LA-ICP-MS AND TIMS U-PB DATA FILES FROM THE ISKUT PROJECT (DEASE LAKE TO KITSAULT) - JOANNE NELSON RICHARD FRIEDMAN BRAM VAN STRAATEN
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LA-ICP-MS and TIMS U-Pb data files from the
Iskut project (Dease Lake to Kitsault)
JoAnne Nelson
Richard Friedman
Bram van Straaten
GeoFile 2021-10
Ministry of Energy, Mines and Low Carbon Innovation Mines, Competitiveness, and Authorizations Division British Columbia Geological Survey Recommendation citation: Nelson, J.L., Friedman, R., and van Straaten, B., 2021. LA-ICP-MS and TIMS U-Pb data files from the Iskut project (Dease Lake to Kitsault). British Columbia Ministry of Energy, Mines and Low Carbon Innovation, British Columbia Geological Survey Geofile 2021-10, 13 p. Front cover: Betty Creek Formation tuff and volcanic breccia exposed on summit ridge above near-horizontal ledges of orange- weathering conglomerate and arkose of Snippaker unit (basal Hazelton Group) on Snippaker Ridge, lower Iskut River area. Back cover. Above, characteristic zircons derived from main Jurassic and older sediment sources in Stikinia. Below, typical Jack Formation conglomerate near Bruce Glacier, with rounded intrusive clasts and carbonaceous mudstone intraclasts.
LA-ICP-MS and TIMS U-Pb data files from the
Iskut project (Dease Lake to Kitsault)
JoAnne Nelson
Richard Friedman
Bram van Straaten
Ministry of Energy, Mines and Low Carbon Innovation
British Columbia Geological Survey
GeoFile 2021-10
LA-ICP-MS and TIMS U-Pb data files from
the Iskut project (Dease Lake to Kitsault)
JoAnne Nelson1, a, Richard Friedman,2 and Bram van Straaten1
1
British Columbia Geological Survey, Ministry of Energy, Mines and Low Carbon Innovation, Victoria, BC, V8W 9N3
2
Pacific Centre for Geochemical and Isotopic Research, University of British Columbia, Vancouver, BC V6T 1Z4
a
corresponding author: JoAnne.Nelson@gov.bc.ca
Recommendation citation: Nelson, J.L., Friedman, R., and van Straaten, B., 2021. LA-ICP-MS and TIMS U-Pb data files from the Iskut
project (Dease Lake to Kitsault). British Columbia Ministry of Energy, Mines and Low Carbon Innovation, British Columbia Geological
Survey GeoFile 2021-10, 13p.
Keywords: Stikinia, Iskut, Golden Triangle, U-Pb zircon crystallization ages, Hazelton Group, Triassic, Jurassic
1. Introduction contributing sediment sources. The main focus of this project
Between 2013 and 2016, stratigraphic and structural studies in was in the central part of the Iskut-Stewart volcanic field,
northwestern Stikinia between Dease Lake and Kitsault (Fig. 1) near the McTagg anticlinorium (areas 1, 2 and 3, Fig. 1) and
focussed on uppermost Triassic to Middle Jurassic volcanic and on Snippaker Ridge in the Snip-Bronson corridor (area 4, Fig.
sedimentary rocks of the Hazelton Group (Fig. 2). In the course 1). Basal Hazelton conglomerates were also sampled near Red
of this work, 14 samples of siliciclastic rock were collected for Chris (area 5, Fig. 1) and near Gnat Pass (area 6, Fig. 1). Two
LA-ICP-MS U-Pb analysis of detrital zircons, and 4 igneous samples of a conglomerate unit in the Iskut River Formation,
samples were collected for U-Pb TIMS analysis. Herein we on Mt. Clashmore near Kitsault (area 7, Fig. 1), represent
present complete data and calculations for the entire sample sedimentation at the southern end of the Eskay rift.
