Cerro Gordo

Site Name

Primary: Cerro Gordo
Secondary: Cerro Gordo Mine
Secondary: Union Mine
Secondary: Ignacio Mine
Secondary: San Filipe Mine
Secondary: Santa Maria Mine
Secondary: Morningstar Mine
Secondary: Hart Mine
Secondary: Newtown Mine
Secondary: Belmont Mine
Secondary: Perseverance Mine
Secondary: Ella Mine
Secondary: Summit No. 2 Mine
Secondary: Armagh Mine
Secondary: Hebrew Mt. Claim
Secondary: Crag Claim
Secondary: Mormon Claim
Secondary: San Filipe Claim
Secondary: Jefferson Claim
Secondary: Santa Maria claim
Secondary: Native Son Claim
Secondary: Enterprise claim
Secondary: Gentile Claim
Secondary: Union Lead
Secondary: Union Placer claim
Secondary: Ragged Edge claim
Secondary: Pagan claim
Secondary: Omega claim
Secondary: November claim
Secondary: Bluff claim
Secondary: Northern Star Claim
Secondary: Bluejay Claim
Secondary: La Despreciada Claim
Secondary: Consolidated Group
Secondary: Bousey Silver
Secondary: Omega Group

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Commodity

Primary: Zinc
Primary: Lead
Primary: Silver
Secondary: Copper
Secondary: Gold

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Location

State: California
County: Inyo
District: Cerro Gordo

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Land Status

Land ownership: BLM Administrative Area
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.

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Holdings

Not available

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Workings

Not available

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Ownership

Owner Name: BLM Ridgecrest, CA

Owner Name: Mike Patterson
Home Office: P.O. Box 221, Keeler, CA, 93530

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Production

Not available

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Deposit

Record Type: District
Operation Category: Past Producer
Deposit Type: Hydrothermal stock, massive; Hydrothermal vein and replacement
Operation Type: Surface-Underground
Discovery Year: 1865
Years of Production:
Organization:
Significant: Y
Deposit Size: S

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Physiography

Not available

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Mineral Deposit Model

Model Name: Polymetallic replacement

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Orebody

Form: Pipe; Tabular, lens

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Structure

Type: R
Description: Swansea-Coso Thrust System, Cerro Gordo Anticline

Type: L
Description: Cerro Gordo Anticline, Cerro Gordo Fault, Buena Vista Fault, La Despreciada Fault, Omega Fault

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Alterations

Alteration Type: L
Alteration Text: Negligible

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Rocks

Name: Shale
Role: Associated
Age Type: Associated Rock
Age Young: Mississippian

Name: Dacite
Role: Associated
Description: porphyry
Age Type: Associated Rock
Age Young: Tertiary
Age Old: Late Cretaceous

Name: Andesite
Role: Associated
Description: porphyry
Age Type: Associated Rock
Age Young: Tertiary
Age Old: Late Cretaceous

Name: Porphyry
Role: Associated
Description: Monzonite
Age Type: Associated Rock
Age Young: Late Cretaceous

Name: Monzonite
Role: Associated
Description: porphyry
Age Type: Associated Rock
Age Young: Late Cretaceous

Name: Diabase
Role: Host
Age Type: Host Rock
Age Young: Tertiary
Age Old: Early Cretaceous

Name: Marble
Role: Host
Age Type: Host Rock
Age Young: Middle Devonian
Age Old: Early Devonian

Name: Limestone
Role: Associated
Age Type: Associated Rock
Age Young: Mississippian

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Analytical Data

Not available

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Materials

Ore: Hydrozincite
Ore: Pyrite
Ore: Chalcopyrite
Ore: Anglesite
Ore: Cerussite
Ore: Tetrahedrite
Ore: Galena
Ore: Smithsonite
Gangue: Limonite
Gangue: Shale
Gangue: Marble

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Comments

Comment (Geology): Jefferson diabase dike Major ore bodies also occurred in the sheared and decomposed rocks of the Jefferson diabase dike which followed the Jefferson Chimney from 700 to 200 levels before diverging eastward. Ore was deposited in shoots raking steeply south or southwest and was mined from below the 900 level to between the 200 and 400 levels. Decomposed diabasic rock contained scatted seams and veinlets of galena, lead carbonate, and limonite with little mineralization or alteration of the marble walls. The greatest concentration of ore minerals was towards the footwall and the dike rock itself was partially replaced in places (Knopf,1918). It is not known why the sulfide bearing solutions did not greatly affect the marble which generally is more receptive to sulfide replacement than diabase. Only at the intersection of the Jefferson Chimney with the Jefferson Dike was shattered marble strongly mineralized. Despreciada Ore Bodies These ore bodies, discovered in 1925, occurred in fractured gray and white Lost Burro Formation marble withion the footwall of the east dipping Despreciada Fault. The ore bodies occurred in a nearly vertical pipe-like geometry suggestive of the Jefferson Chimney. This geometry has led many to inconclusively interpret them as the faulted deeper continuation of the Jefferson Chimney. Zinc Ore Bodies In contrast to the Darwin District, no mineable quantities of sphalerite (primary zinc ore) were discovered at Cerro Gordo. Instead, supergene deposits of the zinc carbonates smithsonite and hydrozincite occurred along the edges of the silver lead chimney stopes and as massive smithsonite bodies. Smithsonite ore extended laterally from the Union Chimney for as much as 100 feet (Knopf, 1918) from which the majority of zinc ore was produced (Union zinc ore body). Since the Union chimney ores were very low in zinc, Stewart (1966) attributed the extensive smithsonite deposits to leaching of the zinc from primary zinc minerals (especially sphalerite) from the lead-silver deposits by meteoric water and its redeposition in adjoining marble as smithsonite and hydrozincite. The size of the Union zinc ore body indicates, however, that it could not have come solely from the Union Chimney ores, but required a much larger upper ore body now lost to erosion.

