The Eureka Peak are lies within the Quesnel terrane of the Intermontane Belt, adjacent to the Omineca Belt - Intermontane Belt tectonic boundary. It represents a convergent zone between the arc related Quesnel terrane and parautochthonous Barkerville terrane. The terrane boundary is defined by the Eureka thrust Underlying the area are middle Triassic to early Jurassic sedimentary and volcanic rocks, represented by the Quesnel River Group and Takla Group, respectively. Petrologic and geochemical studies of the Takla Group volcanics suggest protoliths of island arc and marginal basin affinities. The Quesnel terrane structurally overlies Hadrynian to early Paleozoic metasediments of the Snowshoe Group (Barkerville terrane). The base of the Quesnel terrane is marked by mylonitized mafic and ultramafic rocks of the Crooked Amphibolite. Correlation of features across the plate boundary has established the structural continuity in the region, and recognition of structural phases common to both terranes which developed in response to plate convergence. The deformational history involves two phases of coaxial folding of a mechanically heterogeneous lithologic sequence, accompanied by extensive pressure solution, and later overprinting by NW trending extensional fractures. Synchronous to F₁, detachment surfaces developed along major stratigraphic contacts due to contrasting Theologies of adjacent lithologies. Second phase deformation established the regional map pattern, folding the detachment surfaces and the tectonic boundary. Synchronous to deformation, regional metamorphism is evidenced by the growth of minerals characteristic of amphibolite fades in the Barkerville terrane, and greenschist fades in the Quesnel terrane. Dissipation of heat from the underlying sequences is suggested by the rapid transition in metamorphic grade observed across the boundary. Cleavage surfaces have acted as a locus along which pressure solution has occurred, providing a pathway for the escape of fluids generated during metamorphism. Deposition of material within extensional fractures occurred throughout the deformational history. Fracturing is prominent adjacent to the Quesnel River Group and Takla Group contact, where the viscosity contrast between the two lithologies provided an effective barrier to extensive fluid flow. Concentration of fluids along the contact may have had a buoying effect on the volcanics, allowing furter eastward translation during deformation. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Detailed mapping of a 7.5 km² area at 1: 2,500 and a 1:10,000 compilation map over 60 km² have established Hazelton Group stratigraphy and structure. Hazelton Group stratigraphy begins with at least 1,000 metres of Late Triassic-Early Jurassic (210 ⁺²⁴₋₁₄ Ma; U-Pb zircon) green andesite flows, breccias and tuffs. Less than 1750 metres of green and maroon andesitic to dacitic volcaniclastic rocks overlie the andesite unit. North of Silbak Premier, at Slate Mountain, the volcaniclastic unit is overlain by up to 200 metres of a black tuff unit containing characteristic fresh biotite and white plagioclase fragments. The top of the Hazelton is a regional marker horizon, the Monitor rhyolite breccia and tuff (197 ± 14 Ma; zircon U-Pb). Hazelton volcanics are overlain by three different units. At Slate Mountain the Bowser Lake Group Bathonian/Callovian argillite and siltstone (at least 1500 m thick) lie above Hazelton rocks. Farther north on Mount Dilworth, Monitor rhyolite is succeded by black tuff or a Toarcian buff carbonate. East of Monitor Lake, less than 75 metres of Bajocian Spatsizi Group silicic shale and tuff overlies Hazelton volcanic rocks. Three intrusive episodes are discerned through isotopic dating: Early Jurassic (190 ± 2 Ma; U-Pb zircon) Texas Creek plutonic suite dacitic porphyries; Eocene Hyder suite leucocratic dykes; and oligocene-Miocene (25.2 ± 2.3 Ma; K-Ar biotite and 18 ± 6 Ma; Rb-Sr) biotite lamprophyre dykes. The Jurassic suite includes K-feldspar megacrystic "Premier porphyry" sills and dykes that are in part spatially and possibly genetically associated with mineralization. Structural features include disharmonic tight folds, ductile shear zones, and brittle faults. At least 4 phases of pre-Eocene deformation