic
Rocks
Name: Rhyodacite
Role: Associated
Description: porphyry
Age Type: Associated Rock
Age Young: Miocene
Name: Volcanic Breccia (Agglomerate)
Role: Host
Description: Quartz-hematite hydrothermal
Age Type: Host Rock
Age Young: Miocene
Name: Porphyry
Role: Associated
Description: Rhyodacite
Age Type: Associated Rock
Age Young: Miocene
Analytical Data
Not available
Materials
Ore: Gold
Ore: Sphalerite
Ore: Azurite
Ore: Malachite
Ore: Chrysocolla
Ore: Chalcocite
Ore: Galena
Ore: Chalcopyrite
Ore: Covellite
Gangue: Quartz
Gangue: Hematite
Comments
Comment (Development): MINING HISTORY (continued) 1910 -- 1916: By early 1910 production and profits were down. The Bagdad Chase Gold Mining Company put its Stedman District operations up for sale, and the operations were purchased by the Pacific Mines Corporation in late 1910. Under the direction of mining engineer, John Hays Hammond, production was increased to 100 short tons of ore per day and the labor force increased to 75 men. The entire operation was modernized, and the ore was sent to Clarksdale (near Jerome), Arizona for processing. During this period, the mine reportedly produced $1.5 million in gold, silver, and copper. Production is reported at 120,000 tons ore. The average grade of ore mined and shipped was 0.35 troy oz Au/ton (42,000 troy oz Au), 1.5 troy oz silver/ton (180,000 oz Ag), 1.82% copper (2184 tons) (Tucker and Sampson, 1940, p. 232). By the end of 1915, the Bagdad Chase had four vertical shafts from 120 to 400 feet deep, one decline 450 feet long, and several thousand feet of levels, drifts, and crosscuts. The ore body measured 2000 feet long and 8 to 20 feet wide at the surface. By 1916, equipment had become worn and obsolete, and production and profits were again down; operations ceased and the mine went into receivership. 1916 -- Early 1930s: Bagdad Chase was not economically viable and remained predominantly idle with some high-grading. In 1926, Pacific Mines and Metals, Inc. was organized in Nevada, and one of the new company's goals was to arrange to place the Bagdad Chase group of mines on a paying basis again. Early 1930s -- 1954: Starting in the early 1930s, Bagdad Chase was leased to several different parties who operated from time to time. 1932: In 1932, the Barstow Metals Extraction Co. began construction of a plant in Barstow to process Bagdad-Chase Mine tailings that were sent to the mill during the early 1900s (1904-1910). During this earlier period, 150,000 tons of ore were shipped to Barstow for processing, and the estimated tonnage of tailings available for treatment in 1932 was 130,000 tons. Head samples of tailings assayed: 0.155 troy oz gold/ton (20,150 troy oz Au total; 18,740 troy oz Au recoverable), 0.93 troy oz silver/ton (120,900 troy oz Ag total), and 0.70% copper (910 tons Cu total), with estimated recoveries of 93% of gold, 70% of silver, and 96% of copper. The estimated total value of gold, silver, and copper recovery was $4.69 per ton ($609,700 total; estimate $507,000 in Au) at a cost of $1.97 per ton (Tucker, 1934b). 1938 - 1939: the D'Aix Syndicate operated from 1938 to 1939 and reportedly shipped 850 short tons of ore to Magma Copper Company's smelter at Superior, Arizona; some shipments also went to American Smelting and Refining Company's smelter at Hayden, Arizona. The ore reportedly averaged $9.80/short ton in Au (0.28 troy oz Au/short ton; 238 oz Au total), $2.85/short ton in Ag, and 0.89% Cu (7.6 tons Cu Total). Total production in gold, silver, and copper up to 1940 was $6,013,000 (Tucker and Sampson, 1940, p. 232). 1939 - 1954: the Bagdad Chase was operated by Frank W. Royer from 1939 to 1943, and by Don L. Love beginning in 1943. Between 1943 and 1947 the lessee operated from the 125-foot shaft, stoping ore between the 90-foot level and the glory hole. Approximately 60,000 tons of ore were mined from this area. During 1947 and 1948 ore was mined from the 200-foot level in another vertical shaft. Early in 1949, the lessee worked in and around the old stopes on the 400-foot level of the inclined shaft (decline). The lessee reported mined 5000 tons ore in 1949, 2775 tons in 1950, and an average of one car (100-tons) per week during 1951 (Stewart, 1951). The Bagdad Chase was one of only four gold mines in California to be authorized to remain in production during World War II; the ore's silica content made it useful as a flux in smelting. Although not very profitable, the mine operated continuously from 1940 to 1954.
Comment (Geology): Mainly from Polovina (1987): INTRODUCTION The Stedman gold mining district is 80 km (49.7 mi) east of Barstow, California, in the Bullion Mountains of the eastern Mojave Desert. It is the southernmost member of a northwest trending belt of precious metal mining districts associated with Tertiary volcanic and hypabyssal intrusive rocks within the Mojave Desert. The alignment of the districts suggests that they might collectively constitute a major northwest trending structural lineament. Districts to the north include the Lave Beds and Calico silver districts, and the Randsburg gold district. The Stedman district is a 25 km2 (9.7 mi2) area of hydrothermally altered Miocene hypabyssal intrusive rocks, consisting of upper and lower rhyodacite units. Gold-silver-copper mineralization is associated with hydrothermal breccias that occur as sills beneath northeast-dipping low-angle normal faults, which offset the upper and lower rhyodacite units, and as pipes within the lower unit. ROCK UNITS Upper and Lower Rhyodacites The upper and lower rhyodacites are the two main units that crop out in the Stedman district, and are the wall rocks for the mineralized hydrothermal breccias. Although highly altered, the wall rocks are identified on the basis of their whole rock chemistry. Both units are massive porphyritic hypabyssal intrusive rocks with similar chemistry and mineralogy that were distinguished primarily by color while mapping. The original chemistry and mineralogy of the rhyodacite units are now obscured by pervasive propylitic alteration and oxide-zone leaching that makes them unsuitable for isotopic dating. However, the rhyodacites are probably of Miocene age and may correlate with the Cady Mountain Dacite (Glazner, 1981, cited in Polovina, 1987, p. 46) which crops out 20 km (12.4 mi) to the north and has a potassium-argon date of 20.2 ?1.3 m.y. (Glazner, 1981, cited in Polovina, 1987, p. 46). The upper rhyodacite has an areal extent of 6 km2 (2.3 mi2). Below the oxide zone it is light greenish-gray, propylitically altered porphyry with a devitrified groundmass. Within the oxide zone, the rock exhibits a tan weathered surface which distinguishes it from the lower unit. It is considerably less resistant to weathering than the lower rhyodacite, and typically crops out as a series of low, rounded hills, separated by alluvial washes. The upper rhyodacite is a plagioclase, biotite, hornblende and quartz porphyry that has undergone pervasive propylitic alteration. Original oligoclase is altered to albite flecked with sericite, and contains abundant inclusions of calcite, euhedral biotite phenocrysts are altered to chlorite and pyrite. Pyrite is also finely disseminated within the groundmass, averaging 1-2% of the rock. The lower rhyodacite is younger than and intrusive into the overlying upper rhyodacite, and is of particular significance in that it contains, or is in contact with, all of the important mineralization in the district. The rock is light gray when fresh; but commonly ranges from red-brown to pink and light green because of oxidation and alteration. Phenocrysts of plagioclase, biotite, hornblende and quartz comprise 20-45% of the rock and are set in a devitrified groundmass. The lower rhyodacite exhibits propylitic and potassic alteration. The propylitic alteration assemblage is the same as that described for the upper unit. In the potassic alteration zone the plagioclase feldspars are extensively altered to orthoclase.
