Rochester

Site Name

Primary: Rochester
Secondary: Coeur Rochester
Secondary: Nenzel Hill
Secondary: NBMG Sample Site 2645

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Commodity

Primary: Silver
Primary: Gold
Secondary: Antimony
Secondary: Copper
Secondary: Lead
Secondary: Zinc

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Location

State: Nevada
County: Pershing
District: Rochester

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Land Status

Administrative Organization: Blm Winnemucca District

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Holdings

Not available

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Workings

Not available

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Ownership

Owner Name: Coeur-Rochester Mines, Inc.
Home Office: P.O. Box 1057, Lovelock, Nv 89419

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Producer
Operation Type: Unknown
Year First Production: 1912
Year Last Production: 1993
Discovery Year: 1905
Discovery Method: Ore-Mineral Not In Place
Years of Production:
Organization:
Significant: N
Deposit Size: L

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Physiography

General Physiographic Area: Intermontane Plateaus
Physiographic Province: Basin And Range Province
Physiographic Section: Great Basin
Physiographic Detail: Basin And Mountains

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Mineral Deposit Model

Model Name: Low-sulfide Au-quartz vein

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Orebody

Name: WEST VEIN SET

Name: EAST VEIN SET

Name: WEAVER/ROCHESTER CONTACT

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Structure

Type: R
Description: Broad, Asymmetrical Anticlinal Arch

Type: L
Description: 2 Major Normal Fault Systems; Post Mineral Faults

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Alterations

Alteration Type: L
Alteration Text: Silicification, Oxidation

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Rocks

Not available

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Analytical Data

Analytical Data: 200-300 PPM AS
Analytical Data: 80-100 PPM CU
Analytical Data: 500-700 PPM ZN
Analytical Data: 1: 800-1000 PPM PB
Analytical Data: 200 PPM ZN
Analytical Data: 10 PPM V
Analytical Data: 100 PPM SB
Analytical Data: 2000 PPM PB
Analytical Data: 100 PPM CU
Analytical Data: 1.5 PPM BE
Analytical Data: 70 PPM BA
Analytical Data: 20 PPM B
Analytical Data: 0.65 PPM AU (BY AA ANALYSIS)
Analytical Data: 1500 PPM AS
Analytical Data: 0.005% TI
Analytical Data: 0.025 MG
Analytical Data: APPROX. 50 PPM SB 2: 1% FE

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Materials

Ore: Acanthite
Ore: Chlorargyrite
Ore: Anglesite
Ore: Owyheeite
Ore: Pyrite
Ore: Embolite
Ore: Sphalerite
Ore: Galena
Ore: Stromeyerite
Ore: Polybasite
Ore: Pyrargyrite
Ore: Chalcopyrite
Ore: Argentite
Ore: Silver
Ore: Melanterite
Ore: Chalcanthite
Ore: Pyrrhotite
Ore: Electrum
Ore: Chalcocite
Ore: Covellite
Gangue: Goethite
Gangue: Quartz
Gangue: Hematite
Gangue: Limonite
Gangue: Sericite

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Comments

Comment (Development): EARLY (1912 ) UNDERGROUND MINING OF THE DEPOSIT OCCURRED ON THE EAST AND WEST VEINS ON NW SIDE OF NENZEL HILL. BETWEEN 1912 AND 1913, ORE AVERAGING <35 OZ/TON COULD NOT BE PROFITABLY MINED DUE TO SHIPPING COSTS. BY 1915, ORE ASSAYING AS LOW AS 8 OZ/TON COULD BE EXTRACTED PROFITABLY DUE TO CONSTRUCTION OF A CYANIDE MILL AND THE NEVADA SHORT LINE RAILWAY. A 12,016 FT. TRAMWAY WAS BUILT IN 1917 TO HAUL ORE FROM THE FOOT OF NENZEL HILL TO THE MILL IN LOWER ROCHESTER CANYON. THE 72 BUCKETS EACH HELD 600 LBS OF ORE, REDUCING THE COST OF DELIVERING ORE TO THE MILL TO $0.17/TON. MAJOR PRODUCTION ENDED BY 1923, CAUSED BY GRADE AND PRICE FLUCTUATIONS AND BY LITIGATION. LIMITED MINING CONTINUED UNTIL 1928. OWNERSHIP/LEASEES: 1960-69 SILVER STATE MINING CO.; 1969-1984 ASARCO DRILLED 485 HOLES (160,000 FT.); 1983 COEUR D'ARLENE MINES PURCHASED PROPERTY. ; TOTAL$: >$44 MILLION ; ECON.COM: COEUR ROCHESTER IS AN OPEN PIT, HEAP LEACH MINE. RELATIVELY UNIFORM GRADES AND SIMPLE METALLURGY, MINIMAL

Comment (Development): STRIPPING, AND DOWNHILL HAULAGE HELP KEEP PRODUCTION COSTS LOW. 1993 RECOVERY RATES AVERAGE 55% OF THE AG AND 80-85% OF THE AU IN HEAP LEACH PADS. IN 1993, THE MINE EMPLOYED ABOUT 290 PEOPLE. WEEKLY DORE PRODUCTION AVERAGES 100,000 TROY OZ (98% AG, 1% AU, 1% MISC. IMPURITIES). RELATIVELY UNIFORM GRADE AND SIMPLE METALLURGY, MINIMAL STRPPING, AND DOWNHILL HAULAGE HELP KEEP PRODUCTION COSTS LOW. 1993 CUT OFF GRADE IS 1.4 PER TON AG EQUIVALENT, WITH A STRIP RATIO OF 2.0:1. REMAINING MINE LIFE IS 10 YEARS IN 1993 (STRUHSACKER, 1993).

Comment (Location): LOCATION IS TO ADMINISTRATIVE BUILDING AT MINE SITE. LATITUDE AND LONGITUDE PROVIDED BY KURT CATO, MINE GEOLOGIST

Comment (Commodity): SEE VIKRE (1981, FIG 6) FOR PARAGENETIC SEQUENCE. GOLD AND SILVER ARE STRONGLY ZONED. AG-RICH CORE (FOLLOWING NE STRUCTURES) WITH PERIPHERAL AU HALO. AU SHOWS STRONGER AFFINITY FOR 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 FT. BELOW NENZEL HILL.

Comment (Reserve-Resource): 1985 TONNAGE ESTIMATES WERE INCREASED FROM 88 MILLION ST TO 112.5 MILLION ST AG-AU ORE BASED ON 1984 DRILLING PROGRAM WHICH WAS EXTENDED TO THE SOUTH WHERE THE MINERALIZATION REMAINED OPEN.

Comment (Production): JOHNSON (1977, P.80) GIVES A YEAR BY YEAR PRODUCTION TABLE FOR 1912-1929, 1931-1951, 1953-1966. FIGURES FROM JOHNSON ARE FOR ENTIRE ROCHESTER DISTRICT, BUT MOST OF PRODUCTION CAME FROM ROCHESTER MINE (PRODUCTION FIGURES FOR PLACER AU NOT GIVEN HERE BECAUSE ROCHESTER MINE IS NOT A PLACER DEPOSIT). "HISTORICALLY, THE DISTRICT PRODUCED 8,769,000 OUNCES OF AG AND 81,343 OUNCES OF AU AND IS SECOND ONLY TO THE COMSTOCK DEPOSIT IN AG PRODUCTION," (STRUHSACKER, 1993).

Comment (Geology): REGIONAL 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 W. BEDDING DIPS SHALLOWLY E, AS INDICATED BY EPICLASTIC WEAVER UNITS. BOTHE WEAVER AND ROCHESTER FORMATIONS ARE PARTS OF THE PERMIAN-TRIASSIC KIOPATO 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," (STRUSACKER). "AU, AG, SB, AS, HG, AND S CONCENTRATIONS IN MINERALIZED WEAVER RHYOLITE INCREASE SHARPLY WITH DEGREE OF ALTERATION" (VIKRE, 1981) K/AR DATES OF THE DEPOSIT RANGE FROM 85 TO 114 MY, AVERAGING 99 MY. 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?)

Comment (Deposit): ROCHESTER DEPOSIT HAS SOME OF THE CHARACTERISTICS OF ADULARIA-SERICITE MODEL, BUT STUDIES BY VIKRE AND MINE STAFF SHOW THAT DEPOSIT WAS PROBABLY FORMED AT GREATER DEPTH (>12,000 FT?), TEMPERATURE (300-400C), AND PRESSURE (1KB) THAN ADULARIA-SERICITE MODEL . LOW VOLUME OF CLAYS. NO EVIDENCE OF BOILING. MESOTHERMAL DEPOSIT? VIKRE (1981) GENETICALLY LINKS RICHER VEINS (LIKE EAST AND WEST VEINS) WITH LOWER GRADE, HIGHER TONNAGE ORE, BUT REPORTS STRUCTURAL DIFFERENCES. ROCHESTER DEPOSIT IS OXIDIZED THROUGH TO ITS KNOWN BOTTOM. EAST AND WEST VEINS AVERAGE 8 OZ AG AND 0.1 OZ AU/TON; THE ENTIRE ROCHESTEREPOSIT AVERAGES 1.5 OZ AG AND 0.011 OZ AU/TON (1993). AU GRADE IS EXPECTED TO RISE TO 0.02-0.025 NEAR THE END OF THE MINE LIFE AS A HIGH-GRADE VEIN IS MINED NE AR THE PRESENT TERTIARY CRUSHER. MOST ROCHESTER ORE IS DISSEMINATED IN STOCKWORK AND SILICEOUS BRECCIA. HIGH-GRADE, FAULT-CONTROLLED VEINS PROVIDE SMALLER QUANTITY BUT RICHER ORE. VEINS ARE REPLACEMENT, TIGHT (FEW VUGS), CLOSELY

