Table Name

Field Name

Begin Column

Definition

Valid Values

Descriptions

millmgsbg.shp

Geol_Srce

 

Text, 150

See Below

The bedrock geology mapping units source.

 

 

 

 

MGS Miscellaneous Map Series M-100:  Bedrock Geology of Mille Lacs County 30 X 60 Minute Quadrangle, 1:100,000, 1999

Minnesota Geological Survey (MGS) sourced mapping units at a scale of 1:100,000 covering the northern half of Mille Lacs County

 

 

 

 

MGS Miscellaneous Map Series M-132:  Bedrock Geology and Superimposed Magnetic on Gravity Anomaly for East-Central Minnesota, 1:200,000, 2003

MGS sourced mapping units at a scale of 1:200,000 covering most of the southern half of Mille Lacs County.

 

 

 

 

Interpreted by the MN DNR, 1:200,000, 2006

Mapping unites interpreted by the Minnesota Dept. of Natural Resources    (MN DNR) at a scale of 1:200,000.  The units cover the far southeast corner of Mille Lacs County for purpose of having a complete bedrock geology dataset of Mille Lacs County.

 

GEOC_DATE

 

Number, ,0

Ex: 19990423

Date that the mapping units were delineated

 

MGS_DESC

 

Text, 75

Ex:  Bedrock Near Surface, Bradbury Creek Granodiorite, Cambrian Undifferentiated, Denham Fm, Hillman Migmatite, Mafic-Ultramafic Intrusions, Mille Lacs Group

MGS description of bedrock geology mapping units (21) extracted from source map datasets.  For more information about this datasets visit http://www.geo.umn.edu/mgs/ and search for miscellaneous map series’ M-100 & M-132.

 

MGS_DESC

 

Text, 75

See Below

MN DNR’s generalization/reclassification of MGS bedrock geology mapping units (MGS_DESC) into 8 mapping units for purpose of mapping crushed stone potential of Mille Lacs County

 

 

 

 

Gneiss

Durable medium to coarse-grained, crystalline, metamorphic rock.  This bedrock is pinkish-gray that is variably sheared and foliated.  However, the quality is broadly interpreted as high for crushed stone resources.  Quality and durability are affected by the local extent and degree of metamorphism, which is observed by the orientation of larger mineral grains, shearing, foliation, and mineral elongation. Specific gravity typically ranges from 2.5 to 2.9.  This unit combines MGS bedrock map units Apg, Amc, and Amcu.

 

 

 

 

 

Granitic Rocks

Durable coarse-grained, crystalline rock.  This bedrock unit combines several granitic, tonalitic, and granodioritic rock formations, which vary in color, composition, and physical properties.  The quality is interpreted as high for crushed stone resources.  Local occurrences of preferred orientation of larger minerals, large crystal size, shearing, foliation, and elongation of minerals may lower the quality and durability of this unit in some areas. Specific gravity typically ranges from 2.5 to 2.7.  This unit combines MGS bedrock map units Pbm, Pfm, Pgr, Phm, Phmu, Piw, Piwu, and Pwi.

 

 

 

 

Mafic and Ultramafic Intrusion

Contains a variety of minerals and rock types, typically serpentinized peridotite, pyroxenite, hornblendite, diorite, and gabbro with some granodiorite.  This quality of this rock is variable depending on dominant lithology; however, quality is broadly interpreted be moderate.  Quality and durability improve with larger intrusions, distance from contacts of other rock units, and degree of fracturing within rock.  Specific gravity typically ranges from 2.6 to 3.0.  This unit combines MGS bedrock map units Pmi, Pp, and Ppu.

 

 

 

 

Metamorphosed Sedimentary Rock

Predominantly schist and interpreted to have limited crushed stone potential. Variability of composition and degree of metamorphism all contribute to non-durability and low quality of these rocks.  This unit combines MGS bedrock map units Pps and Ppsu.

 

 

 

 

Schist

Predominantly consists of schist derived from volcanic and sedimentary rocks and is unsound and non-durable rock that is characterized by a high degree of metamorphism.  The minerals in schist tend be elongated and easily fractured into flakes and slabs, which contribute to non-durability and low quality.  This unit combines MGS bedrock map units Pdam, Psm, and Psv.

 

 

 

 

 

Sedimentary Rocks

Poorly lithified sedimentary rocks, which include sandstone, siltstone, and shale. These rocks are friable, commonly contain high clay content, and cleave along bedding planes, which contribute to non-durability and low quality. This unit consists of MGS bedrock map unit C.

 

 

 

 

 

Shear Zone

Highly fractured and deformed granitic rock, cut by numerous northeast-trending mafic dikes. The aggregate potential of this unit is limited due to the extent of alteration and shearing.  This unit consists of MGS bedrock map unit Psz.

 

 

MGS_MAPLBL

 

Text, 5

Ex:  C, Psv, Pp, Pbm, Pfm

A map label related to MGS bedrock geology mapping units (MGS_Desc)