GEOLOGY OF THE FORREST KERR CREEK AREA__ NORTHWESTERN BRITISH

Document Sample
GEOLOGY OF THE FORREST KERR CREEK AREA__ NORTHWESTERN BRITISH Powered By Docstoc
					                   GEOLOGY OF THE FORREST KERR CREEK AREA!,
                       NORTHWESTERN BRITISH COLUMBIA
                                       (104B/15)
                      By J.M. Logan, V.M. Koyanagi and J.R. 1)robe

KEYWORDS; Regionalgeology,Stikineassemblage,                       western British Columbia. In 1988 mapping was centred or
Stuhini Group, McLymont Creek, skams, veins,massive                Galore Creek and map sheets 104Gi3 and 4 (Figure 1-13-1)
sulphides. gold, base metals.                                      The 1989 program extended previous mapping southf:ast 118
                                                                   the lskut River to delimit Paleozoic Stikine assemblage ant1
INTRODUCTION                                                       Upper Triassic Stuhini Group stratigraphy, to a s s e s thl:
                                                                   mineral potentialof the area andupdate !he mineral inventor!'
  Thisreportsummarizes       results of 1 5 0 000-scale
                           the                                     database (MINFILE).
mapping completedduring the 1989 field season in the
Forrest Kerr maparea (104Bi15). This is the second year of a         The 1989 map area is located about 15 kilometre!; north
4-yearprogram of regionalmappingandmineraldeposit                  west of Eskay Creek, 30 kilometres southeast of the Galon:
modelling between theIskutand     Stikine rivers in north-         Creekporphyry copper depositand .about 20 kilometre;




              1989
                 Map      Area                   j
                                             /
                                         /
              ProposedMap              ,.'
               Area 1 9 9 0        (
                               ,,,..




        Figure 1-13-1. Location map showing the 1989 Forrest Kerr Creek map area, the 1988 Galore Creek map area and the
                                                   proposed map area for 1990.
Geologicul Fieldwork 19x9, Azper I990-I                                                                                    1;   :7
northeast of the Snip
                    deposit
                          and       Johnny
                                         Mountain
                                                mine                 REGIONAL GEOLOGY
(Figure 1-13-1).
                                                                       The study area straddles the boundary between the Inter-
    The topography    Forrest
                     Of             map area is characterized        montane andCoast tectonic belts.Stikine Terrane (Stikinia)
by deeplyincisedforestedriver valleys with an abundance of           underlies the area and comprises a mid-Paleozoic Meso-
slide alder anddevils club at lower elevations,and alpine            zoic island arc succession which is overlapped by Middle to

-
areas with highpeaksandridgesmantled            by radiating
glaciers and Dennanentsnow fields.Permanent snow andice
cover about 20 per centof the map area. Accessis by fixed-
                                                                     Late Jurassic sediments of the Bowser basin the east,
                                                                        Paleozoic volcanic and associated sedimentary    rocks of
wing aircraft from Smithers to the Forrest Kerr airstrip, or to      the Stikine assemblage floor Stikinia. Mesozoic arc volca-
the Bronson Creek airstrip on the Iskut River, and from there nism         is represented in the Upper Triassic by Stuhini Group
by helicopter.                                                       and in the Lower Jurassic by Hazelton Group volcanic and

128                                    Geological          Columbia                British                       Survey Branch
                         LEGEND
  OUATERNARI




                                          sedimentary rocks. The Middle Jurassic Spatsizi and Elowser
                                          Lake groups record succ~:ssor basin sedimentation. A t least
                                          four episodes   of pluronism            this
                                                                         affected con~plex
                                          stratigraphy.

                                          STRATIGRAPHY
                                          PALEOZOIC    ASSEMBLAGE
                                                 STIKINI:
                                             The Stikineassemblage of northwestern British Columbis
                                          (Monger, 1977) includes Paleozoic r0ck.s of Early to bliddlt
                                          Devonian, Mississippian. and Permian age (Pitcher. 1960
                                          Logan and Koyanagi, 1089; Anderson, 1989; Read t't a/.
                                          1989).Paleozoicrocks in the map area are divisible intc
                                          eastem and western assemblages (Figure 1-13-2) based or
                                          structural and metamorphic disparities. Stratigraphy ill gen.
                                          era1 can be correlated from one division to the other (l'igurc
                                          1-13-3).

                                          EASTERN ASSEMBLAGE(IDc, F'mv, Pms,PC,h )
                                                                                e
                                             The easternassemblage occupies a north-trendin: bel
                                          west of the ForrestKerr fault as well as small inlierseast of th~
                                          fault. Rocks in this belt young southwards. In the north is ;L
                                          metavolcanic package (Pmv) ranging      from MiddleDevonialt
                                          toEarly Mississippian age (Read et a / . , 1989),cnerlailt
                                          southward by a metasedimentary            and
                                                                              (Pms) siliciclastil:
                                          package of Early Permianage, capped by     Permian platlormal
                                          limestones (PC). Early Permian meta-tuffs and interbeddell
                                          limestones (Ptc) outcrop eastof Forrest Kerr fault. Rocks of
                                                                   are
                                          the eastern assemblage penetratively deformed by id least
                                          two phases of deformation.

                                          LQWER             LIMESTONE
                                                     DEVONIAN       (IDc)
                                             The oldest known unit in the Paleozoic assemblage com.
                                          prises at least four coralline limestone members of E;uly to
                                          Middle Devonian age (Anderson. 1989; Read et a l . , 1989:.
                                          Interbedded with the limestonearepebble conglonterate,
                                          siliceous and carbonaceous shales and both mafic and felsi,:
                                          tuffs. The maximum total thickness is 400 metres. Th.:
                                          succession is exposed in a narrow belt, 4.5 kilometres long,
                                          north of the lskutRiver between McLyrnont andFom::;t Ker I
                                          creeks, where it is intruded by Paleozoic(?) quartz ,&orit:
                                          (Pqd) and thrust eastwatd (Figure 1-13-2). Lower Deionia 1
                                          limestone forms the hangingwallof West Lake fault.(:ReadL I
                                          al., 1989). These are the! most penetratively deformec rocks
                                          in the map area.

                                          PALEOZOIC METAVOLCANICS ( h V )
                                             Paleozoic metavolcanics arevariably foliated to schistose.
                                          dependent upon the protolith.Mafic to    intermediate f k w s a~i
                                          weakly foliated, purple to dark green;and either mas",we c I'
                                          brecciated. Amygdaloidal plagioclase'? augite-phyric flour,
                                                                                             to
                                          predominate. Mottled purple and green mafic felsic lapil
                                          tuffs are well foliated to phyllitic. Lapilli are flattened in t h t :
                                          plane of foliation. Fine-grained crystal tuffs and tuffaceoi!:
                                          sediments have been mc:tamorphosed to chlorite schists and
                                          lesser quartz-sericite schists. Interbedded with these metil

