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Yukon Exploration and GEoloGY 2012 73
Mid-Cretaceous orogenic gold and molybdenite mineralization in the independence Creek area,
dawson range, parts of ntS 115J/13 and 14
Greg G. McKenzie, Murray M. Allan1, James K. Mortensen, Craig J.R. Hart, Matías SánchezMineral Deposit Research Unit, University of British Columbia, Vancouver, BC
Robert A. Creaser2
Department of Earth & Atmospheric Sciences, University of Alberta, Edmonton, AB
McKenzie, G.G., Allan, M.M., Mortensen, J.K., Hart, C.J.R., Sánchez, M., and Creaser, R.A., 2013. Mid-Cretaceous orogenic gold and molybdenite mineralization in the Independence Creek area, Dawson Range, parts of NTS 115J/13 and 14. In: Yukon Exploration and Geology 2012, K.E. MacFarlane, M.G. Nordling, and P.J. Sack (eds.), Yukon Geological Survey, p. 73-97.
aBStraCt
The Boulevard gold prospect, located in the Independence Creek area of the Dawson Range, comprises sheeted, auriferous quartz-sulphide-carbonate veins and fault breccia, hosted mainly by mafic schist. The nearby Toni Tiger molybdenum showing is characterized by quartz-molybdenite veins cutting Late Permian meta-aplite and garnet-pyroxene skarn of uncertain age. We present geochronological evidence that gold and molybdenum were deposited at 96-95 Ma, approximately 3 m.y. after intrusion of the Dawson Range batholith and Coffee Creek granite. Fluid inclusions from mineralized quartz veins suggests that gold at Boulevard and molybdenite at Toni Tiger were formed from similar H2O-CO2-NaCl type fluids between 279 and 310°C and >1 kbar. We conclude that both are part of the same mineralizing system, and that structurally-hosted gold at the nearby Coffee deposit and in the Moosehorn Range of western Yukon may be broadly related, post-arc orogenic systems developed during exhumation of the Dawson Range in mid-Cretaceous time.
Yukon GeoloGical ReseaRch
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introduCtionThe Independence Creek area is a broad upland plateau within the Dawson Range of west-central Yukon, and is incised by stream systems draining north into the Yukon River. The area is located approximately 140 km south of Dawson, 40 km south of the Golden Saddle gold deposit (Kinross Gold Corp.), which contains 1.4 Moz of gold (Underworld Resources Inc., January 19, 2010 press release), and approximately 10 km southwest of the Coffee gold deposit, which contains 3.2 Moz of gold (Kaminak Gold Corp., December 13, 2012 press release) (Fig. 1).
Gold mineralization of the Boulevard zone was first identified by Rimfire Minerals Corp. in 2007 in the headwaters of the Independence Creek drainage. It is a northwest-trending, 450 m by 1.2 km, gold-arsenic-
antimony soil geochemical anomaly with sporadic tellurium and bismuth. Exploration at Boulevard was pursued further by Rimfire in 2008, Silver Quest Resources Ltd. from 2009 to 2011, and Independence Gold Corp. in 2012. Exploration methods at Boulevard have included stream sediment geochemistry, soil geochemistry, trenching, mapping, prospecting, induced polarization and magnetometry surveys, airborne aeromagnetic and radiometric surveys, and diamond drilling.
The Toni Tiger molybdenum showing (Yukon MINFILE 115J 052) is located approximately 2 km east of the Boulevard trend (Fig. 2). Mineralization was discovered by regional silt survey in 1969 by Archer, Cathro and Associates, and the anomaly was attributed to disseminated molybdenite in skarn with associated
Figure 2
!(
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Coffee
Casino
Boulevard
Moosehorn
Golden Saddle
Sonora Gulch
Ladue River
DONJEK RIVER
YUKON RIVER
WHITE RIVER
WH
ITE
RIVE
R
STEWART RIVER
Coffe
e Cre
ekIndepe
ndenc
e Cree
k YUKON RIVER
Big Creek fault
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¯0 20 4010
kilometres
VOLCANIC ROCKS
PLUTONIC ROCKS
Paleocene to Eocene plutonic rocks
Late Cretaceous plutonic rocks
mid-Cretaceous plutonic rocks
Early Jurassic plutonic rocks
Neogene volcanic rocks
Paleocene to Eocene subvolcanic to volcanic rocks
Late Cretaceous volcanic rocks
mid-Cretaceous volcanic rocks
Pennsylvanian volcanic rocks
Devonian to Mississippian metavolcanic rocks
Devonian to Mississippian metaplutonic rocks
Paleozoic metamorphic rocks (undifferentiated)
Triassic volcanic rocks
Paleozoic metamorphic rocks (undifferentiated)
Permian metaplutonic rocks
Permian metavolcanic rocks
Paleozoic ultramafic rocks
METAMORPHIC ROCKS
fault (undifferentiated)
D A W S O N R A N G E
M O O S E H O R N R A N G E
Figure 1. Geological map of the Dawson Range (in greater Yukon Plateau), showing significant mineral deposits and prospects (geology modified from Gordey and Ryan (2005) and Gordey and Makepeace (2003)). The Independence Creek study area is indicated by the black box. Datum: NAD83; Projection: UTM zone 7N.
Yukon Exploration and GEoloGY 2012
McKenzie et al. – Mid-cRetaceous oRoGenic au and Mo, independence cReek aRea
75
chalcopyrite, arsenopyrite, scheelite, and pyrite (Craig, 1970). Trenching at the prospect exposed quartz-molybdenite veins, and Craig (1970) inferred that
molybdenite was associated with, and restricted to, the skarn alteration.
Figure 2. Geologic map of the Independence Creek area, showing geochronological data and mineralized trends in the Boulevard and Coffee prospects (Datum: NAD83; Projection: zone 7N). Additional sources of information include: Tempelman-Kluit, 1974; Jilson, 2000; Gordey and Ryan, 2005; Chartier et al., 2013; J. Ryan, pers. comm., 2012. The white line defines Silver Quest property limits as of June 2011.
inferred contactsgeologic contacts
mineralized trends
U-Pb Ages (Ma)
Re-Os Ages (Ma)
Ar-Ar Ages (Ma)
inferred faults/fracturesfaults
( thrust faults
quartz-feldspar porphyry
leucogranite (alaskite)
biotite granite
biotite-hornblende granodiorite
Volcanic Rocks
Plutonic Rocks
serpentinized harzburgite and dunite
impure quartzite with micaceous layers
quartz-K-feldspar augen schist and biotite-quartz schist
quartz-feldspar leucogranite with blue quartz augen
chlorite-biotite-actinolite schist and minor quartz-feldspar augen schist
quartz-muscovite schist and minor quartz-feldspar augen schist
Metamorphic Rocks
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95 ± 0.4
99.6 ± 0.8
57.2 ± 1.0
99.0 ± 0.3
99.4 ± 0.9102.0 ± 0.4
257.6 ± 4.9260.6 ± 5.1
267.2 ± 5.9
100.2 ± 0.3
255.2 ± 0.6251.3 ± 1.3
249.6 ± 3.2
102.5 ± 0.9
95.9 ± 0.9
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Boulevard Trend
Toni Tiger
Coffee Trends
Independence Creek
Carlisle Creek
Halfway C
reek
0 2 41km
¯ YUKON RIVER
Co�ee deposit outline
Yukon GeoloGical ReseaRch
Yukon Exploration and GEoloGY 201276
The Boulevard and Toni Tiger prospects present an opportunity to investigate the age and geological characteristics of two proximal mineralized systems that have contrasting metal associations (Au-As-Sb and Mo-Cu-W, respectively) and uncertain metallogenesis. The geologic relationships presented below are based on mapping, interpretations of airborne magnetic and radiometric data, and detailed observations of diamond drill core. We present U-Pb zircon ages both for metamorphic rocks (including those hosting molybdenite mineralization), and for samples of the Dawson Range batholith, Coffee Creek plutonic suite, and local subvolcanic units. Petrographic observations and reconnaissance-level fluid inclusion data from mineralized veins are also included. Finally, we present 40Ar/39Ar muscovite ages for gold-bearing veins at Boulevard and Re-Os molybdenite ages for Toni Tiger, both of which are interpreted to date mineralization directly.
FiEld rElationSHipS
GEoloGY
The Independence Creek area is underlain by a 3 km-wide, west-northwest-trending belt of predominantly schistose and gneissic rocks (Figs. 1, 2 and 3). This rock package includes the following map units (Fig. 2): (a) serpentinized harzburgite and dunite; (b) variably pyritic chlorite-biotite-actinolite schist, containing minor quartz-feldspar augen schist; (c) quartz-muscovite schist, containing minor calcareous schist; (d) impure quartzite with micaceous layers; (e) foliated quartz-feldspar-muscovite leucogranite and quartz-feldspar augen schist with distinctive blue quartz augen; and (f) quartz-K-feldspar augen schist and minor biotite-quartz schist. Peak metamorphic grade is inferred to be middle greenschist facies on the basis of biotite-chlorite-actinolite assemblages in mafic schists. Lithological heterogeneities are common on the scale of metres to hundreds of metres, due to a combination of original stratigraphic and intrusive contact relationships, and repetition by tight to isoclinal folding and faulting. Ultramafic rocks are exposed as small lenticular bodies near the south margin of the metamorphic package (Figs. 2 and 3f), and are inferred to delineate a major crustal-scale fault (Templeman-Kluit, 1974; Gordey and Makepeace, 2003; Zagorevski et al., 2012).
