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" Ã Ã ; ! ¦ Ã 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 > Ã 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 Ã ; 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 ÃÃ Ã > > i I Qtl
> ! l Tu boulder-size. Typically on steep slopes of Tertiary intrusive rocks. Normally P v ! ! o ¦ > G T ! Ã 5 > 12 12 Ã
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 Ã 7 > > T 5 Ã 75
0 O_d C Qal r ¦ > o
O Ã 4 O_d !
5 > 0 o > O_d downthrown side 0 Ã » > > ¦2 o h 3
G ¹
! 6
à ! ALT
! Ã T Tr 5 ! > > 50 ph v > Ì Xn c > Xe o 8 > Ã 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 ; Ã
Trp 5 ? E
G 74 ¦ !
! Ã 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 Ã 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)
! Ã 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 Ã ! 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 > Ã ! 29 Ã 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 Ã 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 Ã O 4 E N Tfp ? Phonolite - Light- to dark-green, greenish-gray to gray. Massive to t 5 o 76 Xe A Ã ÃO 5 Ì H
Qal 4 C
! 0 Syncline s ! Ã X o O 0
» e 82 ! D
Terravill ! e ! P E
! O_ M ! d
PÃ 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 Ã of plunge. Long dashed where approximately 0 holocrystalline to aphanitic groundmass of approximately 40-65 percent
! ! 6 Xe ! P Ã 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 Ã 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 Ã 8 Ã 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 ! ! Ã
> 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 Ã Ã ! 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 Â Tr o T 2 o E Ã Ã 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 ÃÃ Ã ! 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 Ã 5 A LEAD
7 X ! 7 ! f
8 a !
! 5
! Ã N
> S ! ! b extensive drill-hole data outside of the original mine area. Available data on
68 > o O_d O Ã !
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. Extension of the
e S T Tph ! shaped bodies of clast supported heterolithic breccia. Composed of > N Xm I R g N
à N 00 Y 33 I
2 > ½ Tbx M C Trp
6 T à oà C Ô X N > hs E L
Ow 75 ! ? Poorman Anticline southeast of Whitetail Summit is uncertain due to later ! 80 Ã 0 > I Tqa I o t K Ã C » approximately 40-60 percent angular to rounded clasts of Tertiary igneous
à L N 0 C 2 o à ¹
! L E 5
13 ! I o à O K Tw Ü refolding and extensive shear displacement. Smaller D folds are generally not N I 1
L G Ã H
Owh 68 Ã 60 N 60
v ¨ rocks and Precambrian schist and quartzite as much as 6 in (15.2 cm) I E E
O N ! !
! Ã 0 ¹
¦ 23 Ã X 0 shown, especially where coinciding with younger folds and modified by later f o 4 45
Tbx à à ! 5
à ;
O E Ã Ã O Ã 49 Ã Tu 88 diameter in a very finely-crystalline to aphanitic, rhyolitic, quartz-feldspar
à à o ? Tp ! shearing. Original names of structures have been retained in most of the
11 Ã O ? Tt Tt h 74 ¦ 40 Ã I 55 Tqat O Xe ¦
> ! ! O_ 84
! Tqat à d Tr
; O_d à ¹ 75 matrix. Typically oxidized, limonitic and iron-stained, or hydrothermally Homestake mine area, but some names have been changed in the present
6 !
o Ã
2 > 00 o Tph 49
6 P
0 à à Ãà 5 65 ¹ o à ! o
0 Ã Ã 80 interpretation ; 85 o 7 ? 0 0 Ã 0 O 11 O altered (Larsen, 1977) !
¹ ! Ã
! 0 6 86
00 Ã 0 o ? o » Xn Tar 4 0 Ã T 80 O 58 8 w
Tph 6 Ã > Ã H
5
à à o
O Ã ; ! 70 ! Ã o O Ã o Xp ; 75 Ã ! 16
O 26 83I 77 ! X ! k
T. 5 N. Mp O_d Tmp hs ? ee !
H
¹ r - Light-gray, yellowish-brown, pinkish, to white. Finely-crystalline Xe ! Ã Rhyolite
Mp Oww O Tt 50 o68 Tph ¹ à ¹ ? ½> C » T. 5 N. G ? Anticline ¹ 82 O à o à O ¦ o Ô o Ô
O 12 ! Ã Tr to aphanitic groundmass of 60-65 percent potassium feldspar and 25-35 Location of trace of axial surface and 0 ! > ! 40
O ! 5 80
T. 4 N. 0 8 80 80 ! 25
0 ! 80 84 Ã
! Ã ! Ã ¹
0 5 O 0 Ìv
o T. 4 N. Ã !
6 Tph à ! Xe à generalized direction of plunge. Long dashed
MDe Bald Tr ! ! percent quartz, contains up to 25 percent zoned, euhedral to subhedral
; O 20 ! Xf
Tb ¦ 35 73 !
G x ¦ ¹ !
reen 78 !
! ¦ 70 !
à ! 60
à » Oww Trojan ¦ à ½ Ô where approximately located; short dashed à ! P o
à à !
M ? o ! O Ã untain
P O ¹ Kirk 45 phenocrysts of quartz up to 0.16 in (4 mm) diameter and feldspar as much
P 87 X
à à 76 ¨ o eq
Mountain à O_d Trp à 54 52 ! Xmg O ¦ 0 > à k! O 0 ! 80 ? where inferred in cross section; dotted where !
à > ¦ v e 50
à > Xeq ! e ¹ ¹ à ¹ r ! X as 0.1 in (2.5 mm) diameter. Some feldspars are replaced by quartz.
X ! mg ¹ Ã 3 4 75 15 f 70 ! Whitetail 88
> ¦
! ¦ G C 10 > concealed; queried where uncertain
à 0
à T ! 16 o u à ph o Ã
Trp à lch 76 0 10 Ü Summi ALT ! t
o 2 Accessory minerals include minor magnetite and garnet. Sericite,
!
