Coeur Rochester Mine

Producer in Pershing county in Nevada, United States with commodities Silver, Gold, Lead, Zinc, Copper, Antimony

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	10310354
MRDS ID	M060371
Record type	Site
Current site name	Coeur Rochester Mine
Alternate or previous names	Rochester Mine, Nenzel Hill, East pit, West pit
Related records	10042547, 10150157, 10247172

Comments on the site identification

This record includes material from MRDS record M060371, an earlier record for the deposit. The Nevada Packard mine reserves are included with Coeur Rochester Mine, although the Nevada Packard mine is described in a separate record.

Geographic coordinates

Geographic coordinates:	-118.14153, 40.29073 (WGS84)
Elevation	2200
Relative position	The Coeur Rochester Mine is located about 26 miles northeast of Lovelock, Nevada.\n\n

Site location context

Political divisions (FIPS codes)

Pershing(county)

Nevada(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Rochester(quadrangle 1:24,000 scale)

Lovelock(quadrangle 1:100,000 scale)

Lovelock(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Dixie Valley(hydrologic unit)

Central Nevada Desert Basins(hydrologic accounting unit)

Central Nevada Desert Basins(hydrologic subregion)

Great Basin(hydrologic region)

Federal lands

Bureau of Land Management(Bureau of Land Management NV)

Bureau of Land Management NV BLM(Type of land area)

BLM(Federal land areas administered by BLM)

Geographic areas

Country	State	County
United States	Nevada	Pershing

Public Land Survey System information

Meridian	Township	Range	Section	Fraction	State
Mount Diablo	028N	034E	01-36		Nevada

Comments on the location information

The Coeur Rochester Mine is located on Nenzel Hill near the crest of the Humboldt Range.

Commodities

Commodity	Importance
Silver	Primary
Gold	Primary
Lead	Secondary
Zinc Critical	Secondary
Copper	Secondary
Antimony Critical	Secondary

Comments on the commodity information

Ore Materials: Pyrite, sphalerite, argentian tetrahedrite, arsenopyrite, chalcopyrite, galena, covellite, chalcocite, stromeyerite, polybasite, pyrargyrite, acanthite, argentite, argentojarosite, chlorargyrite, embolite, native silver, chalcophanite, melanterite, anglesite, manganese oxides, chalcanthite, pyrrhotite, teallite, owyheeite, electrum
Gangue Materials: quartz, k-feldspar, sericite, limonite, hematite, goethite, clays

Materials information

Materials	Type of material
Pyrite	Ore
Sphalerite	Ore
Tetrahedrite	Ore
Arsenopyrite	Ore
Chalcopyrite	Ore
Galena	Ore
Covellite	Ore
Chalcocite	Ore
Stromeyerite	Ore
Polybasite	Ore
Pyrargyrite	Ore
Acanthite	Ore
Argentite	Ore
Argentojarosite	Ore
Chlorargyrite	Ore
Embolite	Ore
Silver	Ore
Chalcophanite	Ore
Melanterite	Ore
Anglesite	Ore
Chalcanthite	Ore
Pyrrhotite	Ore
Teallite	Ore
Owyheeite	Ore
Electrum	Ore
Feldspar	Ore
Sericite	Ore
Limonite	Ore
Hematite	Ore
Goethite	Ore
Clay	Ore
Quartz	Gangue

Alteration

(Local) Silicification and oxidation are prevalent in the deposit.

Mineral occurrence model information

Model code	273
USGS model code	36a
Deposit model name	Low-sulfide Au-quartz vein
Mark3 model number	27
Model code	150
USGS model code	25c
Deposit model name	Epithermal vein, Comstock
Mark3 model number	16

Host and associated rocks

Host or associated

Host

Rock type

Volcanic Rock (Aphanitic) > Felsic Volcanic Rock > Rhyolite

Rock type qualifier

flows

Rock unit name

Rochester Rhyolite, Koipato Group

Stratigraphic age (youngest)	Late Permian
Stratigraphic age (oldest)	Early Triassic

Host or associated

Host

Rock type

Volcanic Rock (Aphanitic) > Pyroclastic Rock > Volcanic Breccia (Agglomerate)

Rock unit name

Rochester Rhyolite, Koipato Group

Stratigraphic age (youngest)	Late Permian
Stratigraphic age (oldest)	Early Triassic

Host or associated

Host

Rock type

Volcanic Rock (Aphanitic) > Felsic Volcanic Rock > Trachyte

Rock unit name

Rochester Rhyolite, Koipato Group

Stratigraphic age (youngest)	Late Permian
Stratigraphic age (oldest)	Early Triassic

Host or associated

Host

Rock type

Volcanic Rock (Aphanitic) > Felsic Volcanic Rock > Rhyolite

Rock type qualifier

tuff

Rock unit name

Weaver Formation, Koipato Group

Stratigraphic age (youngest)	Early Triassic

Host or associated

Host

Rock type

Sedimentary Rock > Mixed Clastic/Volcanic Rock

Rock type qualifier

volcanosedimentary rocks

Rock unit name

Weaver Formation, Koipato Group

Stratigraphic age (youngest)	Early Triassic

Nearby scientific data

(1)	Alluvium, undifferentiated	ListMap

Economic information

Geologic structures

Type of structure	Regional
Structure description	Rocks are folded into a broad, asymmetrical anticlinal arch.
Type of structure	Local
Structure description	There are 2 major normal fault systems and post- mineral faults.

Ore body information

General form tabular, pipelike, blanket, irregular, disseminated

General form	tabular, pipelike, blanket, irregular, disseminated

Controls for ore emplacement

High angle faults control ore formation.

Comments on the geologic information

Quartz-sericite-pyrite alteration is believed to be associated with emplacement of stocks, particularly those in western Pershing County. The regional anticline trends NNW with the axial plane dipping west. Bedding dips shallowly east, as indicated by epiclastic Weaver units. Both the Weaver and Rochester formations are parts of the Permian-Triassic Koipato group. Quartz-sericite-pyrite alteration is associated with mineralized quartz veins in the deposit and is difficult to distinguish from the regional-type hydrothermal alteration. Au, Ag, Sb, As, Hg, and S concentrations in mineralized Weaver rhyolite increase sharply with degree of alteration. K/Ar dates of the deposit range from 85 to 114 Ma, averaging 99 Ma. At least 3 trends of post-mineral movement have been noted: (1) E-W, dipping steeply N or S; (2) N30W-N50W, Dipping 30-70W, (3) N20W-N20E, 70-80E (Late Miocene Basin and Range).

Economic information about the deposit and operations

Operation type	Surface-Underground
Development status	Producer
Commodity type	Metallic
Deposit size	Large
Significant	Yes
Discovery year	1905
Discoverer	John Nenzel
Year of first production	1912
Production years	1912-1928; 1986-2004

Mining district

District name	Rochester District

Land status

Ownership category	BLM Administrative Area
Area name	WInnnemucca BLM Administrative District

Ownership information

Type Owner-Operator

Owner Coeur-Rochester Mines, Inc, wholly owned subsidiary of Coeur d'Alene Mines Corp.

Year 2004

Type	Owner-Operator
Owner	Coeur-Rochester Mines, Inc, wholly owned subsidiary of Coeur d'Alene Mines Corp.
Year	2004

Comments on the workings information

Earlier mining was underground, especially along 3 long tunnels, but mining has been by open pit methods since 1986.

Comments on other economic factors

Production
The Coeur Rochester mine had record silver and gold production in 1997; a total of 6,690,704 ounces of silver and 90,019 ounces of gold from a record 8.7 million tons of ore. Average gold grade increased, also to 0.0119 ounces per ton, up from 0.010 the previous year.
In 2002, the Coeur Rochester mine produced 6.4 million ounces of silver and 71,905 ounces of gold in 2002. Coeur Rochester Mine reached a major milestone in January 2002 by pouring more than one million ounces of gold and 88 million ounces of silver since commencing production in 1986.
In 2003 the Coeur-Rochester mine in Pershing County remained the state's largest silver producer at just under five and one half million ounces produced in 2003. The Coeur-Rochester mine in Pershing County remains the state?s largest silver producer at 5.7 million ounces in 2005.
Reserves
At the end of 1997, mine reserves stood at 74,216,000 ounces of silver and 603,000 ounces of gold.
Year-end 2000 reserves at Rochester and Nevada Packard combined totaled 54 million tons grading 0.93 ounces of silver per ton and 0.008 ounces of gold per ton, for almost 50 million ounces of silver and 410,000 ounces of gold
2003 reserves at Rochester totaled: 32.7 million tons of ore grading 0.01 ounces of gold per ton, 0.91 ounces of silver per ton in proven and probable reserves as well as 40.3 million tons of mineralized material grading 0.01 opt Au and 0.77 ounces of silver per ton

Comments on development

In 1905 a group of prospects was located on Nenzel Hill which later became Rochester Mines in 1912, one of the largest producers in the district. Early (1912 ) underground mining of the deposit occurred on the East and West veins on the northwest side of Nenzel Hill. Between 1912 and 1913, ore had to average more than 35 ounces of silver per ton to justify shipping costs, but by 1915, ore assaying as low as 8 ounces of silver per ton could be extracted profitably, due to the construction of a cyanide mill and the Nevada Short Line railway. A 12,016 foot tramway was built in 1917 to haul ore from the foot of Nenzel Hill to the mill in Lower Rochester Canyon. Major production ended by 1923, caused by grade and price fluctuations and by litigation. Limited mining continued until 1928. In 1929 it closed down. Approximately $7 million in silver and gold was produced from veins in the Rochester District between 1912 and 1928. The veins are opened in depth by three long adit tunnels. In 1960-69, Silver State Mining Co held the property, and from 1969-1984 ASARCO owned it and drilled 485 holes totalling 160,000 feet. In 1983 Coeur d'Alene mines purchased property and began to operate it as an open pit, heap leach mine in 1986. Relatively uniform grades and simple metallurgy, minimal stripping, and downhill haulage help keep production costs low. 1993 recovery rates averaged 55% of the silver and 80-85% of the gold in heap leach pads. In 1993, the mine employed about 290 people. Weekly dore production averaged 100,000 troy ounces of 98% silver. Concurrent reclamation is being done on some former leach pads and mine dumps. Remaining mine life was 10 years in 1993 but Coeur has been successful in finding additional mineable silver mineralization at both the Rochester mine, and the nearby Nevada Packard property. A total of 61,500 feet were drilled in 161 holes around the margins of the Rochester mine. Calculations are in progress to bring this new mineralization into reserve status. At the end of 1999 the reserve at Rochester was 48.3 million tons averaging 1.09 opt Ag and 0.01 opt Au.
Coeur's Rochester Mine reached a major milestone in the third week of January 2002 by pouring more than one million ounces of gold and 88 million ounces of silver since commencing production in 1986. Mining at the Nevada Packard satellite deposit, just 1.5 miles to the south was to begin early in 2003 with road construction and development of access to the pit underway.
In 2003 Coeur Rochester filed a proposal to include expansion and deepening of the existing Rochester Open Pit, increasing the height of the heap leach pad, new haul roads, and closure/reclamation plans.
The Coeur-Rochester mine in Pershing County remains the state?s largest silver producer at 5.7 million ounces in 2005.

Reference information

Bibliographic references

Deposit

Strusacker, E., (ed.), 1993, Gold and Silver Deposits of Western Nevada: Geological Society of Nevada Special Publication No.18, 1993 Fall Field Trip Guide
Deposit

Schrader, F.C., 1914, The Rochester Mining District, Nevada: USGS Bulletin 580-M
Deposit

Knopf, A., 1924, Geology and Ore Deposits of the Rochester District, Nevada: USGS Bulletin 762, pp.78-81
Deposit

Vikre, P.G., 1977, Geology and Silver Mineralization of the Rochester District, Pershing County, Nevada: Stanford University, Unpublished Phd. Dissertation
Deposit

Vikre, P.G., 1981, Silver Mineralization of the Rochester District, Pershing County, Nevada: Economic Geology, v.76, pp 580-609
Deposit

Johnson, M.G., 1977, Geology and Mineral Deposits of Pershing County, Nevada: NBMG Bulletin 89, Pp.78-80
Deposit

Bonham, H.F. and Hess, R.H., 1993, in, The Nevada Mineral Industry-1992: NBMG Special Publication MI- 1992-2002 p26
Deposit

Tingley, J.V., 1985, Nenzel Hill, NBMG Sample 2645, Pershing County, Rochester District; NBMG Unpublished Mining District (Tingley) Files
Deposit

Nevada Bureau Of Mines And Geology, Mining District Files, Various Clippings, 1983-1985
Deposit

Minsearch Annual, 1984-1985, v. vii, pp 380-384; Metals Economics Group, Boulder, CO
Deposit

Bonham, H.F., Garside, L.J., Jones, R.B., Papke, K.G., Quade, J., Tingley, J.V., 1985, A Mineral Inventory of the Paradise-Denio and Sonoma-Gerlach, Winnemucca BLM District, Nevada: NBMG Open File Report 85-5
Deposit

NBMG, 1994, MI-1993
Deposit

Nevada Division of Minerals, 1994
Deposit

Coeur d'Alene Mines Corp.,1997 Annual Report.
Deposit

Long, K.R., DeYoung, J.H., Jr., and Ludington, S.D., 1998, Database of significant deposits of gold, silver, copper, lead, and zinc in the United States; Part A, Database description and analysis; part B, Digital database: U.S. Geological Survey Open-File Report 98-206, 33 p., one 3.5 inch diskette.
Deposit

Crafford, A.E.J. (ed.), 2003, GSN Road Log 44, Coal Canyon Road East from I-80 Exit 112.
Deposit

Coeur d'Alene Mines Corp, press release, 5/14/02
Deposit

The Mining Record, 8/13/02.
Deposit

Harvey, David, Chadwick, Thomas, and Krewedl, Dieter, 2002, Geology and Mineralization in the Rochester and Nevada Packard Deposits, in Geological Society of Nevada Fall 2002 Field Trip Guidebook, Precious Metals Deposits of the Humboldt Range, New Discoveries in an Old District; GSN Special Publication No. 36.

General comments

Subject category	Comment text
Deposit	Mineralization is distributed within an area of regional quartz-sericite-pyrite alteration of the rhyolitic volcanics of the Permian-Triassic Koipato Group. Two Late Cretaceous intrusive events took place in the Humboldt Range, and K-Ar dates suggest that the silver mineralization was related to one or perhaps both events. Low-grade silver-gold mineralization occurs in two stages in thin, randomly oriented, closely spaced fractures associated with major veins along high-angle faults. The Rochester deposit has some of the characteristics of the adularia-sericite USGS model, but studies show that deposit was probably formed at greater depth (>12,000 feet), temperature (300-400c), and pressure (1kb) than adularia-sericite model. It has a low volume of clay and no evidence of boiling. It is possibly a Mesothermal deposit; richer veins (like east and west veins) are genetically linked with lower grade, higher tonnage ore, but structural differences are reported. Gold grade is expected to rise near the end of the mine life as a high-grade vein is mined near the present tertiary crusher. Most Rochester ore is disseminated in stockworks and siliceous breccia. High-grade, fault-controlled veins provide smaller quantity but richer ore. Veins are replacement, tight (few vugs), closely spaced and often laminar. N-S veins cut E-W veins. Two broad west vein zones and at least 6 separate east vein sets have been identified. Intersections of these zones are excellent hosts, especially when the vein set intersections cut the Weaver/Rochester contact. During early mining (1912-1915), the East and West veins averaged 6 feet in width and carried 12 ounces of silver and 0.100 ounces of gold per ton. Veins narrowed (and some dips flattened) and became lower grade with depth. Model name could also be Comstock epithermal veins. Gold and silver are strongly zoned. The deposit has a silver-rich core, following northeast-trending structures, with a peripheral gold halo. Gold shows a stronger affinity for the Rochester/Weaver contact. Quartz is the most common host mineral. Unoxidized blocks of ore are found throughout the deposit and drilling has shown oxidation continuing to at least 1,000 feet below Nenzel Hill.

Subject category

Comment text

Deposit

Mineralization is distributed within an area of regional quartz-sericite-pyrite alteration of the rhyolitic volcanics of the Permian-Triassic Koipato Group. Two Late Cretaceous intrusive events took place in the Humboldt Range, and K-Ar dates suggest that the silver mineralization was related to one or perhaps both events. Low-grade silver-gold mineralization occurs in two stages in thin, randomly oriented, closely spaced fractures associated with major veins along high-angle faults.
The Rochester deposit has some of the characteristics of the adularia-sericite USGS model, but studies show that deposit was probably formed at greater depth (>12,000 feet), temperature (300-400c), and pressure (1kb) than adularia-sericite model. It has a low volume of clay and no evidence of boiling. It is possibly a Mesothermal deposit; richer veins (like east and west veins) are genetically linked with lower grade, higher tonnage ore, but structural differences are reported. Gold grade is expected to rise near the end of the mine life as a high-grade vein is mined near the present tertiary crusher. Most Rochester ore is disseminated in stockworks and siliceous breccia. High-grade, fault-controlled veins provide smaller quantity but richer ore. Veins are replacement, tight (few vugs), closely spaced and often laminar. N-S veins cut E-W veins. Two broad west vein zones and at least 6 separate east vein sets have been identified. Intersections of these zones are excellent hosts, especially when the vein set intersections cut the Weaver/Rochester contact. During early mining (1912-1915), the East and West veins averaged 6 feet in width and carried 12 ounces of silver and 0.100 ounces of gold per ton. Veins narrowed (and some dips flattened) and became lower grade with depth. Model name could also be Comstock epithermal veins.
Gold and silver are strongly zoned. The deposit has a silver-rich core, following northeast-trending structures, with a peripheral gold halo. Gold shows a stronger affinity for the Rochester/Weaver contact. Quartz is the most common host mineral. Unoxidized blocks of ore are found throughout the deposit and drilling has shown oxidation continuing to at least 1,000 feet below Nenzel Hill.

Reporter information

Type	Date	Name	Affiliation	Comment
Reporter	01-DEC-2006	LaPointe, D. D.	Nevada Bureau 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.

Beyond USGS

Supplemental information added by qvyshift.com. Not part of the original USGS MRDS record.

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