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Blue Tent Mining District, Nevada Co., California, USAi
Regional Level Types
Blue Tent Mining DistrictMining District
Nevada Co.County
CaliforniaState
USACountry

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Key
Latitude & Longitude (WGS84):
39° 18' 27'' North , 120° 58' 4'' West
Latitude & Longitude (decimal):
Locality type:


A Au-Pt placer/hydraulic mining area.

Location and History: The Blue Tent District is a Au-Ag-Pt mining area located about 4 miles NE of Nevada City and the Nevada City District in western Nevada County. It lies in secs. 20-23, 26-29 & 32-35, T17N, R9E, MDM. It was discovered before 1850. The area was mined years ago by hydraulicking, but little or no mining has been done since. The gravels are part of the Tertiary channel that extends NNW from You Bet (You Bet District) through Scotts Flat (Scotts Flat District) and Quaker Hill (Scotts Flat District) to North Columbia (North Columbia District). Although the gravels here are extensive, they were reported not to have been very remunerative. Lindgren (1911) estimated that 15 million cubic yards had been removed and 90 million yards remain, much of it barren clay and sand. The gravel next to bedrock was reported to have yielded about $0.50 (period values) in Au per cubic yard. To the E and S the gravels are overlain by andesite. Bedrock is phyllite and slate. The location selected for latitude and longitude by the USGS is the Blue Tent School symbol in section 28, T17N, R9E as shown on the USGS 7/12-minute North Bloomfield quadrangle.

Mineral 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. Ore bodies are irregular in form. Mineralization is hosted in Tertiary sand & gravels. Controls for ore emplacement included mechanical accumulation on irregular bedrock riffles and within river- and stream-channel lag gravels, bars, and point bar deposits. The deposit consists of alluvial gravels and finer sediment that were deposited along a Tertiary channel that extends north-northwest from You Bet through Scotts Flat and Quaker Hill to North Columbia. The bottom gravel fills a deep trough in the bedrock and is coarse and cemented. Similar to neighboring Tertiary gravel deposits, the deposits can be divided lithologically and texturally into a lower and upper unit. The lower unit, or blue lead of the early miners, rests directly on bedrock, and contains the richest ores. These deeper gravels are well-cemented and immature, composed mainly of bluish-black slate and phyllite of the Calaveras Complex, weathered igneous rocks, and quartz. The upper unit forms the majority of the gravel deposits. Upper gravels are much finer, with clasts seldom larger than pebble size and characterized by an abundance of quartz sand and clay and silt beds. Unlike other districts, a large part of these gravels was unusually lean or completely barren of placer gold. Local rocks include Tertiary pyroclastic and volcanic mudflow deposits, unit 9 (Cascade Range).

Geology: In the Blue Tent District, auriferous Tertiary gravels are exposed in the valley N of Harmony Ridge. Oligocene to Pliocene Valley Springs and Mehrten Formation rocks have been stripped from the deposits by erosion, but still cap the higher elevations along Harmony and Ridge and nearby Washington Ridge.

The main body of basement rocks within the district consists of slate, argillite, and phyllite of the Central Belt basement complex. East of the district, basement is cut by the northerly trending Ramshorn Fault.

Basal Eocene Auriferous Gravels: Erosion of the Valley Springs and Mehrten Formations has exposed an area of about one-half square mile of gravels. To the north and south, the gravels are overlain by Mehrten volcanic rocks atop the western extremity of Washington Ridge and Harmony Ridge respectively. The auriferous gravels were deposited by a tributary to the Tertiary Yuba River. The tributary flowed northward from neighboring Scotts Flat District through the Blue Tent District and continued northward to its confluence with the Yuba River within the North Columbia District about five miles to the north.

Similar to neighboring Tertiary gravel deposits, the deposits can be divided lithologically and texturally into a lower and upper unit. The lower unit, or blue lead of the early miners, rests directly on bedrock, and contains the richest ores. These deeper gravels are well cemented and quartz rich. The lower gravels are generally immature and composed of bluish-black slate and phyllite of the Calaveras Complex, weathered igneous rocks, and quartz. Whereas in the neighboring districts, these gravels could yield many dollars per cubic yard, at Blue Tent these gravels yielded only 23 to 50 cents (period values) per cubic yard.

The upper gravels form the majority of the gravel deposits. Upper 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. Unlike other districts, a large part of these gravels was unusually lean or completely barren of placer gold. On average, the upper gravels yielded only 3-4 cents per yard. Regional geologic structures include the Wolf Creek Fault Zone, Ramshorn Fault, and the Melones Fault Zone.

Upper gravels yielded an average $0.034-$0.042 per cubic yard ($35/oz).

Lower gravels yielded an average $0.255 per cubic yard (@ $35/ounce). The ore materials included native gold (fine to coarse gold and nuggets (.900 fine)). Gangue materials include quartz and metamorphic gravels. Accessory minerals are magnetite, ilmenite, zircon, pyrite, amphibole, epidote, chlorite, and siderite.

