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Bald Mountain

Prospect in Aroostook county in Maine, United States with commodities Copper, Gold, Silver, Zinc, Arsenic
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Sections on this page
  1. Identification information
  2. Geographic coordinates
  3. Site location context
  4. Geographic areas
  5. Commodities
  6. Materials information
  7. Alteration
  8. Mineral occurrence model information
  9. Host and associated rocks
  10. Nearby scientific data
  11. Economic information about the deposit and operations
  12. Reserves and resources
  13. Links to other databases
  14. Bibliographic references
  15. General comments
  16. Reporter information

Geologic information

Identification information

Deposit ID 10084601
MRDS ID W102003
Record type Site
Current site name Bald Mountain
Alternate or previous names Bald Mt.

Geographic coordinates

Geographic coordinates: -68.74477, 46.73457 (WGS84)

Site location context

Political divisions (FIPS codes)

Aroostook(county)

Maine(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Greenlaw Pond(quadrangle 1:24,000 scale)

Presque Isle(quadrangle 1:100,000 scale)

Presque Isle(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Fish River(hydrologic unit)

St. John(hydrologic accounting unit)

St. John(hydrologic subregion)

New England(hydrologic region)

Geographic areas

Country State County
United States Maine Aroostook

Comments on the location information

  • LOCATED IN NE QUARTER OF T12R8, ON W SLOPE OF NO NAME RIDGE, TO N OF BALD MTN, TO S OF BISHOP MTN. DEPOSIT IS ON E SIDE OF CARR POND ROAD. ACCURATE TO 100 m. Deposit is about 24 km west of Ashland, Maine.

Commodities

Commodity Importance
Copper Primary
Gold Primary
Silver Primary
Zinc Critical Primary
Arsenic Critical Secondary

Materials information

Materials Type of material
Chalcopyrite Ore
Sphalerite Ore
Pyrrhotite Ore
Arsenopyrite Ore
Galena Ore
Quartz Gangue
Magnetite Gangue
Hematite Gangue
Siderite Gangue

Alteration

  • (Local) Prehnite-Pumpellyite Metamorphism

Mineral occurrence model information

Model code 184
USGS model code 28a
Deposit model name Massive sulfide, kuroko
Mark3 model number 93

Host and associated rocks

  • Host or associated Host
    Rock type Metamorphic Rock > Metavolcanic Rock
    Rock unit name Winterville Formation
    Rock description Winterville Formation
    Stratigraphic age (youngest) Ordovician

Nearby scientific data

(1) -68.74477, 46.73457
ListMap

Economic information

Comments on the geologic information

  • The Bald Mountain Cu-Zn-Au-Ag volcanogenic massive sulfide deposit occurs in marine metavolcanic rocks of the Ordovician Winterville Formation. Massive sulfides are localized in an unusual bowl-shaped depression having a width of about 370 m by 275 m. Footwall rocks are rhyolitic lapilli tuff and underlying pillowed to hyaloclastic basalts. The hanging wall sequence includes a thick chert until up to 28 m thick, generally hematitic, that directly overlies the deposit. A feeder zone consists of quartz-sulfide veins surrounded by chlorite- and locally sericite-rich volcanic rocks (Slack et al., 2002).

Economic information about the deposit and operations

Development status Prospect
Commodity type Metallic
Deposit size Large
Significant Yes

Reserves and resources

  • Type In-situ
    Estimate year 1993
    Total resources 22000000mt ore
    Commodity Subtype Grade units Group Importance Year
    Copper 1.6 wt-pct Copper Major 1993
  • Type In-situ
    Estimate year 1993
    Total resources 13000000mt ore
    Commodity Subtype Grade units Group Importance Year
    Zinc 2.3 wt-pct Zinc Major 1993
  • Type In-situ
    Estimate year 1996
    Total resources 32000000mt ore
  • Type In-situ
    Estimate year 1996
    Total resources 1100000mt ore
    Commodity Subtype Grade units Group Importance Year
    Gold 4.1 g/mt Gold Major 1996
    Silver 91 g/mt Silver Major 1996
  • Type In-situ
    Estimate year 2004
    Reserves 1350000mt ore
    Commodity Subtype Grade units Group Importance Year
    Copper gossan 0.13 wt-pct Copper Major 2004
    Gold gossan 3.74 g/mt Gold Major 2004
    Silver gossan 84.7 g/mt Silver Major 2004
    Zinc gossan 0.05 wt-pct Zinc Major 2004
    Arsenic gossan 0.74 wt-pct Arsenic Minor 2004
  • Type In-situ
    Estimate year 2004
    Reserves 2350000mt ore
    Commodity Subtype Grade units Group Importance Year
    Copper supergene 2.78 wt-pct Copper Major 2004
    Gold supergene 0.75 g/mt Gold Major 2004
    Silver supergene 14.1 g/mt Silver Major 2004
    Zinc supergene 0.53 wt-pct Zinc Major 2004
    Arsenic supergene 1.06 wt-pct Arsenic Minor 2004
  • Type In-situ
    Estimate year 2004
    Reserves 11980000mt ore
    Commodity Subtype Grade units Group Importance Year
    Copper Zn-rich pyrite 0.34 wt-pct Copper Major 2004
    Gold Zn-rich pyrite 0.86 g/mt Gold Major 2004
    Silver Zn-rich pyrite 23.7 g/mt Silver Major 2004
    Zinc Zn-rich pyrite 2.33 wt-pct Zinc Major 2004
    Arsenic Zn-rich pyrite 0.72 wt-pct Arsenic Minor 2004
  • Type In-situ
    Estimate year 2004
    Reserves 13610000mt ore
    Commodity Subtype Grade units Group Importance Year
    Copper Cu-rich pyrite 1.42 wt-pct Copper Major 2004
    Gold Cu-rich pyrite 0.31 g/mt Gold Major 2004
    Silver Cu-rich pyrite 8.6 g/mt Silver Major 2004
    Zinc Cu-rich pyrite 0.34 wt-pct Zinc Major 2004
    Arsenic Cu-rich pyrite 0.26 wt-pct Arsenic Minor 2004
  • Type In-situ
    Estimate year 2004
    Reserves 3610000mt ore
    Commodity Subtype Grade units Group Importance Year
    Copper Cu-rich pyrrhot 1.71 wt-pct Copper Major 2004
    Gold Cu-rich pyrrhot 0.14 g/mt Gold Major 2004
    Silver Cu-rich pyrrhot 6.9 g/mt Silver Major 2004
    Zinc Cu-rich pyrrhot 0.24 wt-pct Zinc Major 2004
    Arsenic Cu-rich pyrrhot 0.11 wt-pct Arsenic Minor 2004
  • Type In-situ
    Estimate year 2004
    Reserves 780000mt ore
    Commodity Subtype Grade units Group Importance Year
    Copper footwall Cu 1.81 wt-pct Copper Major 2004
    Gold footwall Cu 0.07 g/mt Gold Major 2004
    Silver footwall Cu 5.8 g/mt Silver Major 2004
    Zinc footwall Cu 0.08 wt-pct Zinc Major 2004
    Arsenic footwall Cu 0.03 wt-pct Arsenic Minor 2004
  • Type In-situ
    Estimate year 2004
    Reserves 29980000mt ore
    Commodity Subtype Grade units Group Importance Year
    Copper total hypogene 1.03 wt-pct Copper Major 2004
    Gold total hypogene 0.51 g/mt Gold Major 2004
    Silver total hypogene 14.4 g/mt Silver Major 2004
    Zinc total hypogene 1.12 wt-pct Zinc Major 2004
    Arsenic total hypogene 0.42 wt-pct Arsenic Minor 2004

