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North Bloomfield Mining District, Nevada Co., California, USAi
Regional Level Types
North Bloomfield Mining DistrictMining District
Nevada Co.County

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Latitude & Longitude (WGS84):
39° 22' 16'' North , 120° 54' 48'' West
Latitude & Longitude (decimal):
Locality type:

Location: A former Au-Ag-Pt mining area discovered in 1851 by three prospectors scouring the hills near San Juan Ridge. After discovering gold in the Tertiary gravels they set up camp and started mining. Running short of supplies, one miner went to town and attracted attention by paying for his drinks in the local saloon with gold nuggets. On his way back to camp he was secretly followed. The newcomers, however, after trying their luck ended up empty handed. They named the local creek Humbug Creek and moved on. This district is located in north-central Nevada County about 10 miles NE of Nevada City. This district also includes the "diggings" at Lake City to the west, Derbec to the N, and Relief to the E. The location selected by the USGS for latitude and longitude is the approximate center of the Malakoff Diggings hydraulic workings in sec. 1, T17N, R9E, as shown on the USGS 7½-minute North Bloomfield quadrangle.

This district lies within the following T&R sections: secs. 1, 2, 11 & 12, T17N, R9E; secs. 4 through 9, T17N, R10E; sec. 36, T18N, R9E; and, secs. 28 through 33, T18N, R10E, MDM.

History: Gold was discovered here originally in 1851. Hydraulic mining began about 1853 and, by 1855, had become a major industry. An extensive system of ditches and flumes supplied water to the mines from Bowman Lake and other reservoirs to the E in the high Sierra Nevada. The town of North Bloomfield was first known as Humbug City. Its name was changed to Bloomfield and then to North Bloomfield when someone discovered there was a Bloomfield in Sonoma County. As more and more gold-bearing gravel was excavated, the hydraulic pits here became enormous. The pit at the famous Malakoff mine is more than 7,000 feet long, 3,000 feet wide, and up to 600 feet deep. The tailings from the hydraulic operations were allowed to flow into the rivers, a procedure that led to litigation with the farmers who lived downstream. The district's hydraulic workings were so extensive that they were largely responsible for the silting up of the Sacramento and Yuba rivers leading to the Sawyer Decision in 1884 and the demise of hydraulic mining in the Sierra Nevada. In a famous court case in 1884 (Woodruff vs. North Bloomfield Gravel Mining Company (16 Fed. Rep. 25)), Judge Lorenzo Sawyer issued an injunction against the dumping of mine debris into the Sacramento and San Joaquin Rivers and their tributaries. Injunctions against other mines soon followed, and hydraulic mining in the Sierra Nevada has not been important since that date. The Malakoff diggings and part of the old town are now a state park. The U.S. Geological Survey, beginning in 1966, initiated an exploration program in this area to determine the extent of unmined gravels. Drilling and geophysical exploration have been done.

Hydraulic mining of the gravel deposits began in 1853 and the town of Humbug was established. By 1855, hydraulic mining had become a major industry, and Humbug became a regional mining center. In search of a more respectable name, Humbug was renamed Bloomfield, but when it was discovered that a town named Bloomfield already existed in Sonoma County, it was again renamed North Bloomfield.

North Bloomfield prospered and eventually had over 2000 residents. By 1860, many of the individual claims were purchased and consolidated into the North Bloomfield Gravel Mining Company, which pursued a coordinated effort in the Malakoff Diggings. Hydraulic mining techniques were fully developed in the Malakoff pit, which eventually became California's largest single hydraulic operation.

To support the operation, as well as those in neighboring districts along San Juan Ridge, the three leading mining companies (North Bloomfield Gravel Mining Co., Milton Mining and Water Co., and Eureka Lake and Yuba Canal Co.) spent over $5 million constructing an extensive 320 mile system of ditches, flumes, and reservoirs to bring water to the mines from Bowman lake and other sources in the High Sierra. In order to manage the water deliveries, in 1878 the Edison Company built the world's first long distance telephone line at a cost of $6,000. The lines ran 60 miles from French Corral to the west to Bowman Lake and connecting the intervening mining areas of Birchville, North San Juan, Cherokee, North Columbia, Lake City, North Bloomfield, Moore's Flat, Graniteville, and Milton.

To provide better drainage and disposal of tailings, the North Bloomfield Gravel Mining Company dug a 7,874- foot-long tunnel through bedrock under the Malakoff pit. Completed in 1874, the tunnel allowed the wholesale disposal of tailings directly into the South Yuba River rather than little Humbug Creek. With completion of the tunnel, the North Bloomfield Gravel Mining Company reached its zenith, continuously operating seven monitors, round the clock, and processing about 50 thousand tons of gravel a day. In 1880, electric lights were installed in the Malakoff pit and the world's first long distance telephone line was installed to service and monitor activities in the pit and the extensive water supply network.

