Plymouth Consolidated Mine (Plymouth Mine; New London Mine; Phoenix Mine; Empire Mine; Pacific Mine; Southerland claim; Oaks and Pacific claim; Simpson and Aden claim; Reese claim; Phoenix East claim; Plymouth claim; Reese and Woolford claim; Indiana claim [fractions]; Rising Star claim; Conville and Lode claim 5181; Beta claim), Plymouth, Jackson-Plymouth District, Mother Lode Belt, Amador Co., California, USA
|Latitude & Longitude (WGS84):||38° 28' 31'' North , 120° 50' 35'' West|
|Latitude & Longitude (decimal):||38.47528,-120.84333|
A former Au-Cu-Ag mine located in sec. 11, T7N, R10E, MDM, on private land. Discovered in 1852. The holdings include 22.77 acres of other land in addition to the listed claims, for a total of 126.3 acres in all in section 11. Owned by B. Monte Verda and E. C. Taylor (1953). The claims were worked separately until consolidation in 1883 under the name of the Plymouth Consolidated Mining Co. The mine was idle during the period 1892 to 1911. Little work was accomplished between 1928 and 1939, except for the treatment of the tailings and some exploration. The latter shut down in 1943. The Empire workings reopened in 1946 but ceased work in early 1947. MRDS database stated accuracy for this location is 1,000 meters. Most of the ore was produced under the Simpson and Aden claim and the Oaks claim. This is the most northerly major Au mine on the Mother Lode.
The Plymouth Consolidated Mine is located within the town of Plymouth, California in the famous Mother Lode Gold Belt of the Sierra Nevada foothills. The mine is the most northern of the major Mother Lode Mines in Amador County and one of the preeminent mines of the Jackson-Plymouth district. The Jackson-Plymouth district was the most productive district of the Mother Lode belt with an estimated total production of about $180 million (Clark, 1970). The Plymouth Consolidated Mine came into being in 1883 with the consolidation of the Plymouth, Empire, and Amador Pacific mining companies.
The Plymouth Consolidated Mine came into existence in 1883 by way of the consolidation of the Plymouth, Empire, and Amador Pacific mines. Prior to 1883, these mines operated independently, some having started as early 1852. Among the Plymouth Consolidated mine holdings were the Plymouth, Southerland, Oaks, Pacific, Simpson, Aden, Reese, Phoenix East claims, the Phoenix mill site, and interests in the Reese and Woolford, Indiana, Rising Star, Conville, and Beta claims. The mine controlled a total of 126.3 acres (Logan, 1934).
The Plymouth Mine was discovered and first developed in 1852, but very little work was done until 19 years later. In 1871, Alvinza Hayward purchased an interest in the Plymouth Mine. Hayward was a veteran mining man, having made his fortune in the Sutter Creek and Comstock mines. He constructed a new stamp mill and began extensive exploration and deeper mining. By 1878, the Plymouth Mine was producing $30,000 to $50,000 a month in gold. The onslaught of new miners with wages to spend resulted in a boom for the nearby town of Plymouth.
The Phoenix Mine was opened in 1859 on the Southerland, Simpson, and Aden claims, and worked continuously until 1875. The Phoenix Mine had 2 shafts 200 feet apart and 900 feet deep. Ore occurred in a body of low-grade quartz. Soon after, the Phoenix Mine was sold to the Empire Company and renemed the Empire Mine. By 1879 the 2 shafts (renamed the Empire North and Empire South shafts) deepened to 1200 feet and 1280 feet deep (1020 and 100 vertical feet respectively). During this period, ore averaging $9 a ton was being mined between the 1000-foot and 1100-foot levels on the main Empire ore shoot.
About the same time, the Amador Pacific Mining Company was developing the Pacific Mine on the Pacific vein south of the Empire Mine. The Pacific vertical shaft (which became the main working entry of the Plymouth Consolidated Mine) was started in May 1880, and was 1000 feet deep by October 1880. The southward rake of the Empire ore shoot carried it under the holdings of the Pacific Mine where it was mined by the Empire Company. The ensuing lawsuit, while won by the Amador Pacific Company, lead to the consolidation of the Empire, Amador Pacific, and Plymouth mining companies on June 1, 1883. The new venture was operated by the Plymouth Consolidated Mining Company (Irelan, 1888; Logan, 1934). Production of these mines prior to consolidation was reported to be about $2.5 million (Logan, 1934). Soon after they were consolidated, the property became the principal producer in the County. As many as 147 stamps were operated by water power. From June 1, 1883 to January 1, 1888, the company produced $2,804,499 from which 55 dividends totaling $2,200,000 were paid (Logan, 1934).