The metamorphic package is intruded to the south by medium to coarse-grained biotite-hornblende granodiorite of the Dawson Range batholith, a phase of
the mid-Cretaceous Whitehorse plutonic suite (Figs. 1, 2, and 3a). The rock is massive to lineated with locally aligned hornblende and stretched quartz. To the north, metamorphic rocks are intruded by the Coffee Creek phase of the Whitehorse plutonic suite (Templeman-Kluit, 1974), which is composed of medium to coarse-grained biotite granite with volumetrically minor aplitic and pegmatitic phases (Figs. 1, 2, and 3b). A garnet-bearing, quartz-phyric porphyry phase is recognized at the western tip of the Coffee Creek granite. No crosscutting relationships are observed between plutonic rocks and gold mineralization at Boulevard or molybdenite-bearing veins at Toni Tiger.
Locally, subcrop of porphyritic rhyodacite and basalt are observed near the northern margin of the Dawson Range batholith (unit too small to represent on Fig. 2). This unit has been mapped and interpreted as a hypabyssal intrusion (J. Ryan, pers. comm., 2012).
StruCturES
The principal fabric within metamorphic rock units in the study area strikes 280-290°N and is steeply dipping between ~70 and 90°. West of the Coffee Creek granite, the strike of the regional metamorphic fabric rotates to 315°N (Fig. 2). This structural pattern in the metamorphic rocks mirrors a major change in the regional strike of the Dawson Range batholith approximately 20 km west of the study area (Fig. 1).
The main metamorphic fabric has strongly transposed any original depositional features within the metamorphic rock units. The development of this fabric is likely due to D1 and D2 collisional deformation accompanying peak metamorphism of Yukon-Tanana terrane rocks in Late Permian time (Berman et al., 2007; MacKenzie et al., 2008a; Beranek and Mortensen, 2011). Isoclinal, rootless fold hinges and boudinaged quartz veins are interpreted to represent D2 phase folds that overprint the earlier S1 fabric.
A third deformation event (D3) can be recognized as locally developed crenulations (S3) and tight disharmonic folding of the pre-existing metamorphic fabric, and is best developed within micaceous lithologies. These folds have axial traces that are subparallel to the regional west-northwest map trend of the metamorphic rock package and axial planes that are subvertical. Ultramafic bodies along the northern margin of the Dawson Range define a lineament that extends eastward toward the Casino Cu-Mo-Au porphyry deposit and the Sonora Gulch porphyry prospect (Fig. 1), and are interpreted to define a crustal-
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scale fault that was partially intruded by the Dawson Range batholith (Zagorevski et al., 2012). The origin of this structure is uncertain, but it was likely active in the Early Jurassic, when regional scale thrust faulting imbricated slivers of Slide Mountain oceanic crust within the Yukon-Tanana terrane (MacKenzie et al., 2008a,b; MacKenzie and Craw, 2012).
Locally-developed stretching lineations within the Dawson Range batholith are subhorizontal and parallel to the regional west-northwest strike of metamorphic rocks to the north. The Coffee Creek granite is almost entirely massive, suggesting that either fabrics in the Dawson Range batholith were formed prior to emplacement of the Coffee Creek granite, or that syn to post-magmatic deformation was partitioned more strongly in the Dawson Range batholith.
Figure 3. Typical rock types in the Independence Creek area: (a) biotite hornblende granodiorite of the Dawson Range batholith; (b) biotite granite of the Coffee Creek granite; (c) strongly deformed chloritic schist (typical host rock to gold mineralization); (d) folded metagranite; (e) banded diopside-garnet skarn and biotite schist (typical host rock at the Toni Tiger molybdenum showing); and (f) serpentinitzed harzburgite.
a b
c d
e f
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Yukon Exploration and GEoloGY 201278
A fault trending 330°N is obvious in aeromagnetic data, and cuts the metamorphic package and the Dawson Range batholith with 1 km of dextral offset (southwest quadrant of Fig. 2). This fault is the most prominent in a series of northwest to north-northwest-trending structures that truncate the west-northwest-trending magnetic grain of the metamorphic package (Fig. 2). A similar northwest to north-northwest orientation is observed for gold-bearing structures at the Boulevard prospect. The offset of the northern intrusive contact of the Dawson Range batholith by this fault generation indicates that this fault set occurred after emplacement of the Dawson Range batholith in mid-Cretaceous time.
VEinS, altEration, and MinEralization
Observations on veining, alteration, and mineralization are presented for the Boulevard and Toni Tiger prospects separately, since field relationships do not provide sufficient information about the relative timing of these adjacent systems.
BoUlEVARD
Detailed observations of diamond drill core reveal five separate vein generations (Fig. 4), all of which are hosted primarily in biotite-chlorite ± actinolite schist. A paragenetic scheme is presented in Figure 5 and petrographic observations are shown in Figure 6.
V1: The first vein generation
(V1) comprises sugary quartz ± pyrite veins, and is found in all metamorphic rock types in the study area (Fig. 4a). V1 veins are typically ~1 cm wide and contain less than 1% pyrite and trace chalcopyrite as inclusions in pyrite. V1 veins are conformable with the metamorphic fabric, and commonly occur as boudins and rootless hinges in mesoscopic folds. V1 veins are early and are interpreted to be
metamorphic segregations formed during Late Permian tectonism.
V2: V2 veins are composed of quartz, pyrrhotite ±
chalcopyrite, are 5 to 30 mm wide, have irregular margins, and no alteration envelopes (Fig. 4b). V2 veins are generally discordant to the S1/S2 fabric, suggesting they post-date peak deformation.
V3: V3 veins are composed mainly of quartz and ferroan
carbonate with muscovite/illite-pyrite-arsenopyrite
gn-sph-stb
pyaltered schist
qtz
qtzpy
po-cpy
py
Figure 4. Major vein types from the Boulevard gold prospect: (a) foliaform quartz veins, likely formed by silica segregation during peak metamorphism, possibly in the late Permian (V
1); (b) irregular quartz-
pyrrhotite-chalcopyrite veins (V2);
(c) planar quartz vein with a bleached, gold-bearing pyritic alteration halo (V
3); (d) gold-bearing silica-sericite-
pyrite altered fracture zone with ferroan carbonate fracture fill (V
3);
(e) gold-bearing quartz-pyrite-galena-sphalerite-stibnite vein breccia (late phase of V
3); and (f) chalcedonic quartz
(V4). py = pyrite; po = pyrrhotite; cpy =
chalcopyrite; qtz = quartz; gn = galena; sph = sphalerite; stb = stibnite
a b
c d
e
f
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McKenzie et al. – Mid-cRetaceous oRoGenic au and Mo, independence cReek aRea
79
gold
arsenopyrite
pyrite
ferroan carbonate
quartz
sphalerite
V1
V2
V3
V4
V5
pyrrhotite
chalcopyrite
galena
stibnite
tetrahedrite
Aupy
aspy
sph
Au
py qtz
gn
gn
Au
sphpy
gn
py
500µm
50µm
Figure 5. Mineral paragenesis for veins present in the Boulevard gold prospect.
Figure 6. Examples of gold mineralization from the Boulevard area: (a) typical V3-generation quartz-carbonate
vein with a gold-bearing pyrite halo (combined cross-polarized transmitted light and reflected light); (b) backscattered electron microscope image of gold associated with pyrite and arsenopyrite; (c) reflected light photomicrograph of a <5 µm gold grain as an inclusion in galena; (d) backscattered electron microscope image of a 10 µm gold grain associated with galena, sphalerite and pyrite. aspy = arsenopyrite (other mineral abbreviations as in Figure 4).
a b
c d
Yukon GeoloGical ReseaRch
Yukon Exploration and GEoloGY 201280
alteration envelopes (Figs. 4c,d, 6a, and 8a). A paragenetically late phase of sphalerite-galena-pyrite- tetrahedrite ± stibnite is observed in some veins, especially where brecciation has also taken place (Fig. 4e). Veins are typically 2 to 20 mm wide, planar, and occur in sheeted sets that cut the S1/S2 fabric at a high angle. Approximations of vein orientations (using the local metamorphic fabric as a reference plane in unoriented drill core) yield a predominantly northwest strike and a dip of approximately 30o to the southwest. V3 vein swarms are spatially related and subparallel to mineralized fault gouge. The faulting is interpreted to post-date V3 veining since vein fragments have been noted in the fault gouge. Gold has two petrographic associations: (1) inclusions and fracture fillings in pyrite or arsenopyrite in alteration haloes (Fig. 6b); and (2) inclusions in sphalerite-galena- pyrite-tetrahedrite ± stibnite (Fig. 6c,d). Gold grains are typically less than 10 mm.
V4: A fourth vein generation (V4) is characterized by thin,
colloform banded chalcedonic quartz-carbonate ± pyrite ± chalcopyrite veins (Fig. 4f). They vary in width from 5 to 60 mm. Carbonate is typically pink and manganiferous. V4 veins crosscut both the metamorphic fabric and V3 stage veins.
V5: Thin (1-5 mm) ferroan carbonate veinlets (V5) cut the
metamorphic foliation and all pre-existing vein types. This vein generation has no known association with sulphides or gold.