Comment (Geology): Ore Occurrence in the Cerro Gordo Mine The Cerro Gordo Anticline itself is the primary ore controlling structure. Faults and fractures were also important in localization of the Cerro Gordo ore bodies. Some of the faults are thought to have been pre-mineralization features with a long history of pre and post mineralization movement. The two primary structural trends of north and northwest trending fractures permitted entry of ore bearing solutions with their zones of intersection being especially conducive to mineralization of the chimney ore bodies. Mineralized north and northwest trending fissures in the footwall marble of the Cerro Gordo Fault include the Bullion Vein, the Zero Fissure Vein, and numerous feeding fissures encountered within and adjacent to the Union Chimney. Some structural features are clearly post-mineralization, the most important of these being the northwest trending Buena Vista and Despreciada faults which appear to have truncated and offset several ore bodies. Ore zones in the hanging wall of the Buena Vista Fault are thought to be down faulted portions of the upper ore chimneys (Merriam, 1963). The bottoming of the two major ore chimneys at depth have also been attributed to faulting. Contacts between ore material and wall rock marble is sharp and clean. Only locally are areas of wall rock hydrothermally dolomitized but only to a small degree. Unlike mines of the Darwin District, there is very little silicification of carbonate wall rocks to calc silicates. The main Cerro Gordo silver-lead ore bodies occur as massive pipe-like replacement bodies or chimneys, ore shoots in fissures, and as ore shoots and pockets in quartz veins. These ore bodies occur almost exclusively in shattered marble of the Lost Burro Formation, however, ore has also been found in fissures within the Jefferson diabase dike. The best ore bodies occur in a localized northwest trending area measuring only 1,500 feet long by 200 feet wide (Knopf, 1918). The main ore minerals are argentiferous galena, cerussite, anglesite, smithsonite, tetrahedrite, and pyrite. Ore genesis has been attributed to at least two events. Emplacement of the low silica massive lead-silver chimney ores preceded the high silica quartz veins such as the San Filipe Vein which cuts the Union Chimney. Despite the ores not being contemporaneous, the quartz filled fractures and the fissures in which the green porphyry bodies were emplaced were important conduits for the earlier chimney ore fluids. The most noteworthy ore bodies which made Cerro Gordo a great silver and lead producer were emplaced as shoots in to inclined chimneys which raked steeply to the south in the plunge direction of the Cerro Gordo Anticline. The two main bodies are the Union Chimney (or China Stope) at the north end of the mine area and the Jefferson Chimney approximately 1,200 feet to the south. Both chimneys consisted of long vertical to south dipping zones of intensely fractured marble, near the Cerro Gordo Fault, that partly followed and partly crosscut bedding. These zones of fracturing may have been related to movement on the Cerro Gordo Fault.

Comment (Deposit): Approximately 94% of California's lead production and 28% of California's zinc production has come from lead-silver-zinc deposits in the western Basin and Range province which includes the Death Valley region and most of Inyo County. Most California deposits lie in a mineralized belt trending northwest-southeast and extending from the Inyo Mountains to the Nopah Range. The bulk of production comes from three leading mining districts within this trend; the Cerro Gordo District in the southern Inyo Mountains, the Darwin District, and the Tecopa District at the south end of the Nopah Range east of Death Valley. The Darwin District ranks first in mineral production, followed by the Cerro Gordo and Tecopa districts. At Cerro Gordo, marbles of the Devonian Lost Burro Formation are the primary host rocks for the mesothermal lead-silver ore bodies. The two largest ore bodies are the Union Chimney (China Stope) and Jefferson Chimney, two near vertical irregular replacement ore bodies. These ores are composed variously of argentiferous galena, cerussite, anglesite, tetrahedrite, and pyrite emplaced by silica poor mineralized solutions. Lesser ore bodies consist of lenticular shoots which have replaced marble along fractures and fissures distributed throughout a area approximately 1500 feet by 200 feet wide. These ore bodies generally trend north or northwest and dip approximately 70? west. Quartz veins, such as the Santa Maria and San Filipe veins carry ores of argentiferous galena and tetrahedrite. Zinc ore is composed mainly of smithsonite, a secondary zinc carbonate. Cerro Gordo ore bodies are localized by a combination of structural features. The district lies near the apex of the large Mesozoic Cerro Gordo Anticline in an area complexly fractured with normal faults and fractures of both northerly and northwesterly trend. The main fault is the Cerro Gordo Fault, a north trending and westerly dipping normal fault of uncertain age along which the Union Dike intruded. The fault is accompanied by numerous related parallel fractures in the footwall that served as avenues for mineralized solutions. A younger set of northwesterly trending fractures intersect the northerly trend causing vertical zones of fracturing in which the Union and Jefferson chimney massive lead-silver ores formed. A second period of younger mineralization occurred with the emplacement of galena-tetrahedrite bearing silica rich solutions which deposited white quartz vein ores in several of the northwest trending fractures.

Comment (Commodity): Commodity Info: Argentiferous galena, tetrahedrite, cerussite, anglesite, chalcopyrite, and pyrite occured in hydrothermal stock and replacement ore bodies. Argentiferous galena and tetrahedrite occured in quartz veins. Smithsonite and hydrozincite occured as massive supegene zinc ores

Comment (Commodity): Ore Materials: Ag Pb ore materials: Argentiferous galena, tetrahedrite, cerussite, anglesite, chalcopyrite, pyrite Zn ore materials: smithsonite, hydrozincite

Comment (Commodity): Gangue Materials: Marble, shale, limonite

Comment (Development): In 1911, L. D. Gordon and Associates leased the properties. About 160 feet north of the Belshaw Shaft on the 900 level, a winze was sunk to the 1,100 level with drifts on the 1,000 and 1,100 levels. A 250 foot winze was also driven 450 feet south of the main shaft with a drift from the bottom and one at about 1,030 feet. L. D. Gordon and Associates were the first to receognize the value of the zinc carbonate ores. In 1914, they acquired title and reorganized the properties as the Cerro Gordo Mines Co. The Cerro Gordo Mines became a major source of high grade zinc carbonate ore between 1911 and 1919 (Merriam, 1963). Tortuous stopes were opened just east of and adjoining the old Union Chimney (China Stope) to exploit the zinc ore. The largest zinc stopes extended upward roughly on bedding incline from the 550 level to the south end of the Bullion Tunnel workings. During this period, new silver-lead ore bodies were also opened in the Jefferson Dike and Jefferson Chimney. By 1917, Cerro Gordo had electric power for hoisting, compressors, and to operate a newly constructed 5.5 mile Leschen tram (which replaced the older aerial tramway) from Cerro Gordo to the railroad at Keeler. From 1919 to 1923, Cerro Gordo was idle. From 1923 - 1927, it was operated under lease by a W. W. Waterson. In 1925, a significant new ore body was found by the Estelle Mines Company on the La Despreciada claim west of the old Cerro Gordo Mines. From 1928 - 1929, the Estelle Mining Company leased the Cerro Gordo properties, after which they were leased to the American Smelting and Refining Company which operated them until 1933. No important discoveries have been made since the La Despreciada ore bodies. During this period the ore mined and shipped amounted to 10,000 tons with a gross value of $305,630. The approximate grade of ore shipped was .053 oz gold, 29 oz silver, 41% lead. Since 1933, various lessees have driven short and unsuccessful headings from the 200, 400, and 550 levels. From May 1935 to Sept 1936, the property was leased by the "Silver-Lead Syndicate". During 1937 and 1938, the mine was again idle (Tucker & Sampson, 1938). In 1940, the Cerro Gordo group was acquired by the Silver Spear Mining Corp. By this time the Cerro Gordo properties comprised 43 claims and about 550 acres. The property was operated from September 1943 - Sept 1944 by the Golden Queen Ming Company. Their work consisted of diamond drilling and drifting in an attempt to find a faulted segment of the Jefferson Ore body. In 1944, Goldfields of South Africa reevaluated the property and the mine was temporarily reopened with little success. Diamond drilling was conducted at the south end of the mine from the 900 level in search of deep inferred fault segments of the Jefferson chimney but no mineable quantities of ore were found. In 1946, the property was leased to W. C. Rig and associates and purchased by them in 1949. In exploring in and around the China Stope area between the 200 and 550 levels, they did several thousand feet of diamond drilling and drove several thousand feet of drifts, raizes and winzes. Some diamond drilling was also done from the 500 foot level. A small amount of ore was developed and shipped. Cerro Gordo has been idle ever since.

