Lead–zinc–barite veins of the Dorion Area, Thunder Bay District, Ontario

1977 ◽  
Vol 14 (9) ◽  
pp. 1963-1979 ◽  
Author(s):  
James M. Franklin ◽  
Roger H. Mitchell
Keyword(s):  
Lead Isotopes ◽  
Central Zone ◽  
Chloride Ion ◽  
Coarse Grained ◽  
Vein Wall ◽  
Sulphur Isotope ◽  
Thunder Bay ◽  
Basement Rocks ◽  
Lake Formation ◽  
Lead Zinc

The lead–zinc–barite deposits of the Dorion region are spatially associated with the unconformity between the Sibley Group (Helikian) and Archean and Aphebian basement rocks. The veins are coarse grained, and mineralogically zoned with galena–calcite in the central zone, sphalerite–quartz surrounding the central zone, and barite (±chalcopyrite) in the vein extremities. Veins occur near the pinch-out of the "Pass Lake formation" (basal Sibley Group), within the dolomite of the overlying "Rossport formation", or in nearby basement fractures. Rossport dolomite, where it forms a vein wall, is highly altered to metal-enriched chert and calcite. Archean wall rocks are not altered.Potassium–argon isotopic determinations on mica in Archean pegmatite immediately adjacent to a vein indicate that the transporting solutions were too cool to cause re-equilibration of the Ar within the mica. Sulphur-isotope data indicate equilibrium between galena and sphalerite yielding a depositional temperature range of 35–135 °C, and disequilibrium between sulphide–sulphate pairs. Lead isotopes are highly anomalous, yielding a secondary isochron which indicates either an Archean, or more probably a mixed Archean–Aphebian, source of lead.The deposits formed from metal leached from either basement rocks or breakdown of Sibley sandstone matrix. Metals and sulphate moved through the permeable sandstone, probably as chloride-ion complexes, and precipitated at the sandstone pinch-out. Reduced sulphur, possibly derived from organic decay, and probably held in a gas trap at the sandstone pinch out, caused precipitation of the sulphides by reaction with metal-bearing brines.

Tourmaline concentrations in Proterozoic sediments of the southern Cordillera of Canada and their economic significance

1977 ◽  
Vol 14 (10) ◽  
pp. 2348-2363 ◽  
Author(s):  
V. G. Ethier ◽  
F. A. Campbell
Keyword(s):  
Heat Flow ◽  
Sedimentary Rocks ◽  
Local Area ◽  
Economic Importance ◽  
Coarse Grained ◽  
Economic Significance ◽  
Lower Proterozoic ◽  
Lead Zinc ◽  
High Boron ◽  
Boron Level

Local concentrations of tourmaline occur in the lower Proterozoic (Helikian) Aldridge Formation of southeastern British Columbia, in some places in association with stratiform lead–zinc mineralization as at the Sullivan, Stemwinder, and North Star orebodies. The amount of boron in the rock is as much as two orders of magnitude above average levels reported for the Aldridge Formation or other similar types of sedimentary rocks. The concentrations are not detrital, but are caused by an anomalously high boron level, in a local area, at the time of sedimentation. The appearance of tourmaline within rip-up clasts, and in laminae within pebbles, is evidence of syngenetic introduction of boron.Three populations of tourmalines, on the basis of composition as determined by microprobe analyses, are described from the area:(1) A Proterozoic stock intruding the Aldridge Formation contains abundant schorl.(2) A tourmaline intermediate in composition between dravite and schorl is typical of Aldridge metasediments. Texturally this type occurs as (a) fine felted aggregates in the footwall of the Sullivan orebody, (b) disseminated through waste beds, and (c) in local concentrations removed from the Sullivan orebody.(3) Coarse-grained recrystallized tourmaline associated with the Sullivan ore is magnesium-rich. Recrystallization is erratic, and is probably related to uneven heat flow during metamorphism and to differences in bulk composition.The economic importance of tourmaline concentrations in the Aldridge Formation is their association in both space and time with stratiform sulfides.

scholarly journals The geochemistry of the northern part of the Ilímaussaq intrusion, S.W. Greenland

1964 ◽  
Vol 42 ◽  
pp. 1-104
Author(s):  
E.I Hamilton
Keyword(s):  
Central Area ◽  
Confining Pressure ◽  
Coarse Grained ◽  
Residual Liquid ◽  
Relative Time ◽  
Central Mass ◽  
Basement Rocks ◽  
Field Evidence ◽  
Show Evidence ◽  
High Level

