Hayden Hill Mine, Hayden Hill [summit], Hayden Hill [town], Hayden Hill Mining District, Lassen County, California, USAi

Regional Level Types
Hayden Hill Mine	Mine
Hayden Hill [summit]	- not defined -
Hayden Hill [town]	Town
Hayden Hill Mining District	Mining District
Lassen County	County
California	State
USA	Country

An open pit Au mine on Hayden Hill (summit). This recent mining operation subhumed many older, historical mines in the district. Owned by the Lassen Gold Mining, Inc. Closed 1997. 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.

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.

Mineralization is a vein deposit (Deposit Model: 104, Hot-spring Au-Ag), hosted in brecciated Miocene dacite, siltstone (volcaniclastic), sandstone (volcaniclastic), all of the Turner Creek Formation; and volcanic breccia (agglomerate), Miocene tuff of the Dago Springs Formation.

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.
•Ore Materials: Electrum, native gold, auriferous pyrite, acanthite, tetrahedrite-tennantite, polybastite-pearceite
•Gangue Materials: Quartz; chalcedony; goethite; hematite; pyrite; calcite; fault gouge

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.

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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Link to USGS MRDS:	10310628

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References