SUPPORTED IN PART BY THE MINNESOTA MINERALS DIVERSIFICATION PROGRAM MISCELLANEOUS MAP SERIES AS RECOMMENDED BY THE MINERALS COORDINATING COMMITTEE FOR THE MINNESOTA LEGISLATURE MAP M-119, SHEET 1 OF 2 MINNESOTA GEOLOGICAL SURVEY D.L. Southwick, Director MAP OF NORTHEASTERN MINNESOTA SHOWING 91°00' GEOLOGIC MAP OF THE DULUTH COMPLEX AND RELATED ROCKS, NORTHEASTERN MINNESOTA LOCATION OF MAJOR PHYSICAL AND CULTURAL FEATURES THAT FORM PART OF ROCK-UNIT NAMES By CANADA 90°15' 90°30' 90°45' 0 10 20 mi 90°00' 91°15' Gunflint Lake J.D. Miller, Jr. J.C. Green M.J. Severson V.W. Chandler D.M. Peterson Knife Lake R. 4 W. 0 10 20 30 km 91°30' Cucumber 89°45' 89°30' Minnesota Geological Survey Professor Emeritus Natural Resources Research Institute Minnesota Geological Survey Natural Resources Research Institute Poplar Lake Lake 48°00' Tuscarora er iv Pigeon Lake Winchell Lake R R. 5 W. University of Minnesota–Duluth University of Minnesota–Duluth University of Minnnesota–Duluth Pige Point 91°45' on 48°00' Misquah Newton Grand Lake Hills Portage 91°00' Fall Br Lake ule 2001 89°45' Brule Lake T. 66 N. Eagle Pine er * * Mountain R iv Mountain iv R e r Y Hovland 92°00' Ely Farm i Y R. 6 W. Lake hiw White is aw Iron K 90°00' k Lake or SCALE 1:200 000 F h ut 5 0 5 10 MILES So Grand Marais 90°15' LAKE COUNT COOK COUNT 47°45' 5 0 5 10 15 KILOMETERS 47°45' Toohey Lake Good Harbor 90°30' R. 2 W. Birch Lake Bay R. 2 E. Fourmile R. 7 W. Y Lake R. 1 W. R. 1 E. 90°15' R. 3 E. T Sea Gull A Y CANAD N . T r C Lake T. 65 N. C U 90°30' N htal g r ug i n o Lutsen O s U o R. 3 W. H s C O R i T. 65 N. 90°45' C v 90°45' S e I e Lak r r flint e E Ninemile un U G iv N. Clearwater R K B O ra Lake A e L nc Lake Tofte g L h . Osier 90°00' id T 91°15' Lake tr Lake r S Loon Pine a ch M Schroeder P an anito Lake Seven . Br Beaver Greenwood S R. 8 W. e South Lak Lake Lake Blesner u 47°30' R. 9 W. Fowl 92°15' P Lake R c op 47°30' Hoyt Lakes Sonju abi lar Lake iv 91°30' kek Gillis Lake Lake W Lake e Ke T. 64 N. e r 91°00' Little 89°45' st B Lake R. 5 E. is River r. r. Saganaga R. 6 E. ou Cloquet t B R. 4 E. 89°30' L as Meeds t. Lake B E R R. 7 E. S a Lake p Finland t is Little Marais 48°00' m O Ensign I Lake R B iv R e e Illgen Gaskin Lake a Lax r T. 64 N. Greenwood v City e Lake E Lake r Palisade Head Moose R. 7 E. Silver Bay P Lake R Ima iv U R. 11 W. R. 10 W. Lake er 91°15' R. 12 W. 91°45' Snowbank Beaver Bay S Lake Disappointment Frost 47°15' 48°00' Lake Thomas Lake 47°15' Lake Ella Hall Lake Wood Cherokee Goo E seb Lake Lake R. 6 E. erry Split Rock Point Low Swan K Lake S R Lake Cedar Parent ilv ive e r Lake T. 63 N. r A Lake Silver Tom Creek L Brule Lake Bass Lake 91°30' Lake Fall Alice C re Lake Lake Lake 89°45' e srif Split Rock intrusive felsite—Pink, sparsely porphyritic, aphanitic to fine- k Insula Northern Light T. 63 N. Twin Lake Lake grained felsite; intrusive into Gooseberry River basalts (unit ngrb) in Split Rock River area. Shagawa Lake Lake Lake One Two Harbors Polly R. 5 E. 47°00' 47°00' Homer Lake lbdb Lafayette Bluff diabase—Olivine diabase, fine- to medium-grained intergranular; subtle modal layering; distinguished from Silver Creek L 91°45' Two e Farm diabase by Pope (1976). s Island te Lake Alton r Cascade Lake Lake Grace Lake Pipe Lake R Ely Clearwater Three Lake Silver Creek diabase to granophyre—Bimodal intrusive suite; well iv Lake Elbow er Lake Lake T. 62 N. exposed near lakeshore, poorly exposed inland; largely inferred from R. 13 W. 92°00' Phoebe aeromagnetic data and sparse outcrop. Lake aspa Poikilitic olivine gabbroic anorthosite cumulate (PPocf)—Medium- Gabbro R. 4 E. Lake Kawishhiwi to coarse-grained, foliated, plagioclase cumulate contains 1–10-cm- Lake scdg Diabase to gabbro—Includes Silver Cliff diabase of Pope (1976) and Duluth 92°00' White diameter olivine oikocrysts; includes unit ago of Green and others (1966) sparse outcrops north of Two Harbors (Bonnichsen, 1971; Green Iron and units spoa and poa of Miller (1986). 21 Lake 90°00' and others, 1977). Gull Lake Devil Track Lake T. 62 N. asna Poikilitic noritic anorthosite cumulate (PPh)—Medium-grained; unit agh . scgp Granophyre—Inferred from sparse outcrops north of Two Harbors 46°45' of Green and others (1966). 46°45' Isabella Crescent R. 3 E. (Bonnichsen, 1971; Green, 1977) and subdued aeromagnetic N CO N r Lake e Lake signature. Osier Lake intrusion—Unexposed, well-differentiated, circular intrusion TO iv Y Y aspg Porphyritic olivine gabbro—Medium-grained, ophitic olivine gabbro; Elys R 1 Bald inferred from two drill core and a ring-like aeromagnetic signature. Peak Eagle contains 5–15-percent plagioclase phenocrysts; may represent flow- Sawmill Lake gabbro granophyre—Poorly exposed, bimodal intrusive ThomsonCARL is * u Lake differentiated contact zone of anorthositic series at Duluth (Miller and suite largely inferred from aeromagnetic data and rare outcrop. o oltr Troctolitic cumulates—Based one drill core and a subdued aeromag- L Fond . others, 1993). 92°15' t netic low. du S Perent R. 2 E. smgb Gabbro—Inferred from sparse outcrop (Bonnichsen, 1971; Green, Lac Lake Lake 61 90°15' Bog Clara akga Katydid Lake gabbroic anorthosite—Medium- to coarse-grained, poorly 1977) and locally high aeromagnetic signatures. Lake olgb Gabbroic cumulates—Based on one drill core and a strong aeromag- Grand Marais foliated, intergranular, plagioclase-porphyritic gabbroic anorthosite; netic high. smgp Granophyre—Inferred from sparse outcrop (Bonnichsen, 1971) and LAKE COUNT commonly altered. COOK COUNT Pike Lake 47°45' subdued aeromagnetic signature. R. 1 E. Bald Eagle intrusion—Funnel-shaped, concentrically zoned layered aslg Scott Creek leucogabbro—Fine- to coarse-grained, plagioclase-porphyritic T. 61 N. Bear Island Lake T. 61 N. intrusion with incomplete differentiation sequence; contains several leucogabbro to ferrodiorite; cuts Katydid Lake gabbroic anorthosite (unit spdb Stony Point diabase—Medium-grained, ophitic; occurs as slightly discordant Windy R. 14 W. very magnetic inclusions of unknown type in southern area; drill core akga) in roof zone of Duluth Complex. sheet about 35 m thick. Silver Lake 47°45' Deer Yard indicate that one inclusion is mafic hornfels; another may be large Island Caribou Toohey Lake Lake xenolith of gabbroic cumulates (units or glfg) from the Greenwood Lake Lake R. 1 W. glgb Early gabbro series—Early mafic phase of Duluth Complex as lrdb Lester River sill—Composite intrusion of intergranular gabbro at margins Lake intrusion. Birch indicated by U-Pb zircon ages and reverse magnetic polarity; dominantly and ophitic olivine gabbro in core; granophyre in upper part; thickness 90°30' cugd Gabbro to diorite—Upper series; displays cumulate texture in drill core composed of gabbroic cumulates in multiply intruded sheet-like intrusions. about 280 m. Lake from north and west areas; outcrops in southeast have noncumulate betr Troctolite cumulates (PO, POF, POcf)—Medium-grained, well-foliated, modally layered, locally melanocratic; southern area unexposed; texture; characterized by busy aeromagnetic signature. clgb Crocodile Lake gabbro—Generally gabbroic cumulates; identified from nldb Northland sill—Olivine gabbro; locally grades upward into intermediate inferred from subdued aeromagnetic signature. reconnaissance mapping of Grout and others (1959); U-Pb ages 1107.0 and granophyric rocks. Olivine gabbro to troctolite—Upper series; interpreted from subdued Babbit Fourmile cuog ± 1.1 Ma (Davis and Green, 1997) and 1107.9 ± 0.3 Ma (Paces and aeromagnetic signature. begb Gabbro cumulates (PCO, PCOf)—Medium-grained, well-foliated. Endion sill—Composite mafic sill; thickness about 425 m; northern extent Lake R. 2 W. Miller, 1993). Wilson based on scattered outcrop and aeromagnetic data; unit appears to Lake Greenwood Lake intrusion—Poorly exposed, well-differentiated layered Poplar Lake intrusion—Interlayered suite of dominantly gabbroic cumulates cut Duluth Complex. T. 60 N. clmd Monzodiorite and other intermediate rock types—Lower series; based intrusion; inferred from limited outcrop, several drill cores, and aero- on few outcrops and associated strong aeromagnetic signature in magnetic data; maximum thickness about 7 km. and minor troctolite and anorthositic cumulates; known from mapping T. 60 N. southern part of intrusion. by Nathan (Morey and Nathan, 1977, 1978; Mathez and others, 1977); endb Diabase—Ophitic olivine gabbro, intergranular gabbro, and monzodio- U-Pb age 1107.9 ± 0.3 (Paces and Miller, 1993). rite, medium-grained, locally altered. Lutsen glog Noncumulate oxide olivine gabbro—Unexposed; based entirely on clgd Gabbro to diorite—Lower series; cumulate texture in one drill core an aeromagnetic high and one drill core. plcz Contact zone—Varitextured, nonfoliated, biotitic olivine gabbro, augite R. 3 W. in western part; noncumulate texture in gabbroic outcrops in engp Melanogranophyre—Grades upward from intermediate rocks. southeastern part of intrusion. troctolite, and gabbronorite; locally granophyric and sulfide-bearing; Troctolitic cumulates—Inferred from one drill core and subdued gltr unit df of Morey and Nathan (1977, 1978).