The Copper Mountain intrusions, which include the Voigt and Smelter Lake dioritic stocks, Armstrong Bluffs monzonite-syenite complex, and the differentiated Copper Mountain stock are part of a continuous alkali-calcic rock series ranging in composition from pyroxenite to perthosite pegmatite. The series is believed to be derived from a single parent magma of basic diorite composition and to have formed through crystallization differentiation. The age of the series, determined by potassium-argon methods, is about 195 m.y. Parent magma was intruded into Nicola group (Upper Triassic) rocks by forceful injection with structural readjustment of the country rock. The Voigt and Smelter Lake stocks (diorite) crystallized without apparent differentiation. Armstrong Bluffs monzonite-syenite complex is believed to have formed, by repeated tapping of a differentiating magma which was emplaced at intervals after crystallization of diorite in Voigt and Smelter Lake stocks. In Copper Mountain stock, after crystallization of a dioritic roof and outer zone, magma differentiated to form a continuous series from pyroxenite to perthosite pegmatite Differentiation resulted through a combination of thermal convection, chemical diffusion, crystal armoring and crystal settling. Differentiation began with the formation of gabbro and was initiated by convection currents which were formed as a result of temperature gradients in a mobile, volatile-charged magma. When the composition of the magma approached the Ab-Or side of the Ab-Or-An ternary system, subsolvus crystalliza- tion was succeeded by hypersolvus crystallization and the development of perthosite pegmatite. Feldspars from the Copper Mountain intrusions, studied by X-ray powder technique, exhibit a range of thermal state from intermediate to low temperature types. Feldspar geothermometry suggests a range of crystallization from above 8.20°C to about 500°C. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The Troitsa Lake Property is located at latitude 53º 32¹ north and longitude 127º 20¹ west in the Whitesail Lake Map area. Lower Jurassic andesitic flows, tuffs and breccias and intercalated argillite lenses of the Lower Volcanic Division of the Hazelton Group are intruded by a granodiorite stock. A younger sill-like rhyolite complex occurs to the northwest of the stock. A variety of northwesterly trending dykes, including feldspar porphyries of quartz latite composition, cut all other rocks. The stock is zoned from a coarse-grained quartz monzonite in the centre to a relatively fine-grained granodiorite at the margin.Calculated chemical compositions of the rocks show the stock has followed a calc-alkaline differentiation trend. The compositions of plagioclase, alkali feldspar and biotite systematically vary throughout the stock. The thermal effect of the stock is estimated to have produced hornblende hornfels facies conditions up to 400 feet from the contact. The stock was emplaced in the epizone at a probable depth of about four kilometres and was subject to a load pressure of a little over one kilobar. Compositions of coexisting feldspars allow only a crude estimate to be made of the crystallisation temperatures. This indicates a temperature of 720° to 770°C. Compositions of the biotites indicate the stock crystallised under conditions of constant or increasing f0₂ and the melt may have been water saturated. Biotite compositions and experimental data for the 'granite’ system indicate that the stock crystallised under a PH₂0 of about one kilobar and at temperatures ranging from 730° to 850° C. The PH₂0 must have approached, and perhaps equalled Pload. Potassium / Argon data yield an apparent age for the stock of 75.7 ± 2.3 million years. Several stocks in the Whitesail Lake Map area have closely similar ages. The feldspar porphyry dykes have been subject to hydrothermal alteration. In one major dyke this has a zonal distribution pattern; propylitic type alteration in the north passes southwards through quartz - sericite to biotite - ortho-clase types. Sulphide mineralisation, also showing a zonal pattern, is closely associated with the hydrothermal alteration. Weak propylitic alteration and fracture plane sulphide mineralisation affect the central part of the stock. The dykes appear to have acted as channelways for the hydrothermal ore-bearing solutions. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Rocks of the Quesnel Lake area are divided into three units: unit 1, a continental margin sequence; unit 2, The Crooked Amphibolite (an ocean-floor sequence); and unit 3, the Quesnel sedimentary and volcanic sequence. Two conglomerate localities within unit 3 contain clasts identified as being derived from deformed rocks of units 1 and 2. Deformation of the combined package of units 1 and 2 must have accompanied the emplacement of unit 2 onto unit 1 sometime between the deposition of unit 2 (Mississippian - Permian) and the deposition of unit 3 (Triassic - Jurassic). Rocks of unit 1 have been divided by earlier workers into the Barkerville and Cariboo terranes, separated by the Pleasant Valley Thrust. An extensive review shows that the two terranes are stratigraphically similar and share most of their structural history. The Pleasant Valley Thrust, if it exists, is an extremely early structure. These data do not satisfy the criteria for naming these units 'terranes'. The rocks of unit 1 and 2 experienced an extra phase of deformation not seen in rocks of unit 3. A total of five phases of folding are present. Phases 1 through 4 are approximately coaxial with northwest axes and variably oriented axial planes. Phase 5 has northeast trending axes and vertical axial planes. F₁ is seen in units 1 and 2 only and is visible in outcrop as rootless isoclinal folds and a transposed foliation. In thin section, S₁ is only preserved within the earliest garnet porphyroblasts. F₂ folding is the major deformational event. Peak metamorphism accompanied and outlasted it. Major F₂ folds are present in the field and are accompanied by an axial planar foliation. In thin section, S₂ wraps around earlier porphyroblasts but is overgrown by later ones (staurolite, kyanite). F₃ folding is responsible for the major map-scale structures. It postdated the peak of metamorphism and isograds axe folded by it. In thin section S₃ is commonly a crenulation cleavage or transposed foliation. Some late mineral growth accompanied the early stages of F₃. F₄ and F₅ are buckle folds and kinks and may be conjugate fold sets from a single deformational event. They are not generally visible in thin section. The assemblage silica - garnet - aluminosilicate - mica (SGAM) is common in amphibolite grade meta-pelitic rocks, and can be used as a thermobarometer if the activities of muscovite and biotite can be calculated accurately. A new method of calculating the ideal activity of mica components is proposed. Standard models do not adequately account for the degree of coupled substitution that takes place. The proposed method stores the site occupancies in a 4-dimensional array and manipulates the entries to satisfy three criteria. 1: That non-permitted ionic configurations (species) have an activity of zero. 2: That the sum of all activities is unity. 3: That the sum of all activities of species containing a particular ion in a particular site is the site occupancy of that ion. The method is computationally simple and yields activity values that satisfy the distribution of species equations of an ideal complex solution model. Standard state properties for annite and Margules solution parameters for biotite are determined using mathematical programming techniques on published experimental and natural assemblage data. Published volume data indicate that Fe-Mg mixing in biotite is ideal. The data permit the calculation of four Margules parameters (MgTi, FeTi, MgAl, FeAl). The differences MgTi - FeTi and MgAl - FeAl are similar to those found by previous workers but the treatment of the data suggests moderately large individual values for the Margules parameters (up to 75 kJ/mol). Using these activity models the SGAM thermobarometer is applied to several sets of published analyses which show that this calibration offers distinct improvements over previous calibrations. Pressures determined using the new calibration are consistent with other barometers and the aluminosilicate polymorph present. In addition, several data sets show field gradients, particularly in P, not previously recognized and which agree with field observations. The SGAM barometer applied to the analytical data from the Quesnel Lake area yields pressures and temperatures that are consistent with the mapped isograds. The pressure and temperature gradients indicate that the final setting of the thermobarome-ter was diachronous across the area and during the early stages of F₃ folding. Hot rocks in cores of anticlines 'set' at later times and at shallower depths than cooler rocks in adjacent synclines. Tight spacing of isograds is more consistent with post-metamorphic folding than with high thermal gradients. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate