Preliminary geological and geochemical results from
the Silver Creek and Yellow Ridge mineralized
areas in the Washakie Wilderness, Wyoming
by
Frederick S. Fisher, John C. Antweiler, and
Eric P. Welsch
Open-File Report 77-225
1977
This report is preliminary and has not been edited or reviewed for conformity with U.S. Geological Survey standards.
Introduction
Anomalous metal concentrations were discovered in the Washakie Wilderness by the U.S. Geological Survey during mineral-evaluation studies of the area. Cody, Wyo., the nearest town, is about 100 km northeast of the area. The Washakie Wilderness includes the former South Absaroka Wilderness Area, the former Stratified Primitive Area, and several adjoining wilderness study areas in the Shoshone National Forest. The two mineralized areas (fig. 1) described in this report, accessible only by foot or horseback, are as follows:(1) The Silver Creek area located on the Fall Creek 7 1/2-minute topographic quadrangle map, approximately 18 km from the road's end at the South Fork Ranger Station. It is accessible by a good horsetrail along the South Fork Shoshone River trail to the mouth of Silver,Creek, across the river from the trail, and by foot up Silver Creek.(2) The Yellow Ridge area located on the Francs Peak 7 1/2- mlnute topographic quadrangle, approximately 35 km from the end of the Greybull River road. A good horsetrail follows the Greybull River and Yellow Creek to within 1 km of the mineralized area.
Rock samples from the two areas contain anomalous amounts of copper, lead, zinc, molybdenum, gold, and silver. The magnitude of the anomalies is similar to that of those anomalies described by Fisher (1972) in the Stinkingwater Mining Region and by Wilson (1975) in the Meadow Creek area and the Kirwin mineralized area (Wilson, 1964). The pattern and types of alteration associated with the metal anomalies in both areas are similar to those around porphyry copper deposits elsewhere in the Absaroka Mountains (Fisher, 1972; Wilson, 1964).
The Silver Creek area
Copper minerals and molybdenite are exposed in altered rocks of an intrusive complex in the Silver Creek area (fig. 2). Two types of intrusive rocks have been emplaced into Tertiary extrusive rocks of the Wapiti, Trout Peak Trachyandesite, and Wiggins Formations. The host rocks as well as the intrusives have been hydrothermally altered.
An exposed mineralized zone about 600 m by 300 m in the central part of the intrusive contains disseminated malachite, chalcopyrite, and bornite and small amounts of molybdenite. Chalcopyrite also occurs with pyrite in small veins. Pyrite is abundant in the central part of the mineralized zone, and it also occurs with sparsely distributed sulfides of zinc and lead in the outer part of the mineralized area.
Malachite is common along well^-developed fractures that trend from N. 35-°.E. to, N. 80° W. an& dip -vertical to 50° east and south. ! Analytical results of some rock samples Indicate highly anomalous c^dentratiitmSi.of cdpper, (f ig»t 3); some of the coeka also contain smaller, but still anomalous r concentrations^of lead, zinc, molybdenum, silver, and gold (table*.l)vr- " i ?:- t. - .:s :
intruaive .'complex :coirsiista -o£ atl riteas^^twcr-Tkindfif of The larger and more intensely mineralised stcrck is dacite-^rhyodacite porphyry itbat contains iphenocrystsi^orf-^rlagloclalse (25-30%$? (10-45%) v'and bio^ite :C5*10%)>. v A ismalLer-atsi 4tes<& minerarMze'4 is dac ite .porphyry ?thztt &is. .tiharac t er izsd ^jy> euhedral. ihornblfinde phenocrjrs^ta (10-15%^)sj 3±&i&Lso contains plagio/ciase pfeenflOBJcysta'
i intrusive rocks and the adjacent exOEii^ivetvhydrothermally alterexi. :--Alfrer-atloir dn 'the butgmosf zone: is - s - predominantly ̂ iropylitici-(jcharapteri^ed tyf cKLo^te^ical'cite, s and epidote). Alteration^ in "Uie-tenter of the;4d©mple^e ±s ,- predominantly sericitic (characterized by quartz, sericite, and pyritej; the "center contains small, irregular-shaped zones altered rocks characterized by* small quartz-potassium veinlets;and&by secondary-.-biotite and magnetites ^Alterations ^^ : boundaries, are;.indistinct^*and-^the zones commmonly overlap. H 2 Hydrothermal alteration generally preceded-Mneraii^atiOn. T&& ̂ sulf ides of greatest- economic- interest^ '(chalcop-yrlcv, bornitev molybdenite) are- contained" within the sericitlcjand- potassic zones Pyrites is comman throughout the: central part-of the complete but much less abundanfcr in: the-propylitic zone. "~ '- - - ~..~:.~