Geological Fieldwork 1989, Paper 1990-1                                                                   129
volcanicsaresubordinatephyllites,tuffaceouspyritic                 detail, amygdules are distributed parallelto bordersof clasts
argillites and recrystallized limestone.                               are
                                                                   and often  concentrically  zoned      the
                                                                                                     about clasts.
                                                                   Hyaloclastite debris flows contain sparse pillows. Massive
PALEOZOIC    METASEDIMENTSs )
                        (h                                         flows have brecciated tops and bottoms. Light purple to pink
   The metasedimentary unit comprises grey to light green          daciteflowbreccias       are spatially related to ash-flowand
phyllitic siltstone, graphitic argillite, siliceous phyllite and   welded tuffs in the northwest corner of the map area. These
thin lenses of dark brown weathering limestone. Pale green         flows and tuffs contain very angular lapilli averaging 1 to 10
andwhitesiliceousturbidite        couplets,comprised of 2 to       centimetresacross andpinkish grey porphyritic feldspar,
5-centimeue siltstonebedsintercalated         with I-centimetre    often in clusters of three tofourcrystals.The          irregular
beds of fine sandstone, form a distinctive unit at least 200       distribution of quartz, epidote and chlorite amygdules indi-
metres thick. This unit is correlative with Brown and Gun-         catespropyliticalterationratherthanregionalgreenschist
ning’s(1989)“siliceous unit” mapped to the north at the            metamorphism.
Scud River. Apparently high(?) in the stratigraphy are vari-          Fragmental rocksare dominated by heterolithic lapilli
coloured, weakly foliatedsiliceoussiltstonesandribbon              tuffs. Dark green to grey, angular to subrounded, densely
cherts.                                                            amygdaloidal fragments are diagnostic of tuffs interbedded
                                                                   with pillowed flows and scoriaceous hyaloclastites. Domi-
PERMIAN CARBONATES        (PC)                                     nantly green, orange-weathering ash-flow and welded lapilli
   EarlyPermian(Artinskian       toSakmarian; Read ef al.,         tuffs are a distinctive unit. Lapilli  are pale grey, pink and
1989) limestoneis exposed at the southern edge of the map          purple aphyric lithic and crystalfragments. These felsic tuffs
area adjacent to the West Slope fault. The limestone is a          are spatially related to dacitic and rhyolitic rocks exposed
massive, white to buff, sparsely crinoidal calcarenite which       north of the headwatersof Forrest Kerr Creek.A third variety
locally is completely recrystallized to coarse calcite.            consists of thin, planar-bedded siliceous dust tuffs. These  are
                                                                   interbedded with graded and crossbedded crystal and lapilli
                        CARBONATES
PERMIAN META-TUFFS LESSER
                 AND             (Ptc)                             volcaniclastics.
   This metavolcanicunit is exposed east of the bend in               This volcanic succession is interpreted to represent sub-
Forrest KerrCreek.The      unit is foldedandfoliatedand            marinevolcanismfrom              a seamount   (pillows and
comprised of interbeddedchloritic tuffs, tuffaceousand             hyaloclastite) with atoll-fringing reefs (reefal limestone Mc)
siliceous siltstones and numerous thin recrystallized Early        which, over time, became emergent (ash-flow and welded
Permian limestones.                                                ash-flowtuffs)andevolved         from basalt throughdacite to
                                                                   rhyolite.
WESTERN ASSEMBLAGE
(Mv, Mcl, Mcg, Mtp, Pcl, Pvb, Pc2, Pvt)                            MISSISSIPPIAN
                                                                               CARBONATE c )
                                                                                       (M
   The western assemblage is well exposed north of the Iskut
                                                                      Late Mississippian reefal limestone, reef-flank carbonates
icefield and Newmont Lake and separated from the eastern
                                                                   and cherty siltstones overlie hyaloclastites in the northwest
assemblage by aJurassic compositeplutonic body. Mis-
sissippianreefallimestone     (Mc)and underlyingpillowed           corner of the map area (Figure 1-13-2). West of Newmont
basalt (Mv) are the oldest known rocks. A polymictic vol-          Lake thebase is faulted. At Round Lake (about20 kilometres
canic conglomerate (Mcg)   separates Mississippian limestone       northwest) the limestone consists of two distinct members
from Lower Permian (R.G. Anderson, personnel communi-              separated by a wedge of chert and phyllitic volcaniclastic
cation,1989) limestones(Pcl).
                            Intermediate  volcanics                rocks(Monger, 1970; LoganandKoyanagi,            1989). In the
(Pvb), a medial limestone (Pc2) and felsic tuffs (Pvt) com-        northwest corner of the map sheet these same lithologies are
prise theuppermost sections. Thewestern assemblage rocks           recognized, but their relationships are complicatedby fault-
are not penetratively deformed, not metamorphosed and the          ing and swarms of east-trending dikes. The lower limestone
limestones are rarely recrystallized; at the time of mapping       is a bioclastic calcarenite with characteristic coarse (up to
                                 than
they were thought to be younger the eastern assemblage             5-centimeue diameter) crinoid columns. Carbonates inter-
                                                                   preted to be coralline reef mounds, slope-front block breccias
MISSISSIPPIAN    VOLCANICS(Mv)                                     and graded reef-flank deposits interbedded with siliceous
   Mississippian and older(?) mafic to felsic volcanics occur      siltstones comprise an aggregate thickness of 50 metres at
in the northwestern and southwesterncorners of the map area        most. Farther west less than200 metres of thick-bedded, grey
and comprise a southwest-dipping homoclinal sequence of            crinoidal calcarenite with interbeds of amorphous chert are
pillow lavas. flow breccia, ash-flow tuffs and stratified tuffs    exposed on strike. This limestone contains small crinoidal
and epiclastics which are conservatively estimated to exceed       stems and fossil fragments, is locally fetid and resembles the
2000 metres in thickness. The upper contact is conformable         upperlimestone member exposed at Round Lake. Both
with mid-Late Mississippian limestone (M.J. Orchard, per-          limestonemembersareconformablyoverlainby                     a
sonal communication, 1989). The lower contact was not              coarsening-upward sequence of siliceous siltstones and vol-
defined. Interbeddedhyaloclastiteand      pillowed flows are       canic conglomerate.
texturallydistinctiveandvolumetricallyexceedmassive
sheet-flows of basalt in thenorthwest corner of the map.           MISSISSIPPIAN(?)
                                                                                 CONGLOMERATE
Flows vary texturally from aphanitic to porphyritic and are
                                                                   AND SILTSTONE    (Mcg)
commonly amygdaloidal.Plagioclase-phyric flows are more
common than augite-plagioclase porphyries. Basaltic                  At least 300 metres of cherty siltstone and maroon poly-
andesite flows are characterized by scoriaceous fragments. In      micticvolcanic conglomerate overly Mississippianlime-

