Argonaut Mine

Site Name

Primary: Argonaut Mine
Secondary: Pioneer Mine

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Commodity

Primary: Gold
Secondary: Silver

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Location

State: California
County: Amador
District: Jackson

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Land Status

Land ownership: Private
Note: the land ownership field only identifies whether the area the mine is in is generally on public lands like Forest Service or BLM land, or if it is in an area that is generally private property. It does not definitively identify property status, nor does it indicate claim status or whether an area is open to prospecting. Always respect private property.
Administrative Organization: Amador County Planning Department

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Holdings

Not available

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Workings

Not available

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Ownership

Not available

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Past Producer
Deposit Type: Hydrothermal vein
Operation Type: Underground
Discovery Year: 1850
Years of Production:
Organization:
Significant: Y
Deposit Size: M

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Physiography

Not available

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Mineral Deposit Model

Model Name: Low-sulfide Au-quartz vein

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Orebody

Form: Tabular, pinch and swell

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Structure

Type: L
Description: Melones Fault zone

Type: R
Description: Bear Mountains Fault zone, Melones Fault zone

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Alterations

Not available

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Rocks

Name: Amphibole Schist
Role: Host
Age Type: Host Rock
Age Young: Late Jurassic

Name: Greenstone
Role: Host
Age Type: Host Rock
Age Young: Late Jurassic

Name: Slate
Role: Host
Age Type: Host Rock
Age Young: Late Jurassic

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Analytical Data

Not available

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Materials

Ore: Gold
Ore: Chalcopyrite
Ore: Pyrrhotite
Ore: Amphibolite
Ore: Slate
Ore: Quartz
Ore: Arsenopyrite
Ore: Galena
Ore: Pyrite
Ore: Tetrahedrite

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Comments

Comment (Commodity): Ore Materials: Free-milling ribboned structures of quartz, crushed slate, free gold, and sulfides that occurred within a few feet of the foot wall. The yearly average grade of ore varied from $6 to $17 per ton. Auriferous sulfides , primarily pyrite, and to a lesser extent galena and arsenopyrite, comprised about 2 to 2-1/2% of the ore. Concentrates assayed up to $100 per ton.

Comment (Geology): The Argonaut vein is enclosed within greenstone wall rock to a depth of 290 feet. Near the vein, the greenstone has been altered to amphibolite schist (Logan, 1934). From 290 feet to the 470-foot level, the vein traverses a narrow belt of Mariposa slate. The hanging wall side of the slate has been thrust up 125 feet along the fault. To a depth of 2500 feet the vein is on or near the contact between a slate foot wall and schistose greenstone hanging wall contact (Clark, 1952a). From there downward, the foot wall country rock is hard gray schist, but with a casing of Mariposa slate between it and the vein, and the hanging wall is Mariposa slate (Logan, 1934). Sills of greenstone, now standing near vertically and entirely altered to schist, occur within the Mariposa slate, and as a result, on certain levels, the immediate hanging wall is greenstone and the foot wall is slate. The vein is usually accompanied on one or both walls by gouge which varies from several inches to several feet thick. The main quartz ore body in the Argonaut Mine was locally over 1000 feet long horizontally and about 5000 feet long vertically, but included barren or low-grade zones (Logan, 1934). Individual ore shoots ranged from 1 foot to 60 feet wide with an average of about 6-12 feet (Knopf, 1929). The main ore shoot which had been the mainstay of the Argonaut and Kennedy mines did not appear until about 1400 feet downdip from the surface where the upper portion of the veins fissure system intersected a slate-greenstone contact (Zimmerman, 1983). Between the 3600 and 4200-foot levels, because of its north pitch, the ore shoot was in the adjoining Kennedy Mine, then returned to the Argonaut (Logan, 1934). Around the 4800-foot level, the ore shoot was a lens of quartz about 950 feet long and 25-60 feet wide, raking southward about 50? between the vein and the hanging wall, and tapering gradually at each end. On the foot wall side there was a thick zone of post mineralization fault gouge made up of crushed slate and quartz fragments. Ribboned quartz developed along the foot wall side of the vein and showing free gold and carrying appreciable quantities of pyrite with trace amounts of sphalerite, galena, and chalcopyrite provided the best ore (Hershey, 1927). The hanging wall part of the vein was typically very low grade or barren massive quartz with black inclusions of hanging wall slate and scattered pyrite. Between the 4950 and 5100-foot levels, the ore shoot shortened, became flatter, and of lower grade. Ore grade remained unusually poor to the 5500-foot level, where a junction of two veins yielded a large low-grade quartz body (Logan, 1934). On the 5700-foot level, the north drift showed ore from 6 - 17 feet wide extending 200 feet north to the Kennedy Mine property. In the south drift on this level, three ore shoots, 158 feet, 235 feet, and 170 feet long respectively, varied from 5 -12 feet wide and ranging from $3 -$12 per ton (Logan, 1934). The maximum width and length of the largest ore shoot was 65 feet and 1100 feet respectively. The average width mined was about 20 feet (Vanderburg, 1930). This ore shoot split into two branches near the 5400-foot level, below which they were worked independently (Logan, 1934). Other ore shoots above the 4200 foot level reported by Tucker (1914) include one 325 feet long averaging 10 feet wide and anotherf 600 feet long and averaging 10 feet wide.

Comment (Geology): 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).

Comment (Development): Mining was halted in 1919, when a severe underground fire broke out on the 4000-foot level. At this time the mine had reached an inclined depth of 4800 feet. Within a short time, the fire was thought to be under control and work was resumed. But in early March, 1920, fire was discovered on the 3300-foot level of the adjoining Kennedy Mine, having presumably burned its way through old workings and caved ground. On March 17, 1920, 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 within 50 feet of the 3150 level of the Argonaut. Unwatering of the Argonaut began that summer, but they found the job too much for their plant alone and the Kennedy joined in the work which was completed in April, 1921. The fire caused the loss of a year's production. By the end of 1921, operations were back in full swing. On August 22, 1922, however, fire was again discovered on the 3350-foot level in the main shaft. A shift of 47 men working on the 4650 and 4800-foot levels was trapped, and before they could be rescued, the shaft was on fire and all were lost. For 22 days, rescuers tried reach the miners from a neighboring mine tunnel. Their efforts were in vain. A detailed account of the tragedy is captured in the book 47 Down: the 1922 Argonaut Gold Mine Disaster (Mace, 2004). This fire closed the mine for another year. The mine was not cleared and ready for operation until July, 1923 after which it remained in steady operation until 1942. Between 1910 and 1934, the tonnage of ore handled annually ranged from 62,000 to 91,000 tons. By 1930, the Argonaut Mine had produced $16,377,252 (792, 250 ounces of gold), and was producing 260 tons of ore per day (Vanderburg, 1930). The Argonaut Mill used 60 stamps, amalgamation, classifiers, and vanners. Al concentrates were chlorinated until the advent of cyanidation in 1896 and the construction of smelters in the San Francisco area in 1901 (Moore, 1968) From 84 - 91 percent of the gold was recovered from the ore containing about 1/3 ounce of gold per ton. In 1936, ball mills and flotation cells were installed making it possible to raise recovery to 94 % (Clark, 1952a). Details of the Argonaut milling operation during the 1930s are provided by Logan (1934). The tailings were sold to a custom cyanide mill for further treatment (Moore, 1968). Between 1923 and 1938, the Amador Metals Reduction Company treated the Argonaut mine tailings. During this period, about 70,000 tons of tailings were treated resulting in a recovery averaging $60,000 per year (Clark, 1952b). Processing involved hydraulicking the tailings into a classifier and cyaniding. Because of the carbonaceous nature of the ore, sands and slimes were pre-coated with coal tar to prevent precipitation of the dissolved gold in the cyanide solution. The sands were then treated in leaching vats while the slimes were directed to an agitator and filtered on Oliver filters. Sand and slime residues were discharged. The solution was then precipitated, roasted, and the gold melted into bullion (Clark, 1952b). The Argonaut Mine was closed in 1942 under Government Order L-208 (Gold Mine Closing Order) to help the war effort. The upper part of the mine was kept dewatered and in repair in hopes of eventual reopening. Due to escalating costs and the government imposed fixed gold price, the mine never reopened and the Argonaut Mining Company was dissolved in 1948. Through December 31, 1942, production was 2,750,000 tons of ore from which $25,179,160.43 was recovered. The Argonaut Mining Company paid shareholders dividends of $3,789,750 on their original capitalization of $1 million (Clark, 1952a). After closure, the surface plant and other surface facilities were sold to the Mines Engineering a

Comment (Development): Most of the important lode gold deposits in Amador County were discovered in the 1850s while rich Tertiary placer deposits were being worked. During this period, a 20-mile long belt of gold mineralization, part of the famous Mother Lode, was identified running through western Amador County, and the towns of Jackson, Sutter Creek, Amador City, and Plymouth flourished to support the new mines. While many of the local mines had been discovered and several had become large and profitable mines by 1875, several of the more important mines, including the Argonaut, Kennedy, Central Eureka, Bunker Hill, Fremont-Gover, and Lincoln Consolidated Mines did not become important producers until the 1880s and 1890s. The Argonaut property was first opened in 1850 after discovery by two black miners named James Hager and William Tudor. From 1850 to 1893 it was worked in a primitive manner under the name of the Pioneer Mine. During this time exploration was confined to surface trenching and the driving of an adit on the north end of the Pioneer claim to cut the vein at a depth of several hundred feet (Vanderburg, 1930). Meanwhile, the neighboring Kennedy Mine was being actively worked while the Pioneer lay undeveloped. The Pioneer Mine is said to have been offered to the Kennedy Mine owners several times for $30,000, but they declined (Logan, 1927). By 1876, the mine had reached only 150 feet along the 18-foot wide Pioneer ore-shoot (Logan, 1934). In 1893, the mine was purchased by the Argonaut Mining Company and renamed the Argonaut Mine. The Argonaut claims covered 4800 feet along strike of the Mother Lode. The Argonaut Company explored the deeper portions of the ore body by sinking and inclined shaft in the hanging wall of the vein with crosscuts and drifts driven from the main shaft. Shallow ores were rich and highly profitable. The ores were crushed in a 40 stamp mill. Details of early milling operations are provided by Storms (1900). Due to the heavy ground encountered, exploratory work could not be carried very far in advance of actual mining operations, as the maintenance expense entailed in keeping the workings open would have been prohibitive (Vanderburg, 1930). There were two noted lawsuits between the Argonaut and adjoining Kennedy Mine in 1894 and 1897. In both cases, the Argonaut Mining Company accused the Kennedy Mine of conducting mining operations on their claims. In 1894, at a depth of 1200 feet, a vein branched from the main Argonaut vein into the hanging wall. The Kennedy Mine contended that this was an older vein, which had been displaced about 700 feet by normal faulting as measured along the Argonaut fissure. Ultimately, the courts ruled in favor of the Argonaut (Clark, 1952a). When the shaft reached 1750 feet in 1897, another dispute arose with the Argonaut again alleging the Kennedy was encroaching on their ground (Logan, 1927). To prove their case, the Argonaut owners were forced to prove their vein continued through to the apex of their ground. Since the shaft was not on the vein, raises had to be driven the entire distance to delineate the vein. Having proved the apex on their ground, they were awarded heavy damages against the Kennedy (Logan, 1927). Between 1914-1919, the Argonaut was worked between the 3400 and 4800-foot levels and produced the best average grade of ore of any mine along the Mother Lode, averaging $10 - $13 per ton (Logan (1934). Between the 4500 - 4800-foot levels the ore averaged about $14.50 per ton.

Comment (Identification): The Argonaut Mine is located one mile northwest of the town of Jackson, California, in the famous Mother Lode Gold Belt in the Sierra Nevada foothills of western Amador County. 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 Argonaut Mine alone produced $25.2 million (Clark, 1970). While discovered in 1850, the Argonaut Mine lay largely undeveloped until purchased by the Argonaut Mining Company in 1893, after which the mine remained in continuous operation until 1942 except for a period of 3 years when mining was discontinued due to the results of mine fires (Vanderburg, 1930). From the 1890s until 1942, the Argonaut 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 Argonaut Mine, itself became one of the deepest gold mines in the nation, bottoming at a vertical depth of 5570 feet.

Comment (Commodity): Gangue Materials: Quartz, slate, greenstone, amphibolite schist, pyrrhotite, chalcopyrite, and tetrahedrite

Comment (Deposit): The Argonaut Mine produced from typical Mother Lode type mesothermal gold-quartz veins. The principal producing vein known as the Argonaut or Pioneer vein is a fracture-filling quartz vein that strikes N 10? - 18? W and dips between 40? and 63? northeast. The same vein is known as the Kennedy footwall vein in the adjoining Kennedy Mine where it is also the major producing vein. The Argonaut vein ranges from 8 - 10 feet wide in the upper workings, but reached as much as 70 feet wide on the 4800-foot level. Essentially, all ore was contained in the single large vein, but there were numerous splits from the main vein into the hanging wall (Zimmerman, 1983). The best ore consisted of a ribboned structure of quartz, crushed slate, free gold, and sulfides, which was found within a few feet of the foot wall. It was free milling and contained about 2% sulfides, largely pyrite, and to a lesser extent galena and arsenopyrite.

Comment (General): Additional information on the Argonaut Mine is available in file nos. 330-8488 and 322-5904 (CGS Mineral Resources Files, Sacramento).

Comment (Geology): REGIONAL GEOLOGY The Argonaut 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 (Koschmann 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.

Comment (Location): Location selected for latitude and longitude is the Argonaut Mine shaft symbol on the USGS 7.5 minute Jackson quadrangle.

Comment (Workings): The Argonaut Mine was worked through a 5,800-foot 70? inclined shaft sunk in the hanging wall of the vein. An auxiliary shaft was also maintained for ventilation and as an escape route. The three-compartment shaft was divided into one man and two hoisting compartments, each of dimensions 5' 9" x 4' 1". The greater portion of the shaft was timbered with 20 inch x 20 inch fir sets, but later operations employed 16 inch by 16 inch wall plates 16 feet long, 14 inch by 16 inch end plates 6 feet long, 10 inch by 16 inch dividers 6 feet long, and 8 inch by 12 inch posts 3 feet p inches long. The sets were placed on 5-foot centers. Lagging was 2 by 6 or 3 by 6 inch. Drifts and crosscuts were also heavily timbered to combat swelling ground. Details of timbering in drifts, crosscuts and raises are given by Vanderburg (1930). Levels were driven at 290', 380', 470', 560', 740', 830', 920", 1010', 1130', 1240', 1350', 1460', 1570', 1690', 1800,'1920', 2040', 2160', 2280', 2400', 2520', 2640', 2760', 2880', 3000', 3150', 3300', 3450', 3600', 3750', 3900', 4050', 4200', 4350', 4500', 4650', 4800', 4950', 5100', 5250' 5400,' 5500', 5800', 6000', 6150', and 6300'. The lower levels were accessed through a winze sunk from the 5500 foot level, 300 feet south of the shaft. The deepest 6300-foot level was 5570 vertical feet below the collar of the shaft (Clark, 1952a). Levels were turned from the winze at 5700, 5800, 6000, 6150, and 6300 feet. There are approximately 8 miles of drifts, crosscuts, and tunnels, 4 miles of raises, and 50 miles of stope floors (Clark, 1952a). The mine had several connections to the Kennedy Mine (Vanderburg, 1930 figure). A connection to the adjoining Kennedy Mine was maintained at the 4650 level. Vanderburg (1930) provides a plan of the lower mine levels and a vertical projection of the Argonaut shaft. Development consisted of driving a crosscut from the main shaft to the vein. From the crosscut drifts were extended along the foot wall. Crosscuts and drifts, 6 feet by 8 feet in cross section, were timbered with regular drift sets. After a drift was driven several hundred feet, a raise was driven to connect with the level above top provide an additional escape route and to aid air circulation on the level (Vanderburg, 1930). The method of stoping used at the Argonaut Mine was an adaptation of the square-set system followed closely by waste filling. Since the ore body and its walls had insufficient strength to remain open, as stoping progressed, temporary timber support was required, followed promptly by waste filling (Vanderburg, 1930). Stoping was carried out in sections about 100 feet long, or as long as the distance between two consecutive manways. Several sections were usually mined at the same time. Practically all the vein material in the ore shoot was mined without sorting. No pillars were left. Additional details of stoping and methods are provided by Vandenburg (1930). All ore and rock was trammed underground in 1-ton end dump cars. Mechanical haulage was not used since the distance from the shaft to the ore body was small. Before 1936, milling was done in a 60-stamp mill. After stamping, the pulp was concentrated, classified, and the tailings were cyanided. In 1936, ball mills and flotation cells were installed making it possible to raise recovery to 94 % (Clark, 1952a).

Comment (Economic Factors): When the Argonaut mine closed in 1942, total production amounted to 2,750,000 tons of ore, from which $25.2 million. Dividends paid totaled $3,789,750 on an original capitalization of $1 million (Clark, 1952a). Production figures reported by Joralman (1941) for the Argonaut Mine show a grade of 0.5 ounce per ton from 1897 to 1925, and 0.31 ounce /ton from 1926 to 1940, with an overall average grade of 0.406 ounce/ton (Zimmerman (1968).

Comment (Geology): 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 Argonaut Mine developed the Argonaut or Pioneer vein, a mesothermal gold-quartz vein occupying the fissure of a reverse fault that cut through beds of greenstone, schist, and slate. The vein was noteworthy for its continuity, having been followed from the apex down to the 5,400-foot level without a significant break. The quartz filling pinches and swells along both the strike and dip, but never dies out entirely (Vanderburg, 1930). The general strike of the Argonaut vein varies from N 10? - 18? W. At the 290-foot level, the vein dips 40? northeast, from the 470 level to the 4050-foot level it dips at 64?, and below the 4050- foot level the dip varies from 60? - 63? (Clark, 1952a). The vein ranges from 8 - 10 feet wide in the upper workings and thickens with depth. On the 3700-foot level, the Argonaut fissure is 7-10 feet wide and half filled with gouge and half with quartz. On the 4200-foot level it is 20 feet wide, increasing to 30 feet wide on the 4350-foot level. On the 4800-foot level, it widened rapidly to as much as 60 feet before narrowing considerably on the 4950 and 5100-foot levels where the ore shoot shortened, became flatter, and of lower grade (Logan, 1934). Essentially, all ore was contained in the single large vein, but there were numerous splits from the main vein into the hanging wall and foot wall (Zimmerman, 1983).

Comment (Geology): The best ore consisted of a ribboned structure of quartz, crushed slate, free gold, and sulfides that occurred within a few feet of the foot wall. Ore was free milling and most of the gold was recovered by crushing and amalgamation. The yearly average grade of ore varied from $6 to $17 per ton. Sulfides comprised about 2- 2 1/2% of the ore. The amount of sulfides was not indicative of the richness of the ore (Vanderburg, 1930). On average, the concentrate contained about 16% of the gold recovered and ran up to about $100 per ton for the highest grade ore (Logan, 1927). Ore from the 5500 and 5700-foot levels averaged as much as 2.5 % concentrate which contained 2.6-5.0 ounces of gold per ton, and from which yielded 22% of the gold and 38% of the silver recovered. Pyrite was the most abundant sulfide, with galena and arsenopyrite also yielding gold. Pyrrhotite, chalcopyrite, and tetrahedrite occurred sparingly (Logan, 1934). In addition to the pre-mineral fault fissure, post-mineralization faulting was important in modifying the geometries of the Argonaut vein and its contained ore shoots. There are important oblique faults and smaller post-mineral faults within the vein. Three primary post-mineral faults were recognized in the mine. The "No.1 fault" has a horizontal throw of at most 80 feet on the 2880 foot and 3000 foot levels and persisted with depth. The No. 2 fault, south of the No.1, has a horizontal throw of 50 feet on the 5700-foot level. The No. 3 fault (200 feet south of the No.2), also has a 50-foot throw. On the south side of the workings, the ore is thought to be bounded by another oblique northwest striking fault, its trace on the plane of the vein dipping 70?-75? northeast. In several places where the fault cut the vein, a thick section of barren or poorly mineralized quartz comprised the hanging wall, while only a few feet of ribboned quartz ore occurred on the foot wall side (Logan, 1934).

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References

Reference (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.

Reference (Deposit): Storms, W.H., 1900, The Mother Lode region of California: California Mining Bureau Bulletin 18.

Reference (Deposit): Tucker, W.B., 1914, Amador County, Argonaut Mine: California State Mining Bureau, 14th Annual Report of the State Mineralogist, p. 17-19.

Reference (Deposit): Vanderburg, W.O., 1930, Mining methods and costs at the Argonaut Mine, Amador County, California: Bureau of Mines Information Circular 6311, 15 pp.

Reference (Deposit): Moore, L., 1968, Gold resources of the Mother Lode Belt, El Dorado, Amador, Calaveras, Tuolumne, and Mariposa counties, California: U.S. Bureau of Mines Technical Progress Report 5, p. 1-22.

Reference (Deposit): Clark, W.B., 1952a, Argonaut Mine tailings, Amador County: Unpublished preliminary report no. 24 , California Division of Mines, 4 p.

Reference (Deposit): Clark, W.B., 1952b, Argonaut Mine tailings, Amador County: Unpublished preliminary report no. 64 , California Division of Mines, 1 p.

Reference (Deposit): Hershey, O.H., 1927, Report on Argonaut Mine: Unpublished report prepared for the Argonaut Mining Company, 17 p.

Reference (Deposit): Hershey, O.H., 1931, Second Report on Argonaut Mine: Unpublished report prepared for the Argonaut Mining Company, 8 p.

Reference (Deposit): Joralman, T.B., 1941, Report on Argonaut Mining Co. Ltd.: Unpublished report for Argonaut Mining Co., 11 p.

Reference (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.

Reference (Deposit): Carlson, D.W., and Clark, W.B., 1954, Mines and mineral resources of Amador County, California: California Journal of Mines and Geology, 50th Report of the State Mineralogist, p. 168-170.

Reference (Deposit): Clark, W.B., 1970, Gold districts of California: California Division of Mines and Geology Bulletin 193, p. 69-76.

Reference (Deposit): Crawford, J.J., 1894, Amador County Gold: California State Mining Bureau, 12th Annual Report of the State Mineralogist.

Reference (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.

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

Reference (Deposit): Koschmann, A.H., and Bergendahl, M.H., 1968, Principal gold-producing districts of the United States: U. S. Geological Survey Professional Paper 610, 283 p.

Reference (Deposit): Logan, C.A., 1927, Amador County, Argonaut Mine: California State Mining Bureau, 23rd Report of the State Mineralogist, p. 153-157.

Reference (Deposit): Logan, C.A., 1934, Mother Lode gold belt of California: California Division of Mines Bulletin 108, p. 35, 52, 62-70.

Reference (Deposit): Mace, O.H., 2004, 47 Down: The 1922 Argonaut Gold Mine Disaster, John Wiley & Sons, 288 p.

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California Gold

"Where to Find Gold in California" looks at the density of modern placer mining claims along with historical gold mining locations and mining district descriptions to determine areas of high gold discovery potential in California. Read more: Where to Find Gold in California.