Comment (Development): MINING HISTORY (continued) 1954 -- 1968: the mines remained idle. 1968 -- 1975: In 1968, Pacific Mines and Metals, Inc. merged with two other mining companies, Gold Ore Mining Company (an Arizona company) and Crown Oil Company (a Utah corporation), to form a new corporation called Bagdad Chase, Inc. Around 1972 the new company reportedly began open-pit operations at Stedman, which continued through 1975, when the board of directors decided that leasing the mine to other operators might be more profitable (Ross, 2006). Gold production during this period has not been verified by this MRDS reporter. The average annual gold price for the period varied from $58.61/troy oz in 1972 to 161.02/troy oz in 1975, with an average of $118.94/troy oz for this 4-year period. This MRDS reporter estimates that total gold production for this period likely did not exceed 60,000 troy ounces and 400,000 tons of open-pit ore. 1975 - 1987: the Bagdad Chase Mine continued to be leased occasionally. Around 1975, the mine was leased to the United States Oil and Mineral Corporation. From about 1977 to 1987, the district was the object of several exploration and drilling programs. 1987 -- 1988: Proposed open-pit operations (mining and production, if any, not confirmed by this MRDS reporter). In 1987, Bentley Resources, Vancouver, B. C., after acquiring a 50% undivided interest in the 315-claim Bagdad Chase property, announced plans for extensive exploration and drilling around the Bagdad Chase, to bring the Bagdad Chase operations back into production, and to pour the first gold dore bar in the second quarter of 1988. Bentley also acquired a 100% interest in an adjoining block of 102 claims, called Bagdad West, from Echo Bay Mines Ltd. Drill results reportedly established ore reserves of 950,000 open pit short tons grading 0.147 troy oz Au/short ton (Northern Miner, February 29, 1988). On the basis of additional drilling by Bentley, the Northern Miner (April 1988) reported an increase in ore reserves to 1,102,500 short tons grading 0.1514 oz Au/short ton (166,919 oz Au; ~5.2 metric tons Au). Operation plans called for an annual production of 20,000 troy oz Au from three open pits: Bagdad, Middle Mine, and Roosevelt. Capital cost was estimated at $4.5 million; production costs were estimated at $152(U.S.). Test metallurgical work by Hazen Research Inc. showed ~95% gold recovery using an agitated vat cyanide leach. The ore was to be ground to 75% minus-200 mesh; final gold recovery was to be by the Merrill-Crowe system to produce gold dore bars. 1988 - 1993: In June 1988, Bentley was in negotiations to sell its interest in the Bagdad Chase project to a "major U.S. mining company." the sale was conditional upon the signing of an operating agreement with Bentley's co-lessee, United States Oil and Mineral Corporation and certain revisions to the Lease and Royalty agreement with Bagdad Chase Inc. (Northern Miner, July 25, 1988). 1993 -- 2006: United States Oil and Mineral Corporation's lease was terminated by court order in 1993. However, Bagdad Chase, Inc. granted United States Oil and Mineral Corporation (or a qualified third party that United States Oil and Mineral Corporation should locate) an option to buy the mine and all other mining properties that Bagdad Chase, Inc. controlled in the Stedman Mining District for $3.5 million. The United States Oil and Mining Corporation was unable to buy the properties or to locate a qualified third party. On December 17, 1998, by court order, Bagdad Chase, Inc. regained complete control over its Stedman District mining operations. In 1999, the Bagdad Chase Mine consisted of 26 patented claims (Bagdad Chase Inc., 10-K 1999 Annual Report).
Comment (Development): YEAR OF DISCOVERY Copper and gold mineralization in the area of the current Bagdad-Chase and Roosevelt mines was discovered most likely around the early to late 1880s by John Suter, roadmaster for the Atlantic and Pacific subsidiary of the Santa Fe Railway. Discovery dates, which have been reported or which can be inferred from various sources, range from 1880 to 1903: 1880 (Mansfield, 2005); early 1890s (Ross, 2006); 1896 (Tucker, 1934b); 1898 (Feller, 2002); 1899 (USGS, MRDS); 1899 (Belden, 1952); 1903 (Tucker, 1917, 1934a). MINING HISTORY Mid 1880s -- early 1900s: Copper and gold mineralization in the area of the current Bagdad-Chase and Roosevelt mines was discovered most likely around the early to late 1880s by John Suter, a roadmaster for the Atlantic and Pacific subsidiary of the Santa Fe Railway. Discovery dates, which have been reported or which can be inferred from various sources, range from 1880 to 1903: 1880 (Mansfield, 2005); early 1890s (Ross, 2006); 1896 (Tucker, 1934b); 1898 (Feller, 2002); 1899 (USGS, MRDS); 1899 (Belden, 1952); 1903 (Tucker, 1917, 1934a). Suter was in the Bullion Mountains looking for a source of water for the railroad. The first mining district in the area was called the Buckeye Mining District. Suter sold his mines and claims in the early 1890s to stockholders of the New York Central Railroad, who organized the Bagdad Mining and Milling Company. 1901 -- 1910: the Bagdad Mining and Milling Company sent their first shipment of ore to the Randsburg-Santa Fe Reduction Company's stamp mill in Barstow in late 1901. The mill was equipped with fifty (50) 1,000-pound stamps and five regrinders, and had a cyanide plant with a capacity of 200 short tons of ore per day. The mill was owned by the same investors who purchased the Bagdad. The mill was originally built to handle ore from Randsburg. In addition to Suter's original Bagdad and Roosevelt mines, John R. Gentry had developed another productive mine that was purchased by the Benjamin E. Chase Gold Mining Company. Chase, who was president of the Central Bank of Rochester, New York, was also one of the investors in the Bagdad, and the companies merged to form the Bagdad Chase Gold Mining Company. For a time the Buckeye District was called the Rochester District in honor of the home of several of the investors. Chase was also president of the Ludlow and Southern Railway, which had been completed in 1903 to transport ore from the mine to the Santa Fe Railway at Ludlow. The combined mines were known as the Bagdad Chase. By 1905, the district was beginning to be called the Stedman District after the nearby mining town of Camp Rochester was renamed Stedman in honor of J. H. Stedman, Executive Secretary of the group of investors. From 1904, when mining began in earnest, to 1910, production from the Bagdad-Chase Mine reportedly amounted to 150,000 tons of ore with a total value of $4.5 million in gold produced, making the district the largest single source of gold in San Bernardino County. It was also the largest single source of copper in the County and yielded a significant amount of silver, as well. Between 1904 and 1910, the 150,000 tons of ore were hauled from the mine to Barstow where the ore was treated in a cyanide plant. Due to the presence of copper carbonates and silicates in the ore, gold recovery reportedly was about 55%. The ore also had an average reported value of $20.00 in gold per ton, and tailings' loss amounted to $5.00 in gold per ton (Tucker and Sampson, 1940; Tucker, 1934a).
Comment (Geology): STRUCTURE Nearly all structural elements in the Stedman district trend north to northwest, as they do throughout the Mojave (Jennings, 1977, cited in Polovina, 1987, p. 46). In the area of the where the thickest known section of breccia is present, all of the surface exposures of the hydrothermal breccia sill have sharp hanging wall and footwall contacts with consistent northwest strike and 25?-40?northeast dip. The sharp contacts with consistent orientations suggest that the emplacement of the hydrothermal breccia sill was fault controlled. The hanging wall rhyodacite is in sheared contact with the breccia sill and contains rounded cobbles of the breccia unit. This indicates that some post-ore fault movement along the contact has occurred. There is no evidence as to the direction or amount of slip that may have occurred along this pre- and post-ore fault zone. Most of the post-ore faults trend slightly west of north and dip 50?-90? west. In the area of the, north-northwest trending faults offset the hydrothermal breccia sill with left-lateral separation of up to 90 m (295 feet). The predominance of near-horizontal slickensides along these faults indicates that the most recent movement has been largely strike-slip.
Comment (Geology): OVERALL SUMMARY (continued) Mineralization at the Bagdad Chase is believed to be detachment-fault-related and of the same or slightly younger age as the deposit's associated presumed early Miocene-age rhyodacite porphyry intrusive rocks. Such deposits contain either copper-gold or lead-zinc-silver minerals that are typically found along low-angle normal faults (detachment faults) or along high-angle faults in the hanging walls of the detachment faults (Spencer and Welty, 1989, Long, 1992, cited in Tosdal and others, 1992, p. 38). Massive replacement bodies, breccias, and veins of specular hematite are characteristic of these deposits. Tosdal and others (1992, p. 38-39) classified base- and precious-metal deposits found in the extended terranes in the West Mojave Management Area, as detachment-fault-related polymetallic deposits (model 40a of Long, 1992). They included the Bagdad-Chase Mine as a possible example of this type of deposit. Previously, deposits in the Stedman Mining District have been included in the grade and short tonnage models for quartz-alunite systems (Mosier and Menzie, 1986, cited in Tosdal and others, 1992, p. 39). Tosdal and others (1992) cite Polovina (1980) and conclude that the character and texture of the Stedman ores are incompatible with the quartz-alunite deposit model. Age of Mineralization: Miocene -- contemporaneous with or somewhat younger than the enclosing rhyodacite porphyry wallrock; based on correlation of undated, altered rhyodacite porphyry wall rock with the Cady Mountain Dacite, which crops out 20 km (12,4 mi) to the north and has a potassium-argon date of 20.2 ?1.3 m.y. (Glazner, 1981, cited in Polovina, 1987, p. 46). . Host Rock: Hydrothermal quartz-hematite breccia consisting of poorly sorted, angular to subrounded fragments of argillically altered and leached rhyodacite, set in a fine-grained matrix of hydrothermal quartz and specular hematite. Host Rock Age: Miocene -- same as or younger than associated rhyodacite hypabyssal intrusives that may correlate with the Cady Mountain Dacite, which crops out 20 km (12.4 mi) to the north and has a potassium-argon date of 20.2 ?1.3 m.y. (Glazner, 1981, cited in Polovina, 1987, p. 46). Associated Rock Types: Rhyodacite porphyry intrusives. Host Rock Unit: Unnamed hydrothermal breccia. Host Rock Unit Age: Miocene -- contemporaneous with or slightly younger than rhyodacite porphyry wallrock; based on correlation of the rhyodacite porphyry wallrock with the Cady Mountain Dacite, which crops out 20 km (12.4 mi) to the north and has a potassium-argon date of 20.2 ?1.3 m.y. (Glazner, 1981, cited in Polovina, 1987, p. 46).