-.-'-, *L--;- ;: ; The Yellow Ridge area '-£. > ~ - : ,
Copper- minerals : are; Exposed in highly "altered intrusive rocks on'the southeastern slope of Yellow^Ridge (fig. 4). Plutons with avsur.face area of "about 2.5 ka£ihave been emplaced into extnisive^flowsiand breccias of j?the Wiggins Formation of Tertiary age. Pervasive hydrothermal alteration has affected the host rocks as well as the intrusive rocks.
A narrow (60- to 100-m) zone, of mineralized rocks is exposed in a northeasterly direction for. about 750 m along the southeastern part of the intrusive complex. Malachite is the most common ore mineral in this zone; it occurs both as disseminated grains and as coatings on fracture surfaces. Pyrite and smaller amounts of chalcopyrite, bornite(?), and molybdenite(?) are the major sulfide minerals in the zone. Pyrite is also present with quartz in thin irregular veinlets. Analytical results taken from some rock samples indicate highly anomalous concentrations of copper (fig. 5). Some of the samples are also anomalous, but to a lesser extent, in their content of lead, zinc, molybdenum, silver, and gold (table 2).
; At least three types of intrusive rocks are found:in the area. The largest and probably oldest.pluton is granodiorltic to dioritic in composition and contains small ;(about 1 mm) subhedral to euhedral grains of plagioclase (labradorite :- An^|> (60^7QX) ,.. hornblende -£L quartz (2-5%), and potassium feldspar ii:(2«al*%)^r The~d±aTitic rocks have been intruded by an andesite porphyry characterized by J.arge (5 mm to 2 cm) euhedral plagioclase (andesine - An^g) phenocrysts and
to 2;inm)jjeuhe4r]alpheno^aigzsfcs :of shiotite 'and^horribienie.constitutes: aiawctniSito 4§% -of ufr the an4esdte;£~pf the
5 _to 5fcQ%j; hojaiblende:»; e^ it«feidO%; 7«mall' crounded quartz/ grains, iatri»fmateMaiL^S^»oiit 50%,.^Q Ai'tfhird "type oofi intrusive
rock Jb&'-tUcifrXal.loV Ridfee area is_-a iiorntrlende^amdesite that contains small (l~&i^^^^uli&&x!^ pSagi?iclasfe::f4D-"to 5eOX:), . hornblende-(20 to 25%), and anhedral quartz (2 to 3%). The ho£ablende andesite may be simply a finer grained porphyritic phase of the dioritic intrusive;bo4y< Most>af itiiejiiidgafisralizatifion aEppears^tff have been associated with the .andasite porphyry characterized iby the isarge^j '' plagioclas^,pti£finocry&t&5ffiiowever^ irc places ther.diorlM <r rocks fond ' hornblende andesite ^aver-^lso been mineralized. 4. -. jBicr ,^ *-
Ali^st ^ii -of thte infrsnfive. and; extrusiVB -rocks of the Yellqfcrr Ridge ar^ea have been^ hydro thermally uaitereii.^ a The outer -zones of ^the intrusive bodies and surroundingbextrusive : rocks, haawe been propylitically altered and.,- are? ehara^termed,- \>y secondary chioriteVi calcite, and . eipdote* ' Hornblende icryetalsowere apparently mone^ susceptibie^o:, alterat^pn, amd cjpmmonJy^pseudomorphFiAf: chlorite-and eipdote aftet hornfclende ajje preseat:in_..th«asame:rotitivltfei-rcomplBteiy-unaltered biotite^ Nearer tbe^central part fof the^ intrusive;complex, quartz^ sericite, and some pyrite are more common; and: in places the rocks have been completely altered to masses of these minerals. The rocks have been potassically altered in fhe^sdutherniand southeastern parts of the intrusive complex particularly within and immediately adjacent to the most-heavily mineralised zone. :& In these-rocks the-alteration products are secondary biotite, disseminated magnetite, and veinlets of quartz-potassium^feldspar aad magnefefcte. Although quite ext&ensive^ly altered, the original texture of thespbtassically altered Crocks is' commonly well preserved.