set (BCGS_GF2021-10.zip). This dataset provides constraints
on the absolute age of intrusive and stratified protoliths, age 2. McTagg anticlinorium
and affinity of sedimentary sources, and timing of fault-related In this region, the basal unit of the Hazelton Group is an
shearing. These data support previously published (Nelson et unusually mature siliciclastic sequence, the Jack Formation
al., 2018; Nelson and van Straaten, 2021) and forthcoming (Hettangian-Sinemurian), which contains conglomerates with
studies. rounded, primarily granitoid, clasts (Figs. 2, 3; Nelson and
The lower part of the Hazelton Group (Rhaetian- Kyba, 2014; Nelson et al., 2018). Detrital zircon samples
Pliensbachian) is related to island arc construction, along with 13JN01-05, 13JN11-06 and 13JN17-07 are from different
coeval and cogenetic intrusions of the Tatogga and Texas Creek stratigraphic levels in the Jack Formation (Fig. 2). All display
suites (Nelson et al., 2018). The upper part of the Hazelton main peaks ca. 225 Ma (Table 1), consistent with derivation
Group (Pliensbachian-Bajocian) accumulated in a variety of from Late Triassic plutonic sources in the Stikine suite (Nelson
post-arc, syn-collisional settings, including bimodal volcanic and van Straaten, 2021). The youngest population in tuffaceous
and sedimentary strata of the Iskut River Formation in the arkose sample 13JN17-07, collected at the top of the Jack
Eskay rift, widespread mainly sedimentary strata, and collision- Formation in the Brucejack area, is ca. 197 Ma. CA-TIMS
proximal volcanic buildups of the Horn Mountain Formation analysis on zircons from a large plagioclase-phyric leucodiorite
near Dease Lake (Figs. 1, 2; van Straaten and Nelson, 2016; clast in the overlying basal Betty Creek conglomerate (13JN20-
Nelson et al., 2018). Most of the mineral deposits in this very 04) returned an igneous crystallization age of ca. 196 Ma (Table
prolific region, popularly known as the Golden Triangle, are 2), which we consider to define the onset of Hazelton Group
associated with the Hazelton Group and its cogenetic intrusions. magmatism east of the McTagg anticlinorium (Fig. 2; Nelson
Red Chris and the KSM trend are porphyry deposits related to et al., 2018).
the Tatogga and Texas Creek suites respectively. The Brucejack Two samples from the upper part of the Hazelton Group,
(Valley of the Kings) epithermal gold vein system formed at ca. 13JN10-07 from the Spatsizi Formation and 13JN02-16 from the
183 Ma, during a late stage of Hazelton arc activity (Tombe et Bruce Glacier unit (Fig. 2), contain both penecontemporaneous
al., 2018). grain populations and older grains recycled from the Jack
Detrital zircon samples were collected along a northerly Formation (Table 1).
transect extending for 270 km between Dease Lake and A thick (>500 m) unit of coarse conglomerate with two 10
Kitsault (Fig. 1). This sampling was aimed at constraining the m interbeds of maroon pebbly mudstone occurs in a faulted
ages of siliciclastic units in the Hazelton Group and the ages of panel west of the Tennyson porphyry prospect, south of the
British Columbia Geological Survey GeoFile 2021-10
1
132°W
Nelson, Friedman, van Straaten
Dease
128°W
Lake
KLASTLINE-SPATSIZI
VOLCANIC FIELD
Gnat
Pass
6
Pitman fault AR CH
S T IK IN E
132°W
Iskut 58°N
LEGEND
Mess Creek fault
Red
Stikinia (selected units) Chris
Bowser Lake Group 5
Jurassic-Cretaceous
clastic overlap strata
upper Hazelton Group
mainly sedimentary Eskay
Iskut River Formation
Mess rift Kemess
Creek
Horn Mountain Formation 4 Eskay McTagg
lower Hazelton Group: anticlinorium
uppermost Triassic - Oweegee Dome
Lower Jurassic volcanic, Snippaker ridge
sedimentary strata KSM, Brucejack
1
Lagerge Group 2
Lower Jurassic ISKUT-STEWART Bowser
clastic strata VOLCANIC FIELD 3 basin
latest Triassic-
Early Jurassic plutons Red Mtn.