130                                                                               British Columbia Geological Survey Branch
stone in the northwest corner of the study area and west of        Solitary corals, foraminifera, bryozoan,   crinoids and valious
Newmont Lake. Dark grey and black cherty siltstones and            brachiopods are locally abundant. Limonitic and hematitic
interbedded bioclastic limestone shale-out     up section, fol-    limestones are coincident with fault structures and indicate
lowed by thinly laminated rusty weathering cherty siltstones       fluid flow and attendant alteration. This alteration is seleztive
which, in turn, areconformably overlain by maroon con-             and occurs predominantly in the masswe limestonesand
glomerates. Dark purple and green pyroxene-porphyritic and         dolomitic mudstones.
hornblende-plagioclase-porphyritic andesites, scoriaceous
basalt and grey fossiliferous limestone clasts form up to 70       PERMIAN VOLCANICS AND VOLCANIC I3RECCIAS              (Pvb)
per cent of the rock in a plagioclase crystal rich tuffaceous         A Permian intermediate volcanic unit outcrops w i t h ? the
matrix. In general the conglomerates are massive to thickly        northeast-trending Newmont Lake graben. It is a distinctive
bedded making it difficult to determine bedding attitudes.         purple to maroon colour and comprises thick breccia flows,
Angular blocks of limestone up to several metres across are        lahars, tuffs and lesser mudstones and wackes. These vol-
common. A tentative fossil identification from one of these        canicsarefresh       in appearanceandresembleJunssic
blocks is probably Permian hut possibly Mississippian (E.W.        Hazelton Grouprocks, theirintercalationwith         1ime:;tone
Bamber, personal communication, 1989). Near the of thetop          members is an important distinction (Anderson, 1989)
conglomerate,angular limestone clasts increase in abun-               Theflowsarepurple,plagioclase:andhornbiende-
dance near the Permian limestone    contact. From this relation-   porphyritic andesites. Theyare locally amygdaloidal and
ship the conglomerate was formerly interpreted to be post-         generally contain 30 to 40 per cent euhedral white plagio-
Permianand overturned. Mesoscopicdlly it resemblesthe              clase and 15 per cent chloritic acicular hornblende crystals.
basal Triassic conglomerate located to the west, above For-        Breccia and massive flows averaging 5 metres in thimdcness
rest Kerr Creek (Read er a l . , 1989). Bedding-top directions     are interbedded with well-graded interflow epiclastics west
and conformable contacts indicate that the conglomerate is         of Newmont Lake. East of Newmont Lake are light greento
upright and actually either Late Mississippian or Early Per-       pink, block and lapilli tuffs with lesser plagioclase csystal
mian in age. It has tentatively been interpreted to represent      tuff. Maroon lahar and well-bedded grnded conglon1c:rates
Monger’s (1977) post-Mississippian pre-Permian profound            are exposed north of Forrest Kerr Creek
unconformity.                                                         This calcalkaline volcanic package,coarse“proximal
                                                                                                                          ‘>-est
                                                                   facies” breccia flows, antl variable oxidizing statessua,= a
MISSISSIPPIAN  TUFFS AND EPILCLASTICS    (Mtp)                     transgressive submarine to subareal volcanic centre.

 This unit is exposed on nunataks northwest of Newmont             PERMIAN    ALGALLIMESTONE  (Pc2)
Lake. A second outcrop area between McLymont Creek and               Thislimestone is agoodmarker    which can he traced
Newmont Lake is tentativelyincluded. The age of these              around the Newmont Lake syncline. North of the lake 95
clasticsandtuffs      is uncertain: the interbedded tuffs and      metres thickness is exposed. The lime,jtone pinches dong
epiclastics resemble Mississippian epiclastics to the north.       strike and on the eastlimb is only 20 metres thick. It i:. dark
The unit comprises awell-beddedsuccession          of distal(?)    grey to black and finely laminated, weathering buff and is
turbiditesconsisting of finesiliceoussiltstoneandcar-              locally fetid. Pisolite-rich beds and cuspate stacked concave
bonaceous siltstone, interbedded sandstone and polymictic          algal structures are common. The upper sections are :selec-
conglomerate.Fining-upwardsequencesarecommon.                      tively silicified.
Lapilli tuff is interbedded and thick accumulations of coarse
                                                                      The finelaminations are interpreted to hecryptalgal lami-
breccias and lahar attest to periodic volcanic influxes. The
successionsoutheast of NewmontLakeconsists            of well-
                                                                   nations (Aiken, 1967) indicative of algal mats and an inter-
                                                                   tidal zone of deposition for the limestone. The algal lime-
indurated, commonly bleachedandpyritic,finelylayered
                                                                   stone unit is overlain conformablyby well-bedded tuffacenu!
siltstones and conglomerates which are hornfelsed by adja-
                                                                   epiclastics and a thick package of welded tuffs.
cent intrusions. Unit Mtp is thought to represent a basinward
facies equivalent of the coarse conglomerate of unit Mcg.          PERMIAN       (Pvt)
                                                                         VOLCANICS
                                                                      The core of the Newmont Lake syncline contains a basa
PERMIAN LIMESTONE        (PCl)                                     package of maroon,     shallow-water  conglomerates silt.
                                                                   stones, lapilli and plagioclase crystal   luffs. Discontinuou!
   Lower Permian (Artinskian; M.J.Orchard,personnel
communication, 1989) limestone is best exposed on nunataks         thinly bedded siliceous limestones, up to 5 metres thick, arc
along the western edge of the map area and in fault-bound          interspersed throughout. This basal pa,:kage is overkin b)
slivers on the eastern side of the Newmont Lake graben. In         more than 100 metres of brownish grey massive to thick
contrast with thegreaterthan1000          metres of platformal     bedded welded ash tuffs. The tuffs exhibit good eu.axiti1
carbonates present at the Scud River (45 kilometres north)         flow laminae and are oiten      columnar jointed. Air-fall ast
less than 200 metres are present here.                             tuffs are well stratified and contain 5 to 10 per cent angula’
                                                                   lithic lapilli. Flow-banded rhyolites antl breccias occur higlt
   The limestone comprises primarily massiveto thin-bedded
                                                                   in the section.
grey bioclasric calcarenite andlesser huff siltydolomitic
units. Thin-bedded sections are interbedded with black to
yellowish huff amorphous silica beds up to 20 centimetres               TRIASSIC
                                                                   MIDDLE      (mTRs)
thick and comprising as much as 50 per cent of the outcrop.           Middle Triassic(?)rocksarerestricted  to small discon-
These layers are diagenetic(’!) silicified fossil-rich horizons.   tinuous fault-bounded exposures in the centre of the Neu-
Geological Fieldwork 1989, Paper 1990-1                                                                                        13 ’
mont Lake syncline (Figure 1-13-2). Unit mTRs consists of                                                  tuffs are massive to
                                                                  crystal-ash tuffs andfine epiclastics. The
blackcarbonaceous, locally calcareous, silty shales and           weakly stratified. Coarse breccias and block tuffs of augite
argillites whichcontain bivalvesofpresumedMiddle Triassic                              the
                                                                  porphyry occur near top(?) of the succession. Associated
age. These rocks similarto MiddleTriassic rocks mapped
                  are                                             conglomerates and reworked volcaniclastics are comprised
in 1988 above the South ScudRiver (Logan and Koyanagi,            of angular to rounded, green pyroxene porphyry clasts in a
1989). NorthofNewmont Lakethe rocks weatherrecessively            pyroxene-rich matrix.
and are less siliceous but contain characteristic rounded to
elliptical concretions.                                           UNNAMED
                                                                        LOWER To MIDDLE
                                                                                      JURASSIC
                                                                  ROCKS
            STUHINI
UPPERTRIASSIC    GROUP
                                                                     Unnamed Lowerand Middle Jurassic rocks overlie Upper
   Upper Triassic Stuhini Group rocks lie between the West        Triassic Stuhini Group rocks east of the Forrest Kerr fault. A
Slope and ForrestKerr faults southof Forrest Kerr Creek and       generalized stratigraphy consists of: a sedimentary package
east of the Kerr fault in the northeast comer of the map area     of interbedded shales and siltstones, lesser limestones and
(Figure 1-13-21, A generalized stratigraphy following that of     tuffs (Upt): followed by pillowed hasalts, hyaloclastite and
Read etal. (1 989), consists of a lowermost metasedimentary       interflow siliceous sediments (Jvb); andfinallytuffs,sili-
succession (uTrw), a medial metavolcanic succession(uTrva,        ceous wackes and conglomerate (Jtw).
uTrvp) and an overlying tuffaceous metasedimentary succes-           The inherentcomplications of volcanic facieschanges
sion (uTrvt). Contacts between units are faulted or poorly        over short distances and the lack of fossil dates precludes
exposedand, asaresult,thicknesses and overall stratigraphic       assigning these rocks to either the Hazelton or the Spatsizi
relationships are uncertain (Figure 1-13-31,                      Group.
   East of the Forrest Kerr fault Unit uTrw consists of a thick
package of fine-grainedvolcaniclasticsandsediments.
Green to grey massive volcanic wackes        and arenites, and    LOWERJURASSIC SHALES AND SILTSTONES
interbedded black siltstones and argillites predominate, with     (IJN
lesser limestoneand limy conglomerates. Massive to thickly           At least 1000 metres of interbedded shale and siltstone
bedded volcanic sandstones and poorly sorted lithic wackes        outcrop in the valley floor of “Downpour” Creek and extend
contain up to 80 per cent plagioclase, remaining I O to 30
                                         the                      to More Creek north of the map area (Figure 1-13-2). The
per cent being 2 to 4-millimetre pyroxene grains and lithic       shales are fissile; siltstones and thin sandstone beds contain
clasts of plagioclase pyroxene porphyry. Plagioclase crystal      abundant carbonaceous wood fragments. Sandstones grade
tuff, with lapilli to 5 centimetres, are intercalated with the    into thick-bedded granule conglomerates containing inter-
wackes. These volcaniclastics are interbedded thin with           mediate volcanic, sedimentary and limestone clasts. Fossils
planar-beddedtocrudelycrossbedded(locally)carbon-                 from interbeddedlimestonehorizonslocated            north of the
aceous rustyweathering argillites.The fine-grainedsedi-           map areaindicate an Early Jurassic (late Toarcian)age (Read
ments containfossiliferous limy horizons with abundant            etal., 1989). This sedimentarysuccession is intruded by 2 to
brachiopodsintercalatedwithlesserlimyconglomeratic                3-metre sills and dikes of pyroxene and plagioclase-phyric
beds.
                                                                  diorite(Jdi) thought to represent feeders to the overlying
   At the south end of the map, east of the West Slope fault, a   basalts. East of the Forrest Kerr fault,at the northem edgeof
maroon volcanic conglomerate containing        limestone clasts   the map area,  Read eral. (1989) show    felsic tuffsandrhyolite
structurallyunderliesLowerPermianlimestone(Figure                 flows correlativewith theMountDilworth             formation of
 1-13-2). It has been interpreted by Readeta!. (1989) to mark     Alldrick et al. (1989). These rocks are restricted to this one
the base of the Stuhini Group.                                    locale.
   Massive light grey to dark greenaphanitic lapilli tuff and
andesite breccia (uTrva) is a minor though distinctive unit
intercalated with plagioclase porphyry flows of Unit uTrvp.
                                                                  JURASSIC PlLLOW          BASALT FLOW
                                                                                                AND
The tuff is massive to stratified with monolithic scoriaceous     BRECCIA
                                                                        (Jvb)
toaphyricandesitelapilli.       Read ef a[. (1989) suggested         Middle(?) Jurassic pillow and flow-breccia basalts under-
thicknesses of a few hundred to less   than a thousand metres.    lie a large area between Forrest Kerr Creek and the Iskut
   Green,andlesser          maroon, crowded       tosparsely      River south of the bend inForrest KerrCreek (Figure
plagioclase-porphyritic andesite breccia and flows (UTNP)         1-13-2). Smaller fault-bounded slices extend north beyond
underlie the area immediately west and east of the Forrest        the map margin to More Creek. In the north they conforma-
Kerr fault. Euhedral plagioclase ranges to 5 millimetres in       bly overlie shales and siltstones of Unit IJpt.
length and comprises 30 per cent of the rock. Alteration is          The pillows average 30 to LOO centimetres across, arewell
characteristically hematite and chlorite with variable epidote,   preserved andcommonly indicate facingdirections. Out-
quartz and calcite as patches and veinlets.                       crops weather dark brown toorange. Flowbreccias are
   Maroon to dark green tuffs and monolithic    augite plagio-
                                                    -+_           interbedded with the pillows and locally scour and disrupt
clase-phyric fragmentals(uTrvt) are best exposed within the       interflow sediments. The basalt is dense, medium grey to
Forrest Kerr fault zone, north of the bend in Forrest Kerr        green, locallyamygdaloidaland       made up of fine-grained
Creek. Lapilli tuffs with varicoloured porphyritic volcanic       vitreous plagioclase crystals with rare pyroxenephenocrysts
and lesser scoriaceous fragments interbedded with purple
                                        are                       and abundant disseminated pyrite. Pillows and hyaloclastite
to maroon and green well-bedded,locally graded plagioclase        flow-breccias comprise more than 90 per cent of this unit.
I32                                                                               British Columbia Geological Survey Branch
                            Figure 1-13-3. Schematic stratigraphic sections for the eastern and westernportions in the map area




