Geologic Map of the Lead Quadrangle, South Dakota
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Department of Environment and Natural Resources Division of Financial and Technical Assistance Geological Survey Program 7.5 Minute Series Geologic Quadrangle Map 19 Geologic Map of the Lead Quadrangle, Prepared in cooperation with the South Dakota School of Mines South Dakota and Technology, Rapid City, South Dakota EXPLANATION Jack A. Redden1, Alvis L. Lisenbee1, and Mark D. Fahrenbach 2013 38 Alluvium - Unconsolidated to loosely consolidated; clasts to boulder-size. ! ? Contact State of South Dakota South Dakota Geological Survey ) Qal Deposited in present-day stream drainages. Estimated maximum thickness Long dashed where approximately located; H T short dashed and queried where inferred in Dennis Daugaard, Governor Derric L. Iles, State Geologist R 40 ft (12.2 m) O N cross section; arrow indicates contact dip (M A D direction and amount U O R O Landslide - Unconsolidated, locally derived bedrock debris to boulder-size. I W C D E A Quaternary Ql Often associated with steep slopes of the Winnipeg Formation ) E D o ( 5 000m. 5 5 5 o FAULTS 103 52' 30" v 5 (S 5 5 5 5 5 103 45' PEAR ¦ o 90 E. 91 92 93 R. 2 FISH) 95 R. 3 ¹ 50' 94 E. E. 96 47' 30" 97 o 98! 99 o ! 44 22' 30" à à ; ! ¦ à 44 22' 30" ! 10 E ; > O > à X O à o 5 à Tr à à B 35 f ! P à N 21 2 Trp à ! 20 l 2 Tqp ! a 23 > à o I - Unconsolidated, locally derived, angular bedrock debris to Tu > Xpy Xe 49 Talus O o T 24 ¹ bx O 19 Xp 20 30 à ; cG 21 o L v à Tfp ! Xhs 15 30 o k Tbx à Tbx v Tto Trp ta 14 Fault Tq 11 Xe C p à o Tr o 12 ! 12 65 Trp 18 Ãà à > > i I Qtl > ! l Tu boulder-size. Typically on steep slopes of Tertiary intrusive rocks. Normally P v ! ! o ¦ > G T ! à 5 > 12 12 à à à T 23 à 5000 P Long dashed where approximately located; 8 ph 18 o N ! u Tm k Tqmp lch 0 Tt à à p T Xp à I 0 e qp u l Xhs G 0 > à ? > > c A devoid of soil or tree cover ! X 0 p I e ! > ! > 4 8 h o dotted where concealed. Bar and ball on 0 ! Trp r Qal 14 à 7 > > T 5 à 75 0 O_d C Qal r ¦ > o O à 4 O_d ! 5 > 0 o > O_d downthrown side 0 à » > > ¦2 o h 3 G ¹ ! 6 à ! ALT ! à T Tr 5 ! > > 50 ph v > Ì Xn c > Xe o 8 > à o l à 14 Xpy ! à à O Tw ! 18 > > Black Unconformity 5400 0 K tail ¤ k à Tt P > u 0 Tb > o35 35 x ! > 6 ! ¹ 20 e ; à Trp 5 ? E G 74 ¦ ! ! à 0 ; Qa à ! l e Xe Tph Trp 0 > L à v Xe à SYN à o C r à 6 L Trp > v L à M à ! P ? 65 Y IN Oww ¦ ¨ 65 à 5 P ? o à I ! 80 o E ! Trp S ! C 62 l 0 41 A à Tfp i v ! A 0 O ¦ P ! a A ? h 68 t 4 S 38 T Q ? White River Group - Unconsolidated to moderately consolidated. p ! FOLDS (Laramide) ! à a N U 5 w e I E c v e pi E D T v t Gulc ! ? O_d h h S U v C n ! ! S à ! T L ¹ Tmp Tw à ! Clasts to boulder-size, dominantly of Precambrian rock types with Paleozoic a ! - ? ! T A T r r qat Tqmp ! & Oligocene to o 8o6 ! ! >Trp Tr ICLIN p E C entral ! 70 N Tu City T E B P r o N à ! sedimentary and Tertiary igneous rocks. Fine-grained matrix and bentonitic à > ! à m 0 O à L ! 0 A D 74 I 2 H > ! 5 à N Eocene ! ? ; o o O ? Anticline ¦> 75 L h Xf t Tph G 82 R A F Tph t Xp c 49 000m. ! Tbx I l > M ! clay content variable. Estimated thickness up to 230 ft (70.1 m), with 68 > S o 0 M Ow 27 P Xp u L Xn Location of trace of axial surface and direction 13 N. 2 26 A ! 8 45 0 G ! E 25 Tv O r R B Tfp 30 O_d v o N v 0 G 28 Xe > à ! 29 à A O_d r 35 5 O thickest deposits associated with erosional channels of plunge. Long dashed where approximately ¦ N ? ! C à Tbx D ! Tq ; ! mp k à o 0 e I O A 0 0 e 6! 5 ! ! 62 o r ! d ¦ T ? I 49 r 0 à p 8 C o à P located; short dashed where inferred in cross L ! N > K ! a 5 8 Xhs o 13 a Tr p B Tr 8 v E ! > 4 r ! D 5 5 ! r à O_d ; t l ! 8 ¹ 85 D o o A ! E » Tw s 7 i section; dotted where concealed o 5 b 6 a r Unconformity 0 > 75 ! o Xp 76 7 P 4 ! 0 à Trp Xe Ì O 0 a 0 0 L 0 a p à X 4 à 85 ! t hs 5 0 0 e E 2 o o 0 68 N D L 0 8 85 4 8 s ¦ o N b d ! o K e v l ! o o o I ! 5 w 7 l Tqmp d 0 o > o A a ! D a 78 ! De 70 » ¦ O 63 L ! T C 0 ! E Tr qat F Xf 0 B O 15 à O 4 E N Tfp ? Phonolite - Light- to dark-green, greenish-gray to gray. Massive to t 5 o 76 Xe A à ÃO 5 Ì H Qal 4 C ! 0 Syncline s ! à X o O 0 » e 82 ! D Terravill ! e ! P E ! O M _ ! d Pà O a O > Tqhmp Tph 74 O > Qtl ! Xhs layered. Composition varies from alkali trachyte to phonolite. Very fine à à O Location of trace of axial surface and direction à à E 87 80 P ! O O P ! Oo Tqm Tqp Qtl à p O 6 0 ! Thmp Tmp Tr 0 0 o Xhs O O ¦ 0 à of plunge. Long dashed where approximately 0 holocrystalline to aphanitic groundmass of approximately 40-65 percent ! ! 6 Xe ! P à 0 Tqmp R Ì Trp o à O O Xe ! ! ! ? à 70 à M Tr Trp located; short dashed where inferred in cross X ¹ f ! 5 O 74 ! o ! > O_d 40 Tmp alkali feldspar, 23 percent zoned aegirine-augite, and 5 percent nepheline 87 s A O 0 ! o Xhs r ! ! section; dotted where concealed ! » O N à O o S ! Xe Tmp Trp ! and leucite. Groundmass contains 10-45 percent phenocrysts dominantly of ! Y » Ç 85 ! à 77 v > N T P à 8 à 70 G Trp p 5 o h ! ¦ B > ! G 60 C > Tu o à 5 à ! 4 o A euhedral sanidine or nepheline up to 1.4 in (35 mm) across. Typically has I 0 ! ! I L 0 5 à 65 O ! ! à > K o à 6 X R I Ô 4 K p 9 80 ! N 55 M h 0 o à 52 Qt T 80 Xf l o 12 0 N E ¦¦ ! c 55 trachytic texture from aligned feldspar laths, or may have flow layering, ! l I H o à à à O o T FOLDS (Early Proterozoic) 85 ! 44 40 Mine E K O ¦ G u _d 55 ! Tqhmp ! ! U 7 o 8 E à à ! 7 T à 5 I 57 20 Tqmp 80 Ô Ã A ¹ 68 especially along contacts. Accessory minerals include minor biotite, magnetite, War Eagle 85 ! ¦ G 25 ¦ N Tr 49 à p o à d N !o > ump D Ì ? 00 Ow ! 77 o 0 ! o 1 6  Tr o T 2 o E à à T ! Trp » Hill à I 60 ! apatite, ilmenite, and titanite. Hematite, clay, calcite, and zeolite occur as Bald Moun ! S 60 ! tain Mine Xf > C A Owh ! Trp 70 75 o O_d M A75 à X ! e L ! 45 73 à ! 84 P à I P I 85 N N E D1 FOLDS I ¤ Mp N ¦ 5 ! ! Ì Tt 4 E T alterations (Larsen, 1977; Usiriprisan, 1979; Harris, 1991). A dike in the Xp 0 T ! 0 E ? ! R I O_d ! 25 Ãà à ! Xmg ¹ F ¦ T ! ph à G ! C O Generalized interpretation of earliest folds based on various level maps ! 0 82 o 0 ! Tqat ¦ a 0 G > E Homestake mine has a K-Ar date of 58.2 +/- 1.7 Ma (McDowell, 1971) 2 0 R MDe 6 ¦ ! 0 g 6 54 M O 60 ! prepared by Homestake mine geologists from underground workings and 72 >o O 0 5 Tu K K Xe ! 0 à 5 A LEAD 7 X ! 7 ! f 8 a ! ! 5 ! à N > S ! ! b extensive drill-hole data outside of the original mine area. Available data on 68 > o O_d O à ! 3 o G Y à ! T ! a ! O o t ! N 33 à ! 31 I G » Breccia - Reddish- and yellowish-brown to beige dikes and irregularly level maps is limited to the Ellison Formation lower contact, Homestake à C S ¦ à à Qal 34 >3 35 à 36 72 u ! F A ! 3 v à A à à Y 3 O ¨ à à L 2 Xe N à à v R ! X Tbx Formation, and Poorman Formation including the Yates unit.