Stewart
Peri-Laurentian terranes 56°N
Big Bulk
Stikinia
Ank
Quesnellia 7 Kitsault
Cache Creek
Yukon-Tanana
Other
Coast Plutonic Complex/ AL AS KA
Coast Mtns. orogen Smi
Ancestral North America BC
Terrace
(Laurentia)
R CH
Insular; outboard terranes A
KP
Prince NA
4 Sample locality Rupert SR E
54°N E
SK
Stikinia - major mineral deposits
Porphyry deposits
latest Triassic-Early Jurassic JP
Gold deposits Early Jurassic 0 50 100
Volcanogenic massive sulphides
Eskay Creek - Middle Jurassic
km
Gamsby
Fig. 1. Geology of northwestern Stikinia, including the Iskut-Stewart, Klastline-Spatsizi (lower Hazelton Group) and Eskay and Complex
Horn Mountain W
(upper Hazelton Group) volcanic belts, with detrital and igneous zircon sample areas. For stratigraphic context of sample areas 1-7, see Figure 2.
For details of sample areas 1 and 2, see Figure 3. For details of sample area 4, see Figure 4. For details of sample area 7, see Figure 5. F
British Columbia Geological Survey GeoFile 2021-10
2
Nelson, Friedman, van Straaten
1. McTagg west
2. McTagg east 5. Klastline
4. Snippaker (Iskut village) 6. Gnat Pass
1. west 2. east
Aal Baj Bat
4
168.3+1.3
MIDDLE 4
Bowser Lake Group Bowser Lake Group
Bowser Lake Group
170 170.3+1.4 Quock Formation
Iskut River
Formation
upper Hazelton Group
Willow Ridge Horn Mountain
4 Formation
174.1+1.0 Bruce
Glacier Spatsizi
Formation
upper Hazelton Group
13JN2-16
Toarcian
Spatsizi
Formation
Spatsizi Fm. 13JN10-7
JURASSIC
180
Eddontenajon Fm.
4
182.7+0.7
LOWER/EARLY
15BvS3-14
PITMAN FAULT
Pleinsbachian
Brucejack
Lake
v v
v
Betty Creek Fm.
4
190 190.8+1.0 Unuk v Northern
v River
v v v
13JN20-04
v v v
v
Sinemurian
Stikinia
Betty Creek Fm.
v v v v
v v Unuk v
2014JK150
depositional
v v v
River
v v v
Hazelton Group
v v v hiatus
v v v
13JN1-05
17-07
13JN11-06 13JN
199.53+0.19/.29
3
Jack Fm. v v
JK074lower
200 Het. 201.58+0.17/.282
v v v
2014JK228 v v v v v
v v v v
Norian Rhae-
TRIASSIC
v v v
2014JK072 2014
tian
1
v v
UPPER
205.50+0.35 Snippaker
unit
15JK1310
Stuhini Group
Stuhini Group Red
stock Stuhini Group Hotailuh Batholith
210
A B C D
Fig. 2. Stratigraphic columns for sample areas 1-6 (see Fig. 1). Red symbols, LA-ICP-MS detrital zircon samples; yellow symbol, CA-TIMS
igneous sample of boulder at the base of the Betty Creek Formation. Timescale age references: 1. Norian-Rhaetian boundary (Wotzlaw et al.
2014); 2. Rhaetian-Hettangian boundary (Schaltegger et al. 2008); 3. Hettangian-Sinemurian boundary (Schaltegger et al., 2008); 4. Cohen et
al., (2013).
McTagg anticlinorium (area 3, Fig. 1). It contains clasts of zircon samples were collected to document evolving sediment
andesite, basalt, black siliceous argillite, diorite, chert, quartz, sources. Sample 2014JK072 is a Stuhini Group volcaniclastic
limestone and silicified, cherty limestone, from sources in greywacke from below the basal Hazelton unconformity.