Comment (Environment): 1. 01 Private (1934: 25 patented claims including the Bagdad-Chase Group of 20 patented claims and Roosevelt Group of 5 patented claims; 1987: 184 lode and 16 placer claims; 1997: 26 patented lode claims, 31 Stedman district placer claims; Nov. 2006: 77 patented claims reported); 2. 50 Department of Defense (Twentynine Palms Marine Corps Base about 1 mile to the west and 0.75 mile to the south); 3. 49 U.S Bureau of Land Management (surrounding Federal lands).
Comment (Geology): Geochemical dispersion halo: According to Polovina (1987), there is a primary geochemical dispersion halo of base and precious metals that is roughly coincident in extent with the potassic alteration zone, and does not extend into the upper rhyodacite. "The plot of geochemical data versus distance from the breccia sill indicates that there is a dispersion halo of "Au"* (should read "Ag"*), Cu, and Pb that extends approximately 12 m (39.4 ft) into the lower rhyodacite." the plot indicates that the upper rhyodacite contains anomalously high values of these metals within 1 m (3.3 ft) above the breccia contact, beyond which there is a rapid decline to background values. * the text of Polovina's report refers to "Au", Cu, and Pb; Polovina's Figure 9 shows a plot of "Ag", Cu, and Pb within the dispersion halo; "Ag" values range from about 1.5 to about 3.5 ppm and are consistent with Polovina's Figure 5. Production and Reserves: (~14 metric tons). Summary of gold production and reserves: 1. 1904 - 1954: Underground mining; 344,000 to 400,000 short tons ore mined; ~228,900 troy ounces (~7.1 metric tons) gold produced; total gold content of the ore was ~246,700 troy ounces (~7.7 metric tons). 1904-1910 average ore grade: ~1.21 troy ounces gold per short ton; 1910-1916 average ore grade: 0.35 ounces gold per short ton. 2. 1972 -- 1975: Open-pit mining; estimated 400,000 short tons ore mined; estimated 60,000 troy ounces (1.9 metric tons) gold recovered. 3. 1988: Reported open-pit reserves; 1,102,500 short tons ore reserves; 166,919 troy ounces (5.2 metric tons) gold reserves. Average ore grade: 0.147 ounces gold per short ton.
Comment (Deposit): Mineralization at the Bagdad Chase is believed to be detachment-fault-related and of the same or slightly younger age as the deposit's associated presumed early Miocene-age rhyodacite porphyry intrusive rocks. Such deposits contain either copper-gold or lead-zinc-silver minerals that are typically found along low-angle normal faults (detachment faults) or along high-angle faults in the hanging walls of the detachment faults (Spencer and Welty, 1989, Long, 1992, cited in Tosdal and others, 1992, p. 38). Massive replacement bodies, breccias, and veins of specular hematite are characteristic of these deposits. Tosdal and others (1992, p. 38-39) classified base- and precious-metal deposits found in the extended terranes in the West Mojave Management Area, as detachment-fault-related polymetallic deposits (model 40a of Long, 1992). They included the Bagdad-Chase Mine as a possible example of this type of deposit. Previously, deposits in the Stedman Mining District have been included in the grade and short tonnage models for quartz-alunite systems (Mosier and Menzie, 1986, cited in Tosdal and others, 1992, p. 39). Tosdal and others (1992) cite Polovina (1980) and conclude that the character and texture of the Stedman ores are incompatible with the quartz-alunite deposit model.
Comment (Development): MINING HISTORY (continued) 1910 -- 1916: By early 1910 production and profits were down. The Bagdad Chase Gold Mining Company put its Stedman District operations up for sale, and the operations were purchased by the Pacific Mines Corporation in late 1910. Under the direction of mining engineer, John Hays Hammond, production was increased to 100 short tons of ore per day and the labor force increased to 75 men. The entire operation was modernized, and the ore was sent to Clarksdale (near Jerome), Arizona for processing. During this period, the mine reportedly produced $1.5 million in gold, silver, and copper. Production is reported at 120,000 tons ore. The average grade of ore mined and shipped was 0.35 troy oz Au/ton (42,000 troy oz Au), 1.5 troy oz silver/ton (180,000 oz Ag), 1.82% copper (2184 tons) (Tucker and Sampson, 1940, p. 232). By the end of 1915, the Bagdad Chase had four vertical shafts from 120 to 400 feet deep, one decline 450 feet long, and several thousand feet of levels, drifts, and crosscuts. The ore body measured 2000 feet long and 8 to 20 feet wide at the surface. By 1916, equipment had become worn and obsolete, and production and profits were again down; operations ceased and the mine went into receivership. 1916 -- Early 1930s: Bagdad Chase was not economically viable and remained predominantly idle with some high-grading. In 1926, Pacific Mines and Metals, Inc. was organized in Nevada, and one of the new company's goals was to arrange to place the Bagdad Chase group of mines on a paying basis again. Early 1930s -- 1954: Starting in the early 1930s, Bagdad Chase was leased to several different parties who operated from time to time. 1932: In 1932, the Barstow Metals Extraction Co. began construction of a plant in Barstow to process Bagdad-Chase Mine tailings that were sent to the mill during the early 1900s (1904-1910). During this earlier period, 150,000 tons of ore were shipped to Barstow for processing, and the estimated tonnage of tailings available for treatment in 1932 was 130,000 tons. Head samples of tailings assayed: 0.155 troy oz gold/ton (20,150 troy oz Au total; 18,740 troy oz Au recoverable), 0.93 troy oz silver/ton (120,900 troy oz Ag total), and 0.70% copper (910 tons Cu total), with estimated recoveries of 93% of gold, 70% of silver, and 96% of copper. The estimated total value of gold, silver, and copper recovery was $4.69 per ton ($609,700 total; estimate $507,000 in Au) at a cost of $1.97 per ton (Tucker, 1934b). 1938 - 1939: the D'Aix Syndicate operated from 1938 to 1939 and reportedly shipped 850 short tons of ore to Magma Copper Company's smelter at Superior, Arizona; some shipments also went to American Smelting and Refining Company's smelter at Hayden, Arizona. The ore reportedly averaged $9.80/short ton in Au (0.28 troy oz Au/short ton; 238 oz Au total), $2.85/short ton in Ag, and 0.89% Cu (7.6 tons Cu Total). Total production in gold, silver, and copper up to 1940 was $6,013,000 (Tucker and Sampson, 1940, p. 232). 1939 - 1954: the Bagdad Chase was operated by Frank W. Royer from 1939 to 1943, and by Don L. Love beginning in 1943. Between 1943 and 1947 the lessee operated from the 125-foot shaft, stoping ore between the 90-foot level and the glory hole. Approximately 60,000 tons of ore were mined from this area. During 1947 and 1948 ore was mined from the 200-foot level in another vertical shaft. Early in 1949, the lessee worked in and around the old stopes on the 400-foot level of the inclined shaft (decline). The lessee reported mined 5000 tons ore in 1949, 2775 tons in 1950, and an average of one car (100-tons) per week during 1951 (Stewart, 1951). The Bagdad Chase was one of only four gold mines in California to be authorized to remain in production during World War II; the ore's silica content made it useful as a flux in smelting. Although not very profitable, the mine operated continuously from 1940 to 1954.
