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Sixteen-to-One Mine

Producer in Sierra county in California, United States with commodities Gold, Silver
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Geologic information

Identification information

Deposit ID 10310678
Record type Site
Current site name Sixteen-to-One Mine
Alternate or previous names Original Sixteen-to-One, Tightner, Ophir, Oriental, Rainbow, Twenty-One, Red Star, South Fork, Bald Mountian, Contract, Contract Extension, Eclipse

Comments on the site identification

  • Having produced an estimated one million ounces of gold, the Sixteen-to-One Mine is the most productive mine in the Alleghany Mining District and one of the most famous high-grade gold mines in California. The present mine properties consist of 550 acres on the southeast flank of Pliocene Ridge and include the original Sixteen-to-One Mine as well as neighboring mines and claims that were acquired by the Sixteen-to-One over the years. These mines include the Tightner, Twenty-One, Ophir, Rainbow, Rainbow Extension, Red Star, and South Fork mines (Clark and Fuller, 1968). Billed by the present operator as the oldest operating hard-rock gold mine in California, the mine is presently operated on a small scale by the Original Sixteen-to-One Mine, Inc. Currently the mine is notable not for the volume of gold produced, but for the high-quality specimens of native gold in quartz that find their way into collections and fine jewelry. Bullion gold is used to produce small commemorative bars.

Geographic coordinates

Geographic coordinates: -120.8434, 39.46498 (WGS84)
Elevation 1250
Location accuracy 100(meters)
Relative position 0.25 miles south of Alleghany; 21 miles northeast of Grass Valley.
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Geographic areas

Country State County
United States California Sierra

Public Land Survey System information

Meridian Township Range Section Fraction State
Mount Diablo 019N 010E 34 SE of SE of SW California

Comments on the location information

  • The location point selected for latitude and longitude is the Sixteen-to-One Mine adit symbol on the USGS Alleghany 7.5-minute quadrangle. The adit is just south of the town of Alleghany on the steep southeast flank of Pliocene Ridge. The mine is on private property. Access is via the paved Ridge Road, which begins two miles north of the community of North San Juan from State Highway 49. Take Ridge Road east approximately 16 miles to the town of Alleghany. The mine is active, and access is by permission only. The mine office is in the town of Alleghany.

Commodities

Commodity Importance
Gold Primary
Silver Secondary

Comments on the commodity information

  • Commodity Info: Native gold in quartz, including museum-quality crystallized gold and jewelry-quality gold. 870 fine gold. The gold in arsenopyrite is present as blebs and fracture fillings. Lesser amounts of gold are present in pyrite.
  • Ore Materials: Native gold and auriferous arsenopyrite and pyrite.
  • Gangue Materials: Quartz, ankerite, sericite, serpentine, chromium-mica

Materials information

Materials Type of material
Gold Ore
Arsenopyrite Ore
Pyrite Ore
Quartz Gangue
Ankerite Gangue
Sericite Gangue
Serpentine Gangue
Mica Gangue

Alteration

  • (Local) Chloritic; chlorite, epidote Silicic; quartz, albite Carbonate; ankerite, sericite, chromium mica (?mariposite? in older literature) Steatization; talc Extensive carbonatization aureoles up to 10 feet thick are present adjacent to the veins in the Sixteen-to-One: chlorite schist, amphibolite, and serpentinite of the wall rock have been variously altered to ankerite, sericite, and chromium-mica, and quartz. Oxidation is inconspicuous according to Ferguson and Gannett (1932).

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 > Amphibolite
    Rock unit name Feather River Peridotite Belt
    Stratigraphic age (youngest) Mesozoic
    Stratigraphic age (oldest) Paleozoic
  • Host or associated Host
    Rock type Metamorphic Rock > Schist
    Rock type qualifier Chlorite
    Rock unit name Feather River Peridotite Belt
    Stratigraphic age (youngest) Mesozoic
    Stratigraphic age (oldest) Paleozoic
  • Host or associated Associated
    Rock type Sedimentary Rock > Clastic Sedimentary Rock > Conglomerate
    Rock type qualifier meta-
    Rock unit name Feather River Peridotite Belt
    Stratigraphic age (youngest) Mesozoic
    Stratigraphic age (oldest) Paleozoic
  • Host or associated Associated
    Rock type Metamorphic Rock > Serpentinite
    Stratigraphic age (youngest) Paleozoic
  • Host or associated Associated
    Rock type Metamorphic Rock > Metasedimentary Rock > Marble
    Rock type qualifier Mariposite
    Stratigraphic age (youngest) Early Cretaceous
    Stratigraphic age (oldest) Late Jurassic

Nearby scientific data

(1) -120.8434, 39.46498
ListMap

Geologic structures

Type Description Terms
Local Alleghany fracture system
Regional Melones Fault Zone

Ore body information

  • General form Tabular

Controls for ore emplacement

  • High-grade gold-bearing ore shoots are found within quartz veins, which fill fissures that cut the Paleozoic-Mesozoic crystalline basement. Favorable locations that controlled deposition of these ore shoots within the veins include changes in dip and strike, swellings, splitting, minor faulting, and junctions with other veins. Also important are locations where the veins encounter serpentinite. Some hydrothermal minerals in wall-rock aureoles adjacent to the veins contain minor gold.

