摘要:

The altered rocks of the Mattagami Lake Mine, a stratabound, volcanogenic, massive sulphide deposit, were examined using whole rock analyses and electron microprobe studies of the constituent minerals. The significant chemical and mineralogical transformations involved in the progressive alteration of the footwall, vitroclastic tuff of rhyodacitic composition, are: (1) the removal of alkalies (sodium followed by potassium), and the addition of magnesium and iron during initial chloritization; (2) substantial removal of silica by the solution of quartz, to produce a chlorite-rich rock, and (3) gradual removal of aluminum and the transformation of chlorite (Mg2.5Fe2.5Al2Si3O10(OH)8) to talc (MG2.5FE0.5Si4O10(OH)2to produce units of talc–actinolite schist. The reaction: 3 chlorite + 10H2S(g) + 2.5 O2 + 11,H4SiO4 + 5Mg2+ = 5talc + 5pyrite +  + 19H2O + 16H+(logK, 25 °C = +145; logK, 100 °C = +102; logK, 250 °C = +68.2) is favoured by high temperature and Mg2+activity, and low activity of aluminum.The alteration pipe zone immediately beneath the orebody is assumed to have been the discharge site of a thermally induced, convective flow system. The upper part of the system would have been characterized by the movement of seawater, of comparatively short residence time in the rocks, to areas of discharge. Under conditions of high permeability and high water flux in these zones, bulk seawater composition of comparatively high magnesium and low aluminum concentrations would ultimately control the composition of the volcanic material by the formation of alteration products in equilibrium with it, rather than the volcanic material significantly affecting the seawater chemistry. This would ensure the early development of magnesian chlorite in the vitric tuff. The transformation chlorite to talc took place at discharge sites, the locations of highest surface temperatures, under hydrologic conditions such that the flux rate was sufficiently high to remove the comparatively immobile aluminum.The massive sulphide units were emplaced in association with the development of talc. Layered pyrite–sphalerite, overlying and extending beyond talc units are chemical sediments.

ISSN:0008-4077    

DOI:10.1139/e78-001

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The rocks of the Wirral – Big Lake area occupy a transitional zone between a Silurian – Lower Devonian volcanic sequence of the Coastal and Mascarene–Nerepis Belts and turbiditic rocks of the Fredericton Trough. Most of the rocks of the Wirral – Big Lake area were included by previous workers in the "Pale and Dark Argillite Divisions of the Charlotte Group." It is proposed that the term Charlotte Group be discontinued because the subdivisions of this group do not conform with and locally cut across formational boundaries. Moreover, both Ordovician and Silurian strata were included in the Charlotte Group.The Coastal and Mascarene–Nerepis volcanic belts probably represent an ensialic island arc sequence that developed simultaneously with the deposition of sedimentary strata of the same age in the Wirral – Big Lake area and in the Fredericton Trough. It is suggested that these turbiditic sediments represent a behind-the-arc basin. The stratigraphic succession and structure of the map-area reflect several distinct stages in the closing of this basin.

ISSN:0008-4077    

DOI:10.1139/e78-002

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

A method is presented to determine the radio-equilibrium of the uranium–actinium series in rock samples by low energy photon spectroscopy. The equilibrium pattern is indicated by the relative abundance of the isotopes238U,231Pa,226Ra,222Rn and210Pb. For whole rock analysis no elaborate sample preparation is needed and the measurements can be performed in the field. On chemically separated material the uranium-234, -235 and -238 ratio can also be determined by the present method. A practical table for radioactive rock analysis, listing intense photons below 250 keV energy, is also included.Measurements on uranium-bearing rocks indicate that radioactive disequilibrium is common, especially in near-surface specimens. This should be taken into consideration in calculating equivalent uranium (eU) values from scintillometric measurements, and in interpreting anomalies by radon geochemistry. The deduced isotopic ratios can be used for age determination and to monitor industrial enrichment of uranium-235.

ISSN:0008-4077    

DOI:10.1139/e78-003

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Approximately 15 species of terrestrial and freshwater mollusks are reported from Pleistocene deposits in the unglaciated Old Crow Basin of the northern Yukon Territory. Of those species,Bulimus leachi(Sheppard), a widespread Eurasian species; andValvata piligera yukonensis(n. ssp.), closely related to an unusualValvatanow confined to Lake Baikal, U.S.S.R., are recorded from North America for the first time. Possible causes for the failure of these species of freshwater mollusks to become established in North America are considered.