! ¦ ! n ¹ Ã
i O_d à 50 40 G 14 ¹ 5
0 Tph Tbx ! 70
0 !
à ta Tph 62 64 O ¤ !
0 Ü 76 ; 0
n 8 ! 5200 ! ¦ 5
o 57 ! o hematite, and limonite occur as alterations. May have breccia along contacts, u Ow Xe > o à d
49 o à ¨ à 78 à ¹ o k à H k > > Xe 85 o Ã
10 ! M ¤ T Ã L ?
e > t w Xn ¹5 e Syncline ! 6
25 ! 75 o E
O K
e e flow layering from aligned biotite crystals, or sheeting from closely spaced
0 o
¨ o t e O 0 O 85 ¹
2 63 ¦ Ov Xm i r r 5 O g ¹ A 3 Tph o h O Tqat 8 Location of trace of axial surface and O_d o » ¦ Ã X D
Oww C Ã Ã O ¹ mg W C
¦ Ã > Ã Ã 71 Xp 49 fractures parallel to the flow layering (Usiriprisan, 1979)
à ! Xe
O > 20 5 ; 76 Ã Ã
à O 80 10 generalized direction of plunge. Long dashed > !
Tph 8 a Mine > 75 ¹ Ü 82 ? ¹ 25
> Ã Tu ½ Ì ¦ O_d 80 78 d O Ã 4 » 82 5
> ; à dump ¨ ½ 4 5 3 where approximately located; short dashed à ¹ à >
0 Tar 1 a ! > ¹ 0
3 0 2 v à Ã6 à 0 81 0 2 » O ; à > 34 Ì
½ X o K 80 6 Xe e ? ! Tph hs Tph Rhyolite porphyry - Light-gray, reddish- to yellowish-brown, to pinkish. where inferred in cross section; dotted where
5 0 à à à Creek > 56 o à y Tu I
0 N K ¹ ¹ Trp ¹ 0
le 4 ¹ B 560 25 75 Tr concealed; queried where uncertain
6 ! O T P 78 U Trp White where weathered, with feldspar phenocrysts nearly indistinguishable
o 400 ph 76 l 37 o5 6 Ã ¹ i 22 R
Xe à Xmg ! 13¦25
F Trp ¹ 5 ¦
Tph à à a L
P t 2 I ¦ Ã 0 I
0 Ã P
! O 0 Ã N Tr from the finely-crystalline to aphanitic groundmass of 40-50 percent
Tar 58 ? 0 Ã ! > 86 e
O_d O o
à > t e G MDe ¦ i P à il > Xf à 68 i Xmg à ! à à à ! T n a Ì O P t h Tar O O O 10 H
O O n n ¦ 17 ¹ o potassium feldspar, 8-15 percent oligoclase, and 30 percent quartz.
! a O Ã w I ?
O Ã > 68 87 N Overturned anticline A ! F Xp
20' Xe v W o
Terry l 20'
Mp Tt ¨ ÃÃÃà à l O_d Tar à ! o Contains 30-50 percent euhedral phenocrysts of orthoclase, sanidine,
! » 70 Tph Location of trace of axial surface, dip direction e ! Xe
> > > o à o
O_d Tt Tmp à 40 85 ¹ ¹ 22 à à Y
! Ã ¹ 3 5 Ã Ã A 6
» Ã Ã Ã Ã Ô 00 plagioclase, and albite up to 0.2 in (5 mm) across. Has minor anhedral, of limbs, and generalized direction of plunge.
Oww 88 ¹
L 75 S
! Ã 68 N
à !
o » Ã » ¹ ! Y
60 o
s 00 T O Tt 5 1 ph O O_d 4
O_d 37 71 T Long dashed where approximately located; Tp ¹
h T Tr O_d N ph ! Ã o t P ¹ 0 partially resorbed quartz, and 4-6 percent biotite as much as 0.08 in (2 mm)
> 83 76 ¹ Xhs O I
0 G F ! v C O_d O 8 » 83 B dotted where concealed; queried where à 5 O 49 11 0 ¹ Tph à ! 0 P 80 A ; L
! 6 o à I 09 o Tt T à à R diameter that may be replaced by chlorite. Accessory minerals include minor
C 5 ph 7 O Xf à ! 5 Tt I R
a M > uncertain ! O N
m Ow à Ta à Tph 77 ¹ 75 r !
p Mp à O_d > Tu Ô T N
à E 70 à ! 14 » > ? ¹ > à I magnetite and garnet. Hematite, limonite, calcite, and clay occur as ¦ à E ! T 49
! à H Xmg 5 o à à ¦ T 09 à ¦ ; Ãà 60 à E Ã
o 4 5 22 Ã Xeq alterations. May have flow layering from aligned biotite crystals (Larsen, P
58 Ã Ã O 0 G 00 Ã Ã P ! ÃÃ 0 0 ¹ 6 > Tph 57 H
¦ ¦ Terry Peak » ¦ Ã ¹
u 6 80 27 » 16 Ã Ã 5 ? Overturned syncline
l 53 2 » Ã Ã 60 1977; Usiriprisan, 1979)
c > Ã o 0 O ¦ 0 Ã O Ã h 0 ¦ Ì
31 Ã Ã Ã j Location of trace of axial surface, dip direction ¦ o Tr
Oww Tar Tar 8 Ã Ã ! 70 o
MDe 79 O_d ¦ Ã
à ¦ à à O_d j 55 H of limbs, and generalized direction of plunge. ? o Ã
47 15 ¦ Sugarloaf O 6 t Ìo
¦ ar Qal à o à F Xhs o Alkali rhyolite - Light-gray, reddish-brown to pinkish. Includes aegirine Long dashed where approximately located;
¦ o
w h O 30 ! o à 5 1o 2
0 te ulc O Mountain > 3 72 Xf ; 0 S G 62 o à H ¦
54 0 O r Tar
à o Tph 6 » 7 12 58 à 4 10 79r 78 rhyolite, quartz-aegirine porphyry, and grorudite. Groundmass of finely- dotted where concealed; queried where
P ¦ 77 Ã » > P Ã 3 78 6
o
; Xf
! ¦ Tar à Mine
¦ uncertain 7 P ¦
Tw 15 ¦ > 0 ¦ ¦ à crystalline quartz and alkali feldspar is often partially replaced by quartz, o à 80 à 6 > 50 à o 6 ¦ à à 5 Ã
8 à Tr à o dump à 0 10 3 » 80 0 Tph 6 à » O_d aegirine-augite, and albite. Contains 10-50 percent phenocrysts of subhedral
à à à O_d à O_d 10 15 à P à 7 !
