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Kennedy Mine

Past Producer in Amador county in California, United States with commodities Gold, Silver
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Sections on this page
  1. Identification information
  2. Geographic coordinates
  3. Site location context
  4. Geographic areas
  5. Public Land Survey System information
  6. Commodities
  7. Materials information
  8. Mineral occurrence model information
  9. Host and associated rocks
  10. Nearby scientific data
  11. Geologic structures
  12. Ore body information
  13. Controls for ore emplacement
  14. Economic information about the deposit and operations
  15. Mining district
  16. Land status
  17. Ownership information
  18. Bibliographic references
  19. General comments
  20. Reporter information

Geologic information

Identification information

Deposit ID 10310634
Record type Site
Current site name Kennedy Mine

Comments on the site identification

  • The Kennedy Mine is located one mile northwest of the town of Jackson, California in the famous Mother Lode Gold Belt of the Sierra Nevada foothills. The Kennedy was the most productive mine in the Jackson - Plymouth district which was the most productive district of the Mother Lode with an estimated total production of about $180 million. The Kennedy claims covered 3100 feet along strike of the Mother Lode between the adjoining Oneida Mine to the north and the Famous Argonaut Mine to the south. The Kennedy Mine alone is credited with producing $34.28 million (Clark, 1970).

    The Kennedy Mine developed typical Mother Lode northerly trending and easterly dipping hydrothermal quartz veins carrying free milling gold and auriferous sulfides within a narrow band of Mariposa Formation slate and greenstone. Principal veins included and east vein and west vein which merged with a main foot wall vein. The Kennedy mine is noteworthy for being the most productive mine in the Mother Lode and for being the deepest gold mine in North America with a vertical depth of 5,912 feet.

    While discovered in 1856, the Kennedy Mine did not become a major producer until after 1885 when the mine was purchased by well capitalized investors and the Kennedy Mining and Milling Company was incorporated. The mine was then operated continuously until 1942. The Mine is currently owned by the Kennedy Mine Foundation, an historical preservation organization that offers tours of the remaining historic surface facilities.

Geographic coordinates

Geographic coordinates: -120.78017, 38.36695 (WGS84)
Elevation 418
Location accuracy 100(meters)
Relative position The Kennedy Mine is located 1 mile north of Jackson, California

Site location context

Political divisions (FIPS codes)

Amador(county)

California(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Jackson(quadrangle 1:24,000 scale)

San Andreas(quadrangle 1:100,000 scale)

Sacramento(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Upper Mokelumne(hydrologic unit)

San Joaquin(hydrologic accounting unit)

San Joaquin(hydrologic subregion)

California(hydrologic region)

Geographic areas

Country State County
United States California Amador

Public Land Survey System information

Meridian Township Range Section Fraction State
Mount Diablo 006N 011E 16 SW/4 SW/4 California

Comments on the location information

  • Location selected for latitude and longitude is the Kennedy Mine shaft symbol on the USGS 7.5 minute Jackson quadrangle.

Commodities

Commodity Importance
Gold Primary
Silver Secondary

Comments on the commodity information

  • Commodity Info: Sulfides comprised 1-2% of the ore and carried 6-7 ounces of gold per ton.
  • Ore Materials: the best ore was banded ore seams consisting on white quartz showning free gold with numerous ribbons of finely ground slate, and often ribbons of pyrite, arsenopyrite, and galena.
  • Gangue Materials: Quartz, slate, greenstone

Materials information

Materials Type of material
Gold Ore
Pyrite Ore
Arsenopyrite Ore
Galena Ore
Quartz Gangue
Slate Gangue

Mineral occurrence model information

Model code 273
USGS model code 36a
Deposit model name Low-sulfide Au-quartz vein
Mark3 model number 27

Host and associated rocks

  • Host or associated Host
    Rock type Metamorphic Rock > Metasedimentary Rock > Slate
    Rock unit name Mariposa Formation
    Stratigraphic age (youngest) Late Jurassic
  • Host or associated Host
    Rock type Metamorphic Rock > Metavolcanic Rock > Mafic Metamorphic Rock > Greenstone
    Rock unit name Mariposa Formation
    Stratigraphic age (youngest) Late Jurassic

Nearby scientific data

(1) -120.78017, 38.36695
ListMap

Economic information

Geologic structures

Type of structure Local
Structure description Melones Fault zone
Type of structure Regional
Structure description Bear Mountains Fault zone, Melones Fault zone.