          Whiteand grey siliceousargillites or tuffs and pyritic silt-           .iURASSIC
                                                                                 -             TUFFAND WACKE (.Il.w)
                                                                                                             ~-~ ~~
                                                                                                                                  I


          stones are &;bedded with the basalts. Sills or feeders(?) to
          theseflowsaredioritictogabbroicwithcharacteristic                         This unit outcrops at !.he southern edge of the map area
          euhedralfeltyplagioclasetexturesandaninterstitial                      between Iskut River and Forrest  Kerr Creek,northwest of the
                                                                                 Iskut River 18 kilometres upstream from its confluence wit1
          pyroxene-rich groundmass.
                                                                                                                                        of
                                                                                 Forrest Kerr Creek,and a s a fault-bounded wedge ea%t the
             Greyandkhakisiliceoussiltstones,conglomeratesandForrest                     Kerr fault nearthenorthern     edge of the mil)) are:
          tuffs (Jtw) overlie and interfinger with the pillow basalts.           (Figure 1-13-2).
eldwork   Geological                    Paper 1990-1                                                                                      133
   These rocks are characteristically drab, olive to grey in          The diorite is massive, medium grained and contains about
colour, unlike the maroonanddark         green Upper Triassic       20 per cent quartz;plagioclase occurs as glomeroporphyritic
Stuhini Group, and commonly fractured and brecciated. Dark          patchesand makes up the bulk of thefeldspar content.
green andgrey siliceous siltstonesand pyritic cherts are            Hornblende also occurs as glomeroporphyritic patches to IS
crackle fractured and brecciated in situ, forming subangular        per cent.
to angular centimetre-scale fragments. Tuffaceous wackes              The quartz diorite intruded Paleozoic rocks in post-Early
arecarbonaceous andvariably sheared. Interhedded with               Permian to pre-Middle Triassic time (Read et a / . , 1989).
tuffaceous arenites are sedimentary conglomerates contain-
ing clasts of chert, black siltstone and intermediate to felsic
volcanics. Volcaniclastics characteristically
                            are                brownish             EARLY(?)
                                                                           JURASSIC SUITE
grey lapilli and crystal tuffs comprised of euhedral plagio-        PLAGIOCLASE PORPHYRITIC MONZONITE(eJm)
clase and scoriaceous greenand grey fragments. Thecontact
withtheMiddleJurassicBowserLakeGroupis                                Dikes,sillsandplugs        of plagioclase-hornblende-
conformable.                                                        porphyritic monzonite are restricted to the Newmont Lake
                                                                    grahen. They are characterized by a hematitic groundmass,
                                                                    commonly purple to grey with pink subhedral to euhedral
MIDDLE              LAKEGROUP
      JURASSIC BOWSER                                               plagioclase (upto 50 percent) and hornblende crystals.
(JBP)                                                               Trachytic textures are common.
                                           on
    Bowser LakeGroup sediments outcrop the easternedge
of the map area along the flanks of the Iskut River valley.         POTASSIUM FELDSPAR MEGACRYSTIC GRANITE
South of the lskut River, planar-beddedshaleand locally                A hornblende biotite potassium feldspar megacrystic gra-
crossbedded sandstone couplets are interbedded with local           nite outcrops between McLymont and Forrest Kerr creeks
granule conglomerate.Theconglomeratecontainsquartz                  north of the Iskut River. A U-Pb zircon date of 19I to 195 Ma
and siltstone clasts in a limonitic sandy feldspathic matrix.       (Anderson and Bevier. 1990) indicates this body to be the
Argillites have a well-developed pencil cleavage and locally        same age as the Texas Creek pluton of Grove (1986).
host pressure solution quartz veinlets. These grey shales and
siltstones are late Middle Jurassic (Callovian) age and    are
                                                                         JURASSIC SUITE
                                                                    MIDDLE
correlated with the Ashman Formation of the Bowser Lake
Group (Read e f a l . , 1989). West of theIskut River the           DIORITE (Jdi)
lithologies consist of mainly fine to medium-grained sand-             Coarse-grained diorite stocksand sills arespatially associ-
stones containing I O to 15 per cent detrital quartz, and fine      ated with Unit Jvb and outcrop within the Forrest Kerr fault
siltstones.                                                         zone. Plagioclase crystals are euhedral subhedral acicular
                                                                                                            to
                                                                    clots which impart a distinctive felty interlocking texture.
                                                                    Euhedral plagioclase to SO per cent, pyroxene, and up to 1
INTRUSIVE ROCKS                                                     per cent pyrite disseminations comprise these subvolcanic
   Intrusive rocks underlie one third the maparea. They are
                                    of                              intrusions, which may represent feeders to the pillow basalts
                                                                    (Jvb).
chieflyrestricted to anorth-trendingbelt I kilometres wide,
                                             O
in the centreof the map. Wheeleret. a l . , (1988) interpret this
composite plutonic belt to beJurassic. An early Jurassic            JURASSIC     SUITE
U-Pb date has been obtained from a porphyritic granite south
of the map area (R.G. Anderson, personal communication,             DIORITE (J@, QUARTZ MONZONITE (Jqm), BIOTITE
1989). A Paleozoic intrusive suite bas been recognized by           GRANITE (Jg)
Read et a / . (1989) on the eastern margin, but the belt as a          Composite Jurassic intrusions comprise a batholithic body
whole is thought to be Jurassic or younger. A preliminary           extending north from McLymont Creek to north of Forrest
plutonic chronology based on mineralogy, textural and intru-        Kerr Creek.Three separate mappablephases havebeen
sive relationships follows. This will be refined by isotopic        recognized; diorite (Jd). quartz monzonite (Jqm), and biotite
dating currently in progress.                                       granite (Jg) (Figure 1-13-2).
                                                                       The mostmaficphase         (Jd)occurs in the north. It is a
PALEOZOIC(?)
         SUITE                                                      heterogeneousmix of porphyritic to massivehornblende
                                                                    diorite with more mafic hornblendite phases. Hornblende is
HORNBLENDE QUARTZ DIORITE/TONALITE (Pqd)                            chloritic and comprises more than 30 per cent of the rock,
   This unit outcrops as discrete bodies, elongatenorth-south       quartz is less than S per cent, but variable to quartz diorite
and situated west of Forrest Kerr Creek. Therock is hetero-         proportions. The remainder is subhedral plagioclase. Intru-
geneousduetoabundantxenoliths             of pyroxeneand/or         sive breccias, gneissic sills and pendants of metavolcanic and
plagioclase-porphyritic phases and younger felsic intrusive         metasedimentaryrocksare common.        Contacts with Unit Jqm
breccias. Locally the diorite is foliated and deformed. Parts       are gradational over short distances of complexintrusive
of the intrusioncontainwell-rounded        to irregularshaped       mixing which commonly exhibit conflicting intrusive rela-
inclusions from 2 to 100 centimetresacross.Theseare                 tionships. North of Forrest Kerr Creek a 9 square kilometre
                                   felty
always more mafic, finer grained textured amphibolites              zone of metamorphosed Paleozoic rocks(Pu)      separates Units
and compriseup to 65 per cent (by volume) of the inrrusion.         Jd and Jqm.
134                                                                                 British Columbia Geologicaal Survey Branch
    The intermediate phase (Jym) outcrops at the northern end       scalenorthwest-trending ;Inticlinal-sync’linal pair is inter-
of the belt on both sides of More Creek. It is composed of          preted west of Newmont Lake.
cwarse to medium-grained hornblende quartz monzodiorite                Domain I1 is confined to the northeast-trending Newmont
to monzonite. Hornblende averages 20 per cent, as 5 milli-          Lake graben, west of the composite plutonic body. and is
metre crystal laths and poikilitic clots; biotite, where present,   characterized by alargeupright, opennortheasterly trending,
is fine grained and lessthan 5 per cent. Quartz averages I O to     doublyplungingsyncline in Permianvolcanics and lime-
 15 per cent. Feldspars comprise the remainder, in a 60:40          stone. Left-lateral motion alongthebounding          faults has
ratio of plagioclase to potassium feldspar. The rocks are cut       interleaved stratigraphy and resulted in transtensional flult-
by flat-lying sill-like       and
                        bodies swarms            of darkgreen       ing and fracturing in a north-south direction. The syncline is
diabase dikes. Contacts with the younger granite are sharp.         cored by Upper (?) Permian limestone and volcanic rocks.
    The youngestintrusive phase is a quartz-richgranitoid              Domain 111 is west of the Forrest Ken fault in the “cast-
suitecomprisedprincipally        of biotite granite (Jg) which      ern” Stikine assemblage    and is characterized by a modcrate
occupies the southern half of the intrusive belt. A second          west-northwest-dipping schistosity and   tight recumbenl. iolds
body is centred on the Verrett River southwest of McLymont          that are overprinted by a gently southwest-plunging crerlula-
Creek. Granite intrudes all other igneous rocks in the map          tion with its axial plane dipping steeply :southeast.
area as dikes and forms the anastomosing matrix of intrusive           Domain IV is restricted 1:o the Permian,outlier where large,
breccias. The   granite is coarse tomedium grained and deeply       upright,tight,east-trendingfoldsoccur           in thin-bedded
weathered producing a sandy to rubbly outcrop surface. It is        tuffaceous siltstone and limestone.
pink on fresh surfaces and contains about 30 to 40 per cent            Domain V, east of the Forrest Kerr falllt, includes Meso-
quartz and S to I per cent biotite, the remainder being pink        zoic rocksfrom Stuhini Gr’sup to   Bowser Lake Group. Large-
euhedral feldspars. Less commonly hornblende is the mafic           scale folds are generally open, upright, northwesterly trend-
 mineral. The granite varies from equigranular to “quartr-          ing and isoclinal in volcanic rocks, to more tightly chevron
eye” porphyritic. Coarse-grained quartz-rich phases (up to          folded in sediments.
 SO per cent quartz) are spatially related to fault structures.
These pegmatitic phases occur north of McLymont Creek at
 its headwaters and east of the Newmont Lake syncline. They         FAULTS
 characteristically weather hematitic.                                 Regional faultscross the map area and controlthe dirtribu-
                                                                    tion of lithostratigraphic packages. Fault trends are mainly
QUARTZ FELDSPAR PORPHYRY (Kp)                                       northeast to north; northwesterly faults are less    significant
   Small plugs and dikes of quartz feldsparporphyry are             structurally, but are impo!:tant controls for mineralization.
intruded along north-trending faults in Forrest Kerr Creek             Thenortheast-trendingNewmontLakegrabenis                    3
valley north to the headwaters of “Downpour” Creek. The             kilometres-wide. Theeas1:ern side is comprised of a network
rockscontainfinelydisseminatedpyrite      and outcrops are          of parallel fault structures which separ8te various Jurassic
oxidized to yellow and red colourseasilyvisible     from a          intrusivephases from Permian limestones, volcanic1;istics
distance. These rocks extend north onto the Telegraph sheet         andclastics. The western fault is a single,strong, 040”-
(104G) where Souther ( I 972) grouped them with late Cre-           trendingstructureseparatingMississippian          from Pelmian
taceous to early Tertiary felsic bodies.                            strata. Overall apparent movement across the graben is left
                                                                    lateral. North and northeasterly trending faults crossc:ut this
ALTERED DIORITE (A)                                                 structure. Both left and right lateral senses of motion are
                                                                    evident along these steep faults,with offsets of no more than
  Massive,silicifiedandpropyliticallyalteredintrusive               tens of metres.
rocks are exposed along the western slopes of Forrest Kerr             Read et a / . (1989) hav? recognized folded regional-scale
Creek, south of the main bend. They are distributed along           faults. Deformation of the West Lake, West Slope and Kerr
major north-northeasterly fault structures west ofthe Forrest       Bend (not shown) faults occurred durinj: the Middle 1c Late
Kerr fault. Primary textures and mineralogy  have been oblit-       Jurassic and is characterized by low-angle easterly directed
erated. The rocks are aphanitic, vitreous to dull green and         movement
thoroughly fractured. Pyrite is ubiquitous as disseminations
                                                                       The West Lake fault dips moderately to the west.Ha.nging-
and in quartz-carbonate veinlets. The rocks are cliff formers
                                                                    wall rocks, Unit IDc in the south and Unit Pqd in the north,
which weatherwhite to lightgreen; Read ef ul. (1989)
                                                                    have been thrust eastward with respect to the Early Pelmian
included them in Unit Jfp Jurassic feldspar porphyry.
                                                                    footwall.
                                                                       The West Slope fault is moderately steep and easterly
                                                                    dipping, Upper Triassic Stuhini Group volcanics and sedi-
STRUCTURE                                                           ments are exposedin the down-dropped footwallwith Paleo-
  Five structural domains are apparent from a preliminary           zoicmetasedimentsandmetavolcan,icsoccupyin:                  the
examination of the structural data. All five arefault bounded.      hangingwall. The fault is marked by a wide limonitic >.Itera-
  Domain 1 includes the area     west of the Newmont Lake           tion zone along its length.
graben. Strata include Mississippian volcanics, limestones             The Forrest Kerr fault is a northeaste:rly trending, vertica
and coarse clastics with lesser Permian limestones (Stikine         to steepeasterlydipping      normal fault. It separate!; meta.
“western” assemblage)   and comprisefor the part   most             morphosed and deformed Paleozoic strata on the wesl fron
southwest-dipping and facing (7) homoclinal panels. A large-        Lower to Middle Jurassic rocks on the east. Read er a1
Geological Fieldwork 1989, Paper 1990.1                                                                                        I35
                                                                                                         . ..
                                                                                                           :
                                                                                                           .