¦
¦ Xmg 7 Ã ¦ 8 Ç ÃÃ A Oww ¦ 20 o 0 quartz, and euhedral sanidine, albite, and orthoclase as much as 0.2 in ¦ o
Tw Tph à P o 0
à 11 o 1 O_d » 10 à o 80 4 MAJOR D2 FOLDS 2 !
à 0 10 à 1 à ¦ 0 à 5 à 75 7 P 8 9 10 49 M à 8 p 0 8 3 5
h à ¦ ¦ o (5 mm) in diameter. Some feldspars are replaced by quartz and aegirine-
08 c 6 ¦ > 15 à 2 70 I Trace of folds based on subsurface data. Original names of structures have l Ì Ã P à > P 6 u 6à 6 Tar à à o
O »
2 68 8
G Ã Ã P > > > Ã
»P 0 augite. Accessory minerals include minor biotite, phlogopite, and sulfides.
o T !
à ar ¦Ã >3 à à 80 N been retained in most of the Homestake mine area, but some names have 0 P
P Ã > ¦ ¦ >
à à 16 O Ã
à à à > à o > 49 ¦ >
0 Ã 82 R Ã Ã O_d > ¦ 0 Ow 78 P 35 Ã 08 been changed in the present interpretation
60 Ã Ã 15 > E Feldspars are locally altered to clay, sericite, and natrolite (DeWitt and others, T
> ¦ Ã Ã Ì ¹
15¦ Ã L !
P H o ¦Ã Ã
P 00 Ã L 5 Ã o 3
2 ¨ E
P 6 > Ã > 6 1986; Harris, 1991). An intrusive near Terry Peak has a K-Ar date of 58.5
y > 85 44 28 o> P I 0
R
e Dutch Flats ¹ S Â Tr
s 4 PP 6 ¦ Ã Ã 8 Ã 53 6 0 ) ¦ 5
t 3 > 80 ¦ Ã >> P o O v N e 34 H Xf !
s +/- 4.3 Ma (McDowell, 1971)
à H B o Ç Ã 58 Aà Xe Xe F ¦ O_ 17 > 00 N ? Antiform t 70 d à > T e o P 86 G
e ¦ à æ 3 à  U
Sw Tar à o Location of trace of inferred axial surface and M O p à 10¦ ! K
) 7
à Ow » 66  S Quartz porphyry - Leucocratic, light-gray to tan. Aphanitic groundmass of generalized direction of plunge. Long dashed 5
Y Ã Ã 7 Tw Â
MDe o 0 o Xeq » 0 D O 4 R O_d 3 ? 0 6 o u where approximately located; dotted where Oww 9 b ! 80 Tqp alkali feldspar contains up to 50 percent medium to very coarsely crystalline V Ã 6000 y O
à 4 Tar à e 2¦0 o Tr 53 5 A concealed; queried where uncertain
> o
> > O o O S Ã phenocrysts of alkali feldspar, and gray, tear drop-shaped quartz that are
à 5 o ( !
Tw W 1 6
4 0 ! 50
à > 0 à D
à à 0 3 3 Tar M 6 16 F partially resorbed. Exposures are highly weathered. Most feldspar ¦ 49 o4 o> P ¦ l ¹ 4 A oà ¦ ¦ a
07 35 t !
à E > s H > Mp à ! 42 ? Tar 6200 ¦ o phenocrysts are replaced with clay and iron oxide. Mafic minerals are absent. Synform >3 à ¨ Tph à D K o à à 8 ¹ ( 4 35 à Location of trace of inferred axial surface and
4 ! Similar in appearance to rhyolite porphyry (Larsen, 1977) o O_d o à !
Qal O_d 65 7 ¹ generalized direction of plunge. Long dashed 56 3
> o S 49
0 o o 45
0 o ; Ã Tph 50 ¹ 07 ! ¹
3 o à 35 85 P 45¹ Y where approximately located; dotted where ¦ 2 !
à Tr 65 N - Gray where fresh, purplish-pink and green where
ALT 9 Tr Feldspar porphyry à Â
3 85 C Tertiary concealed; queried where uncertain ;
14 O_d o o  o 60 ¤ 69 ;
o4 Oww 00 Tar à à L ! Tfp à à I 2 weathered. Composed of 34-50 percent clear to grayish, subhedral to 8 ¦
Oww à Q ! 5 à al T N 8
> Ã Tar ph 00 00
à 4 > o4 Qal ¦ à P 58 ¹ E Tr à o Oww Xf 6 anhedral anorthoclase phenocrysts 0.2-0.31 in (5-8 mm) diameter in a
à à à à à à 75 70 o! à ¦ Â
48 6 6000 ? o 4 Ã !
0 ; 40 o 25 0 Ã 6 O 60 ?
o4 ¦ 78 ¹
o7 6 80 Xmg dark-colored, aphanitic, potassium feldspar groundmass. Contains 3-8 MINOR D2 AND YOUNGER FOLDS
15 > H 13 18 Â ¦ 80 ¦17 >
Ä Eocene to à 80 ¦ 5 16 ! 15 S h 14 8 88  Includes smaller folds formed during development of major D structures
0 ulc MDe 20 ÂÃ percent lath-shaped oligoclase and aegirine crystals, and rounded quartz 2 0 o
G ; Ã Ã o
p 58 ¦ 76 Paleocene
¦ 5
¦
e ¦ 48 and younger folds developed largely by localized shear zones mainly in the Mp Ä 85
O 5 ¦
MDe ¹ ! 6 ¹
a 21 Tph 60 ¹ 6 ; phenocrysts 0.04-0.08 in (1-2 mm) long. Very fine-grained disseminated 0
o  33 40 r o ¦ 80 Lead synform. Only generalized traces of axial surfaces are shown. Plunges
f 5800 12 ¦ 0 i 12 à à 87 s ry o à O_d pyrite occurs near contacts with quartz monzonite porphyry. Small
r ¹ Ã Ã ! commonly vary, even in individual folds. Small sheath folds modify some
h be Tph 59 6 K 58
p 4 ¦
Oww as à O_d structures. All minor D2 folds are not shown at this map scale
à oà ¹ hematite-filled, lath-shaped voids are from altered aegirine. Groundmass R O_d 35 56 F
P ¦
49 !
5 o à ; 7 28 4 10
06 o 60 ¦7 Ã ¹ typically alters to iron oxide and clay (Larsen, 1977)
0 40 0
Tw Ow Tph o Xe 0 0 o O_ Ã 0 M d 3 ¦
0 o 0 ¦ Ã ;
4 4 ¦ 3 ; 0 !
5 3 à 4 à Tph à ¦ 7 e o 2 à o 3 à à e 49 o 6 Undifferentiated fold
4 o Deer 38 Ã Ã ¦ 4 5 06
Qal o 4 Ã > 4 10¦ 8 10 Trp Trachyte - Tan to reddish-brown, iron-stained. Finely-crystalline,
¦ 0
4 Mp ¦ 6 Tr Location of trace of inferred axial surface.
à 6 !
o o à 6 à ¦ 0
4 o à Mountain
o 4 o
MDe 4 o ¦ Ã
3 20 Ã P 6 ¦ 7 ¹ ¦ O_ A 47 5 14 d Tt mesocratic to leucocratic groundmass of orthoclase, sanidine, quartz, and ¦ Ä Long dashed where approximately located;
o à > 65 ¦ ¦ ¦ à e 40
C ¦Ã ¦
> 5 ! o dotted where concealed r
à à 16 49 O_d o biotite typically has a trachytic texture. Contains up to 20 percent lath-
e 8 > ¦ Ã 5 Ã Ã ¦
o > Ow > 16 4 ¦ 3 ¦ ¦ e MDe
Mp Oww à à 42 Qal à 4
à ! shaped phenocrysts of sanidine, orthoclase, and anorthoclase as much as k Ã
18 Ã Ã 50 ¦ Xf o
Ic 7 o à W e 3 ¦
bo à à à à 0 ¨ ¥ ¦  O x 0 0 80 0.2 in (5 mm) diameter, and minor aegirine-augite, nepheline, and biotite.
3 > o 0 o P 2 o 0 0 6 5 0 ! Ã 52 e Ä
60 o 0 Ä STRIKE AND DIP OF BEDDING O 0
_d 6 4 à o à ¦ 6 8
à 6 o May contain unoxidized and oxidized pyrite, minor clay and calcite replacing à 0 d
Ql 3 20 Ã 28 0 5 40 60 5 O
Qal P 0 v 5 o ¥
Oww à 60 o à ¦ !
85 à o ALT à Oww Englewood à ¦ 5 à ¥ i Ã
¤ à ¦ ¦¦ 7 à mafic minerals, and zeolites (Larsen, 1977) à l ¦ 8
o ¨ Ã o 14 3 17 ¦ T l 0
10 55 85 ¤ e ¦ 4 o 33
12 ¤ Ã C 60 0 Cheyenne o 75 Ã P ¦ Ã 4 O 70 70 o
o > U Â o Inclined
¥ ! ¦ ¦ 50
>o 5 o 5 P 65 ; D 60 4 E o ¦
Crossing o Qal ¦ Ã ¨ Â 3 Ã Ã 49 65 5 Quartz alkali trachyte - Light-gray where fresh, weathers tan to
à > 87 U 30 à 2 o 30 Ä Ã
05 o 6 P ¦ o Q
o 6 >
3 !
0 3 3 2 o ¦ 65
o à  Ã
A P
3 0 o 5 5 ¦ 80 3 7
o o Tqat
 o reddish-brown. Groundmass of microcrystalline to cryptocrystalline 0 o P ¦
Â
à o
à 70
à à Mp Ão o 80 ¦ 5 6 Inclined
6o 49 O 6 70 0 Ã 5 5
à o ¦ 3 78
2 ! 22 P 3 24 Tph 2 Â 05 0 0 Xe potassium feldspar, aegirine-augite, and partially resorbed quartz
O 6 19 ¦ 60 21 o > r Ball indicates top direction of beds known 4
10 o à 22
5 4 > 30 ¦ o 31 ¦
e MDe ¦ 70 ¦ 80 Woodville > Qal contains 30-60 percent euhedral albite or sanidine phenocrysts as much as to be in dip direction
o 60 ?
¦ ! 17' 30" Q P
6 4 MDe 4 35 60 80 ¦ al 1
16 Ã ¦ 30 ¦ A 7' 30"
o o3 o 80 4 O
o ¦30 o N ¦ ¦ 0.39 in (10 mm) diameter. Some phenocrysts are zoned, hydrothermally Ä Ã O ¨
o 10 o Ä I ¦
o T
¨ Ã
3 6200 60 R !