Ore body information

  • General form Tabular, pinch and swell

Controls for ore emplacement

  • Ore shoots within mesothermal gold bearing quartz veins.

Comments on the geologic information

  • REGIONAL GEOLOGY

    The Kennedy Mine is located within the Sierra Nevada foothills, where bedrock consists of north trending tectonostratigraphic belts of metamorphosed sedimentary, volcanic, and intrusive rocks that range in age from late Paleozoic to Mesozoic. Locally, the Mesozoic rocks are capped by erosional remnants of Eocene auriferous gravels and once extensive volcanic rocks of Tertiary age. The structural belts, which extend about 235 miles along the western side of the Sierra, are flanked to the east by the Sierra Nevada Batholith and to the west by sedimentary rocks of the Cretaceous and Jurassic Great Valley sequence. In Amador County, the structural belts are internally bounded by the Melones and Bear Mountains fault zones. Schweickert and others (1999) provide one interpretive overview of the regional geology of this part of the Sierra Nevada.

    Gold deposits in the Plymouth - Jackson district occur within the north and northwest trending mile-wide Mother Lode Belt, which is dominated by gray to black slate of the Upper Jurassic Mariposa Formation and associated greenstone and amphibolite schist bodies assigned to its Brower Creek Volcanics member. In Amador County, the Mother Lode Belt approximately parallels Highway 49 southeastward from Plymouth through the town of Jackson. The geology of this segment has been mapped by Zimmerman (1983) and Duffield and Sharp (1975). The lode gold deposits along this stretch are responsible for most of the gold production in the county, which has been reported to be 7.68 million ounces (Koschman and Bergendahl, 1968). Clark (1970) placed the value of this production at $180 million. The Amador County portion of the belt was one of the most productive gold mining areas in the United States, and the Plymouth - Jackson district in Amador County was the most productive part of the belt.

    The Mariposa Formation contains a distal turbidite, hemipelagic sequence of black slate, amphibolite, schist, and fine-grained tuffaceous rocks, and volcanic intrusive rocks. The thickness of the Mariposa Formation is difficult to ascertain due to structural complexities, but is estimated to be about 2,600 feet thick at the Cosumnes River. Massive greenstone of the Upper Jurassic Logtown Ridge Formation lies west of the Mother Lode Belt. The contact between the Logtown Ridge and Mariposa Formation is generally gradational (Zimmerman, 1983). The Logtown Ridge Formation consists of over 9,000 feet of volcanic and volcanic-sedimentary rocks of island arc affinity. These rocks are mostly basaltic and include flows, breccias, and a variety of layered pyroclastic rocks. Metasedimentary rocks, chiefly graphitic schist, metachert, and amphibolite schist of the Calaveras Complex (Carboniferous to Triassic) are to the east.

    Mother Lode Gold Quartz Veins
    Mother Lode-type veins fill voids created within faults and fracture zones. The Mother Lode Belt consists of a vein system ranging from a few hundred feet to a mile or more in width. The vein system consists of a fault zone containing several parallel veins separated by hundreds of feet of highly altered country rock containing small quartz veins and occasional bodies of low-grade ore. Veins are generally enclosed within numerous discontinuous fault fissures within Mariposa Formation slate, associated greenstone, amphibolite schist, or along lithologic contacts. Mineralized fault gouge is abundant.
  • Mineralization is characterized by steeply dipping massive gold-bearing tabular quartz veins striking north to northwest and dipping between 50 to 80? east. Veins are discontinuous along both strike and dip, with maximum observed unbroken dimensions of 6,500 feet in either direction (Zimmerman, 1983), but individual veins more commonly range from structures 3,000 feet long and 10 to 50 feet wide to tiny veinlets. In rare instances, veins are known to reach as much as 200 feet thick (Keystone Vein). Veins may be parallel, linked, convergent, or en echelon, and commonly pinch and swell. Few can be traced more than a few thousand feet. At their terminations, veins pass into stringer zones composed of numerous thin quartz veinlets or into gouge filled fissures (Knopf, 1929).

    Ores consist of hydrothermally deposited minerals and altered wall-rock inclusions. Gold occurs as free gold in quartz and as auriferous pyrite and arsenopyrite. Quartz is the dominant mineral component in the veins, comprising 80-90% or more with ankerite, arsenopyrite, pyrite, albite, calcite, dolomite, sericite, apatite, chlorite, sphalerite, galena, and chalcopyrite in lesser amounts of a few percent or less. Cumulative sulfides generally range 1% - 3% of the rock (Carlson and Clark, 1954; Zimmerman, 1983).

    Ore grade material is not evenly distributed throughout the veins, but was localized in ore shoots, which tend to occur at vein intersections, at intersections of veins and shear zones, or at points where the veins abruptly change strike or dip (Moore, 1968). Ore shoots generally display pipe-like geometries raking steeply in the veins at 60-90%. Horizontal dimensions of the ore shoots are commonly 200-500 feet, but pitch lengths were often much greater, and often nearly vertical. Pockets of high grade ore are relatively abundant. Single masses of gold containing over 2,000 ounces and single pockets containing more than 20,000 ounces have been found. Silver is subordinate. Gold fineness averages 800.

    While most of the Mother Lode ore shoots mined have been less than 300 feet in strike length, many have extended down dip for many thousands of feet. In the deeper mines, mining continued to almost 6,000 feet on the dip of the vein with no evidence of bottoming. Cessation of operations in the deep Kennedy (5912') and Argonaut (5570') mines was caused by increasing costs at the greater depths rather than an absence of ore. Milling ore was generally low to moderate in grade (1/7 to 1/3 ounce per ton).

    Alteration
    Wall rocks have invariably been hydrothermally altered, having been partially to completely converted to ankerite, sericite, quartz, pyrite, arsenopyrite, chlorite, and albite with traces of rutile and leucoxene (Knopf, 1929). The mineralization is usually adjacent to the veins in ground that has been fractured and contains small stringers and lenses of quartz.. Locally, greenstone bodies (altered volcanic rocks) adjacent to the quartz veins contain enough disseminated auriferous pyrite in large enough bodies to constitute what has been called "gray ore". Altered slate wallrock commonly contains pyrite, arsenopyrite, quartz, chlorite, and sericite with or without ankerite (Zimmerman, 1983).

    Large bodies of mineralized schist also form low-grade ore bodies throughout the Mother Lode. This ore consists of amphibolite schist which has been subjected to the same processes of alteration, replacement, and deposition that formed the greenstone gray ores. The altered schist consists mainly of ankerite, sericite, chlorite, quartz, and albite. Gold is associated with the pyrite and other sulfides that are present. Pyrite comprises about 8 percent of the rock. The average grade of mineralized schist is about 0.1 oz per ton (Moore, 1968).
  • Ore Genesis

    Several mechanisms have been suggested as the source of the Mother Lode gold deposits. The most widespread belief is that plutonic activity magmatically differentiated vein constituents or provided the heat to circulate meteoric fluids or to metamorphose the country rocks to liberate the vein constituents. Knopf (1929) proposed that carbon dioxide, sulfur, arsenic, gold, and other constituents were emitted from a crystallizing magma but the components were carried by meteoric water in a circulation system driven by plutonic heat. Most theories suggest that gold deposits formed at temperatures of 300 to 350 degrees centigrade with a possible magmatic or metamorphic origin.

    Zimmerman (1983) proposed that the Mother Lode veins were generated by and localized near a major late Nevadan shear zone, the mechanism of ore genesis being the shearing and redistribution of mass within a major fault zone. He suggested that the early reverse faults had strike slip component, which is evident in the correlation of expected strike-slip dilatant zones with the geometries and steeply raking attitudes of the ore shoots. Fault movement and shearing would cause recrystallization of the rocks within the fault zone, releasing the more mobile elements including gold and most of the other vein constituents. Moreover, the heat generated by shearing would contribute to the metamorphism of the rocks in the fault zone and cause fluid circulation in the fault zone. Mineral laden auriferous fluids generated by this shearing channeled into the fault fracture system into dilatant zones, which represented avenues of increased flow and lower strain.

    LOCAL GEOLOGY

    The Kennedy Mine adjoins the Argonaut Mine to the south and both mines exploited the same .quartz vein system. The veins are true fissure veins which are wholly independent of the strike and dip of the enclosing rocks.

    The primary gold bearing veins in the Kennedy mine are the main foot wall vein (Kennedy vein) and the East vein (Tucker, 1914). The Kennedy vein is the most important vein in both the Kennedy and Argonaut mines. The vein has and average strike of N 20? W and dips of 57? - 70? northeast (Carlson and Clark, 1954). Average thickness is 8-10 feet, but in places it reaches as much as 40 feet thick. The Kennedy vein can be followed continuously from its apex in the neighboring Argonaut Mine to the lowest level of the Kennedy Mine without break or interruption. The dip of the vein varies from a comparatively small angle at the apex to about 67? in the lower levels of the Kennedy Mine (Storms, 1900).

    Wallrock consists of greenstone and Mariposa Formation slate. The contacts between the slate and greenstone are often so gradational as to make specific contacts arbitrary (Logan, 1934). Much of the greenstone in the proximity of veins has also been altered to schistose rocks. The vein outcrops in greenstone, but soon passes in to slate, wherein it approximately follows the main eastern contact of the Mariposa slates and greenstone. Crawford (1894) gives a good account of the shallow geologic conditions to an inclined depth of 2000 feet. A narrow greenstone dike lies close to the vein but tapers to a wedge and pinches out about the 3150 foot level (Logan, 1927), below which the vein is wholly in slate. There is usually a heavy gouge from 4-10 feet thick along the hanging wall. Wallrock slates have been disturbed by folding, faulting, and crushing.
  • Between the 1700 and 2200-foot levels, the vein splits. A large horse of hanging wall greenstone broke away allowing the formation of the East vein within the fracture. At its widest part, the horse separated the Kennedy vein from the East vein by about 150 feet. To the north of the main shaft on the 3900-foot level and south of it on the 4300 foot level, these veins begin to merge and in the adjoining Argonaut Mine they have recombined into to a single foot wall vein through this entire depth (Logan, 1934). By the 4500-foot level, the merged veins consist of a single large vein with 9 feet of ore on one wall and 16 feet on the other with a mass of lean bull quartz between them. In deeper levels of the Kennedy and in the adjoining Argonaut mine the merged veins become the main foot wall vein (Logan, 1927).

    Two main ore bodies occurred in the Kennedy Mine, a north ore body on the Kennedy vein, and the south ore body on the East vein. The principal Kennedy vein ore body of the Kennedy and Argonaut mines did not appear until about 1400 feet down dip from the surface exposure where the fissure system intersected a slate-greenstone contact (Zimmerman, 1983). The ore body was locally over 1000 feet long horizontally and over 4,500 feet long vertically including a few barren or low-grade zones (Logan, 1934). The main ore body had an irregular downward course near the property line between the two mines. In places it was partly in each mine; elsewhere it raked north or south so much as to carry it entirely into one property or the other. Between the 3600 and 4200-foot levels of the Argonaut Mine (wherein it was called the Pioneer or Argonaut ore body), for example, the ore body occurred on the Argonaut property, but its north pitch carried it into the Kennedy; below there it returned to the Argonaut, furnishing a large tonnage of ore in the deeper levels of that mine (Logan, 1934).

    The veins pinched and swelled abruptly, on both strike and dip. Ore shots occurred where the veins swell into quartz lenses. Accordingly, ore was not continuous either longitudinally or in depth. Storms (1900) noted that workings could be driven over the top and along either side of an ore shoot, and beneath it, in fact completely surrounding it in barren quartz. Both the Kennedy vein and the East vein branches furnished ore shoots near and at their north junction to form the main vein but the foot wall vein was the more important (Logan, 1934). In the middle levels of the mine, ore shoots occurred as en echelon lenses over a length of 800 feet, with from 7-11 feet of ore on the Kennedy foot wall vein and 6 feet on the East vein. Where the two veins joined on the 3900-foot level, 140 feet north of the shaft, a large ore shoot was followed northward several hundred feet. On the 4350-foot level, south of the shaft, they were separated by only a few feet of slate. Here the foot wall (Kennedy) ore body lengthened to 700 feet with ore values averaging $10 per ton (Logan, 1934).

    The thickness of the ore mined usually ranged between 8 and 40 feet. Ore from the East vein was more slaty and carried more sulfides than the foot wall vein, which showed more free gold and pyrophyllite. Coarse free gold was usually associated with light green pyrophyllite (Logan, 1934). Generally, the pay in the foot wall vein occurs near the foot wall, and the vein has a heavy black gouge on the foot wall from 1-2 feet thick, which contains some gold (Tucker, 1914). The best ore was banded or ribbon rock consisting of hard white quartz showing free gold with numerous ribbons of finely ground slate and often ribbons of pyrite, arsenopyrite, and galena with the sulfides averaging 1-2%of the ore. Little specimen ore was recovered.

    Ore is free milling gold in quartz with auriferous pyrite, arsenopyrite, and minor amounts of galena. Sulfides concentrates have been generally high for a Mother Lode mine, carrying 6-7 ounces of gold per ton (Logan, 1934).

Economic information about the deposit and operations

Operation type Underground
Development status Past Producer
Commodity type Metallic
Significant Yes
Discovery year 1856

Mining district

District name Jackson - Plymouth

Land status

Ownership category Private
Area name Amador County Planning dept.

Ownership information

  • Type Owner
    Owner Kennedy Mine Foundation
    Home office PO Box 684 Jackson, CA 95642

Comments on the workings information

  • The Kennedy Mine was developed through three shafts on the property. The shallow early workings were accessed through the North shaft, sunk on an incline to a depth of 2500 feet and a South shaft 2300 feet on the incline, being vertical for 376 feet, from which point it was inclined 66? to conform to the dip of the vein. The North shaft was located 600 feet north of the South shaft. The later East shaft was the main working shaft through which the lower levels were generally worked. The East shaft was a 3-compartment shaft 4764 feet deep. Each compartment was 4 by 5feet. It was sunk 1950 feet east of the older workings and cut the East vein at 3680 feet and the Kennedy vein at 4400 feet. Work at the lowest levels was done through an inclined winze off the 4650-foot level to the lowest 5900 foot level. The greatest vertical depth reached was 5912 feet (Carlson and Clark, 1954), making the Kennedy mine the deepest mine in North America. There are approximately 50 miles of underground workings.

    Levels were driven at 500', 1000', 1700', 1800', 1900', 2100', 2200', 2300', 2400', 2550', 2700', 2850', 3000', 3150', 3300', 3450', 3600', 3750', 3900', 4050', 4200', 4350', 4500', 4650', 4800', 4950', 5100', 5250', 5400', 5550, 5700', and 5900 feet.

    Drifts were generally run northward from the shaft crosscuts on the Kennedy vein and southward from shaft crosscuts on the East vein. The upper levels were drifted north and south to the property lines and stoped out to the surface from the 2250 foot level. Due mainly to heavy swelling ground and gouge, a large amount of timbering was used for square set timbering with waste filling to within one set of the roof (Tucker, 1914). Stopes were filled with waste obtained by raising in the hanging wall or drifting (Logan, 1921).

    By 1914, mining was conducted with air drills. Nine, oil fired, 80 hp boilers furnished steam for hoist and compressors. The mine had an Allis Chalmers 800 hp double-drum hoist that raised and lowered 4-ton skips. When steam powered, the hoist could drop the skips at speeds up to 2200 feet per minute. Ore was dumped over a grizzly, the fines going to 200 ton capacity storage bins in the head frame, and the coarse material to a 12" x 16" Blake crusher. From the storage bins, ore was trammed in 2-ton cars to 2000 ton capacity mill bins (Tucker, 1914).

    Prior to 1931, the Kennedy Mill contained 100 stamps, with a capacity of 15,000 tons per month. There were 42 6-foot Frue vanners in use. Concentrates from Frue vanners were reconcentrated on two 6-foot Gates concentrators. The sulfides were treated in the chlorination works at the mine. Tailings went from the mill to hydraulic classifiers where the coarse sands were eliminated and overflow slimes were directed to a slimes plant where the slimes were distributed over sixty 10' x 12' canvas tables. The slimes plant was one of the first built and successfully operated on the Mother Lode (Storms, 1900). Washings from the canvas tables went to two bumping circular tables and one Gates concentrator. The overflow from these went to eight additional tables. From here, tailings were conveyed to a tailings reservoir (Tucker, 1914). The average recovery was about 94% (Storms, 1900).