Under the Plymouth Consolidated Mining Company, the main shaft was sunk 900 feet from 3400 feet to 4300 feet (Loga, 1927). For some time prior to this, ore had been mined through a winze, hoisted to the 3400 foot level then trammed to the shaft to be hoisted to the surface. Both shaft and winze were in poor shape, necessitating this change.
On January 24, 1888 a fire was reported on the 1200-foot level and the mine was flooded to extinguish the blaze. In 1889, the Pacific workings were reopened and produced $215,515 by 1892 when operations ceased. The mine lay idle until 1911 when, with British capital, the California Exploration Company Ltd. was formed to explore the mine. In 1914, after the California Exploration Company had identified $100,000 tons of ore assaying $6.35 a ton, the Plymouth Consolidated Mine Company Ltd was incorporated to reopen and operate the mine. The operation was capitalized with 240,000 shares of one pound sterling, of which 204,482 pounds sterling was paid for the property (Logan, 1934). The Pacific shaft was reopened and a winze was sunk from below the 1600-foot level to 2000 feet. A 30-stamp mill was built and began operating in July, 1914. The adjacent Plymouth Gold Quartz and new London claims were purchased to obviate any danger of apex litigation (Knopf, 1929).
Operations continued profitably until 1920, during which time the company milled 1,037,373 tons of ore yielding $5,718,000 and paid $758,000 in dividends. During this period, about 125 men were employed underground and 60 on the surface. After 1920, however, costs escalated to the point where the mine was no longer profitable and the mine was forced into receivership. By that time, the workings had reached an inclined depth of 4300 feet (the shaft below 1600 inclined of 60?).
In 1925, the Plymouth Consolidated Mine was sold to the Argonaut Mining Company for less than $75,000 (Knopf, 1929). The Argonaut Mining Company deepened the main shaft an additional 150 feet making a total depth of 4450 feet. Some ore was milled between 1925 and 1928 which yielded $525,292. Based on these results they decided not to rehabilitate the mine ore sink any more workings.
Very little work was done between 1928 and 1939. Some exploration was conducted on the 400 and 500-foot levels between 1928 and 1931 and a combined flotation and cyanide plant was put into operation by the Argonaut Mining Company to treat tailings. The plant was shut down in 1943 as a result of World War II. In 1946, the Empire workings were reopened by the Argonaut Mining Company. This was a resumption of the prospecting interrupted by WWII. On the 400-foot level, an old drift was extended north 700 feet. Only a small amount of ore was found and the mine was permanently closed in 1947. The head frame, tailings, and stamp mill foundation remain, and the most notable structure in the town of Plymouth, the Empire building, was the mining company's office.
Mineralization is a vein deposit (Mineral occurrence model information: Model code: 273; USGS model code: 36a; Deposit model name: Low-sulfide Au-quartz vein; Mark3 model number: 27) hosted in Late Jurassic slate of the Mariposa Formation. The ore body is tabular, pinch & swell in form, strikes N and dips 65E. Three parallel vein systems occur here with slate on both vein walls, usually accompanied by black gouge. The principal body consists of a large chimney of ribbon quartz 30 to 50 feet thick and 350 to 400 feet long. 70% of the produced gold having been recovered by milling and amalgamation. Controls for ore emplacement included ore shoots within mesothermal gold bearing quartz veins. Sulfides comprised 1.25% to 1.5% of the ore, contribute the remaining 30%. The Au is 800 fine. Ore materials include free-milling banded white gold quarts seams composed of ribbons or bands containing free gold, slate, auriferous pyrite, arsenopyrite, and minor chalcopyrite. Gangue materials include quartz, slate and calcite. Local rocks include Jurassic marine rocks, unit 1 (Western Sierra Nevada and Western Klamath Mountains).