Comments on the reserve resource information

  • Reserves given for 1993 are for the 1.1 million ton gossan with gold and silver overlying 32 million tons of base metal sulfides (copper, zinc, gold and silver). The base-metal geologic reserve is somewhat misleading in that a variety of lower tonnage/higher grade combinations are possible (Beck, 1993). Reserves given for 1996 are from USGS (1999).
  • Geologic reserves for 2004 and grade are from Slack et al. (2004). Reserves are undiluted with no grade cutoffs.

Comments on the workings information

  • 153+ Mineral Exploration Holes Drilled; 200+ 6-Inch Core Holes For Metallurgical Studies; 100+ Exploration Holes Drilled In Surrounding Areas; In Addition, Many Holes Drilled For Monitoring and Baseline Studies. Permitting In Progress By Blackhawk, 199

Comments on development

  • 153+ MINERAL EXPLORATION HOLES DRILLED; 200+ 6-INCH CORE HOLES FOR METALLURGICAL STUDIES; 100+ EXPLORATION HOLES DRILLED IN SURROUNDING AREAS; IN ADDITION, MANY HOLES DRILLED FOR MONITORING AND BASELINE STUDIES. PERMITTING PURSUED BY NNM RESOURCES, INC., A WHOLLY OWNED SUBSIDIARY OF BLACK HAWK MINING INC. UNTIL 1998.
  • The deposit was discovered in 1977 using soil geochemical methods. It has been extensively drilled by four companies and until 1999 was under detailed review for a production decision. At the end of 1999 Black Hawk Mining Inc., withdrew its permit application to open a gold an silver mine, stating its intent to pursue this project if world prices improved.

Reference information

Bibliographic references

General comments

Subject category Comment text
Deposit Slack et al. (2002) recognized five major stages of mineralization. Stage I comprises exhalative fine-grained pyrite +/- sphalerite +/-arsenopyrite +/- galena +/- boulangerite +/- pyrrhotite in a gangue of quartz +/- greenalite +/- Fe-oxyhydroxide +/- minnesotaite, which was deposited in chimneys and mounds.. The hangingwall chert formed shortly after, mainly by exhalative precipitation but locally by replacement of rhyolite tuff. Stage II massive pyrrhotite +/- chalcopyrite formed by subseafloor replacement of Stage I sulfide. Stage III consists of volumetrically minor quartz +/- chalcopyrite veins that cut and replace the older stages, the irregular nature of these veins suggesting emplacement into unconsolidated sulfide. Stage IV comprises coarse-grained pyrite +/- chalcopyrite +/- magnetite +/- quartz +/- siderite veins and replacements. Stage V consists of minor siderite +/- quartz +/- magnetite +/- hematite +/- sulfide veins.
Deposit About 30-40 volume % of exhalative Stage I sulfide deposits were replaced in the subsurface by Stage II - V, reflecting processes that were likely facilitated by formation of the thick hangingwall chert that acted as a thermal and chemical seal to the evolving hydrothermal system. Variations in mineral assemblages (pyrite-pyrrhotite; magnetite-hematite) and sphalerite compositions (about 2 to 22 mol % FeS) record fluctuations in sulfur and oxygen fugacity during seafloor and subseafloor mineralization (Slack et al., 2002).

Reporter information

Type Date Name Affiliation Comment
Reporter 01-JAN-1983 Whitlow, S. U.S. Geological Survey
Updater 01-OCT-1998 Beck, F.M. Maine Geological Survey
Editor 07-JAN-2004 Woodruff, Laurel G. U.S. Geological Survey Work done in Filemaker

Beyond USGS

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

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