    In 1931, a ball mill and flotation cells were installed. The stamp mill was then used only for primary crushing. From 1936 until the mine closed, an average of 3,000 tons of ore per month was milled. The last full crew at the mine and mill was 125 men (Carlson and Clark, 1954).
  • Somewhat unique to the Kennedy Mine was the use of tailings wheels to elevate tailings over a local ridge into a tailings reservoir. Built in 1912, four tailings wheels were originally housed in a building, which no longer exists. Two wheels remain and two have crumbled to the elements. Each wheel was 68 feet in diameter and equipped with 176 18 inch by 8 inch buckets. Each wheel had a lift capacity of 48 feet. Tailings flowed by mean of a 900-foot flume to the first tailings wheel elevator, which elevated the tailings to a second flume 75 feet long at the end of which a second wheel elevated the tailings to an 800-foot flume. At the end of this flume, a third elevator wheel raised the tailings to another flume 160 feet long. This flume conveyed the tailings to the last elevator wheel where they raised to a flume 1000 feet long that flowed to a storage reservoir. There, the tailings were impounded by a concrete dam 540 feet long and 50 feet high.

Comments on other economic factors

  • Clark (1970) reported that the Pacific Mine produced $34.28 million. The purity of the gold produced between 1886 and 1942 averaged 83% and the average yield during this same period was 0.38 ounces per ton.

Comments on development

  • Exploration and Development history

    Most of the important lode gold deposits in the Amador County Mother lode were discovered in the 1850s while rich Tertiary placer deposits were being worked. The Kennedy Mine was discovered in 1856. While many of the neighboring mines were very profitable by 1875, the Kennedy Mine (and nearby Argonaut, Central Eureka, Bunker Hill, Fremont-Glover, and Lincoln Consolidated mines) did not become a major producer until the 1880s and 1890s. From the 1890s until 1942, the Kennedy Mine and its neighbors become one of the most important gold mining districts in the nation, with the district producing $2 million - $4 million annually.

    The Kennedy Mine was named for Andrew Kennedy, an Irish immigrant who discovered quartz outcropping in 1856. In 1860, several properties were consolidated and Kennedy, with some partners, formed the Kennedy Mining Company, which began digging shallow shafts. The mine controlled 3,100 feet on the lode and was comprised of the Kennedy, Kennedy Mill site, Silva, Hall placer mine, Bellwether, Clyde, North Clyde, and North Clyde placer mine claims, totaling 156 acres.

    Kennedy sold his one-quarter interest in the undeveloped mining claims within a year, on October 4, 1861, for $5,000. The remaining partners operated the mine sporadically with one shaft with only a whim for hoisting until 1869, when the mine was sold to eleven Jackson businessmen for $1.00. The partners formed the Kennedy Mining Company. Peter Reichling, one of the nine members, became the superintendent from 1870 - 1878. In 1871, the first hoist and a 20-stamp mill were erected. Three new shafts which yielded ore were sunk during this period. One of these would later be referred to as South Shaft. In 1873 two ore shoots were being worked. The Kennedy shoot on the north was 150 feet long and 2 - 12 feet wide, and the Pioneer (Argonaut) shoot was on the south end of the mine, with 170 feet of it on the Kennedy property where it was 18 feet wide (Logan, 1927) at the Argonaut property line. Only four miners were employed in stoping to produce 20 tons per day, the mill capacity (Logan, 1934). At 750 feet in the south shaft, the ore gave out with the raking of the ore shoot into the Argonaut Mine property (Logan, 1934). No ore was found or milled during 1875. The Kennedy Mining Company recovered $300,000 in gold between 1870 and 1878. The amount of gold recovered before 1870 is unknown, but is considered modest compared to the $300,000.

    Several attempts by the Kennedy Mining Company to reopen the mine after 1878 were unsuccessful, and in 1885, the mine was sold for $97,500 to fifteen San Francisco investors after prominent mining engineer J.J. Thomas had performed and extensive analysis of the property. The new investors incorporated under the name of the Kennedy Mining and Milling Company and reopened the mine. Unwatering was beguin January, 1886 and by October of that year a 40 stamp mill with 16 Frue vanners had been erected. The mill capacity was 100 tons per day. The south shaft was sunk 200 feet deeper, and ore was found, and this shaft was continued on the incline to a depth of 2276 feet. The north shaft was also sunk to an inclined depth of 2500 feet. By 1897, the Kennedy had produced $3.6 million and had paid $2.0 million in dividends (Logan, 1934).
  • The results after reopening were so successful that in 1900, a new vertical East shaft was started 1950 feet east of the north shaft. The East shaft was designed to allow the lower grade ores to be worked and was very successful, allowing 140,000 and 170,000 tons of ore per year to be produced between 1904 and 1916. The East shaft struck the east vein at 3680 feet, the west vein at 4000 feet, and became the main working entry since 1904. In 1904, a new 60 stamp mill was in full operation at the east shaft, as well as the old 40 stamp mill at the north shaft. By this time, the Kennedy was the deepest and largest producer on the Mother Lode. The larger mill was promptly upgraded to 100 stamps and for 12 years up to 1916, from 140,000 to 170,000 tons of ore was crushed annually (Logan, 1934). Most of this ore was taken from stopes between the 2250 and 3450 foot levels and averaged $ 4-$5 per ton.