After the 1884 Sawyer Decision had brought an end to hydraulic mining at North Bloomfield, drift mining was implemented at several locations to recover the lower gravels. By 1888, 10,135 feet of tunnels had been driven under the former Malakoff hydraulic pit. The pay channel averaged 400 feet wide. The blue lead gravel was in places as much as 135 feet thick and extremely cemented. Gravel required blasting and breaking with sledges before washing. Washing was done with 3 monitors. A hydraulic gravel elevator raised the gravel to a flume in which it was washed and conducted to an impounding reservoir

Hydraulic mining was also replaced by drift mining at Relief Hill. By 1919, the Union Tunnel had been driven 2,500 feet from which $30,000 to $90,000 was produced annually for a number of years.

Gravels in the Derbec area were not hydraulicked. At the Derbec workings, drifts exploited a generally easterly trending section of the channel, which was buried deep under San Juan Ridge. The gravel deposits are 415 feet thick at the shaft. The basal gravels extracted ranged front 6-18 feet thick. The width of the channel varied greatly. The gravel was breasted to a width ranging from 150 feet to 600 feet. Bedrock in the tunnel consisted of slate, which at places swelled.

The drift mine was accessed by a shaft 475 feet deep with a steam-powered hoist works to raise the ore. A main bedrock drift ran from the foot of the shaft up the bedrock channel. Careful timbering of the tunnel was required to shore up weak roof rocks. 4,500 feet up the drift from the shaft, an upraise to the surface allowed emergency escape. The ore was moved in 1,550 pound ore cars. A drain tunnel 5,000 feet long extended from the bottom of the shaft to the town of North Bloomfield.

Cross drifts were run from the main pay channel to the west and the gravel breasted out.

The pay gravel was not cemented and included fine gravel to boulders. Gold was extracted by washing. Gravel was first washed through a 600-foot flume then impounded to allow complete slaking. It was then flushed down a 4,000-foot flume with the tailings being impounded in a series of impoundments. Flumes were two feet wide by two feet deep. Monitors were used on the washing dump.

The historic town of North Bloomfield and the Malakoff Diggings are now within the Malakoff Diggings State Historic Park administered by the California Department of Parks and Recreation.

The total output of the Malakoff mine was about $13.5 million (period values), and the Derbec mine has probably yielded $1 million to $2 million (period values) according to Lindgren (1911). He estimated that 30 million cubic yards had been removed and 130 million remained at North Bloomfield. Jarman (1927) estimated that 40 million cubic yards had been removed and more than 50 million remained.

Mineralogy: Mineralization is hosted in unconsolidated Tertiary sand & gravels. Ore materials included native gold, fine to coarse gold and nuggets (.900 fine). Gangue materials included quartz and metamorphic gravels. Accessory minerals included magnetite, ilmenite, zircon, pyrite, amphibole, epidote, chlorite, and siderite.

Geology: The main channel of the Tertiary Yuba River entered this district from the NE via Derbec. A branch joined this channel from Relief Hill to the SE. At North Bloomfield the main channel curves west and north and then west again as it continued toward the North Columbia district. Although the gravels are as much as 600 feet thick, most of the values were obtained from the lower 130 feet of blue gravel. These gravels yielded from 4 to 10 cents (period values) of Au per cubic yard. Bedrock consists of slate, schist, and phyllite. Local rocks include Eocene nonmarine rocks, unit 1 (Northern and Central California).

In the North Bloomfield District, basement rocks include metasedimentary rocks of the Lake Combie-Slate Creek Complexes on the west and metavolcanic rocks, slates, and argillites of the Calaveras Complex to the east. These differing basement rocks are juxtaposed along the Ramshorn Fault, which bisects the district in a north-northwesterly direction.

Bedrock is overlain by thick Eocene auriferous gravels that are in turn overlain by Valley Springs and Mehrten Formation rocks on San Juan Ridge in the north part of the district. Elsewhere in the district, the Valley Springs and Mehrten rocks have been stripped by erosion exposing the underlying gravels.

Basal Eocene Auriferous Gravels: Due to extensive erosion of the Valley Springs and Mehrten Formation formations, the North Bloomfield and neighboring districts are known for immense bodies of exposed gravels. The North Bloomfield District contains several separate hydraulic workings including the extensive workings at Malakoff Diggings west of the town of North Bloomfield, and smaller operations at Lake City (1 mile west), Derbec (2 miles NE), and Relief Hill (2 miles SE). In part because of the volcanic capping of San Juan Ridge, which encroached upon the workings at Lake City, Derbec, and Relief, these workings were limited in scale relative to the Malakoff workings.

The auriferous gravels were deposited by a main branch of the Tertiary Yuba River. This branch flowed southwestward from the vicinity of Snow Point in the adjacent Moore's Flat District and entered the North Bloomfield District near Derbec. It then continued southwestward, depositing the extensive placer deposits near North Bloomfield. A smaller tributary joined the river from Relief Hill to the southeast. The main channel curves west and north at North Bloomfield, then westward again before exiting the district.

As is common in most of the auriferous Tertiary gravels of the northern Sierra Nevada, the deposits can be divided lithologically and texturally into a lower and upper unit. Total thickness of both units within the district reached upwards of 600 feet. The lower unit, or blue lead of the early miners, rests directly on bedrock, and contains the richest ores. Gold was .900 fine. At the Malakoff Diggings, the lower unit consists of cobbles, pebbles, and boulders. The deep gravels are generally well-cemented and quartz-rich. At North Bloomfield, the best recoveries came from the lower 130 feet of blue gravels, with average values in the Malakoff Diggings being approximately $0.56 per cubic yard ($35.00 oz. gold). At the Derbec working, the lowermost gravels yielded an average $6.30 per cubic yard ($35.00 oz. gold).

Lower gravels are generally immature and composed of bluish-black slate and phyllite of the Calaveras Complex, weathered igneous rocks, and quartz. In the Malakoff Diggings, large boulders of siliceous phyllite 6 to 10 feet in diameter rest on bedrock within the lower gravels.

The upper gravels form the majority of the deposits and, unlike the lower gravels, are often well-exposed in cliffs and bluffs along the old river channels. In the Malakoff pit, the upper gravel unit is at least 325 feet thick. These gravels are much finer, with clasts seldom larger than pebble size and characterized by an abundance of quartz sand and clay and silt beds. Large-scale cross-bedding and cut-and-fill features are common. Upper gravels generally have significantly lower values than the deeper gravels and are often barren. Average values in the upper gravels at Malakoff ran $0.49 - $0.67 per cubic yard (at $35.00 ounce gold). Clay beds exposed in the old pit walls have frequently failed and mud and earth flows in the old pit are common.

Regional geologic structures include the Big Bend-Wolf Creek Fault, Ramshorn Fault and the Melones Fault Zone. Local,structures include the Ramshorn Fault.

Ore deposits: Mineral occurrence model information: Model code: 119; USGS model code: 39a; BC deposit profile: C01. C02; Deposit model name: Placer Au-PGE; Mark3 model number: 54. The ore bodies are irregular in form. Controls for ore emplacement included mechanical accumulation on irregular bedrock riffles and within river- and stream-channel lag gravels, bars, and point bar deposits.

Commodity Information: The average value of lower gravel at Malakoff Diggings was $0.56 per cubic yard (at $35/ounce). Average value of upper gravel was $0.049-$0.067 per cubic yard (at $35/ounce).

Average value of lower gravels at Derbec workings was $6.30 per cubic yard (at $35/ounce).

Average value of the undifferentiated gravels at Relief Hill ranged from $0.15-$0.22 per cubic yard (at $35/ounce).

Regions containing this locality

North America PlateTectonic Plate

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Standard Detailed Strunz Dana Chemical Elements

Commodity List

This is a list of exploitable or exploited mineral commodities recorded from this region.

Mineral List

Mineral list contains entries from the region specified including sub-localities

13 valid minerals.

Detailed Mineral List:

'Amphibole Supergroup'
Formula: AX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
Reference: USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10310656.
Formula: TiO2
Description: Occurs as crystals in placer gravels.
Reference: Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 72.
Formula: BaSO4
Reference: Hanks, Henry Garber (1884), Fourth report of the State Mineralogist: California Mining Bureau. Report 4, 410 pp. (includes catalog of minerals of California pp. 63-410), and miscellaneous observations on mineral products): 78; Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 97.
'Chlorite Group'
Reference: USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10310656.
Formula: Fe2+Cr3+2O4
Reference: U.S. Geological Survey, 2005, Mineral Resources Data System: U.S. Geological Survey, Reston, Virginia.
Formula: {Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Reference: USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10310656.
Formula: Au
Localities: Reported from at least 16 localities in this region.
Formula: Fe2O3
Reference: U.S. Geological Survey, 2005, Mineral Resources Data System: U.S. Geological Survey, Reston, Virginia.
Formula: Fe2+TiO3
Formula: (Fe,O,OH,H2O)
Reference: U.S. Geological Survey, 2005, Mineral Resources Data System: U.S. Geological Survey, Reston, Virginia.
Formula: Fe2+Fe3+2O4
Formula: Mn, O
Reference: U.S. Geological Survey, 2005, Mineral Resources Data System: U.S. Geological Survey, Reston, Virginia.
Formula: FeS2
Reference: USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10310656.
Formula: SiO2
Formula: Mn2+SiO3
Reference: U.S. Geological Survey, 2005, Mineral Resources Data System: U.S. Geological Survey, Reston, Virginia.
Formula: FeCO3
Reference: USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10310656.
Formula: Zr(SiO4)
Reference: USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10310656.

List of minerals arranged by Strunz 10th Edition classification

Group 1 - Elements
Group 2 - Sulphides and Sulfosalts
Group 4 - Oxides and Hydroxides
Group 5 - Nitrates and Carbonates
Group 7 - Sulphates, Chromates, Molybdates and Tungstates
Group 9 - Silicates
Unclassified Minerals, Rocks, etc.
'Amphibole Supergroup'-AX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
'Chlorite Group'-
'Psilomelane'-Mn, O

List of minerals arranged by Dana 8th Edition classification

Metals, other than the Platinum Group
Group 2 - SULFIDES
AmBnXp, with (m+n):p = 1:2
Group 51 - NESOSILICATES Insular SiO4 Groups Only
Insular SiO4 Groups Only with cations in >[6] coordination
Group 58 - SOROSILICATES Insular, Mixed, Single, and Larger Tetrahedral Groups
Insular, Mixed, Single, and Larger Tetrahedral Groups with cations in [6] and higher coordination; single and double groups (n = 1, 2)
Group 65 - INOSILICATES Single-Width,Unbranched Chains,(W=1)
Single-Width Unbranched Chains, W=1 with chains P=5
Group 75 - TECTOSILICATES Si Tetrahedral Frameworks
Si Tetrahedral Frameworks - SiO2 with [4] coordinated Si
Unclassified Minerals, Mixtures, etc.
'Amphibole Supergroup'-AX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
'Chlorite Group'-
'Psilomelane'-Mn, O

List of minerals for each chemical element

H Limonite(Fe,O,OH,H2O)
H Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
H Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
C SideriteFeCO3
O QuartzSiO2
O PsilomelaneMn, O
O HematiteFe2O3
O RhodoniteMn2+SiO3
O Limonite(Fe,O,OH,H2O)
O ChromiteFe2+Cr23+O4
O MagnetiteFe2+Fe23+O4
O IlmeniteFe2+TiO3
O BaryteBaSO4
O AnataseTiO2
O ZirconZr(SiO4)
O Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
O Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
O SideriteFeCO3
F Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
Al Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
Al Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Si QuartzSiO2
Si RhodoniteMn2+SiO3
Si ZirconZr(SiO4)
Si Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
Si Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
S BaryteBaSO4
S PyriteFeS2
Cl Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
Ca Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Ti IlmeniteFe2+TiO3
Ti AnataseTiO2
Ti Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
Cr ChromiteFe2+Cr23+O4
Mn PsilomelaneMn, O
Mn RhodoniteMn2+SiO3
Fe HematiteFe2O3
Fe Limonite(Fe,O,OH,H2O)
Fe ChromiteFe2+Cr23+O4
Fe MagnetiteFe2+Fe23+O4
Fe IlmeniteFe2+TiO3
Fe PyriteFeS2
Fe Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Fe SideriteFeCO3
Zr ZirconZr(SiO4)
Ba BaryteBaSO4
Au GoldAu


Sort by

Year (asc) Year (desc) Author (A-Z) Author (Z-A)
Irelan, William, Jr. (1888b), Eighth annual report of the State: California Mining Bureau. (Report 8), 946 pp.: 454-459.
Hobson, John B. & E.A. Wiltsee (1893), Nevada County, North Bloomfield Mining District, California Information Bureau (Report 11): 11: 311-312.
Lindgren, Waldemar (1900), Description of the Colfax sheet, California: USGS Geological Atlas, Colfax folio (Folio No. 66), 10 pp.
Lindgren, Waldemar (1911), The Tertiary gravels of the Sierra Nevada of California: USGS Professional Paper 73, 226 pp.: 139-141.
MacBoyle, Errol (1919), Mines and mineral resources of Nevada County, North Bloomfield Mining District, California Journal of Mines and Geology, California Mining Bureau (Report 16): 16: 45-51.
Jarmin, Arthur (1927), Report of the Hydraulic Mining Commission upon the feasibility of the resumption of hydraulic mining in California, Bloomfield hydraulic mine, California Division of Mines 23rd Report of the State Mineralogist (Report 23): 107-110.
Clark, Wm. B. (1970a) Gold districts of California: California Division Mines & Geology Bulletin 193: 101.
USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10310656.
USGS 7½-minute quadrangle, North Bloomfield, California, topo map.

USGS MRDS Record:10310656

Localities in this Region

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