Comment (Geology): Two main zones, the lower Zone A and upper Zone B can be recognized in the district. Zone A is highly fossiliferous, containing numerous, bioherms, stromatolites, and coral. The more fossiliferous zones are commonly light and dark gray banded due to the presence of carbon. Zone B is primarily light gray - white marble with infrequent stromatolite beds in the lower part. Only rocks of the Lost Burro Formation and Chainman Shale have been largely penetrated in the Cerro Gordo Mines. In almost all important ore bodies, fractured Lost Burro marble was the most favorable host for sulfide ore replacement. Stratification in the Lost Burro formation also influenced ore disposition and bedded ore bodies are found in a small portion of the Union Chimney. The Tin Mountain limestone conformably overlies the Lost Burro marble. Where it makes up Cerro Gordo Peak, it is 350 feet thick and thins northward along the crest of the range. A thin fine grained white to cream colored quartzite of the middle Mississippian Perdido Formation overlies the Tin Mountain. This unit thins to extinction towards the northwest and was included with the overlying Chainman Shale in mapping by Merriam (1963). The upper Mississippian Chainman Shale in the Cerro Gordo area is approximately 1,000 feet thick and is exposed in a belt 0.5 - 1 mile wide along the crest of the Inyos from 2 miles south of Cerro Gordo to Daisy Canyon to the north. Paleozoic rocks in the Cerro Gordo area are intruded by igneous intrusive rocks of 2 general ages. The major plutons in the area tend to be quartz monzonites and related rocks coeval with the Sierra Nevada plutons. The smaller stocks are composed of varying compositions suggesting magmatic differentiation (Merriam, 1963). The quartz monzonite Newsboy stock is exposed one mile east of Cerro Gordo. The Hart Camp stock (half mile northwest of Cerro Gordo in the Chainman shale) is composed of monzonite porphyry, the Cerro Gordo stock (immediately south of Cerro Gordo Peak) is a garnetized syenodiorite (Knopf, 1918) and the Ignacio stock ( half mile southwest of Cerro Gordo) is a hornblende-quartz monzonite porphyry (Merriam, 1963). Younger igneous rocks tend to be andesitic-dacitic porphyry dikes that cut the older granitoid rocks. An isolated rock type represented by a single diabasic dike in the Cerro Gordo Mines, is older than the andesitic-dacitic porphyry rocks but its age is uncertain relative to the granitoid rocks (Merriam, 1963). Local areas of intense contact metamorphism occur, especially in those rocks in contact with the Ignacio and Cerro Gordo stocks. Hydrothermal alteration and replacement in some of the smaller igneous intrusions themselves is also common, especially in the diabase, andesite, and dacitic dikes and sills. In the Cerro Gordo Mine's workings, several important igneous intrusions cut the Lost Burro marbles and the Chainman shale. These include north trending monzonite and diabase dikes, and northwesterly trending dacite and andesite porphyry dikes.

Comment (Geology): Dunne and others (1978) recognized three episodes of Mesozoic deformation in the Inyo Mountain area. The earliest (mid Triassic-early Jurassic) involved regional folding and thrusting during which late Precambrian and Cambrian rocks were thrust over rocks as young as Permian in the Last Chance Thrust System. The most significant episode was of mid - late Jurassic age (Nevadan) and included fold deformation in the Swansea-Coso thrust system and the emplacement of many plutonic bodies in the Inyo Mountains and the Coso Range which are considered comagmatic with the Sierra Nevada Batholith. The Swansea-Coso Thrust System is a zone of high angle thrusts with little lateral slip that extends almost continuously from the southern Inyo Mountains to the Slate Range. During this pulse, Paleozoic and Triassic rocks were strongly folded into a series of broad northerly trending folds that were faulted, and intruded by igneous bodies. At Cerro Gordo, this deformation is represented by the large asymmetrical Cerro Gordo Anticline that dominates the structure of the Southern Inyos. Final Mesozoic deformation is represented by the White Mountains Fault Zone in the White Mountains and by minor numerous conjugate strike slip faults in the Inyo Mountains. Large scale northwest trending faults also divide the southern Inyo Mountains into linear blocks (Merriam, 1963). Most of these faults are reverse or thrust faults. A series of younger, more northerly trending normal faults, characteristic of the Great Basin are also present. Cenozoic tectonics are responsible for the current topographic features of the Basin and Range area. Stewart (1978) believes that back-arc spreading and right hand transform wrenching of the western continental margin invoked the Basin and Range horst and graben topography and extensive volcanic activity. Cenozoic faults are generally northerly striking high angle en-echelon normal faults, downthrown to the east and superimposed on the earlier Mesozoic structures. The southern Inyo Mountains are considered to be the western edge of the Basin and Range. Metallogeny The association of the lead-silver-zinc deposits in California's Basin and Range with granitic intrusives, carbonate rocks, and fracture systems, suggest future discoveries could be expected near known plutons or associated stocks, sills, and dikes. However, while the developed deposits were easily located by virtue of their rich oxidized surface ores, future deposits will be more obscure requiring an exploration program involving detailed regional geologic studies and employing all available geological, geochemical, and geophysical tools to define areas exhibiting promising geological and structural histories. Within the mineralized trend extending from the Inyo Mountains to southeast Inyo County, however, much of the land has been permanently withdrawn from exploration and incorporated in the Death Valley National Park, leaving only the northwestern and southeastern ends open for exploration or extension. Similarly, large tracts are also off-limits by inclusion in the China Lakes Naval Weapons Center.