Comment (Geology): HYDROTHERMAL BRECCIAS The Stedman breccias all have a matrix of hydrothermal quartz and specular hematite but occur as two morphological types: 1) subhorizontal hydrothermal breccia sheets or "sills" and 2) hydrothermal breccia pipes. The prefix "hydrothermal" is used here in accordance with the recommended terminology of Bryner (1968, cited in Polovina, 1987, p. 48) to distinguish the units clearly from breccias with an igneous matrix. The ore body at the Bagdad Chase Mine is within a hydrothermal breccia sill. Two hydrothermal breccia pipes crop out 1 km (0.6 mi) southwest of the in hills of the lower rhyodacite. The general compositional and textural similarities of the breccias indicate that the two morphological types formed by the same mechanism. The hydrothermal breccia consists of poorly sorted angular to subrounded fragments of argillically altered and leached lower rhyodacite, set in a fine-grained matrix of contemporaneous hydrothermal quartz and specular hematite. The breccia fragments are often entirely surrounded and supported by the homogeneous matrix; however, there is no evidence that the hydrothermal minerals replaced any prior matrix material. The fact that there are identifiable fragments of wall rock within the breccias indicates that there has been no major transport of fragments. Gold occurs in the breccia matrix as finely disseminated metallic intergrowths with quartz and hematite. The fine grain size, averaging 20 microns, and intimate intergrowths with matrix minerals, suggest that the gold precipitated contemporaneously with these minerals. Sulfide minerals in the breccia matrix are, in order of decreasing abundance, pyrite, covellite, chalcopyrite, galena, and sphalerite. From Hill (1968): Other minerals disseminated in the breccia include sparse chalcocite, magnetite, intergrowths of magnetite plus ilmenite; trace pyrolusite and possibly other manganese oxides; and, chalcopyrite and alabandite, both tentatively identified. Veinlets in breccia from the oxidized zone contain chrysocolla, malachite, and azurite; barite veinlets that crosscut chrysocolla veinlets were also identified. Emission spectroscopy revealed spectral lines for silver and strong spectral lines for Niobium from a sample of the hydrothermal breccia. Hill interpreted some breccia fragments to be 95-99% replaced by quartz and to show resorption textures. Resorption, at least in part, might account for the rounding of some breccia fragments.
Comment (Geology): STRUCTURAL EVOLUTION OF THE HYDROTHERMAL BRECCIAS There was initially an incipient normal fault cutting across the upper and lower propylitically altered rhyodacite units. Potassium-rich magmatic-hydrothrmal fluids rose upwards along a fracture system present prior to emplacement of the breccia pipe(s), spreading laterally along the incipient normal fault zone. The country rocks were altered by potassium metasomatism, forming the potassic alteration zone. The hydrothermal breccias formed subsequent to potassium metasomatism through fracturing of the lower rhyodacite by hydrothermal fluids derived from a magmatic source. Hydrothermal fluids accumulating in a magma chamber were forced out in several pulses, and rose to the surface along faults and fractures. When the fluids were near enough to the surface so that there existed a pressure or temperature differential between the magmatic fluids and the wall rock, the fluids brecciated the rock by thermal and/or hydraulic-fracturing mechanisms (Polovina, 1980b, cited in Polovina, 1987, P. 50). The brecciation that occurred was initially in the form of breccia pipes within the lower rhyodacite. As the fluids reached the incipient normal fault, they traveled along it brecciating the footwall to form the hydrothermal breccia sill. Associated with the mineralization event was the formation of a symmetrical primary geochemical dispersion halo about the breccia sill and pipe(s) that was roughly coincident with the zone of potassic alteration. Polovina (1984) suggests that after the mineralization event, there was normal movement along this and other en echelon faults causing the rotation of the fault to its present low-angle dip. The potassically altered and mineralized lower rhyodacite hanging wall was displaced to its present position. This model explains why the upper rhyodacite unit is not mineralized or potassically altered. Drill holes intersected the contact between the two rhyodacite units beyond the down-dip extent of the breccia, and there is no evidence of faulting at the contact as the model implies; however, the drill holes were terminated just below the contact. That the breccia unit and the clay gouge zone were not encountered in these down-dip drill holes, might be an indication that the fault and possibly more mineralized breccia are present below the drilled depth. MINERALIZATION Gold (along with silver and copper) occurs in a hydrothermal breccia matrix as finely disseminated metallic intergrowths with quartz and specular hematite. The fine grain size, averaging 20 microns, and intimate intergrowths with matrix minerals, suggest that the gold precipitated contemporaneously with these minerals. Sulfide minerals in the breccia matrix are, in order of decreasing abundance, pyrite, covellite, chalcopyrite, galena, and sphalerite (Polovina, 1987). From Hill (1968): Other minerals disseminated in the breccia include sparse chalcocite magnetite, intergrowths of magnetite plus ilmenite; trace pyrolusite and possibly other manganese oxides; and chalcopyrite, tentatively identified. Veinlets in breccia from the oxidized zone contain chrysocolla, malachite, and azurite; barite veinlets that crosscut chrysocolla veinlets were also identified. Emission spectroscopy revealed weak spectral lines for silver and strong spectral lines for Niobium from a sample of the hydrothermal breccia. Depth of mineralization: 400 feet maximum (122 meters) (Tucker, 1917).
Comment (Geology): TECTONIC SETTING (continued) The Bagdad Chase Mine is located near the northern margin of the Bullion Terrane, about three miles south of the Kane Springs Fault, a northeast-striking predominantly right-lateral internal transform fault zone that separates the Bullion Terrane south of the fault from the Daggett (extensional) Terrane north of the fault (Dokka, 1986). At its western limit, the strike of the Kane Springs fault curves to a northwesterly trend and becomes the western bounding "break-away" (detachment) fault of the Daggett Terrane. Strata in the Bullion Terrane dip 20?-40? east-northeast in contrast to beds in the Daggett Terrane, which dip 55?-65? to the southwest. In the area of the Bagdad Chase Mine, all of the surface exposures of the hydrothermal breccia have sharp hanging wall and footwall contacts with consistent northwest strike and 25?-40?northeast dip. Comprehensive geologic studies, undertaken with regard to recent developments in plate tectonics, have not been possible in the Bullion Terrane, because most of it lies within the Twentynine Palms Marine Training Center, an area of restricted access. Tosdal and others (1992, p. 38-39) classified base- and precious-metal deposits found in the extended terranes in the West Mojave Management Area, as detachment-fault-related polymetallic deposits (model 40a of Long, 1992). They included the Bagdad-Chase Mine as a possible example of this type of deposit. Previously, deposits in the Stedman Mining District have been included in the grade and tonnage models for quartz-alunite systems (Mosier and Menzie, 1986, cited in Tosdal and others, 1992, p. 39). Tosdal and others (1992) cite Polovina (1980) and conclude that the character and texture of the Stedman ores are incompatible with the quartz-alunite deposit model. Gangue materials: Altered rhyodacite wall rock, altered rhyodacite breccia fragments, quartz, specular hematite, pyrite, sphalerite, magnetite, magnetite plus ilmenite intergrowths; trace pyrolusite and possibly other manganese oxides, barite. Alteration: Pervasive propylitic alteration; zoned potassic alteration; argillic alteration of rhyodacite breccia fragments. Upper and Lower Rhyodacites The original chemistry and mineralogy of the rhyodacite units are obscured by pervasive propylitic alteration and oxide-zone leaching. Upper rhyodacite - pervasive propylitic alteration: A plagioclase, biotite, hornblende and quartz porphyry with a devitrified groundmass; original oligoclase is altered to albite flecked with sericite, and contains abundant inclusions of calcite; euhedral biotite phenocrysts are altered to chlorite and pyrite; pyrite is also finely disseminated within the groundmass, averaging 1-2% of the rock. Lower rhyodacite - Pervasive propylitic alteration; potassic alteration zone surrounding the hydrothermal breccia sill and associated breccia pipe(s) in lower rhyodacite: Phenocrysts of plagioclase, biotite, hornblende, and quartz comprise 20-45% of the rock and are set in a devitrified groundmass; exhibits propylitic and potassic alteration; the propylitic alteration assemblage is the same as that described for the upper rhyodacite unit; in the potassic alteration zone the plagioclase feldspars are extensively altered to orthoclase. Hydrothermal breccia - Argillic alteration: Consists of poorly sorted angular to subrounded fragments of argillically altered and leached lower rhyodacite, set in a fine-grained matrix of contemporaneous hydrothermal quartz and specular hematite.