                                                          sc.*   lkilom.tr.rl




       Figure 1-13-4. MINFILE locations, mineral occurrences and gossanous zones (shaded) in the Forrest Kerr Creek map area
                                                                        of
                               104Bi15 (see Table 1-13-1 for descriptions MINFILE occumences).


(1989) suggests a minimum of 2 kilometres east-side-down                  Gulf International Minerals Limited completed diamond
and 2.5 kilometres of left-lateral oblique-slip motion. Move-          drilling (approximately 7Mx) metres), geophysics and sur-
ment along these major structureshas continued into the                face mapping on its Northwest s k m mineral zone. Kestrel
Miocene (Souther, 1972).                                               Resources Limited camed outsoil and rock geochemical
                                                                       sampling, prospecting and trenching on vein mineralization
                                                                       on its Tic,Arc and Monclaims. PamiconDevelopment
                                                                       Limited cut lines, mapped and sampled its Ridge and South
EXPLORATION ACTIVITY                                                   Forrest mineral zones on the Forrest claims. Cominco Ltd.
   Themap area is located at the northwest end of the                  carried out prospecting,boulder tracking, and a geophysical
Stewart-Sulphurets-Iskut gold belt, 15 kilometres northwest            program (UTEM and magnetometer) tolocate the source of
                                                         of
of Eskay Creek. It is completely staked, including sections            more than 200 massive sulphide boulders on its Fore More
the Iskut icefield. Exploration activity was accelerated after         claims, located O kilometresnorth of theheadwaters of
                                                                                         I
the release of assay results from Eskay Creek.                         Forrest Kerr Creek on NTS sheet 104G/2.
136                                                                                  British Columbia Geological Survey Branch
MINERAL PROSPECTS                                                  either 135170NE or 360190, hosted by ,Stikine assenhlage
                                                                   rocks (Eastern assemblage)close tothe c'ontact with Jurassic
   MINFILE lists 14 mineral occurrences in themaparea              graniticrocks.Plagioclase-porphyriticdioriteintrwions
(Table 1-13-1). Figure 1-13-4 showstheirdistribution,              (Pqd) are spatiallyrelated to veining in the Ridge ,xes.
includingtwo new mineralshowingslocatedduring          our         Mineralization consists of goldand silver-bearing quartz-
work. A directrelationship is evident between epigenetic           chalcopyriteveins with or without    malachite, ai:t.rite,
mineral occurrences and northeast-trending regional struc-         arsenopyrite, galena, bornite and hematite.
     Mineralization
tures.                                into following
                       can be divided the
categories:
   0 gold-copper-iron skarns;
                                                                            MASSIVE
                                                                   STRATABOUND    SULPHIDES
   0 mesothermalcopper-gold-silver-bearing    quartz veins;           Stratabound pyritic horizons, associated with dac:i::ic(?)
   0 stratabound massive sulphides.                                pyroclastics or altered hyaloclastite horizons outcrop dixcon-
                                                                   tinuously within cherty siltstones     and black carbon;u:eous
                                                                   argillites in a thick succession of basic pillow and breccia
              SKARNS
GOLD-COPPER-IRON                                                   flows north of the Iskut River, 12 kilometres upstream from
   NewmontMiningCorporation          of CanadaLimited first        the mouth of Forrest Kerr Creek (A, Figure 1-13-4). Massive
assessedthe copper potential of theseskarns in theearly            fine-grained pyrite and pyrrhotite occur as bedding-parallel
1970s but it was not until 1987 that the potential for gold                                           and
                                                                   layers several centimetres thick as disseminations. Rusty
enrichment was discovered by Gulf International Minerals           limonitic gossans and the white-weathering felsic rocks can
Limited. On its McLymont Creek property, the Northwest             be traced along theridge for 1500 metres. Samples have been
zone (MINFILE 104B 281) contains stratabound skarn min-            submittedforassayandgeochemicalanalysis.            The strati-
eralization hosted by up to 200 metres of thin to medium-          graphic similarities to Eslcay Creek wan-ant follow-up.
bedded siltstones, chert, sandstone, marble and minor con-            Foliation-parallel masriive pyrite zones occur in pyritic
glomerate of Mississippian age (Unit Mtp). Mineralization is       felsicvolcaniclastic rocks 6 kilometres northwest cf the
developed in marble horizons and along contacts        between     confluence of Forrest Kerr Creek and the Iskut River (B,
tuffaceous sandstones and marble where faults and fractures        Figure 1-13-4). Mineralization lies stratigraphically t d o w
have providedpermeability for the ore solutions.Several            Lower Devonian limestone within a package of tuffaceous
mineralized zones are semiconformable with bedding and             sediments and pyritic felsic sills. Preliminary analytical data
extend outward from a central northeast-trending structure         show no elevated base or precious metal values.
(the 040" western-bounding fault of the Newmont Lake                  Polymetallic massive sulphide float occurs on Coninco's
graben).                                                           Fore More claims. The claims are situated outside the map
   Sulphidesincludepyrite,chalcopyrite,sphalerite           and    area, on the south tributary of More Creek (NTS 104G12)
galena with a gangue of barite,calcite,gypsum,coarse-              about IO kilometres north of the headw;aters of Forresl Ken
grainedmagnetiteand       specular hematite. The best gold         Creek. More than 200 mxssive sulphide boulders have been
mineralization is associated with coarseeuhedralpyrite             found in glacialoutwashgravels.They           arechiefly fine-
(E.W. Grove, personnel communication, 1989). The 1989              grained massivesulphide!; containing, in order of abundance,
drilling has tested the zone for 300 metres along strike and       pyrite, sphalerite, galena, barite, chalcopyrite and, locally,
200 metres below the surface.                                      silverminerals. Texturally the mineralization varies from
   Strong structure,proximity to intrusive bodies and chemi-       massive to layered. Ins!; common are limestone boulders
cally reactive hostrocks have all contributed to localizing this   with crosscutting massive pyrite mineralization. A thirl bed-
deposit.                                                           dedfossilliferouslimestonebouldershowsprefermtial
                                                                   replacement by massivesulphidesalongbedding]?lanes.
                                                                   Thislimestone  containsprobable algallaminations            01
          COPPER-GOLD-SILVER-
MESOTHERMAL                                                        stromatoporoid Favosifes sp. of Late Ordovician to .Middle
     VEINS
QUARTZ                                                             Devonian age (B.S. Norford. personla1 communi'xtion;
   Early exploration on the McLymont properly (MINFILE             1989). Stream sediment !;ampling (RGS, 1988) detected nc
 104B 126) focused on testingpreciousmetalveins.          'ho      geochemical anomalies in streams draining the area coltain.
types of veins were recognized. The first are an early quartz-     ing these massive sulphide boulders.
pyrite-chalcopyrite vein set that trends 120" to 140" (Camp
zone). The veins and attendent potassic alteration selvages
fill fractures inquartz-rich granite. Mineralizationcomprises
                                                                   MINERAL POTENTIAL
minor sphalerite, galena and free gold (Grove, 1987). The               Deposit models applicable to the geological settrng a n t 1
second vein type consists of northwest or northeast-trending       known mineral occurrences in the map area indicate favour.
en echelon vein swarms that postdate theearlierquartz veins.       able potential for the following:
The veins are ankerite-quartz-pyrite replacement veins which       ( I ) Precious metal bearing skarn min.eralizationoc,:urs a t
contain sparse chalcopyrite and local gold values.                       the McLymont Creek prospect and Ken showing. Mis.
   The Forrest claims extendapproximately 10 kilometres                  sissippian and Permian limestones are abundant in t , h:
north from the Iskut River along west side of Forrest Kerr
                                 the                                     western part of the map area but significant mineraliza-
Creek. They cover 11 mineral occurrences concentrated in                 tion is confined to thin-bedded limy horizons a n i on1 i
three areas; South Forrest, Ridge and North Ridge. Mineral-              where these rocksare cut by northeasterly trendin;
ization consists of quartz stockworks and veins which trend              structures.
GeoloRical Fieldwork 1989, Paper 1990.1                                                                                      13:'
                     TABLE 1-13.1. MlNFlLE OCCURRENCES IN   THE FORREST KERR CREEK MAP AREA 104BI15.
~                                                              ~




