The Poplar copper-molybdenum porphyry deposit, located 270 km west of Prince George, is centered in a late Upper Cretaceous differentiated calc-alkaline stock, which intruded Lower and Upper Cretaceous sedimentary rocks. The stock is capped by late Upper Cretaceous volcanic flow rocks. The lower Cretaceous Skeena Group consists of intermediate tuff, siltstone, and interbedded sandstone, which steeply dip to the south. This unit is unconformably overlain by a moderately sorted polylithic pebble conglomerate belonging to the Upper Cretaceous Kasalka Group. The Poplar Stock, which hosts mineralization, includes a border phase of hornblende quartz monzodiorite porphyry which grades in to a central biotite quartz monzonite porphyry. The stock is intruded by several post-ore dyke units, which include porphyritic dacite, porphyritic rhyolite, felsite, and andesite. Ootsa Lake porphyritic volcanic flow rocks overly the deposit, and are dacite in composition. Pre-ore, and post-ore rock units have been K-Ar dated, and are within analytical error of each other, having a mean age of 74.8 ±2.6 Ma. The deposit is covered extensively with glacial till and alluvial sediments. Therefore the majority of geologic information was obtained from logging the drill core from 34 diamond drill holes, twelve of which were logged in detail using a computer compatible logging format. Information logged in this manner was used in statistical studies , and for producing computer generated graphic logs and plots of various geologic parameters, along two cross-sections through the deposit. Alteration zoning at the Poplar porphyry consists of a 600 m by 500 m potassic alteration annulus which surrounds a 300 m by 150 m argillic alteration core. These are enclosed by 750 m wide phyllic alteration zone, which is itself bordered by a low intensity propylitic alteration zone. Phyllic alteration is defined by the occurence of sericite, and is the most abundant type of alteration present. Potassic alteration, recognized by the occurence cf secondary K-feldspar and/or secondary biotite, is most closely associated with chalcopyrite and molybdenite. At least two episodes of alteration are recognized at the Poplar porphyry. The first was contemporaneous with mineralization, following intrusion and crystallization of the Poplar Stock. This episode consisted of potassic alteration in the center of the deposit, which surrounded a 'low grade1 core, and graded out to phyllic and propylitic alteration facies at the periphery. The second alteration event took place after the intrusion of the post-ore dykes and consisted mainly of hydrolytic alteration of pre-existing alteration zones which were adjacent to more permeable centers, such as faults, contacts, and highly jointed areas. This alteration event is responsible for the anomalous central argillic zone, and the alteration of dykes, in addition to probably intensifying and widening the phyllic alteration halo surrounding the deposit. Chalcopyrite and molybdenite were deposited in the potassic zone at approximately 375° C and less than 250 bars, with relatively low oxygen, and relatively high sulfer, activities and moderate pH. As the potassic alteration zone was invaded by more acidic solutions feldspars were altered sericite and clay, and chalcopyrite was destroyed to form pyrite and hematite. Copper was removed from the system. Statistical studies include univariant one-way and two-way correlation matrices, and multivariant regression analysis. Statistical correlations generally support empirical correlations made in the field. These include positive correlations between various potassic alteration facies minerals, and these minerals and chalcopyrite and molybdenite. Multivariant regression analysis was used to determine which alteration minerals were best suited for indicating chalcopyrite and molybdenite. These minerals are quartz, biotite, magnetite, sericite, K-feldspar, and pyrite. Large error limits and poor correlation statistics in the results from these studies are attributed to deviations from normal distributions for all minerals. A possible cause of this may have been the multistage alteration events that the deposit has undergone. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

No description available.

Porphyry copper and molybdenum deposits in west-central British Columbia are associated with plutons of Late Cretaceous and Tertiary age which intrude Mesozoic volcanic and sedimentary rocks of the Intermontane Tectonic Belt. The porphyry deposits are contained in an area bounded on the west by granitic rocks of the Coast Plutonic Complex, and on the east and southeast by a belt containing Mesozoic granitic stocks and an extensive area of Tertiary volcanic rocks. The porphyry intrusions take the form of small stocks, plugs , dykes, and dyke swarms generally not exceeding 1 square mile in surface area. The intrusions are commonly multiple and range in composition from quartz diorite to granite. Copper and molybdenum sulphides occur as fracture fillings and as veinlet stockworks within and adjacent to the intrusive bodies. Sulphide and alteration minerals exhibit concentric zoning patterns. Volcanic and sedimentary rocks marginal to the intrusions are thermally metamorphosed to biotite hornfels. Results of potassium-argon dating indicate four crudely parallel north to northwest-trending belts of porphyry intrusions, each being distinctive in age, rock composition, and contained metallic mineralization. From west to east these include: (1) Alice Arm intrusions - 50 m.y. molybdenum-bearing quartz monzonite and granite intrusions; (2) Bulkley intrusions - 70 to 84 m.y. copper-molybdenum and molybdenum-bearing porphyries of granodiorite to quartz monzonite composition; (3) Nanika intrusions - 50 m.y. copper-molybdenum and molybdenum-bearing intrusions of quartz monzonite composition; (4) Babine intrusions - 50 m.y. copper-bearing intrusions of quartz diorite and granodiorite composition. Potassium-argon analyses were carried out mainly on biotite separates from the mineralized porphyry phases within the deposits. Dating of inter-mineral and post-mineral porphyry phases, common at many of the deposits, yielded ages equivalent to, or 2 to 3 m.y. younger than, the mineralized phases, indicating that the age of mineralization is essentially synchronous with the age of intrusion. Limits of analytical errors in these potassium-argon analyses are within 3 per cent of the calculated ages. The distribution of potasslum-argon ages for porphyry deposits in west-central British Columbia does not fit the plate tectonic theories proposed for the origin of similar deposits elsehwere in the Cordillera of North and South America, in which deposits are progressively younger in a given direction. Here, four crudely parallel belts of porphyry intrusions display a reversal in age from 50 m.y. to 70 - 84 m.y. to 50 m.y. in an eastward direction. This distribution of ages may have been caused by periodic movement from Late Jurassic to Tertiary time along a subduction zone beneath the Coast Plutonic Complex which forms the west border of the area containing the porphyry deposits. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

No description available.

In recent years our understanding of the genesis of porphyry copper systems has advanced to a sufficient level to be able to construct predictive models that enhance exploration for these deposits. Our understanding of primary and secondary geochemical dispersion around these deposits is not so advanced as variables such as climate and topography cause geochemical patterns to be distorted or masked at surface with the result of different deposits having quite different geochemical characteristics. In this study the geology and geochemistry of a porphyry copper-molybdenum from the Canadian Cordillera is examined with the aim of demonstrating how primary geochemical patterns are affected by the development of a supergene enrichment blanket and leached capping. Topographic controls on the extent of leaching and supergene enrichment are also explored. The Berg porphyry copper-molybdenum deposit is in the Tahtsa Mountain Ranges, approximately 84 km southwest of Houston, central British Columbia. Mineralized zones are centered on a circa 50 Ma composite quartz monzonite stock. Hydrothermal alteration zones are similar to those of the classic model by Lowell and Guilbert. Central zones are potassic (orthoclase and biotite) while peripheral zones are propylitic (chlorite, epidote, carbonate). Intense phyllic alteration (quartz, sericite, pyrite) occurs at the north and south margins of the stock. Hypogene mineralization (characterized by pyrite, chalcopyrite and molybdenite) is concentrated in an annular zone straddling the quartz monzonite contact. Best grades are localized in altered quartz diorite and altered and