the Hazelton and Stuhini groups and possibly the Stikine Youngest peaks at ca. 205 and 211 Ma (Table 1) likely represent
assemblage (Nelson and Kyba, 2014). Sample 13JN26-06 is the end stages of Stuhini volcanism in this region. Two
of this conglomerate. Main peaks are Early Jurassic (Table Snippaker unit samples, 2014JK074 and 2014JK228, show
1), compatible with deposition during Betty Creek volcanism. ca. 220 Ma peaks (Table 1) that probably reflect Stikine Suite
Alternatively, this could be a coarse clastic facies of the Iskut plutonic sources. Sample 2014JK150, from the basal Betty
River Formation (Kinaskan unit, Nelson et al., 2018) deposited Creek conglomerate (Kyba and Nelson, 2015), has a youngest
at the base of a fault scarp along the margin of the Eskay rift, peak ca 199 Ma (MDA, Table 1), along with ca 204 and 216
that did not incorporate zircons from Iskut River Formation Ma peaks from Stuhini sources. A sample of plagioclase-phyric
(ca. 175-170 Ma). diorite (2014JK227) that cuts the Betty Creek Formation on
Snippaker Ridge is ca. 192 Ma (Table 2), providing a minimum
3. Snippaker Ridge and vicinity age for the volcanic sequence.
The lower part of the Hazelton Group is well-exposed at The Snip-Bronson mineralized corridor is bounded to the
Snippaker Ridge, south of the lower Iskut River (Figs. 1, 4). south by the Sky fault system (Fig. 4), a long-lived, repeatedly
The basal part of the Snippaker unit consists of siliciclastic reactivated fault array (Kyba and Nelson, 2015; Nelson
rocks with granitoid-rich conglomerates that strongly resemble and van Straaten, 2021). Syn-kinematic dikes from the Sky
those of the Jack Formation. However, the Snippaker rocks fault zone yielded U-Pb TIMS ages of ca. 194 Ma (sample
contain Upper Triassic (Rhaetian) macrofauna (Nelson et al., 14JN18-03) and 191 Ma (sample 2014JK308; Table 2). These
2018). The Snippaker unit unconformably overlies arc-related ages demonstrate faulting in the Early Jurassic, during Betty
volcaniclastic strata of the Stuhini Group (Fig. 2; Kyba and Creek volcanism, intrusion of Texas Creek Suite plutons,
Nelson, 2015). In turn, the Snippaker unit is unconformably and associated porphyry-style and intrusion-related gold vein
overlain by volcanic strata of the Betty Creek Formation, also mineralization (Nelson and van Straaten, 2021).
in the lower part of the Hazelton Group (Fig. 2). Four detrital
British Columbia Geological Survey GeoFile 2021-10
3
Nelson, Friedman, van Straaten
1
13JN02-16
13JN01-05
13JN10-07
13JN11-06
2
13JN17-07
13JN20-04
13JN17-07 LA-ICP-MS detrital zircon
13JN20-04 TIMS zircon from igneous
boulder
Fig. 3. Geology of the McTagg anticlinorium region with geochronologic sample sites. Geology of sample area 1 (Bruce Glacier) from Lewis
(2013); see details in Nelson and Kyba (2014). Geology of sample area 2 (Mitchell-Iron Cap–Brucejack) from Nelson and Kyba (2014).
British Columbia Geological Survey GeoFile 2021-10
4Nelson, Friedman, van Straaten
Stratified Rocks Legend Intrusive Rocks
Quaternary
Eocene Coast Plutonic Suite
Edziza volcanic rocks
Early Jurassic Texas Creek Plutonic Suite
Paleozoic Stikine Pluitonic Suite
Upper Jurassic
Cretaceous -
Bowser Lake Group undivided
Hazelton Group
Volcanic and sedimentary rocks undivided
C
Volcanic Rocks
Volcanic rocks undivided
Felsic Volcanic rocks, undivided
I
Coherent rhyolite, autoclastic breccia
Variably welded felsic lapilli tuff
Epiclastic felsic breccia and crystal tuff
S
Andesitic- basaltic volcanic rocks
Subareal calc-alkalic andesite and dacite flows,
pyroclastic and epiclastics and lapilli tuff
MINFILE
S
Pillow lavas, pillow breccias, interbedded
mudstone and mafic volcanic rocks
_
^ significant deposit
Sedimentary rocks # 2013 flycamp
A
Sedimentary rocks undivided
section lines
Limestone
Calcareous sandstone
rivers
R
Turbiditic mudstone - siltstone lakes
Intercalated sedimentary rocks
glaciers
Sandstone, siltstone, mudstone, wacke, tuff; Intermediate grey-green,
U
Jack Formation beige and maroon, very fine to coarse grained, thin to thickly bedded,
arkosic arenites, lesser quartz, graded in part, minor fossils.