MlNFlLE                                          DEPOSIT
NO.            NAME               COMMODITY      TYeE               DESCRIITION
~




    104B W3    Don. Don 12,       Cu, Ag, Au     SKARN              Skam mineralization occurs near the contact between Permian
               Don 40                                               limestone and a Jurassic(?) diorite intrusion: mineralization includes
                                                                    disseminated pyrite, chalcopyrite and tetrahedrite.
    1048 024   Mag                Fe. Cu         SKARN              Skam mineralization occurs near the contact between Permian
                                                                    limeilone and a Jurassic diotite intmsmn; mineralization consists of
                                                                    massive magnetite with minor pyrite and chalcopyrite.
    104B 027   Ken, Dirk.         A". Cu         SKARN              Limy beds within a Permian volcaniclsedimentary package of rocks
               Glacier. Rope                                        contains gold-bearing skarn mineralization consisting of garnet.
                                                                    epidote. magnetite, chalcopytite, pyrite and possibly tetrahedrite:
                                                                    grab samples returned assay values lo 33.7 grams per tonne gold.
1048 126       McLymont, Camp     Au. Ag, Cu     VEIN               Northwest-trending pyrite-chalcopyrite-quam-carbonale-bar it^ veins
                                                                    hosted by a quartz-rich granite.
104B 281       Northwest          Au. Ag,        SKARN              Minerallzed zones consisting of barite, calcite, gypsum, coarse-
               Warrior 4          Cu, Ba                            grained magnetite. hematite. pytite. chalcopyrite. sphalerite and
                                                                    galena occur as suatabound bands within chen layers and along
                                                                    bedding contacts between marble and chen; hornocks are of
                                                                    probable Mississippian or Permian age.
1 0 4 282
      ~        Gab 9. Gab 7       A", Ag. Cu     SHEANFAULT         A northeast-trending fault structure hosts gold-bearing sulphide and
               Wamor 7                                              onads material: 1988 diamond drilling reparts indicate 900 metres in
                                                                    five holes.
104B 332       NE McLymont        Au. Ag         VEIN               Narrow auriferous quartz-pyrite veins cut a granitic intrusion:
                                                                    narrow rusty limonitic dikes of granite cut Permian and
                                                                    Mississippian stratified rocks: hornfeired siltstone pendants within
                                                                    the granite body contain massive and disseminated pyrite and some
                                                                    sphalerite.
104B 333       Gab NW             A"             SKARN              Mineralization consisting of tetrahedrite. malachite and barite occurs
                                                                    along a northeast-trending fault thought to be an extension of the
                                                                    McLymont Northwest zone (MINFILE 104B 281); ten diamond-
                                                                    drill holes totalling about 900 metres returned best assay value of
                                                                    4.78 grams per tonne gold over an interval of 2.5 metres.
I048 334       Cuba. Gab 8        Ag. Pb. Zn,    SKARN              Mineralization consisting of silver. sphalerite, galena and barite is
                                  Ba. Cu                            found within a northeastbtrending fault that cuts Permian limestone;
                                                                    seven best samples from two copper-barite areas returned values
                                                                    averaging 1023.0 grams per tonne silver.
104B 335       Gab 12, SW         Ag. Zn. Pb,    VEIN               Mineralization consisting of magnetite, chalcopyrite, galena and
                                  Cu,As, Au                         sphalerite is associated with B northeast-trending fault crosscutting
                                                                    sediments of probable Permian and Mississippian age; gold
                                                                    mineralization occurs within iron-carbonate veins and pods
                                                                    mineralized with pyrite and coarse-grained magnetite; assay samples
                                                                    from a 1988 diamond-dtill hole intersection returned values grading
                                                                    77.14 grams per tonne gold over 60.0 centimetres.
1048 336       Gab 11. SE         Au, As, Fe,   SHEANFAULT          Massive fine-grained pytite occurs within sedimentary rocks of
                                  Cu. Ag                            Permian and Mississippian age; a grab sample from a pyritized zone
                                                                    returned values of 23.5 grams per tonne gold and 116.9 grams per
                                                                    tonne silver.
1 1 8 337
 14            Gab 12 NE          A"            SHEAWFAULT          A northeast-trending fault within Permian and Mississippian
                                                                    sedimentary rocks contains massive and disseminated magnetite.
                                                                    chalcopytite. sphaletite and galena: grab samples from a gossanous
                                                                    zone contain values as high as 26.7 grams per tonne gold.
104B 347                          AU            VEIN                Quartz-barite veins intilling shear or fracture systems arc
                                                                    mineraliwd with pyrite, chalcopyrite, galena, hematite, magnetite
                                                                    and malachite; gold values are low but silver, cobalt and copper
                                                                    values are above background: massive pyrite veins to 5.0
                                                                    Cenlimetres width contain chalcopytite, hematite and magnetite.
1048 350       Adrian             Au, Ag, Cu,   VEIN                Quartz veins hosted by quartz-rich granite returned gold values
                                  Pb. Zn                            ranging from 2.7 to 30.0 grams per tonne.
               North Ridge.       A", Ag. Cu.   VEIN                Mineralization consists of gold and silver-bearing chalcopyrite-
               Ridge. South       Pb, Zn                            quartz stockwork veins and shears with one or more of the
               Forrest                                              following: malachitelazurite. arsenopyrite. galena, bornite, and
                                                                    hematite: these mineralized veins are hosted within Eastem
                                                                    assemblage rocks ofthe Paleozoic Stikine assemblage.