Regional geologic structures include the Bear Mountain Fault zone and the Melones Fault zone. Local structures include the Melones Fault zone.
The Mother Lode Mariposa slate belt at the Plymouth Consolidated Mine is one mile wide, within which there are three parallel vein systems called the Empire, Pacific, and Reese and Woolford veins. The Empire and Pacific veins were productive, while no paying ore was developed in the easternmost Reese and Woolford vein. All three veins have a general north-south strike and dip from 62 to 90 degrees East.
The most important vein is the Empire which occupies a reverse fault fissure within the Mariposa slates. The vein strikes north and dips 62? east, cutting across the schistosity of the slate wall rocks at a small angle and strike. In the deeper levels it is a typically composed of ribboned structures of crushed slate-quartz stringers (Logan, 1934). The large Empire ore shoot was located in this vein. The Empire shoot raked to the south into adjacent claims resulting in litigation and the resultant formation of the Plymouth Consolidated Mining Company. From the surface to 400 feet it was only average grade, and from there to 1000 feet even lower, so that much of it between 600 and 1000 feet was left unstoped. From 1000 to 1500 feet it became richer, and in 1886 this ore resulted in a profit of $254,402.13 from a gross production of $ 447,547.13. Dividends of $225,000 were paid out that year. The ore shoot at the time was claimed to be 800 feet long. The vein averaged 30 feet wide and carried 1.5% sulfide concentrates worth $135 a ton. The average value of the ore was $6 to $8 per ton (Logan, 1934).
The Empire ore shoot ended to the north at a greenstone dike entering from the footwall side. The dike crops out 2850 feet north of the Pacific shaft and persisted to the lowest level of the mine at 4450 feet. The dike was about 100 feet where encountered in crosscuts. In the lower mine levels, the dike turns away from the shaft on a curved course suggesting a lens shape. On the 4450 level, the northern end of the ore body is 800 feet north of the main shaft (Logan, 1934). A longitudinal cross section of the Plymouth Mine in the plane of the Empire vein is given by Logan (1934).
The Pacific vein strikes N 20? W and dips between 70? to nearly vertical, conforming more with the cleavage of the slate wall rocks. The Pacific vein merges with the Empire vein near the surface in the vicinity of the Empire North and Empire South shafts Three ore shoots were worked in the Pacific vein between the 835-foot and 1600-foot levels above which they pinched out. The ore bodies rake towards the Empire shoot, so that the Empire shoot on the north and Pacific shoots on the south merged at about the 2900-foot level. Their occurrence was attributed to the junction of the two main veins (Logan, 1927).
Due to the nature of their junctures, the Pacific vein is considered a spur of the Empire vein, leaving it a little north of the Empire North shaft and striking a little east of south. The Empire vein extended southward to the New London claim.
The Reese and Woolford vein, while located only 500-700 feet east of the Pacific vein, did not yield any paying ore
Ore shoots appear to have occurred at and near vein intersections or the junctions of spur veins. Also, contact zones between slate and interbedded andesites seem to have been a controlling factor in determining the location of veins, as well as ore shoots. The occurrences of open spaces in the main fault fissures or adjacent spurs was another factor (Logan, 1934).
In general, ore shoots were found at or near the intersection of main veins and various spur and stringer veins. Ore occurs as seams or series of seams of banded white quartz, the ribbons or bands containing free gold, slate, auriferous pyrite and arsenopyrite, and minor chalcopyrite. Ore is free milling with 1.25% to 1.5% sulfides, the concentrates assaying $100 - $200 per ton (Irelan, 1888). Gold is 800 fine. Most of the gold is free gold with 70% of the gold recovered by amalgamation. The remaining 30% came from concentrates. Gold content of concentrates fluctuated between 24%-32% (Knopf, 1929).
Workings include underground openings comprised of 4 shafts on the vein.
Prior to the Consolidation of the Plymouth, Empire, and Pacific Mines, several independent shafts opened each mine. Little information is available regarding the underground workings of these early mines. After 1883, the Plymouth Consolidated Mine was opened by at least 4 shafts including the Pacific shaft, the Empire North shaft, and Empire South shaft. The North Empire shaft was a 1065 foot inclined shaft located about 350 feet north of the 1280 foot inclined Empire South shaft.