are defined by: (1) moderate west-plunging recumbent folds, (2) north-plunging inclined folds, (3) north-plunging upright folds, and (4) moderate west-plunging pencil lineations. The map area is divisible into three structural domains: the North, East and Silbak domains. The North domain is characterized by a marked structural discordance between warped Hazelton volcanic rocks and disharmonically folded Bowser Lake Group argillite and siltstone. Three phases of folding are: first phase tight to isoclinal disharmonic, recumbent folds; second phase open folds with shallow northwest-dipping axial planar cleavage; and a third phase upright, shallow north-plunging synclinorium. Structural continuity is difficult to establish due to lack of marker horizons and inferred detachments. The East domain is characterized by phase 3 gently north-northwest-plunging folds and locally east-verging asymmetric chevron folds in the Spatsizi Group. In contrast to North domain, Monitor rhyolite and/or Spatsizi Group are structurally conformable with Bowser Lake Group rxks. The Silbak domain is characterized by phase 4 pencil lineations and quartz veins. Stope geometry illustrates that mineralization occurs along two trends (1) northeast zone and (2) northwest zone of unknown phase. Steeply dipping, east-striking ductile fabrics occur in the Texas Creek batholith at the Riverside mine, Alaska and in maroon volcaniclastics along Bear River Ridge. Mylonitic fabrics at Riverside mine suggest a dextral sense of shear. A biotite lineation in the mylonitic foliation yields a totally reset Eocene K-Ar date. The width of Eocene Hyder dyke swarms indicates that there has been at least one kilometre of northeast brittle crustal extension. About 1400 metres of dextral transcurrent movement along the Long Lake-Fish Creek fault is post-Eocene dyke emplacement. oligocene-Miocene lamprophyre dykes fill fractures produced during east-west extension. Regional syntectonic greenschist grade metamorphism produced a carbonate-chlorite-sericite-pyrite mineral assemblage, probably in Middle Cretaceous time, bracketed by isotopic dating results. Hazelton Group volcanic rocks and coeval Texas Creek porphyritic rocks are subalkaline high-K to very high-K andesites and dacites. Tectonic discrimination diagrams indicate a calcalkaline, volcanic arc setting, with similar geochemical patterns to those for Andean volcanic rocks. Mineralization is hosted in Hazelton Group andesites and coeval Texas Creek porphyritic dacite sills and dykes. Mineralization and porphyry emplacement appear to have been controlled by northeast- and northwest-striking structures. Ore is predominantly discordant but locally concordant with moderately northwest-dipping andesite flows and breccias. No mineralization occurs in or above overlying maroon volcaniclastic rocks. Sericite alteration gives a Paleocene K-Ar date (63 ± 5 Ma); this is interpreted to be partially reset. The spatial link with Texas Creek K-feldspar porphyry and discordant nature of the ore suggests mineralization is Early Jurassic age and supports an epigenetic model. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The problems encountered by mineral explorationists when sampling stream sediments for gold were investigated by considering the sparsity of free gold particles and their tendency to form small placers at certain locations in the stream bed. Fourteen 20-kg samples of -5-mm sediment were collected from contrasting energy and geochemical environments in five streams draining gold occurrences in southern British Columbia. The samples were sieved to six size fractions (420 µm to 52 µm) and gold content was determined by neutron activation analysis following preparation of two density fractions using methylene iodide. Gold concentrations were converted to estimated number of free gold particles and the Poisson probability distribution was used to show that much larger field samples (>100 kg of -1 mm screened sediment) would be required to reduce random variability due to nugget effects to acceptable levels. However, in a comparison of conventional sampling methods, the lowest probability of failing to detect a stream sediment gold anomaly is obtained using the sampling method described in this study. Small-scale placer formation was investigated by collecting twenty 60-kg samples of -2-mm sediment from ten locations along five kilometres of Harris Creek in the Okanagan region, east of Vernon. Samples were prepared and analysed as described above though heavy-mineral concentrates were only prepared for two size fractions. Gold was found to be considerably enriched in sandy-gravel deposits compared to sand deposits, with the effect decreasing as sediment size decreased. The level of enrichment varies on the stream in response to changing channel slope and local hydraulic conditions. Gold anomaly dilution is apparent in sand deposits but not apparent in sandy-gravel deposits since gold is preferentially deposited in gravels as channel slope decreases. These results are presented in the framework of H.A. Einstein's sediment transport model. Sediment collected from gravels may represent the best geochemical sample since placer-forming processes produce high gold concentrations, however in very high energy streams, the small quantities of fine sediment in gravels may lead to unacceptable nugget effects. In the latter case, a sample collected from a sand deposit is a satisfactory alternative. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Tatla Lake Metamorphic Complex (TLMC) underlies 1000 km² on the western side of the Intermontane Belt (1MB) northeast of the Yalakom fault Three fault-bounded lithotectonic assemblages are recognized in the area studied: an amphibolite grade gneissic and migmatitic core, structurally overlain by a 1 to 2.5 + km-thick zone of amphibolite and greenschist grade mylonite and ductilely sheared metamorphic rocks, the ductilely sheared assemblage (DSA), which is in turn structurally overlain by weakly deformed to unstrained subgreenschist grade rocks of the upper plate which flank the TLMC on three sides. Structures in the gneissic core include a gneissic foliation and schistosity (Sic), which has been deformed by west to northwest-trending tight to isoclinal folds (F2c). Tectonic fabrics observed throughout the DSA which formed during Ds deformation include a gently dipping mylonitic foliation (Ss), containing a mineral elongation (stretching) lineation (Ls) which trends towards 280° ± 20°. Minor folds of variable trend (Fs), almost exclusively confined to DSA metasedimentary rocks, are interpreted as coeval with ductile shear. Vergence of these folds defines movement sense and direction of top towards 290° ± 20°. Kinematic indicators from DSA rocks which have not been deformed by syn-ductile shear folds indicate a top-to-the-west sense of shear while those deformed by Fs folds yield conflicting results, with a top-to-the-west sense predominating. The entire lower plate comprising the TLMC has been deformed by broad, upright, west to west-northwest trending, shallowly plunging map-scale folds (F3) during D3, which deform Sic and Ss surfaces. The steeply dipping, northwest-trending Yalakom fault truncates all units and structures of the TLMC. Gently to moderately dipping normal faults of Ds and post-D3 relative age are the southern and eastern boundaries between DSA upper plate rocks and 1MB lower plate rocks. U-Pb zircon dates from igneous arid meta- igneous rocks from the lower plate range from Late Jurassic (157 Ma) through Eocene (47 Ma). These dates bracket the timing of Cretaceous (107 Ma to 79 Ma, in the core) and Eocene (55 Ma to 47 Ma, in the DSA) deformation and metamorphism in the lower plate. Biotite and hornblende K-Ai dates of 53.4 Ma to 45.6 Ma for lower plate rocks are in sharp contrast to Jurassic dates from nearby upper plate rocks; they record the uplift and cooling of the TLMC. Whole rock initial ⁸⁷Sr/⁸⁶Sr ratios (and for most samples present-day values) of less ≤0.704 have been determined for igneous and meta-igneous rocks of the TLMC; such values are typical of magmatic arc rocks of the 1MB and Coast Plutonic Complex of B.C. Whole rock major and trace element chemistry of lower plate igneous and meta-igneous rocks indicate sub-alkaline, calcalkaline, volcanic arc affinities. Garnet-biotite temperatures (interpreted as Eocene in age), from pelitic schist in the southern part of the DSA increase from about 400 ± 50 to 650 ± 50 C with increasing structural depth. A GT-BI-QZ-Al₂SiO₅ pressure of 8 ± 3 kb has been calculated for one of these samples. A T-P of 650 ± 50 C and 5.3 ± 3 kb, calculated from inclusions and garnet cores in a small pelitic pendant in the northwest part of the DSA, reflects conditions during intrusion of the surrounding 71 ± 3 Ma igneous body. A pressure of 7.2 ± 1.4 kb, based on the total Al in hornblende, has been calculated for this body. Cretaceous ductile deformation in the gneissic core may be related to folding and thrusting which occured in high level rocks to the west and east of the field area. During Early Eocene time (55-47 Ma) the TLMC acquired the characteristics of a Cordilleran metamorphic core complex. Mylonites of the DSA were emplaced by faulting beneath weakly deformed, low metamorphic grade rocks of the upper plate. Synchronously, metamorphic rocks of the gneissic and migmatitic core of the TLMC were moved to higher crustal levels along the footwall of the DSA normal ductile shear zone. The formation of F3 folds and final uplift of the TLMC (47-35 Ma) is postulated to be the consequence of transpression related to later Eocene dextral motion along the Yalakom fault The TLMC has structural style and timing of deformation similar to metamorphic core complexes in southeastern B.C. Local and regional evidence is consistent with the formation of the TLMC in a regional extensional setting within a vigorous magmatic arc. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Sampling of soils and till are conventional methods of gold exploration in glaciated regions. However, the exact nature of the residence sites and behaviour of gold within soil and till are poorly known. A gold dispersion train extending from the Nickel Plate mine, Hedley, southwest British Columbia, was investigated in order to determine the distribution and behaviour of gold within soils developed from till. Three hundred and twelve soil, till and humus samples (representing LFH, A, B and C horizons) were collected from fifty-two soil pits and thirty-four roadcut locations within the dispersion train. Soil and till samples were sieved into four size fractions; the resultant -212 micron (-70 mesh) fraction of each sample was analysed for Au by FA-AAS. Humus samples were ground to -100 micron powder and analysed for Au by INAA. Based on the analytical results, each LFH, A, B and C horizon was subdivided into anomalous and background populations. Detailed size and density fraction analysis was carried out on soil profiles reflecting anomalous and background populations, and a mixed group of samples representing the overlap between both populations. Samples were sieved to six size fractions; three of the size fractions (-420+212, -212+106, -106+53 microns) were separated into two density fractions using methylene iodide and analysed for Au by FA-AAS. The Au content of the -53 micron fraction was analysed by FA-AAS and cyanide extraction - AAS. Results indicate that the Au content of soil profiles increase with depth while decreasing with distance from the minesite. Heavy mineral concentrates and the light mineral fraction Au abundances reveal that dilution by a factor of 3.5 occurs within the till over a distance of 800 metres. However, free gold within the heavy mineral fraction is both diluted and comminuted with distance. Recombination of size and density fractions indicate that the Au contents of each size fraction are equivalent; variation in Au abundance is not observed with a change in grain size. Seventy percent of the Au in the -53 micron fraction occurs as free gold. Chemical activity has not altered the composition of gold grains within the soil profiles. Compositional and morphological differences between gold grains are not indicative of glacial transport distance or location within the soil profile. Relative abundances of gold grains between sample locations can be used as an indicator of proximity to the minesite. The sampling medium with the best sample representivity and contrast between anomalous and background populations is the -53 micron (-270 mesh) fraction of the C horizon. Geochemical soil sampling programs in the vicinity of the Nickel Plate mine should collect a minimum mass of 370 grams of -2000 micron (-2 mm) soil fraction in order to obtain 30 grams of the -53 micron fraction. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Pioneer Ultramafite, south of Bralorne, British Columbia, is a fault-bounded lens of alpine-type peridotite enclosed in lower greenschist facies sediments and volcanics of the middle Triassic Fergusson Group and late Triassic Noel, Pioneer and Hurley Formations. The body consists of a core of well layered harzburgite, dunite and orthopyroxenite, rimmed by serpentinite and talc-carbonate alteration zones containing tectonic inclusions of sediments, volcanics and rodingite. Foliated harzburgite forms approximately 80 per cent of the ultramafite; dunite, as dikes, sills and irregular pods in harzburgite, comprises about 17 per cent; and orthopyroxenite as layers (1 to 15 cm thick), parallel to the foliation, in harzburgite, constitutes the remaining 3 per cent. Electron microprobe analyses of the primary minerals indicate olivine composition ranges from Fo 90.2 to 92.5, orthopyroxene from En 89.2 to 90.2 and clinopyroxene averages Ca₄₆․₉Mg₄₉․₇Fe₃․₄. Compositions of coexisting primary minerals indicate a temperature of equilibration of about 950°C at an unknown pressure. Alteration assemblages in the serpentinized contact zone indicate migration of 0, H₂O, C0₂, CaO, MgO and S10₂ resulting in metasomatism of the ultramafite and country rocks, producing rodingite, nephrite (jade) and talc-carbonate. Serpentinization apparently occurred during emplacement of the ultramafite into the surrounding country rocks. Plastic deformation and recrystallization of the peridotite produced the pervasive planar foliation or layering, which has been disrupted by several later episodes of folding and fracturing. Country rocks show evidence of two phases of deformation prior to emplacement of the ultramafite, A strong foliation of serpentinite and country rocks, near the contact, was produced during emplacement. The ultramafite and country rocks are interpreted as a partial, dismembered ophiolite which was emplaced in the late Triassic or early Jurassic by obduction of oceanic crust onto the continental margin. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Yale Creek area is underlain by the pelitic Settler Schist, Spuzzum hornblende quartz diorites, and minor gneiss and granodiorite. Mineral textures in the schists define three phases of folding. The structural geology is dominated by the second phase, f₂, characterized by northwest plunging isoclinal folds. Regional metamorphism reached its culmination just after f₂. The structurally concordant and broadly syn-tectonic Spuzzum intrusions were emplaced over a period of time encompassing the period of folding and regional metamorphism and served as a heat source for the regional metamorphism and early contact metamorphism. Late faulting has juxtaposed Settler Schist and Custer Gneiss across the Hope Fault, and Settler Schists of contrasting metamorphic grades across the Cogburn Creek Fault. A Triassic Rb-Sr date obtained for the Settler Schist is interpreted as the date of deposition of original—eugeosyclinal sedimentsHornblende K-Ar ages of 75.5±2.6 and 92.1±3.2 Ma obtained for Spuzzum quartz diorites conform to a regional east-younging trend in Spuzzum K-Ar ages which reflects the cooling history of the area rather than age of intrusive emplacement. The date of emplacement of the structurally discordant and post-tectonic body of granodiorite was defined as 32±2Ma by concordant Rb-Sr and K-Ar dates. The distribution of aluminosilicate assemblages in the Settler Schist defines three regional metamorphic zones increasing in grade to the north. The kyanite zone and two sillimanite zones are separated by two isograds which mark equilibrium and overstepped kyanite-sillimanite transitions. The metamorphic conditions near the first sillimanite iso- grad are estimated to be 705±45°C and 7.6±0.5kb from the mutual intersection of equilibria calculated from thermodynamic data and microprobe analyses. Anatectic relations established to date for pelitic systems appear to be inconsistent with, this thermodynamic P-T estimate. Mineral assemblages in scattered ultramafic pods are consistent with the metamorphic P-T estimates for the pelitic assemblages. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Unknown