Comment (Development): Mexican prospector Pablo Flores is credited with discovering the rich ore bodies at Cerro Gordo in 1865. For the first few years, Mexicans worked the surface exposures and smelted the ores in crude smelters or "vasos". When news of the discovery reached the Comstock Lode, the rush to Cerro Gordo was on. Cerro Gordo was originally included in the Lone Pine Mining District established in 1866, but when federal mining laws were implemented in 1872, the area was reorganized into the separate Cerro Gordo Mining District. One of the first newcomers to arrive was the experienced mining engineer M. W. Belshaw. He immediately recognized the richness of the ores and the need for a smelter to efficiently process the ore. Seeing opportunity, he bought an interest in the Union Mine, the richest mine in the district, in exchange for an interest in the first smelter he was to build at Cerro Gordo. Wanting to control all the mines in the district and thwart competition, Belshaw constructed the narrow road from Owens Lake to Cerro Gordo and imposed a toll. With the road built, Belshaw wasted no time building the Belshaw-Judson works based on his own methods for fluxing and smelting the Cerro Gordo ores. By 1868, Belshaw was producing silver lead bullion. Not satisfied with its early output, Belshaw invented and installed the Belshaw water jacket which equalized the heat in the furnace and resulted in output of 5 tons of bullion (worth $3,500) per day (De Decker, 1993). Meanwhile, Victor Beaudry, a local merchant, had acquired a half interest in the Union Mine through attachments on unpaid bills. In 1870, Beaudry built the second smelter at Cerro Gordo. Rather than compete with each other, Belshaw and Beaudry joined forces and by 1870 were the most powerful men in Cerro Gordo In 1870, the Union Mine was the most prolific of the Gordo Mines and was developed by a vertical shaft on the Union Chimney and by the Union Tunnel which struck the ore body 175 feet vertically below the discovery pit. Since 1869, the eastern firm, the Owens Lake Silver-Lead Company had encroached on Belshaw's ambitions by building a smelter/furnace on the shore of Owens Lake at Swansea and by buying interests in neighboring claims. To stifle this competition, Belshaw allowed his access road to fall into disrepair so the Owens Lake Company could only haul half loads at double the tolls and thus could not provide a continuous supply of ore to their furnace. Public outcry resulted in construction of a new road partway up the mountain. However, through a particularly difficult stretch, the original Belshaw road presented the only option, over which he collected reduced tolls. By 1872, Cerro Gordo was a well established camp with eleven active mines in the district. Regular shipments of lead-silver bullion were being shipped to San Francisco by way of Los Angeles and San Pedro (Merriam, 1963). This early trade with the settlement of Los Angeles was largely responsible for its survival and growth. Production was so prolific that the wagon trains could not keep up with the smelter output. In 1872, to shorten the trip, a small steamboat, the "Bessie Brady" was put to work hauling the bullion bars across Owns Lake from Keeler. Cerro Gordo's peak production occurred in 1874 with its smelters producing eighteen tons a day of lead-silver bullion. During this time, the output of a single smelter at Cerro Gordo amounted to 300 silver lead "base-bullion" bars each weighing 87 pounds and valued at $335 each. The freight wagons could not keep up with output and the bullion bars stacked up like cordwood and were frequently used to build temporary building s and shelters.

Comment (Environment): The Cerro Gordo District is centered around Cerro Gordo Peak (elevation 9,188 feet) within he rugged topography of the southern Inyo Mountains. Elevations within the district generally range from between 7, 500 feet and 9,188 feet. The Inyo Mountains mark a portion of the western edge of the Basin and Range geoprovince and are surrounded by the Saline Valley to the east, Owens Valley to the west, the White Mountains to the north, and the Darwin Plateau and Coso Range to the south. Relief between Cerro Gordo Peak and the Saline and Owens valleys are 8,129 feet and 5,618 feet respectively. The terrain is particularly rugged and steep and population is sparse. Most of the historic mine workings are on public lands administered by the BLM or on private lands. Since the early 1990s, portions of the Cerro Gordo mining camp have been undergoing restoration by private individuals as a historical and recreational destination. Remaining buildings include the American Hotel, the oldest standing hotel in California east of the Sierra Nevada. The town generally has a population of a few hardy souls for most of the year. In addition to the townsite are a main mine building that houses the lift for the main shaft, the large Union Mine dump above the town, various waste rock piles, the remains of an original smelter furnace, and at least 25 various openings. The closest community is the tiny hamlet of Keeler at the foot of the Inyo Mountains eight miles to the west. Lone Pine (pop. 1,660), the next larger community, is approximately 23 miles northwest. Vegetation above 7,500 feet consists primarily of juniper and pinon pine, below which are scattered joshua trees. On the lower slopes and valley floor sagebrush, greasewood, rabbit brush, desert holly, and salt brush dominate. The climate is arid mountainous high desert. Total annual precipitation is 6.67 inches at Haiwee Station (approximately 30 miles south in the Owens Valley), but is considerably greater at the higher elevations in the mountains. On the valley floor, average summer high temperature is 95.3? in July and average low temperature 28.8? degrees in January but these values decrease with elevation. Drainage is to the west and east into the Owens and Saline valleys respectively. The primary drainages from Cerro Gordo near the crest of the Inyos are Cerro Gordo Canyon which drains to the west into Owens Valley and San Lucas Canyon which drains the east flank into the Saline Valley. Perennial drainages in the arid mountains are rare and normal runoff is greater on the steeper east side of the Inyos where a few spring fed streams supplement normal runoff.

Comment (Identification): The Cerro Gordo lead-silver-zinc district comprises a rather localized area surrounding Cerro Gordo Peak (elevation 9,188 feet) in the southern Inyo Mountains of west central Inyo County, California. Formerly, the peak was called Buena Vista Peak, before later being renamed Cerro Gordo (Fat Hill) peak. Mines in the district were operated from the 1865 until 1949, during which time Cerro Gordo's mines produced in excess of 35,000 short tons of lead, 4.4 million ounces of silver, and 11,800 short tons of zinc worth over $17 million. Ore bodies consisted largely of argentiferous galena rich vertical replacement chimneys and fissure deposits in fractured Devonian Lost Burro Formation marble and silver bearing quartz veins. While there were a number of mines and prospects within the Cerro Gordo District, almost 90% of the production came from independent mines and workings localized in an area of less than 1 square mile below Cerro Gordo Peak and which later became collectively known as the Cerro Gordo Mines. These included the Union Mine, Santa Maria Mine, and San Filipe Mine. Given the Cerro Gordo Mines' preeminence, it is considered synonymous with the district for the purposes of this report. Mining activities in the district ceased in 1949. Currently, the remaining structures of the Cerro Gordo ghost town are undergoing private restoration.

Comment (Location): The Cerro Gordo District is located east of Owens Lake in the southern Inyo Mountains surrounding Cerro Gordo Peak. In the early days, the district included several individual mines which were later consolidated as the Cerro Gordo Mines. Other mines in the district included the Belmont, Morning Star, Sunset, Silver Spear, Ella, and Perseverance mines. The district covers an area of approximately eight square miles although the principle Cerro Gordo Mines lie within a radius of 1 mile of Cerro Gordo peak. Since Cerro Gordo Peak lies geographically near the center of the district, it has been chosen to represent the district location. The location latitude and longitude identify Cerro Gordo Peak on the USGS Cerro Gordo Peak 7.5 minute quadrangle. The reach the district, take State Highway 136 east from Lone Pine for 13 miles to the hamlet of Keeler. Turn left (northeast) on Cerro Gordo Road and travel 8 miles to the ghost town of Cerro Gordo and the Cerro Gordo Mines. The road ascends 4,600 feet through Cerro Gordo Canyon and is quite steep and precipitous in places.

