Silverado-Palisade Deposit

Past Producer in Napa county in California, United States with commodities Silver, Gold, Copper, Lead, Zinc, Antimony, Arsenic, Mercury

Sections on this page

Identification information
Geographic coordinates
Site location context
Geographic areas
Public Land Survey System information
Commodities
Materials information
Alteration
Mineral occurrence model information
Host and associated rocks
Nearby scientific data
Geologic structures
Ore body information
Controls for ore emplacement
Economic information about the deposit and operations
Mining district
Land status
Ownership information
Bibliographic references
General comments
Reporter information

Geologic information

Identification information

Deposit ID	10310677
Record type	District
Current site name	Silverado-Palisade Deposit

Comments on the site identification

This deposit consists of a SE-trending corridor of mineralization about one mile wide by nine miles long. The corridor includes the two producing mines of the district, Palisade and Silverado, as well as several prospects. The Palisade Mine was also known as the Grigsby, while the Silverado Mine was also known as the Calistoga and Mount St. Helena.

Geographic coordinates

Geographic coordinates:	-122.58138, 38.61959 (WGS84)
Elevation	195
Location accuracy	100(meters)
Relative position	The Palisade Mine is about 2.5 miles directly north of Calistoga. The Silverado Mine is about 5 miles north-northwest of Calistoga.

Site location context

Political divisions (FIPS codes)

Napa(county)

California(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Calistoga(quadrangle 1:24,000 scale)

Healdsburg(quadrangle 1:100,000 scale)

Santa Rosa(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

San Pablo Bay(hydrologic unit)

San Francisco Bay(hydrologic accounting unit)

San Francisco Bay(hydrologic subregion)

California(hydrologic region)

Geographic areas

Country	State	County
United States	California	Napa

Public Land Survey System information

Meridian	Township	Range	Section	Fraction	State
Mount Diablo	009N	007W	2, 11, 24		California
Mount Diablo	009N	006W	30, 34		California

Comments on the location information

The deposit extends southeastward from Mount St. Helena along the western flank of the Howell Mountains, which here form the northeast side of Napa Valley. The location point selected for latitude and longitude is the adit symbol for the Palisade Mine as shown on the USGS Calistoga 7.5-minute quadrangle map. The Palisade Mine is accessible by paved road from Calistoga (State Highway 29) and then by a dirt road about 1.5 miles long. The Silverado Mine is accessible by paved road from Calistoga (State Highway 29) or Middletown (State Highway 29) and then by either a short hiking trail or longer gravel road.

Commodities

Commodity	Importance
Silver	Primary
Gold	Primary
Copper	Secondary
Lead	Secondary
Zinc Critical	Tertiary
Antimony Critical	Tertiary
Arsenic Critical	Tertiary
Mercury	Tertiary

Comments on the commodity information

Commodity Info: Silver is present in various sulfides, sulfosalts, and selenides. Enderlin (1993) reported an overall silver- to-gold ratio of 74:1 in the district and that gold is in the free state, although rarely macroscopic. Grains of native gold up to 100 microns in diameter are common in quartz bands (Rytuba and others, 1993). Crutchfield (1953) speculated that the gold was present within the sulfides. Hydrocarbons are present in vugs of vein material and may be late stage. The presence here of ore-grade silver, gold, and base metals in one deposit is unusual in the Coast Ranges.
Ore Materials: Argentite, pyrargyrite, polybasite, proustite, aguilarite, native gold, chalcopyrite, galena, sphalerite, arsenopyrite, pyrite, cinnabar
Gangue Materials: Quartz, chalcedony, adularia, calcite

Materials information

Materials	Type of material
Argentite	Ore
Pyrargyrite	Ore
Polybasite	Ore
Proustite	Ore
Aguilarite	Ore
Gold	Ore
Chalcopyrite	Ore
Galena	Ore
Sphalerite	Ore
Arsenopyrite	Ore
Pyrite	Ore
Cinnabar	Ore
Quartz	Gangue
Chalcedony	Gangue
Adularia	Gangue
Calcite	Gangue

Alteration

(Local) As interpreted from Enderlin (1993) and Crutchfield (1953):

Early Phase:
Propylitic; chlorite, calcite, albite, epidote

Late Phase:
Argillic (no mineral phases reported by authors)
Silicic; quartz, chalcedony, adularia

Crutchfield (1953) reported marcasite, limonite, and selenite as supergene alteration. Laizure (1929, unpublished) reported oxidized ore in the upper mine levels.

Mineral occurrence model information

Model code	104
USGS model code	25a
Deposit model name	Hot-spring Au-Ag
Mark3 model number	45

Host and associated rocks

Host or associated

Host

Rock type

Volcanic Rock (Aphanitic) > Intermediate Volcanic Rock > Andesite

Rock unit name

Sonoma Volcanics

Stratigraphic age (youngest)	Pliocene
Stratigraphic age (oldest)	Miocene

Host or associated

Host

Rock type

Volcanic Rock (Aphanitic) > Felsic Volcanic Rock > Rhyolite

Rock unit name

Sonoma Volcanics

Stratigraphic age (youngest)	Pliocene
Stratigraphic age (oldest)	Miocene

Nearby scientific data

(1)	-122.58138, 38.61959	ListMap

Economic information

Geologic structures

Type of structure	Local
Structure description	Enderlin (1993) concluded that the ore bodies formed along dilational segments of NE-trending conjugate Reidel shears associated with the NW-trending right-lateral Yellowjacket fault zone. The bodies are confined to the northeast side of this zone. All appear to be less than one mile in length.
Type of structure	Regional
Structure description	Maacama Fault Zone

Ore body information

General form Tabular

General form	Tabular

Controls for ore emplacement

Ore bodies are present as a series of steeply dipping, NE-trending sulfide-bearing quartz veins orthogonal to a structure known as the Yellowjacket fault zone. Of possible significance is Enderlin?s (1993) observation that the richest ore shoots in the Palisade and Silverado mines were discovered along segments of the veins that trended more northerly rather than northeasterly.

Comments on the geologic information

INTRODUCTION

In the northern Coast Ranges, mercury, gold, and silver have been mined since the 1860s. A few of the gold deposits are known to be closely associated with mercury mines. The McLaughlin deposit represents the only known large-volume, world-class gold deposit in the Coast Ranges. McLaughlin, the Cherry Hill gold deposit, which is in the Sulphur Creek (Wilbur Springs) District 14 miles to the north, and the Silverado-Palisade silver-gold deposit, which is about 20 miles to the southwest and discussed here, originated in hot-spring environments within two large volcanic fields, the Clear Lake and Sonoma. These fields are the northernmost and most recent of a NNW-trending chain of Neogene-Holocene volcanic fields that follow and cut across a regional fold and thrust belt better known for petroleum and mercury resources than for gold and silver. The Silverado-Palisade, McLaughlin, Cherry Hill, and other hydrothermal systems within the Clear Lake and Sonoma volcanic fields formed by extensional and compressional tectonics, high heat flow, and intermediate-silicic magmatism (Griscom and others, 1993).

The McLaughlin deposit has been well studied. In contrast, the Silverado-Palisade deposit has received very little attention because of its apparently smaller size, dominance of silver over gold, and its location on the edge of the cultivated Napa Valley. The most recent summary of geologic and geochemical characteristics of the deposit is that by Enderlin (1993).

REGIONAL TECTONICS AND STRUCTURE

The northern Coast Ranges have experienced several deformational episodes (i.e., Mesozoic compression and Neogene-Holocene intermittent dextral translation, transtension and transpression, and volcanism). The resulting complicated structure of the northern Coast Ranges is defined primarily by a broad region of numerous, closely spaced, generally north-northwest-trending faults, folds, ridges, and pull-apart basins (Hearn and others, 1988; Namson and Davis, 1988). A secondary system of short (less than a quarter mile) faults trends east-west (Jennings, 1994). In the Clear Lake region, the NNW-trending structures exceed one mile in length; some represent active components of the San Andreas Fault system.

Since the Mesozoic, the development of the northern Coast Ranges has been dominated by the tectonic interaction of three major plates: the North American, Farallon, and Pacific. During this time, the Farallon Plate has been subducting beneath the North American Plate (Thorkelson and Taylor, 1989). Seafloor sediments, exotic terranes, and ophiolites that failed to subduct were accreted to the continental margin. The accreted material formed several packages of north-trending lithotectonic belts. The Coast Ranges are composed of a package of the three westernmost belts. From east to west, they are Great Valley Sequence (forearc basin sedimentary rocks), Coast Range Ophiolite, and Franciscan Complex (thick accretionary prism of sedimentary and volcanic rocks). The Coast Range Ophiolite is an assemblage of serpentinized ultramafic rocks, mafic intrusions, and submarine volcanic rocks. The ophiolite is tectonically dismembered. In some localities, it occurs as a serpentinite-matrix melange (Hopson and others, 1981). In a few areas, large lenses of sedimentary serpentinite, presumably derived from subjacent ophiolite, are interbedded with lower Cretaceous and Miocene sediments. The Franciscan Complex and Great Valley Sequence are coeval and formed on opposite sides of the subduction zone. With time, these marine deposits were progressively compressed and uplifted in a fold and thrust belt. Once uplifted, this over-thickened package may have become gravitationally unstable leading to collapse through extensional faulting (Platt, 1986).
Associated with the three main lithologic units described above are deposits of sedimentary serpentinite. Such deposits are present in the Wilbur Springs quadrangle, near the Cherry Hill deposit. There, lenses of sedimentary serpentinite are found interbedded in the upper Knoxville Formation (locally named the Stony Creek Formation) of the Great Valley Sequence. The origin of these enigmatic masses has been controversial. They may represent brecciated ophiolite, landslide deposits, or diapirs or protrusions from serpentine mud volcanoes. Recent studies of active mud volcanism in the Mariana subduction complex may provide clues to relationships in the Coast Ranges. The mud volcanoes erupt slab-derived fluids, serpentinite mud, and blocks of blueschist (Fryer, 1992; Fryer and others, 1999; Carlson, 1981a, b; 1984a, b; McLaughlin and others, 1980; Bailey and others, 1964; Phipps, 1992).

Interpretations vary regarding the process by which the fault-bounded portions of Coast Range Ophiolite came to reside between the two sedimentary units. Seismic reflection profiles reveal a stack of detached ophiolite-like slabs encased in fault-bounded wedges that underlie most of the eastern margin of the Coast Ranges. The uppermost, subsurface ophiolitic slab produces a prominent magnetic anomaly. It is shaped like an airfoil and measures about 600 km along strike, 10-20 km wide, and about 4 km deep (Griscom and others, 1993). A 3-km-deep geothermal exploration well near the Manzanita Mine in the Sulphur Creek District corroborates the seismic data. It revealed two layers of ophiolite separated by melange and overlain by Great Valley Sequence (McLaughlin and others, 1990).

Over the past decade, two structural models have been used to explain the above relationships of the ophiolite with the surrounding sedimentary units. One model suggests that imbricate thrusting produced the stack of wedges and ophiolite slabs. This process inserted Coast Range Ophiolite between the Great Valley Sequence and Franciscan Complex. The other model proposes that the ophiolite slid beneath both units, as the leading edge of the subducting slab of oceanic crust, until it locked up. Eventually the locked ophiolite broke off the oceanic slab, and subduction resumed at a lower level. The wedges are interpreted as abandoned accretionary prisms. The continued subduction drove outboard Franciscan sediments beneath the ophiolite. This process would indicate a cycle of ophiolite generation and wedge abandonment. Later extensional faulting, as mentioned above, exhumed the slab of ophiolite.

The first model requires that the bounding faults are thrusts. Conversely, the second model requires them to be normal faults. The kinematics and significance of these faults remains unresolved. Field evidence seems ambiguous and may represent a more complicated history. Tectonic blocks of blueschist, which are thought to have formed deep in the subduction zone, crop out in the Franciscan Complex. Proponents of extensional dynamics have suggested that these blocks were brought up from depth by normal faulting (Platt, 1986; Jayko and others 1987). To the south, Harms and others (1992) determined the timing of such extension in the Diablo Range to about 60-70 Ma. Conversely, Ring and Brandon (1994) suggested that exhumation could be accomplished by both out-of-sequence faulting in the upper plate and erosion. Their model negates the need for extension. Namson and Davis (1988), who conducted structural studies in the southern Coast Ranges, concluded that the Franciscan Complex was thrust eastward over itself, Coast Range Ophiolite, and lower Great Valley Sequence, which developed a series of east-dipping backthrusts that form the tectonic wedge geometry.
Regarding development of transform structures and magmatism in the northern Coast Ranges during the Cenozoic, a spreading ridge initially separated the Farallon and Pacific plates. While the Farallon Plate progressively subducted under the North American Plate, the Pacific Plate and intervening ridge approached the North America continent. The ridge system was locally offset and generally oblique to the subduction zone. Because of the geometry and motion between the plates, a proximal portion of the ridge moved into the subduction zone. At this location, subduction ceased and the North American and Pacific plates made contact. This event marked the birth of a triple junction. This contact essentially bisected the Farallon Plate into two smaller plates, the Juan de Fuca and Cocos plates. The new triple junction marked the point where the two new plates and the Pacific Plate met. However, it was short-lived. As subduction continued, the area of contact between the Pacific and North American Plates lengthened. What was a single triple junction split into two, joined by an incipient transform fault, the proto-San Andreas Fault.

With time, the transform lengthened and the triple junctions separated farther. The growth of this proto-San Andreas Fault created a gap, or window, behind the subducting slab as it descended beneath the North American Plate. This window was increasingly enlarged and represented a region on the North American Plate-side of the proto-San Andreas Fault where the process of subduction was no longer operable. The path of the northward-migrating triple junction (Mendocino Triple Junction) is delineated by the San Andreas Fault (Dickinson, 1981, 1997; Atwater, 1970, 1989). A northward-younging sequence of Neogene-Holocene volcanic fields is thought to represent the surficial expression of a progressive upwelling of asthenosphere into the enlarging slab window. In the southern Coast Ranges, the volcanic fields are located along the San Andreas proper. However, in the north, starting just south of San Francisco Bay, the San Andreas Fault splays out into three codominant active strands. The western strand, the main San Andreas Fault, extends directly to the current position of the Mendocino Triple Junction. The volcanism shifted inboard along the eastern splays of the San Andreas system, which include the Bartlett Springs and Collayomi faults. It then extended northward to its current position just north of the Clear Lake volcanic field (Thorkelson and Taylor, 1989; Dickinson, 1981, 1997; Griscom and others, 1993). Debate exists concerning the interaction of the San Andreas Fault and the triple junction and is beyond the scope of this discussion.

As the Mendocino Triple Junction and the track of volcanism migrated northward, localized transtension due to wrench faulting accompanied the strike-slip tectonics and produced a N-S string of pull-apart basins. This Neogene faulting as well as inherited Mesozoic structures controlled the locus of shallow magmatism and hydrothermal activity associated with the slab window. The most recent volcanic rocks, the Clear Lake Volcanics and Sonoma Volcanics, and their associated intrusions and hot- spring deposits, are localized within active pull-apart basins along the Collayomi and Bartlett Springs faults (Griscom and others, 1993).
In the Clear Lake area, several lines of geophysical, geochemical, and geologic evidence suggest that a NE-trending zone of extension cuts across NW-trending structures. The zone extends from the Collayomi Fault in the west to at least the Bartlett Springs Fault in the east. Farther east, NE-trending structures in the Sulphur Creek District seem to be related to the zone. The Clear Lake and Sonoma volcanics occur within and may be genetically related to this zone also (Stanley and others, 1997). Overall, the zone of extension corresponds with a NE-trending basement structure proposed by Griscom and others (1993), which trends N70E and is defined by the alignment of magnetic and gravity anomalies and the alignment of the Geysers geothermal field, the Sonoma and Clear Lake volcanics, and the Sutter Buttes volcano. The gold deposits at McLaughlin and Cherry Hill lie above the intersection of the proposed structure and the contact between Coast Range Ophiolite and Great Valley Sequence. Also, above this intersection is a possible local window in the ophiolite slab, indicated by an anomalous magnetic low. These deep structures may have been important in the development of the ore deposits (Griscom and others, 1993).

Hot Springs-Type Mineral Deposits

Several hot-springs-type mineral deposits are present within the Clear Lake and Sonoma volcanic fields. Some, including Cherry Hill, are still hydrothermally active. Hydrothermal activity at the Silverado-Palisade deposit was dated from adularia in vein material from the Silverado Mine at about 2.6 Ma and from the Palisade Mine at about 1.4 Ma (cited in Rytuba and others, 1993). Hydrothermal activity at the McLaughlin Mine persisted from about 1.0 to 0.5 Ma (Dean Enderlin, Homestake Mining Company, personal communication, 1999). Sulphur Bank Mine, at Clear Lake, is in an active vapor-dominated hydrothermal system, which continues to deposit mercury, but not precious metals. Precious-metal deposition is restricted to water-dominated hydrothermal systems, such as at Cherry Hill, where hot springs are actively depositing gold and mercury (Rytuba, 1993).

LOCAL GEOLOGY

The Silverado-Palisade deposit is hosted in the Sonoma Volcanics. This complex was deposited on a basement of disrupted oceanic deposits and serpentinite of the Franciscan Complex and sedimentary rock of the Great Valley Sequence as a series of overlapping flows and tuffs, which probably emanated from several local vents (Fox, 1983). Compositions range from silicic to mafic, but are predominantly intermediate. Volcanism occurred during the Late Miocene and Pliocene (8.9?4.5 to 2.9?0.2 Ma). The youngest unit, a welded tuff, caps Mount St. Helena (Enderlin, 1993). Intrusive rocks, including a series of 28 NE-trending dikes aligned along a northwest trend, display similar compositional variation as the flows and tuffs and have been considered to represent feeders (Fox, 1983). Post-depositional faulting has disrupted the units, which are generally poorly exposed. These characteristics, plus compositional heterogeneity and lateral discontinuity of the units, make regional correlation of the units difficult (Fox, 1983; Flexser, 1980; Crutchfield, 1953; and Enderlin, 1993).
In the Calistoga Mining District, Enderlin (1993) reported three distinct episodes of volcanism. Andesitic flows and coarse pyroclastic rocks formed thick accumulations during the first episode. Typically, the andesites are highly propylitized and poorly exposed. The second period consisted of extensive silicic volcanism. The earliest phase of this silicic volcanism consists of pumiceous and lithic-rich pyroclastic deposits, some of which appear water-lain; this basal unit buried and preserved the Petrified Fossil Forest of California, west of Calistoga, dated at 3.5 Ma by Evernden and James (1964). A pulse of more explosive silicic volcanism ensued, which distributed widespread pyroclastic deposits as well as flows and lahars. Locally, the silicic tuffs were capped by a final episode of renewed andesitic volcanism. Well-developed columnar jointing is present in andesitic flows known as the Palisades, which are adjacent to the ore deposit (Enderlin, 1993). Regarding host rock for ore bodies at the two mines in the deposit, the Silverado is in silicic rock, while the Palisade is in andesitic rock.

The Silverado-Palisade deposit is within a deformed structural entity known as the Santa Rosa block (Fox, 1983). The structural grain of the Santa Rosa block is dominantly NNW-trending with numerous right-stepping en echelon, dextral strike-slip faults and closely spaced, parallel fold belts. Within the block, the Napa Valley, which is the site of the deposit, is a graben formed by syn- and post-volcanic transtensional downwarping along Quaternary faults and folds (Enderlin, 1993). Also, within the block, the NE-trending dikes mentioned above are orthogonal to the strike-slip faults. Fox (1983) interpreted the dikes to represent conjugate Reidel shears developed during dextral shearing on the strike-slip faults; they may also represent feeders for the Sonoma Volcanics (Fox, 1983).

Physically associated with the deposit is a San Andreas-style, NW-trending dextral shear zone known as the Yellowjacket fault (Enderlin, 1993). The fault is best recognized within serpentinite exposed through erosional windows in the Sonoma Volcanics. Its presence both parallel to and adjacent to the mineralized zone suggested a genetic relationship to Enderlin (1993).

The deposit consists of a group of mostly NE-trending quartz-chalcedony-adularia veins that crop out on the northeast side of the Yellowjacket fault in a NW-trending belt about 8 miles long. From northwest to southeast, these veins are the Monitor, Easley, Palisade, Elephant, Grigsby-Knapp, Manuel, Sunnyside, and Dutch Henry (Enderlin, 1993); all are probably less than a mile in length. Anomalous to the orientation of these veins is the Linn vein, which is south of the Palisade Mine and strikes northwesterly. Ore was mined from the Monitor (Silverado Mine) and both the Easley and Palisade (Palisade Mine). The other veins have been prospected only. The Monitor vein complex trends N20-40oE and dips 65-75oNW; it is traceable for at least 2,500 feet with a maximum reported thickness of at least 25 feet (Enderlin, 1993). Both the Easley and Palisade veins strike N6oE; the former dips 63-75oNW and the latter dips 57oNW. Where mined, the Easley ranged from 4 to 24 feet thick, averaging 5 to 8 feet. Vein textures, mineralogy, and geochemistry indicate formation under epithermal conditions (see Deposit Description Comments above).

Similar to the idea of Fox (1983) about the volcanic dikes, Enderlin (1993) proposed that during dextral shear along the Yellowjacket fault, an en echelon series of NE-trending Reidel shears developed, which became conduits for the hydrothermal fluids that produced the veins discussed above. This model may also explain the northwesterly trend of the Linn vein; it may have formed in a dilational zone between right-stepping en echelon segments of the Yellowjacket fault (Enderlin, 1993).
Three main types of hydrothermal alteration are present in the deposit. These include an older phase of propylitic alteration, which broadly affects the older andesitic units, and a younger phase of more restricted argillic and silicic alteration directly associated with the vein complexes and other fractures (Enderlin, 1993; Crutchfield, 1953). Sulfide mineralization appears to be confined to veins rather than extending into wallrock. From the Palisade Mine, Crutchfield (1953) developed the following paragenetic sequence for sulfide ore minerals of the deposit: First phase - chalcopyrite, galena, sphalerite; second phase - argentite, polybasite; third phase - cinnabar. Of these sulfides, chalcopyrite is the most common. The Linn and Dutch Henry vein complexes also have sulfides; the Dutch Henry has anomalous Ag and Se values, which suggest the presence of silver selenides (Enderlin, 1993).

Economic information about the deposit and operations

Operation type	Surface-Underground
Development status	Past Producer
Commodity type	Metallic
Deposit size	Small
Significant	Yes
Discovery year	1858

Mining district

District name	Calistoga District

Land status

Ownership category	Private
Area name	Napa County Planning Department
Ownership category	State Park
Area name	Robert Louis Stevenson State Park

Ownership information

Type Owner

Owner State of California (Silverado Mine)
Type Operator

Owner Patten Family (Silverado Mine)

Year Silv

Type	Owner
Owner	State of California (Silverado Mine)

Type	Operator
Owner	Patten Family (Silverado Mine)
Year	Silv

Comments on the workings information

The deposit has been exploited at only two mines, the Palisade and Silverado, mainly by underground mining methods. of the two, the Palisade was the most extensively developed. Other known workings elsewhere in the deposit include adits and open-cuts. Except for those shown on a generalized map by Enderlin (1993), the location and extent of these workings is not published and thus not well known.

Workings at the Palisade Mine consist of a vertical main shaft and at least 7 levels that drifted along the Easley Vein; winzes and raises connected all the levels. The main shaft and the mill site, which is to the north, are separated by a NE-trending ridge. They are connected at depth by a 1400-foot-long Z-pattern tunnel (Mill Tunnel), which drifted along the Easley Vein for at least 920 feet. This tunnel was about 270 feet below outcrop, with additional workings developed between them. Averill (1929) reported that drifting from the main shaft along the shallower levels averaged 750 feet. Stoping was accomplished along all levels, with the main stope off the 160 level; this was about 700 feet long, 4 feet wide, and extended 170 feet down-dip (Enderlin, 1993). Workings reached a vertical depth of 700 feet below the Mill Tunnel, but low ore-grades discouraged further development below this depth (Crutchfield, 1953). Present condition of the workings is unknown.

Workings at the Silverado Mine consist of at least two cross-cut tunnels (possibly three), shafts, drifts, and open-cuts driven into the Monitor Ledge vein complex over a distance of at least 1,200 feet. The deepest known working is the No. 1 Tunnel, which was driven westerly about 600 feet to intersect the complex approximately 400 feet below outcrop. Many daylighted stopes and open-cuts are still accessible from the ground surface over a length of at least 500 feet. The most spectacular working is at the north end of the vein complex where it is exposed in complete cross-section.

Comments on other economic factors

Silver was by far the most important commodity produced, with lesser amounts of gold, copper, and lead. Cumulatively, this deposit reportedly produced 1.5-2.0 million ounces of silver, an estimated 12,000 to 15,000 ounces of gold, at least 65,000 lbs. of copper, and at least 768 lbs. of lead (Enderlin, 1993). The main periods of production in the district were the mid-1870s, late 1880s, late 1920s, and the 1930s (Enderlin, 1993). Most production was from the Palisade Mine. In 1902, 1,000 tons of shipped dump material reportedly assayed at $1.10/ton Au and $2.65/ton Ag (Crutchfield, 1953). Bradley (1916) reported assay values of $14-15/ton at the Silverado and $24.50/ton at the Palisade. Ore mined at the Palisade during the late 1930s was reported by Crutchfield (1953) to average $12/ton Ag and $2/ton Au.

Because of its epithermal origin, it is possible that the grade of the deposit may decline significantly with depth. Nonetheless, there is no reliable estimate of reserves in this deposit as its component vein complexes have never been systematically and comprehensively explored through sampling and drilling.

Comments on development

Enderlin (1993) reported that the deposit was discovered in the winter of 1858-1859. Both the Silverado and Palisade mines were opened in the 1870s and worked intermittently over the next several decades. The Silverado Mine was last worked in 1951. The Palisade Mine was last operated in the 1950s, but no production ensued.

Most development and production at the Palisade Mine was on the Easley Vein, with lesser development on the companion Palisade Vein. Initial development and production at the Silverado Mine took place in the 1870s on the Monitor Ledge, which was the main target of mining activity during the life of the mine. Small quantities of ore, concentrates, and dump material were periodically shipped from the mines to smelters over many decades.

Milling and processing at both mines was generally by conventional techniques. During the 1870s, ore at the Silverado Mine was processed using pan amalgamation (Washoe Process) at a 10-stamp mill reportedly about a mile south or southeast of the mine in King Canyon. Part of this mill was later moved to the Palisade Mine in the late 1880s. Here at the Palisade in the 1920s, flotation and a mercuric-cyanide process were also used. Tailings from flotation were pumped to a dammed pond near the mill. The mine was closed in 1941 and all equipment removed. During the 1950s, a 50-ton flotation plant was constructed and workings above the Mill Tunnel were explored. The mill burned in 1964.

The Silverado Mine was purchased by the State of California in about 1952-53 for inclusion within Robert Louis Stevenson State Park. Open-cuts and daylighted stopes still remain accessible along strike of the vein complex for at least 500 feet, but there are no known remaining surface facilities. Waste rock partially fills a gulch at the north end of the complex. The Palisade Mine is on private property and was not accessible to the reporter during field work in the mining district; it is probable that any remaining surface facilities are in ruins and that waste dumps are still present; extent of the latter is unknown. As both mines were abandoned many decades ago, reclamation under the State Surface Mining and Reclamation Act of 1975 is not applicable.

Comments on the environmental information

The physiographic setting of the Silverado-Palisade deposit is one of high-relief. The deposit forms a northwest-trending narrow belt of mineralization, which is restricted to the mountainous northeast side of the upper Napa Valley. At its southeast end, in Dutch Henry Canyon, the deposit is only a few hundred feet above the flat floor of the valley. From there, it climbs nearly nine miles through the Howell Mountains to the south summit peak of Mount St. Helena at an elevation of about 4,000 feet. At the Silverado Mine, the vein complex known as the Monitor Ledge stands out as a bold wall of resistant rock several hundred feet long. Vegetation along the deposit is variable depending on substrate, slope orientation, and steepness; some areas have bold outcrop, while others are cloaked in mixed oak and conifer forest. Chaparral and grass are common on south-facing slopes. The drainage pattern is mainly dendritic, with most stream courses dry in the summer. The climate is Mediterranean, with warm, dry summers and cool, wet winters. At Calistoga, precipitation averages about 38 inches per year, mostly falling as rain, although the high ridges at and southeast of Mount St. Helena receive snow on occasion. Settlement of the area is mainly residential and agricultural. The floor of Napa Valley is heavily developed, while the mountainous slopes above are sparsely developed. The city of Calistoga (population approximately 5,000) is within a few miles of the deposit. The Silverado Mine area is within a state park, while the Palisade Mine area is private property, mostly estate- and ranch-type parcels. Wine-making and tourism are the economic mainstays of the valley.

Reference information

Bibliographic references

Deposit

Atwater, T., 1970, Implications of plate tectonics for the Cenozoic tectonic evolution of western North America: Geologic Society of America Bulletin, v. 81, no. 12, p. 3513-3536.
Deposit

Atwater, T., 1989, Plate tectonic history of the northeast Pacific and western North America, in Winterer, E.L. and others, editors, The eastern Pacific Ocean and Hawaii: Geological Society of America, The Geology of North America, Vol. N, p. 21-72.
Deposit

Averill, C.V., 1929, Napa County: California Division of Mines and Mining 25th Report of the State Mineralogist, v. 25, no. 2, p. 213-242.
Deposit

Bailey, E.H. and others, 1964, Franciscan and related rocks and their significance in the geology of western California: California Division of Mines and Geology Bulletin 183, 177 p.
Deposit

Berger, B.R., 1986, Descriptive model of hot-spring Au-Ag, in Cox, D.P. and Singer, D.A., editors, Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 143-144.
Deposit

Bradley, W.W., 1916, The counties of Colusa, Glenn, Lake, Marin, Napa, Solano, Sonoma, Yolo: California State Mining Bureau 14th Report of the State Mineralogist, p. 173-370.
Deposit

Carlson, C., 1981a, Sedimentary serpentinites of the Wilbur Springs area -a possible Early Cretaceous structural and stratigraphic link between the Franciscan Complex and the Great Valley Sequence: Master's thesis, Stanford University, 105p.
Deposit

Carlson, C., 1981b, Upwardly mobile melanges, serpentinite protrusions, and transport of tectonic blocks in accretionary prisms: Geological Society of America Abstracts with Programs, v. 13, no. 2, p. 48.
Deposit

Carlson, C., 1984a, Depositional environments and sedimentary facies of foliate serpentinite breccias, Wilbur Springs, in Carlson, C., editor, Depositional facies of sedimentary serpentinite: Selected examples from the Coast Ranges, California: Society of Economic Paleontologists and Mineralogists Field Trip Guidebook No. 3, Tulsa, Oklahoma, p. 113-116.
Deposit

Carlson, C., 1984b, Stratigraphic and structural significance of foliate serpentinite breccias, Wilbur Springs, in Carlson, C., editor, Depositional facies of sedimentary serpentinite: Selected examples from the Coast Ranges, California: Society of Economic Paleontologists and Mineralogists Field Trip Guidebook No. 3, Tulsa, Oklahoma, p. 108-112.
Deposit

Chapman, R.H. and others, 1982, Gravity, structure, and geothermal resources of the Calistoga area, Napa and Sonoma counties: California Geology, v. 35, no. 8, p. 175-183.
Deposit

Crutchfield, W.H., Jr., 1953, The geology and silver mineralization of the Calistoga District, Napa County, California: University of California, Berkeley, M.A. thesis, 71 p.
Deposit

Davis, F.F., 1948, Mines and mineral resources of Napa County: California Journal of Mines and Geology, v. 44, no. 2, p. 159-188.
Deposit

Dickinson, W.R., 1981, Plate tectonics and the continental margin of California, in Ernst, W.G., editor, The geotectonic development of California (Rubey volume 1), Prentice-Hall, Englewood Cliffs, New Jersey, p. 1-28.
Deposit

Dickinson, W. R., 1997, Tectonic implications of Cenozoic volcanism in coastal California: Geological Society of America Bulletin, v. 109, p. 936-954.
Deposit

Donnelly-Nolan, J.M. and others, 1993, The Geysers-Clear Lake area, California: Thermal waters, mineralization, volcanism, and geothermal potential: Economic Geology, v. 88, p. 301-316.
Deposit

Enderlin, D.A., 1993, Epithermal precious metal deposits of the Calistoga mining district, Napa County, California, in Rytuba, J.J., editor, Active geothermal systems and gold-mercury deposits in the Sonoma-Clear Lake volcanic fields, California: Society of Economic Geologists Guidebook Series, v. 16, p. 52-76.
Deposit

Evernden, J.F. and James, G.T., 1964, Potassium-argon dates and the Tertiary floras of North America: American Journal of Science, v. 262, no. 8, p. 945-974.
Deposit

Flexser, S., 1980, Geology of a portion of the Sonoma Volcanics near Calistoga, Napa County: University of California, Berkeley, M.S. thesis, 106 p.
Deposit

Fox, K.F., Jr., 1983, Tectonic setting of Late Miocene, Pliocene, and Pleistocene rocks in part of the Coast Ranges north of San Francisco, California: U.S. Geological Survey Professional Paper 1239, 33 p.
Deposit

Fox, K.F., Jr. and others, 1973, Preliminary geologic map of eastern Sonoma County and western Napa County, California: U.S. Geological Survey Miscellaneous Field Studies Map MF-483, scale 1:62,500.
Deposit

Fryer, P., 1992, Volcanoes of the Marianas: Scientific American, v. 266, no. 2, p. 46-52.
Deposit

Fryer, P. and others, 1999, Mariana blueschist mud volcanism: Implications for conditions within the subduction zone: Geology, v. 27, p. 103-106.
Deposit

Griscom, A. and others, 1993, Regional geophysical setting of gold deposits in the Clear Lake region, California, in Rytuba, J.J., editor, Active geothermal systems and gold-mercury deposits in the Sonoma-Clear Lake volcanic fields, California: Society of Economic Geologists Guidebook Series, v. 16, p. 289-310.
Deposit

Hamilton, F., 1921, Napa County: California State Mining Bureau 17th Report of the State Mineralogist, p. 158-161.
Deposit

Harms, T.A. and others, 1992, Kinematic evidence for extensional unroofing of the Franciscan Complex along the Coast Range Fault, northern Diablo Range, California: Tectonics, v. 11, no. 2, p. 228-241.
Deposit

Hearn, B.C., Jr., and others, 1988, Tectonic framework of the Clear Lake basin, California: Geological Society of America Special Paper 214, p. 9-20.
Deposit

Hopson, C.A. and others, 1981, Coast Range ophiolite, western California, in Ernst, W.G., editor, The geotectonic development of California: Prentice-Hall, Englewood Cliffs, New Jersey, p. 418-510.
Deposit

Jayko, A.S. and others, 1987, Attenuation of the Coast Range Ophiolite by extensional faulting, and nature of the Coast Range ?Thrust?, California: Tectonics, v. 6, no. 4, p. 475-488.
Deposit

Jennings, C. W., 1994, Fault activity map of California and adjacent areas with locations and ages of recent volcanic eruptions: California Division of Mines and Geology, Geologic Data Map No. 6, scale 1:750,000.
Deposit

McLaughlin, R. J. and others, 1980, Structure of Late Mesozoic rocks in the core of the Wilbur Springs Antiform, northern Coast Ranges, California: Geological Society of America Abstracts with Programs, v. 12, no. 3 , p. 119.
Deposit

McLaughlin, R. J. and others, 1990, Geologic map and structure sections of the Little Indian Valley-Wilbur Springs geothermal area, northern Coast Ranges, California: U. S. Geological Survey Miscellaneous Investigations Series Map I-1706, scale 1:24,000.
Deposit

Namson, J.S. and Davis, T.L., 1988, Seismically active fold and thrust belt in the San Joaquin Valley, California: Geological Society of America Bulletin, v. 100, no. 2, p. 257-273.
Deposit

Nelson, C.E., 1987, Gold deposits in the hot springs environment, in Schafer, R.W. and others, editors, Bulk mineable precious metal deposits of the western United States: Symposium Proceedings of the Geological Society of Nevada, p. 417-432.
Deposit

Pearcy, E.C. and Petersen, U., 1990, Mineralogy, geochemistry and alteration of the Cherry Hill, California, hot-spring gold deposit: Journal of Geochemical Exploration, v. 36, p. 143-169.
Deposit

Peters, E.K., 1991, Gold-bearing hot spring systems of the northern Coast Ranges, California: Economic Geology, v. 86, p. 1519-1528.
Deposit

Phipps, S.P., 1992, Late Cenozoic wedging and blind thrusting beneath the Sacramento Valley and eastern Coast Ranges, in Erskine, M.C. and others, editors, Field guide to the tectonics of the boundary between the California Coast Ranges and the Great Valley of California: American Association of Petroleum Geologists, Pacific Section, p. 63-84.
Deposit

Phipps, S.P. and Unruh, J.R., 1992, Crustal-scale wedging beneath an imbricate roof-thrust system: Geology of a transect across the western Sacramento Valley and northern Coast Ranges, California, in Erskine, M.C. and others, editors, Field guide to the tectonics of the boundary between the California Coast Ranges and the Great Valley of California: American Association of Petroleum Geologists, Pacific Section, p. 117-140.
Deposit

Platt, J.P., 1986, Dynamics of orogenic wedges and the uplift of high-pressure metamorphic rocks: Geological Society of America Bulletin, v. 97, no. 9, p. 1037-1053.
Deposit

Ring, U. and Brandon, M.T., 1994, Kinematic data for the Coast Range Fault and implications for exhumation of the Franciscan subduction complex: Geology, v. 22, no. 8, p. 735-738.
Deposit

Rytuba, J.J., 1993, Epithermal precious-metal and mercury deposits in the Sonoma and Clear Lake volcanic fields, California, in Rytuba, J.J., editor, Active geothermal systems and gold-mercury deposits in the Sonoma-Clear Lake volcanic fields, California: Society of Economic Geologists Guidebook Series, v. 16, p. 38-51.
Deposit

Rytuba, J.J. and others, 1993, The Sonoma volcanic field and associated gold and mercury deposits: Road Log, in Rytuba, J.J., editor, Active geothermal systems and gold-mercury deposits in the Sonoma-Clear Lake volcanic fields, California: Society of Economic Geologists Guidebook Series, v. 16, p. 117-123.
Deposit

Sherlock, R.L., 1993, The geology and geochemistry of the McLaughlin mine sheeted vein complex, northern Coast Ranges, California: University of Waterloo, Ontario, Ph.D. dissertation, 309 p.
Deposit

Sherlock, R.L. and others, 1995, Origin of the McLaughlin Mine sheeted vein complex: Metal zoning, fluid inclusion, and isotopic evidence: Economic Geology, v. 90, p. 2156-2181.
Deposit

Stanley, W. D. and others, 1997, Tectonic controls on magmatism and geothermal resources in the Geyers-Clear Lake region, California: Integration of new geologic, earthquake tomography, seismicity, gravity, and magnetotelluric data: U. S. Geological Survey Open File Report 97-95, 40p.
Deposit

Thorkelson, D.J. and Taylor, R.P., 1989, Cordilleran slab windows: Geology, v. 17, no. 9, p. 833-836.
Deposit

Tosdal, R.M. and others, 1996, Precious metal mineralization in a fold and thrust belt: The McLaughlin hot spring deposit, northern California, in Coyner, A.R. and Fahey, P.L., editors, Geology and ore deposits of the American Cordillera: Geological Society of Nevada Symposium Proceedings, Reno/Sparks, Nevada, April 1995, p. 839-854.
Deposit

Wakabayashi, J. and Unruh, J.R., 1995, Tectonic wedging, blueschist metamorphism, and exposure of blueschists: Are they compatible?: Geology, v. 23, no. 1, p 85-88.
Deposit

Laizure, C., 1929, Report on Palisade Mine (CDMG Mineral Resources Files, Sacramento)
Deposit

Miscellaneous field reports on Palisade and Silverado mines (File Numbers 330-3409 and 330-3404, CDMG Mineral Resources Files, Sacramento).

General comments

Subject category	Comment text
Deposit	A shallow, epithermal system associated with hot springs is believed to be the origin of the Silverado-Palisade silver-gold deposit. This mineralization developed within a fault-controlled hydrothermal system driven by high heat flow associated with waning stages of formation of the Sonoma volcanic field and possibly with incipient stages of the Clear Lake volcanic field. The system emplaced precious- and base-metal-bearing quartz-chalcedony-adularia vein complexes as a series of injections along NE-trending faults. Some repetitive fracturing, vein-filling, and local hydrothemal brecciation at shallow levels indicate a somewhat active seismic history during the mineralization. This seismic activity was not as intense as that of the nearby McLaughlin gold deposit to the northeast, where sealing-rupturing activity was more repetitive (Enderlin, 1993). Associated with the McLaughlin deposit are sinter terraces, hydrothermal breccia, open and banded vein textures, and maar rings all of which strongly indicate a hot-spring origin. The Cherry Hill deposit farther north hosts active hot springs, which are currently depositing precious metals (Pearcy and Petersen, 1990). The Silverado-Palisade deposit lacks the surface manifestations present at the McLaughlin and Cherry Hill deposits and appears to have formed at higher temperatures. Nonetheless, isotopic, mineralogic, and textural similarities between the gold deposits at McLaughlin and Cherry Hill and the Silverado-Palisade deposit suggest similar origins. Based on fluid-inclusion and isotope studies of vein material, Sherlock (1993) concluded that the metal-bearing fluids were boiling, low-salinity (NaCl-dominated), and meteoric in origin, similar to mineralizing fluids at McLaughlin. Homogenization temperatures averaged 249?C at the Silverado Mine and 212oC at the Palisade Mine. Metals were presumably transported mainly as bisulfide complexes (Enderlin, 1993). Other features that indicate epithermal conditions include banded and vuggy quartz and chalcedony, hydrothermal brecciation, and adularia. In addition, ore-grades appear to be higher at shallower depths, although there has been insufficient exploration to confirm this trend. Based on both a hydrostatic boiling curve for the fluid inclusions and inferred erosion rates, the vein outcrop at the Silverado Mine probably formed about 400 feet below the paleo-surface, while the outcrop at the Palisade Mine probably formed at a depth of about 200 feet (Enderlin, 1993; Sherlock, 1993). These depths may explain the lack of surface features and the higher temperatures at the deposit compared to McLaughlin (Dean Enderlin, Homestake Mining Company, 1999, personal communication).

Subject category

Comment text

Deposit

A shallow, epithermal system associated with hot springs is believed to be the origin of the Silverado-Palisade silver-gold deposit. This mineralization developed within a fault-controlled hydrothermal system driven by high heat flow associated with waning stages of formation of the Sonoma volcanic field and possibly with incipient stages of the Clear Lake volcanic field. The system emplaced precious- and base-metal-bearing quartz-chalcedony-adularia vein complexes as a series of injections along NE-trending faults. Some repetitive fracturing, vein-filling, and local hydrothemal brecciation at shallow levels indicate a somewhat active seismic history during the mineralization. This seismic activity was not as intense as that of the nearby McLaughlin gold deposit to the northeast, where sealing-rupturing activity was more repetitive (Enderlin, 1993).

Associated with the McLaughlin deposit are sinter terraces, hydrothermal breccia, open and banded vein textures, and maar rings all of which strongly indicate a hot-spring origin. The Cherry Hill deposit farther north hosts active hot springs, which are currently depositing precious metals (Pearcy and Petersen, 1990). The Silverado-Palisade deposit lacks the surface manifestations present at the McLaughlin and Cherry Hill deposits and appears to have formed at higher temperatures. Nonetheless, isotopic, mineralogic, and textural similarities between the gold deposits at McLaughlin and Cherry Hill and the Silverado-Palisade deposit suggest similar origins. Based on fluid-inclusion and isotope studies of vein material, Sherlock (1993) concluded that the metal-bearing fluids were boiling, low-salinity (NaCl-dominated), and meteoric in origin, similar to mineralizing fluids at McLaughlin. Homogenization temperatures averaged 249?C at the Silverado Mine and 212oC at the Palisade Mine. Metals were presumably transported mainly as bisulfide complexes (Enderlin, 1993). Other features that indicate epithermal conditions include banded and vuggy quartz and chalcedony, hydrothermal brecciation, and adularia. In addition, ore-grades appear to be higher at shallower depths, although there has been insufficient exploration to confirm this trend.

Based on both a hydrostatic boiling curve for the fluid inclusions and inferred erosion rates, the vein outcrop at the Silverado Mine probably formed about 400 feet below the paleo-surface, while the outcrop at the Palisade Mine probably formed at a depth of about 200 feet (Enderlin, 1993; Sherlock, 1993). These depths may explain the lack of surface features and the higher temperatures at the deposit compared to McLaughlin (Dean Enderlin, Homestake Mining Company, 1999, personal communication).

Reporter information

Type	Date	Name	Affiliation	Comment
Reporter	31-MAY-2001	Fuller, Michael S. (Higgins, Chris T.)	California Division of Mines and Geology
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.

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