Comment (Geology): Mineralization controls: Faulting: hydrothermal breccia sill emplacement along a (presently) low-angle (possibly detachment related) normal fault; impermeable gouge developed in the hanging wall of the fault. Changes in pressure and temperature of the hydrothermal fluid: the hydrothermal breccia fragments are angular and appear to have undergone little transport. Some of the individual fragments can be pieced together yielding the image of a chattered block. Individual fragments are surrounded and supported by a fine-grained homogeneous matrix of quartz with specular hematite, which implies that the rock was brecciated and the matrix precipitated simultaneously by a single pulse of hydrothermal fluid. Polovina concludes that a single rapid injection of magmatic fluid under high hydraulic pressure brecciated the lower rhyodacite by hydraulic- and /or thermal-fracturing mechanisms and provided the mineralized matrix filling the voids (Polovina, 1980b, cited in Polovina, 1987, p. 49). Ore deposits Hydrothermal breccia sill: The hydrothermal breccia sill is 8 to 15 feet wide and covers approximately 0.13 square mile as mapped in surface and underground workings and drill holes. The hanging wall and footwall contacts with the enclosing altered rhyodacite porphyries consistently strike northwest and dip 25?-40?northeast. The sharp contacts with consistent orientations and the hanging wall gouge indicate that emplacement of the breccia was fault controlled. The hanging wall rhyodacite is in sheared contact with the breccia sill and contains rounded cobbles of the breccia unit, indicating that some post-ore fault movement along the contact has occurred. There is no evidence as to the direction or amount of slip that may have occurred along this pre- and post-ore fault zone. Most post-ore faults that displace the hydrothermal breccia trend slightly west of north and dip 50?-90? west. The breccia sill comprises four layered units that have sharp contacts and distinct textural differences. Sub-unit 1 is characterized by predominantly subrounded fragments of lower rhyodacite in a quartz-hematite matrix that constitutes 30-40% of the rock. The breccia fragments are not strongly leached or altered, and copper oxides are absent. Sub-unit 2 is 70-90% matrix by volume, containing angular, argillically altered rhyodacite fragments, and copper oxides. Sub-units 1 and 2 are of limited extent, while Sub-unit 3 is the most continuous and has a maximum thickness of 7 m (23 ft) in the Bagdad Chase Mine. Sub-unit 3 is composed of 20-60% quartz-hematite matrix that contains angular to subrounded, argillically altered rhyodacite fragments. Copper and iron oxides are abundant in this sub-unit as fracture coatings and late stage cavity fillings. Sub-unit 4 is a transition zone of breccia into the lower rhyodacite, which exhibits argillic or potassic alteration. Gold (along with silver and copper) occurs in the hydrothermal breccia matrix as finely disseminated metallic intergrowths with quartz and specular hematite. The fine grain size, averaging 20 microns, and intimate intergrowths with matrix minerals, suggest that the gold precipitated contemporaneously with these minerals.
Comment (Location): Longitude and latitude represent the open pit mine symbol immediately above the name "Bagdad Chase Mine" on the Ludlow 7.5 minute quadrangle. Six mine shaft symbols are located within 0.1 mile NE to W of the open pit mine symbol. The mine is 47 miles by Interstate 40 east from Barstow to Ludlow, CA, then 7.6 miles south from Ludlow on Bagdad Chase Road. The historic townsite of Stedman is located 0.2 miles north of the mine on Bagdad Chase Road.
Comment (Development): MINING HISTORY (continued) With a gold price of $20.67 per troy ounce during the period 1904-1910, the reported $4.5 million in gold production amounts to ~217,700 troy ounces gold recovered. At 55% recovery, total gold content of the 150,000 tons of ore would be ~395,800 troy ounces and an ore grade of 2.639 troy ounces gold per ton. A tailings loss of $5.00 per ton in gold amounts to a loss of 0.242 troy ounces gold per ton for a total of 36,300 troy ounces gold lost to the tailings. [Approximately 130,000 tons of these tailings were available for reprocessing which began in 1932, and head samples reportedly assayed 0.155 troy ounces gold per ton (20,150 troy oz total gold; 18,740 troy ounces recoverable gold at 93% recovery; Tucker, 1934b)]. If the reported average value of $20.00 per ton of ore refers to gold recovered from the 150,000 tons of ore, the total amount and value of gold produced would be ~145,000 troy ounces (0.968 troy ounces gold per ton recovered) and $3 million, respectively. Using a total gold value of $25.00/ton ($20.00 recoverable plus $5.00 tailings loss), the average ore grade equates to 1.21 troy ounces gold per ton, which amounts to 181,500 troy ounces gold in 150,000 tons ore. Although the reported $20.00 per ton gold value of the ore and the $5.00 per ton loss in gold value to tailings are not consistent with the reported 55% recovery, the amount of gold produced (~145,000 troy ounces), the total gold content of the ore (181,500 troy ounces) and the corresponding grades (0.968 troy ounces gold per ton recovered, 1.21 troy ounces gold per ton of ore) are probably reasonable for the period 1904-1910. From the apparent inconsistencies in the reported figures given above for the period 1904-1910, either the dollar value ($4.5 million) of gold produced during 1904-1910 is overstated, or the amount of ore processed (150,000 tons) and/or the average per-ton value of the ore are understated. Although ore grades during the early period of mining (1904-1910) can be expected to be higher due to high-grading than during later years (1910-1916), using the $4.5 million value of gold recovered to estimate average ore grade for 1904-1910 gives a significantly higher average ore grade (2.639 troy ounces gold per ton) than reported from various other sources for the period 1910-1916: average ore grades of 0.159 to 0.486 troy ounces gold per ton for various blocks of ore mined from 1910-1916 (Tucker, 1934a); average of 0.35 troy ounces gold per ton mined from 1910-1916 (Tucker and Sampson, 1940, p 232). An upper limit on the estimate of gold recovered during 1904-1910 is ~217,700 troy ounces based on the reported $4.5 million value of gold produced and gold price of $20.67. The upper limit of total gold content for the 150,000 tons of ore processed in Barstow is ~395,800 troy ounces gold (average grade of 2.639 troy ounces Au/ton) based on the reported $4.5 million value of gold produced and reported 55% recovery. This MRDS reporter estimates that gold production and value of gold produced during 1904-1910 are probably on the order of ~145,000 troy ounces and $3 million, respectively. Total gold content in the 150,000 tons of ore is estimated to be ~181,500 troy ounces with average grade of ~1.21 troy ounces gold per ton.
Comment (Economic Factors): Production and Reserves: (~9 metric tons Au produced; 5.2 metric tons open-pit reserves); plus Ag and Cu (amount undetermined). Reserves: 166,919 troy oz Au (~5.2 metric tons; 1,102,500 short tons ore grading 0.1514 oz Au/short ton; Northern Miner, April 1988). Total Production plus Reserves 1,846,500 to 1,902,500 short tons ~455,800 troy ounces (~14.2 metric tons) F. W. Royer, Consulting Engineer, Report on shipments made from property from 1910 to 1916 (Royer, cited in Tucker, 1934a): Dry short tons ore Gold troy oz/short ton Silver troy oz/short ton Copper % 98 0.159 0.700 0.35 8,951 0.425 2.124 3.47 39,600 0.324 1.755 2.31 19,970 0.403 1.357 1.04 5,555 0.486 1.356 1.46 29,513 0.333 1.177 1.26 103,687 Total 0.359 Av. 1.524 Av. 1.825 Av. 37,220 troy oz Au total 158,019 troy oz Ag total 1892 short tons Cu total Au:Ag ratio = 1:4.2 (~1:4) Tucker (1934a) reported the following "estimated available tonnage": Bagdad-Chase: 95,000 short tons 0.25 troy oz/st Au 0.90 troy oz/st Ag 1.23 % Cu Middle section: 50,000 short tons 0.30 troy oz/st Au 1.03 troy oz/st Ag 0.90 % Cu North section: 300,000 short tons 0.225 troy oz/st Au 1.00 troy oz/st Ag 1.10 % Cu Misc. sections: 25,000 short tons 0.45 troy oz/st Au 1.00 troy oz/st Ag 1.20 % Cu 470,000 short tons 0.25 troy oz/st Au 0.98 troy oz/st Ag 1.11% Cu (Average) (Average) 117,500 tr oz Au total 462,000 tr oz Ag total 5419 short tons Cu total Gold:silver ratio: ~1:4
Comment (Geology): OVERALL SUMMARY (continued) Tectonic Setting: The Bagdad-Chase Mine is located in the northern part of the Bullion Terrane in the central Mojave Desert, southern Basin and Range Province. Bagdad-Chase mineralization occurs mainly within a quartz-hematite, gold-silver-copper-bearing, hydrothermal breccia sill in association with Miocene-age hypabyssal rhyodacite porphyry intrusive rocks. In contrast to Miocene extension and concurrent calc-alkaline volcanism that was taking place in east-central Nevada in a back-arc setting east of the subducting Farallon Plate north of the Mendocino Triple Junction, contemporaneous Miocene extension and associated calc-alkaline volcanism in southeastern California (which includes the central Mojave) developed opposite and east of the transform that was active along the North American plate margin south of the Mendocino Triple Junction. The central Mojave underwent extensional deformation, preceded by and contemporaneous with basalt to rhyolite volcanism in Miocene time (Gans and others, 2005; Dokka, 1986; Walker and others, 1990; Dokka and others, 1998; Glazner and others, 2002). During late Cenozoic time, the central Mojave experienced three structurally different and temporally separated intervals of deformation (Dokka and others, 1998): 1. ~N-S directed opening of the ~24-21 Ma Mojave Extensional Belt (Dokka 1989; Ross, 1995). The northern Mojave Desert underwent extension beginning ~24 Ma; detachment faults accounted for much of the extension and locally exhumed mid-crustal rocks (metamorphic core complexes). 2. ~E-W striking, dextral shearing (~21-18 Ma) along the Trans Mojave-Sierran shear zone (Dokka and Ross, 1995, 1996, 1998). At ~20 Ma, the kinematics along the northern boundary changed from extension to dextral shear and minor extension in the Trans Mojave-Sierran shear zone, and rocks within this east-west trending zone (southern Sierra Nevada and the central Mojave Desert) were rotated about vertical axes as much as ~40-60 degrees clockwise. 3. ~13-0 Ma Eastern California shear zone (Dokka and Travis, 1990ab; Dokka, 1993). From ~13-0 Ma, the region has been subject to right-lateral shearing within the Eastern California shear zone, which accounts for the numerous active, right-lateral, dominantly strike-slip faults in the Mojave region.
Comment (Geology): OVERALL SUMMARY (continued) Alteration: Propylitic, potassic, argillic. Ore control(s): An incipient, presumably detachment-related, low-angle, normal fault cut across upper and lower propylitically-altered hypabyssal rhyodacite porphyry intrusive rocks. Potassium-rich, magmatic-hydrothermal fluids spread upward along fractures and laterally along the developing normal fault zone. A zone of potassic alteration formed along the fault and along fracture zones (incipient breccia pipes) in the footwall. The gouge zone that developed in the hanging wall eventually formed an effectively impermeable barrier to fluid migration into the hanging wall. Hydrothermal fluids, accumulating in a magma chamber, were subsequently forced out in several pulses, and rose along the faults and fractures. As the fluids neared the surface, a pressure and/or temperature differential between the magmatic fluids and the wall rock caused the wallrock to brecciate by thermal and/or hydraulic-fracturing mechanisms (Polovina, 1980b, cited in Polovina, 1987, P. 50). Brecciation was initially in the form of breccia pipes that developed in permeable, fractured rock within the lower rhyodacite. As the fluids reached the normal fault, they traveled laterally along it beneath the impermeable hanging wall gouge zone, brecciating the footwall to form a hydrothermal breccia blanket (or sill). Hydrothermal breccia fragments mixed with gouge at the base of the hanging wall indicate that some movement along the fault occurred after emplacement of the hydrothermal breccia sill. A primary geochemical dispersion halo, roughly coincident with the zone of potassic alteration, developed in the footwall adjacent to the hydrothermal breccia sill. Alternatively, the geochemical halo formed around the breccia sill in both the footwall and hanging wall rhyodacite, and subsequently a portion of the hanging wall that was not K-altered or mineralized was structurally juxtaposed upon the mineralized column.
Comment (Geology): OVERALL SUMMARY The Bagdad-Chase Mine is located in the northern part of the Bullion Terrane in the central Mojave Desert, southern Basin and Range Province. The mine is about three miles south of the Kane Springs Fault, a northeast-striking dominantly right-lateral internal transform fault zone that separates the Bullion Terrane south of the fault from the Daggett (extensional) Terrane north of the fault (Dokka, 1986). At its western limit, the strike of the Kane Springs fault curves to a northwesterly trend and becomes the western bounding "break-away" (detachment) fault of the Daggett Terrane. Strata in the Bullion Terrane dip 20?-40? east-northeast in contrast to beds in the Daggett Terrane, which dip 55?-65? to the southwest. Just north of the Bagdad Chase Mine area, bedding appears from aerial photographs to dip to the southeast. In the area of the Bagdad Chase Mine, all of the surface exposures of the hydrothermal breccia have sharp hanging wall and footwall contacts with consistent northwest strike and 25?-40?northeast dip. The central Mojave underwent extensional deformation preceded by and contemporaneous with basalt to rhyolite volcanism in Miocene time (Gans and others, 2005; Dokka, 1986; Walker and others, 1990; Dokka and others, 1998; Glazner and others, 2002). During late Cenozoic time, the central Mojave experienced three structurally different and temporally separated intervals of deformation (Dokka and others, 1998): 1. ~N-S directed opening of the ~24-21 Ma Mojave Extensional Belt (Dokka 1989; Ross, 1995). The northern Mojave Desert underwent extension beginning ~24 Ma; detachment faults accounted for much of the extension and locally exhumed mid-crustal rocks (metamorphic core complexes). 2. ~E-W striking, dextral shearing (~21-18 Ma) along the Trans Mojave-Sierran shear zone (Dokka and Ross, 1995, 1996, 1998). At ~20 Ma, the kinematics along the northern boundary changed from extension to dextral shear and minor extension in the Trans Mojave-Sierran shear zone, and rocks within this east-west trending zone (southern Sierra Nevada and the central Mojave Desert) were rotated about vertical axes as much as ~40-60 degrees clockwise. 3. ~13-0 Ma Eastern California shear zone (Dokka and Travis, 1990ab; Dokka, 1993). From ~13-0 Ma, the region has been subject to right-lateral shearing within the Eastern California shear zone, which accounts for the numerous active, right-lateral, dominantly strike-slip faults in the Mojave region. Although widely accepted that plate motions directly controlled Neogene deformation of coastal areas of the southern Cordillera (e.g., Luyendyk, 1991, cited in Dokka and Ross, 1995), application to the interior of the North American plate has been hampered by lack of clear-cut geometric and kinematic links to the global plate circuit, and the poor correlation of plate boundary type with interior deformation (Dokka and Ross, 1995). Current understanding suggests that early Miocene extension in east-central Nevada occurred in a back-arc setting east of the subducting Farallon Plate north of the Mendocino Triple Junction, while extension and concurrent basalt to rhyolite volcanism in southeastern California developed opposite and east of the transform that was active along the North American plate margin south of the Mendocino Triple Junction. The calc-alkaline suite of rocks commonly occurs along destructive plate margins, but is also associated with regions undergoing extension. Not all terranes with calc-alkaline rocks are associated with subduction zones (Sheth and others, 2002).
Comment (Commodity): Commodity Info: the economic viability of this deposit is a function of recoverable gold content; silver and copper are byproducts.
Comment (Commodity): Ore Materials: Native gold, covellite, chalcopyrite, galena, chalcocite, chrysocolla, malachite, azurite, sphalerite
Comment (Commodity): Gangue Materials: Quartz, specular hematite, altered rhyodacite breccia fragments, altered rhyodacite porphyry wall rock
Comment (Geology): Breccia Sill Detailed mapping of the Bagdad Chase underground workings has shown that the breccia sill comprises four layered units that have sharp contacts and distinct textural differences. Subunit 1 is characterized by predominantly subrounded fragments of lower rhyodacite in a quartz-hematite matrix that constitutes 30-40% of the rock. The breccia fragments are not strongly leached or altered, and copper oxides are absent. Subunit 2 is 70-90% matrix by volume, containing angular, argillically altered rhyodacite fragments, and copper oxides. Subunits 1 and 2 are of limited extent, while Subunit 3 is the most continuous and has a maximum thickness of 7 m (23 ft) in the Bagdad Chase Mine. Subunit 3 is composed of 20-60% quartz-hematite matrix that contains angular to subrounded, argillically altered rhyodacite fragments. Copper and iron oxides are abundant in this sub-unit as fracture coatings and late stage cavity fillings. Subunit 4 is a transition zone of breccia into the lower rhyodacite, which exhibits argillic or potassic alteration. The clay gouge interval overlying the breccia is a fault gouge in upper rhyodacite that contains fragments of the hydrothermal breccia; this implies that there was fault movement after the emplacement of the breccias. The sharp hanging wall and footwall contacts and consistent strikes and dips of the breccia sill indicate that emplacement of this unit was fault controlled. However, the layering in the sill, and the fact that the breccias have a matrix of hydrothermal minerals rather than of rock flour, indicate that faulting alone could not have formed the breccias. Geochemistry The breccia sill subunits are geochemically distinct. Subunit 2 has a distinctly higher Au content than the other two units, while Subunit 1 is significantly lower in Cu content than the other two units. Each breccia unit represents a distinct brecciation and mineralization event, and the data suggest that there was a change in the chemistry of the hydrothermal fluids that formed the subunits. The concentration of Cu and Ag in the lower rhyodacite footwall to the breccia sill is anomalously high and is part of a primary geochemical dispersion halo that occurs only in the lower rhyodacite. The Cu and Ag contents in the upper rhyodacite hanging wall drop off to near zero above the breccia sill. Origin of the Hydrothermal Breccias The best evidence for the origin of the hydrothermal breccias is exhibited in a specimen of early-state (early-formed) breccia collected from one of the breccia pipes. The breccia fragments are angular and seem to have undergone little transport. Some of the individual fragments can be pieced together yielding the image of a shattered block. Individual fragments are surrounded and supported by a fine-grained homogeneous matrix; this implies that the rock was brecciated and the matrix precipitated simultaneously by a single pulse of hydrothermal fluid. Polovina concludes that a single rapid injection of magmatic fluid under high hydraulic pressure brecciated the lower rhyodacite by hydraulic- and/or thermal-fracturing mechanisms and provided the matrix filling the voids (Polovina, 1980b, cited in Polovina, 1987, p. 49).
Comment (Development): MINING AND PROCESSING METHODS Early high-grading of mineralized outcrops was followed by shaft-sinking [vertical and inclined (decline)], and underground drifting, stoping, and room and pillar mining. From 1901-1910, ore was processed by stamp mill, other crushing methods, and by cyanide plant in Barstow, California. From 1910-1916, ore was sent to a smelter in Clarksdale (near Jerome), Arizona for processing. In 1932 the Barstow Metals Extraction Co. began construction of a plant in Barstow to process Bagdad-Chase Mine tailings that were sent to the mill during the early 1900s. The tailings processing circuit included: tube mill grinder using Oceanside (San Diego Co.) pebbles; water washing; agitation using Dorr agitator and Pachucas (air agitation tanks); acid treatment (H2SO4 and HCl); neutralization with lime; addition of iron scrap and zinc shavings; Dorr thickeners; cyanide treatment; and filtering (Merrill filters). From 1938-1939, ore was shipped from the Bagdad Chase Mine to Magma Copper Company's smelter at Superior, Arizona; some shipments also went to American Smelting and Refining Company's smelter at Hayden, Arizona. Around 1972 Bagdad Chase, Inc. reportedly began open-pit operations at Stedman, which continued through 1975. In 1987, Bentley Resources, Vancouver, B. C., announced plans for extensive exploration and drilling around the Bagdad Chase, to bring the Bagdad Chase operations back into production, and to pour the first gold dore bar in the second quarter of 1988. Operation plans called for an annual production of 20,000 troy oz Au from three open pits: Bagdad, Middle Mine, and Roosevelt. Capital cost was estimated at $4.5 million; production costs were estimated at $152(U.S.). Test metallurgical work by Hazen Research Inc. showed ~95% gold recovery using an agitated vat cyanide leach. The ore was to be ground to 75% minus-200 mesh; final gold recovery was to be by the Merrill-Crowe system to produce gold dore bars. This MRDS reporter found no record of implementation of these plans. RECLAMATION The nature and amount of reclamation in the Bagdad-Chase Mine area is unknown to this MRDS Reporter; this can be determined by contacting the California Department of Conservation's Office of Mine Reclamation, Sacramento, CA, or the San Bernardino County, CA, Land Use Services Department (phone: 909-387-8311), which oversees mine reclamation; San Bernardino County is Lead Agency for mine reclamation. Satellite imagery and high-altitude aerial photographs from Google Earth and NASA World Wind 1.3 suggest that the mine is idle and has not been fully reclaimed; little if any equipment remains onsite. Open-pit workings (~1972-1975; possibly late 1980s): three relatively shallow pits (Bagdad, Middle Mine, and Roosevelt pits) and adjacent hillside excavations involving approximately 0.02 square mile of disturbed ground (estimated from satellite imagery and aerial photos from Google Earth and NASA World Wind 1.3). CURRENT STATUS The mine appears to have been idle since about 1976 when the first open-pit mining operations reportedly ceased; some additional open-pit mining may have taken place during the late 1980s, but no record of late 1980s mining has been found by this MRDS Reporter.
Comment (Geology): HYDROTHERMAL ALTERATION The hydrothermal alteration and geochemical dispersion pattern at the Stedman district are evidence for the structural evolution of the mineral deposit. A schematic cross-section showing the relative distribution of the alteration zones about the breccia sill is displayed and discussed by Polovina (1987, p. 49-50). There is an asymmetric alteration pattern about the breccia sill in the area of the . In the lower rhyodacite, going towards the ore, the alteration types are propylitic, potassic, and argillic; whereas the overlying upper rhyodacite exhibits only propylitic alteration. The hydrothermal breccias are associated with potassic alteration in the lower rhyodacite, but the breccias have argillically altered clasts and a matrix of quartz and hematite and do not contain potassium minerals. This implies that there was a change in the composition of the hydrothermal fluids. The K2O content of the lower rhyodacite decreases toward the contact with the breccia sill, suggesting that the siliceous fluids were injected later and leached the previously high-K2O content from rocks near the contact. GEOCHEMICAL DISPERSION HALO There is a primary geochemical dispersion halo of base and precious metals that is roughly coincident in extent with the potassic alteration zone, and does not extend into the upper rhyodacite. The plot of geochemical data versus distance from the breccia sill indicates that there is a dispersion halo of "Au"* (should read "Ag"*), Cu, and Pb that extends approximately 12 m (39.4 ft) into the lower rhyodacite. The plot indicates that the upper rhyodacite may contain anomalously high values of these metals within 1 m (3.3 ft) above the breccia contact, beyond which there is a rapid decline to background values. This implies that the mineralizing fluids traveled through the lower unit, but the upper unit was either not involved in the mineralizing event, or subsequently unaltered/unmineralized upper rhyodacite was structurally juxtaposed upon the mineralized column. [Also, it is likely that the clay gouge along the breccia sill-upper rhyodacite contact acted as a nearly impermeable barrier to the migration of hydrothermal fluids into the upper rhyodacite (MRDS Reporter).] * the text of Polovina's report refers to "Au", Cu, and Pb; Polovina's Figure 9 shows a plot of "Ag", Cu, and Pb within the dispersion halo; "Ag" values range from about 1.5 to about 3.5 ppm and are consistent with Polovina's Figure 5.
Comment (Workings): Workings Type: 1. Historic underground workings (1901-1954); 2. Open-pit workings: (~1972-1975). Description of Mine Workings: 1. Historic underground workings (1901-1954): 4+ vertical shafts from 125 to 400 feet deep; 450-foot, 40? (30? also reported), N 72? W- trending inclined shaft (decline); over 5000 feet of drifts and crosscuts at various levels (90-, 140-, 200-, 300-, and 400-foot levels); glory hole from the 90-foot level to the surface (working from the 125-foot shaft). Mining was by a modified method of coal mining using pillars (room and pillars), also post and head board occasionally, with practically no timbering. 2. Open-pit workings (~1972-1975): three relatively shallow pits (Bagdad, Middle Mine, and Roosevelt pits) and adjacent hillside excavations involving approximately 0.02 square mile of disturbed ground (estimated from satellite images and aerial photos from Google Earth and NASA World Wind 1.3).
Comment (Geology): TECTONIC SETTING The Bagdad-Chase Mine is located in the northern part of the Bullion Terrane in the central Mojave Desert, southern Basin and Range Province. The central Mojave has undergone extensional deformation, preceded by and contemporaneous with basalt to rhyolite volcanism in Miocene time (Gans and others, 2005; Dokka, 1986; Walker and others, 1990; Dokka and others, 1998; Glazner and others, 2002). Mineralization at the Bagdad Chase is believed to be detachment-fault-related and of the same or slightly younger age as the deposit's associated presumed early Miocene-age rhyodacite porphyry intrusive rocks. Such deposits contain either copper-gold or lead-zinc-silver minerals that are typically found along low-angle normal faults (detachment faults) or along high-angle faults in the hanging walls of the detachment faults (Spencer and Welty, 1989, Long, 1992, cited in Tosdal and others, 1992, p. 38). Massive replacement bodies, breccias, and veins of specular hematite are characteristic of these deposits. During late Cenozoic time, the central Mojave experienced three structurally different and temporally separated intervals of deformation (Dokka and others, 1998): 1. ~N-S directed opening of the ~24-21 Ma Mojave Extensional Belt (Dokka 1989; Ross, 1995). The northern Mojave Desert underwent extension beginning ~24 Ma; detachment faults accounted for much of the extension and locally exhumed mid-crustal rocks (metamorphic core complexes). 1.2. ~E-W striking, dextral shearing (~21-18 Ma) along the Trans Mojave-Sierran shear zone (Dokka and Ross, 1995, 1996, 1998). At ~20 Ma, the kinematics along the northern boundary changed from extension to dextral shear and minor extension in the Trans Mojave-Sierran shear zone, and rocks within this east-west trending zone (southern Sierra Nevada and the central Mojave Desert) were rotated about vertical axes as much as ~40-60 degrees clockwise. 2.3. ~13-0 Ma Eastern California shear zone (Dokka and Travis, 1990ab; Dokka, 1993). From ~13-0 Ma, the region has been subject to right-lateral shearing within the Eastern California shear zone, which accounts for the numerous active, right-lateral, dominantly strike-slip faults in the Mojave region. Although widely accepted that plate motions directly controlled Neogene deformation of coastal areas of the southern Cordillera (e.g., Luyendyk, 1991, cited in Dokka and Ross, 1995), application to the interior of the North American plate has been hampered by lack of clear-cut geometric and kinematic links to the global plate circuit, and the poor correlation of plate boundary type with interior deformation (Dokka and Ross, 1995). Current understanding suggests that early Miocene extension in east-central Nevada occurred in a back-arc setting (east of the subducting Farallon Plate north of the Mendocino Triple Junction), while extension and concurrent basalt to rhyolite volcanism in southeastern California developed opposite and east of the transform that was active along the North American plate margin south of the Mendocino Triple Junction. The calc-alkaline suite of rocks commonly occurs along destructive plate margins, but is also associated with regions undergoing extension. Not all terranes with calc-alkaline rocks are associated with subduction zones (Sheth and others, 2002).