Comment (Geology): Union Chimney The Union Chimney was the largest and richest ore body. It was localized within highly sheared and fractured marble in the foot wall of the Cerro Gordo Fault. Fracturing related to and parallel to the Cerro Gordo Fault provided avenues for the ascending mineralizing solutions. Ore was not continuous throughout the chimney, but occurred in erratic chambers, within the cracks and fractures of the shattered marble, and sometimes in open cavities. Usually, the wall rock contact was sharp with little or no alteration. The upper part of the chimney was nearly vertical, but below the 400 level it was inclined 30?-40? southward. On the 400 level, the chimney measured 147 feet x 48 feet. In the early days, ore was extracted from the surface downward to where the chimney bottomed between the 500 and 550 levels near an intersection the north green porphyry dike. Bottoming of the Union Chimney has been attributed to post mineralization faulting, but exploration efforts have not confirmed this (Merriam, 1963). Jefferson Chimney The Jefferson Chimney is in close proximity to the Cerro Gordo and the Buena Vista faults. The ore body raked southwest at about 80? and extended from the surface to below 900 feet where the chimney bottomed. Its lower terminus is thought to be the result of normal displacement along the Jefferson Fault but exploratory drilling has not confirmed this. The chimney pinches and swells throughout its length and is highly variable with a maximum cross section of 4,800 feet (Merriam, 1963). Ores were similar to those in the Union Chimney. The Jefferson Chimney is thought to be genetically related to the Jefferson diabase dike. Between the 200 and 700 levels, the dike passes through the chimney. Northerly trending fractures responsible for the Jefferson Dike and the northwesterly trending fractures responsible for the Zero Fissure Vein strike into the Jefferson Chimney. These fractures are thought to have been avenues that carried mineralized solutions into the Jefferson Chimney and also deposited important ore bodies within the dike itself. On the 900 level, the dike is on the west side of the chimney. Above the 200 foot level, the dike lies east of the chimney, paralleling the long axis of the chimney's cross section. The north-south elongation of chimney and its ore shoots on several levels indicates the northerly tending fractures which allowed intrusion of the dike influenced the shape and position of the chimney (Merriam, 1963). Similar to the Union Chimney, fracturing associated with the Cerro Gordo Fault provided a conduit for the ore solutions while fracture and fissure intersections help localize the individual ore shoots. Siliceous Veins Two siliceous veins, the San Filipe and Santa Maria veins, contained galena-tetrahedrite-barite type silver-lead ores within a quartz matrix. These veins were also important sources of silica for fluxing material in the Cerro Gordo smelters. The San Filipe Vein strikes about N 48? W and dips steeply to the southwest. It outcrops just 100 feet south of the Union Chimney. The vein cuts the Union Dike, but doesn't extend through the Cerro Gordo Fault into the Chainman Shale. On the 400 & 550 level it converges with the north green porphyry dike and then follows the dike contact with the marble. The Santa Maria quartz vein generally parallels the San Felipe Vein. The ores consisted of pockety ore bodies scattered for several hundred feet along the white quartz vein. Massive galena and masses of limonitic matter occurred within the vein while pockets of cavernous limonite and iron filled fractures were present in the brecciated marble between the Santa Maria and San Filipe veins. Like the San Felipe vein, it cuts the Union Dike and in places it is in contact with this monzonite porphyry dike.

Comment (Workings): For the first few years after discovery in 1865, the exposed ore bodies at Cerro Gordo were worked in pits and trenches. By 1870, the Union Mine's Union Chimney had become the most important working and was being developed by a vertical shaft and by the Union Tunnel (65 level) which was driven eastward 400 feet to encounter the chimney 175 feet below its outcrop. Similarly, the rich Jefferson Chimney was mined vertically to the level of the Buena Vista Tunnel. Between 1865 and 1877, various tunnels were driven eastward on the west flank of the peak to work specific shallow ore bodies. The more significant of these were the Buena Vista and the Santa Maria tunnels. The Buena Vista Tunnel (@ 68' level) was driven eastward almost 350 feet to intersect the Buena Vista Fault. The tunnel continued 400-500 feet south along the fault and east to work the Jefferson Chimney on the south end of the mine area (this tunnel was opened up and extended as the 86 level in the later Belshaw Shaft). The Santa Maria Tunnel (@ 90' level) extended 400 feet southeast to access the Santa Maria quartz vein. North of the Union Chimney, the Bullion Tunnel (@42' level) was driven 300 feet east to exploit the Bullion Vein surface exposure and approximately 600 feet of north and south drifts were driven along the vein. The Omega Tunnel (@ 200' level) was driven about 700 feet southeast to the ore bodies along the Omega Fault. Similarly, the Zero Tunnel (0' level) extended 200 feet east to intersect the Zero Vein which was drifted northward for approximately 100 feet. Over the years, numerous exploratory drifts have been driven from these tunnels adding several miles to their original courses. In 1877, when the ore quality declined and the principal workings had been consolidated into the Cerro Gordo Mines, the Belshaw Shaft was sunk about 1,800 feet west of Cerro Gordo Peak to explore for deeper ore bodies and to serve as the main mine entrance. The shaft was sunk vertically to 900 feet with levels at 86, 200, 400, 550, 700, and 900 feet. Extensive workings were extended to the north, east, and south from these levels. Upon completion of the shaft, ore could be hoisted to the Union Tunnel level, then trammed to the Belshaw furnace located 450 feet from the tunnel portal. In 1911, 160 feet north of the Belshaw Shaft on the 900 level, a winze was sunk to the 1,100 level with drifts on the 1,000 and 1,100 levels. A 250 foot winze was also driven 450 feet south of the main shaft with a drift from the bottom and one at about 1,030 feet. The total underground workings at Cerro Gordo are estimated at approximately 15 miles of tunnels and drifts (Tucker and Sampson, 1938).