The Pacific shaft ultimately became the main working shaft for the mine and was ultimately sunk to a depth of 4450 feet in 1925. It consisted of a 3-compartment vertical shaft to 1600 feet, below which the balance was inclined eastward at 60? (Carlson & Clark, 1954).
No comprehensive descriptions of all the workings of the Plymouth Consolidated or its earlier component mines is available. Logan (1934) presented a longitudinal section in the plane of the Empire vein showing the underground workings of the Pacific and Empire shafts in that plane. Records contained in the California Geological Survey Mineral Resources Files and historic California State Mineralogist reports provide limited snapshots of some of the workings at various points in time.
During the mine's heyday between 1883 and 1889, the Plymouth Consolidated mills were considered the second largest quartz mills in the world. The mills had an aggregate of 160 stamps crushing 400 tons a day (Knopf, 1929).
Production data are found in: Carlson, D.W. & W.B. Clark (1954).
Total production was estimated to be in excess of $13,500,000 (period values). The Empire and Pacific locations are shown on the USGS Sutter Creek, California, quadrangle map (1957, 1962). The 1957 edition also shows a dredged area E & S of the Pacific shaft.
Production of Cu was less than 100,000 pounds .
Sulfide concentrates assayed $100-$200 per ton.
Mineral ListMineral list contains entries from the region specified including sub-localities
7 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
|Late Jurassic - Triassic|
145 - 252.17 Ma
|Jurassic marine rocks, unit 1 (Western Sierra Nevada and Western Klamath Mountains)|
Age: Mesozoic (145 - 252.17 Ma)
Stratigraphic Name: Agua Fria Formation; Colfax Formation; Cosumnes Formation; Galice Formation; Hunter Valley Cherts; Mariposa Formation; Merced Falls Slate; Salt Spring Slate; Jasper Point Formation
Comments: Western Klamath Mountains, western Sierra Nevada. Primarily slate and metamorphosed graywacke; minor siltstone, conglomerate, chert, and volcanic rocks. Mainly Late Jurassic in age, but also includes some Early Jurassic or older rocks
Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. 
Localities in this Region
- Amador Co.
- Mother Lode Belt
- Jackson-Plymouth District
- Plymouth Consolidated Mine (Plymouth Mine; New London Mine; Phoenix Mine; Empire Mine; Pacific Mine; Southerland claim; Oaks and Pacific claim; Simpson and Aden claim; Reese claim; Phoenix East claim; Plymouth claim; Reese and Woolford claim; Indiana claim [fractions]; Rising Star claim; Conville and Lode claim 5181; Beta claim)
- Jackson-Plymouth District
- Mother Lode Belt
- Amador Co.
Ransome, Frederick Leslie (1900), Description of the Mother Lode district, California: USGS Geological Atlas, Mother Lode, folio No. 63, 11 pp.
Logan, Clarence August (1921), Amador County, Central Eureka Mine: California State Mining Bureau, 17th Report of the State Mineralogist (Report 17): 409-410.
Logan, Clarence August (1927), Amador County, California Mining Bureau. (Report 23): 23: 179-180.
Knopf, Adolf (1929), The Mother Lode system of California: USGS Professional Paper 157, 88 pp.; […(abstract): Engineering & Mining Journal: 128: 24 (1929); […Geol. Zentralbl., Band 41: 364-367 (1930)]: 35.
Eric, J.C. (1948), Tabulation of Copper Deposits in California in: Copper in California: California Division of Mines Bulletin 144: 216.
Carlson, D.W. & W.B. Clark (1954), Mines and Minerals of Amador County, California: California Journal of Mines and Geology (Report 50): 50: 190-193, 256, Pl. 1.
Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 76.
Clark, Wm. B. (1970a) Gold districts of California: California Division Mines & Geology Bulletin 193.
Pemberton, H. Earl (1983), Minerals of California; Van Nostrand Reinholt Press: 12 (map 2-3), 218.
USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10028108, 10235201 & 10310668.
U.S. Bureau of Mines, Minerals Availability System (MAS) file ID #0060050048.
fiile nos. 339-1329, 331-9829, and 339-1334 (CGS Mineral Resource files, Sacramento).