    During 1914, the mill recovered about 83% of the gold. Tailings ran $0.60 - $0.80 per ton and concentrates assayed about $100/ton, while slimes from the canvas plant ran about $50/ton. The concentrates were treated at the mine by a 10 ton chlorination plant, which consisted of two 85' x 12'roasting furnaces.

    By the end of 1915, at a vertical depth of 3450, the Kennedy Mine had produced a total of 792,000 tons giving a gross total recovery of $6,378,000, or an average $8.00 per ton (Logan, 1927). For the period 1916 - 1926, inclusive, the production was $5,991,530 (Logan, 1927). At that time ore worth $4-$5/ton was being milled (Logan, 1927). With the addition of the East Shaft, the Kennedy was one of the largest producers in the Mother Lode (Clark and Carlson, 1954).

    In 1920, a severe underground fire on the 4000-foot level of the adjoining Argonaut Mine spread to the 3300-foot level of the Kennedy Mine, having presumably burned its way from the Argonaut through old workings. The Kennedy management began filling the mine with water, and as the two mines were connected, the lower levels of both were flooded. Water rose to the 2700-foot level in the main shaft. Unwatering began that summer and was completed in April, 1921. By the end of 1921 operations were back in full swing (Logan, 1927).

    The ground became extremely heavy at depth and required much timbering. As costs continued to increase during the early 1900s and were accelerated during WW I, it became necessary to mine more selectively, so from the middle of the 1920s until 1942 the tonnage of ore produced decreased, but the gold content increased to 1/3 to 2/5 once per ton. The main production during this period was from between the 4650-5900-foot levels. Operating stamps in the mill declined form 100 to 60. On September 7, 1928, a disastrous fire destroyed all of the surface plant except for the mill and main office (all other buildings and foundations that remain today were built after 1928). Latter that year, a new steel head frame was built to replace the original wooden one. In 1929, the surface plant was rebuilt and a 63? inclined winze was started from the 4650-foot level to the 5250-foot level. In 1935, a 1500-ton cyanide plant was erected south of the mine to re-treat accumulated tailings from the mill. This plant was in operation until 1939 (Carlson and Clark, 1954).
  • In August 1941, increasing costs caused all work below the 4650-foot level to be discontinued and in 1942 the mine was closed in compliance with Government Order L-208 issued to help the war effort. At the time, it was the deepest gold mine in North America with a vertical depth of 5,912 feet and over 50 miles of underground excavations. After the war, it was decided not to reopen the mine because of the extensive flooding of the deep underground workings. In 1948-1949, the tailings were worked intermittently by Frank Fuller of Jackson who reported that 20,000 tons of gold bearing tailings were treated with an average recovery of $2.00 per ton (Carlson and Clark, 1954). In 1949-1950 a Michael Hagel of Sacramento unsuccessfully tried to reprocess additional mine tailings. In September 1950, the Kennedy Mining and Milling Company was dissolved, formally ending one of the best known mining operations in California. Since the mine averaged only 0.38 ounces per ton, a high degree of efficiency was required to make a profit. The first two owners of the Kennedy Mine found this hard to do, but the Kennedy Mining and Milling Company' better capitalization and more efficient operation, allowed them to book total receipts of $28,205,831.30 during its 56 years of operations and to pay out $5.8 million in dividends to its stockholders on an original capitalization of $100,000.

    The property lay idle until 1961 when it was acquired at a liquidation sale for $41,600, by a San Francisco ceramics teacher. She lived on the property until her death in 1994, specifying in her will that the property remain open as habitat, and that the mine be maintained for its historical value. The Kennedy Mine Foundation was formed in 1996 to fulfill those wishes. The Kennedy Mine Foundation currently offers tours of the remaining historic surface facilities. The remaining surface plant at the Kennedy Mine is now a museum. Its large steel, head frame, wooden tailings wheels and the superintendent's office also remain as historical displays.