Regions containing this locality

North America PlateTectonic Plate

Select Mineral List Type

Standard Detailed Strunz Dana Chemical Elements

Mineral List

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

9 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 #10310592.
'Chlorite Group'
Reference: USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10310592.
Epidote
Formula: {Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Reference: USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10310592.
Galena
Formula: PbS
Reference: U.S. Geological Survey, 2005, Mineral Resources Data System: U.S. Geological Survey, Reston, Virginia.
Gold
Formula: Au
Ilmenite
Formula: Fe2+TiO3
Reference: USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10310592.
Magnetite
Formula: Fe2+Fe3+2O4
Reference: USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10310592.
Pyrite
Formula: FeS2
Quartz
Formula: SiO2
Siderite
Formula: FeCO3
Reference: USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10310592.
Zircon
Formula: Zr(SiO4)
Reference: USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10310592.

List of minerals arranged by Strunz 10th Edition classification

Group 1 - Elements
Gold1.AA.05Au
Group 2 - Sulphides and Sulfosalts
Galena2.CD.10PbS
Pyrite2.EB.05aFeS2
Group 4 - Oxides and Hydroxides
Ilmenite4.CB.05Fe2+TiO3
Magnetite4.BB.05Fe2+Fe3+2O4
Quartz4.DA.05SiO2
Group 5 - Nitrates and Carbonates
Siderite5.AB.05FeCO3
Group 9 - Silicates
Epidote9.BG.05a{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Zircon9.AD.30Zr(SiO4)
Unclassified Minerals, Rocks, etc.
'Amphibole Supergroup'-AX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
'Chlorite Group'-

List of minerals arranged by Dana 8th Edition classification

Group 1 - NATIVE ELEMENTS AND ALLOYS
Metals, other than the Platinum Group
Gold1.1.1.1Au
Group 2 - SULFIDES
AmXp, with m:p = 1:1
Galena2.8.1.1PbS
AmBnXp, with (m+n):p = 1:2
Pyrite2.12.1.1FeS2
Group 4 - SIMPLE OXIDES
A2X3
Ilmenite4.3.5.1Fe2+TiO3
Group 7 - MULTIPLE OXIDES
AB2X4
Magnetite7.2.2.3Fe2+Fe3+2O4
Group 14 - ANHYDROUS NORMAL CARBONATES
A(XO3)
Siderite14.1.1.3FeCO3
Group 51 - NESOSILICATES Insular SiO4 Groups Only
Insular SiO4 Groups Only with cations in >[6] coordination
Zircon51.5.2.1Zr(SiO4)
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)
Epidote58.2.1a.7{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Group 75 - TECTOSILICATES Si Tetrahedral Frameworks
Si Tetrahedral Frameworks - SiO2 with [4] coordinated Si
Quartz75.1.3.1SiO2
Unclassified Minerals, Mixtures, etc.
'Amphibole Supergroup'-AX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
'Chlorite Group'-

List of minerals for each chemical element

HHydrogen
H Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
H Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
CCarbon
C SideriteFeCO3
OOxygen
O QuartzSiO2
O MagnetiteFe2+Fe23+O4
O IlmeniteFe2+TiO3
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
FFluorine
F Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
AlAluminium
Al Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
Al Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
SiSilicon
Si QuartzSiO2
Si ZirconZr(SiO4)
Si Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
Si Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
SSulfur
S GalenaPbS
S PyriteFeS2
ClChlorine
Cl Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
CaCalcium
Ca Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
TiTitanium
Ti IlmeniteFe2+TiO3
Ti Amphibole SupergroupAX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
FeIron
Fe PyriteFeS2
Fe MagnetiteFe2+Fe23+O4
Fe IlmeniteFe2+TiO3
Fe Epidote{Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)
Fe SideriteFeCO3
ZrZirconium
Zr ZirconZr(SiO4)
AuGold
Au GoldAu
PbLead
Pb GalenaPbS

References

Sort by

Year (asc) Year (desc) Author (A-Z) Author (Z-A)
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.: 143.
Logan, Clarence August (1918), Platinum and allied metals in California: California Mining Bureau. Bulletin 85, 120 pp.: 26.
Jarman, A. (1927), Sailor Flat and Blue Tent: California Mining Bureau (Report 23): 110-111.
Clark, Wm. B. (1970a) Gold districts of California: California Division Mines & Geology Bulletin 193: 31.
Yeend, W.E. (1974) Gold-bearing gravel of the ancestral Yuba River, Sierra Nevada, California. USGS Professional Paper 772, 44 pp.
Pemberton, H. Earl (1983), Minerals of California; Van Nostrand Reinholt Press: 43.
Saucedo, G. J. and Wagner, D. L. (1992), Geologic map of the Chico Quadrangle, California: California Department of Conservation, Division of Mines and Geology Regional Geologic Map Series, Map No. 7A, scale 1:250,000.
USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10310592.

USGS MRDS Record:10310592

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