ToNI TIGER
The local host rocks include meta-aplite (Fig. 7a,b), biotite- quartz-feldspar schist (Fig. 7c-e), biotite hornfels, and garnet-diopside skarn (Fig. 7f). All rock types are cut by 1 cm to 1 m-wide, milky white quartz ± molybdenite veins (Figs. 7c-e and 8c) that occupy subvertical, conjugate fracture sets trending north and northeast. Molybdenite is also observed as wall rock disseminations in vein halos in biotite-quartz-feldspar schist and skarn. Veins have biotite-destructive chlorite-muscovite envelopes where they cut biotite-bearing host rocks (Fig. 7c,f). Idiomorphic garnet of hydrothermal origin is common along the margins of quartz ± molybdenite veins cutting the skarn unit.
Fluid inCluSion propErtiES
BoUlEVARD
Petrographic observations and a small number of microthermometric analyses were carried out on samples
of quartz-hosted fluid inclusions from gold-stage V3 veins at Boulevard. A homogenous population of aqueous-carbonic fluid was observed, which, based on clathrate melting and CO2 homogenization temperatures, contains 15 to 24 mol % CO2, ~2 to 3 wt % NaCl, and a bulk density of 0.8 to 0.85 g/cm3 (Fig. 8a,b). Homogenization temperatures and equation-of-state modeling, using the approach of Allan et al. (2011), suggest that fluids were trapped between 280 and 310°C or greater, at a pressure of 1100 bar or more. This pressure corresponds to a minimum depth of approximately 4.0 km at lithostatic pressures (assuming a rock density of 2800 kg/m3).
ToNI TIGER
A homogenous population of aqueous-carbonic fluid inclusions was observed in vein quartz from Toni Tiger (Fig. 8c). Microthermometric measures of clathrate melting and CO2 homogenization demonstrate that this fluid contains ~16 mol % CO2 and ~3 wt % NaCl, with a bulk density of ~0.88 g/cm3 (Fig. 8d). Fluids were trapped at 280°C or more, at a minimum pressure of 1050 bar (>3.8 km at lithostatic pressure, assuming a rock density of 2800 kg/m3). The composition and trapping conditions of fluid inclusions from Toni Tiger veins are therefore indistinguishable from those in V3 veins at Boulevard.
u-pb GEoCHronoloGY
SaMplES and MEtHodoloGY
U-Pb dating of zircon was used to determine the crystallization age of various units in the Independence Creek area, including the metamorphic rock package, Dawson Range batholith, Coffee Creek granite, and subvolcanic rocks. The sample suite includes six samples of metaplutonic rocks, including meta-aplite cut by quartz-molybdenite veins at Toni Tiger (I034207); orthogneiss containing minor disseminated molybdenite (I034224); and quartz-feldspar-biotite schist (GM11-9b, MA11-004BV, MA11-005BV, MA11-006BV). The suite also includes three samples of the Dawson Range batholith (I034239, YGR-BV-004, 99M-106-b); three samples of the Coffee Creek phase (YGR-BV-002, 99M-105, 99M-107); and a single sample of quartz-feldspar rhyodacite porphyry (MA11-001BV).
Zircon grains recovered from plutonic and metaplutonic rocks are all relatively coarse grained (up to 200 mm long) and show a similar range of external morphology and internal structure. Zircons are typically clear, euhedral,
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81
moly
moly
Figure 7. Rock types and vein features of the Toni Tiger molybdenum occurrence: (a) weakly foliated meta-aplite from the Toni Tiger occurrence; (b) same meta-aplite as in (a), but interfoliated with biotite schist and affected by a later phase of folding; (c) biotite metagranitoid cut by a quartz-molybdenite vein with a chloritic alteration halo; (d) typical milky quartz vein with molybdenite from the Toni Tiger occurrence; (e) milky quartz vein with molybdenite along its margins (and as wall rock disseminations); and (f) pyroxene-garnet skarn with domains of biotite hornfels. moly = molybdenite.
a b
c d
e f
Yukon GeoloGical ReseaRch
Yukon Exploration and GEoloGY 201282
and colourless to pale yellow-brown. No obvious internal zoning was observed and morphologies range from stubby octahedral prisms to multi-faceted terminations.
The methodology for laser ablation ICP-MS analysis at the Pacific Centre for Isotopic and Geochemical Research (PCIGR), University of British Columbia, follows that described in Tafti et al. (2009) and Beranek and Mortensen (2011). The 206Pb/238U age is the most precisely determined age for the Phanerozoic zircons in question and is interpreted as the best estimate for the crystallization age of the samples. Assigned ages are based on a weighted average of overlapping, concordant 206Pb/238U ages of individual analyses for each sample. Errors are quoted at the 2s level.
rESultS
Results are presented in conventional U-Pb concordia plots and weighted average 206Pb/238U age summary plots in Figures 9-12 and are shown with sample locations in Table 1. Full analytical data are presented in Appendix 1.
All meta-igneous samples yielded Late Permian crystallization ages in the range of 250 to 267 Ma (Figs. 9 and 10). The molybdenite-bearing, weakly foliated meta-aplite sample (I034207) from Toni Tiger yields a well-constrained age of 251.3 ± 1.3 Ma (Fig. 9b), which suggests that this unit may be part of a post-D2 intrusive suite of crustally derived intrusions that includes the Jim Creek pluton of the southern Klondike District (Beranek and
Figure 8. (a) photomicrograph of a V3-generation quartz-carbonate vein (cross-polarized light) from the
Boulevard gold prospect; (b) quartz-hosted fluid inclusions from the vein in (a), containing aqueous liquid (aq), Co
2 liquid, and Co
2 vapour (photograph taken at 25°C); (c) photomicrograph of molybdenite in quartz from
the Toni Tiger occurrence (combined cross-polarized transmitted light and reflected light); (d) photomicrograph of fluid inclusions in quartz associated with molybdenite mineralization in (c). Fluid inclusions contain aqueous liquid and a supercritical Co
2 phase (photograph taken just above the homogenization temperature of the
carbonic liquid and vapour phase at 29°C). The inset shows both Co2 phases below the homogenization
temperature (~25°C), for the same large fluid inclusion in (d). cb = carbonate; g = gas phase; l = liquid phase; aq = aqueous phase (other abbreviations as in Figures 4 and 7).
cb
qtz
CO2(g)aq
CO2(l)
aqCO2
moly
qtz
100 µm
100 µm
10 µm
10 µm
aq
CO2(g)
CO2(l)
25°C
29°C25°C
a b
c d
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weighted average = 255.2 ± 0.6 Ma(MSWD = 0.92; prob. of fit = 0.56)
weighted average = 249.6 ± 4.4 Ma(MSWD = 1.3; prob. of fit = 0.27)
weighted average = 251.3 ± 1.3 Ma(MSWD = 0.25; prob. of fit = 1.0)
270
250
230
210
0.030
0.032
0.034
0.036
0.038
0.040
0.042
0.044
0.18 0.22 0.26 0.30 0.34 0.38195
205
215
225
235
245
255
265
264
260
256
252
248
244
0.038
0.039
0.040
0.041
0.042
0.25 0.27 0.29 0.31244
248
252
256
260
264
280
270
260
250
240
230
220
2100.033
0.035
0.037
0.039
0.041
0.043
0.045
0.20 0.22 0.24 0.26 0.28 0.30 0.32 0.34215
225
235
245
255
265
275
206 P
b/23
8 U
207Pb/235U
207Pb/235U
207Pb/235U
206 P
b/23
8 U20
6 Pb/
238 U
Figure 9. Conventional concordia diagrams and plots of weighted average 206Pb/238U ages for meta-igneous samples from the study area: (a) and (b) sample I034207 – molybdenite-bearing meta-aplite from Toni Tiger; (c) and (d) sample I034224 - orthogneiss with disseminated molybdenite; (e) and (f) sample GM11-9b – quartz-feldspar-biotite schist. Error ellipses on concordia diagrams and error bars on weighted average age plots are shown at 2s level. Red bars on weighted average age plots were used in the age calculation; blue bars were rejected.
a b
c d
e f
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Yukon Exploration and GEoloGY 201284
weighted average = 260.6 ± 5.4 Ma(MSWD = 11.1; prob. of fit = 0.00)
weighted average = 257.6 ± 4.9 Ma(MSWD = 1.7; prob. of fit = 0.04)
weighted average = 267.2 ± 5.9 Ma(MSWD = 1.7; prob. of fit = 0.11)
290
280
270
260
250
240
0.037
0.039
0.041
0.043
0.045
0.047
0.24 0.26 0.28 0.30 0.32 0.34 240
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250
240
230
0.035
0.037
0.039
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0.047
0.18 0.22 0.26 0.30 0.34 0.38 0.42 225
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0.025
0.035
0.045
0.055
0.0 0.2 0.4 0.6 180
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220
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300
320
340
360
206 P
b/23
8 U
207Pb/235U
206 P
b/23
8 U20
6 Pb/
238 U
207Pb/235U
207Pb/235U
Figure 10. Conventional concordia diagrams and plots of weighted average 206Pb/238U ages for meta-igneous samples from the study area: (a) and (b) sample MA11-004BV - quartz-feldspar-biotite schist; (c) and (d) sample MA11-00BV – quartz-feldspar-biotite schist; (e) and (f) sample MA11-006BV - quartz-feldspar-biotite schist. Symbols as in Figure 9.
a b
c d
e f
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Mortensen, 2011) and the Teacher intrusion in the White Gold area (Mortensen, unpublished data). A sample of quartz-feldspar-biotite schist (GM11-9b) yields a similar age of 249.6 ± 4.4 Ma (Fig. 9f); however, only a small amount of zircon was recovered from this sample and the age is therefore relatively imprecise (based on only seven analyses). All of the other well-foliated meta-igneous rock units yield Late Permian ages ranging from 255 to 267 Ma, which are consistent with ages reported elsewhere for metavolcanic and metaplutonic phases of the Klondike arc assemblage (Mortensen, 1990; Ruks et al., 2006; Beranek and Mortensen, 2011).
Two samples of granodiorite from the Dawson Range batholith give ages of 102.0 ± 0.4 Ma and 100.2 ± 0.3 Ma (Fig. 11b,d). An aplite dyke that cuts Dawson Range granodiorite gives an age of 102.5 ± 0.9 Ma (Fig. 11f). Three biotite granite samples of the Coffee Creek granite give ages ranging from 99 to 100 Ma (Fig. 12b,d,f). The ages are therefore consistent with the Coffee Creek granite being a slightly younger magmatic phase of the Whitehorse plutonic suite than the Dawson Range batholith.
The sample of quartz-feldspar rhyodacite porphyry from subcrop in the study area (sample MA11-001BV) gives an age of 57.2 ± 1.0 Ma (latest Paleocene), which is similar to ages obtained for felsic dykes and plugs throughout the Dawson Range and areas to the north (Mortensen, unpublished data).
40ar/39ar GEoCHronoloGY
SaMplE and MEtHodoloGY
40Ar/39Ar geochronology was used to determine the age of a sample of hydrothermal sericite from a quartz-carbonate-stibnite-gold vein with a strong sericite selvage (sample BV23_70.37m from diamond drill core). The hydrothermal sericite is interpreted to have formed at the same time as gold and stibnite mineralization.
Sericite grains were hand-picked from the sample under a binocular microscope, wrapped in aluminum foil, and stacked in an irradiation capsule with similar-aged samples and neutron flux monitors (Fish Canyon Tuff sanidine (FCS); 28.03 Ma (Renne et al., 1998). The methodology used in this study for 40Ar/39Ar dating at PCIGR is similar to that described by Mortensen et al. (2010). The Boulevard sericite sample was irradiated from May
4 to 5, 2011 at the McMaster Nuclear Reactor in Hamilton, Ontario, for 45 MWH, with a neutron flux of approximately 6 x 1013 neutrons/cm2/s. Analyses (n = 45) of 15 neutron flux monitor positions produced errors of <0.5% in the J value. The sample was split into two separate aliquots after irradiation, and the samples were analysed from June through October 2011 at the Noble Gas Laboratory in the PCIGR.
rESultS
The first aliquot of hydrothermal sericite yielded a plateau age of 95.9 ± 0.9 Ma (MSWD = 0.97, probability = 0.41; plateau based on 74.3% of the 39Ar; Fig. 13; Table 2). The duplicate analysis did not settle to enough steps to yield a plateau age, but the results are consistent with the age obtained from the first aliquot.
187re/187os GEoCHronoloGY
SaMplES and MEtHodoloGY
187Re/187Os dating methods were utilized to constrain the age of molybdenite mineralization at the Toni Tiger showing. Two samples of molybdenite were dated: (a) a quartz-molybdenite vein crosscutting a meta-aplite (I034208); and (b) a quartz-molybdenite vein crosscutting garnet-actinolite-diopside skarn (I034229). Molybdenite in each sample occurs as coarse-grained rosettes mantled by vein quartz.
Samples were prepared and analysed by R. Creaser at the Radiogenic Isotope Laboratory at the University of Alberta according to the methods described by Selby and Creaser (2004) and Markey et al. (2007).
rESultS
Analytical results for the two samples are given in Table 3. Sample I034208 yielded a Re-Os age of 95.0 ± 0.4 Ma. Sample I034229 contains high common Os, hence the derived age is sensitive to assumed initial 187Os/188Os ratio. Assuming an initial 187Os/188Os value of 0.3, a somewhat younger age of 92.4 ± 0.7 Ma is determined for this sample.
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Figure 11. Conventional concordia diagrams and plots of weighted average 206Pb/238U ages for samples of the Dawson Range batholith in the study area: (a) and (b) sample I034239 - biotite-hornblende granodiorite; (c) and (d) sample YGP-BV-004 - biotite-hornblende granodiorite; (e) and (f) sample 99M-106-b – aplite dyke cutting granodiorite. Symbols as in Figure 9.
106
104
102
100
98
96
0.0148
0.0152
0.0156
0.0160
0.0164
0.0168
0.092 0.096 0.100 0.104 0.108 0.112 0.116 96
98
100
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108
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0.0146
0.0150
0.0154
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0.0162
0.0166
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97
99
101
103
105
107
109
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112
108
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100
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0.0145
0.0155
0.0165
0.0175
0.0185
0.08 0.09 0.10 0.11 0.12 0.13 0.14 94
98
102
106
110
114
weighted average = 100.2 ± 0.3 Ma(MSWD = 0.97; prob. of fit = 0.49)
weighted average = 102.5 ± 0.9 Ma(MSWD = 2.8; prob. of fit = 0.00)
weighted average = 102.0 ± 0.4 Ma(MSWD = 1.13; prob. of fit = 0.32)
206 P
b/23
8 U
207Pb/235U
206 P
b/23
8 U20
6 Pb/
238 U
207Pb/235U
207Pb/235U
a b
c d
e f
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114
110
106
102
98
94
90
86
0.013
0.014
0.015
0.016
0.017
0.018
0.08 0.09 0.10 0.11 0.12 0.13 86
90
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98
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106
110
114
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100
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0.014
0.018
0.022
0.026
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0.038
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weighted average = 99.5 ± 0.7 Ma(MSWD = 1.16; prob. of fit = 0.28)
weighted average = 57.2 ± 1.0 Ma(MSWD = 0.96; prob. of fit = 0.5)
weighted average = 99.0 ± 0.3 Ma(MSWD = 1.12; prob. of fit = 0.33)
weighted average = 99.2 ± 0.9 Ma(MSWD = 2.1; prob. of fit = 0.004)
206 P
b/23
8 U
207Pb/235U
206 P
b/23
8 U20
6 Pb/
238 U
206 P
b/23
8 U
207Pb/235U
207Pb/235U
207Pb/235U
Figure 12. Conventional concordia diagrams and plots of weighted average 206Pb/238U ages for samples of the Coffee Creek intrusions and a young subvolcanic rock in the study area: (a) and (b) sample YGR-BV-002 – biotite granite; (c) and (d) sample 99M-105 – biotite granite; (e) and (f) sample 99M-107 – biotite granite; (g) and (h) sample MA11-001BV - quartz-feldspar rhyodacite porphyry. Symbols as in Figure 9.
a b
c d
e f
g h
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Sample rock description unitlocation (nad83
utM zone 7n) age (Ma) ± 2sEasting northing
MEtaMorpHiC roCkS
I034207 meta-aplite* Klondike assemblage 577980 6966729 251.3 1.3
I034224 felsic orthogneiss* Klondike assemblage 578139 6966731 255.2 0.6
GM11-9b quartz-feldspar-biotite schist Klondike assemblage 572444 6980691 249.6 4.4
MA11-004BV quartz-feldspar-biotite schist Klondike assemblage 563229 6972572 267.2 5.9
MA11-005BV quartz-feldspar-biotite schist Klondike assemblage 561996 6976060 260.6 5.4
MA11-006BV quartz-feldspar-biotite schist Klondike assemblage 561398 6975930 257.6 4.9
plutoniC roCkS
I034239 biotite-hornblende granodioriteDawson Range batholith
574610 6963807 100.2 0.3
YGR-BV-004 biotite-hornblende granodioriteDawson Range batholith
566127 6967606 102.0 0.4
99M-106-b aplite cutting granodioriteDawson Range batholith
566278 6961313 102.5 0.9
YGR-BV-002 biotite granite* Coffee Creek granite 573497 6968539 99.5 0.7
99M-105 biotite granite Coffee Creek granite 577775 6968097 99.2 0.9
99M-107 biotite granite Coffee Creek granite 560386 6973241 99.0 0.3
SuBVolCaniC roCkS
MA11-001BVquartz-feldspar rhyodacite porphyry
Skukum volcanic suite 574845 6964377 57.2 1.0
*molybdenite observed in heavy mineral separates
Table 1. 206Pb/238U zircon ages for Independence Creek samples.
0
40
80
120
160
0 20 40 60 80 100
plateau age = 95.9 ± 0.9 MaMSWD = 0.97, prob. of fit = 0.41
includes 74.3% of the 39Ar
age
(Ma)
cumulative 39Ar percent
Figure 13. Age spectra for step-heating of sericite sample BV23-70.37m from the Boulevard property. Error boxes and the calculated age are given at the 2s level. Steps shown in red define the calculated plateau age; steps in blue were rejected.
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diSCuSSion
u-pb GEoCHronoloGY
The 250 to 267 Ma age range of meta-igneous rocks in the Independence Creek area overlaps with that of the Late Permian Klondike volcanic arc assemblage and intrusive equivalents (Sulphur Creek orthogneiss) elsewhere in western Yukon (Mortensen, 1990; Ruks et al., 2006; Beranek and Mortensen, 2011). We therefore concur with recent mapping by the Geological Survey of Canada which demonstrates that exposures of Klondike arc rocks in the Ladue River area (NTS 115N) continue eastward along the northern margin of the Dawson Range batholith into the Stevenson Ridge map sheet (NTS 115J) (Ryan et al., in prep.).