Comment (Geology): Two important normal fault groups occur at Cerro Gordo. Absolute ages of these fault sets remains unknown. It is possible that some of these faults originated early under Nevadan compression as reverse or tear faults only to be reactivated later with normal displacement. The older of the two fault groups trends northerly and faults of this group are commonly cut by faults and fractures of a younger northwesterly trending group. The Cerro Gordo Fault is the most prominent fault in the Cerro Gordo Mine and is largely responsible for the mine's geology. The Cerro Gordo Fault, acting as a zone of weakness, allowed the intrusion of the Union Dike. It lies in a northerly trending zone of shearing that can be traced from Soda Canyon (2.5 miles south of Cerro Gordo) northward for approximately 6 miles towards the Saline Valley (Merriam, 1963). The fault itself trends northerly through the Cerro Gordo Mines and exhibits normal displacement with the Chainman shale (hanging wall) juxtaposed against the Lost Burro Formation (foot wall). In the footwall are numerous parallel fractures, fissures, and veins. These smaller breaks show no offset but are believed to be sympathetic to the Cerro Gordo Fault and served as avenues for ascent of the lead-zinc ore solutions (Merriam, 1963). In the deeper mine levels, the Omega fault parallels the Cerro Gordo fault on the west where it also separates Lost Burro marble from the Chainman Shale. The fault has not been recognized in the shallow mine levels or at the surface. It is believed to have originated as a sympathetic fault of the Cerro Gordo Fault. Several northwest trending faults, dikes, and foot wall veins terminate against the fault and don't cross into the Chainman shale. Younger, northwesterly trending faults, veins, and dikes cut the older northerly trending features. Within the northwesterly trending fault group, a zone of fracturing (Bonham Canyon Fault Zone) almost 1 mile wide trends southwest from Bonham Canyon to Cerro Gordo where it intersects the northerly trending faults at Cerro Gordo in an area of intense crushing and brecciation. A number of these northwesterly trending fractures provided the planes of weakness into which the green porphyry dikes were intruded and the silver bearing quartz veins (San Filipe and Santa Maria) were emplaced. Some of the northwesterly faults were pre-mineralization breaks and likely have a long history of movement. Intersections of these features with north trending breaks were important in ore fluid migration and the localization of ore body chimneys. The major faults in this group include the Despreciada, Buena Vista, and Jefferson faults. Both the Despreciada and Buena Vista faults cut and offset the older Cerro Gordo Fault. These two faults are thought to meet in an area of intensely fractured rock above the 900 level. The Despreciada Fault trends northwest and dips easterly. It was encountered between the 500 and 900 levels in the south part of the mine. At the 900 level, marble of the Lost Burro Formation makes up the footwall on the west. The hanging wall is composed of highly shattered marble, shale, and porphyry. Between the Despreciada Fault and the Jefferson Chimney on the 900 level are other east dipping faults which roughly parallel the Despreciada Fault. Among these is the Jefferson Fault which is thought to have cut the Jefferson Chimney below the 900 level. The westerly dipping Buena Vista Fault strikes N 28? W and has been traced downward to the 550 level.

Comment (Geology): Successful extensions of known deposits are more likely to be found by applying knowledge of the controls affecting ore deposition and post mineralization faulting. In the Cerro Gordo District, for example, the largest ore bodies occurred as fracture related replacement chimneys that abruptly terminated at depth, presumably due to faulting. While considerable efforts have been made to locate the presumed extensions, they have failed to conclusively confirm or disprove this interpretation, much less locate additional high grade ore. Only a thorough integrated study of the complex structural history integrated with geochemical and geophysical studies, and exploratory drilling is likely to yield new ore bodies nearby or at depth in former or new workings. Since exploration for and production of metallic deposits in this country are largely driven by international economics, environmental regulations, and inexpensive imports, significant efforts to locate and develop new reserves in the foreseeable are not expected. GEOLOGY OF THE CERRO GORDO DISTRICT Lead, silver, and zinc are the primary commodities of the district and are largely mined from replacement and fissure filling deposits within Devonian marble. Available information is limited to the more significant workings in the district which were consolidated under the name Cerro Gordo Mines in 1914. The main workings included the Union Mine, San Filipe Mine, and Santa Maria claim. Smaller mines in the district include the Morning Star, Belmont, Newsboy, Newtown, Ella, and Perseverance mines. Extensive mining preceded any detailed and comprehensive geologic studies at Cerro Gordo. Most of the deposits were mined out by the time Merriam published the first comprehensive study of the district in 1963. Stratigraphy The oldest exposed rocks in the district are early Ordovician Pogonip Group dolomites that outcrop 2 miles northeast of Cerro Gordo on the east flank of the Inyos. The exposure is in fault contact with the younger Ely Springs Dolomite and is conformably overlain by the mid-Ordovician Eureka Quartzite. The undifferentiated late-Ordovician Ely Springs and Silurian Hidden Valley dolomites outcrop in a narrow band approximately 4 miles long along the east flank of the Cerro Gordo Anticline from just east of Cerro Gordo Peak to Bonham Canyon on the north. Quaternary alluvial cover within San Lucas Canyon just north of the Cerro Gordo Mine bisects the outcrop. In the Cerro Gordo District, Merriam (1963) measured approximately 1,750 feet of massive saccharoidal Hidden Valley dolomite with quartzite and chert that, locally, has been hydrothermally altered to tremolitic material or commercial talc deposits. Marbles of the Devonian Lost Burro Formation host the main ore bodies at Cerro Gordo. It outcrops along the axis of the Cerro Gordo Anticline in a northwesterly trending belt about one mile wide from Cerro Gordo Peak to just west of New York Peak. North of Bonham Canyon, its outcrop widens where an arcuate exposure of Lost Burro marble follows the north wall of the canyon and trends northeast towards the east flank of the Inyo Range. Farther east, the Lost Burro rocks are obscured under Quaternary alluvium. As measured by Merriam (1963) on the northwest side of Cerro Gordo Peak, the unit is 1,600 feet thick and is composed of massive finely crystalline - subporcelaneous bluish-gray- dark gray marble that is generally pure and very low in clay, silica, iron, and magnesium. Along fractures , where metasomatic activity has occurred, the rock is mainly calcite. Siliceous zones are rare with the exception of localized hydrothermal jasperization along fractures.

Comment (Economic Factors): The Cerro Gordo District was California's preeminent silver and lead producing area during the decade following the Civil War. Total recorded production was on the order of 4.4 million ounces silver and 37,000 tons of lead. Zinc production, which commenced in 1911, totaled approximately 12,000 tons. Gold and copper production, important byproducts from the siliceous quartz vein ores, totaled about 2,000 ounces and 300 tons respectively (Merriam, 1963). In dollar terms, the total value of the Cerro Gordo District is estimated at $17 million of which the Cerro Gordo Mine produced $15 million. During its peak years the Cerro Gordo silver-lead bullion contained about 140 ounces of silver per ton. Average value of the bullion was $300/ton at $0.06/pound for lead and $1.29/ounce silver. Net profit after all costs of refining and transport often exceeded $150/ton.

