Maine's Mineral Resources

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Description of Data Views

  • Significant Mineral Commodities - Mining in Maine has a long history unknown to many citizens. Some of us have seen the granite quarries which remain from an industry established more than 150 years ago. Gravel pits are a common sight today, and many people are familiar with Maine's limestone, slate, and crushed stone operations. However, the well-known resources of modern times are but a few of the mineral products that have been produced in Maine. This view gives a general overview of the mineral commodities important to Maine's economic history.

  • Significant Metal Deposits - Prospectors have searched for metals in Maine since the 1800's. During a flurry of excitement in the early 1880's, metal deposits were mined along the coastal volcanic belt from Blue Hill to Lubec. Extensive manganese deposits were delineated during World War II. More intensive exploration from the mid-1970's to early 1990's produced several important discoveries. This view locates nine of the largest known metal deposits in the state.

  • Selected Historical Metal Mines, Pegmatite Quarries, and Stone Quarries - Mining and quarrying have been an integral part of Maine's economy since the 1800's. Over time, changing economic conditions created boom and bust cycles in the demand for different commodities. Witness the Maine granite industry which reached its high point in 1901, with 152 quarries employing at least 3,500 men. However, the development of Portland cement as a building material in the early 1900's, and the depression of the 1930's, dealt Maine's granite industry a blow from which it would never recover. The mines and quarries in this view were selected to give an overview of the activities that were important in Maine's history of mineral production.

  • Maine Mineral Resources Data System - This database was produced by the Maine Geological Survey in 2009. It was derived from the U.S. Geological Survey's Mineral Resources Data System (MRDS). MRDS is a worldwide database of mineral site records with related geologic, commodity, and deposit information. The USGS data were combined with records from the Maine Geological Survey's "Maine Metallic Mineral Deposits Database" and "Maine Mineral Localities Index."

    • Specific Commodities - Commodity-specific queries enable the user to view the geographic distribution of specific commodities or commodity groups. Use the Query tool in the upper right of the map window to select a single commodity or groups of commodities and then show the geographic distribution.
      • Ferrous Metals - chromium, cobalt, iron, manganese, tungsten
      • Base Metals - copper, lead, molybdenum, nickel, tin, zinc
      • Precious Metals - gold, platinum, silver
      • Light Metals - aluminum, beryllium, lithium, titanium
      • Other Metals - antimony, arsenic, bismuth, cesium, iridium, niobium, rhenium, rubidium, sodium, tantalum, tellurium, thorium, uranium, zirconium
      • Minerals - boron-borates, calcium, clay, corundum, emery, feldspar, fluorite, garnet, gemstone, graphite, kyanite, magnesite, mica, perlite, phosphorus-phosphates, quartz, silica, sulfur
      • Stone - crushed stone, dimension stone, granite, limestone, slate
    • About the data
      • Data Sources - The Maine Mineral Resources Data System is derived from three separate databases:
        • Data records/location coordinates - shapefile for Maine downloaded from the U.S. Geological Survey's MRDS website.
        • Data records/location coordinates - shapefile created from the "Maine Metallic Mineral Deposits Database" (created for the Maine Geological Survey by F. M. Beck, Inc. in 1999).
        • Location coordinates - shapefile created for the following publication: Thompson, W. B., Wintringham, N. A., and King, V. T., 2000, Maine mineral locality index, in King, V. T. (editor), Mineralogy of Maine; Volume 2: Mining history, gems, and geology: Maine Geological Survey, p. 355-426.
      • Data Modifications - The three data sources listed above were combined and modified as follows:
        • Database Content - Sand and gravel operations are not included in the Maine Mineral Resources System database. All sand and gravel operations were deleted from the USGS MRDS database at the start of the project.
        • Location Coordinates - All coordinates for the original data were projected to WGS84. Corrections to location coordinates were determined as follows: Coordinates with the highest degree of confidence were contained in Thompson and others (2000) and Beck (1999). USGS MRDS locations were corrected to use coordinates from Thompson where possible, coordinates from Beck if Thompson did not exist, and the original USGS coordinates if neither of the previous were available. Other locations were corrected using original source materials where MRDS coordinates did not match the town/county location listed in the database.
        • Duplicate Records - Duplicate records were identified and deleted using comparison of locality name, synonym, geographic proximity, commodity listings, and reference to original source material when necessary.
        • Consolidation of Database Fields - Fields from Beck (1999) were correlated with USGS MRDS fields and renamed with common field names.
        • Merging of Records - The USGS MRDS data was merged with the Thompson and F.M. Beck databases to create the final master database. Data for localities with multiple records were combined into a single record using the record with the most accurate coordinates.
        • Additional Database Fields - Town, county, and quadrangle fields were added. Fields for record source, record comment, location source, and location comment were added.
    • Annotated List of Maine MRDS Database Fields

      Site identification
        OBJECTID Unique record number.
        MGS_RECNO Unique Maine MRDS record number.
        RECORD_SOURCE Source of data record - either U.S. Geological Survey MRDS record, Maine Geological Survey Maine Metallic Mineral Deposits Database, or combination of both.
        RECORD_COMMENT Comment describing source of combined records.
        DEP_ID A unique 12-digit system generated sequence number which references records of information pertaining to a mineral property
        MRDS_ID Identification number used to refer to this entry in the Mineral Resources Data System, if the record appeared in that database.
        MAS_ID Identification number for this site as it appeared in the Mineral Availability System/Mineral Industry Locator System database.
        RECNO A unique code which references records of the Maine Metallic Mineral Deposits Database.
        NAME Current name of the site, deposit, or operation to which the record refers.
        SYNONYM Alternative names of the site, deposit, or operation to which the record refers.

      Geographic location
        TOWN Name of the town in which the site is located
        COUNTY Name of the county in which the site is located
        QUAD_7_5 Name of the 7.5-minute USGS quadrangle in which the site is located
        LOCAT_SOURCE Source of the location coordinates: (1) U.S. Geological Survey MRDS; (2) Maine Geological Survey - Maine Metallic Mineral Deposits Database; (3) Thompson, W. B., Wintringham, N. A., and King, V. T., 2000, Maine mineral locality index, in King, V. T. (editor), Mineralogy of Maine; Vol. 2: Mining history, gems, and geology: Maine Geological Survey, p. 355-426.
        LOCAT_COMM Comment indicating how location was corrected.
        LOCAT_ACC Accuracy of the location in meters where known.
        WGS84_LAT Geographic latitude of the site (WGS84 datum)
        WGS84_LONG Geographic longitude of the site (WGS84 datum)

        COM_TYPE Type of commodities present: metallic (M), non-metallic (N), or both (B)
        COM_ALPHA Alphabetical list of commodities present.
        COM_MAJOR Major commodities present, a comma-separated list.
        COM_MINOR Minor commodities present, a comma-separated list.
        COM_TRACE Trace commodities present, a comma-separated list.

      Site characteristics
        DEV_STAT Status of development of the resource or operation.
        OPER_TYPE Type of operation existing or proposed at the site.
        WORK_TYPE General type of workings at the site.
        PROD_SIZE A broad characterization of the magnitude of production at the site.
        ORE_MAT Name of the ore mineral or material found in this deposit.
        HROCK_TYPE Controlled term(s) indicating the type of host rocks, taken from Lithclass 6.2
        DEP_TYPE_USGS General type of deposit or resource present at the site.
        MODEL Mineral deposit models that characterize the site.
        REPORTER Names of the persons primarily responsible for entering information about the site.
        REFERENCE Bibliographic references providing information supporting the database record.

      Site characteristics - Maine Metallic Mineral Deposits Database only (limited number of records)
        COM_CLS Commodity classification, from an MRDS list - Base metal, Precious metal, Other metal, Fe(Mn), etc..
        DEP_SIZE MRDS has specific definitions for Small, Medium, and Large deposit size for different commodities. These were not useful. A general field indicating relative importance of a deposit.
        REV_DEP_TYPE General type of deposit or resource present at the site, revised from USGS MRDS type by F.M. Beck.
        MODEL_NUM Model number assigned by F.M. Beck, Inc. from Cox, D. P., and Singer, D. A. (editors), Mineral deposit models: U.S. Geological Survey, Bulletin 1693, 379 p.
        WORKINGS Description of workings.
        REP_AFF Reporter affinity.
        REP_DATE Report date.
        UPDATER Record update author.
        UPDATE_DATE Date of update.
        INFO_SOURCE Source of information for record.
        STATUS_TEXT Status of locality - occurrence, active prospect, producer, etc.
        OTHER_RECS If a common name is assigned to a group of deposits, such as the Blue Hill District, or Aroostook Co. Manganese deposits, it is indicated here.
        GEOL_COMM Geologic comments entered by F.M. Beck, Inc.
        COMMENTS General comments.

    • Download the data - Maine MRDS data is available as a data file (CSV 1.0 MB).
  • Occurrences of Critical Minerals - Localities in the Maine Mineral Resources Data System at which commodities have been reported that are on the 2022 USGS Critical Minerals list. Critical Minerals are commodities considered to be critical to the economic and national security of the United States. Most reported occurrences are small and have not been investigated.

  • Critical Minerals Project Citations - Point locations of critical minerals literature search results. These were compiled between 2019-2021 as part of a USGS Earth MRI grant to identify mineral deposits that are important to the nation's infrastructure.


Geologists or others who use this database should note any discrepancies or necessary changes and report problems to the Maine Geological Survey.