The mid-Cretaceous crystallization ages determined for the Dawson Range batholith (ca. 100 to 103 Ma) are consistent with current geochronological compilations (Breitspreicher and Mortensen, 2004). The slightly younger 99 to 100 Ma zircon ages for the Coffee Creek granite are consistent with the interpretation of Templeman-Kluit and Wanless (1975) that this unit is a slightly younger intrusive phase of the Whitehorse plutonic suite.
Subvolcanic rocks cutting the Dawson Range batholith were determined to be 57.2 ± 1.0 Ma, and are therefore age-equivalent to the previously mapped Paleocene Skukum volcanic rocks 4 km to the south (Templeman-Kluit, 1974), and volcanic and subvolcanic rocks elsewhere in western Yukon (Breitsprecher and Mortensen, 2004).
isotope ratios
laser power (%) 40ar/39ar 1s 37ar/39ar 1s 36ar/39ar 1s Ca/k %40ar atm f 39ar 40ar*/39ark age 2s
2.20 W 22.38 0.40 0.62 0.09 0.067 0.006 1.13 88.77 0.34 2.515 27.44 ± 39.95
2.60 W 24.21 0.22 0.07 0.03 0.061 0.002 0.12 74.58 1.54 6.154 66.43 ± 12.64
3.00 W 13.67 0.09 0.47 0.02 0.010 0.000 0.87 22.50 6.68 10.596 112.92 ± 2.08
3.50 W 10.72 0.07 0.28 0.01 0.002 0.000 0.52 4.35 14.70 10.259 109.44 ± 1.43
4.00 W 9.20 0.06 0.01 0.00 0.001 0.000 0.02 2.27 51.34 8.987 96.21 ± 1.17
4.40 W 9.26 0.06 0.01 0.00 0.001 0.000 0.02 2.69 12.50 9.014 96.50 ± 1.23
5.00 W 9.70 0.06 0.02 0.01 0.003 0.000 0.04 8.38 5.12 8.891 95.22 ± 1.59
6.00 W 10.11 0.06 0.06 0.01 0.004 0.000 0.10 12.15 5.39 8.883 95.13 ± 1.61
7.00 W 13.01 0.14 0.02 0.02 0.016 0.001 0.03 35.99 2.39 8.330 89.36 ± 5.12
J = 0.0060810 ± 0.0000304 Volume 39ArK = 0.378 Integrated Date = 99.34 ± 0.58 Ma
Plateau age = 95.93 ± 0.89 Ma (2s, including J-error of 0.6%)
MSWD = 0.97, probability = 0.41
Includes 74.3% of the 39Ar (steps 5 through 8)
Inverse isochron (correlation age) results, plateau steps: Model 1 Solution (± 95%-conf.) on 9 points
Age = 98.4 ± 7.6 Ma
Initial 40Ar/36Ar = 350 ± 170 MSWD = 75, probability = 0
Table 2. 40Ar/39Ar data for Boulevard sericite (Sample BV23_70.37m)
Sample re (ppm) ± 2s 187re (ppb) ± 2s 187os (ppb) ± 2s total common os (pg)
Model age (Ma)
± 2s
I034208 42.96 0.11 27002 71 42.76 0.04 1.6 95.0 0.4
I034208 (duplicate)
43.00 0.11 27029 70 42.76 0.04 1.6 94.9 0.4
I034228 27.62 0.08 17361 53 26.74 0.16 90.8 92.4 0.7
Table 3. Re-os data for Toni Tiger molybdenite samples.
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tiMinG oF MinEralization
The 95.0 ± 0.4 Ma 187Re/187Os model age for molybdenite at Toni Tiger overlaps within 2s error with the 95.9 ± 0.9 Ma 40Ar/39Ar cooling age for hydrothermal sericite at Boulevard. While the latter age could be interpreted as a minimum, there is sufficient geological evidence (e.g., common structural style and fluid inclusion properties) that Boulevard and Toni Tiger are related hydrothermal systems. Therefore, we interpret the 187Re/187Os and 40Ar/39Ar methods as recording coeval mineralizing events at ca. 96-95 Ma. Importantly, the mineralization age post-dates crystallization of the Dawson Range batholith and Coffee Creek granite by 3-4 m.y. No younger phase of the Whitehorse plutonic suite has yet been recognized in the Independence Creek area (or anywhere else in western Yukon), nor do the field relationships suggest a magmatic role in mineralization. It is likely that heat and fluid flux related to the emplacement of the Dawson Range batholith and Coffee Creek plutonic suites were responsible for hornfelsing and skarnification in the vicinity of the Toni Tiger showing. However, the geochronologic results of this study suggest that Au-As-Sb-(Pb-Zn-Cu) and Mo mineralization record a distinct and younger event.
The low-salinity, aqueous-carbonic composition of fluids attending mineralization is consistent with orogenic fluids documented worldwide (Groves et al., 2003). The association between gold and pyritic alteration halos to quartz-carbonate veins suggests that wall rock sulphidation is an important gold-precipitating mechanism. Depressurization associated with faulting and brecciation may also play an important role in destabilizing gold-bisulphide complexes (e.g., Wilkinson and Johnston, 1996).
Molybdenite is not commonly reported in orogenic systems; however, the geochronological and fluid inclusion evidence suggests that Toni Tiger is part of the same post-magmatic orogenic system as Boulevard. The association of molybdenite with moderate temperature, moderate pressure, dilute aqueous-carbonic fluids implies that molybdenite transport occurs in nature at P-T-X conditions quite dissimilar to those encountered in high-temperature, low-pressure systems such as porphyry Mo deposits. We speculate that molybdenite may have been remobilized from the felsic metaplutonic host rocks, which locally contain significant background concentrations of molybdenite.
rEGional SiGniFiCanCE
This study contributes to the metallogenic framework of the Dawson Range, and may be relevant to other structurally-hosted gold prospects, such as the Coffee gold deposit northeast of the Independence Creek drainage (Kaminak Gold Corp.), and gold in the Moosehorn Range (parts of NTS 115N and 115K; Fig. 1). Mineralization in the Coffee area occurs within a series of structural corridors that cut all rock units, including the mid-Cretaceous Coffee Creek granite (Wainwright et al., 2011). A common, ca. 96-95 Ma metallogenesis for gold mineralization at Boulevard and Coffee is permissible given field relationships, although Coffee is dominated by brittle (shallow?) features, whereas vein swarms at Boulevard more likely represent deeper crustal levels. In the case of the Moosehorn Range, mineralization has been dated by 40Ar/39Ar methods to 93-92 Ma, which post-dates the main phase of the magmatism by ~8 m.y. (Joyce, 2002). Fluid inclusions associated with the Moosehorn veins also overlap strongly in composition and trapping conditions with those at Boulevard. On the basis of currently available geochronological data and geological relationships, we propose a general model in which exhumation of the Dawson Range shortly after cessation of arc magmatism in mid-Cretaceous time was accompanied by brittle deformation, fluid flow, and mineralization. However, the tectonic and structural setting of the Dawson Range at this time is still not completely understood.
aCknoWlEdGEMEntSThis study is part of GGM’s MSc project, which was a component of the Yukon Gold Project, a collaborative research venture between the Mineral Deposit Research Unit (UBC) and a consortium of industry participants, including Aldrin Resource Corp., Barrick Gold Corp., Full Metal Minerals Corp., Gold Fields Canada Exploration, Northern Freegold Resources Ltd., Kinross Gold Corp., Radius Gold Inc., Silver Quest Resources Ltd., Taku Gold Corp., Teck Resources Ltd., and Underworld Resources Inc. The Natural Science and Engineering Research Council of Canada (NSERC) also provided matching funds for the industry contribution. We are grateful for the logistical, financial, scientific, and editorial contributions of Silver Quest Resources (now Independence Gold Corp.) and Equity Exploration Ltd., and in particular Kendra Johnston, Darcy Baker, Dave Pawliuk, Randy Turner, and Ryan Congdon. Jim Ryan of the Geological Survey of Canada is thanked for his thoughtful review and his contributions to the geological understanding of the Dawson Range.
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Frac
tion
isot
opic
rat
ios
isot
opic
age
sB
ackg
rou
nd c
orre
cted
mea
n co
unt
s pe
r se
cond
at
spec
ifie
d m
ass
207 p
b/23
5 u%
1s
206 p
b/23
8 u%
1s
rho
207 p
b/20
6 pb
% 1
s20
7 pb/
235 u
± 1s
20
6 pb/
238 u
± 1s
20
7 pb/
206 p
b±
1s
202
204
206
207
208
232
235
238
MEt
aM
or
pH
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oC
kS
Met
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er (s
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10.
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20.
0082
90.
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70.
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30.
360.
0521
10.
0018
120
8.0
6.9
210.
32.
729
0.2
77.5
013
1126
357
818
2684
416
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20.
2756
90.
0049
50.
0383
00.
0002
60.
380.
0529
80.
0008
824
7.2
3.9
242.
31.
632
8.0
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00
1713
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437
8917
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6270
73
30.
2444
40.
0065
80.
0350
70.
0003
40.
360.
0515
00.
0013
122
2.0
5.4
222.
22.
126
3.4
57.2
480
1399
671
025
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5597
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40.
2675
30.
0181
90.
0390
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90.
340.
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20.
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924
0.7
14.6
247.
05.
511
9.8
143.
80
067
1132
013
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50.
2809
40.
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90.
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0003
30.
370.
0535
30.
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725
1.4
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242.
92.
135
1.3
48.8
4619
2635
613
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60.
2826
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20.
360.
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80.
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025
2.8
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249.
52.
031
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011
1697
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70.
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30.
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30.
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340.
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225
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11.2
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34.
227
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30
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80.
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80.
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60.
350.
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14.
126
1.5
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40
053
8027
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439
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90.
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40.
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20.
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60.
350.
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228
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9.8
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93.
543
6.3
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426
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388
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100.
2749
40.
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20.
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60.
0002
90.
370.
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10.
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224
6.6
4.3
251.
41.
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130
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9095
2839
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110.
3070
90.
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80.
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10.
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360.
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727
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9.7
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33.
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153
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526
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315
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120.
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70.
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20.
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360.
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0010
225
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4.7
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11.
935
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30
1658
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130.
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60.
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40.
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724
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82.
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69.8
310
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112
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51
140.
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10.
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50.
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80.
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925
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62.
428
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5513
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150.
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350.
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80.
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325
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7.7
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32.
931
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160.
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30.
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10.
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60.
360.
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10.
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725
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251.
92.
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170.
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20.
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50.
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726
0.5
5.8
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62.
226
9.9
51.2
320
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180.
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340.
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40.
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524
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714
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50
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190.
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60.
360.
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20.
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925
3.8
5.7
250.
82.
229
5.1
51.3
013
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326
2612
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2486
5364
85
200.
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60.
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40.
0395
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40.
350.
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40.
0011
324
9.0
5.4
250.
32.
127
8.5
49.1
170
2591
413
3357
6026
2716
4384
9341
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te (s
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10.
2793
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80.
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350.
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225
0.2
7.5
251.
42.
924
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71.3
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105
270
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20.
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70.
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50.
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10.
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60.
400.
0524
50.
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825
8.0
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254.
21.
030
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30.
2934
80.
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60.
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20.
370.
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326
1.3
3.4
256.
91.
434
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30.4
1615
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130
5152
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40.
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426
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210
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326
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60.
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325
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90.
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110.
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380.
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30.
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51.
128
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5214
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120.
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10.
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130.
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40.
0037
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20.
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125
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61.
220
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295
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20.
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225
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432
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20.
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125
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253.
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123
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21.8
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170.
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256.
51.
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130
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180.
2915
80.
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30.
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10.
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10.
360.
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70.
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254.
11.
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45.5
290
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190.
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10.
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350.
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20.
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1.9
5.6
251.
32.
225
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52.6
590
1160
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200.
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60.
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40.
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10.
360.
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10.
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1.8
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254.
71.
330
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80
1176
560
190
529
190
1845
2829
46
Qua
rtz-
feld
spar
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st (s
ampl
e G
M11
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10.
2565
70.
0147
00.
0367
30.
0008
40.
400.
0495
70.
0027
323
1.9
11.9
232.
55.
217
5.0
123.
60
030
7915
373
341
387
542
1193
34
20.
2923
30.
0076
30.
0390
50.
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40.
630.
0519
50.
0013
126
0.4
6.0
246.
94.
028
3.2
56.4
00
7907
413
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5370
912
8328
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30.
2884
70.
0114
70.
0413
20.
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80.
470.
0500
30.
0018
925
7.4
9.0
261.
04.
819
6.5
85.7
00
5523
277
737
3812
587
519
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40.
2783
20.
0072
90.
0393
20.
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40.
620.
0512
90.
0013
024
9.3
5.8
248.
64.
025
3.9
57.5
00
6710
346
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50.
2758
50.
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80.
0389
40.
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90.
560.
0508
00.
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524
7.4
7.0
246.
24.
323
1.9
68.9
300
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442
1383
6605
914
6632
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60.
2804
00.
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20.
0390
70.
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20.
520.
0544
00.
0018
525
1.0
7.9
247.
04.
538
7.7
73.9
6437
6024
329
1068
5205
210
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70.
2805
00.
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70.
0398
90.
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60.
640.
0508
20.
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725
1.1
5.8
252.
14.
123
2.7
56.6
00
1091
555
716
4486
173
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40
80.
2936
20.
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70.
0392
10.
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50.
470.
0518
00.
0020
226
1.4
9.4
247.
94.
627
6.7
86.9
016
4022
209
382
1806
265
214
8050
Qua
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feld
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st (s
ampl
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A11
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)
10.
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40.
0093
30.
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50.
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40.
590.
0523
30.
0015
226
9.9
7.3
256.
84.
629
9.8
64.7
140
7901
419
1187
4923
512
8729
6695
20.
2892
40.
0073
10.
0417
50.
0007
10.
670.
0495
60.
0011
925
8.0
5.8
263.
74.
417
4.6
55.3
00
9084
456
1323
6031
614
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30.
2928
70.
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00.
0419
00.
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00.
520.
0517
00.
0018
226
0.8
8.5
264.
65.
027
2.3
78.6
430
4293
225
608
2902
971
815
6037
40.
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90.
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20.
0426
90.
0008
40.
490.
0524
70.
0020
126
5.9
9.4
269.
55.
230
5.8
84.8
08
3209
170
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1635
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311
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50.
3104
40.
0093
70.
0428
60.
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70.
600.
0518
10.
0014
827
4.5
7.3
270.
54.
827
6.8
64.1
480
6435
338
950
4678
510
1822
9090
ap
pEn
dix
1: L
A-IC
P-M
S da
ta fo
r U
-Pb
anal
ysis
of z
ircon
s
Yukon GeoloGical ReseaRch
Yukon Exploration and GEoloGY 201294
60.
2812
70.
0106
10.
0432
70.
0008
40.
510.
0479
60.
0017
225
1.7
8.4
273.
15.
296
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078
3838
185
041
679
1267
2762
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70.
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60.
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90.
0435
40.
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90.
570.
0485
40.
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825
3.5
7.2
274.
74.
912
5.7
70.4
00
4986
245
687
3445
480
917
4536
Qua
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feld
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st (s
ampl
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A11
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10.
2730
20.
0150
20.
0390
30.
0007
10.
330.
0486
60.
0025
424
5.1
12.0
246.
84.
413
1.5
118.
410
054
2827
011
0562
508
940
2114
02
20.
2683
70.
0087
70.
0409
50.
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40.
330.
0490
90.
0015
324
1.4
7.0
258.
72.
715
1.9
71.5
720
5311
266
900
4670
094
419
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30.
2994
00.
0065
70.
0437
00.
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40.
350.
0497
90.
0010
226
5.9
5.1
275.
72.
118
5.1
47.0
00
1605
381
637
7319
2569
2596
5586
01
40.
2758
10.
0099
60.
0434
60.
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90.
310.
0485
80.
0016
724
7.3
7.9
274.
33.
112
7.6
79.2
00
4741
235
709
3280
181
216
5891
50.
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50.
0096
50.
0418
70.
0004
70.
340.
0513
80.
0016
126
0.1
7.6
264.
42.
925
7.7
70.2
290
6807
356
1568
7447
811
6524
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60.
2698
30.
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10.
0418
50.
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90.
320.
0477
60.
0019
724
2.6
9.4
264.
33.
786
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1659
6629
011
2857
105
1027
2169
58
70.
2663
10.
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50.
0417
90.
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80.
250.
0446
10.
0041
423
9.7
20.3
263.
96.
00.
113
5.3
101
1174
5314
667
5919
142
770
80.
2898
90.
0095
70.
0424
10.
0004
70.
340.
0494
70.
0015
425
8.5
7.5
267.
72.
917
0.0
71.0
030
9214
464
2131
1131
5715
3033
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90.
2784
40.
0164
80.
0394
60.
0007
20.
310.
0505
40.
0028
724
9.4
13.1
249.
54.
522
0.0
126.
20
927
0813
959
232
543
478
1045
28
100.
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20.
0109
90.
0420
90.
0005
10.
330.
0529
70.
0018
726
3.5
8.6
265.
83.
232
7.3
78.2
400
4220
227
775
4073
673
415
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110.
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00.
0185
60.
0405
50.
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30.
270.
0532
10.
0034
525
0.2
14.7
256.
34.
533
7.8
139.
80
1515
1481
268
1522
928
056
894
120.
2710
90.
0101
30.
0407
10.
0004
80.
320.
0486
70.
0017
324
3.6
8.1
257.
23.
013
2.1
81.7
00
4395
217
651
3019
176
816
4560
130.
2703
00.
0153
20.
0381
20.
0007
50.
350.
0524
90.
0028
424
2.9
12.3
241.
24.
730
7.0
118.
453
053
2928
486
141
672
1007
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50.
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810
1.4
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11.
115
0.3
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60.
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2015
1648
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2247
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6176
5585
Frac
tion
isot
opic
rat
ios
isot
opic
age
sB
ackg
rou
nd c
orre
cted
mea
n co
unt
s pe
r se
cond
at
spec
ifie
d m
ass
207 p
b/23
5 u%
1s
206 p
b/23
8 u%
1s
rho
207 p
b/20
6 pb
% 1
s 20
7 pb/
235 u
± 1s
20
6 pb/
238 u
± 1s
20
7 pb/
206 p
b±
1s
202
204
206
207
208
232
235
238
ap
pEn
dix
1 (c
ontin
ued)
: LA
-ICP-
MS
data
for
U-P
b an
alys
is o
f zirc
ons
Yukon Exploration and GEoloGY 2012
McKenzie et al. – Mid-cRetaceous oRoGenic au and Mo, independence cReek aRea
95
170.