Comments on the geologic information

  • INTRODUCTION The Sixteen-to-One Mine is part of the Alleghany Mining District in southern Sierra County. The Alleghany District is distinguished from the Mother Lode districts farther south by its much higher grade ores and ?pockety? distribution of ore bodies . While the district's total production is unknown, it was estimated at approximately $50 million by Clark (1970) as of the late 1960s, much of which came from extraordinarily rich ore shoots such as those in the Sixteen-to-One Mine. The district is primarily a lode-gold district, but several mines have produced from thick sections of exposed Tertiary auriferous channel gravels. Geologically, it is part of a northerly trending belt of gold mineralization that extends from Goodyear?s Bar to the Washington Mining District in Nevada County to the south. REGIONAL SETTING The northern Sierra Nevada is home to numerous lode and placer gold deposits. It includes the famous lode districts of Alleghany, Johnsville, Sierra City, Grass Valley, and Nevada City and the famous placer districts of La Porte, North Columbia, Cherokee, Michigan Bluff, Forest Hill, and Dutch Flat. The geological and historical diversity of most of these deposits and specific mine operations are covered in numerous publications produced over the years by the U.S. Bureau of Mines, U.S. Geological Survey, California Division of Mines and Geology (now California Geological Survey), and others. The most recent geologic mapping covering the area is the 1:250,000-scale Chico Quadrangle compiled by Saucedo and Wagner (1992). Large-scale mapping of the district is presented in Ferguson and Gannett (1932). Stratigraphy The northern Sierra Nevada basement complex has a history of both oceanic and continental margin tectonics recorded in sequences of oceanic, near-continental, and continental volcanism and sedimentation that have been divided into four lithotectonic belts; the Western Belt, Central Belt, Feather River Peridotite Belt, and Eastern Belt (Day and others, 1988). The Western Belt is composed of the Smartville Complex, a late Jurassic volcanic arc complex (Beard and Day, 1987), consisting of basaltic to intermediate pillow flows overlain by pyroclastic and volcaniclastic rock units with diabase, metagabbro, and gabbro-diorite intrusives. The Cretaceous Great Valley sequence overlies the belt to the west, and to the east it is bounded by the Big Bend-Wolf Creek Fault Zone. East of the Big Bend-Wolf Creek Fault Zone is the Central Belt, which is in turn bounded to the east by the Goodyears Creek Fault. This belt is structurally and stratigraphically complex and consists of metasedimentary, metavolcanic, and plutonic rocks of Paleozoic to Mesozoic age, including a sliver of Calaveras Complex on its east side. The Feather River Peridotite Belt separates the Central Belt from the rocks of the Eastern Belt for almost 95 miles along the northern Sierra Nevada (Day and others, 1988). Its eastern margin coincides with the Melones Fault Zone of Clark (1960). The Alleghany District lies along the eastern margin of this belt, within the Melones Fault Zone where bedrock consists of north-northwesterly trending beds of Paleozoic-Mesozoic metamorphic rocks, serpentinite, greenstone and granitic intrusives. Near Alleghany, the Paleozoic-Mesozoic complex historically has been divided into six units: Blue Canyon Slate, Tightner member (chiefly chlorite schist and amphibolite), Kanaka member (conglomerate, chert, and slate), Relief Quartzite, Cape Horn Slate, and the Delhi member (phyllite and slate). These units have been widely intruded by many gabbro, peridotite, and dunite intrusives, the majority of the ultramafic intrusives having been almost completely serpentinized.
  • The Eastern Belt, or "Northern Sierra Terrane," is composed primarily of Devonian-to-Jurassic metavolcanic rocks, siliciclastic metasedimentary rocks of the Lower Paleozoic Shoo Fly Complex, and Mesozoic granitic rocks of the Sierra Nevada batholith. The Upper Devonian-Jurassic rocks unconformably overly the Shoo Fly Complex and are of island-arc origin (Brooks, 2000). They consist of the Devonian-Permian Taylorsville Sequence, Permian-Triassic Arlington, Goodhue, and Reeves Formations, and the Jurassic Sailor Canyon Formation. Regionally, the northern Sierra Nevada experienced a long period of Cretaceous to early Tertiary erosion, after which it underwent extensive Oligocene to Pliocene volcanism. The oldest Tertiary units are basal Eocene auriferous gravels, preserved in basement paleochannels, and associated bench gravels deposited by the predecessors of the modern Yuba and American Rivers. In contrast to the earlier volcanism, Tertiary volcanism was continental and deposited on top of the eroded metamorphic rocks, channel deposits, and Mesozoic intrusives. An important widespread unit of intercalated rhyolite tuffs and intervolcanic channel gravels is the Oligocene-Miocene Valley Springs Formation. The youngest volcanic unit, the Miocene-Pliocene Mehrten Formation, consists largely of andesitic flows and breccias overlying the Valley Springs Formation. Pliocene-Pleistocene westward uplift of the Sierra Nevada caused existing drainages to carve deep river gorges. During this process, the modern rivers became charged with placer gold deposits from both newly eroded basement rocks and from the reconcentration of the Eocene placers. The discovery of these modern Quaternary placers in the American River is what sparked the California Gold Rush. Structure Most Upper Jurassic and older basement rocks of the northern Sierra Nevada were metamorphosed and deformed during the Jurassic-Cretaceous Nevadan Orogeny. Deformation features in the lithotectonic blocks of the northern Sierra Nevada are best developed in the Eastern, Central, and Feather River Peridotite Belts, where they have been collectively described as the "Foothills Fault System" (Clark, 1960). Compressive deformation produced northwesterly trending faults, folds, and regional greenschist facies metamorphism (Harwood, 1988). Many of the intrusive granitic plutons of the Sierra Nevada were also part of this compressive episode. Most of the dominant faults dip steeply east and display reverse displacement. Regionally, the metamorphic rocks display northerly trending and steeply dipping foliation, bedding, and contacts. The Alleghany fracture system, in which most of the district's ore bodies occur, is thought to be both the result of regional compression as well as more local compression associated with the many nearby intrusives. Much of the reverse faulting followed weaknesses along internal contacts and foliation in the metasedimentary and metavolcanic rocks and along serpentinite contacts in which later hydrothermal fluids deposited quartz and gold (Burke, 1997). Gold-Quartz Veins The primary gold-quartz veins of the Alleghany District consist of a series of Upper Jurassic-Lower Cretaceous quartz veins in north-northwest-trending en-echelon, easterly dipping reverse faults Secondary veins of similar strike fill steep westerly dipping reverse faults that commonly displace the easterly dipping veins. The easterly dipping fault planes are generally flatter, more persistent, and have been the most productive. However, in some mines north of the Sixteen-to-One Mine, a few west-dipping veins have been producers.
  • Within the district, veins occur mostly in amphibolite and schist, but also cut slate, quartzite, and chert within the members of the metamorphic complex. The largest number of mines are in schist and amphibolite of the Tightner unit. Regionally, veins are present in all pre-Tertiary rocks. While veins commonly come in contact with serpentinite bodies, they seldom penetrate it. Where fissures extend into a serpentinite body, the veins fray into small stringers that grade into a replacement mixture of carbonate (chiefly ankerite) and mariposite. Alleghany District ore bodies are characterized by extreme richness, erratic distribution, and small size. Ore shoots occur within generally barren white quartz veins that ordinarily are 2-5 feet wide, although swellings to 50 feet are not uncommon (Clark and Fuller, 1968). The gold occurs as coarse free gold as well as with arsenopyrite and pyrite. Unlike most Mother Lode districts and the neighboring Downieville area to the north, few other sulfides are present in any appreciable quantity. Ore shoots range from small masses of gold and quartz yielding a few hundred dollars to ore bodies yielding many hundreds of thousands of dollars. One ore shoot in the Sixteen-to-One mine, with a length of only 40 feet, contained nearly $1 million ($20/troy ounce), while another in the Oriental Mine, measuring only 14 feet long, yielded $736,000 (Clark, 1970; Ferguson and Gannett, 1932). Irregularities in the veins, such as vein junctions, bends, twists, changes in strike or dip, and sheared or fractured portions of the veins, are favorable locations for high-grade ore shoots. The numerous masses of serpentinite and associated mariposite are also important in localization of the ore bodies (Clark and Fuller, 1968). Approximately 80% of the district's production has come from portions of the veins where serpentinite either formed one wall or was less than 100 feet from the ore (Ferguson and Gannett, 1932). Veins tend to fray or deflect around and approach parallelism with serpentinite contacts. These frayed or bent portions of the veins are often the sites for high-grade ore shoots and have contributed to much of the district's production. Smaller serpentinite dikes appear to have also had some influence on localization of high-grade ore (Carlson and Clark, 1956). Alleghany District veins are locally characterized by ribbon structure, which is characterized by bands of quartz interlayerd with thin sheets of country rock or other material. Carbonate material predominates in these sheets, but micas and sulfides also occur (Carlson and Clark, 1956). Some of the ribbons are straight and some are irregular ("crinkly banding"). Ferguson and Gannett (1932) attributed ribbon structures to accretion, where later fracturing of the quartz vein was followed by deposition of still later minerals along the closely spaced fracture planes. McKinstry and Ohle (1949), however, attributed ribboning to be entirely the result of replacement. Cooke (1947) concluded that both accretion and replacement were responsible for the ribbon structures in the Sixteen-to-One Mine. Alteration and Mineralization in the Alleghany Mining District Understanding of the hydrothermal alteration and mineralization at the Sixteen-to-One Mine is complicated because of their episodic nature as well as the different mineralogic responses of the diverse wall rock to these episodes. Ferguson and Gannett (1932) concluded that the rocks in the Alleghany District had undergone four main stages of mineralization. From oldest to youngest, they termed these stages the 1) chlorite, 2) quartz, 3) carbonate, and 4) final.
  • The first stage involved regional chloritization of the hornblende within the altered schists and gabbros and partial serpentinization of the intrusive ultramafic rocks. This stage largely involved recrystallization of existing wall rock minerals without the introduction of significant new minerals species. In the second, or ?quartz? stage, hydrothermal fluids rich in carbon dioxide and arsenic began to alter wall-rock schist, amphibolite, and serpentinite by sulfidization and carbonatization. Filling of the faults and fractures with vein quartz was accompanied by sulfidization of the veins and wall rock (Wittkopp, 1983), with arsenopyrite and pyrite being the primary sulfides. Pyrite was formed in the veins and wall rock, but reacted with the nickel in the magnesium silicates in the serpentinites to form pentlandite (Wittkopp, 1983). Arsenopyrite, which formed the nucleus for the later replacement by gold, and pyrite were deposited in the fissures and veins, both slightly earlier than and contemporaneous with the quartz. Most of the silica forming the quartz veins has been attributed to leaching from the wall rocks themselves (Cooke, 1947; Coveney, 1981). Whole rock chemical analyses of altered and unaltered wall rock from the neighboring Oriental Mine indicated that enough silica to source the veins had been leached from the walls by hydrothermal alteration (Coveney, 1981). With time, the veins solidified and the faults in which the veins formed became temporarily inactive. The third stage involved extensive carbonate alteration of the wall rock. Where carbonatized, all wall rocks display enhanced carbonate mineralization and depleted silica values compared to their fresh counterparts (Coveney, 1981). Serpentinite, amphibolite, and schist wall rocks all display carbonate alteration zones up to 10 feet thick surrounding most of the veins. Wall rocks reacted with carbon dioxide-rich fluids producing carbonate (chiefly ankerite) and the minerals sericite and chromium-mica. That the vein-forming solutions were rich in carbon dioxide is indicated by the presence of free liquid carbon dioxide and carbon dioxide-rich fluid inclusions in the quartz. Carbonatization along serpentinite contacts resulted in the formation of massive bodies of bright green mariposite rock (known locally as ?blue jay?) and the release of additional silica. Bohlke and Kistler (1986) demonstrated that the mariposite formed along the Melones Fault Zone in early Cretaceous time between 108 and 127 Ma. At the same time, the older quartz veins were selectively fractured in those areas of the veins most susceptible to stress fracturing by intermittent tectonic activity. Brecciation and rehealing of veins in the Oriental Mine suggests that some fault movement was contemporaneous with vein emplacement (Coveney, 1981). Most of this fracturing occurred on a microfracturing scale and was concentrated at vein junctions, bends, changes in strike or dip, and vein deflections associated with serpentinite bodies. The main stretches of the veins that have uniform dip or lenses of extraordinarily thick quartz were not preferentially fractured.
  • Into these locally fractured veins, the hydrothermal fluids introduced the gold and other constituents. Gold was deposited in the microfractures and as replacement of non-quartz minerals. In many mines, the gold is closely associated with arsenopyrite where it occurs as fracture fillings, inclusions in, or replacements of arsenopyrite. While most investigators agree that the carbon dioxide was derived at depth, the origin of the gold remains unknown. Fluid-inclusion and sulfide geothermometry investigations conducted by Coveney (1981) on principal quartz veins in the neighboring Oriental Mine indicate gold deposition occurred late during the end stages of mineralization at temperatures between 200 and 300? C and at depths exceeding 2.5 km (Coveney, 1981). Fluid inclusions from quartz within ore shoots indicate slightly lower average filling temperatures than elsewhere in the veins. This supports the interpretation that the ore-shoot material was deposited at lower temperatures during a declining temperature regime in the later stages of mineralization. Furthermore, Ferguson and Gannett (1932) reported the local presence of opal and chalcedony in the quartz veins at the Sixteen-to-One, which suggests epithermal conditions at some point in development of the veins. Wittkopp (1979) reported the presence of mercury within gold at several mines in the Alleghany District. The final stage of alteration intrepreted by Ferguson and Gannett (1932) involved the deposition of minor amounts of calcite, pyrite, and marcasite as small veinlets or as coatings on drusy quartz. In contrast to the general history of hydrothermal alteration in the district as interpreted by Ferguson and Gannett (1932), Cooke (1947) interpreted the main development of the Sixteen-to-One quartz veins (silicification) to have occurred after the period of carbonatization of the wall rocks. His sequence of alteration of the wall rock at the mine was: chlorite>carbonate>sericite>quartz. At the nearby Oriental Mine, Coveney (1981) was uncertain as to the relative timing of the hydrothermal alteration of the wall rock versus deposition of the quartz veins; his observation that quartz veinlets crosscut the alteration envelopes in the wall rock suggested that deposition of the quartz veins at the Oriental postdated the hydrothermal alteration. Another possibility is that these veinlets are from a different episode than that of the main quartz veins. Metallogeny The northern Sierra Nevada harbors many individual mining districts, each known for important deposits of lode and/or placer gold. Lode gold occurs primarily as native-gold ore shoots within hydrothermal quartz veins and, to a lesser degree, in low-grade altered wall rocks. Most significant exposed deposits have probably been discovered given the intense scrutiny the area was subjected to during the later half of the 19th century. However, there are undoubtedly undiscovered deposits in the region. Deposits might exist where the veins do not crop out or where surface exposures do not reflect mineralized ore shoots at depth. Zones of barren quartz commonly separate known ore shoots within veins. More likely to be discovered would be deposits concealed under the extensive covers of Tertiary volcanic rocks and Quaternary alluvium and glacial debris. GEOLOGY OF THE SIXTEEN-TO-ONE MINE Sixteen-to-One Vein The main Sixteen-to-One vein occupies an easterly dipping reverse fault that cuts both the Tightner and Kanaka metamorphic units. The mine's underground workings have developed the vein for approximately 4,000 feet along strike and to a maximum down-dip depth of 3,000 feet. Throughout most of its development along strike, the outcrop of the vein is largely concealed beneath the Miocene-Pliocene andesitic volcanic rocks that cap Pliocene Ridge.
  • Most of the mine's workings are within amphibolite or chlorite and hornblende schists of the Tightner unit with the remainder in the conglomerate, chert, and shale of the Kanaka unit (Burke, 1997). The Tightner unit forms the hanging wall throughout the mine. The footwall is comprised of both Tightner and Kanaka rocks, the Kanaka unit being present only in the footwall above the 250 foot level in the southern half of the mine. The Tightner unit near the vein is thought to be largely of sedimentary origin. A fine banding of hydrothermal minerals follows foliation developed along bedding, and abundant graphite (3.0%) also implies a sedimentary origin (Cooke, 1947). Two large serpentinite bodies within the Tightner unit are cut by the fault and display variable offset along the fault's strike. Dip displacement ranges from less than 300 feet at the south end of the mine to a maximum of 900 feet in the vicinity of the Tightner shaft in the north part of the mine. Offset then decreases to less than 500 feet near the mine's northernmost limits. While the regional strike of the vein is generally northwest, it displays varying strike and dip within the developed portions of the mine. In the southern part of the mine the vein strikes N 30? W. Farther north, in the Tightner workings, the strike becomes more northerly for about 1,000 feet before resuming a northwesterly strike. The dip also varies greatly from less than 20? to 60?, but throughout the most productive part of the mine, dip averages 25-30? east. The dip steepens to 35? in the northern limits of the mine and to 40? in workings below the 1,500- foot level. Steep dips of 40-60? also occur in the shallow workings above the No. 2 tunnel (100-foot level) in the southern part of the mine (Ferguson and Gannett, 1932) Near both the northern and southern limits of the mine, the Sixteen-to-One vein tends to split up into smaller veins and stringers, some of which abruptly pinch out. The Ophir vein, one of the larger offshoots, branches off to the southeast from the Sixteen-to-One vein just south of the Sixteen-to-One shaft in the southern half of the mine. Where it occurs in the workings north of this shaft it appears as a stringer in the hanging wall of the Sixteen-to-One vein. The K vein, which branches off near the 2,600 level in the far south end of the mine, branches into the footwall of the Sixteen-to-One vein. The east-dipping Sixteen-to-One vein is cut by two distinct groups of northwesterly striking and steep westerly dipping reverse faults. The two groups of faults occur at approximately the borders of an area of relatively flat dip on the main vein. Ferguson and Gannett (1932) suggested that this change in dip may have been a factor in determining their position. The upper "Tightner fault zone", strikes N 24? W and cuts the vein in the shallow workings above the 300-foot level. The number of faults varies along strike in the different areas of the mine due to displacement in some areas along a single fault and in others divided among a group of faults (Ferguson and Gannett, 1932). Displacement reaches a maximum of 135 feet near the Tightner shaft and decreases to both the north and south. The lower "2,100 fault zone" cuts the vein between the 1,800- and 2,100-foot levels. At least three faults comprise this zone and display a cumulative displacement of 250 feet.
  • The Sixteen-to-One vein averages 2-5 feet thick, but local thickenings are common. Three areas have been encountered where lenticular developments of quartz are many times thicker than average. These occur where the vein flattens and/or where there is a change in strike. Displacement along the fault plane in these areas produced enlarged open spaces amenable to thick quartz fillings. The largest, which extends southward down-dip from the 600 level north of the Tightner shaft thickens to as much as 50 feet. The second is located at the north end of the mine at the 250 level. The third extends down dip and to the south of the Compromise raise near the center of the mine. In each of these areas, large horses of country rock are incorporated in the thick quartz. The best ore shoots are found where the quartz vein is 5-15 feet thick, and little high-grade ore has come from these large vein swellings. Where these swellings begin to thin along strike, however, has been found to be productive (Ferguson and Gannett, 1932). Ore Shoots The high-grade ore shoots of the Sixteen-to-One vein were the richest in the district. Several hundred shoots have been mined, producing up to 78,000 oz each. The gold is distributed in small pockets and shoots distributed throughout vein quartz that is mostly barren. Vein quartz peripheral to the ore shoots generally assays $5 or less per ton (Carlson and Clark, 1956), grading to vein quartz outside the shoots that assays only 0.04 ounces/ton (Cooke, 1947). Mine development has revealed that the rich high-grade ore shoots are erratically distributed within the vein and occur only where conditions were favorable for localized ore deposition. As the vein cooled and solidified, these areas tended to be within the vein where discontinuities concentrated and focused stresses imposed by later tectonic activity. These stresses caused localized microfracturing, shearing, or brecciation of the quartz prior to gold mineralization. The fractures provided the necessary conduits for late-stage hydrothermal fluids as well as sites for gold deposition. Foremost among these sites are changes in strike or dip associated with serpentinite bodies, changes in vein thickness, vein branchings or intersections, fault intersections, and general changes in the vein's strike or dip. Also, deformed lamellar quartz with abundant micro-inclusions (termed ?live? quartz by miners) was considered favorable for gold, while undeformed lustrous quartz with few micro-inclusions (termed ?dead?) was considered unfavorable for gold (Cooke, 1947). The presence of serpentinite bodies within the Tightner member played a major role in controlling fault plane and vein location and in turn, many of the high-grade ore shoots. Where a vein approached or contacted a serpentinite body, it was either deflected around it, the vein split, or it died out abruptly in the serpentinite. Where a vein entered the serpentinite, it soon frayed out into fine quartz stringers that are now surrounded by mariposite and last for only a few feet. Since the veins tend to twist, bend, and change strike and dip around serpentinite bodies, these areas of flexure were more susceptible to later stress fracturing. Throughout the mine, the veins are more fractured at and near serpentinite contacts, and the correlation of serpentinite bodies with nearby high-grade ore shoots is so strong that both the mere presence of serpentinite or mariposite is considered highly prospective by miners.
  • Junctions of minor branch veins with the Sixteen-to-One vein were responsible for numerous high-grade ore shoots. Ferguson and Gannett (1932) attributed the ore shoots in the upper part of the mine, just below a steepening of dip, to be related to vein intersections. Small high-grade ore shoots at the south end of the 250 and 400 levels were localized near the junction of two branches that fork to the south and crop out above the Twenty-One tunnel. The junction of the Ophir and Sixteen-to-One veins localized high-grade ore in the area just south of the Sixteen-to-One shaft. Operations during the last decade have yielded several smaller ore shoots ranging from 40-600 ounces each in the vicinity of the junction of the Sixteen-to-One and K veins in the deeper south part of the mine. The northwesterly trending cross faults were also effective in localizing gold. On the 200-foot level, north of the Sixteen- to-One shaft, rich ore shoots extended up dip to the fault, but although the quartz filling was continuous in both the main vein and the fault, the cross fault was barren. Ore shoots were generally richer near the walls than in the center of the vein. Cooke (1947) attributed this to fresher shears along the walls that were not sealed by earlier quartz. Furthermore, most occur near the footwall rather than the hanging wall. Only rarely did they extend completely across the width of the vein, but were usually confined to strands near the footwall or the hanging wall. The ore shoots also tended to form "crossings" in which ore shoots start on or near the footwall and cross the vein diagonally up dip for perhaps 50 feet or more, dying out near the hanging wall. They generally cross the vein at a very low angle and a complete crossing is seldom made. Cooke (1947) attributed this geometry to intra-vein shearing. In summary, Burke (1997) estimated that the vein itself, from initial hydrothermal alteration to gold deposition, was emplaced and mineralized between 110 and 125 million years ago in a series of events consistent with the paragenetic stages proposed for Alleghany district veins by Ferguson and Gannet (1932). Hydrothermal fluids, high in carbon dioxide, leached silica and other minerals from the surrounding schists and amphibolites. Barren quartz crystallized within the fault plane forming the main Sixteen-to-One vein. In places, up to 50 feet of quartz crystallized within large open voids along the fault plane. As the vein formed, it assimilated portions of the wall rock and in many places a ribbon structure was formed by layers of altered wall rock, ankerite, sericite, and mariposite. Movement within the Alleghany fault system and cross faulting occurred during and after the initial vein quartz was emplaced. Many of the reverse westerly dipping cross faults were also filled with vein solutions. The veins remained barren until renewed fault movement caused localized areas of the vein to be subjected to microfracturing, fracturing, and brecciation. Further hydrothermal activity introduced gold, which precipitated in the native state in open microfractures and locally replaced earlier arsenopyrite. Aresenopyrite was apparently effective, at least in part, in causing the deposition of gold and its presence has been used a gold indicator by mine operators.

Economic information

Economic information about the deposit and operations

Operation type Underground
Development status Producer
Commodity type Metallic
Deposit size Medium
Significant Yes
Discovery year 1896

Mining district

District name Alleghany District

Land status

Ownership category Private
Area name Sierra County Planning Department

Ownership information

  • Type Owner-Operator
    Owner Original Sixteen-to-One Mine, Inc.
    Home office P.O. Box 909 527 Miners St. Alleghany, CA 95910 (530) 287-3223

Comments on the workings information

  • The mine developed the Sixteen-to-One vein via two primary inclined shafts (technically winzes), the Sixteen-to-One and Tightner, and two main winzes, the 49 and 83. The Sixteen-to-One and the Tightner shafts were originally the principal means of access for the two competing Sixteen-to-One mines and Tightner mines until the Tightner was acquired by the Sixteen to-One in 1924. Both saw continued usage until 1954 when a fire obstructed access in the Tightner shaft, after which the Sixteen-to-One shaft became the main mine access. The Tightner shaft was maintained for pumping, servicing, and ventilation (Carlson and Clark, 1956). The Tightner shaft developed the northern half of the mine. The shaft is collared at the 250-foot level and then inclined to the east following the dip of the vein to the deepest level of the mine at 3,000 feet. The upper part of the shaft was driven at an angle of about 35? to only 2,100 due to limited hoist capacity. North and south drifts were driven every 100 feet to the 1,100-foot level, then every 200 feet to the 1,700-level. Limited exploratory drifts were driven at the 1,800-foot level in the hanging wall of the fault zone and within the fault zone at the 2,100-foot level. The lower part of the shaft was sunk separately and at a steeper angle of about 60?. The steeper incline was necessitated by downward offset of the Sixteen-to-One vein in the footwall of the "2,100 fault zone" and by steeper dips on the vein below the fault zone. The lower section penetrated the vein at the 2,700-level, and crosscuts were driven to the west and east to drifts on the 2,700- and 3,000-foot levels. The Sixteen-to-One shaft is a two-compartment winze used to develop the upper levels in the south half of the mine. At the 250 level, the shaft is located about 1,500 feet south of the Tightner shaft. It was driven along the vein to the northeast and obliquely to dip from the end of a 300-foot access adit at about the 100-foot level (No. 2 tunnel) to the 1,300-foot level where it connects with the Tightner shaft almost 800 feet to the north and the 49 winze 500 feet to the south. North and south drifts were driven every 100 feet with the exception of several haphazard early drifts in the shallow workings above the 300 level. The Sixteen-to-One shaft is also connected to the Tightner shaft on the 250 level and on the 800-, 1,000-, and 1,100-foot drift levels. The 250 level is connected with the Tightner tunnel, which was originally driven 1,200 feet west from Kanaka Creek canyon to replace the older Knickerbocker tunnel. The 800 level was also connected with the old Twenty-One Mine adit after acquisition of the neighboring mine. Today, the mine's main access is through the 800 level portal, which was driven approximately 1,500 feet due north from Kanaka Creek ravine to connect with the 800-level station on the 49 winze. The deeper levels in the south part of the mine are reached through the 49 winze and the 83 winze. The 49 winze follows the vein's dip from a point on the 800 level about 250 feet south of the Sixteen-to-One shaft to the 2,400 level. The winze is parallel to and 1,500 feet south of the Tightner shaft. North and south drifts occur at the 1,100, 1,300, 1,500, 1,700, 1,900, 2,050, 2,200, and 2,400 levels. All but the 2,050 and 2,200 levels connect with the Tightner shaft. During the early 1990s, development of the mine was expanded to the 2,600 level in the extreme south end of the mine with the 83 winze between the 2,000 and 2,600 levels. Much of the mining conducted in the 1990s took place in this area (Burke, 1997). This winze was driven to explore an area where the vein splits into hanging wall and footwall sections. The mine tested these levels in the Tightner shaft in the 1920s, but this area was abandoned for lack of ore bodies.
  • Workings in the shallower portions of the mine above the 500 level are somewhat haphazard having been mined by early competing operators before consolidation of those operations with the Sixteen-to-One Mine. Significant early workings include the Knickerbocker tunnel (an early Eocene placer drift tunnel in which the Sixteen-to-One vein was first discovered), the Compromise raise (driven between the 300 and 700 levels to define the property line between competing mines), the North shaft, and numerous raises in the northernmost portions of the mine. Surface facilities remain at both the original main adit of the mine (No. 2 Tunnel) and the current main adit (800 level). Operations During the mine's operation in the decades prior to its closure in 1965, exploration was conducted by drifting horizontally along strike of the vein until encountering a high grade ore shoot, then mining by raising or stoping along the shoot. Generally, drifts were run along the footwall and raises were put up about 200 feet apart on the footwall. Wherever prospective free gold was found, raises were also driven. To reduce costly mining of large volumes of barren quartz, prospective areas of veins were cut up into small blocks by means of drifts and raises so as not to miss the small elusive shoots. The blocked-out ore was then drilled and blasted in stopes. Little support and timbering was required in the mine, except where serpentinite was encountered and in stopes. Open timbered stopes utilizing stoppers were typical. Pneumatic and electric slusher scrapers and pneumatic mucking machines were used to muck the broken ore into ore chutes. Waste rock was disposed of in old stopes. Battery locomotives hauled 1-ton side dump ore cars to a skip at the level station. In developing the lower levels of the south part of the mine (prior to the later 800 level portal), ore was hoisted up the 49 winze in rail mounted skips to the 1,300-foot level, trammed northward to the Sixteen-to-One shaft, then hoisted up the shaft to the No. 2 tunnel. From there it was trammed to the mill (Carlson and Clark, 1956). The lower levels of the 49 winze were the main producing areas in the 1950 and 1960s prior to the mine shutting down. With the later addition of the 800-foot level portal, ore was no longer hauled through the Sixteen-to-One shaft. Instead it was trammed out the portal from the 800 level station on the 49 winze. With the development of the 83 winze in the 1990s, the ore was hoisted up the winze, then trammed north to the 49 winze, then trammed out the 800 level portal. While stamp mills were used in the early days, they were soon supplanted by jaw crushers and ball mills. At the mill, ore was crushed by a primary jaw crusher, wet ground in a secondary ball mill, classified by a Dorr rake classifier, and the fines concentrated on Deister tables. Gold concentrates were amalgamated and retorted. Sulfide concentrates, while not a significant part of the mines output, were shipped to a smelter (Carlson and Clark, 1956). High-grade ore, was handled separately and not processed in the mill. Instead it was often crushed in lab sized rod mills, gyratory crushers, or rolls, then amalgamated. Especially high-grade jewelry- and specimen-quality material was hand-sorted.

Comments on other economic factors

  • The Sixteen-to-One Mine is the most productive mine in the Alleghany District as well as one of California's most famous mines. The mine is noteworthy for its fabulously rich small ore pockets. A single shoot with a length of only 40 feet yielded ore worth more than $2 million (Clark and Fuller, 1968). Of the estimated $50 million produced by the district up to the 1960s, the Sixteen-to-One Mine was credited with having produced over 1 million ounces (Clark and Fuller, 1968) before it shut down in 1965. Since then, the mine has produced at least several thousand ounces from newly discovered ore shoots. Because of the spotty nature of the ore shoots and limited capital for exploration, however, establishment of any reserves has been difficult. Nonetheless, there is no indication that all high-grade ore shoots have been exhausted. Ferguson and Gannett (1932) concluded that conditions are favorable for persistence of high-grade ore at depth in the Alleghany District.

Comments on development

  • Gold mining near Alleghany commenced in 1851 when placer gold was discovered in Kanaka Creek, just downstream of Alleghany near its junction with French Ravine. The source was traced to the buried auriferous Tertiary gravels on Pliocene Ridge just west of Alleghany. When the Knickerbocker tunnel was driven just east of Alleghany between 1853-1855 to exploit these gravels, a bedrock quartz vein was discovered, but left unexplored. In the 1860s, several lode mines were opened in the Alleghany District including the Oriental and Rainbow mines, in which several high-grade ore shoots were encountered. These discoveries rekindled interest in the lode deposits, and in 1891 a partnership was formed to relocate the bedrock vein in the abandoned Knickerbocker tunnel. The partnership reopened the tunnel and located the Contract and Contract Extension claims extending north and south of the tunnel. While drifting to the north on the vein, the vein "tightened", and thus the mine was named the Tightner Mine (Clark and Fuller, 1968). In 1896, Tom Bradbury located the Sixteen-to-One claim on a quartz outcrop just south of the Contract claims. The name Sixteen-to-One was based on the current silver-to-gold exchange ratio (Clark and Fuller, 1968). This claim proved to be on the same vein being worked by the Tightner Mine on the Contract claims, which came to be known as the Sixteen-to-One vein. In 1903, H.L Johnson took over the Tightner Mine and drifted the vein southward where, in 1907, he encountered the first high-grade pocket, which yielded nearly $470,000. In 1908, he acquired the Red Star, Rainbow, and El Dorado claims and consolidated them with the Tightner Mine. In 1909, the Tightner Mine was sold to the Tightner Mines Company, which drove the Tightner tunnel to replace the old Knickerbocker tunnel and continued development of the mine. The Tightner tunnel cut the vein 400 feet below the old Knickerbocker tunnel. Between 1911 and 1918, the Tightner Mines Company produced $3 million. In 1907, Tom Bradbury drove a lower crosscut (now the No. 2 tunnel) to prospect the vein below its outcrop. Drifting to the south proved the vein was not well-developed in this direction and after depleting his funds he leased the claims to the Wilson and Van Beugle partnership. The partnership drifted to the north and encountered a high-grade pocket containing $100,000. Wilson reportedly absconded with the proceeds, and the mine was forced into receivership (Clark and Fuller, 1968). In 1911, Bradbury issued a new lease to another partnership, which incorporated as the Original Sixteen To One Mine, Inc. (the same corporate entity that currently owns the mine). The mine was deepened with new levels at 250 and 300 feet. Meanwhile, the neighboring Tightner Mines Company was developing the vein southward towards the Sixteen-to-One Mine. In 1919, it was discovered that the neighboring Twenty-One Mine to the south had been trespassing on the Sixteen-to-One claims. Litigation resulted in a judgment against the Twenty-One Mine for $93,000. As settlement, the Twenty-One Mine was sold to the Sixteen-to-One for $60,000 (Clark and Fuller, 1968). The Twenty-One tunnel ultimately became part of the 800-foot level of the Sixteen-to-One Mine.
  • In the same year, the Tightner Mines Company optioned the Tightner Mine to the Alleghany Mining Company, which developed the vein to the 1,000-foot level. After taking $600,000 from the Sixteen-to-One vein, the Alleghany Mining Company and the Sixteen-to-One agreed to establish a definitive boundary between their competing claims. The Sixteen-to-One drove the Compromise raise along their side of the line between the 300- and 700-foot levels. It later proved that almost all the high-grade ore lay to the south of the Compromise raise in the Sixteen-to-One Mine. In1924, the Sixteen-to-One purchased Alleghany's option and incorporated the Tightner Mine into the Sixteen-to-One. The Tightner Mining Company retained the adjoining Red Star claim to the north (Clark and Fuller, 1968). During the 1920s, the Sixteen-to-One also acquired several more competing claims and mines including the Ophir and Eclipse properties. After acquisition of the Tightner Mine, the main development work was conducted through the Tightner shaft, but by 1925 the Sixteen-to-One shaft had also been deepened to the 1,300-foot level to develop the deeper ore bodies to the south. Several rich ore bodies were discovered in the Sixteen-to-One Mine during the 1920s and 1930s. One ore shoot yielded $2 million, another more than $1 million, and several produced more than $200,000. In 1924, an 80-pound piece of quartz produced $5,000, and in 1928, a 160-pound piece of ore yielded $28,000. Another pocket encountered in the mid-1930s yielded $750,000 (Clark and Fuller, 1968). . During the Depression years of the 1930s, low costs and an increase in the price of gold from $20.67 to $35.00 per ounce created a time of prosperity for the mine. The Sixteen-to-One Mine operated continuously during those years, with a payroll of between 85-100 men. By the end of the decade, the mine had paid out dividends totaling $4,437,000 (Clark and Fuller, 1968). During World War II, War Production Board Order 208 curtailed activity. The mine was allowed to continue operations on a limited basis and was only allowed to mill 200 tons every 6 months. During this time, the Sixteen-to-One continued its expansion, acquiring the Rainbow, South Fork, and Bald Mountain Mines (Clark and Fuller, 1968). After the war, operations resumed with an average payroll of 45 men. Alleghany became the only town in California after the war in which gold mining was the main industry. During the 1950s, the mine continued its expansion, acquiring the Rainbow Extension, Fraction, and Sixteen-to-One Extension claims as well as the Tightner Mines Company's Red Star Mine. In 1954, a fire on the 250 level near the Tightner shaft collar caused sufficient damage that the shaft was relegated to a service shaft and the Sixteen-to-One shaft became the main working shaft for the mine. After the war, and into the 1950s and early 1960s, the areas below the 1,700-foot level on the 49 winze were the main producing areas of the mine. The lowest level worked after the war was the 2,400 level (until the later 83 winze), the lower levels having been flooded.
  • By 1963, the Alleghany District's annual production had declined from over $500,000 to $100,000 as more and more mines closed. Rising costs, depletion of high-grade areas of the mine, and disappointing exploration efforts resulted in the curtailment of normal operations at the Sixteen-to-One Mine in 1962. By that time, costs had escalated to $50 to produce an ounce of gold worth only $35.00. In an effort to stay operational, the company resorted to auctioning its world-class specimen collection in 1965 for only $24,000. In the same year, the mine equipment and buildings were also auctioned off and by the end of the year, the Sixteen-To-One Mine was completely shut down despite remaining ore in underground dumps, pillars, and in unexplored areas. This ended the major period of operations at the mine, during which $5,750,000 in dividends were paid making it one of the most profitable gold mines in California history (Clark and Fuller, 1968). Interest in the mine waned until the mid-1970s when escalating gold prices rekindled exploration of many Sierra Nevada gold mines. In 1976, the Original Sixteen-to-One Mine, Inc. leased the mine to an unrelated Nevada corporation, called the Sixteen to One Mining Company. Over the next few years the mine was briefly operated on a limited basis. In 1977, a proxy fight resulted in the installation of new management within the Original Sixteen-to-One Mine, Inc., which remains in place today. In 1983, the properties consisted of 550 acres, and the mine was leased to the Last Chance Mining Corporation. In 1985, this company formed the Kanaka Creek Joint Venture (KCJV) with Transwestern Mining Company to operate the mine. By 1987, Royal Gold Corp. had replaced Transwestern Mining in the venture, and the KCJV had spent over $6 million to dewater the mine, rehabilitate the mill, install new hoists and develop new reserves. The mill began processing ore in December, 1987. The KCJV concentrated their efforts on the 1,500-, 1,700-, and 2,200-foot levels of the mine in the search for rich ore shoots. Additionally, the venture experimented with mining old pillars. One test run of visibly barren pillar material yielded 200 ounces of gold when processed in the mill. When the current management of the mine took over direct operations in the early 1990s, operations were curtailed from milling lower grade ores and confined primarily to the location and exploitation of high-grade specimen- and jewelry-quality material. In addition to normal drifting, hand-held metal detectors were introduced in 1992 to exploit old muck piles in former paying stopes and search the mine walls for shallow hidden ore shoots (Burke, 1997). Presently, the ore is separated by hand, with specimen gold being sold to collectors at a premium. Jewelry-quality material is sold to jewelers as well as incorporated into jewelry designs offered by the company itself. The remaining ore-grade material is processed at the mine and poured into ingots. During the last decade, the southern portion of the mine mine was expanded down to the 2,600-foot level off the 83 winze. Even though the mine reached the 3,000-foot level off the Tightner shaft in the late 1920s, there was no evidence of significant gold in that part of the vein. However, in the vicinity of the 83 winze between the 2,400 and 2,600 levels, the Sixteen-to-One vein was found to split horizontally, the hanging wall vein being the Sixteen-to-One vein and the footwall vein being designated the K vein. By the late 1990s, mining was concentrated near the 2,400 level south of the 83 winze. The discovery of a 600-ounce ore shoot on the 2,200 level of the K vein indicated the area of the vein split might be prospective (Burke, 1997).
  • During the 1990s, the mine also experienced several brief periods of prosperity, but true to the nature of Alleghany District pocket mines, it was a period of intermittent feast or famine. In August, 1993, a 13-pound specimen containing 140 ounces of gold was recovered from the 2203 stope. This specimen, dubbed "The Whopper," is maintained by the company as its flagship specimen in its collection of high-grade and crystallized gold specimens. On December 17, 1993, 2,600 ounces of gold were recovered from 890 pounds of ore from a small shoot on the 1,300 level. This discovery became known as the "million dollar day" in the company annals. In July, 1995, another shoot yielded 5,000 ounces of gold. This single pocket produced more than the average annual gold production for the previous 3 years. As of December, 2002, the Sixteen-to-One Mine has been in a period of famine for several years since no significant ore shoots have been recently discovered. As a result, it has fallen on a period of difficult financial times. Similar to the case in 1965, the company has again announced that it intends to liquidate its large specimen collection in order to continue operations.

Reference information

Bibliographic references

  • Deposit

    Averill, C. V., 1942, Mines and minerals resources of Sierra County: California Journal of Mines and Geology, v. 38, no. 1, p. 17-48.

  • Deposit

    Beard, J. S. and Day, H. W., 1987, The Smartville intrusive complex, Sierra Nevada, California: The core of a rifted volcanic arc: Geological Society of America Bulletin, v. 99, no. 6, p. 779-791.

  • Deposit

    Bohlke, J.K., 1989, Comparison of metasomatic reactions between a common CO2-rich vein fluid and diverse wall rocks: Intensive variables, mass transfers, and Au mineralization at Alleghany, California: Economic Geology, v. 84, p. 291-327.

  • Deposit

    Bohlke, J. K. and Kistler, R. W., 1986, Rb-Sr, K-Ar, and stable isotope evidence for the ages and sources of fluid components in gold-quartz veins of the northern Sierra Nevada foothills metamorphic belt, California: Economic Geology, v. 81, p. 296-322.

  • Deposit

    Carlson, D. W., and Clark, W. B., 1956, Lode gold mines of the Alleghany-Downieville area, Sierra County, California: California Journal of Mines and Geology, v. 52, no. 3, p. 237-272.

  • Deposit

    Clark, L. D., 1960, Foothills fault system, western Sierra Nevada, California: Geological Society of America Bulletin, v. 71, p. 483-496.

  • Deposit

    Clark, W. B., 1966, Gold in Mineral resources of California: California Division of Mines and Geology Bulletin 191, p. 179-185.

  • Deposit

    Clark, W. B., 1970, Gold districts of California: California Divisions of Mines and Geology Bulletin 193, p. 49-50.

  • Deposit

    Clark, W. B., and Fuller, W. P., Jr., 1968, The Original Sixteen to One Mine: California Division of Mines and Geology Mineral Information Service, v. 21, no. 5, p. 71-75.

  • Deposit

    Cooke, H. R., Jr., 1947, The Original Sixteen-to-One gold quartz vein, Alleghany, California: Economic Geology, v. 42, no. 3, p. 211-250.

  • Deposit

    Coveney, R. M., Jr., 1981, Gold quartz veins and auriferous granite at the Oriental Mine, Alleghany, California: Economic Geology, v. 76, no. 8, p. 2176-2199.

  • Deposit

    Day, H. W. and others, 1988, Metamorphism and tectonics of the northern Sierra Nevada, in Ernst, W. G., editor, Metamorphism and crustal evolution of the western United States (Rubey Volume VII): Prentice-Hall, Englewood Cliffs, New Jersey, p. 738-759.

  • Deposit

    Ferguson, H. G., and Gannett, R. W., 1932, Gold-quartz veins of the Alleghany district, California: U. S. Geological Survey Professional Paper 172, 139 p.

  • Deposit

    Harwood, D.S., 1988, Tectonism and metamorphism in the northern Sierra Terrane, northern California, in Ernst, W. G., editor, Metamorphism and crustal evolution of the western United States (Rubey Volume VII): Prentice-Hall, Englewood Cliffs, New Jersey, p. 764-788.

  • Deposit

    Lindgren, W., 1895, Characteristic features of California gold quartz veins: Geological Society of America Bulletin, v. 6, p. 221-240.

  • Deposit

    Logan, C.A., 1929, Sierra County: California Division of Mines 25th Annual Report of the State Mineralogist, p. 171-172.

  • Deposit

    Marshall, B. and Taylor, B.E., 1981, Origin of hydrothermal fluids responsible for gold deposition, Alleghany district, Sierra Nevada, California: U.S. Geological Survey Open-File Report 81-355, p. 280-293.

  • Deposit

    McKinstry, H. E., and Ohle, E. L., 1949, Ribbon structure in gold quartz veins: Economic Geology, v. 44, no. 2, p. 87-109.

  • Deposit

    Saucedo, G. J. and Wagner, D. L., 1992, Geologic map of the Chico Quadrangle: California Division of Mines and Geology Regional Geologic Map Series Map No. 7A, scale 1:250,000.

  • Deposit

    Weir, R. H. and Kerrick, D. M., 1987, Mineralogic, fluid inclusions, and stable isotope studies of several gold mines in the Mother Lode, Tuolumne and Mariposa Counties, California: Economic Geology, v. 82, p. 328-344.

  • Deposit

    Wittkopp, R. W., 1979, Mercury-bearing metallic gold, Alleghany District, Sierra County, California: California Geology, v. 32, no. 1, p. 20-21.

  • Deposit

    Wittkopp, R. W., 1983, Hypothesis for the localization of gold in quartz veins, Alleghany District, Sierra County, California: California Geology, v. 36, no. 6.

  • Deposit

    Burke, J., 1997, Geology and current mining at the Original Sixteen-to-One Mine, Alleghany, California: Unpublished report, 11 p.

General comments

Subject category Comment text
Deposit The Sixteen-to-One Mine is the most prolific and famous mine in the Alleghany District. Known for its remarkable specimen-quality pockets of native gold, the mine has been in nearly continuous operation since its discovery in 1896, with only minor hiatuses. While a marginal producer today, the "pockety" nature of its ore bodies has resulted in several noteworthy discoveries in recent years including the "million dollar day" when, on December 17, 1993, 2,600 ounces of gold were taken from a single small pocket. The gold deposits occur in fissure-filling hydrothermal quartz veins that cut amphibolite, chlorite schist, metaconglomerate, and, to a minor extent, serpentinite. The non-serpentinite rocks were originally mapped as the Tightner and Kanaka formations of the Calaveras group, thought to be Carboniferous to Permian in age (Ferguson and Gannett, 1932; Carlson and Clark, 1956). More recently, Saucedo and Wagner (1992) have placed these metamorphic rocks in a category (PzMz) of uncertain age (Paleozoic-Mesozoic) associated with the Feather River Peridotite Belt. The main vein is the Sixteen-to-One, which occupies an easterly dipping reverse fault within the Alleghany fracture system of the Melones Fault Zone. The vein is typically milky white quartz. Gold occurs as erratic, but extremely rich ore shoots and pockets hydrothermally introduced into an earlier barren quartz vein during the later stages of mineralization. Sulfides are generally minor in volume, but consist of several types including: pyrite, arsenopyrite, sphalerite, chalcopyrite, tetrahedrite, and galena, among others. Ore shoots are localized by discontinuities in the vein where fracturing and shearing provided conduits and sites for later gold mineralization. These discontinuities include vein deflections near serpentinite bodies, intersections of veins or faults, and changes in strike and dip. During the late Jurassic Nevadan Orogeny, much of the Sierra Nevada was metamorphosed and folded into a complex series of parallel northwest-trending folds and reverse fault complexes, the most famous being the Melones Fault Zone. The Melones Fault Zone forms the eastern boundary of the Feather River Peridotite Belt, upon which the Sixteen-to-One Mine is located. After this upheaval, low-sulfide, native-gold-bearing hydrothermal veins were emplaced throughout much of the western Sierra Nevada; Bohlke and Kistler (1986) concluded that this period of mineralization took place about 140 to 110 m.y. ago. Fluid inclusion and paragenetic mineral assemblage studies from the neighboring Oriental Mine indicate the main veins are mesothermal deposits formed at temperatures between 200?- 300?C and at pressures up to 2.5 kilobars (Coveney, 1981).
Environment The Sixteen-to-One Mine is located in the northern Sierra Nevada about 145 miles northeast of San Francisco between the Middle and North Forks of the Yuba River in southern Sierra County. The mine workings are on the southeast flank of Pliocene Ridge, a northeast-southwest-trending drainage divide that separates the Oregon Creek and Kanaka Creek tributaries of the Middle Fork. It is one of many northeast-southwest-trending ridges present along the western flank of the northern Sierra Nevada. Sierra County, with a total population of 3,555, is rural and sparsely populated. The community of Alleghany, which is home to some 30 families, lies immediately north of the mine. The next largest community, Downieville (pop. 350), lies seven miles to the north. Kanaka Creek drains the ravine below the mine between Pliocene Ridge and Lafayette Ridge to the south and joins the Middle Fork of the Yuba River six miles to the southwest. Topography is dominated by heavily forested and mountainous terrain punctuated by riverine canyons, which support a mixed cover of ponderosa, sugar, yellow, and red pine, red, white, and douglas fir, and western cedar. In places, barren rock and talus alternate with patches of shrubs that include manzanita, ceanothus, buckthorn, and bitter cherry. The flanks of Pliocene Ridge and Lafayette Ridge are dissected by small gullies and ravines, which support mostly ephemeral streams draining into Kanaka Creek. Relief from the crest of Pliocene Ridge to Kanaka Creek exceeds 1,700 feet. The original Sixteen-to-One Mine portal lies at an elevation of about 4,100 feet. Climate of the Alleghany area is probably somewhat similar to that at Downieville where records are available. There, summer highs typically reach the 80s and 90s F, while winter lows reach the 20s. Precipitation averages over 60 inches annually as both rain and snow. Because of its higher elevation, Alleghany probably has more snow and lower average temperatures.

Reporter information

Type Date Name Affiliation Comment
Reporter 25-MAR-2003 Downey, Cameron I. (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.