ISSN:0008-4077    

DOI:10.1139/e78-004

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The Snyder Group is an Aphebian sedimentary sequence unconformably overlying Archean rocks that has undergone deformation and a medium to high grade contact metamorphism as the result of the emplacement of the Elsonian Kiglapait intrusion. Five lithostratigraphic units totaling 239 m in thickness have been recognized; in ascending order they are: (1) a lower quartz arenite with local arkosic arenites, pelites, conglomerates and a discontinuous basal conglomerate; (2) a manganiferous silicate iron formation; (3) a marble with associated calc-silicates and quartzites; (4) a sphalerite- and pyrrhotite-bearing quartz-rich, graphitic siltstone; and (5) an upper quartzite. The several intrusive rocks are largely basic and intermediate in composition and are grouped as being emplaced either before or after the contact metamorphism by the Kiglapait intrusion. Collectively, their sills and dikes have expanded the section to 355 m.The lower and upper quartzites with their high maturity; poly modal festoon, trough crossbedding; reactivation surfaces; flaser and lenticular bedding; ripple marks; graded bedding; and conglomerates were probably deposited on a shallow, subtidal, tide- and current-dominated sand flat dissected by tidal channels. The few metapelites record deposition during an occasional less turbulent environment. The fine grain size, intraformational conglomerates, cross-laminations, and thin laminations of the intermediate formations indicate that they were deposited in a quiet, probably shallow water environment disturbed only by occasional storms. The sedimentary structures, lithologies and thin, sheet geometries of the beds suggest that the Snyder Group represents a siliciclastic sea shelf sedimentation, which, if reconstructions of the North Atlantic craton are correct, was epicontinental.

ISSN:0008-4077    

DOI:10.1139/e78-005

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The Crowsnest Formation consists of trachytes, analcime phonolites and blairmorites, metamorphosed to zeolite facies. The latter rocks contain large analcime phenocrysts variously suggested as being of primary igneous origin or due to transformation from original leucite by reaction of Na-rich fluids. Although neither field relationships or petrography provide convincing data favouring either hypothesis, the presence of primary undisrupted inclusion trails in the analcime tend to support the former hypothesis. Compositions of the analcimes differ from that of an analcime formed by transformation from leucite. The chemistry of the rocks and their constituent pyroxenes are consistent with a sodic rather than a potassic differentiation trend; feldspar and garnet analyses support this conclusion. Oxygen isotope values for the pyroxenes indicate no extensive exchange with a low temperature fluid. Thus it seems unlikely that leucite was ever a constituent of the Crowsnest suite as necessitated by the hypothesis of transformation from leucite. Geochemistry and known experimental data indicate that the analcime phonolites and blairmorites differentiated from a trachytic magma under restricted conditions at depths greater than 25 km by early sanidine and later analcime fractionation. The parental trachyte may be produced by partial fusion of crustal material at depths greater than 35 km.

ISSN:0008-4077    

DOI:10.1139/e78-006

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The use of direct arrivals and multiple reflections that have travelled completely in water from source to receiver to determine epicentral distances is a standard technique in the analysis of marine seismic profiles. The configuration of a source at the air–water interface and a seismometer at the water–sediment interface is investigated in the ray parameter – distance plane and the travel time – distance plane. Vertical component synthetic seismograms are computed by the Cagniard – de Hoop algorithm and are compared with seismograms recorded at the ocean bottom. The results explain the prominent features of the observed wavetrains, including the asymptotic behaviour of arrivals, the location of caustics and the variable observability of arrivals as a fu nction of distance.

ISSN:0008-4077    

DOI:10.1139/e78-007

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The Southern Park Ranges lie immediately east of the Rocky Mountain Trench, near the Big Bend of the Columbia River, B.C. They are composed of quartzites, pelites and carbonates in an uninterrupted sequence from the Proterozoic Windermere Supergroup, through the Lower Cambrian Gog Group, to the Middle Cambrian Chancellor Group.Two phases of folding and metamorphism are recognized. The first phase of folding (F1) occurred before and during the first phase of metamorphism (M1), whereas the second phase of folding (F2) was associated with a second (very minor) phase of metamorphism (M2). Both F1and F2structures are apparently associated with the rise of the Porcupine Creek Anticlinorium, a major fold complex trending northwest–southeast across the eastern part of the study area. Associated with F2folds are several west-dipping thrust faults, some of which terminate upwards in the cores of F2anticlines. All structures are cut by late-stage, west-dipping normal faults.The first phase of metamorphism (M1) resulted in a Barrovian sequence of isograds such that chlorite zone rocks occur in the east and sillimanite zone rocks occur in the west. Phase equilibria studies suggest that the metamorphic temperatures in the area ranged from less than 480 °C (east) to 570 °C (west) at a pressure of approximately 5 kbar (5 × 105 kPa).The M1isograds in the Park Ranges outline a thermal antiform whose western limb is truncated by the Purcell Fault (a major Cordilleran structure) on the western slopes of the study area.A comparison of main metamorphic phases between the Park Ranges and the Selkirk and Monashee Mountains across the Purcell Fault, suggests that the western (Selkirk–Monashee) terrane underwent temperatures approximately 40 °C higher than the study area (for equivalent metamorphic zones) and a pressure between 2 and 3 kbar (2 × 105and 3 × 105 kPa) higher than the study area. This pressure difference suggests that there has been a minimum of 7 km post-metamorphic vertical motion on the Purcell Fault. A difference in structural style across the Purcell Fault, due to a higher ductility in the western terrane, is interpreted as a result of the difference in depth during the deformation of the two terranes.

ISSN:0008-4077    

DOI:10.1139/e78-008

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The Lower Jurassic, Ashcroft Formation contains a thick section of carbonaceous marine shale and a few graded sandstones. Along the south and east margins of the Ashcroft Basin, Ashcroft strata rest unconformably on calc-alkaline and alkaline volcanic flows and sediments of the Upper Triassic, Nicola Group. On the west margin Nicola and Ashcroft strata lie against mélange of the Cache Creek Group. This contact is faulted in some places, but it may be a depositional unconformity elsewhere.South of Cache Creek village, overturned allochthons of Nicola strata were placed on top of Ashcroft beds in Early Jurassic time before Ashcroft sediments were lithified. Turbidity currents flowed southeast contemporaneous with sliding or thrusting of allochthons.Near the Guichon Creek Batholith, the Ashcroft Formation contains a disconformity that separates Sinemurian–Pliensbachian from Callovian strata. However, in the western part of the Ashcroft basin strata appear continuous from Sinemurian–Pliensbachian to Callovian. The Guichon Creek Batholith was emplaced into Nicola strata along the eastern edge of the Ashcroft Basin about 200 Ma ago (late Sinemurian*) and was quickly unroofed to provide granitic debris to the basin.The Ashcroft Basin appears to have been an early Mesozoic outer arc basin. It formed seaward of calc-alkaline magmatism and landward of and possibly on top of a mélange. Middle or Late Triassic radiolaria found in the Cache Creek show that deformation of the mélange took place as late as Late Triassic time. Arc-directed thrusting and sliding may be gravity processes due to elevation of the outer arc ridge during subduction.

ISSN:0008-4077    

DOI:10.1139/e78-009

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Recent geological mapping and geochemical studies of the late Proterozoic rocks of the Burin Peninsula in the southwestern part of the Avalon Zone of Newfoundland show the following sequence: (1) The basal Rock Harbour Group, a sedimentary assemblage ranging from conglomerates to turbidites, was derived from a subaerial volcanic–plutonic source region. (2) The overlying Burin Group, a belt of mafic volcanic and intrusive rocks that have alkalic affinities at the base but are dominated by oceanic tholeiite. (3) The Marystown Group, a bimodal sequence of alkalic basalts and rhyolites deposited in a subaerial environment unconformably above the Burin Group, and apparently conformably overlain by Infracambrian to Cambrian sedimentary rocks. Stromatolites occur within resedimented limestone breccias and conglomerates at the top of the Rock Harbour Group and throughout the Burin Group.These assemblages are interpreted to indicate that after a period of continental type bimodal volcanism, the Avalon terrain was rifted in Burin Group times to form some kind of small ocean basin, which was abruptly closed with a reversion to continental type bimodal volcanism of the Marystown Group.

ISSN:0008-4077    

DOI:10.1139/e78-010

出版商:NRC Research Press    

年代:1978

数据来源: NRC