Comment (Geology): The Union Dike is the largest and most significant. Lithologically similar to the Hart Camp and Ignacio stocks. It occurs along the main Cerro Gordo Fault plane throughout most of the mine and extends from surface exposures to below the deepest levels of the mine below 1,100 feet. The dike and fault plane strike northerly and dip steeply west separating the Lost Burro marbles in the footwall from the downthrown Chainman Shale in the hanging wall. Westerly normal displacement has faulted out the intervening Tin Mountain Limestone. The dike intruded along a northerly trending fracture zone which later influenced ore deposition and subsequently experienced post mineralization fault movement (Merriam, 1963). At shallow depths, the dike diverges from the fault plane and cuts the Chainman Shale section in the hanging wall. The Union Dike ranges in thickness form 12 feet at 400 level but thickens to as much as 65 feet at depth. The dike is highly altered and leached by hydrothermal activity (Merriam, 1963) The Jefferson Dike is another important intrusive body. Composed of altered diabase, the dike also trends northerly and dips to the west paralleling the Cerro Gordo Fault and Union Dike between the 550 and 900 levels where it lies west of the important Jefferson Chimney ore body. The dike is undated and may correlate with the regionally extensive diabase dikes of the Independence swarm. It intersects the Jefferson Chimney at the 550 level and above the 200 level lies to the east of the chimney. Near the south end of the mine, the Jefferson Dike intersects and cuts the Union Dike near the Jefferson Chimney. Elsewhere, between the 400-550 levels, the Jefferson Dike itself is cut and offset by a northwesterly trending green porphyry dike. Northwesterly trending porphyritic andesite and dacite dikes are common in the southern Inyo mountains. Three of these dikes strike northwesterly through the Cerro Gordo mine area. Designated the north, middle, and south green porphyry dikes (due to their green hue derived form chloritization), they intruded along northwesterly trending fault planes which experienced renewed movement after emplacement (Merriam, 1963). The north green dike cuts the Jefferson Dike on the 400 and 550 levels. It also cuts and offsets the Cerro Gordo Fault 150 feet west on the 400 level (Merriam, 1963). The middle green porphyry dike cuts the Cerro Gordo Fault and the Union Dike on the 900, 700, and 400 levels but with no apparent offset. Structure The structural features responsible for ore control are the Cerro Gordo Anticline, Cerro Gordo Fault, and fissures and faults that trend roughly north-south or northwest-southeast. Late Jurassic Nevadan compression folded the Paleozoic through Triassic section into the broad northwesterly trending Cerro Gordo Anticline with attendant thrusting and reverse faulting. Cenozoic extension later superimposed Basin and Range features on the Mesozoic structure. Normal faulting was especially active in the late Tertiary to recent time (Merriam, 1963). The Cerro Gordo Mine area itself is dominated by normal faults. Cerro Gordo lies along the axis of the anticline near its southern end where it begins to plunge southward. The anticline strikes approximately N 22? W and is roughly coincident with the axis of the southern Inyo Mountains. The limbs and crest of the asymmetric anticline are further deformed with superimposed small drag folds, disharmonic folds, and normal faults. The anticline is characterized by a steeply dipping west flank with exposed beds of Chainman Shale, Keeler Canyon limestone, and Tin Mountain limestone with a gently dipping east flank on which the Lost Burro Formation and Hidden Valley dolomite are exposed. Ore bodies and the majority of mine workings are localized on the west limb near the axis of the anticline.

Comment (Geology): INTRODUCTION The Cerro Gordo District is primarily a lead-silver district located in the southern Inyo Mountains within a localized zone of mineralization controlled in part by normal faulting and igneous intrusives. Replacement lead and silver deposits are concentrated in chimney-like replacement bodies and fractures in a zone associated with the Cerro Gordo Fault and associated faults and fractures. Smithsonite has been mined as commercial zinc ore, largely from one large deposit in the vicinity of the Union Chimney lead-silver ore body. The majority of the district's production has come from ore bodies within Devonian marble of the Lost Burro Formation. REGIONAL SETTING The Cerro Gordo District is one of several lead-silver-zinc districts in a mineralized trend extending over 100 miles from Cerro Gordo in the southern Inyo Mountains to the Tecopa District in the Nopah Range of southeastern Inyo County. The smaller Ubehebe, Modoc, and Panamint districts are also considered part of this trend. The Inyo Mountains form the western fringe of the Basin and Range which is characterized by Cenozoic northwesterly trending parallel mountain ranges separated by structurally controlled valleys. West of the Inyo Mountains is the Owens Valley, a structural valley marking the eastern front of the Sierra Nevada Range. To the east lies the Saline Valley. The Inyo Mountains extend into the White Mountains to the north and into the Talc City Hills to the south. Stratigraphy Rocks in the southern Inyo Range consist of a deformed Ordovician through Permian sedimentary sequence including limestones, dolomites, quartzites and shales, and terrestrial and volcanic Triassic rocks. Granitic plutons, sills, and dikes are common. Various intrusions have caused localized contact metamorphism and hydrothermal alteration of carbonate rocks and regional metamorphism of limestones to marbles is common. At Cerro Gordo, Devonian age marbles host the primary ore bodies. Tertiary volcanic rocks cover much of the southern Inyo Mountains. Regionally, the Ordovician - Permian section comprises approximately 11,100 feet of marine limestone, dolomite, shale, and minor quartzite (Merriam, 1963) deposited as a miogeoclinal wedge on the passive continental margin, and later thrusted eastward as allochthonous thrust sheets during the Antler and Sonoma orogenies. Pre-Mississippian rocks are mainly dolomite while Mississippian through Permian rocks are primarily limestone. Ordovician beds are exposed from Cerro Gordo to as far south as the Talc City Hills. The early-Middle Ordovician Pogonip Group dolomite is overlain by the middle Ordovician Eureka Quartzite. Dark gray, thick bedded and cherty dolomite of the late Ordovician Ely Springs dolomite overlies the Eureka Quartzite. The Silurian-Devonian periods are represented by the Hidden Valley Dolomite and the Lost Burro Formation, but in the Cerro Gordo area the Ely Springs dolomite and the Hidden Valley dolomite are often undifferentiated. Merriam (1963) assigned the upper part of the Hidden Valley Dolomite to the early Devonian with the conformably overlying Lost Burro Formation being of middle to late Devonian age. The Lost Burro Formation is the host rock of the main Cerro Gordo ore bodies. Unlike its type area where the Lost Burro Formation is relatively pure dolomite, in the southern Inyos it is primarily pure limestone or marble with limited dolomitization confined only to the transition zone with the Hidden Valley dolomite. The Mississippian is represented by three distinct lithologic units; the lower Mississippian Tin Mountain limestone, middle Mississippian Perdido Formation, and the upper Mississippian Chainman shale. The dark gray resistant of the Tin Mountain limestone forms the prominent high western slope of Cerro Gordo Peak.

