Value of Water Well Drilling Data in

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Value of Water Well Drilling Data in
Understanding the Precambrian Geology of
Northeastern Minnesota Jim
Miller University of Minnesota Duluth
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Precambrian Bedrock Geology of NE MN
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The Geologic Record in Minnesota
LAURENTIA
KENORALAND
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Terrane 2 The Superior Province
(Granite- Greenstone Terrane) 2.7-2.5 Ga
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GREENSTONE Metamorphosed Basalt Flows Pillowed
Structures indicative of submarine eruption
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SEDIMENTARY ROCKS
BANDED IRON FORMATION
GRAYWACKE
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GRANITE Crystallized from Magmas intruded into
the crust
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The Superior Province Multiple Accreted Terranes
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TECTONIC MODEL FOR THE SUPERIOR
PROVINCE Accretion of Island Arcs, Oceanic
Plateaus, and Protocontinents
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Terrane 3 The Penokean (and Yavapi and
Mazatzal) Orogen 1.9-1.6 Ga Making Laurentia
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MESABI-TYPE IRON FORMATION Geologic Marker of a
Major Evolutionary Event
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Penokean Orogeny 1.85 Ga
Thomson Dam
Eveleth
St. Cloud
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Penokean Mountains (1.85 -1.75 Ga)
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Terrane 4 The Midcontinent Rift 1.1 Ga An
Attempt at Unmaking Laurentia
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MIDCONTINENT RIFT A 1.1 Ga attempt at continental
separation
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Gabbro
Sandstone
Basalt
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Precambrian Geology of Minnesota
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Direct Evidence OUTCROP
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Glacial Overburden
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Indirect Evidence GEOPHYSICAL DATA
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More Direct Evidence DRILL CORE
Image from Dale Setterholm, MGS
Location of core hole
Drill core
Drill hole locations provided by Minnesota
Department of Natural Resources, Division of
Lands and Minerals, Hibbing 2002
1st vertical derivative of aeromagnetic data
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Even in Areas of Good OutcropBedrock
Information is Sparse
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• Usefulness of (well located)
• Water Well Drilling
• Information
• to Precambrian Geology
• Depth to bedrock info
• General rock descriptions
• Well chip samples

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Helpful Crystalline Rock Descriptions in Water
Well Logs
Color can be a good indicator of minerals in
the rock Coarseness can individual mineral be
seen with the naked eye? Internal Fabrics
layers, bands, laminations Fragment Shapes -
irregular chunks, thick flakes, thin flakes
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Usefulness of Water Well Rock Chips
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The Precambrian Research Center at UMD