Gulch o 80 I 70 ¦ Ã C ¨ M 3 3 o 80 80 altered, and replaced by sericite, barite, carbonate, iron oxides, or pyrite. v 4 Ä 6 Ã L Ä ¦ A H Ã e 5 0 Ã o 8 Ã I Vertical 80 ¦ 0 N
6 4 Trp 75 0 N
o ! Cavities formed from alteration of mafic minerals or entrapment of gas
o à i E à ¦
Mp 800 4 00 l 60 60 o MDe Ã
0 o 5 8 88 l à o A o 5 s
0 M ¦
4 4 o 5 ¦ 80 ¦ 65 o
6 o bubbles are abundant. Accessory minerals include rutile, titanite, and
o Ä
Tw ¨ ¨ 5 ¦ à ! O_d ¨ 70 ¦ 6 Ä A à o à 85 5
3 3 6 à 0 ¨ ¨  Trp à e
8 P 4 10 0 apatite (Harris, 1991) Horizontal k 0 o
O_d à e ¦ P à o O > Ä ¨ 70
à 4 > re ! >Â5 à Mp à ¨ o à à C 80 ¦ P
à à 6 o P Qal Ä Trp 60
oà 5 à P ¦ ¨¨¨ 80 60 ¦ A' - Melanocratic, porphyritic !
o 4 Ã ¨ Hornblende monzonite porphyry
49 2 Â
o 30 Ä Overturned
o >
04 ¦ 8 ¦ 33
¦ 30 5 Ão à ¨
5 P 6 Thmp 2 ¦ P à 6 o 6 o  5 with an aphanitic groundmass. Contains approximately 60 percent Where direction of younging is known; top
ÃÃ 0 P 45 70 80 2 s 0 !
o MDe à 0 ¦ ¦ 0 70
> 70 0
à P ¦ 49
5 80 plagioclase and 30 percent ferromagnesian grains averaging 0.04 in (1 mm) direction of beds is opposite dip direction
M ¦
o6 4 p N 88 60 ¦ 04
o R ¦ ¦ O_d
5 6 ¦ o à E 0  Ã
5 ¦ 4 H 8 !
à T 00 ¦ 45 à diameter. Ferromagnesian grains may be altered to magnetite and chlorite.
Oww Ã> 0 o Oww R 75 8 70 6 O Ã Ä 0 5 0 Ã
à 0 à P 5 > N Ä ¦ Ã
5 3 o à 6 ¦ 4 0 2 H 0 ¦ 5 6 o e 60 à 6 6 6
o o P ¦ 40 ¦ Poorly exposed, generally occurring only as cobbles in soil
0 0 > ! o 5 Ã j
0 > 0 Ã 70
0 0 3 3 à d Ħ ¦ ¦ Top of bed
0 o 5 o O_d 70 80 50 60 000
8 o 6
à 60 ¨
5 4 P 6 Ã Direction of younging indicated by sedimentary
w ¦¦ ¦ P 0 80
e !
MDe o ¨
o o t 0 Ä o
i ¨ E 2 o 0 ¦
o 62 h ¦ Quartz-bearing hornblende monzonite porphyry - Light- to structures ¦ Ä 50
a > 4 00 80 ¦65 Trp
à ¨ ¦
5 Ã ¨ W 11 > 70
Ã Ä s 4 Ã
o P 13 o 88 80 ! o ¨ 3 ¦ Tqhmp
Mp t P à 4 à à ¨ ¦ à medium-gray, porphyritic, with an aphanitic groundmass. Contains 25 à 7 3 ¨ o oo à ¨ 4 ¨ Ä
4 60 ¨ ¨8Â5 Ã percent plagioclase, 5-20 percent biotite, and 1-5 percent hornblende
à !
27 4 2 26 25 4 30 30
o4 o à o à 29 ¨ ¦2 STRIKE AND DIP OF FOLIATION
o o 8
4 Ã ¦ 27 phenocrysts less than 0.2 in (5 mm) diameter, and minor quartz. Locally,
4 ¦ ¨ 30 Ã>
à o o o à ¦
> ¨
3 ! ¨
6 N P A 55 plagioclase is typically altered to sericite, and the ferromagnesian grains to
o 0 O Ã Ã Ì o o 00 P 70
49 à T 4 ¦ G 33 o à ¨
03 Ã ! calcite, chlorite, and magnetite 3 e N ¹
6000 4 3 I à h à L 60 Inclined
lc à 6 5 R Qal Gu 2 4 M 0 o U 62 ¦70 ¦
Qal o 49 M ! 0 o p 5
at o 3 B o 03
c o 6 0
d o 3 4 0 0 00 Monzonite porphyry - Leucocratic, gray where fresh, tan, red, yellow
il AQ 0 Ã 0 2 60
U 5 o
ED O_d 600 5 3 0 0 6 Ã
W 2 ½
UC F 6 4 Ã ! o Tmp T Â to white where weathered. Phaneritic, granular groundmass of plagioclase 5 Ä Vertical 800 o o o e 85 S 5 o 3 80 Mp p and alkali feldspar includes quartz that is commonly anhedral and overgrows 4 M Ì Ã ! o Ä Mp o2 Â Oww e MDe o o5 e O_d
o à 3 Ã
a 3 Ìo 4
! feldspars. Contains 50-70 percent zoned, euhedral to subhedral, plagioclase r 4 3 3 o 10 >
f Ow ! w i o s ! Ã > STRIKE AND DIP OF FLOW FOLIATION IN
h à and alkali feldspar phenocrysts to over 0.39 in (10 mm) diameter, and 3-5 ! Ã
3 > Ã
3 ! MDe
o à !
o o3 MDe Oww à Oww Ì percent quartz phenocrysts as much as 0.16 in (4 mm) diameter. Sulfide- à ! IGNEOUS ROCKS 3 60 5 o 0
à ! à 0 bearing where fresh, highly oxidized where exposed, with hematite and clay
e 00 !