References
Fisher;, F. S., 1972.,, Tertiary mineralization and hydrothermal
alteration in: the Stinkingwater Mining Region, Park County,
Wyoming: U.S. Geol. Survey Bull. 1332-C, 33 p.' '"i *'
Wilson, W. H, .19(54, tli^^r^in mineralized area, Park County, ..
Wyoming: Wyoming- Gepl«,_ SurVey. Prelim. Rept. 2 , ?1^> p.
- 1975, The copper-bearing feadow Creek granodiorite, Uppers: i' '"' - " \r . -,:- * f " '_; ,
Wood Rivet area, Park County, Wyoming, in Wyoming Geol. Asfeoc.
Guidebook 27th Aiiii'; Field Cpnf., BighTOb Basin, 1975, p. ^5-241,
Table 1. -, Analyses of rock samples from the Silver Creek mineralized area [Analyses for copper, lead, zinc, and gold are by atonic absorption. Silver and molybdenum are by a six-step spectrochemical.procedure by R. T. Hopkins, Jr. Numbers.in paBeistheaes beneath element symbols raSre'febe lowest^ abundance levels at which the elements can be satisfactorily determined by the analytical method used; L, detected fc but in amount below satisfactory measurement level; N, not .detected. Values in parts per million (ppsa)] ^ . :^ t'..,-,.? , I >v^ > ; Tr,
Sample , No.
- -
FA346RCQ JFA347RFA34£R,FA349RFA3533
* - ' ' . ^_ - * »J
FA352RFA354RFA356RFA357RFA360R
FA363RFA366RFA367RFA369RFA371R
FA373RFA375RFA377RFA379RFA380R
FA381RFA385RFA387RFA389RFA391R
FA394RFA396RFA398RFA1300RFA1304R
FA1306RFA1308RFA1309RFA1311RFA1313R
FA1315RFA402RFA404RFA406RFA407R
FA408RFA17R
"' ~Ag :
! .j<?£5> .
.^iN;,;,;N
...,. -,-- N, ,-.., -_>. >. iT^ 1
-rl-: .N N
20NN
NNNN.5
.7NNNN
NNNNN
N1LN1.5
1NNNN
N7.5NN
3N
. .. . _ . . , i. _ . - Cu
,.^_ q>.,..---.- r*70' ^j",'i: '.>" *. w" . "~ 5
10o: , 4o-s
170; : ^. .f-fon .: .: 3
10530
20,00026020
401010
5,5001,500
1,3001,200
1595
150 -
452510125
152,0001,800
L140
3805
32026025
- no*280500 N250100
L240
" '-;4io " "(5)
SVT.T:-, .... '.x9 *'' ' ' " T
'^.f - 7i,; '.'N:^ 7;
N...,,N ; '^ <: ;"*
201030
150N
N NN
10020
7020NNN
NNNN5
N100'5
NN
10NNNN
N3030N70
N5
u -:^ ->' '^H T->b
, J5) v"i - '
.-30 .- -" ' 1 ""i'l !. "" "*, 'io~
20i- - ' 85 ..,
J 130' '.... ,\.T i-. ritJ
55
1010A5
1020 '
102010
155
102510
1010101540
1040102070
2050501515
15440
555
1010
,--. : i : -* '. "4n>,
(5)
N'? ':>,.. 35. - ":
*. 60.-.^ r-s 180 -i
2 ,,000Ei " ~ J" ("' '
L354020
160
16095403020
1555552510
1045556045
65203040160
180120602060
401,400
251010
5030
- 1 1 1
ii:^u :-?
(0.05)
N^ N*~H
, N. Nr L'
N0.80LN
NNN.20.10
.20
.10NNN
NNNN .N
N.10L
. NN
NNNNN
NLL
, NN
NN
Table 2. Analyses of rock samplog from the Yellow Ridge mineralized area (Analyses lor copper, lead, zinc, .and gold are.^by atomic absorption. Silver and molybdenum are by a six-stop spectrocliemical procedure by R. T- Hopklns, Jr. Numbers in parentheses beneath element symbols are the lowest abundance levels at which the elements can be satisfactorily determined by the analytical method used; L, detected, but in amount below satisfactory measurement level; N, not detected. Values in parts per million (ppm))
Sample No.
FR1373RFR1375RPR1389R tFR1391RFR1392R
FR1393RFR1394RFR1335RFR1396RFR1397R
FR1398RFR1399RFR2300RFR2301RFR2302R
FR2303RFR2304RFR2306RFR2307RFR2308R
FR2309RFR2310RFR2311RFR2312RFR2313R
FR2314RFR2315RFR2316RFR2317RFR2318R
FR2319RFR2320RFR2321RFR2322RFR2323R
FR2324RFR647RFR648RFR649RPR650R
FR652RFR653RFR654RFR655R -FR1065R
FR10S6R "FR1067RFR1070RFR1071R "FR1072R
Ag (0.5)
-,, NN -
» N
NN
NNNNN
NNHNN
NNNNN
HNN
'" N
2
NN1.5N
10
N333N
NNNNU _
NA,NNNN
~ - N " »>NN
- - H A?"1.5
Cu (5)
2015301510
30 ; -1010455
1020551035
53025 ,5
A0
255
102080
4
25 -30
280 ;3,400 .'3,600 -
6,2003,3008 , 1-002WT65
55302520
; 1025305520
4S25L255
Mo (53
NNNNN
~ N.
L. _ 2.
N' N
LN
NLN
'' - 7
N10NN
NNNNN
..* ../ L50N7
73010
100/ N
5N5NN
NNN10H
NLN
, N15
Pb (5)
2015 -50 ~
520
10'205
5030
100 '
20351010
' 5 "'
10152515
2051015
500
55.60201020
20;1565 -
2401075 '
25153015
75152070.10
1025102510
Zn (5) .
3570804040
65'80
L5(5 "
130
130",20351035
L355560>H'(!0 ;
40507550340
130 :152070.35
11090
1805
40
9085'
606055
17060708080
50555
9015
Au -(0-.051 _
V **"* -
^ - N "' >.
'- ;»
N
NH
- -liNTN
N '':. N '"' N
' N
N
N^NNN - N
7 N'.',. NNNN
, ,--" y
NN0.05.05
N.25L.70N
NNNNN . .-
N8^R-NN
NNHNN
Sample
FR656RFR6S7RFR658RFR659RFR660R :.
FR661R. . ,FR663RFR665RTR667R~FR669R
FR670RPR671RFR672RFR673RFR674R
FR675R.FR676RFR677RFR678RFR679R
FR680R ^FR681RFR682RFR683RFR684R
FR685RFR686RFR687RFR1404RFRli407R
FR1408R. FR14118,FR1412RTFR1413RFR1420R
7R1421RFR1422RFR1423RFR1424RJR1425R
FR1426RFR1427R fFR1428RFR1074RFR1078R >
FR1079RFR1080R
4,-' N
NNN0.7
i5-tc</-tf/yN
v--...jj _ .
N
N,'N*,N*
IfN
NNR~
.NN
J
NN
' N
NN
N" N " '
NNN
NNNNN
NNN1.51
NNNN ~
1.5
N1
Cu (5)
10153535
950
920 ,';2,80tt-'
29.06D-- - : - '-"iJio^-i-.'--, 40'"3ti
15f 15
353D
1510101010'
^15
12010
' 255
15- 45
10, 1525
3510752530
1535
-C; 80
30,0006,600 _
2520301020
5130
Mo (5)
5t_H
JH"
20C100
^30 '
NN
10. _.10
-i JA/ir7NN7N
LNHN7
L177 -:,N
5NNN20
NNNNN
NNNNN
1020NNN
N10
-
Pb (5)
155ft' 20"-
50?5 1
2502030ML.65
]-; p \^f
255
10W is-1010101020
207520455
2010102515
2020201515
302515
30030
55101010
270
1020
Zti
15 -704020
120
10090
1909010
r ~ \8535505065
40405011040
4016060855
404030605
4025304050
' 55
40100210110
LL9040320
4510
_
Au - (0.05)
tf N^ N
: N-'- . N
0.10
.10LLNS '"
NNNNN
NNyNN
NNNNN
NNNN.05
NNNNN
NN ~ x
L.10.05
N NNNN
NN
44*30'110*00' 109*45 108*30' '109M5'
44*16
44*00
52*30'
SHOSHONE NATIONAL FOREST
TETON NATIONAL FOREST
W LDERNESS
PRIMITIVE AREA
SHOSHONE NATIONAL FOREST
Wilderness Area
National Forest BoundaryFigure 1. Map of the Washakie Wilderness, showing
the location of the Silver Creek and Yellow Ridge mineralized areas. National Park Boundary
Topographic Quadrangle
(1
44*2
130'
44*2
EXPLAN
ATION
Intr
usiv
e ro
cks
Figure 2. Map sh
owin
g location of
'r
ock
samp
les
from the
Silver Creek
mineralized
area,
and-area of
intrusive
rock
s
Extrusive
rocks
of th
e Wi
ggin
s, Trout
Peak
, and
Wapa
ti Formations
3f
9 Sample lo
cation
Faul
t 300
1000
600 meters
2000 fee
t
44
44»2
'30
Figure 3. Map sh
owin
g copper con
cent
rati
on in ro
ck, samples
from
the
Silver Cr
eek
mineralized
</V(
^>' '
v> .-
'-r\iL
,/ ^
-''
>'.-
jsJm
'M^&
s'--
, - J .
£Mh v
area
x <5
Q
ppm
Cu
50 -
100
ppm
Cu
o 100
- 50
0 ppm
Cu
3 500
- 1,
000
ppm
Cu
>1,POO ppm
Cu
_JJ
OO
______600
met
ers
1000
20
00 f
eet
44»1'1
0
109°21'
43«54'30
\VC\Y/' ; --rr^ ! ._;* \-_--^" '.. > XVvcr 7 r^T-3Yir»T*a»»ir~w?r"Tt«?5r*^^'feW^ :; ,>tii/*si gs&z&P'"-^\VHM ; \«*<,,W3^£«; -r.-/^^
MILE"~t'_ y^ '~r ~ ~'~jf-^~-^~'~'T~~~ j[^
ya KILOMETER
Figure A. Map showing location of rock samples from the Yellow Ridge mineralized area, and areas of in trusive rocks
EXPLANATION
Intrusive rocks
Extrusive rocks of the Wiggins Formation
Sample location
ESS'
100*21 1 100*20'
43*54'30'
"N,
43*53'45"
F^zst-^-%6 V
_ _-_ f 'r - _- --. . , -' ' ' ' i" j f 'f i K» T -T yjp TT ^ - - *r . " .T ^ V
'/a MILE
I"JE=£B
% KILOMETER
Figure 5. Map showing concentration of copper in rock samples-from the Yellow Ridge mineralized area
EXPLANATION
* <50 ppm Cu
50 - 100 ppm Cu
o 100 - 500 ppm Cu
3 500 - 1,000 ppm Cu
>1,000 ppm Cu