I38                                                                              British Columbia Geological Survey Branch
  (2) Stratahound mineralization      occurs in Paleozoic and      Anderson, R.G. and Bevier, M . L . (199011:A Note on Meso-
      Jurassic strata as the following:                                 zoicand Tertiary K-Ar Geochronometry of Plutonic
      (a)
        Polymetallic  massive sulphide mineralization                   Suites. IskutRiver MapArea, Northwestern ELritish
           occurs north of the map area on the Fore More                Columbia; in Current Research, Part E, Geo1q:ical
          claims and pyritic volcanic horizons are interca-             Survey o Canada. Paper 90- I E. (ir, press).
                                                                                   f
           lated within the Lower Devonian limestone sec-          Brown,D.A. and            Gunning M.(1989): Geology o f the
           tion. The Paleozoic Stikine assemblage rocks are             Stikine River Area, Northwestern British Colunlbia,
           a potential explorationtarget for volcanogenic               B . C . M i n i s f r y o Energy, Minrs and Petrrderdm
                                                                                                 f
           massive sulphide deposits. The Devonian mafic                Resources, Geologicd Fieldwork, 1988, Paper 19Ei9-I,
           and felsic metavolcanic package appears to have              pages 25 1-267.
           the highest potential.                                  Grove, E.W. (1986): Geology and Mineral Deposits        of the
      (b) Middle(?) Jurassic basaltic and dacitic submarine             Unuk River-Salmon River-Anyox Area; B.C. Mfrisrry
           volcanicstrataunderlietheeastern        and south-           ofEnergy, Minesand Petroleum Resources,Bul1el:i 163,
          eastern parts of the map. This stratigraphy resen-            152 pages.
                                      of
           bles the geological setting the Eskay Creek gold        ~           (1987): Geological and Drilling Report and Work
           prospect. Mineral potential is high.                         Summary on theGulfInternationalMineralsLtd.
  (3) Mesothermal quartz veins and stockworks located                   McLymont Creek fioperty; B.C. .Ministy o Energy,
                                                                                                                       f
      adjacent to the Newmont Lakegraben and West Slope                 Mines and Petroleum Resources, Assessment It,:port
      fault warrant further exploration.                                16932.
                                                                   Logan, J.M. and Koyanagi, V.M. (1989):        Geology and
                                                                        MineralDeposits oi theGaloreCreek          Area, Uorth-
ACKNOWLEDGMENTS                                                         western B.C. (104Cii3, 4); B . C . Ministry o Energy,
                                                                                                                       f
   The authors would like to thank Rick Lavack of Northern              Mines and Petroleum Resources, Geological Fieldwork
MountainHelicoptersforsafeandcourteousflying                            1988, Paper 1989-1, pages 269-284.
throughoutthesummer.       We thank KestrelResources and           Monger,J.W.H.(1970),UpperPaleozoicRocks                 of the
especially John Buchholzfor support during the latter partof            Stikine Arch, British Columbia; in Report of Activities,
the field season. We are grateful to Dr. R . G . Anderson of the        Part A, Geological Survey of Canada, Paper 70.1, Part
Geological Survey of Canada for contributing his support and            A, pages 41-43.
advice and Dr. Wayne Bamber of the Geological Survey of            ~            (1977):UpperPaleozoicRocks       of the Wrstem
Canada for providing prompt fossil identifications. Gabriel             Cordillera and their Bearing on Cordilleran Evolution;
“Grub” Viehweger is gratefully acknowledged for his capa-               Canadian Journal ofEarth Sciences, Volume 14, ;pages
ble assistance.                                                         1832-1859.
                                                                   Pitcher, M.G. (1960): Fuulinids of the ‘CacheCreek Croup,
                                                                        Stikine River Area, llassiarDistricl., B.C.; unpublished
REFERENCES                                                              M.Sc. thesis, Brigham Young Universit), 6 4 p a y s
Aiken, J.D. (1967): Classification and Environmental Sig-          Read, P.B., Brown, R.L., Psutka, J.F., Moore, J.M., Jour-
     nificance of CryptalgalLimestonesandDolomites,                     neay, M., Lane, L.S. and Orchard, M.J. (1989): Seol-
     with Illustrations from the Cambrian and Ordovician of     ogyofPartsofSnippakerCreek(104B/10),Forres:Ken
     Southwestern Alberta; .lournu1 o j Sedimentary Petrol-     Creek (104B115). Bob Quinn La:ne (104B/16), Iskul
     ogy, Volume 37, pages I163 1178.
                                    ~                           River (104G/I), and More Creek (104Gi2): Geologicai
Alldrick, D.J., Britton, J.M., Webster, I.C.L. and Russell,     Survey o Canada, Open File 2094..
                                                                        f
     C.W.P. (1989): Geology and Mineral Deposits of the     Souther, J.G. (1972): Telegraph Creek Map Area, E-ritish
     LJnuk Area; B . C . Ministry o Energy, M i m s and
                                    f                           Columbia; Geologiral Survey o Canadu, Paper 7 1 - 4 4
                                                                                             f
     Petruleurn Resorrrces, Open File 1989-10.                  38 pages.
Anderson, R.G. (1989): Stratigraphic, Plutonic and Struc-
                           A                                Wheeler, J.O., Brookfield, A.J., Gabrielse, H., Monger.
     tural Framework for the lskut Map Area,Northwestern        J.W.H., Tipper, H.W. and Woods,worth, G.J. (1988)
     B.C.;inCurrentResearch,PartE,Gen/o~icalSurveyof            TerraneMap of the: CanadianCordillera; Geologica,
     Canada, Paper 89-1E, pages 145-154.                        Survey o Carrada, Open File 1894.
                                                                        f




Geolugical Fieldwork 1989, Paper 1990-1
NOTES

				
DOCUMENT INFO