2 ! !
! o o
6 o 4
! Oww Ã
4 4 à o à à ! o
o 6 4 2 ! >
3 00 ! 3 replacing many plagioclase phenocryst cores. Aggregates of pyrite and
! o 33
3 ! P
! 5 o P !
à ! o2 ¦
o o à ! à Ã
49 4 P
! calcite replace original mafic minerals. Gradational into quartz monzonite Inclined o 3 >!
02 o 0
! 4 ! 0 A
o à M Xf
2 6 De O
o4 8 P 0 3
» !
0 5 P porphyry, but phenocrysts are more abundant and larger than 0.2 in (5 mm) o o 3 Ã 0 o o Ice Cave 3 o A
5 3 o 600 49
! 0
6 o3 02 diameter (Larsen, 1977) ¨
2 o o 4 o 3 0 ! 6200 o Vertical
H 4 o 3 o 6 o MDe 62 0 10 H
P 00 e P P
! 3
à 8 à o
o !
o 4 o o3 o M 4 o - Gray where fresh, red, yellow, to white 34 5 0 > 35 4 3 36 O_d 31 32 Quartz monzonite porphyry o 0 Ã Ã 3 33 ¥
0 34 o à >o Horizontal
6 Mp 0 4 Tqmp 4 Ã ! where weathered; typically iron-stained. Phaneritic groundmass is finely Mp 6 4 3 4 32 o 2 o 6 o 3
62 Mp 0 3 P
0 5 0 k crystalline, equigranular, quartz-plagioclase-alkali feldspar. Contains 0 o
o e
4 ! Ã
e o o o Xe r
o6 3 Hanna à 6 approximately 10 percent potassium feldspar and 40 percent plagioclase as
4 0 0 3 C
o o 0 > F 0
0 5 0 STRIKE AND DIP OF FRACTURES o3 0 2 !
5 73 6 Mp
o à euhedral to subhedral, zoned phenocrysts as much as 0.2 in (5 mm) o à 5
o 3 à o à 3 e Oww
¹ à 4 Mp o diameter, and 10-15 percent euhedral quartz. Some feldspars are altered to 3 o 4 ! à MDe C P o4 33 r à 3 Qal 0 e o3 0 T clay, sericite, and calcite. Contains abundant resorbed quartz. Pyrite,  0 . 49 e MDe 3 o P 4 N. Inclined
o > 6 15 à 5 k o o à 01 P à ! à 3 à o 5 O_d o > chlorite, calcite, and clay replace ferromagnesian minerals. May have up to 5 o3 25 T. 4 N. 4 Oww o4 4 o à o3 ! 49 000m. 5 percent pyrite and 0.1 percent molybdenite, especially along argillized and M o à Mp 01 N. Ä
o à 3 Vertical 4 à 4 >
à P o silicified contacts with schist and amphibolite. Gradational into monzonite T. 3 N. Mp à o ! à 6 Oww o 2 o 0 3 6 O_d porphyry, but phenocrysts are less abundant and smaller than 0.2 in (5 mm) 0 w o3 4 0
4 MD 0 ! T. 3 N. o e a M 6 Oww
6 4 6 o r 0 diameter (Larsen, 1977) 40 w 0 LINEAR STRUCTURES
o 0 o M 4 De D a 5 6 0 O_ r d 3 o ! 0 6 Mp 3 2 D 1 5 o4 0 o 8 4 0 3 0 3
4 5 o à 6 o MDe h Undifferentiated Tertiary igneous rocks - Leucocratic to 6 Oww g 3 ! Elk 2 e Lineation u
d 0 60 o Tu 45
4 r 0 o MDe 0 3 mesocratic, aphanitic to porphyritic, hypabyssal intrusive rocks. Includes Ql e 0 Qal Ü Mineral lineation in Tertiary igneous
a H O_d
o à Mp o !
3 K
o 4 o 0
à 3 o à 20 phonolitic, rhyolitic, trachytic, and latitic rocks rocks; showing bearing and plunge 4 6 o W o à o Mp 4 3 44 15' 3 à o 4 o 0 5 5 5 5 5 5 5 5 5 44 15' o 90 91 92 93 50' 94 R. 2 E. (NAHANT) 95 R. 3 E. 96 47' 30" 97 598 99000m.E. 0 Intrusive Contact 103 52' 30" 103 45' (M ) IN Minor fold R N 40 E E Showing bearing and plunge. Related W S - White, beige, to gray massive limestone Ô O O Pahasapa Limestone T T to D2 and younger folds S A Mp and dolomitic limestone. Finely- to coarsely-crystalline. Contains thin lenses K R O ID and beds of gray to brown chert and local solution breccia. Vuggy, with O G R E ! ! ! (C ) caves occurring mainly in the upper third. Forms prominent cliffs. Exposed Quartz vein Lower 1 thickness approximately 450 ft (137.2 m) South Dakota School of Mines and Technology, Rapid City, South Dakota Digital cartography by Lori L. Roinstad, Mark D. Fahrenbach and Wesley P. Christensen Mississippian Mississippian BIOTITE Metamorphic isograd Englewood Limestone - Pink, gray, to purple-gray shale grading GARNET MDe upward into purple- to pinkish-gray argillaceous limestone and dolomite. Upper Laminated to medium-bedded, very finely- to medium-crystalline; Map base modified from U.S. Geological Survey 1:24,000-scale Lead digital line Devonian Devonian SCALE 1:24,000 NORTH bioturbated. Thickness 40-60 ft (12.2-18.3 m) OTHER FEATURES graph. ^ Projection is Universal Transverse Mercator, Zone 13N. MN Disconformity 1 0.5 0 1 GN Datum is 1983 North American. Mile Mine Whitewood Limestone-Winnipeg Formation Dump Mine dump Oww (undifferentiated) - Includes the Winnipeg Formation and 1,000 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 o The South Dakota Geological Survey Program, Department of Environment and Feet 8 29' Whitewood Limestone o Natural Resources, engages in an ongoing data collection and interpretation 0 53' 148 MILS South Dakota Ì Open pit mine or glory hole process. An outcome of that process is to reflect those interpretations on maps 15.5 MILS Whitewood Limestone - Variegated yellowish-brown, brownish-
such as this one. Reasonable efforts have been made to ensure that this map 1 0.5 0 1 Owh orange, to gray dolomitic limestone and dolomite. Finely- to medium- Ç Kilometer Upper crystalline. Thin-bedded to massive with thin shale partings; bioturbated. Gravel pit accurately reflects the source data used in its preparation. This map is date Ordovician specific. As additional data become available, geologic interpretations may be Thickness 40-80 ft (12.2-24.4 m) & revised and the map may be updated by the Geological Survey Program. This Contour Interval 40 Feet UTM GRID AND 2012 MAGNETIC NORTH Quadrangle location Mine shaft DECLINATION AT CENTER OF SHEET Ordovician Winnipeg Formation - Includes the Ice Box Shale Member - 30-45 ft map should not be enlarged or otherwise used in an attempt to interpret more Ow (9.1-13.7 m) of greenish-gray to gray fissile shale containing small, black detail than can be seen at a scale of 1:24,000. O phosphatic pebbles, grading upward into the Roughlock Siltstone Member - Mine adit or cave 25-40 ft (7.6-12.2 m) of tan to yellowish-gray, calcareous siltstone and
sandstone. Combined thickness 55-85 ft (16.8-25.9 m) P Trench Disconformity > Group of prospect pits Lower Ordovician Deadwood Formation - Brown, gray, to green basal conglomerate and O_d massive sandstone overlain by glauconitic shale, siltstone, sandstone, and à h Prospect pit c l 5 minor intraformational conglomerate. Middle and upper beds of laminated to u 8 k
e G y s
l e thick-bedded, brown, gray, to dark-green, bioturbated, glauconitic shale and a l Upper y r i E s t E e w C H
N Cambrian
s a
h Cambrian I
N sandstone, intraformational conglomerate, and limestone. Approximately l t I d
e A' g L F e l
A i L l o
i C
B Outline of open pit mine o
H 15-25 ft (4.6-7.6 m) of medium-bedded to massive "Scolithus sandstone" h C
v 7,000
I 7,000 t N c . l l d w t e T O_d e Y S e o e u occurs at the top. Thickness 250-400 ft (76.2-121.9 m) . e t v N v i S o
D O_d e U w Tw O_d e h
A Tar Tar l l
W
Tw S a W a Tph O_d O_d Trp e e Unconformity s s Tph Tar Qal 6,000 6,000 O_d Qal O_d MDe Mp n n Trp
O_d a a ? Outline of mine waste pile e e O_d Metagabbro - Grayish-green to greenish-black, finely- to medium-
Oww m m
?
e e Xmg crystalline dikes and sills composed of plagioclase, hornblende, biotite, v v o o 5,000 ? 5,000
? b b ? and calcite. May have a schistose appearance. Protolith is gabbro a a
?
? t t e e ? Xe e e Xe Xf ? f
f Xu
?
Xe Flag Rock Formation - Light-gray to greenish-gray sericitic schist, n n i i
4,000 4,000 Xf n laminated pyritic and graphitic phyllite, and hornblende-plagioclase schist. n o o i i t t Locally with pillow structures, streaked graphitic quartzite, metachert, and a a v v ? ? e e
l metamorphosed carbonate iron-formation with cummingtonite, biotite, and l E E 3,000 3,000 chlorite similar in appearance to the Homestake Formation. Protolith is pillow basalt with interflow deposits of siltstone, carbonaceous shale, chert, and iron carbonate. Thickness up to 5,250 ft (1,600.2 m) in the area of the Homestake Mine (Slaughter, 1968; Caddey and others, 1991)
Unconformity
Northwestern Formation - Gray to dark-gray phyllite, slate, and Xn biotite-sericite schist. Thin- to medium-bedded, however laminations and bedding are rare. May contain minor tourmaline and titanite. Protolith is shale, carbonaceous shale, and siltstone. Thickness up to 4,265 ft Index to sources of geologic data Selected References (1,299.9 m) in the area of the Homestake Mine (Caddey and others, 1991) (letters correspond to those listed in Selected References) Xe Ellison Formation - Xe - Light-gray to black, banded, well foliated, Xeq sericite-quartz phyllite; light-brown, thick-bedded to massive, biotite-quartz Caddey, S.W., Bachman, R.L., Campbell, T.J., Reid, R.R., and Otto, R.P., 1991, The Miller, P.A., 1962, A study of the Bald Mountain mining area, Lawrence County, South Dakota: phyllite; light-gray to pale-brown quartz-mica schist; and minor amphibolite. Homestake gold mine, an Early Proterozoic iron-formation-hosted gold deposit, Rapid City, S. Dak., South Dakota School of Mines and Technology, E.M. thesis, 133 p. Conglomerate beds rare. Few thin beds of limestone occur in the area of c Lawrence County, South Dakota d e : U.S. Geological Survey Bulletin 1857-J, p. 1-67. Lead and increase in abundance to the south. Xeq - Quartzite, light to Noble, J.A., and Harder, J.O., 1948,Stratigraphy and metamorphism in a part of the northern dark-gray. Probably derived from chert. Locally contains minor graphite a b DeWitt, E., Buscher, D., Wilson, A.B., and Johnson, T., 1986, Map showing locations of Black Hills and the Homestake Mine, Lead, South Dakota: Geological Society of and sulfides. Formation protolith is sandstone with siltstone and shale. mines, prospects, and patented mining claims, and classification of mineral deposits America Bulletin, v. 59, no. 9, p. 941-975. Thickness approximately 1,312-4,921 ft (399.9-1,499.9 m) in the area of the in the Lead 7 1/2-minute quadrangle, Black Hills, South Dakota: U.S. Geological Homestake Mine (Caddey and others, 1991). A metatuff in the lowermost f Survey Miscellaneous Field Studies Map MF-1978-E. Redden, J.A., Peterman, Z.E., Zartman, R.E., and DeWitt, E., 1990, U-Th-Pb geochronology Ellison Formation has an age of 1,974 +/- 8 Ma (Redden and others, 1990) and preliminary interpretation of Precambrian tectonic events in the Black Hills, South a. Harris, K., 1991, Petrology, geochemistry, and petrogenesis of the Tertiary igneous intrusions Dakota: in Lewry, J.F., and Stauffer, M.R., eds., The Early Proterozoic Trans-Hudson Homestake Formation - Gray, brown, to green carbonate-facies iron- in the Annie Creek and Foley Ridge mines, Black Hills, South Dakota, and their orogen of North America: Geological Association of Canada Special Paper 37, p. 229-251. Xhs formation with chloritic and biotitic schist and phyllite and thin quartzite beds. relationship to the gold-silver mineralization: Rapid City, S. Dak., South Dakota School Typically occurs as olive-green to gray-green siderite phyllite with moderately of Mines and Technology, M.S. thesis, 112 p. d. Shapiro, L.H., and Gries, J.P., 1970, Ore deposits in rocks of Paleozoic and Tertiary Lower well developed graphite-rich layers as much as 0.2 in (5 mm) thick in the age, northern Black Hills, South Dakota: U.S. Geological Survey Open-File Precambrian Proterozoic upper greenschist facies, and as olive-green to dark-green cummingtonite- b. Jumnongthai, M., 1979, Geology of the Sugarloaf Mountain area, Lead, South Dakota: Report 70-300, 235 p. grunerite schist with minor chlorite and almandite in the lower amphibolite Rapid City, S. Dak., South Dakota School of Mines and Technology, M.S. thesis, 101 p. facies. Thin-bedded to massive, with lenses of chloritic schist, thin metachert e. Slaughter, A.L., 1968, Homestake mine: Wyoming Geological Association, 20th Annual beds, white quartz veins, and approximately 3 ft (0.91 m) of layered chloritic c. Larsen, R.K., 1977, Geology, alteration, and mineralization of the northern Cutting Stock, Field Conference Guidebook to the Black Hills area, South Dakota, Montana, and schist transitional into the Ellison and Poorman Formations. Gold is Lawrence County, South Dakota: Rapid City, S. Dak., South Dakota School of Mines and Wyoming, p. 157-172. associated with a quartz-chlorite-pyrrhotite-arsenopyrite assemblage. Technology, M.S. thesis, 147 p. Original thickness approximately 66-98 ft (20.1-29.9 m) before f. Usiriprisan, C., 1979, Geology of the Woodville Hills intrusive body, Lawrence County, South metamorphism. Presently 0-164 ft (0-49.9 m) thick, increasing to 410 ft McDowell, F.W., 1971, K-Ar ages of igneous rocks from the western United States: Dakota: Rapid City, S. Dak., South Dakota School of Mines and Technology, M.S. thesis, (124.9 m) thick in fold hinges. Protolith is carbonate iron-formation with Isochron/West, v. 2, p. 1-16. 74 p. interbedded shale and chert (Caddey and others, 1991)
Poorman Formation - Xp - Light-gray to black, graphitic phyllite, Xp sericite- and biotite-rich carbonate, and quartz-bearing phyllite. Fine-grained, laminated to thin-bedded with prominent banding, especially in the upper 100 ft (30.5 m). Locally with white to gray metachert layers containing Xpy variable amounts of graphite, ankerite, garnet, tremolite, and streaks and blebs of pyrrhotite. Chlorite increases around quartz veins, amphibolite Acknowledgements masses, and near the Homestake Formation. Protolith is siltstone, calcareous and carbonaceous shale, tuff, carbonate, and chert. Thickness 656-3,280 ft (199.9-999.9 m) in the area of the Homestake mine (Slaughter, Unpublished field maps were generously made available for the completion of this project by the Golden Reward Mining Company, J.A. Noble and Homestake Mining Company, and Wharf Resources (USA) Incorporated. Compilation of the geology of this 1968; Caddey and others, 1991) quadrangle was underwritten by the South Dakota Govenor's Office of Economic Development "Future Fund'" Homestake Mining Company, Brohm Mining Corporation, Wharf Resources (USA) Incorporated, and LAC Minerals Incorporated. We also thank Dan Costello of the Geological Survey Program for assistance with review of the map layout, and the many South Dakota landowners who have allowed access to their properties. Yates unit of the Poorman Formation - Xpy - Dark-green, massive to faintly banded, finely-crystalline, hornblende-plagioclase schist. Contains white calcite bands and veinlets to 0.79 in (2 cm) thick. Locally, partially to completely replaced by chlorite-calcite-biotite. Contains interflow deposits of graphitic quartz-sericite phyllite, grunerite iron-formation without sulfides, and metachert. Protolith is tholeiitic basalt, tuff, siltstone, and shale. Yates unit in the northwest corner of the map by Labrador Gulch may not be equivalent to the Yates unit at other areas. Thickness 1,968-3,937 ft (599.8-1,199.9 m) in the area of the Homestake mine (Caddey and others, 1991)
Undifferentiated Early Proterozoic rocks - Shown only in cross Xu section