ON THE DISTRIBUTION AND DISPERSION OE ' PLATINUM IN THE SOILS OF THE TULAMEEN ULTRA . MAFIC COMPLEX , SOUTHERN BRITISH COLUMBIA
INTRODUCTION Exploration for platinum in British Columbia is hampered by a lack of data on its distribution and behavior in the surficial environment. To obtain some of the information required and suggest practical guidelines for exploration, this study, involving systematic sampling and analysis of soils and other media in the vicinity of a platinum deposit in the Tulameen district of southwestern British Columbia, was initiated in 1988 (Fletcher. 19x9). Preliminary results of work in progress are described. Tulameen River, approximately 25 kilometres west of Prince-The field area, on Grasshopper Mountain north of the ton, is divided into the main study area, on the southern slope of the mountain, and a second, smaller area near the summit (Figure 6.2-I). The lower part is accessible by pack trail from the Tulameen River road. Several kilometres of recently constructed drill road on the north and west sides of g e o l o g y , Tulameen ultramafic c o m p l e x. B. C. Figure 6-2-1, Location of the study areas and generalized (1) Nicola Group (2) syenogabhrn. (3) dunite. (4) olivine clinopyroxenite,(5) homblendr~linopqmxenite. (6)rnyloni-tic rocks. (7) Eagle granodiorile (modified after Nixon and Rublee. 1988). Grasshopper Mountain connect with the Lawless 'Creek forestry road and provide access from both the village of Tulameen and the Coquihalla Highway. BEDROCK GEOLOGY dissected dunite core of the Tulameen ultramafic complex, a Grasshopper Mountain is the northern segment o' the Late Triassic zoned Alaskan-type ultramafic-gabbroic intrusion within metasedimentary and metavolcanic rocks c,f the Upper Triassic Nicola Group. Geology of the complex, described by Findlay (1969) and Nixon and Rublea (1988). comprises a dunite core surrounded by crudely concentric shells of olivine clinopyroxenite, hornblende c h o p r o x-enite and gabbroic rocks ((Figure 6-2-1). The focus of the current study is within the dunite :ore. The dunite is typically Fine grained, extensively sepen-tinized, and weathers buff-brown on exposed surfaces "lati-num mineralization is restricted to chromite-rich dunite (Nixon e t a /. is best exposed in the summit region and in the sub\ertical randomly distributed massive to discontinuous pods, segre-gations. schlieren and disseminated grains. Schlierel are randomly distributed thrcmughout the dunite and are thought to represent foliation-concordant remnants of former cumu-late layers (Nixon and Rublee, 1988:1. Several cons of central region of the cor'? (Bohme, 19x7). but till-covered mineralization have beer1 defined within the well-exposed areas are largely untested. platinum-iron alloys and platinum antimonides …
ALASKAN-TYPE ULTRAMAFIC ROCKS IN BRITISH COLUMBIA : NEW CONCEPTS OF THE STRUCTURE OF THE TULAMEEN COMPLEXY
Alaskan-type ultramafic rocks in British Columbia are potential hosts forcommerciallyexploitabledeposits ofplatinummetals(Rublee, 1986;Evenchicketa/., 1986)aswellas other commodities (for example, chrome, nickel, cobalt, asbestos and jade). In 1987 the British Columbia Geological Survey initiated a program designed to investigate the mineral potential of these intrusions through detailed geologic mapping and lithogeochemical sampling specifically for platinum group elements. In the first year of this project, a concerted effort is being made to more thoroughly understand one of these intrusions, the Tulameen ultramafic complex in southern British Columbia. The Tulameen complex warrants careful attention as it has been the largest producer of platinum in the province and bas been taken as a typical example of a zoned Alaskan-type ultramafic intrusion (Findlay, 1963, 1969; Evenchick et a / . , 1986). The general structure of Alaskan-type complexes is characterized by a crudely concentric outward zonation of rock types ranging from olivine-bearing to hornblende-rich or magnetite-rich clinopyroxenites about a steeply dipping dunite core (Taylor, 1967). Lesser proportions of hornblendite and mafic pegmatite usually occur as isolated masses toward the periphery of the intrusion. Typical cumulate minerals include forsteritic olivine, diopsidic augite, chromite and magnetite; orthopyroxene is characteristically absent, indicating an alkalic affinity. Gabbroic rocks associated with the intrusion are commonly tholeiitic, and in this respect the syenogabbros and syenodiorites of the Tulameen complex are unusual (Findlay, 1969).