Comment (Development): The lack of water was an early problem. Water was originally imported by pack train or acquired from snowmelt in the winter. In 1874, a pipeline was brought in from the Cerro Gordo Spring, 3 miles to the north. Steam pumps lifted water 1,860 vertical feet to storage tanks at the summit, from where it flowed by gravity. This cut the cost of water in half, but was plagued by freezing in winter. This water system remained in operation until the 1930s. In 1873, the Owens Lake Silver Mining and Smelting Company, owners of the San Filipe Mine interfered with Belshaw's plans to take control of all of Cerro Gordo by disputing Belshaw's claim to the Union Lode. The San Filipe Mine exploited a silver quartz vein near the Union shaft. Originally surface works, they purchased a local tunnel (San Filipe Tunnel) and began driving it towards the vein until Belshaw noticed galena on their waste dumps. Belshaw alleged they were mining his Union Chimney lode and in response made claim to the Santa Maria and San Felipe claims. Meanwhile, Beaudry acquired the mortgage on the San Filipe Tunnel and foreclosed to shut down their operations. These actions led to bitter and lengthy litigation when the Owens Lake Company countered with a claim to the Union Mine. The courts finally ruled in favor of the Owens Lake Company, giving them rights to the Union Mine. Belshaw appealed the decision to the State Supreme Court and in 1876, the litigation was concluded with the San Filipe owners settling for a small interest in the Union Mine. The two opposing companies combined the properties into the Union Consolidated Company which included the San Filipe and Santa Maria veins, the Union Chimney, and the Cerro Gordo Fault and its associated ore bodies. Cerro Gordo prospered until 1876, during which time Los Angeles had grown from a frontier outpost to an established city due to prosperity brought about by the Cerro Gordo silver & lead trade. Belshaw and Beaudry's Union Mine, the Owens Lake Silver Mining and Smelting Company's Santa Maria Mine and the San Felipe Mine had become the main silver lead producers in the region. But Cerro Gordo's demise was swift. While production peaked in 1874, the higher grade ore bodies were rapidly depleting with the Union Chimney being largely worked out. Even the Jefferson Chimney, having been mined from the surface to the 900 level abruptly ended. In 1877 a new vertical shaft, the Belshaw Shaft was sunk to a 900 foot depth in a effort to locate deeper ores and stop the decline in ore coming from the mine. The main reason for the shaft was to locate the continuation of the Union Chimney which was lost at the 550 level, presumably by faulting. Crosscuts were extended at 86, 200, 400, 550, 700, and 900 feet but the Belshaw shaft failed to find the continuation of the Union Chimney or any other significant high grade ore bodies. In 1877, fire destroyed the Union Mine hoist works and the Belshaw-Judson Furnaces were shut down the following year. The Beaudry smelter continued to operate until late 1879. Cerro Gordo was nearly deserted when the last load of bullion was shipped in 1879. The Carson and Colorado Railroad, which reached Keeler in 1883, rekindled interest in Cerro Gordo. The mines were reopened by small mining companies and lessees on a limited basis. While the Union Mine again produced small quantities of ore, exploratory activity produced few new reserves. In 1905, the Great Western Ore Purchasing Company acquired the Union Mine and produced a little ore into 1907 at which time the mine was taken over by the Four Metals Mining Company. With the intent of both reopening the mine and working the old smelter slags, the company built a 200 ton smelter near Keeler and built an aerial tramway connect the two. The company instead went bankrupt.

Comment (Geology): A change from normal marine carbonate environment to terrestrial sand and silt is recorded in the unconformably overlying thin quartzite beds of the Middle Mississippian Perdido Formation which ranges from 50-200 feet thick at Cerro Gordo. The Perdido is conformably overlain by the upper Mississippian Chainman Shale, a dark gray-black carbonaceous, silty, sandy shale to argillite with limestone interbeds up to 70 feet thick. It separates the Tin Mountain from the conformably overlying Permo-Pennsylvanian Keeler Canyon Formation. Close to 4,000 feet of Permo-Pennsylvanian section is exposed in the southern Inyo Mountains (Merriam, 1963). Generally, these rocks are impure carbonate and argillaceous rocks that have been variously metamorphosed and recrystallized to marble, argillites, and hornfels. Near intrusive bodies, the carbonates are commonly altered to tactite and calc-hornfels (Merriam, 1963). The Keeler Canyon is a widespread unit of impure, shaly limestone with shale interbeds that become purer towards the base. The unit is generally incompetent and highly deformed exhibiting thicknesses of between 1,300 and 2,500 feet at Cerro Gordo suggesting both fault shortening and compressive thickening. Generally barren in the southern Inyo mountains, a metamorphosed and silicified section of the Keeler Canyon Formation is the host rock for the important silver-lead-zinc ores in the Darwin District to the south. The Permian system in represented by interbedded silty and pure limestones, argillaceous shales, siltstones and conglomerates of the Owens Valley Formation. These units rest with local unconformity on the Keeler Canyon and are exposed from the Darwin Hills almost to Independence. Undifferentiated Triassic marine and terrestrial volcanic rocks overlie the Owens Valley Formation to the west at the foot of the Inyo Mountains. Overlying the Owens Valley Formation to the west and at the foot of the Inyo's are undifferentiated Triassic marine and terrestrial volcanic rocks. Tertiary and Quaternary sedimentary deposits are regionally abundant with Plio-Pleistocene fanglomerates flanking the Inyo and surrounding ranges. Regionally, the Paleozoic section was intruded by several Mesozoic batholiths and associated stocks, sills, and dikes that are frequently important to ore localization. These include the Hunter Mountain batholith to the east and the Coso Range batholith to the south (both considered coeval with Sierra Nevada). Quartz monzonite is the primary rock type. During the Cenozoic, regional extension produced widespread normal and strike-slip faulting, volcanism, and shallow intrusive activity. Extensive Cenozoic volcanic rocks are present in large parts of the southern Inyo Mountains, but are absent in the area of the Cerro Gordo Mines. Most of the sedimentary rocks in the Cerro Grodo region have undergone mild metamorphic or metasomatic alteration due to igneous plutonic activity. In general, purer limestones have been regionally metamorphosed to marbles in the Cerro Gordo area or locally silicified into calc silicate rocks and tactites as at Darswin. Shaly limestones and shales have been altered to calc-hornfels and argillites and sandstones to quartzites. Regional structure The Inyo Range is a long narrow elevated fault block within a regional structural fabric resulting from several periods of deformation in the western Basin and Range area including Mesozoic folding and faulting which dictated the overall structure of the Paleozoic rocks, and late Cenozoic faulting which superimposed the present Basin and Range topography.

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References

Reference (Deposit): De Decker, M, 1993, Mines of the Eastern Sierra, La Siesta Press, Glendale, California, pp 57-65.

Reference (Deposit): Merriam, C. W., 1963, Geology of the Cerro Gordo Mining District, Inyo County, California: U. S. Geological Survey Profession Paper 408, 83 p.

Reference (Deposit): Nadeau, R. A., 1965, City-makers, the story of southern California's first boom, 1868-76, Trans-Anglo Books, 168 p.

Reference (Deposit): Nadeau, R. A., 1965, Ghost towns and mining camps of California, Ward Ritchie Press, 278 p.

Reference (Deposit): Tucker, W. B. and Sampson, R. J., 1938, Mineral resources of Inyo County, in California Journal of Mines and Geology, vol 34, no. 4, pp. 431 -434.

Reference (Deposit): Miscellaneous information on the Cerro Gordo District is contained in File Number 322-7211 (CGS Mineral Resources Files, Sacramento)

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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.