Faults
Polymictic conglomerate with well rounded clasts of mainly (70%)
felsic to intermediate intrusive rocks. Intrusive clasts are generally
Type
J
plagioclase-hornblende-phyric and crowded plagioclase porhyries with
tonalitic to granodioritic compositions. Common intraclasts of black
defined
Basal Jack Formation
argillite (10%). Minor clasts of white polycrystalline quartz (10%),
andesite (5%), siltstone + tuff (3%), gossanous quartz-sericite-pyrite approximate
replaced clasts (1%) and carbonate (1%). Quartz-rich arkoses and
pebbly arkoses. Isolated basal carbonaceous mudrocks.
inferred
Stuhini Group
C
Undivided volcanic and sedimentary rocks Motion
I
Volcanic Rocks
4 4
normal
S
Intermediate volcanic rocks ( (
thrust
Mafic volcanic rocks
S
Andesite boulder conglomerate & strike slip
A
Sedimentary Rocks
Structure Lines
Sedimentary rocks undivided
antiform, upright
I
Limestone and Marble F
Argillite, siltstone turbidites, sandstone and wacke
synform, overturned
R
P
Arkosic sandstone, siltstone, mudstone
Arkosic sandstone, tuffaceous polylithic conglomerate
M synform, upright
T
Fig. 3. continued
British Columbia Geological Survey GeoFile 2021-10
5Nelson, Friedman, van Straaten
390000
.
375000
tCr
on
Iskut River
ym
EJIR Bronson
airstrip
cL
M
EJ?B
13JN17-07 LA-ICP-MS
McLymontdetrital
Creek zircon
staging area
Snippa
195.0+1.0 2014JK227 TIMS igneous zircon
Snip Bronson Slope 2014JK072 Snippaker Ridge
ker Cre
EJRB 2014JK228
2014JK227
ek
Br
on 2014JK074
so Billygoat fault 6280000
n Cr Billygoat
ee bowl
k
Johnny 194.0+3.0
Mtn. 2014JK150
193.0+1.0
Mt.
Johnny EJI Inel
2014JK308
S 190.0+3.0 ge
K
Rid
Boundary fault
Y
icite
Khyber
Jek
Pass
Khyber Lehto
Ser
ill
Fault Pyramid Pluton
Ridge
Rive
14,17b
r
F 6270000
A Lake Ridge
U
L
T
e
14JN18-03 dg
S Ri
SCALE Y in
s
S P
0 1 2 4 5 T
3
E
kilometres M
Fig. 4. Geology of the Snip-Bronson mineralized corridor and Snippaker Ridge with geochronologic sample sites (sample area 4, Fig. 1). For
details and locality descriptions see Kyba and Nelson (2015).
British Columbia Geological Survey GeoFile 2021-10
6Nelson, Friedman, van Straaten
LEGEND
Intrusive rocks
LAYERED ROCKS
Quaternary-Recent volcanic rocks: Eocene granite
red-weathering well-bedded flows and tuffs
Early Jurassic
Hazelton Group Lehto plutonic suite
Lehto pluton, Inel, Red Bluff,
Pleinsbachian-Toarcian Iskut River and ?Bronson stocks,
undifferentiated sedimentary rocks volcanic centres on Snippaker Ridge;
many dike swarms not shown on map
Lower Jurassic (Sinemurian) Zone of pervasive
quartz-sericite-pyrite
Snippaker Ridge: andesite, dacite pyroclastic alteration
and epiclastic rocks; volcanic breccias, greywacke,
siltstone; platey tuff Symbols
Johnny Mtn:
dacite lapilli tuff and tuff-breccia, unwelded Past-producing mine
and welded, polylithic; strong planar fabric
dacite flow and welded tuff Developed prospect
Highly variable polymictic coarse conglomerate,
andesitic breccia; black argillite; basalt breccia
(may be Upper Triassic)
Upper Triassic (Upper Norian) Line of section
Snippaker unit
orange-weathering polymictic conglomerate, Uranium-lead zircon age
sandstone, basalt breccia, siltstone, mudstone; (Lewis et al., 2001)
fossiliferous broken limestone formation
orange-weathering laminated siltstone,
black argillite, sandstone
Stuhini Group
Upper Triassic
green polymictic conglomerate with
porphyritic intrusive clasts,
green volcanic sandstone, tuff
heterolithic conglomerate,
mainly andesitic clasts
limestone, marble
andesitic volcanic breccia
undifferentiated volcanic rocks
undifferentiated sandstone, mudstone,
conglomerate, limestone; includes some
volcanic units
undifferentiated greenschist-grade volcanic
and sedimentary rocks, some highly silicified;
may include Paleozoic units
Stikine assemblage?
Upper Paleozoic?
"crinkled chert": laminated, banded,
pink, manganiferous metachert
Fig. 4. continued.
British Columbia Geological Survey GeoFile 2021-10
7Table 1. Summary, Hazelton Group detrital zircon geochronology and age population determinations. Tuffzirc and Unmix calculations from methods of Ludwig (2008).
Breaks in Wtd averages Geological constraints
N distribution
UTM UTM Probability
Sample DescriptionTable 1. continued
Breaks in Wtd averages Geological constraints
N distribution
UTM UTM Probability
Sample Description =203.4 Ma MSWD 0.82 prob .59 latest Triassic ammonite fauna
(Table 1. continued
Breaks in Wtd averages Geological constraints
N distribution
UTM UTM Probability
Sample DescriptionNelson, Friedman, van Straaten
Table 2. Summary, Hazelton Group-allied plutonic rock CA-TIMS
geochronological results.
Within mainly bimodal volcanic
Bajocian; 176-170 Ma). Same
fossil and U-Pb TIMS ages as
unit as 16JN9-6, 600 m along
Geological constraints
Sample # Easting Northing Description TIMS age
which is dated regionally by
sequence of Iskut River Fm.
Middle Jurassic (Aalenian-
Zone 9
14-JN-18-3 388213 6265776 Plagioclase-phyric dike with sheared margins 194.28+0.18 Ma
cutting into and across S-C fabric on Pins ridge. C
= 305/56 NE; S = 324/23 NE.
2014JK308 373530 6274904 Plagioclase-phyric dike with sheared margins and 190.70+0.17 Ma
strike.
foliated chlorite cutting Sky fault system south
side of Johnny Mountain. Internal flattening fabric
327/65 parallels bounding faults and fabrics in host
conglomerates.
best population, Stikine
MSWD 1.2, prob. .26 -
0.000. 14 grains 208.2-
poorly as 16JN9-6. 10
0.000. 8 grains 176.9-
Wtd averages
grains 166.7-174.7:
191.5: 182.2+/-5.0,
222.3: 215.4+/-2.1,
Weighted averages
MSWD 3.7, prob
MSWD 7.0, prob
2014JK227 378594 6280926 Plagioclase-phyric diorite, top of Snippaker 191.55+0.20 Ma
170.7+/-2.3 Ma,
Mountain
suite derived.
13JN20-04 425715 6260099 Boulder, base of maroon volcaniclastic 196.26 +0.12 Ma
conglomerate facies of Betty Creek Fm. atop Jack
Fm, near Katir mine. Crowded plagioclase
porphyry (High level intrusive source?)
Ma (.37) and
215.19+/-1.8
populations.
(.38) - Max
193.3+/-2.3
240.7+/-3.9
specified 4
It suggests
172.13+/-
Ma (.15),
Ma (.10).
0.97 Ma
Unmix
4. Red Chris
Unmix
Dep.,
The Red Chris porphyry deposit (area 5, Fig. 1) is hosted
by the ca. 206 Ma Red stock, part of the Tatogga suite (latest
finds coherent group of
Triassic; Nelson et al., 2018). On the slope west of the mine,
182.90 +8.10 -4.90 Ma
peak, representing IRF
1.55 Ma (Stikine Suite
168.75+5.05 -1.75 Ma
For all grains, tuffzirc
multiple Texas Creek
grains between 166.7
(max dep). 8 grains
18 at 215.45+4.55 -
a thin basal Hazelton Group conglomerate unconformably
detrital grains). 10
176.6-191.5 give
peak, reflecting
overlies Stuhini Group basalt and thin-bedded sedimentary
and 174.7 give
strata (Rees et al., 2015). Sample 2014JK1310 is of this
Tuffzirc
sources.
conglomerate. It yielded multiple peaks between 214 and 230
Ma (Table 1), which span the entire known age range of the
Stikine plutonic suite. It also contains a significant population
of late Paleozoic grains, presumably derived from a nearby
(158.2 Ma) and rest;
decline in ages from
partly Pb loss from
222-231 Ma. Steep
overlap at 1σ, 2σ)
191-198, 210-214,
210 to 167; partly
Scatterplot shows
(Scatterplot and
uplift of the Stikine assemblage and associated intrusive bodies.
multiple sources,
TRUE/FALSE
breaks between
youngest grain
distribution
IRF grains?
Breaks in
5. Gnat Pass
In the Gnat Pass area, near the northern edge of Stikinia
(area 6, Fig.1), the oldest Hazelton Group strata are Spatsizi
Formation sandstone, siltstone, and tuff (Toarcian) that rest
(IRF). 1 grain
"Old" peak at
peaks at 168,
Small Texas
Probability
Creek peaks
peak at 158.
at 190, 200.
nonconformably on the Cake Hill pluton (ca. 215 Ma; van
plot peaks
Main peak
secondary
(double)
216 Ma;
245 Ma.
174 Ma
Straaten and Nelson, 2016). The sedimentary sequence passes
gradationally upwards into Middle Jurassic, mainly volcanic
rocks of the Horn Mountain Formation. Sample 15BVS03-14,
of the basal Spatsizi conglomerate, was collected immediatelyNelson, Friedman, van Straaten
443000
440000
LEGEND
Toarcian-Bajocian
Iskut River Formation
Anyox sub-basin
basalt, pillow basalt
(eastern belt of
Evenchick and McNicoll
Mt. Clashmore 2002)
Clashmore sub-basin
16JN09-08
rhyolite tuff; monomictic,
6148000 polymict conglomerate
62
polymict conglomerate,
16JN09-06 siliceous argillite, tuff
(=EP-96-319-14)
fault
67 siliceous argillite, chert,
55 rhyolite tuff
54
54
Break
basalt pillow breccia
77
basalt tuff
39 58
Main
48 84
44 gabbro, diabase
64 45
52
basalt, gabbro;
58 conglomerate with
gabbro clasts
Clashmore sub-basin monomict granodiorite
Eskay rift system breccia, crudely sorted
and layered; argillite,
basalt, conglomerate
6146000
undivided Iskut River
Formation (central
and western belts of
Bo Evenchick and McNicoll 2002).
na
nz
a
La Late Early Jurassic
SYMBOLS ke (ca 177 Ma) granodiorite:
sheared, brecciated,
LA-ICP-MS locally mylonitic
detrital zircon
Late Devonian (ca 363 Ma)
bedding Anyox sub-basin deformed mafic intrusive
1 km Eskay rift system complex
foliation
mineral lineation
Fig. 5. Mt. Clashmore geology. For geological details and locality descriptions, see Nelson (2017). Previously reported sample EP-96-319-14
from Evenchick and McNicoll (2002).
800 m along strike (16JN09-08) yielded only Mesozoic zircons Febbo, G.E., Kennedy, L.A., Nelson, J.L., Savell, M.J. Campbell,
(Table 1). Both samples show youngest reliable peaks ca. 170 M.E., Creaser, R.A. Friedman, R.M., van Straaten, B.I., and
Ma, which is a reasonable age for the Iskut River Formation. Stein, H.J., 2019. The evolution and structural modification of
Older peaks likely reflect recycling from the Stikine suite and the supergiant Mitchell Au-Cu porphyry, northwestern British
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13Texas Creek suite - lower Hazelton Gp. (205-178 Ma) Paleozoic plutonic and volcanic sources (360-290 Ma)
ca 337 Ma
ca 196 Ma ca 182 Ma ca 329 MaYou can also read
