Lowell Hill Mining District, Nevada Co., California, USAi

Regional Level Types
Lowell Hill Mining District	Mining District
Nevada Co.	County
California	State
USA	Country

Location and History: A former Au-Ag-Pt mining area, discovered before 1850, this district is in south-central Nevada County about six miles NE of Dutch Flat in secs. 5 to 8, 17 & 18, T16N, R11E, and in secs. 31 & 32, T17N, R11E, MDM. It includes the Remington Hill, Negro Jack Hill, and Liberty Hill areas. The district was hydraulicked from the middle 1850's through the 1870's, and Liberty Hill was worked again from around 1896 to 1915. The total output is unknown, but it exceeds $1 million (period values). Lindgren, in 1911, estimated that two million cubic yards had been removed and 16 million remained at Liberty Hill and that 1.75 million cubic yards had been removed and 6 million remained at Remington Hill. Other estimates of remaining gravel at Liberty Hill range from 6 to 10 million yards. Location selected for latitude and longitude by the USGS is the Mammoth Springs Mine portal symbol on the south side of Negro Jack Hill on the USGS 7 1/2-minute Washington quadrangle.

The placer deposits in the Lowell Hill District were placer-mined from the mid-1850s through the 1870s, with the Liberty Hill workings being worked again between 1886 and 1915. Hydraulic mining at Lowell Hill was hampered by the heavy overlying beds of clay. Drift mining was done at the Valentine and Swamp Angel mines.

Mineralogy: The native gold is fine to coarse gold and nuggets (900 fine). Gangue materials include quartz, metamorphic and ultramafic gravels and boulders. Accessory minerals include magnetite, ilmenite, zircon, pyrite, amphibole, epidote, chlorite, and siderite.

Geology: The deposits are in a southwest-trending Tertiary channel that joins the Dutch Flat channel. There is a lower well-cemented blue gravel that contains gabbro and serpentine boulders and yielded 18 to 23 cents (period values) a cubic yard. An upper quartz-rich gravel is in places covered by heavy clay. Bedrock is slate of the Blue Canyon Formation (Carboniferous) and some serpentine.

Within the district, the Feather River Peridotite Belt narrows to less than a mile wide. Consequently, basement rocks consist of Calaveras Complex rocks to the west, ultramafic rocks and serpentinites of the Feather River Peridotite Belt, and slates of the Shoo Fly Complex of the Eastern Belt to the east, A large part of the district is overlain by volcanic rocks of the Valley Springs and Mehrten formations.

Basal Eocene Auriferous Gravels: The Lowell Hill District contains several separate placer deposits at Lowell Hill, Liberty Hill, Negro Jack Hill, and Remington Hill. By far, the most extensive of these workings are those at Lowell Hill where the auriferous gravels are exposed.

The channel gravels in this district were deposited by a small tributary that drained into a larger tributary of the ancestral Yuba River. This tributary flowed southwestward from the Remington Hill area to join the main tributary at Dutch Flat. The main tributary then flowed generally north-northwestward and deposited the placer gravels in the Dutch Flat, You Bet-Red Dog, Scotts Flat, and Blue Tent districts before joining the ancestral Yuba River in the North Columbia District.

Consistent with the Tertiary gravel deposits in neighboring districts, the deposits can be divided lithologically and texturally into lower and upper units. The thickness of the combined units at Liberty Hill is only 60 feet and equally divided between the two units. The lower unit, or blue lead of the early miners, rests directly on bedrock and contains the richest ores. Lower gravels are well-cemented, quartz-rich, and contain abundant gabbro and serpentinite boulders reflecting erosion of the ultramafic rocks of the Feather River Peridotite Belt bedrock. Lower gravels have been reported to yield between $0.18 and $1.43 per cubic yard.

In most of the workings, the upper unit gravels form the bulk of the deposits. This unit's thickness varies widely. Upper gravels are quartz-rich and much finer, with clasts seldom larger than pebble size and locally including interbeds of clay. Large-scale cross-bedding and cut-and-fill features are common. The upper gravels are considerably leaner than lower gravels, with a reported average yield of $0.24 ($35.00 ounce/gold) being reported at Liberty Hill.

The gravel deposits at Lowell Hill are overlain by a 30 foot layer of light colored clay.

Regional geologic structures include the Foresthill Fault and the Melones Fault Zone. Local structures include the Melones Fault Zone.

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. Deposits are hosted in unconsolidated Tertiary sand and gravels. 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. Local rocks include ultramafic rocks, chiefly Mesozoic, unit 2 (Western Sierra Nevada and Klamath Mountains)

Commodity Information: Upper gravels at the Liberty Hill workings averaged about $0.24 per cubic yard (@ $35/ounce). Lower gravels at the Liberty Hill workings are reported to have ranged between $0.18 and $1.43 per cubic yard (@ $35/ounce).

Production Statistics: The total production of the district exceeds $1 million (period values), but actual production figures are unknown. Lindgren (1911) estimated that 2 million cubic yards had been removed and that 16 million remained at Liberty Hill. He also estimated that 1.75 million had been removed and 6 million remained at the Remington Hill workings.

References

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Link to USGS MRDS:	10310640

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