Browsing by Author "Hocker, Stephanie M"

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    Electron Microprobe Analysis of Alteration Mineralogy at the Archean Five Mile Lake Volcanic Associated Massive Sulfide Mineral Prospect in the Vermilion District of Northeastern Minnesota
    (University of Minnesota Duluth, 2003-05) Hocker, Stephanie M; Hudak, George J; Heine, John J
    Alteration mineral assemblage mapping at the Five Mile Lake Prospect in the Vermilion District of northeastern Minnesota has identified two distinct types of alteration zones within 2.7 billion year-old volcanic and volcaniclastic rocks associated with volcanic-hosted massive sulfide (VHMS) mineralization (Hudak et al., in press; Odette et al., 2001a, 2001b; Peterson, 2001). Regional semi-conformable alteration zones are composed of various proportions of quartz + epidote ± amphibole ± chlorite ± plagioclase feldspar. These regional, semiconformable alteration zones are locally crosscut by several relatively narrow, northeasttrending disconformable alteration zones composed of fine-grained chlorite and/or sericite that are closely associated with synvolcanic fault zones. Electron microprobe analyses of the various alteration mineral phases (epidote group minerals, chlorite, amphibole, white mica, and feldspar) have been conducted in an effort to better understand the hydrothermal processes associated with the development of the semiconformable and disconformable alteration zones at the Five Mile Lake Prospect. These analyses indicate that: a) epidote group minerals range in composition from zoisite/clinozoisite to pistacite; b) chlorite is dominantly ripidolite; c) amphibole is primarily actinolite and ferroactinolite, with magnesio-hornblende and ferro-hornblende also present; d) sericite is finegrained muscovite; and e) feldspar is albite. This mineral chemistry suggests the presence of a complex, long-lived hydrothermal system that evolved from seafloor-proximal (hundreds of meters) to deeper subseafloor environments (~1-3 km) as the volcanic rocks were buried by rapid, dominantly effusive mafic to intermediate volcanism and associated sedimentation. Alteration mineral chemistry at the Five Mile Lake Prospect is remarkably similar to that from the Noranda VHMS mining camp of Canada as well as other VHMS orebodies. This mineral chemistry, combined with favorable volcanology and numerous untested geophysical targets, suggest that the Five Mile Lake Prospect, as well as the uppermost several hundred meters of the Lower Member of the Ely Greenstone, have excellent exploration potential for VHMS mineral deposits.
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    Electron Microprobe Analysis of Alteration Mineralogy at the Archean Five Mile Lake Volcanic Associated Massive Sulfide Mineral Prospect in the Vermilion District of Northeastern Minnesota
    (University of Minnesota Duluth, 2003-05) Hocker, Stephanie M; Hudak, George J; Heine, John J
    Alteration mineral assemblage mapping at the Five Mile Lake Prospect in the Vermilion District of northeastern Minnesota has identified two distinct types of alteration zones within 2.7 billion year-old volcanic and volcaniclastic rocks associated with volcanic-hosted massive sulfide (VHMS) mineralization (Hudak et al., in press; Odette et al., 2001a, 2001b; Peterson, 2001). Regional semi-conformable alteration zones are composed of various proportions of quartz + epidote ± amphibole ± chlorite ± plagioclase feldspar. These regional, semiconformable alteration zones are locally crosscut by several relatively narrow, northeast trending disconformable alteration zones composed of fine-grained chlorite and/or sericite that are closely associated with synvolcanic fault zones. Electron microprobe analyses of the various alteration mineral phases (epidote group minerals, chlorite, amphibole, white mica, and feldspar) have been conducted in an effort to better understand the hydrothermal processes associated with the development of the semiconformable and disconformable alteration zones at the Five Mile Lake Prospect. These analyses indicate that: a) epidote group minerals range in composition from oisite/clinozoisite to pistacite; b) chlorite is dominantly ripidolite; c) amphibole is primarily actinolite and ferroactinolite, with magnesio-hornblende and ferro-hornblende also present; d) sericite is finegrained muscovite; and e) feldspar is albite. This mineral chemistry suggests the presence of a complex, long-lived hydrothermal system that evolved from seafloor-proximal (hundreds of meters) to deeper subseafloor environments (~1-3 km) as the volcanic rocks were buried by rapid, dominantly effusive mafic to intermediate volcanism and associated sedimentation. Alteration mineral chemistry at the Five Mile Lake Prospect is remarkably similar to that from the Noranda VHMS mining camp of Canada as well as other VHMS orebodies. This mineral chemistry, combined with favorable volcanology and numerous untested geophysical targets, suggest that the Five Mile Lake Prospect, as well as the uppermost several hundred meters of the Lower Member of the Ely Greenstone, have excellent exploration potential for VHMS mineral deposits.
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    Geological Mapping of the Needleboy Lake – Six Mile Lake Area, Northeastern Minnesota: a Summary of Volcanogenic Massive Sulfide Potential
    (University of Minnesota Duluth, 2002-09) Hudak, George J; Heine, John J; Hocker, Stephanie M; Hauck, Steven A
    The Needleboy Lake and Six Mile Lake areas has focused on evaluating the stratigraphic succession, hydrothermal alteration, and synvolcanic and post-volcanic structures in an effort to better understand the VHMS potential in this region of the Lower Ely Greenstone. Field mapping in the Needleboy Lake area (performed during August, 2001) investigated all outcrops within a 100 to 200 meter perimeter of the Lake. A north-south section was also completed from the north-central shoreline of Five Mile Lake to the western shoreline of Needleboy Lake. Field mapping in the vicinity of Six Mile Lake (performed August-September, 2002) included three detailed north-south traverses (Fig. 4). Traverse 1 extended from the northwestern shoreline of Needleboy Lake to the western shoreline of Six Mile Lake. Traverse 2 extended from the northeastern shoreline of Needleboy Lake to approximately 200 meters north of Six Mile Lake. Traverse 3 extended from the southeastern part of Needleboy Lake to approximately 500 meters northeast of Six Mile Lake. In addition, all outcrops occurring along roads in the study area were investigated.
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    Needleboy Lake – Six Mile Lake Geological Mapping Progress Report: June 2003
    (University of Minnesota Duluth, 2003-08) Hudak, George J; Heine, John J; Hocker, Stephanie M; Hauck, Steven A
    Detailed mapping and hydrothermal alteration studies have identified several areas in the Archean Vermilion District of NE Minnesota that have excellent potential to host volcanic-hosted massive sulfide (VHMS) deposits. Over the past three summers, the detailed volcanology, hydrothermal alteration, and VHMS mineral potential have been investigated in the Five Mile Lake, Quartz Hill, Eagles Nest, Skeleton Lake, Needleboy Lake, and Six Mile Lake areas.