1050
40.
0029
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60.
360.
0492
30.
0014
010
1.4
2.7
100.
11.
015
8.9
65.2
110
1391
465
315
5412
7026
5480
8421
57
180.
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0019
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10.
0001
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340.
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30.
0009
010
1.6
1.8
100.
50.
794
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091
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579
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75
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1036
30.
0021
30.
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10.
0001
10.
350.
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40.
0009
810
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2.0
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0.7
80.4
48.7
261
1014
148
213
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9430
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Daw
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310
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913
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298
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899
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777
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103
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40.
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40.
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60.
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249
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80.
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320.
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10.
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796
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410
0.7
1.2
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88.3
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316
610
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14
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340.
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40.
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760
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33
Daw
son
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lith
(sam
ple
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10.
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90.
0065
00.
0167
90.
0003
10.
310.
0462
00.
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210
4.1
6.0
107.
32.
08.
314
0.8
7811
2679
124
271
2750
513
3619
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20.
1122
80.
0033
90.
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10.
0001
70.
360.
0514
20.
0015
810
8.0
3.1
100.
51.
125
9.7
69.2
140
1179
6741
210
3211
5385
4255
6360
20
30.
1076
10.
0029
30.
0161
90.
0001
50.
340.
0483
10.
0013
310
3.8
2.7
103.
51.
011
4.3
63.8
9014
5766
280
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230
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40.
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70.
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40.
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70.
0001
30.
340.
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40.
0011
810
2.4
2.3
101.
50.
912
5.5
56.2
135
2571
4634
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50.
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40.
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50.
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40.
0002
10.
300.
0436
30.
0019
093
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810
3.2
1.3
0.1
0.0
5828
4303
189
573
6820
622
6833
4918
60.
1106
00.
0030
70.
0164
30.
0001
50.
330.
0482
50.
0013
610
6.5
2.8
105.
11.
011
1.5
65.1
577
5408
262
664
7607
027
5841
3346
70.
1040
30.
0038
70.
0160
30.
0002
00.
340.
0475
80.
0018
010
0.5
3.6
102.
51.
377
.588
.192
041
7920
053
666
458
2236
3275
51
80.
1040
20.
0037
30.
0155
70.
0001
80.
320.
0491
80.
0017
910
0.5
3.4
99.6
1.2
156.
283
.212
00
4379
217
757
8391
524
2335
3458
90.
1063
60.
0029
30.
0158
80.
0001
50.
340.
0480
80.
0013
410
2.6
2.7
101.
51.
010
3.3
64.6
588
5301
256
755
8570
628
0842
0096
100.
1129
00.
0051
30.
0159
50.
0002
40.
330.
0498
10.
0023
010
8.6
4.7
102.
01.
518
6.0
104.
171
3138
8819
548
857
385
2011
3067
18
110.
1109
60.
0063
50.
0166
70.
0002
90.
300.
0486
40.
0028
310
6.8
5.8
106.
61.
913
0.3
131.
31
1221
3410
422
024
960
1097
1612
05
120.
1072
90.
0035
40.
0166
40.
0001
80.
330.
0471
90.
0015
810
3.5
3.3
106.
41.
258
.678
.446
141
8419
959
261
085
2160
3167
05
130.
1072
00.
0022
60.
0160
50.
0001
20.
350.
0480
60.
0010
210
3.4
2.1
102.
60.
810
2.4
49.4
028
9342
452
2235
2432
1449
2373
3931
140.
0997
30.
0047
20.
0161
40.
0002
20.
290.
0461
40.
0022
196
.54.
410
3.2
1.4
5.1
111.
559
1224
7911
532
538
244
1349
1937
59
150.
1039
70.
0043
10.
0158
10.
0002
00.
310.
0470
50.
0019
810
0.4
4.0
101.
11.
351
.397
.622
035
5516
846
355
385
1892
2836
47
160.
1013
90.
0030
50.
0158
80.
0001
60.
330.
0464
80.
0014
298
.12.
810
1.6
1.0
22.4
70.6
9821
5410
253
779
8093
529
1842
9910
170.
1043
20.
0032
80.
0159
40.
0001
70.
340.
0482
30.
0015
410
0.8
3.0
101.
91.
111
0.5
73.6
111
057
9828
297
811
6648
3159
4594
89
180.
1054
80.
0036
80.
0157
90.
0001
80.
330.
0480
40.
0017
010
1.8
3.4
101.
01.
110
1.0
81.6
810
3905
189
459
4695
320
9731
2493
190.
1000
10.
0037
50.
0156
70.
0002
00.
340.
0479
90.
0018
396
.83.
510
0.2
1.3
97.4
89.1
418
4915
237
479
5538
327
8239
6486
200.
1121
10.
0085
00.
0168
40.
0004
30.
340.
0481
10.
0037
110
7.9
7.8
107.
62.
710
4.6
172.
912
312
3241
157
379
4086
316
4124
3420
Cof
fee
Cre
ek g
rani
te (s
ampl
e Y
GR
-BV
-002
)
10.
1026
60.
0028
30.
0156
00.
0001
50.
350.
0472
30.
0013
099
.22.
699
.81.
060
.664
.813
056
0927
110
9210
0851
2652
4019
05
20.
1035
10.
0031
40.
0155
50.
0001
70.
360.
0486
30.
0014
810
0.0
2.9
99.5
1.1
130.
169
.97
353
1826
476
377
001
2568
3822
95
30.
1025
40.
0036
50.
0156
20.
0001
90.
340.
0466
70.
0016
799
.13.
499
.91.
232
.483
.50
034
1516
245
340
592
1598
2444
94
40.
1105
30.
0028
20.
0159
30.
0001
50.
370.
0500
20.
0012
610
6.4
2.6
101.
91.
019
5.8
57.7
16
1777
390
737
6440
9591
8271
1247
606
50.
1018
10.
0038
80.
0154
00.
0002
10.
360.
0475
60.
0018
298
.43.
698
.51.
376
.689
.40
051
5525
092
082
488
2477
3746
15
60.
1017
60.
0065
10.
0146
10.
0003
40.
360.
0499
00.
0032
598
.46.
093
.52.
119
0.5
144.
733
1939
3820
088
868
418
1987
3018
34
70.
1020
10.
0032
00.
0151
90.
0001
70.
360.
0482
80.
0015
298
.63.
097
.21.
111
3.0
72.4
08
1031
450
612
4716
3869
5025
7599
97
80.
1023
80.
0057
30.
0154
00.
0003
00.
350.
0478
70.
0027
199
.05.
398
.51.
991
.613
0.0
014
3232
157
468
3818
015
5623
4992
90.
1040
20.
0036
90.
0154
90.
0002
00.
360.
0482
70.
0017
210
0.5
3.4
99.1
1.2
112.
481
.80
1050
2524
689
779
070
2401
3633
08
100.
1059
10.
0083
40.
0155
70.
0004
40.
360.
0474
90.
0037
910
2.2
7.7
99.6
2.8
73.3
180.
413
1431
3115
045
841
514
1447
2253
12
110.
1060
10.
0051
20.
0155
00.
0002
80.
370.
0505
50.
0024
710
2.3
4.7
99.2
1.8
220.
210
9.3
024
7264
372
1020
1106
0935
7152
5287
120.
1057
70.
0075
50.
0160
50.
0003
90.
340.
0495
30.
0035
910
2.1
6.9
102.
62.
517
3.0
160.
70
3218
4292
252
2876
688
912
8710
Frac
tion
isot
opic
rat
ios
isot
opic
age
sB
ackg
rou
nd c
orre
cted
mea
n co
unt
s pe
r se
cond
at
spec
ifie
d m
ass
207 p
b/23
5 u%
1s
206 p
b/23
8 u%
1s
rho
207 p
b/20
6 pb
% 1
s 20
7 pb/
235 u
± 1s
20
6 pb/
238 u
± 1s
20
7 pb/
206 p
b±
1s
202
204
206
207
208
232
235
238
ap
pEn
dix
1 (c
ontin
ued)
: LA
-ICP-
MS
data
for
U-P
b an
alys
is o
f zirc
ons
Yukon GeoloGical ReseaRch
Yukon Exploration and GEoloGY 201296
130.
1026
60.
0053
50.
0155
60.
0002
70.
330.
0477
70.
0025
199
.24.
999
.51.
786
.912
1.1
00
1877
9022
224
641
901
1353
31
140.
1044
80.
0052
90.
0156
60.
0002
70.
340.
0483
70.
0024
710
0.9
4.9
100.
21.
811
7.5
116.
20
026
0012
743
742
164
1242
1862
88
150.
1096
50.
0033
20.
0154
10.
0001
70.
360.
0515
80.
0015
510
5.6
3.0
98.6
1.1
266.
967
.515
087
5345
612
6811
9562
4250
6372
30
160.
1032
20.
0045
80.
0158
30.
0002
50.
360.
0466
40.
0020
899
.74.
210
1.2
1.6
30.7
103.
60
1577
8236
616
0314
2208
3631
5520
01
170.
1093
20.
0080
50.
0166
90.
0004
20.
340.
0470
70.
0035
010
5.3
7.4
106.
72.
752
.616
8.7
013
2355
111
322
3047
610
4815
8469
180.
1011
00.
0038
00.
0152
10.
0002
00.
350.
0474
90.
0017
897
.83.
597
.31.