hornfelsed Telkwa Formation (Hazelton Group) volcanic rocks at the east side of the deposit. The nature of these altered hornfelsed rocks has been a subject for much debate in previous studies. One school of thought suggests that they are part of a hornfels aureole associated with the quartz diorite. Others suggest that it is an alteration zone associated with the quartz monzonite stock. Thirteen diamond drill holes on a north south cross section of the deposit were logged (GEOLOG) and sampled. Outcrop samples were collected where possible close to each drill hole. Major elements were determined by XRF, trace metals by flame AAS and fluorine by specific ion electrode. A sequential extraction was used to study the distribution of copper between different host minerals. The origin of the hornfelsed rocks is solved by field mapping and geochemistry. In the field cross cutting relationships show that the quartz diorite predates the stock and that the hornfels zone is spacially related to it. Major element binary and ternary plots demonstrate that significant amounts of potassium have been added to these rocks in the mineralized zone. This implies that biotite alteration was superimposed onto an earlier hornfels. Trace metal data was partitioned into anomalous and background populations with probability graphs. In the hypogene zone Cu, Mo and Ag occur in an annular zone corresponding with the mineralogically defined potential ore zones. Fluorine is anomalous over the area of the potassic alteration zone. Lead and zinc are anomalous in peripheral haloes around the potential orebodies. These zones can be traced to surface through an extensive supergene enrichment blanket and leached capping. Three zones of supergene mineralization are recognized: supergene sulphide (covellite, digenite, chalcocite), supergene oxide (malachite/azurite, cuprite, tenorite, native Cu) and leached capping. Sulphides are the dominant host for Cu throughout most of the deposit but locally on steep slopes where supergene oxide is developed Cu is hosted in carbonate and oxide minerals. Enrichment or depletion of elements in the supergene is demonstrated with interelement ratios. Enrichment factors can be derived in two ways: a) by ratioing supergene values to hypogene values, or, b) by ratioing to a constant (e.g. TiO₂ ) for each zone and then ratioing this value between zones. Enrichment factors of <1 therefore imply depletion and >1, enrichment (1=hypogene grade). Results show that all elements (studied) are enriched in the supergene sulphide and oxide zones. In the leached cap Cu, Mn and Zn are depleted while Mo, Pb and Ag are significantly enriched. These elements are incorporated into immobile limonite mineral's (ferrimolybdite, jarosite, goethite etc.). / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Copper-silver mineralization at Sam Goosly occurs as a conformable lens within pyroclastic dacites of probable late early Cretaceous age. Most mineralization is contemporaneous with development of aluminous alteration minerals. Distribution zones of scorzalite, andalusite, and an innermost corundum zone, are concentric and broadly outline the mineralized zone. Southwards, along strike, the andalusite zone becomes an andalusite-pyrophyllite zone in which mineralization post-dates aluminous alteration. Regional metamorphlsm has overprinted a propylitic, or greenschist, assemblage on aluminous alteration. Country rocks and mineralization are intruded by two stocks: a 59 ± 3 m.y. quartz monzonite to the west of the ore zone, and a 51 ± 3 m.y. gabbro-monzonite stock to the east. Contact metamorphlsm associated with the gabbro-monzonite has produced a narrow, discontinuous zone of biotite hornfels and recrystallized metallic minerals in the ore zone. Alteration mineral assemblages and sulphide exsolution textures imply temperatures between 350°C and 625°C in the main ore zone. The assemblage andalusite-pyrophyllite-quartz indicates alteration temperatures of about 350°C in the andalusite-pyrophyllite zone. Chemical analysis of the altered volcanic host rocks suggests significant loss of soda and lime, and residual concentration of silica and alumina. These chemical changes probably result from exchange of Na⁺ and Ca⁺⁺ for H⁺ from a hydrothermal fluid, resulting in formation of aluminous minerals and quartz. The value of log mK+/mH+ of the fluid phase is deduced to be between 1 and 2. By analogy with other occurrences, this process probably takes place in a high-temperature solfataric, or geothermal environment. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate