Hayden Hill Deposit

Site Name

Primary: Hayden Hill Deposit
Secondary: Golden Eagle
Secondary: Providence City

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Commodity

Primary: Silver
Primary: Gold
Tertiary: Arsenic
Tertiary: Manganese
Tertiary: Mercury

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Location

State: California
County: Lassen
District: Hayden Hill District

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Land Status

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

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Holdings

Not available

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Workings

Not available

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Ownership

Owner Name: Lassen Gold Mining, Inc.

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Production

Not available

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Deposit

Record Type: District
Operation Category: Producer
Deposit Type: Hydrothermal stockwork; hydrothermal vein
Operation Type: Surface-Underground
Discovery Year: 1870
Years of Production:
Organization:
Significant: Y
Deposit Size: M

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Physiography

Not available

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Mineral Deposit Model

Model Name: Hot-spring Au-Ag

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Orebody

Form: Tabular; irregular

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Structure

Type: L
Description: Ore was originally discovered and mined on the southwest flank of Hayden Hill from many steeply dipping faults and fractures, which generally trend northeast or northwest. Most significant of these are the Providence, Golden Eagle, Juniper, and Brush Hill. Modern mining exploited these sets as well as those on the northeast flank of Hayden Hill, which included north-trending faults in addition to northeast- and northwest-trending faults and local stockworks. Intersections of these faults and fractures were particularly important sites of concentration.

Type: R
Description: Walker Lane; Hayden Hill volcanic complex

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Alterations

Alteration Type: L
Alteration Text: As interpreted from Finn (1987) , Finn and Laskowski (1994), and Detra and Burnett (1994): Early (?): Propylitic (early phase?); albite, chlorite, epidote, montmorillonite, quartz, calcite, pyrite Stage-One: Silicic; quartz, chalcedony Potassic; adularia, sericite Stage-Two: Carbonate; calcite (Finn, 1987) Silicic; quartz, chalcedony (Detra and Burnett, 1994) Stage Three: Silicic; quartz, chalcedony Potassic; adularia, sericite Argillic; illite, montmorillonite Late: Oxidation; goethite, hematite Oxidation was reported to a depth of at least 835 feet, the depth of the Golden Eagle shaft (Tucker, 1919). All of the ore in the Providence Pit and about two-thirds of the ore in the Lookout Pit was oxidized based on observations up to 1994 (Detra and Burnett, 1994).

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Rocks

Name: Volcanic Breccia (Agglomerate)
Role: Host
Age Type: Host Rock
Age Young: Miocene

Name: Mixed Clastic/Volcanic Rock
Role: Host
Description: Volcaniclastic sandstone
Age Type: Host Rock
Age Young: Miocene

Name: Sandstone
Role: Host
Description: Volcaniclastic
Age Type: Host Rock
Age Young: Miocene

Name: Mixed Clastic/Volcanic Rock
Role: Host
Description: Volcaniclastic siltstone
Age Type: Host Rock
Age Young: Miocene

Name: Siltstone
Role: Host
Description: Volcaniclastic
Age Type: Host Rock
Age Young: Miocene

Name: Volcanic Breccia (Agglomerate)
Role: Host
Description: Dacite
Age Type: Host Rock
Age Young: Miocene

Name: Dacite
Role: Host
Description: breccia
Age Type: Host Rock
Age Young: Miocene

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Analytical Data

Not available

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Materials

Ore: Electrum
Ore: Pearceite
Ore: Polybasite
Ore: Tennantite
Ore: Tetrahedrite
Ore: Acanthite
Ore: Pyrite
Ore: Gold
Gangue: Quartz
Gangue: Chalcedony
Gangue: Goethite
Gangue: Hematite
Gangue: Calcite

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Comments

Comment (Geology): INTRODUCTION The northeastern corner of California is underlain by an extensive composite volcanic terrane of Cenozoic age, which overlaps three geomorphic provinces. From west to east, these provinces are the Cascade Range, Modoc Plateau, and Great Basin. Within this region, there are only three notable mining districts that produced gold and silver: High Grade in the Warner Range, near the Oregon border; Winters, between Adin and Alturas in Modoc County; and the largest of the three, Hayden Hill, in northern Lassen County. Hayden Hill is situated approximately at the somewhat ill-defined boundary between the Cascade Range and Modoc Plateau. REGIONAL SETTING Compared to the rest of California, the northeastern corner of the state has received relatively minor study of its geology. Except for the volcanic complexes of Medicine Lake and Lassen Peak, intense detailed geologic mapping (1:24,000) is generally sparse; on a moderate scale, L. Trowbridge Grose and several students from Colorado School of Mines have mapped parts of all of many 15-minute quadrangles in this area (Grose, 2000). A definitive regional synthesis of the stratigraphy and tectonic setting of this area remains to be accomplished, however. The paper by Macdonald (1966) provides a classical geologic view of this region, while that by Christiansen and Yeats (1992) provides a modern view of the region as part of the Cenozoic development of the Cordillera of the western U.S. Grose (2000) presented an overview of volcanism in the southeastern part of this region, which includes the Hayden Hill deposit. Hutchinson and Albers (1992) presented an overview of Late Cenozoic metallogenesis in the Cordillera of the western U.S., particularly that in the Great Basin. Stratigraphy The Modoc region consists mainly of Miocene to Pleistocene intermediate to mafic volcanic rocks, with subordinate sedimentary deposits of volcanic material that filled intervening basins and troughs formed by tensional faulting. Based on a seismic-refraction survey, Fuis and others (1987) interpreted this Cenozoic material to be a 2- to 5-km thick cover over a basement of igneous and metamorphic crust similar to that of the Sierra Nevada. Fuis and others (1987) believed the crystalline basement may represent a composite of the deeper portions of magmatic arcs. In contrast, Catchings (1987) interpreted the basement to be similar to the crust of the northwestern Basin and Range province. The overlying Cenozoic volcanic rocks include all types of eruptive products as well as local hypabyssal intrusions. The Miocene rocks are generally intermediate to silicic in composition, with pyroclastic and epiclastic origins, while the Pliocene and younger rocks are more mafic, characterized by less pyroclastic material and more lava. Classically, most of the Miocene rocks were included in a unit known as the Cedarville Series, while most of the younger widespread mafic rocks were included in a unit known as the Warner Basalt (Macdonald, 1966). Subsequent mapping has demonstrated that this stratigraphy is overly simplified. Correspondingly, detailed correlation of units across the Modoc Plateau is not possible at this time because of the numerous local centers of eruption, with their accompanying complexity of chemical variations, and the general scarcity of radiometric ages.

Comment (Location): The deposit is associated with a topographic eminence known as Hayden Hill. The location point selected for latitude and longitude is the original summit point of Hayden Hill as shown on the USGS Said Valley 7.5-minute quadrangle map. The mine is accessible by paved road from Susanville (State Highway 139) or Alturas (State Highway 139) and then by a gravel road a few miles long.

Comment (Workings): Development of the Hayden Hill deposit consists of both extensive historic underground workings and modern open-pit workings. The underground workings include numerous shafts and adits, with associated drifts and crosscuts, most of which were of dimensions of hundreds of feet; some drifts in the Golden Eagle ran more than 1,000 feet. Most workings were confined to the southwest slope of Hayden Hill where large veins were discovered at the surface. Maximum known depth of any underground working is 835 feet at the main shaft of the Golden Eagle Mine (Averill and Erwin, 1936). Workings developed in the soft ?rubble? zones along faults had to be timbered extensively because of the unstable ground. The modern surface workings include two main open pits, the Providence, which is on the southwest flank of Hayden Hill, and the Lookout, a larger pit on the northeast flank. A total of 30 million tons of ore and 27 million tons of waste rock were removed from the two pits. Final maximum dimensions of the pits are about 1,000 feet by 1,200 feet for the Providence and about 2,000 feet by 3,000 feet for the Lookout. Ultimate mining depth in the Lookout was expected to be about 600 feet below the original summit of Hayden Hill.

Comment (Deposit): The main part of the Hayden Hill deposit is up to about 3,000 feet wide by about 5,000 feet long. It consists mainly of two ore bodies, the Providence and Lookout, which are on the southwest and northeast flanks of Hayden Hill, respectively. Hayden Hill was a favorable site for deposition of precious metals because of extensive tensional faulting, which provided open channels for migration of precious-metal-bearing hydrothermal fluids associated with local volcanism. Initial phases of silica-adularia flooding of the site hardened the volcaniclastic country rock to allow additional fracturing and brecciation of the rock, with subsequent migration of and deposition of metals by the fluids along these passageways. The Lookout ore body is thought to be the locus of a hot -spring system associated with the mineralization . The deposit is classified under the Hot-Spring Au-Ag model because of the following aggregate of characteristics: 1) Presence of probable siliceous sinter on the east flank of Hayden Hill, 2) presence of extensive banded quartz (coarse-grained to chalcedonic) veins and stockworks, 3) presence of silica-cemented hydrothermal breccia, 4) deposit interpreted to have formed at about 185-215 degrees C according to measurements on fluid inclusions by Finn (1987), 5) evidence of boiling indicated by pebble dikes, by variations in both vapor percentages and homogenization temperatures of fluid inclusions in quartz veins, and by intergrowth of fine-grained adularia with quartz to form veins (Finn, 1987), 6) presence of As and Hg, and 7) pervasive silica and adularia as alteration of the volcaniclastic country rock. Study of the salinity and origin of the fluids apparently has not been conducted. The deposit is also characterized by small amounts of sulfide (total sulfide is generally less than 5% and is dominantly pyrite) and by faults and fractures that contain sheared material (?rubble?), which consists of a composite of broken wallrock and scarce quartz vein material set in a soft matrix of gouge, iron-oxide, manganese-oxide, and native gold. The Hayden Hill deposit was originally classified under the Sado Epithermal Vein model in Cox and Singer (1986). The features described above and the general scarcity or absence of chalcopyrite, sulfosalts, and tellurides warrant placement of the deposit under the Hot-Spring Au-Ag model.

Comment (Geology): Stratigraphy Hayden Hill is underlain by lacustrine and terrestrial volcaniclastic deposits that are flat-lying to gently dipping. Staff at the Hayden Hill Mine (Finn and Laskowski, 1994; Detra and Burnett, 1994) have mapped the bulk of Hayden Hill as part of the Miocene Turner Creek Formation, which here was largely associated with a lacustrine environment. Members of this unit mapped at the deposit include a lower ?siltstone? unit, dacite breccia (possibly formed as a debris avalanche off a volcanic dome), and an upper ?siltstone? unit. Overlying this formation are members of the MioceneTuff of Dago Springs, which exhibits evidence of local transition to a terrestrial environment. Here, this unit consists of an ?epiclastic? tuff, which capped Hayden Hill. In contrast, Gross and others (1992) show the bulk of Hayden Hill to be composed of the Miocene Tuff of Anderson Ranch (breccia, tuff, and fine-grained volcaniclastic rock) overlain in its summit area by Miocene Tuff of Preston Canyon (tuff). Both groups of workers appear to agree in general with their determinations of the lithologic character of the stratigraphy despite differences in names of their units. A few radiometric dates in the vicinity of the deposit indicate emplacement of these rock units about 10 Ma. Detailed mapping of the deposit itself has not revealed any definite intrusive rock, although dikes and domes have been mapped in the immediate area (Finn, 1987). Structure McCusker (1990) interpreted the Hayden Hill deposit to be part of what is informally termed the ?Willow Creek graben,? a poorly defined NW-trending structure that locally controlled vents and deposition of the above described volcanic units. This feature may be the same as the Hayden Hill volcanic complex, a volcano-tectonic depression tentatively identified by Grose (2000). Hayden Hill itself is a structural high, bounded on all sides by steeply dipping normal faults. The deposit forms a small local aeromagnetic high relative to its surroundings. There are three sets of faults, which strike north, northwest, and northeast. They show evidence of both oblique slip and strike slip, and are interpreted to have been active before, during, and after mineralization (Finn and Laskowski, 1994). Major faults include the NE-trending Providence, NW-trending Golden Eagle-Excelsior, and a north-trending fault that cuts the east flank of the summit area of Hayden Hill. The maximum mapped length of faults cutting the main edifice of Hayden Hill is about one mile. Maximum displacements are probably a few hundred feet. Faulting was the main control of ore deposition. Alteration and Mineralization Genesis of the Hayden Hill deposit may be related to development of the Hayden Hill volcanic complex. Simultaneous fracturing of country rock and intrusion of magma in this volcano-tectonic depression may have established local hydrothermal circulation, which led to pervasive alteration and mineralization of the country rock at Hayden Hill.

Comment (Development): Mining and processing of ore in this district are generally unremarkable, but a few features are important: 1) the modern era of mining was notable for severe overestimation of reserves during its periods of exploration, development, and early production at this deposit. 2) Clay gouge associated with the mineralized faults has caused problems in drilling, mining, and ore recovery; Hill (1915) estimated that gold recovery in the cyanide-tanks at the Golden Eagle Mine was proabably only about 50%. 3) Determination of fracture density was critical in outlining ore zones in modern mining. Gold and silver were mostly confined to fractures rather than intervening wall rock. All ore-processing is accomplished at facilities on the southwest edge of Hayden Hill. Reclamation is still active, with the main work being done at the Lookout Pit. The Providence Pit is partially backfilled. Past concerns at the site include landslides on the north side of Hayden Hill, the presence of minor amounts of mercury and arsenic (possibly from pyrite or arsenopyrite), and acid rock drainage associated with oxidation of disseminated sulfides in the pits, waste dumps, and heap-leach pad. The low concentration of sulfide minerals is considered an advantage regarding acid rock drainage. Regarding potential buffering of acidic conditions, calcite is present in places in both veins and replacement of wallrock, although it does not appear to be extensive (Finn, 1987). In the past, waste rock was dumped on the northwest flank of Hayden Hill, which experienced a few landslides in 1993 and 1994 after placement of the waste rock. Final uses of this nearly 1,000-acre mining property will include wildlife habitat, grazing, watershed, and recreation (Dillard, 1992).

Comment (Economic Factors): From records of historic production, prior to the onset of modern surface mining, Finn (1987) reported almost 100,000 troy oz. of gold and 50,000 troy oz. of silver for mines of the Hayden Hill District. Using estimated dollar values of production for individual mines, obtained from various sources, Finn (1987) calculated an amount of about 128,000 troy oz. of gold. More than 90% of the total gold and silver was produced between 1880 and 1910 (Finn, 1987). In contrast, Buchanan (1983) reported production of 77,000 troy oz. of gold and 1,320,000 troy oz. of silver for the period 1876-1940. The source of the large discrepancy for silver is not known. In its 1991 annual report, Amax Gold, Inc. reported that the Hayden Hill deposit contained 1,429,000 troy oz. of gold (44,923,000 tons of ore with a grade of 0.032 troy oz./ton). In 1993, based on actual mining and milling, reserves were down-graded to 503,000 troy oz. from 21,870,000 tons of ore with a grade of 0.023 troy oz./ton.

Comment (Development): The mining history of the Hayden Hill deposit has been long and complicated. Discovery of the deposit is credited to a party of travelers in either 1869 (Clark, 1970) or 1870 (Hill, 1915), who discovered fine gold in a spring on the southwest side of Hayden Hill. Known originally as Providence City, the district was later renamed for one of the original discoverers of the gold-bearing veins on the hill. Most historic mining was confined to the western flank of Hayden Hill. More than 80% of the total production during this historic era was from the Golden Eagle and Juniper mines. The first mining of the deposit consisted of very shallow shafts and adits, and sluicing and hydraulicking of the minor placers on the hill. Targets of these early miners were the soft iron oxide- and manganese oxide-stained gouge and breccia along faults and fractures in the altered volcanic rock. This ?rubble? contained free electrum and generally little quartz-vein material; the presence of pyrolusite was considered a guide to high-grade ore. In the 1880s, many small, shallow mines were developed. Because it offered a perennial water supply, milling of ore from these mines was accomplished at stamp mills and arrastres on Willow Creek, a few miles to the east. Nonetheless, the remoteness of the district and its severe winter weather continued to hinder extensive or efficient development of the deposit. With the consolidation of mines and introduction of the cyanide process here, the most productive period of mining was from about 1900 to 1910, when a fire destroyed the Golden Eagle Mine and much of the town. Production was minor from the 1920s to the 1940s when mining came to an end. The extensive dumps of the district were worked periodically. In the 1930s and 1940s, the deposit was investigated for its potential for large-tonnage, low-grade open-pit mining (Grant and Check, 1944). The modern era of mining at Hayden Hill commenced in the mid-1970s with exploration programs by Fischer-Watt Mining Company among others. A series of joint ventures with Lacana Mining Corporation and Peco Resources Ltd. for exploration and development, including drilling, followed in the 1980s. In 1983-84, these companies initiated a pilot heap-leach project to evaluate dump material at Hayden Hill. In 1988 and 1989, Amax Gold, Inc. in partnership with U.S. Gold Corporation (formerly Silver State Mining Corp.) drilled the deposit, with concentration mainly on the area that was to become the Lookout Pit. Development of the mine itself started in 1991 under Lassen Gold Mining, Inc., a subsidiary of Amax that acquired the interests of U.S. Gold in 1990, and production began in 1992. Two main pits were developed: the Providence on the southwest flank of the hill and the Lookout on the northeast flank. Finn and Laskowski (1994) reported the economic depth of mining to be at the 5,700 foot elevation. The mining operation was designed to recover gold and silver from both a conventional mill (fine crushing, gravity separation, cyanide leaching, carbon-in-pulp recovery) and cyanide heap-leaching. After a short period of operation in 1992, the mine encountered problems with ore grade and recovery in the mill, which led to re-evaluation of reserves and processing of ore. In 1993, mining was reduced in scope, the mill was idled, and recovery of gold and silver was confined to heap-leaching. Mining ceased in 1997 after only five years of operation of the surface workings. Since then, operation of the heap-leach pad, with associated recovery of gold and silver, has continued.

Comment (Commodity): Commodity Info: Gold occurs in both low-grade and high-grade conditions. Low-grade ore typically is found in stockworks (small veinlets and fractures) and hydrothermal breccia, averages about 0.015 troy oz./ton, and is confined to the volcaniclastic units of theTurner Creek Formation. High-grade ore typically is found in quartz-adularia veins and ?rubble? (gouge) zones along faults, has assayed as high as 11 troy oz./ton, and is found in both the Turner Creek Formation and Tuff of Dago Springs units, but mainly in members of the Turner Creek Formation. Gold is present as discrete grains that range from 8-1,000 microns in size and averages 40 microns (Finn and Laskowski, 1994; EIR/EIS, 1991). In oxidized ore (most common), it is found mainly as electrum and less commonly as native gold associated with quartz, goethite, and manganese oxide. In sulfide ore (unoxidized), it is found as grains encapsulated in pyrite and as native gold and in acanthtite on surfaces of pyrite. In ?rubble? zones, it is present as electrum. Silver is found mainly as electrum and acanthite. The gold:silver ratio overall is very low, with electrum the dominant ore mineral. Hayden Hill is notable for its low -sulfide mineralization. Pyrite and marcasite are the dominant sulfides in the deposit, although microscopic chalcopyrite, sphalerite, galena, and pyrrhotite have been observed (Detra and Burnett, 1994). Arsenopyrite, pyrolusite, cinnabar, and barite are also present in the deposit.

Comment (Commodity): Ore Materials: Electrum, native gold, auriferous pyrite, acanthite, tetrahedrite-tennantite, polybastite-pearceite

Comment (Commodity): Gangue Materials: Quartz; chalcedony; goethite; hematite; pyrite; calcite; fault gouge

Comment (Environment): The Hayden Hill deposit is situated in a dissected volcanic landscape of hills and valleys of generally low to moderate relief. The region southwest of the deposit is noticeably flat, while the remainder of the landscape is rugged, with substantial local relief caused by both constructional volcanic features and their subsequent dissection by erosion and faulting. The deposit itself underlies Hayden Hill, a circular prominence about 6,300 ffet high that has resisted erosion because of extensive hydrothermal alteration, and corresponding densification, of the underlying country rock. Much of the hill has been altered or removed by modern open-pit mining. The area is drained by many small creeks, most of which are intermittent; nearby Willow Creek flows year-round. Springs are present locally. Depth to water table at Hayden Hill was estimated by Hill (1915) to be about 625 feet based on observations in the shaft of the Golden Eagle Mine. The current mine operator had to drill to about 1,000 feet to obtain production water (Dillard, 1992). Vegetation varies in its distribution, but is typical of the arid high-elevation uplands of the Modoc Plateau. Open grasslands with sagebrush are common as are open stands of evergreen trees (Jeffrey pine) and outcrop of volcanic rock. The climate is warm and dry in summer and cold and wet in winter. Average total precipitation at nearby Adin is 16 inches; average total snowfall is 45 inches. Because of its exposure above the surrounding landscape and its higher altitude, Hayden Hill is often a site of turbulent weather; correspondingly, the figures given for Adin are likely less than those at Hayden Hill. A large state game refuge is on the southwest side of the deposit.

Comment (Geology): Hydrothermal alteration has affected all Tertiary volcanic units at Hayden Hill, with quartz the most widespread alteration mineral. At the surface, the zone of silicic alteration was elliptic in plan view and estimated to be about 1,500 feet by 3,500 feet (Hayden Hill Operating Company, Inc., 1989). Because of its complexity, the sequence and composition of the alteration is still not fully established. Argillic alteration has a negative correlation with gold. Mineralization is strongly associated with areas that exhibit quartz-adularia alteration (fissure-filling and local replacement of wall rock). All ore from the Providence Pit and most ore from the Lookout Pit was oxidized. Most of the unoxidized sulfide ore occurs in fine-grained volcaniclastic rock in the uppermost part of the Turner Creek Formation, which contained pyrite-bearing quartz veins and disseminated fine-grained pyrite. Mercury and arsenic are present locally in elevated concentrations, but the historic use of amalgamation at Hayden Hill obscures the natural background of mercury concentration. The relationship between alteration and precious-metal mineralization is interpreted as follows from Detra and Burnett (1994) and McCusker (1990) as follows: Phase 1: Intense silicification with deposition of adularia in the volcanic rock to form a stratiform zone or ?silica cap.? This phase was barren of precious metals. Phase 2: After additional fracturing of the silica cap and production of hydrothermal breccias, precious-metal-bearing hydrothermal fluids invaded these structures to produce low-grade ore zones in the form of silicified breccias and stockworks of quartz veinlets. A funnel-shaped core of silicified rock near the summit of Hayden Hill and exposed in the walls of the Lookout Pit may represent the main vertical feeder zone for the metal-bearing hydrothermal system at Hayden Hill. Phase 3: Additional fracturing and movement of hydrothermal fluids along these fractures to produce high-grade quartz-adularia veins, which cut the earlier low-grade ore zones. Phase 4: Subsequent shearing of the veins and fractures from Phase 3, with concomitant oxidation of sulfides and concentration of gold and silver to produce high-grade ?rubble? zones along these structures. Overall, the deposit can be envisioned as a north-trending tabular zone of low-grade ore about 1,000 feet by 2,500 feet cut locally by later stage NW- and NE-trending veins (Hayden Hill Operating Company, Inc., 1989). This zone was characterized by silicic alteration grading downward into propylitically (?) altered rock and laterally into argillically altered rock. The deposit consists of two main ore bodies, the Lookout and Providence, with additional smaller areas of mineralization. At the surface, the Lookout body was approximately 1,800 feet long (north-south) and 600-800 feet wide, narrowing with depth. This body was characterized by a low-grade mass of irregular and anastomosing zones of quartz veins, stockworks, and hydrothermal breccias. Superimposed on this mass was a series of higher-grade NW- to NE-trending quartz-adularia veins. Sets of N- and NE-trending faults controlled the bulk of the ore in this body, with fault intersections hosting the richest lenses (Finn and Laskowski, 1994). Based on drill-holes, the extent of mineralization is not known beyond a depth of about 900 below the original summit of Hayden Hill. In contrast, the less-productive Providence body was characterized by several narrow, steeply dipping ore zones associated with discrete NW- and NE-trending quartz veins, breccia, and stockworks, all of which were principally controlled by faults of the same structural trends. The age of the mineralization has been determined at about 8-9 million years based on K/Ar analysis of adularia in the deposit (Finn and Buchanan, 1984; Finn, 1987).

Comment (Geology): Low-grade ore consists of extensive stockworks and hydrothermal breccias, while high-grade ore consists of quartz-adularia veins and soft seams of sheared material along fault planes; the gold-bearing seams are notable because they contain mainly iron- and manganese-stained zones of soft ?rubble? that commonly show little or no vein material. They probably represent the sheared sites of gold-bearing quartz-adularia veins that were subsequently oxidized by downward movement of ground water (Hill, 1915). Thicknesses of quartz-adularia vein range from inches to swarms tens of feet wide; most veins are less than one foot wide. Individual veins have been traceable for up to about 300 feet (Detra and Burnett, 1994) and commonly are found along fault planes (Finn and Laskowski, 1994).

Comment (Identification): The Hayden Hill deposit includes many individual historic mines and prospects developed mostly on the topographic feature known as Hayden Hill. It also includes the currently active open-pit mining operation known as Hayden Hill Mine.

Comment (Geology): Structure Fundamentally, the Modoc region has structurally evolved in response to plate tectonism characterized first by convergence and then by convergence-transform faulting, which has affected this part of western North America. At present, the region is inland of the active Cascade volcanic arc, which has formed because of subduction of the Gorda Plate, situated to the west, beneath the North American Plate. Previous phases of this subduction during the Miocene produced ancestral arc volcanism here. The Modoc region is also interpreted to be where the extensional tectonics and associated back-arc mafic volcanism of the Basin and Range province have been impinging from the east upon the Cascade volcanic arc since the late Miocene (Christiansen and Yeats, 1992; Grose, 2000; Guffanti and others, 1990; Mooney and Weaver, 1989). Radiometric dating (Guffanti and others, 1990; Grose, 2000; Saucedo and others, 1990) indicates that volcanism of this arc has also migrated westward. The overall interaction between the Cascade arc and the Basin and Range extensional regime is complicated and not yet fully understood. It appears that a major episode of extension began in this region about 7-9 Ma (Guffanti and others, 1990; McKee and others, 1983), and it was in this environment that the Hayden Hill deposit formed. The Modoc Plateau itself is a subprovince of intense volcanism cut by numerous normal and strike-slip faults that generally trend north to northwest. Within this terrane is a major structural zone of deformation known as the Walker Lane Belt, which is a N30W-trending, 25-35-km-wide zone of normal and right-lateral faults that is interpreted to extend at least 125 km north-northwest of Honey Lake (Grose, 1993; Bowens, 1998). Gross (1993) considered the belt to be a transitional boundary between the Cascade volcanic arc on the west and the Basin and Range on the east. A volcano-tectonic depression, informally termed the Hayden Hill volcanic complex, has been tentatively identified within this belt (Grose, 2000; Grose, 1993; Hazlett and Grose, 1983). This complex includes the Hayden Hill deposit and may be part of a larger caldera (Grose, 2000). Metallogeny The Modoc Plateau is not noted for metallic ore deposits. As mentioned above, only three mining districts are present in this region. Given the potential for hydrothermal activity associated with this large volcanic environment in northeastern California, there are undoubtedly other ore deposits in this terrane, but they lie buried beneath younger volcanic cover or may have less-obvious physical clues to their presence. Worthy of additional study is the hypothesis that mineralization at Hayden Hill, the Winters Mining District, and Little Gold Hill (about 8 miles NNW of Hayden Hill) is contemporaneous and structurally related to inferred collapse structures postulated by Hazlett and Grose (1983) , Bowens (1998), and Grose (2000). Bowens (1998) described small areas of hydrothermal alteration in the Stone Coal Valley region, about 50 km northwest of Hayden Hill, along the eastern margin of the mapped continuation of the Walker Lane Belt. Garman (1991) also recognized areas of alteration northeast of the Hayden Hill Mining District. As additional detailed mapping is accomplished in this region, other areas of hydrothermal alteration and possible epithermal mineralization will likely be recognized. Determination, however, of the overall potential for discovery of additional metallic ore deposits in this region must depend on improved understanding of the intersection and interaction of three major tectonic regimes (subduction, transform, and extension) in this complicated area. GEOLOGY AT HAYDEN HILL DEPOSIT

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References

Reference (Deposit): Crawford, J.J., 1894, Lassen County: California State Mining Bureau 12th Report of the State Mineralogist, p. 149-150.

Reference (Deposit): Averill, C.B. and Erwin, H.D., 1936, Mineral resources of Lassen County: California Journal of Mines and Geology, v. 32, no. 4, p. 405-444.

Reference (Deposit): Buchanan, L.J., 1983, Geology and ore deposits of Hayden Hill, Lassen County, California: Geological Society of America Abstracts with Programs, v. 15, no. 5, p. 326.

Reference (Deposit): Catchings, R.D., 1987, Crustal structure of the northwestern United States: Ph.D. dissertation, Stanford University, 183 p.

Reference (Deposit): Christiansen, R.L. and Yeats, R.S., 1992, Post-Laramide geology of the U.S. Cordilleran region, in Burchfiel, B.C. and others, editors, The Cordilleran Orogen: Conterminous U.S.: Geological Society of America, The Geology of North America, v. G-3, p. 261-406.

Reference (Deposit): Detra, E.H. and Burnett, J.L., 1994, Geology of Hayden Hill - A new mine revitalizing an old mining district: California Geology, v. 47, no. 5, p. 134-138.

Reference (Deposit): Dillard, G., 1992, Amax?s original plan survives gauntlet intact: Rocky Mountain Pay Dirt, November, p. 4A-7A.

Reference (Deposit): Finn, D.R., 1987, Geology and ore deposits of the Hayden Hill District, Lassen County, California: M.S. thesis, University of Nevada, Reno, 84 p.

Reference (Deposit): Finn, D.R. and Buchanan, L.J., 1984, Hayden Hill, California: Epithermal Au-Ag mineralization associated with Cascade volcanism: Geological Society of America Abstracts with Programs, v. 16, no. 6, p. 509.

Reference (Deposit): Fuis, G.S. and others, 1987, A geologic interpretation of seismic-refraction results in northeastern California: Geological Society of America Bulletin, v. 98, no. 1, p. 53-65.

Reference (Deposit): Garman, C.E., 1991, Geology and tectonism of the northeast Hayden Hill area, Lassen County, California: M.S. thesis, Colorado School of Mines, 84 p.

Reference (Deposit): Gay, T.E., Jr., 1966, Economic mineral deposits of the Cascade Range, Modoc Plateau, and Great Basin region of northeastern California, in Bailey, E.H., editor, Geology of Northern California: California Division of Mines and Geology Bulletin 190, p. 97-104.

Reference (Deposit): Grose, T.L.T., 1990, Basin and Range transition east of Lassen Peak: EOS, Transactions of American Geophysical Union, v. 71, no. 43, p. 1613.

Reference (Deposit): Grose, T.L.T., 1993, The Walker Lane Belt in northeastern California: Geological Society of America Abstracts with Programs, v. 25, no. 5, p. 44-45.

Reference (Deposit): Grose, T.L.T., 2000, Volcanoes in the Susanville region, Lassen, Modoc, Plumas counties, northeastern California: California Geology, v. 53, no. 5, p. 4-23.

Reference (Deposit): Grose, T.L.T. and others, 1994, Geologic map of the Hayden Hill 15-Minute Quadrangle, Lassen County, California: California Department of Conservation, Division of Mines and Geology Open-File Report 93-06, scale 1:62,500.

Reference (Deposit): Guffanti, M. and others, 1990, Late Cenozoic volcanism, subduction, and extension in the Lassen region of California, southern Cascade Range: Journal of Geophysical Research, v. 95, no. B12, p. 19,453-19,464.

Reference (Deposit): Hanks, H.G., 1888, Lassen County: California State Mining Bureau 8th Report of the State Mineralogist, p. 330-331.

Reference (Deposit): Hannah, J.L., 1977, Tectonic setting of the Modoc region, northeastern California: California Division of Mines and Geology Special Report 129, p. 35-39.

Reference (Deposit): Hazlett, D.P., 1984, A volcanotectonic and paleomagnetic investigation in the Hayden Hill area: M.S. thesis, Colorado School of Mines, 155 p.

Reference (Deposit): Hazlett, D.P. and Grose, T.L.T., 1983, The Hayden Hill volcanic center, northeastern California: Geological Society of America Abstracts with Programs, v. 15, no. 5, p. 330.

Reference (Deposit): Hill, J.M., 1915, Some mining districts in California and Nevada: U.S. Geological Survey Bulletin 594, p. 30-38.

Reference (Deposit): Hutchinson, R.W., and Albers, J.P., 1992, Metallogenic evolution of the Cordilleran region of the western United States, in Burchfiel, B.C. and others, editors, The Cordilleran Orogen: Conterminous U.S.: Geological Society of America, The Geology of North America, v. G-3, p. 629-652.

Reference (Deposit): Macdonald, G.A., 1966, Geology of the Cascade Range and Modoc Plateau, in Bailey, E.H., editor, Geology of Northern California: California Division of Mines and Geology Bulletin 190, p. 65-96.

Reference (Deposit): McKee, E.H. and others, 1983, Late Miocene and early Pliocene basaltic rocks and their implications for crustal structure, northeastern California and south-central Oregon: Geological Society of America Bulletin, v. 94, no.2, p. 292-304.

Reference (Deposit): Mooney, W.D. and Weaver, C.S., 1989, Regional crustal structure and tectonics of the Pacific coastal states; California, Oregon, and Washington, in Pakiser, L.C. and Mooney, W.D., editors, Geophysical framework of the continental United States: Geological Society of America Memoir 172, p. 129-161.

Reference (Deposit): Preston, E.B., 1890, Lassen County: California State Mining Bureau 9th Report of the State Mineralogist, p. 211-213.

Reference (Deposit): Preston, E.B., 1892, Hayden Hill Mining District: California State Mining Bureau 11th Report of the State Mineralogist, p. 241-242.

Reference (Deposit): Saucedo, G.J. and others, 1990, Age and distribution of volcanism - Susanville/Eagle Lake area, northeastern California: EOS, Transactions of American Geophysical Union, v. 71, no. 43, p. 1613.

Reference (Deposit): Tucker, W.B., 1919, Lassen County: California State Mining Bureau 15th Report of the State Mineralogist, p. 229-235.

Reference (Deposit): Finn, D. and Laskowski, E., 1994, Hayden Hill Mine tour and roadlog: Newmont Exploration Ltd., unpublished field guide.

Reference (Deposit): Grant, W. and Check, E.E., 1944, Report on Lassen Eagle Company property, Hayden Hill (CDMG Library, Sacramento).

Reference (Deposit): Hayden Hill Operating Company, Inc., 1989, Plan of operations for the Hayden Hill gold venture, Lassen County, California: Report submitted to U.S. Bureau of Land Management.

Reference (Deposit): McCusker, R.T. (adapted from), 1990, Geology of the Hayden Hill project: Unpublished report, 6 p.

Reference (Deposit): Steffen, Robertson and Kirsten (U.S.), Inc., 1991, Final Environmental Impact Report/Environmental Impact Statement for the Hayden Hill Project, Lassen County, California: Unpublished report, p. 3-1 to 3-7.

Reference (Deposit): Cox, D.P. and Singer, D.A., 1986, Mineral deposit models: U.S. Geological Survey Bulletin 1693, 379 p.

Reference (Deposit): Clifton, C.G., 1986, Primary gas dispersion halos in disseminated gold deposits: Examples from Nevada and California: Journal of Geochemical Exploration, v. 25, no. 1/2, p. 259.

Reference (Deposit): Clark, W.B., 1970, Gold districts of California: California Division of Mines and Geology Bulletin 193, 186 p.

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California Gold

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