References
Reference (Deposit): Northern Miner, June 15, 1987: NM on-line archives.
Reference (Deposit): Dokka, R. K., 1986, Patterns and modes of early Miocene crustal extension, central Mojave Desert, California, in Mayer, Larry, Editor, Extensional Tectonics of the Southwestern United States: A Perspective on Processes and Kinematics: Geological Society of America Special Paper 208, p. 75-95.
Reference (Deposit): Wright, L. A., Stewart, R. M., Gay Jr., T. E., and Hazenbush, G. C., 1953, Mines and mineral deposits of San Bernardino County, California: California Journal of Mines and Geology 49, nos. 1 & 2, p. 49-192.
Reference (Deposit): Walker, J. D., Bartley, J. M., Glazner, A. F., 1990, Large-magnitude Miocene extension in the central Mojave Desert: implications for Paleozoic to Tertiary paleogeography and tectonics: Journal of Geophysical Research, Vol. 95, No. B1, p. 557-569.
Reference (Deposit): Tucker, W. B., and Sampson, R. J., 1940, Economic mineral deposits of the Newberry and Ord Mountains, San Bernardino County: California Journal of Mines and Geology, v. 36, no. 3, p. 232-233.
Reference (Deposit): Tucker, W. B., 1934b: Bagdad-Chase Mine tailings: California State Mining Bureau Field Report #37; CGS (formerly CDMG) Minefile Folder No. 322-5555.
Reference (Deposit): Mansfield, Ross, 2005: Off Road touring in the Buckeye mining district; Ludlow, Ragtown, Stedman and the Ludlow & Southern Railway: http://www.off-road.com/dirtbike/features/2005/ludlow_stedman/
URL: http://www.off-road.com/dirtbike/features/2005/ludlow_stedman/
Reference (Deposit): Long, K. R., 1992, Descriptive model for detachment-fault-related polymetallic deposits, in Bliss, J. D., ed., Developments in mineral deposit models: U.S. Geological Survey Bulletin 2004, p. 52-58.
Reference (Deposit): Glazner, A. F., Walker, J. D., Bartley, J. M., and Fletcher, J. M., 2002, Cenozoic evolution of the Mojave block of southern California: Geological Society of America Memoir 195, p. 19-41.
Reference (Deposit): Feller, Walter, 2002: Stedman: Mojave Desert Ghost Town Books: http://digital_desert.com/stedman/.
URL: http://digital_desert.com/stedman/
Reference (Deposit): Gans, Philip, DeVecchio, D., Singleshort ton, J., Van Pelt, J., Wong, M., and Reynolds, J., 2005, Cenozoic magmatic and structural evolution of the central Mojave Desert, California: new constraints from 40Ar/39Ar geochronology and thermochronology: Geological Society of America, Cordilleran Section 101st Annual Meeting, April 29-May 1, 2005, Paper No. 44-10.
Reference (Deposit): Dokka, R. K., Ross, T. M., and Lu, G., 1998, The trans Mojave-Sierran shear zone and its role in Early Miocene collapse of southwestern North America, in Holdsworth, B., Dewey, J., and Strachan, R., Eds., Continental Transpressional and Transtensional Tectonics: Geological Society of London Special Publication 135, p. 183-202.
Reference (Deposit): Cloudman, H.C., 1913: Pacific Mines Corp., formerly Bagdad Chase & Roosevelt Consolidation: California State Mining Bureau Field Report 111; CGS (formerly CDMG) Minefile Folder No. 322-5555.
Reference (Deposit): California Mining Journal, 1987, Old Bagdad Chase gold mine, gearing up for new production: California Mining Journal, v. 57, no. 3, p. 3-4.
Reference (Deposit): Northern Miner, April 11, 1988: NM on-line archives.
Reference (Deposit): Northern Miner, February 29, 1988: NM on-line archives.
Reference (Deposit): Northern Miner, July 25, 1988: NM on-line archives.
Reference (Deposit): Mosier, D. L., and Menzie, W. D., 1986, Grade and short tonnage model of epithermal quartz-alunite Au, in Cox, D. P., and Singer, D. A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 159-161.
Reference (Deposit): Belden, L. B., 1952, as reported in an article in the San Bernardino Sun-Telegram: Bagdad Chase was discovered in 1899 by John Suter; cited in the California Mining Journal, November 1987, p. 4.
Reference (Deposit): Bagdad Chase Inc., 2006, 10-K 1999 Annual Report: http://www.getfilings.com/o0000009128-00-000001.html.
URL: http://www.getfilings.com/o0000009128-00-000001.html
Reference (Deposit): Portions of various unpublished reports, and information from various Internet websites, contained in CGS (formerly CDMG) Minefile Folder No. 322-5555.
Reference (Deposit): Tucker, W. B., 1934a: Bagdad Chase & Roosevelt Mines: California State Mining Bureau Field Report #111, revised; CGS (formerly CDMG) Minefile Folder No. 322-5555.
Reference (Deposit): Polovina, J. S., 1987, Origin and structural evolution of gold-silver-copper bearing hydrothermal breccias in the Stedman mining district, southeastern California in Bulk mineable precious metal deposits of the western United States, Guidebook for field trips, April 6-8, 1987, p. 45-51.
Reference (Deposit): Polovina, J. S., 1984, Origin and structural evolution of gold-silver-copper bearing hydrothermal breccias in the Stedman mining district, southeastern California, in Wilkins, Joe, Jr., Gold and silver deposits of the Basin and Range province, western U.S. A.: Arizona Geological Society Digest, Vol. XV, Tucson, Arizona, p. 159-165.
Reference (Deposit): Polovina, J. S., 1980b, The geology and mineral deposits of the and vicinity, Stedman district, San Bernardino County, California [M. S. Thesis], University of California, Los Angeles, 125 p.
Reference (Deposit): Royer, F. W., Mining Engineer, 1934, Report on ore shipments from the Bagdad Chase property from 1910 to 1916 in Tucker, W. B., 1934: State Mining Bureau Field Report 111, May 20, 1934; CGS (formerly CDMG) Minefile Folder No. 322-5555.
Reference (Deposit): Ross, D. G., 2006: The Bagdad Chase Mine: www.ttrr.org/ls_text/lspb_002.html.
Reference (Deposit): Polovina, J. S., 1980, Mineralized hydrothermal breccias in the Stedman district, San Bernardino County, California, in Fife, D. L. and Brown, A. R., Editors, Geology and Mineral Wealth of the California Desert: South Coast Geological Society; Santa Ana, California, p. 314-317.
Reference (Deposit): Tucker, W. B., 1917: Pacific Mines Company, formerly Bagdad, Chase, and Roosevelt Mines: California State Mining Bureau Field Report Supplement 111; CGS (formerly CDMG) Minefile Folder No. 322-5555.
Reference (Deposit): Tosdal, R. M., Rytuba, J. J., Theodore, T. G., Ludington, S. L., Jachens, R. C., Miller, R. J., Keith, W. J., 1992, Evaluation of selected metallic and nonmetallic mineral resources, West Mojave Management Area, southern California: U.S. Geological Survey Open-File Report 92-595, 89 p.
Reference (Deposit): Stewart, R. M., 1951, Preliminary Report No. 30, San Bernardino Co., April 1951, 2 p.; CGS (formerly CDMG) Minefile Folder No. 322-5555.
Reference (Deposit): The Gold Ledge, p. 3 of 6: www.goldledge.com/history/docs_html/metals_san_bernardino.html
Reference (Deposit): Sheth, H. C., Torres-Alvarado, I. S., and Verma, S. P., 2002, What is the "Calc-alkaline rock series"?: International Geology Review, vol. 44, no. 8, 1 August 2002, p. 686-701.
California Gold
"Where to Find Gold in California" looks at the density of modern placer mining claims along with historical gold mining locations and mining district descriptions to determine areas of high gold discovery potential in California. Read more: Where to Find Gold in California.