Comment (Deposit): 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. INTESECTIONS OF THESE ZONES ARE EXCELLENT HOSTS. WHEN THE VEIN SET INTERSECTIONS CUT THE WEAVER/ROCHESTER CONTACT, ORE DEVELOPMENT IS FUTHER ENHANCED. DURING EARLY MINING (1912-1915), THE EAST AND WEST VEINS AVERAGED 6 FT. IN WIDTH AND CARRIED 12 OZ AG AND 0.100 OZ AU/TON. VEINS NARROWED (AND SOME DIPS FLATTENED) AND BECAME LOWER GRADE WITH DEPTH (VIKRE, 1981).; MODEL NAME COULD ALSO BE: COMSTOCK EPITHERMAL VEINS.

Comment (Workings): 1986 TO PRESENT-OPEN PIT. EARLIER MINING ON EAST AND WEST VEINS CREATED 3 LONG TUNNELS: PITT, FRIEDMAN, AND CROWN POINT LEVELS, SHOWN IN FIG 5 OF VIKRE, 1981.

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References

Reference (Deposit): NEVADA BUREAU OF MINES AND GEOLOGY, MINING DISTRICT FILES, VARIOUS CLIPPINGS, 1983-1985

Reference (Deposit): MINSEARCH ANNUAL, 1984-1985, V. VII, PP 380-384; METALS ECONOMICS GROUP, BOULDER, CO

Reference (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 DISTRICT, NEVADA: NBMG OPEN FILE REPORT 85-5

Reference (Deposit): NBMG, 1994, MI-1993

Reference (Deposit): NEVADA DIVISION OF MINERALS, 1994

Reference (Production): JOHNSON (1977, P.80); BONHAM AND HESS (1993, P.26) MI-1993

Reference (Reserve-Resource): MI-1993

Reference (Analytical Data): 1: ORAL PRESENTATION DURING ROCHESTER MINE TOUR, GSN, 25 SEPT/93 2: DATA FRO M NBMG SAMPLE 2645

Reference (Deposit): STRUSACKER, E., (ED.), 1993, GOLD AND SILVER DEPOSITSF WESTERN NEVADA: GEOLOGICAL SOCIETY OF NEVADA SPECIAL PUBLICATION NO.18, 1993 FALL FIELD TRIP GUIDE

Reference (Deposit): SCHRADER, F.C., 1914, THE ROCHESTER MINING DISTRICT, NEVADA: USGS BULLETIN 580-M

Reference (Deposit): KNOPF, A., 1924, GEOLOGY AND ORE DEPOSITS OF THE ROCHESTER DISTRICT, NEVADA: USGS BULLETIN 762, PP.78-81

Reference (Deposit): VIKRE, P.G., 1977, GEOLOGY AND SILVER MINERALIZATION OF THE ROCHESTER DISTRICT, PERSHING COUNTY, NEVADA: STANFORD UNIVERSITY, UNPUBLISHED PHD. DISSERTATION

Reference (Deposit): VIKRE, P.G., 1981, SILVER MINERALIZATION OF THE ROCHESTER DISTRICT, PERSHING COUNTY, NEVADA: ECONOMIC GEOLOGY, V.76, PP 580-609

Reference (Deposit): JOHNSON, M.G., 1977, GEOLOGY AND MINERAL DEPOSITS OF PERSHING COUNTY, NEVADA: NBMG BULLETIN 89, PP.78-80

Reference (Deposit): BONHAM, H.F. AND HESS, R.H., 1993, IN, THE NEVADA MINERAL INDUSTRY-1992: NBMG SPECIAL PUBLICATION MI-1992, P26

Reference (Deposit): TINGLEY, J.V., 1985, NENZEL HILL, NBMG SAMPLE 2645, PERSHING COUNTY, ROCHESTER DISTRICT; NBMG UNPUBLISHED MINING DISTRICT (TINGLEY) FILES

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Nevada Gold

Nevada has a total of 368 distinct gold districts. Of the of those, just 36 are major producers with production and/or reserves of over 1,000,000 ounces, 49 have production and/or reserves of over 100,000 ounces, with the rest having less than 100,000 ounces. Read more: Gold Districts of Nevada.