POTENTIAL FOR SIGNIFICANT UNDISCOVERED METALLIC ORE DEPOSITS IN MAINE. John F. Slack U.S. Geological Survey (Emeritus), Farmington, ME 04938

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1 POTENTIAL FOR SIGNIFICANT UNDISCOVERED METALLIC ORE DEPOSITS IN MAINE John F. Slack U.S. Geological Survey (Emeritus), Farmington, ME 098 Geological Society of Maine, Augusta, 7 November 207

2 Outline Important Deposit Types Well Known in Maine Important Deposit Types Minimally Explored in Maine (or in new settings/terranes)

3 2 Important Deposit Types Well Known in Maine. Cu-Zn-Pb-Au-Ag in VMS deposits 2. Mn-Fe in stratiform sedimentary deposits. Cu-Mo in porphyry deposits. Fe-Ni-Cu-Co in mafic/ultramafic plutons. Zn-Pb-Ag-Au in epithermal volcanic deposits 6. Li-Cs-Ta-Be in granitic pegmatites Interactive databases of mineral deposits and occurrences: 6 Maine Geological Survey explore/mining/mrds/mrds.htm U.S. Geological Survey The Diggings me /map Mindat.org

4 Important Deposit Types Well Known in Maine. Cu-Zn-Pb-Au-Ag in VMS deposits Major potential exists for new discoveries of VMS deposits within early Paleozoic volcanic belts of Cambrian to Ordovician age, both in the interior and coastal belts.

5 Well Known in Maine 2 2. Mn-Fe in stratiform sedimentary deposits The Maple-Hovey Mountain area contains the largest known Mn resource in the United States. Use of modern geochemical-genetic models offers the possibility of finding higher grade, and potentially economic, Mn-Fe deposits, within Silurian sedimentary rocks of this area.

6 Important Deposit Types Well Known in Maine. Cu-Mo in porphyry deposits Major potential exists for new discoveries of porphyry Cu-Mo (or Mo only) deposits in middle Paleozoic granitoid plutons in western and northern Maine, and near the coast.

7 Well Known in Maine. Fe-Ni-Cu-Co in mafic/ultramafic plutons Classic orthomagmatic Ni-Cu-Co deposits likely exist west in the Greenville area and Washington County, within diverse mafic intrusions that have known occurrences of these metals, as well as in others that do not.

8 Well Known in Maine. Zn-Pb-Ag-Au in epithermal volcanic deposits Epithermal volcanic-hosted Zn-Pb-Ag-Au deposits in the Pembroke area have not been thoroughly explored and thus potential exists for economic deposits, especially those having elevated Au and/or Ag grades.

9 Well Known in Maine 6. Li-Cs-Ta-Be in granitic pegmatites Metal-rich granitic pegmatites in southwestern Maine have been known for 200 years but no modern and focused exploration for economic Li-Cs-Ta-Be deposits has been done. 6

10 Minimally Explored in Maine (or in new settings/terranes). Cu-Zn-Pb-Au-Ag in VMS deposits (potential Bathurst belt extension based on presence of magnetite iron formation; see Peter and Goodfellow, Can Jour Earth Sci ) Cu-Ni-Co-PGE in gabbroic dikes, sills, and feeder pipes in Moxie-Greenville area (see model: USGS Sci Invest Rept I). PGE in Cr-rich zones of Boil Mountain ophiolite (see model: Prichard and Brough 2009, in book edited by Li and Ripley New Developments in Magmatic Ni-Cu and PGE Deposits Geological Publishing House Beijing). Au in granitoid intrusions (see model: Hart 200, The Gangue [Canadian Inst Mining] 87). REE-Nb-Ta in alkaline/peralkaline intrusions (see model: USGS Sci Invest Rept J) 6. Li in spodumine-rich granitic pegmatites (see model: USGS Sci Invest Rept O)

11 Minimally Explored in Maine (or in new settings/terranes). Cu-Zn-Pb-Au-Ag in VMS deposits (potential Bathurst belt extension based on presence of magnetite iron formation; see Peter and Goodfellow, Can Jour Earth Sci ) The small volcanic belts in eastern Washington County have potential for undiscovered VMS deposits that may be similar to the high-grade polymetallic ores of the Bathurst (N.B.) district, based on the presence of magnetite iron formation within one of these small belts.

12 Minimally Explored in Maine (or in new settings/terranes) 2. Cu-Ni-Co-PGE in gabbroic dikes, sills, and feeder pipes in Moxie-Greenville area (see model: USGS Sci Invest Rept I) 2 Gabbroic intrusions west of Greenville have major potential for significant Ni-Cu-Co- PGE deposits. Detailed exploration in this area is over 0 years old, and far out of date with respect to current genetic models in which extensional dikes, sills, and feeders are prime targets. An analogy is the Eagle deposit in the upper peninsula of Michigan.

Example of genetic model change Simplified geologic map of the Sudbury, Canada, structure showing the locations of major Cu-Ni sulfide deposits.

13 Example of genetic model change Simplified geologic map of the Sudbury, Canada, structure showing the locations of major Cu-Ni sulfide deposits. General acceptance of a magmatic origin for Ni-Cu±PGE sulfide ores at Sudbury led to the model that magmatic sulfide ore bodies form along the base of large, layered mafic intrusions owing to gravitational settling of a dense sulfide liquid segregated from the parental magmas upon emplacement. This led to exploration for magmatic sulfide deposits along the basal contacts of many large, layered maficultramafic intrusions. USGS Sci Invest Rept I

14 Example of genetic model change Conduit model for Ni-Cu+PGE sulfide deposits. Eagle Mine example. Magma-conduit systems provide an ideal environment for segregation of immiscible sulfide liquid entrained in ascending mafic-ultramafic magmas. Changes in flow dynamics along conduit systems can lead to the deposition of sulfide as massive or highly concentrated bodies of sulfide ore. USGS Sci Invest Rept I

15 Minimally Explored in Maine (or in new settings/terranes). PGE in Cr-rich zones of Boil Mountain ophiolite (see model: Prichard and Brough 2009, in book edited by Li and Ripley New Developments in Magmatic Ni-Cu and PGE Deposits Geological Publishing House Beijing) Cr-rich zones of the Boil Mountain ophiolite have potential for undiscovered PGE deposits. In the field, such deposits would be cryptic and difficult to identify without detailed sampling.

16 Minimally Explored in Maine (or in new settings/terranes). Au in granitoid intrusions (see model: Hart 200, The Gangue [Canadian Inst Mining] 87) Potential for intrusion-related Au deposits exists in one or more plutons in Hancock and Washington Counties, and likely in other areas of Maine as well. These deposits are characterized by associated W-Bi-Te-As-Mo-Sb mineralization in veins and/or disseminations.

17 Minimally Explored in Maine (or in new settings/terranes). REE-Nb-Ta in alkaline/peralkaline intrusions (see model: USGS Sci Invest Rept J) Alkaline and peralkaline intrusions in southern Maine, and perhaps elsewhere, could host economic REE-Nb-Ta deposits. These intrusions include both Paleozoic and Mesozoic bodies.

18 Minimally Explored in Maine (or in new settings/terranes) 6. Li in spodumine-rich granitic pegmatites (see model: USGS Sci Invest Rept O) The region of southwestern Maine that contains myriad Li-Cs-Ta-Be pegmatites should be re-explored for large spodumene-rich zones that may be potentially economic. A significant portion (ca. 0%) of the world s Li comes from spodumene in pegmatites, and the predicted huge increase in national and global demand for Li warrants new exploration efforts in this region. 6

19 Summary 2 Maine has significant potential for undiscovered mineral resources in many geologic settings. Maine has not seen serious mineral exploration in almost 0 years. Exploration techniques and genetic models have advanced dramatically in that time. 6 Application of new models and advanced exploration techniques will likely result in new discoveries.

Magmatic Ore Deposits:

Magmatic Ore Deposits: A number of processes that occur during cooling and crystallization of magmatic bodies can lead to the separation and concentration of minerals. 1- Pegmatites 2- Layered intrusions