Geologic Atlas of Wadena County, Minnesota
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Prepared and Published with the Support of COUNTY ATLAS SERIES ATLAS C-40, PART A MINNESOTA GEOLOGICAL SURVEY THE WADENA COUNTY BOARD OF COMMISSIONERS, AND Wadena County Harvey Thorleifson, Director the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-CitiZen Commission on Minnesota Resources, Plate 2—Bedrock Geology AND the Minnesota Legacy Amendment'S Clean Water Fund 95° 7' 30" 95° 94° 52' 30" R. 33 W. HUBBARD COUNTY R. 35 W. R. 34 W. HUBBARD COUNTY A Ku 420 435 420 Blueberry 420 Lower 6 1 420 420 River 6 420 1 435 Twin 6 ]71 Amv Lake 1 Blueberry 420 Acg Shell River 420 River Aif 420 Acg BEDROCK GEOLOGY 420 WAD-3 CASS COUNTY Lake 420 435Kettle Acd 420 87 420 ) Stocking Wing By River Lake BLUEBERRY SHELL RIVER 420 Amy L. Radakovich and V.W. Chandler T. 138 N. T. 138 N. Finn Acg Menahga 420 HUNTERSVILLE Jim Cook 420 Lake Crow � Aif Lake 420 46° 45' 46° 45' dn Spirit LOCATION DIAGRAM Lake 2016 )87 420 420 450 435 420 420 Acv Acg Burgen �as Lake 31 36 Acd Creek 36 31 31 36 CORRELATION OF MAP UNITS BECKER COUNTY 435 450 Acv 420 1 6 1 6 420 1 6 INTRUSIVE ROCKS SUPRACRUSTAL ROCKS 435 Yaeger Lake p 420 m Ku Cretaceous MESOZOIC a 420 w Mud S unconformity Cat Lake River Foreland basin, ANIMIKIE GROUP as 450 420 Penokean orogen Kenora-Kabetogama dike swarm PALEO- OTTER TAIL COUNTY TAIL OTTER ]71 Intrusions of PROTEROZOIC Rice Aci 435 Lake uncertain age dn dr 420 ig 420 B Kitten 435 420 Am Ag WAWA SUBPROVINCE Creek 420 ORTON 435 Creek RED EYE MEADOW T. 137 N. T. 137 N. Miscellaneous intrusions Cass batholith PRECAMBRIAN Kitten Agg Agm Agt Acg Acd Acm Aci Creek NEOARCHEAN 420 A�m 420 Ams Acv Amv Aif 435 AcvRiver Redeye Acg Swamp Creek 435 Sebeka 36 31 36 31 420 420 River 36 31 Nimrod Redeye Cat )227 Little 405 Crow )227 )227 River Wing 46° 37' 30" INTRODUCTION GEOLOGIC CROSS-SECTION ARCHEAN ROCKS 46° 37' 30" Beaver 1 6 Creek 1 6 1 6 ]71 420 Hay Wadena County bedrock consists of a complex assemblage of Precambrian supracrustal Computer modeling of gravity and magnetic anomaly data was conducted along a Neoarchean �dn River A�m WAD-2 and intrusive rocks, locally overlain by varying thicknesses of weathering residuum (saprolite) northwest–southeast profile (A–A'; Figs. 2, 3) in Wadena County to provide some insight into 435 435 420 Intrusive rocks—Unless stated in an individual unit description, all intrusive rocks in Wadena Acd and Cretaceous sedimentary strata. Quaternary glacial sediment covers the bedrock across the the third dimension—particularly relevant to interpretations of Precambrian bedrock. The 405 County are identified and described solely on the basis of aeromagnetic and entire county (Plate 3, Surficial Geology). The bedrock map depicts the type of bedrock likely geophysical model along this profile was modified slightly in Figure 3 to depict a more schematic Redeye density properties. The depiction and characteristics of intrusive units are 435 Ku 405 to be encountered below the unconsolidated sediment. interpretation based on what is known about the bedrock, and to highlight important features. 435 thus speculative and subject to revision should additional or new data become Acg 420 There are no known exposures of bedrock at the surface in Wadena County, thus the The original model and the data on which it is based appear in digital files that accompany this Strike 405 available. Hay 264-HLV geologic atlas. Constrained by rock properties data (specific gravity and magnetic susceptibility 435 435 Lake interpretation of the bedrock geology relied almost entirely on geophysical data augmented by Acg Cass batholith—Cass batholith is an informal name applied to a volumetrically 435 RiverAcd 405 sparse drilling data (Plate 1, Data-Base Map). One hole was drilled in 1986 for the purpose of measurements) derived from similar rock types elsewhere in Minnesota (Chandler and Lively, 420 Granning extensive, unexposed suite of generally granitic rocks centered in adjacent Cass 405 2011a), the model indicates that most of the anomaly sources in Wadena County extend to 435 Creek 420 Lake minerals exploration, but because no bedrock drill core or cuttings from this hole were preserved, Acd 405 T. 136 N. County that extends west through parts of Wadena, Hubbard, and Becker Counties T. 136 N. 405 the geologic interpretation relied on the original written logs. Two other drill cores (1985-3 depths of approximately 4.3 miles (7 kilometers) below the surface. Below this depth, a uniform Agm 405 LYONS (Jirsa and Chandler, 2016; Chandler and Radakovich, in press; Radakovich and Acd NORTH GERMANY 405 and 1985-4) obtained as part of a scientific study by the Minnesota Geological Survey, stored rock of intermediate composition, such as granodiorite (gray unit on cross section) is assumed, ROCKWOOD Ku Chandler, in press). May represent a northeastern continuation of the Otter Tail 405 at the Minnesota Department of Natural Resources—Hibbing office, were re-examined as part which is consistent with model studies in central Minnesota (Chandler and others, 2007, 2008). 405 batholith, which is centered in Otter Tail County. On its eastern end in Cass of this study. Additional bedrock information came from bedrock and saprolite core intersected Significant results from modeling in Wadena County include refining the location and dip of the County, the Cass batholith is fault offset against the Giants Range batholith, to � in two of three rotary-sonic holes drilled by the Minnesota Geologic Survey for this atlas. In Vining Geophysical Lineament and better constraining the depth and extent of the Nimrod outlier Acg as which it may be equivalent. 420 420 addition to exploration and scientific drill-hole data, driller's logs from both municipal and sedimentary basin. Profile A–A' trends nearly perpendicular to the strike of Archean bedrock 405 405 405 Granite to granodiorite—Weakly to moderately magnetic, low gravity intrusive private well drilling were used to characterize the depth to and nature of the bedrock. In areas units, and coincidentally the Vining Geophysical Lineament. The model demonstrates a steep Acg rocks. Inferred to be granite to granodiorite. Map label is italicized where the 405 405 lacking any subsurface drilling information, the bedrock geology was mapped using geophysical northward to vertical dip for all unit contacts across the profile and highlights the contrast in 420 435 405 geophysical properties across the Vining Geophysical Lineament, which is consistent with its unit is buried by rocks of the Animikie Group (unit <as). Ku data, specifically gravity and magnetic data (Fig. 2). Geophysical interpretations were based Diorite to tonalite—Moderately magnetic, very dense intrusive rocks. Inferred to 405 interpretation as a major terrane-bounding structural feature that likely accommodated north- Acd 420 36 31 36 on comparisons with areas to the east where the bedrock is better understood through surface 31 36 31 directed continental accretion in the Late Archean Eon. Also apparent is an abrupt change in be diorite to tonalite. Map label is italicized where the unit is buried by rocks 405 exposures and more complete drilling data (Fig. 1; Southwick and others, 1988; Jirsa and Aci 405 Boerboom, 2003; Jirsa and Miller, 2004; Jirsa and Chandler, 2007). In addition, active seismic the thickness of the Nimrod outlier sedimentary rocks across the Vining Geophysical Lineament, of the Animikie Group (unit <as). 405 Sand 390 data collected by the Minnesota Department of Natural Resources, and Horizontal to Vertical indicating that the Vining Geophysical Lineament was reactivated as a normal fault during or Granite—Highly magnetic, low density granitic intrusion. Drill hole 1985-3 Lake Acm 1 after the deposition of the Paleoproterozoic Animikie Group. 6 1 6 1 6 Spectral Ratio (HVSR) passive seismic data collected by the Minnesota Geologic Survey, were intersected this unit, where it is composed of coarse-grained, weakly deformed, 405 390 used to refine depth to bedrock (Plate 1). highly altered granite (Southwick and others, 1986). � dr 405 POTENTIAL FOR MINERAL DEPOSITS IN BEDROCK Prior to this mapping, the most recent depictions of the bedrock geology for all or parts Aci Tonalite—Non- to weakly magnetic, dense tonalitic intrusion. Drill hole 1985-4 390 of Wadena County were a 1:250,000 regional map by Southwick and others (1988; Fig. 1) There is an elevated potential for mineral deposits in the bedrock in Wadena County. Wadena intersected this unit, where it is composed of brittle, fractured leucotonalite Acm Creek and a 1:500,000 statewide bedrock geologic map (Jirsa and others, 2011). A bedrock map of County's Precambrian bedrock is part of a large greenstone-granite terrane of the Archean with minor hornblende-rich mafic metamorphic inclusions (Southwick and ]71 1985-3 H ay neighboring Todd County was completed in 2007 (Boerboom, 2007), and bedrock geology maps Superior Province (Fig. 1). Similar, better exposed, and more fully understood rocks further others, 1986). Map label is italicized where the unit is buried by rocks of the Redeye 390 Creek for adjacent Becker (Jirsa and Chandler, 2016) and Hubbard (Chandler and Radakovich, in north and east in the Superior Province have been known to host metallic mineral deposits, Animikie Group (unit <as). 390 405 press) Counties (Fig. 1) are in progress. This map reflects moderate revisions from the statewide locally of extractable quality and quantity. Economic deposits in the Superior Province are Agg Gabbro to diorite—Strongly magnetic, very dense metamorphosed gabbroic to Farnham Farnham bedrock geologic map (Jirsa and others, 2011), and largely correlates with mapping underway commonly mafic to ultramafic in composition, and host copper-nickel, platinum group element, dioritic intrusions.