373
.187
.50
548
8023
373
760
813
2368
3602
74
190.
1026
10.
0032
60.
0157
60.
0001
80.
360.
0472
80.
0014
999
.23.
010
0.8
1.1
62.9
73.7
300
7450
354
1101
9932
535
4853
0908
200.
1047
60.
0042
10.
0154
40.
0002
20.
350.
0479
90.
0019
310
1.2
3.9
98.8
1.4
97.5
93.7
01
1056
650
931
8929
5478
5004
7690
69
Cof
fee
Cre
ek g
rani
te (s
ampl
e 99
M-1
05)
10.
1033
90.
0032
00.
0153
40.
0001
70.
360.
0482
50.
0014
399
.93.
098
.11.
111
1.5
68.4
016
1173
158
019
9018
9507
6334
8777
76
20.
1047
40.
0031
20.
0156
10.
0001
70.
370.
0486
90.
0013
810
1.1
2.9
99.8
1.1
132.
965
.20
1820
315
1013
3402
3337
8810
921
1493
286
30.
1082
40.
0036
10.
0159
90.
0002
00.
380.
0496
30.
0016
010
4.4
3.3
102.
31.
217
7.9
73.3
06
9917
504
2341
2211
7052
5671
1046
40.
2439
80.
0074
60.
0345
80.
0003
90.
370.
0514
90.
0014
822
1.7
6.1
219.
22.
426
3.0
64.5
1020
2918
915
3830
7915
0998
7117
9674
39
50.
1015
00.
0048
60.
0148
10.
0002
50.
350.
0484
60.
0023
198
.24.
594
.81.
612
1.7
108.
40
039
0619
356
455
271
2151
3019
57
60.
1000
90.
0049
40.
0151
20.
0002
70.
360.
0483
70.
0023
896
.94.
696
.81.
711
7.6
112.
00
039
1919
346
645
604
2183
2965
40
70.
1028
10.
0035
10.
0151
40.
0001
90.
370.
0482
40.
0015
899
.43.
296
.81.
211
1.0
75.7
310
7273
358
1100
1093
9239
3254
9627
80.
1045
30.
0040
70.
0156
60.
0002
20.
360.
0495
40.
0018
810
1.0
3.8
100.
11.
417
3.3
86.5
00
5663
286
1160
1063
7130
9141
3592
90.
1037
40.
0032
50.
0157
70.
0001
80.
360.
0477
70.
0014
110
0.2
3.0
100.
91.
186
.869
.70
1320
375
992
4707
4410
6010
790
1474
918
100.
1028
10.
0040
60.
0153
20.
0002
20.
360.
0485
40.
0018
799
.43.
798
.01.
412
5.9
88.1
00
8598
425
1609
1549
0746
6764
0612
110.
1047
30.
0036
60.
0155
80.
0002
00.
370.
0481
40.
0016
110
1.1
3.4
99.6
1.3
106.
377
.432
2094
2446
220
9019
3303
4977
6903
28
120.
1030
00.
0037
50.
0158
50.
0002
10.
360.
0467
50.
0016
499
.53.
510
1.4
1.3
36.4
82.0
7414
6636
315
1111
1070
4434
5947
7455
130.
1051
40.
0052
90.
0155
60.
0002
80.
360.
0492
70.
0024
610
1.5
4.9
99.6
1.8
160.
611
2.7
6220
3412
170
494
5044
318
3324
9767
140.
1027
80.
0043
30.
0152
90.
0002
30.
360.
0489
50.
0020
299
.34.
097
.81.
514
5.7
93.8
740
8571
426
1615
1497
4046
7863
8081
150.
1058
40.
0040
60.
0153
70.
0002
10.
360.
0490
90.
0018
210
2.1
3.7
98.3
1.4
151.
984
.726
1686
9443
313
1012
2623
4619
6438
45
160.
1049
20.
0052
50.
0159
00.
0002
80.
350.
0480
90.
0023
810
1.3
4.8
101.
71.
810
3.5
113.
00
047
7523
371
074
355
2505
3415
46
170.
1086
10.
0039
20.
0152
10.
0002
00.
360.
0517
40.
0017
810
4.7
3.6
97.3
1.3
273.
977
.16
2720
121
1055
6714
6125
0410
958
1502
498
180.
1090
70.
0046
10.
0152
80.
0002
30.
360.
0512
00.
0021
110
5.1
4.2
97.8
1.5
249.
792
.10
1243
1922
473
667
610
2316
3209
53
190.
1031
00.
0042
30.
0156
80.
0002
30.
360.
0466
20.
0018
599
.63.
910
0.3
1.5
29.9
92.8
027
5749
271
821
7638
029
6941
6182
200.
1062
20.
0035
80.
0158
50.
0001
90.
360.
0482
10.
0015
310
2.5
3.3
101.
41.
210
9.4
73.2
890
6101
929
7822
748
2E+0
631
613
4368
048
Cof
fee
Cre
ek g
rani
te (s
ampl
e 99
M-1
07)
10.
1034
90.
0014
30.
0156
10.
0000
90.
420.
0480
20.
0006
710
0.0
1.3
99.9
0.6
98.9
34.0
4513
1992
696
936
6740
4003
1095
518
0430
7
20.
1102
70.
0015
80.
0160
90.
0000
90.
390.
0491
20.
0007
210
6.2
1.5
102.
90.
615
3.7
33.8
00
1750
187
118
4120
8355
9242
1537
814
30.
1046
90.
0013
90.
0155
20.
0000
90.
440.
0483
40.
0006
510
1.1
1.3
99.3
0.6
115.
931
.610
2027
749
1359
7450
9007
7815
197
2526
153
40.
1033
80.
0028
80.
0155
90.
0001
60.
370.
0479
80.
0013
799
.92.
799
.71.
097
.167
.312
096
1846
725
7628
2684
5296
8718
89
50.
1028
30.
0014
60.
0154
80.
0000
90.
410.
0481
10.
0006
999
.41.
399
.10.
610
4.9
33.7
021
2596
212
6540
3445
1622
1442
623
6808
8
60.
1029
70.
0009
70.
0155
90.
0000
70.
480.
0477
80.
0004
599
.50.
999
.70.
487
.623
.421
139
500
1911
6471
7063
6421
778
3577
980
70.
1058
90.
0015
60.
0154
10.
0000
90.
400.
0489
70.
0007
310
2.2
1.4
98.6
0.6
146.
334
.80
2318
733
929
2609
3128
5810
297
1716
416
80.
1019
70.
0014
00.
0153
90.
0000
90.
430.
0478
80.
0006
798
.61.
398
.40.
692
.333
.80
1227
552
1335
6336
7021
2415
385
2527
561
90.
1012
60.
0040
90.
0152
90.
0002
20.
360.
0470
80.
0019
497
.93.
897
.81.
453
.196
.010
80
4816
229
834
9173
826
6544
4486
100.
1026
60.
0016
70.
0153
40.
0001
00.
400.
0480
80.
0008
099
.21.
598
.10.
610
3.2
38.8
4244
2065
410
0538
8047
1386
1151
818
9984
2
110.
1032
80.
0014
60.
0154
70.
0000
90.
410.
0480
70.
0006
999
.81.
398
.90.
610
2.8
33.6
430
2222
810
8127
4830
8437
1232
520
2692
7
120.
1012
20.
0010
80.
0154
70.
0000
70.
420.
0470
60.
0005
197
.91.
098
.90.
551
.925
.00
229
494
1404
4534
5327
2716
343
2689
094
130.
1043
80.
0021
00.
0154
80.
0001
20.
390.
0481
50.
0009
910
0.8
1.9
99.0
0.8
106.
947
.832
099
4648
423
6927
5786
5474
9055
11
140.
1116
90.
0020
60.
0152
80.
0001
10.
390.
0517
10.
0009
810
7.5
1.9
97.8
0.7
272.
442
.757
1224
701
1291
3507
4028
2913
647
2278
058
150.
1037
80.
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736
Frac
tion
isot
opic
rat
ios
isot
opic
age
sB
ackg
rou
nd c
orre
cted
mea
n co
unt
s pe
r se
cond
at
spec
ifie
d m
ass
207 p
b/23
5 u%
1s
206 p
b/23
8 u%
1s
rho
207 p
b/20
6 pb
% 1
s 20
7 pb/
235 u
± 1s
20
6 pb/
238 u
± 1s
20
7 pb/
206 p
b±
1s
202
204
206
207
208
232
235
238
ap
pEn
dix
1 (c
ontin
ued)
: LA
-ICP-
MS
data
for
U-P
b an
alys
is o
f zirc
ons
Yukon Exploration and GEoloGY 2012
McKenzie et al. – Mid-cRetaceous oRoGenic au and Mo, independence cReek aRea
97
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258
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14
2088
250
230
4321
068
214
5736
Frac
tion
isot
opic
rat
ios
isot
opic
age
sB
ackg
rou
nd c
orre
cted
mea
n co
unt
s pe
r se
cond
at
spec
ifie
d m
ass
207 p
b/23
5 u%
1s
206 p
b/23
8 u%
1s
rho
207 p
b/20
6 pb
% 1
s 20
7 pb/
235 u
± 1s
20
6 pb/
238 u
± 1s
20
7 pb/
206 p
b±
1s
202
204
206
207
208
232
235
238
ap
pEn
dix
1 (c
ontin
ued)
: LA
-ICP-
MS
data
for
U-P
b an
alys
is o
f zirc
ons