Igneous Rock Associations 23. The Bushveld Complex, South Africa: New Insights and Paradigms
SUMMARYThe Bushveld Complex has continued to serve as the basis for study into the fundamental nature of petrological processes for layered intrusion formation and for oxide and sulphide hosted Platinum Group Element (PGE)–Cu–Ni ore deposits. These studies have included discoveries in terms of the physical extent of Bushveld magmatism, both laterally and internally. Lateral variations in the mafic to ultramafic Rustenburg Layered Suite of the Northern Lobe of the complex have also revealed petrologically distinctive Upper Critical Zone equivalent rocks (the so-called Flatreef) with enhanced contamination and mineralization traits that reflect a transition between Eastern and Western Lobe equivalent stratigraphy and Platreef-style complexity. Traditional magma mixing models have been re-examined in light of radiogenic isotopic evidence for crustal involvement early in the chromite precipitation or formation process, combined with evidence for associated heterogeneous fluid contents, cryptic layering profiles, and textural evidence. A wide variety of alternative ore-genesis models have been proposed as a consequence. The fundamental mechanics of magma chamber processes and the existence of the magma chamber as an entity have been called into question through various lines of evidence which have promoted the concept of progressive emplacement of the complex as a stack of not-necessarily-quite-sequentially intruded sills (with or without significant quantities of transported phenocrysts), emplaced into variably crystallized and compacted crystal-liquid mush mixtures, modified by compaction-driven late magmatic fluid (silicate and aqueous) activity. Alternatively, petrological and geochemical observations have been used to discount these interpretations in favour of more conventional cooling and gravity-driven accumulation of silicate and ore minerals in a large, liquid-dominated system.RÉSUMÉLe complexe de Bushveld a demeuré à la base d’études sur la nature fondamentale des processus pétrologiques de formation d’intrusions litées et des gîtes des éléments du groupe platine (ÉGP)-Cu-Ni hébergés dans les oxydes et les sulfures. Ces études ont comporté des découvertes sur l’étendue physique, à la fois latérale et interne, du magmatisme de Bushveld. Les variations latérales de la suite stratifiée et mafique à ultramafique Rustenburg du lobe nord du complexe ont également révélé des roches équivalentes pétrologiquement distinctes de la zone critique supérieure (le communément désigné Flatreef) avec des traits de contamination et de minéralisation accrus qui reflètent une transition entre la stratigraphie équivalente des lobes est et ouest et la complexité de type Platreef. Les modèles traditionnels de mélanges magmatiques ont été réexaminés à la lumière de preuves isotopiques radiogéniques indiquant une implication de la croûte au début du processus de précipitation ou de formation de la chromite, combinées à des preuves de contenu fluide hétérogène associé, de profils de litage cryptique et de preuves texturales. Ainsi, une grande variété de modèles alternatifs de genèse de minerai a été proposée. La mécanique fondamentale des processus de la chambre magmatique et l'existence de la chambre magmatique en tant qu'entité ont été remises en question au moyen de divers éléments de preuve qui ont mis en avant le concept de mise en place progressive du complexe sous forme d'un empilement non-nécessairement séquentiel de sills injectés (avec ou sans quantités significatives de phénocristaux transportés) mis en place dans des mélanges de bouillie cristaux/liquide à cristallisation et compaction variable, modifiés par une activité tardive de fluide magmatique (silicaté et aqueux) induite par la compaction. Alternativement, des observations pétrologiques et géochimiques ont été utilisées pour écarter ces interprétations en faveur d'un processus plus conventionnel de refroidissement et d’accumulation de minérais silicatés et minéralisés induite par la gravité dans un vaste système à dominance liquide.