Manzanita Placer Mine (Manzanita Mining Co. property), Nevada City, Nevada City Mining District, Nevada County, California, USAi

Regional Level Types
Manzanita Placer Mine (Manzanita Mining Co. property)	Mine
Nevada City	City
Nevada City Mining District	Mining District
Nevada County	County
California	State
USA	Country

A former placer Au-Ag-Pt occurrence/mine located in secs. 6 & 7, T16N, R9E, and in secs. 1 & 12, T16N, R8E, MDM, about ½ mile N of Nevada City. MRDS database stated accuracy for this location is . The location selected by the USGS for latitude and longitude is the crest of Harmony Ridge (under which the mine lies) on the USGS 7 1/2-minute Nevada City quadrangle.

NOTE: The coordinates presented were extracted from USGS MRDS database file #10310643, which place this locality as otherwise described. The geographic coordinates presented in the other 2 MRDS files are in agreement and are both in error, placing this locality in the Rough and Ready District fer to the N.

The Manzanita Mine is one of the more important hydraulic/drift mines in the Nevada City District, which is otherwise generally known for its lode gold deposits. The district is in western Nevada County, and the Manzanita Mine is adjacent to the town of Nevada City on its north side. The mine produced about $3-$5 million from auriferous Tertiary gravels deposited by a tributary to the ancestral Yuba River and preserved under a protective capping of Valley Springs and Mehrten volcanic rocks along the crest of Harmony Ridge.

The gravels underlying Harmony Ridge are thought to have been discovered in 1850. Both drift and extensive hydraulic mining of the deposits commenced sometime in the early 1850s. Drift mining continued until around 1900. Hydraulic mining continued until the mid-1880s when the Sawyer Decision curtailed hydraulic mining. Prior to the Sawyer Decision, hydraulic mining developed two pits in the exposed gravels on the south (Manzanita Workings) and north (Odin Workings) flanks of Harmony Ridge. Hydraulic mining is reported to have produced $1.5 million and drift mining more than $3.5 million. After cessation of hydraulic mining, the channel gravels were extensively developed by drift mining. The mine was accessed from the Manzanita Workings hydraulic pit, just north of Nevada City, by a 12-degree inclined shaft to a total depth of 225 feet. The gravels were drifted northward to Howe Cut, a distance of about 3,000 feet at a cost of $104,000. All drifts were thoroughly timbered and tunnels were generally 4 feet wide and 6 feet tall. The average depth of gravels drifted was 4 feet. As of 1888, the mine employed 25 men and was extracting and sluicing 100 tons of gravel per day. The mine operated eleven miles of ditches and flumes and 3,000 feet of 22-inch iron pipe. By the early 1890's, the mine was ventilated by water blast. Hoisting was done by horses.

Mineralization is a placer Au-Ag-Pt deposit (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), hosted in Tertiary unconsolidated sand and gravel. The ore body is irregular in form. Controls for ore emplacement included the mechanical accumulation on irregular bedrock riffles and within river- and stream-channel lag gravels, bars, and point bar deposits. Local rocks include Tertiary pyroclastic and volcanic mudflow deposits, unit 9 (Cascade Range).

Basement beneath the Manzanita Mine consists primarily of Jurassic granodiorite within the Central Belt basement complex of the Northern Sierra Nevada. The northwest-southeast trending Grass Valley Fault cuts basement about 3 miles west of the mine and the Ramshorn - Gills Hill Fault system lies about 5 miles to the east. Basal Eocene Auriferous Gravels The Manzanita Mine produced from Tertiary channel gravels that were part of a tributary of the ancestral Yuba River. Based on its location off the major known tributaries, reconstruction of the "Manzanita Channel" tributary is more difficult than those at most other Northern Sierra Tertiary gravel deposits. Yeend (1974), noted that the gravels at Nevada City are largely traceable to the northeast into the gravels exposed in the Scotts Flat and Blue Tent districts to the east. He thus concluded that the Manzanita Channel flowed northeast ward to join the major Yuba River tributary that flowed northward from the Blue Tent district to join the ancestral Yuba River in the North Columbia District. However, Lindgren (1911) concluded that the tributary flowed westward from Nevada City. Since the gravels cannot be traced west of Nevada City, this controversy remains unresolved. The gravels rest directly on basement, into which the ancient river incised its channel. Rocks of the Valley Springs and Mehrten formations preserve the gravels underlying Harmony Ridge. North and south of the ridge the gravels and overlying volcanics have been stripped away by erosion. Consistent with most Tertiary gravel deposits in neighboring districts, the deposits can be divided lithologically and texturally into lower and upper units. The lower unit, or blue lead of the early miners, rests directly on bedrock, and contains the richest ores. The basal gravels are characteristically quartzitic, sub-angular, and well-cemented. Granite boulders are common. In the Manzanita Mine, the lower pay gravels were approximately 150-200 feet wide and seldom more than 4 feet thick with the better pay streaks yielding coarse gold and assaying $1.55 - $2.50 per ton. Gravels from the hydraulic "Manzanita Workings" on the south side of Harmony Ridge are said to have been richer than those of the "Odin Workings" on the north side of the ridge.
Overlying the lower gravels is a section of fine gravel, which carries fine gold and was exploited during the hydraulic operations. The upper gravels are quartz-rich, much finer, with clasts seldom larger than pebble size and locally covered by heavy clays. Large-scale cross-bedding and cut-and-fill features are common.

Regioanl geologic structures include the Big Bend-Wolf Creek Fault Zone, Weimar Fault Zone, and the Gills Hill Fault.

Commodity information: Ore materials: native Au (0.900 fine), fine to coarse gold and nuggets. Gangue materials: quartz and metamorphic gravels; accessory minerals include magnetite, ilmenite, zircon, pyrite, amphibole, epidote, chlorite, and siderite.

Production estimates for the Manzanita Mine range from $3 to $5 million (period values). Producing gravels were generally thin (2 to 4 feet thick), but often rich, with pay streaks yielding as much as $1.55 - $2.50 (period values) per ton.

Other Databases

Link to USGS MRDS:	10031729

Other Regions, Features and Areas containing this locality

References