Five major units were mapped in shoreline exposures of the Coast Plutonic Complex adjacent to Douglas, Sue and Loretta Channels: 1) paragneiss and migmatite of the Central Gneiss Complex, 2) quartz-biotite schist, amphibolite, quartzite,and marble of the Metasedimentary Rocks, 3) quartz diorite and quartz monzonite of the Kitkiata pluton, 4) granodiorite of the Quottoon pluton and 5) Agmatite, composed of early xenoliths of banded metamorphic rock, middle stage intrusions of granitic rock, and late pegmatite, aplite and lamprophyre dikes. Pressure estimates of 7 ± 1 kb for this part of the Coast Mountains are arrived at from the stable assemblages in a kyanite-staurolite schist, and by comparison with pressures published for areas along strike to the north. Amphibolites provide a low temperature estimate o f 550°C. Calcsilicate assemblages place the high temperature limit of metamorphism between 560 and 660°C at 5 kb. Elevated pressures would increase temperature somewhat. The area is structurally characterized by a well developed, steeply dipping foliation that strikes northwest, widespread isoclinal folds with axial plane foliation parallel to regional foliation, and a moderate to steeply plunging fold axis lineation. Interference structures show that the abundant isoclinal folds deform earlier approximately northeast-trending folds. Later tight to isoclinal folds deform the regional foliation. Metamorphic recrystallization outlasted deformation. The Kitkiata pluton has an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.7042 to 0.7043, depending on its age. One radiogenic Sr-rich sample gives a model date of 165 ± 11 Ma, but the possibility of anomalous initial ⁸⁷Sr/⁸⁶Sr ratio makes this result highly uncertain. The Quottoon pluton gives a whole-rock isochron of 51 ± 2 Ma with 0.7045 ± 1 initial ratio. The low initial ratios indicate a preponderance of mantle-derived magma of Mesozoic or early Cenozoic age in the plutons studied. Sr isotopic composition of the Central Gneiss Complex is compatible with late Paleozoic-early Mesozoic ages for precursor detrital and volcanic strata and local presence of marine carbonate with moderately enriched ⁸⁷Sr/⁸⁶Sr. The generally low radiogenic Sr content of these core gneisses rules out an origin by remobilization of greatly older rocks. Plutons of the Coast Plutonic Complex may have been generated by partial melting of the Central Gneiss Complex, and emplaced not far from their source of origin during regional metamorphism, as the surrounding rocks cooled from maximum temperature and pressure of metamorphism. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Sediments from the northern end of Juan de Fuca Ridge are Late Quaternary in age and contain widely correlatable cycles of turbidity current and hemipelagic sedimentation. Sediments from the Ridge were examined for their mineralogy, structure, components of the sand fraction, rates of sedimentation and grain size distribution to establish processes of sedimentation, stratigraphy, correlation and local hydrothermal relationships. Ten gravity and Phleger core sites along two profiles of the Ridge were examined in detail, one section was perpendicular to West Valley, the main spreading centre, and one section was within and parallel to West Valley. Sediment from Cascadia Basin was compared to the results of the Ridge study. Changes in sedimentation defined by core X-radiograph structure, components of the sand fraction and grain size distribution, indicated cycles of relatively coarse sediment overlain by finer bioturbated sediment with a repeated stratigraphic relationship in all but one Juan de Fuca Ridge core. Changes in sediment composition are attributed to brief, episodic, continent derived turbidity current deposition followed by lengthy periods of hemipelagic sedimentation for each cycle. Differences in composition exist between sediment of ridges and valleys, with a greater winnowed foraminiferal-hemipelagic and a lesser turbidity current influence in the former area. Radiocarbon dated foraminiferal-rich intervals from ridge sediments were exclusively Late Pleistocene with Middle Ridge sediment having an inferred 9000-9500 B.P. Late Pleistocene-Holocene boundary. Similar sedimentation cycles between Middle Ridge and valley localities enabled correlation of ridge and valley stratigraphy and the Late Pleistocene-Holocene boundary. A stratigraphic relationship based on the episodic deposition of continent derived turbidites exists between the northern end of Juan de Fuca Ridge and the continental Pacific Northwest. Pulses of turbidity current sedimentation coincide with initial interglacial warming trends during the Late Pleistocene. Holocene sedimentation for Juan de Fuca Ridge is of hemipelagic origin with rare local turbidity current deposition. Hydrothermal minerals were not detected. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The upper Tsaytis River area, about 150 km² in extent, straddles the Coast Plutonic Complex-Intermontane Belt boundary about 580 km northwest of Vancouver, British Columbia. The boundary, here, is the Sandifer Lake Fault Zone, a highly disrupted, northeastward directed, imbricated thrust complex of middle to Late Cretaceous age. Rocks of the Coast Plutonic Complex occur in imbricate sheets above a frontal thrust. In this gently dipping, homoclinal sequence of tectonic sheets, amphibolites, amphibolite-grade granitoid gneisses, migmatites and metacarbonates of the Central Gneiss Complex tectonically overlie greenschist facies, metavolcanic and metaplutonic schists and mylonites of the Gamsby Group. The Central Gneiss Complex and the Gamsby Group appear to be stratigraphically equivalent units, metamorphosed to different grade and structurally juxtaposed in the thrust complex. Major and trace element chemistry of metavolcanic rocks in the Gamsby Group indicates that protoliths were tholeiitic and calc-alkaline basalt-andesite and calc-alkaline dacite-rhyolite which originated in a mature island arc setting. A minimum, Upper Triassic protolith age for the Gamsby Group is provided by a 210 Ma, near concordant U/Pb zircon date for metarhyolite, and a 230±39 Ma Rb/Sr whole rock isochron date. Mylonitic granite in the Gamsby Group gives a 160±24 Ma Rb/Sr whole rock isochron date, and amphibole from a related, deformed injection agmatite gives a 145±5 Ma K-Ar date. Hornblende from a dyke with chilled margins, which intrudes the Gamsby Group, gives a 66±2 Ma K-Ar date, indicating that the metamorphic complex was cold and close to the surface before the end of the Cretaceous. These results and geology reported for the Prince Rupert area (Crawford and Hollister 1982, and unpublished GSC and UBC zircon data) indicate that at this latitude in the Coast Plutonic Complex, regional metamorphism, polyphase ductile deformation, and intrusion of granitoid material occured in a two-sided, Jurassic and Cretaceous orogenic welt. The orogen was superimposed on the pre-Upper Triassic island arc in the western edge of Stikinia, as a consequence of initial suturing of Stikinia with the allochtonous Wrangellia-Alexander terrane at an unknown distance to the southwest of the thesis area. A Lower Cretaceous volcanic-plutonic complex forms the eastern and lowest thrust sheet of the Coast Plutonic Complex. The volcanic rocks may be correlative with the Gambier Group of the southern Coast Plutonic Complex, and were perhaps deposited unconformably on the uplifted Jurassic orogen. They were invaded and hornfelsed by Cretaceous granitic stocks before being thrust northeastward over strata of the Intermontane Belt. Middle-Upper Cretaceous shortening and associated brittle shearing along the Sandifer Lake Fault Zone occured in a high heat flow, back-arc setting. The Central Gneiss Complex, Gamsby Group, and Gambier Group(?) were imbricated and thrust over Intermontane Belt rocks of the Telkwa Formation. The imbricate tectonic front was disrupted, successively, by strike-slip and dip-slip faults in Late Cretaceous to early Cenozoic time. The latest movement on high angle faults postdates Eocene intrusions, nearby, and Eocene strata, Regionally, but predates Miocene Plateau basalts (Woodsworth 1979, 1980). Several dated, cross-cutting intrusive stocks in the Whitesail Lake map area (Woodsworth 1980), indicate that the Sandifer Lake Fault Zone, juxtaposing the Coast Plutonic Complex and Intermontane Belt, had definitely ceased movement by Eocene time and quite possibly by Late Cretaceous time. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate