Hammonton Mining District (Yuba River Mining District), Yuba County, California, USAi

Regional Level Types
Hammonton Mining District (Yuba River Mining District)	Mining District
Yuba County	County
California	State
USA	Country

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An extensive Au-PGE placer/hydraulic mining area on the lower Yuba River, 10 miles E of Marysville, around the town of Hammonton. Discovered in 1849 by W. P. Hammon and R. D. Evans. The land is of varied ownership and includes private land, Yuba County Planning Department land and Bureau of Land Management land (includes 129 acres of patented land).

This extensive mining area is located in the following T&R units:

secs. 1, 2, 11, 12, T15N, R4E, MDM.
secs. 4, 5, 6 T15N, R5E, MDM.
secs. 25, 35, 36 T16N R4E, MDM.
secs. 22, 23, 25-34 T16N R5E, MDM.

Ownership was varied but most recently included Alan Bond, Inc. Sydney, Australia (1988), and operator Yuba Placer Gold Co., Sydney Australia (1988).

This district comprises the extensive dredging field in Quaternary sediments along the Yuba River east of Marysville. It extends for approximately eight miles between a point about five miles northeast of Marysville to Long Bar. It was the most productive gold-dredging district in California and for many years was the principal source of gold in the state.

Mineralization is a Au-PGE (Pt) deposit hosted in Quaternary gravels (Mineral Deposit model: model code 119; USGS model code 39a; BC deposit profile C01. C02; deposit model name: Placer Au-PGE; Mark3 model number 54). Ore controls included mechanical accumulation within stream-channel lag gravels, bars, and point-bar deposits. Local rocks include Quaternary alluvium and marine deposits.

REGIONAL GEOLOGY: The Hammonton District is situated within both the Sierra Nevada geologic province and the Great Valley geologic province, which is here represented by the Sacramento Valley. The Great Valley province is characterized by Cenozoic sedimentary and volcanic rocks, while the Sierra Nevada province is characterized by complex lithologies and structures that were assembled through various plate-tectonic processes. In this region, the Sierra Nevada province is composed of belts of Paleozoic-Mesozoic metamorphic complexes that are intruded by various Mesozoic plutons. Together, they compose the basement of the province. This basement is overlain at higher elevations by erosional remnants of Cenozoic volcanic and sedimentary rocks, including gravels. Most of these various lithologies contain gold in places. Structurally, the metamorphic rocks and some of the plutonic rocks have been deformed by folding and faulting. The major fault zones typically trend northerly or northwesterly, although in places intrusion of the younger plutons has deformed some of the zones so as to assume other trends as well. In contrast, the overlying Cenozoic rocks are relatively undeformed. The rocks of the Great Valley province overlie the basement of the Sierra Nevada where it extends westward underneath the San Joaquin Valley. LOCAL GEOLOGY The Hammonton District is associated with Cenozoic alluvial deposits of the main drainage of the Yuba River where it discharges into the Sacramento Valley after passing through the Sierra Nevada basement terranes. The materials in these deposits have been derived by erosion of the various basement and Cenozoic rocks at higher elevations. In places, the basement rocks contain gold within quartz veins and altered rock, while the Cenozoic deposits contain placer gold derived by erosion of these older basement rocks. Erosion of both the gold-bearing basement rocks and the older Cenozoic rocks provided the gold that was eventually deposited in the Cenozoic placer deposits along the Yuba River here at Hammonton. Some of these deposits are composed of debris that was washed down from the extensive hydraulic mining farther upstream in the watershed of the Yuba River. Platinum was probably derived from erosion of ultramafic rocks and serpentinite in the Sierra Nevada basement.

WORKINGS: Workings from small-scale placer mining were developed during the gold rush. The main workings of the district are those from dredging operations. More than a billion cubic yards of gold-bearing gravels have been dredged in this district. The tailings are present over a length of about eight miles and a width of up to about three miles. They are mostly on the south side of the present channel of the Yuba River. Maximum dredging depths ranged from 60-80 feet on the upstream end of the field to 100-125 feet at the downstream end of the field. Dredge No. 21, the most recently active dredge at the field, was capable of digging 140 feet below water level, which made it one of the deepest-digging dredges in the world. It processed about 4 million cubic yards of gravel annually. The processes of placer mining, including sections on dredging, are described in Averill (1946).

The Yuba River in this area was first worked by small-scale surface placering during the gold rush. Bucket-line dredging began in 1903. Dredging continued until 1968 when the last dredge stopped operation because of poor economic conditions. Dredging resumed with Dredge No. 21 in 1981 through a joint venture between Yuba Consolidated Goldfields and Placer Service Corporation. Cal Sierra Developments, Incorporated purchased Dredge No. 21 and all support assets and rights to minerals in 1992. In 2003, Dredge 21, the main dredge operated by Cal Sierra Development, sank out of sight in its 125-foot-deep pond. The cause was unknown at the time. To replace Dredge No. 21, Cal Sierra Development planned to obtain one of its sister dredges, No. 18, which was in Bolivia, South America. The Hammonton District is currently the site of controversy concerning public access versus private ownership at the site. Many dredges have operated in this district over the last century, and it has been the site of various innovations in the gold-dredging industry. Altogether, at least 21 separate dredges have operated in this field. Most of the district has been dredged at least twice and some areas three or four times, each time to a greater depth with more-efficient equipment for recovery. Natural replenishment of the field by the Yuba River has been curtailed since construction of Englebright Dam on the river in 1941. Amalgamation has been used in the recovery process. Also, mercury from the historic hydraulic mines is present in the deposits of this district. Vast deposits of dredge tailings still remain in this district. Some of them have been exploited as sources of aggregate, most recently by Western Aggregates, Inc..

Koschmann and Bergendahl (1968) reported gold produced from this district through 1959 was about 4,387,000 ounces. Clark (1970) estimated that total production of gold for this district was at least $130 million as of the late 1960?s and 4.8 million ounces as of 1964. As of 1992, more than 5 million ounces of gold had been produced from this district (Cal Sierra Development, Inc., 1992). The recent period of operation was expected to annually produce about 20,000-25,000 ounces of gold per year.

The Pt averaged 65.8% Pt (ferroalloy, and 15.77% Os & Ir).

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

9 valid minerals.