Reference information

Bibliographic references

  • Deposit

    Carlson, D.W., and Clark, W.H., 1954, Mines and mineral resources of Amador County, California: California Division of Mines and Geology, 50th Report of the State Mineralogist, p. 182-185.

  • Deposit

    Clark, W. B., 1970, Gold districts of California: California Divisions of Mines and Geology Bulletin 193, p. 69-76.

  • Deposit

    Crawford, J.J., 1894, Gold in Amador County, Kennedy Mine, California State Mining Bureau, 12th Report of the State Mineralogist, p. 74 -77.

  • Deposit

    Duffield, W.A. and Sharp, R.V., 1975, Geology of the Sierra foothills melange and adjacent areas, Amador County, California: U.S. Geological Survey Professional Paper 827, 30 p.

  • Deposit

    Knopf, A., 1929, The Mother Lode system of California: U. S. Geological Survey Professional Paper 157, 88 p.

  • Deposit

    Koschman, A.H., and Bergendahl, M.H., 1968, Principal Gold-Producing districts of the United States: U. S. Geological Survey Professional Paper 610, 283 p.

  • Deposit

    Logan, C.A., 1921, Amador County, Argonaut Company: California State Mining Bureau, 21st Report of the State Mineralogist, p. 406-408.

  • Deposit

    Logan, C.A., 1927, Amador County, Lincoln Consolidated Mines: California State Mining Bureau, 23nd Report of the State Mineralogist, p. 166-169.

  • Deposit

    Logan, C.A., 1934, Mother Lode gold belt of California: California Division of Mines Bulletin 108, p. 85-91

  • Deposit

    Schweickert, R.A., Hanson, R.E., and Girty, G.H., 1999, Accretionary tectonics of the Western Sierra Nevada Metamorphic Belt in Wagner, D.L. and Graham, S.A., editors, Geologic field trips in northern California: California Division of Mines and Geology Special Publication 119, p. 33-79.

  • Deposit

    Storms, W.H., 1900, The Mother Lode region of California: California Mining Bureau Bulletin 18, p. 52-65.

  • Deposit

    Tucker, W.B., 1914, Amador County, Lincoln Consolidated Mines: California State Mining Bureau, 14th Annual Report of the State Mineralogist, p. 31-34.

  • Deposit

    Additional information on the Kennedy Mine is available in file no. 322-5920 (CGS Mineral Resources Files, Sacramento).

  • Deposit

    Zimmerman, J.E., 1983, The Geology and structural evolution of a portion of the Mother Lode Belt, Amador County, California: unpublished M.S. thesis, University of Arizona, 138 p.

  • Deposit

    The Kennedy Mine Foudation publishes a number of informational pamphlets and brochures which are available at the mine, or on their website: http://www.kennedygoldmine.com

General comments

Subject category Comment text
Deposit The Kennedy Mine produced from typical Mother Lode type low sulfide mesothermal gold quartz veins. The producing veins are part of a single NNW-SSE striking, steeply dipping vein system that extends northward through the Kennedy Mine and adjoining Argonaut Mine to the south. The principle Kennedy or foot wall vein strikes N 20? W and dips 57? - 70? northeast. The East vein branches from the Kennedy vein between the 1700 and 2000 foot levels, but merges again with the Kennedy foot wall vein to the north and to the south where it is the primary orebody in the Argonaut Mine.

The thickness of the ore mined usually ranged between 8 and 40 feet. Ore from the East vein was more slaty and carried more sulfides than the foot wall vein, which showed more free gold and pyrophyllite. Coarse free gold was usually associated with light green pyrophyllite (Logan, 1934). Generally, the pay in the foot wall vein occur near the foot wall, and the vein has a heavy black gouge on the foot wall from 1-2 feet thick, which contains some gold (Tucker, 1914). The best ore was banded or ribbon rock consisting of hard white quartz showing free gold with numerous ribbons of finely ground slate and often ribbons of pyrite, arsenopyrite, and galena with the sulfides averaging 1-2%of the ore.

Reporter information

Type Date Name Affiliation Comment
Reporter 10-MAR-2006 Downey, Cameron (Higgins, Chris, T.) California Geological Survey CGS (Formerly CDMG)
Editor 01-SEP-2007 Schruben, Paul G. U.S. Geological Survey Converted from S&A FileMaker format to Oracle. Edit checks on rocks, units, and ages with Geolex search, and other fields.

Beyond USGS

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