The Ilímaussaq intrusion (S.W. Greenland) was emplaced into granitic Precambrian basement rocks. The intrusion is of a highly alkaline nature and in terms of rocks types, its major-, minor- and trace elements, may be compared to the Khibina-Lovozero intrusion of the Kola Peninsula, U.S.S.R. The present paper describes the geochemistry of the northern part of the intrusion and the marginal rocks. New total rock analyses are given together with the detailed geochemistry of U, Th, Radioactivity, Nb, Rb, Li and Be. The Ilímaussaq intrusion consists of an early augite syenite chilled against the country rocks. The augite syenite forms a more or less continuous ring around and above the intrusion. The main central mass of the intrusion consists of poorly layered, very coarse-grained, Na-rich "foyaite" containing relatively large amounts of sodalite and eudialyte. Differentiation of the "foyaite magma" gave rise to a volatile rich residual liquid from which lujavrites were formed. Differentiation of the lujavrites in the central area of the intrusion resulted in a lower banded sequence, the kakortokites, and an upper lujavrite liquid. When the confining pressure was exceeded, explosive brecciation occurred and lujavrite was intruded into the surrounding rocks. At a high level in the intrusion a sheet-like body of soda granite was emplaced together with various quart-bearing syenites. The relative time of intrusion of the quartz-bearing syenite is uncertain through lack of field evidence. Emplacement of the early augite syenite may be related to ring faulting followed by cauldron subsidence. The later Na-rich rocks may have replaced the earlier layered augite syenite or have been emplaced into a "magma chamber" developed by cauldron subsidence. The Na-Zr-Cl-rich rocks show evidence of cooling inwards with the development of a central volatile-rich pocket. The Ilímaussaq rocks probably represent a final highly fractionated stage of the more normal augite syenite magma common to the S. W. Greenland alkaline province.

Alluvial–playa sedimentation in the lower Keweenawan Sibley Group, Thunder Bay District, Ontario

1986 ◽  
Vol 23 (4) ◽  
pp. 527-542 ◽  
Author(s):  
Burns A. Cheadle
Keyword(s):  
Depositional Environments ◽  
Midcontinent Rift ◽  
North Shore ◽  
The North ◽  
Thunder Bay ◽  
Lake Formation ◽  
Playa Lake ◽  
Main Period ◽  
Sand Flats ◽  
Middle Proterozoic

The Middle Proterozoic Sibley Group is a mixed clastic–carbonate red bed sequence located in the Thunder Bay – Nipigon area on the north shore of Lake Superior. The lowest unit, the Pass Lake Formation, consists of a basal paraconglomerate member, of probable alluvial debris-flow origin, overlain by 20–80 m of plane-bedded and cross-bedded quartz arenites, which were probably deposited by sheetfloods and eolian processes on alluvial outwash sand flats. The overlying Rossport Formation is dominated by red and buff dolomicritic mudstone. The association of these mudstones with relatively pure massive carbonate beds and sheetflood sandstone units is strongly suggestive of a playa lake depositional environment. Fluctuations in playa lake levels may have resulted in oscillations between carbonate-dominated and clastic-dominated sedimentation. The upper unit, the Kama Hill Formation, consists of horizontally laminated purple shales and ripple cross-laminated buff siltstones to fine sandstones. The presence of stacked "powering-down" sequences and abundant dessiccation features is suggestive of sheetflood deposition on a distal alluvial floodplain.The sequence of depositional environments suggests that the Sibley Basin formed by stretching and sagging of the Middle Proterozoic crust preceding the main period of volcanic activity along the Keweenawan Midcontinent Rift Zone. In this sense, the Sibley Group red beds represent the earliest products of Keweenawan rifting. They were not, however, deposited in a classical aulacogen or "failed arm."

Geochemistry of a fossil hydrothermal system at Barton Peninsula, King George Island

1995 ◽  
Vol 7 (1) ◽  
pp. 63-72 ◽  
Author(s):  
Chil-Sup So ◽  
Seong-Taek Yun ◽  
Maeng-Eon Park
Keyword(s):  
Hydrothermal System ◽  
Meteoric Water ◽  
Volcanic Rocks ◽  
King George Island ◽  
Sulphur Isotope ◽  
Alteration Zones ◽  
Vein Formation ◽  
Calcite Veins ◽  
Lead Zinc ◽  
Barton Peninsula

A fossil hydrothermal system on Barton Peninsula, King George Island, Antarctica, formed a series of lead-zinc- and pyrite + native sulphur-bearing epithermal quartz ± calcite veins, filling fault-related fractures in hydrothermally altered volcanic rocks of Eocene age. The lead-zinc veins occur within argillic hydrothermal alteration zones, whereas the pyrite + native sulphur veins are found within advanced argillic alteration zones. Fluid inclusion data indicate that the vein formation occurred at temperatures between about 125° and 370°C (sphalerite deposition formed at 123–211°C) from fluids with salinities of 0.5–4.6 wt.% eq. NaCl. Equilibrium thermodynamic interpretation of mineral assemblages indicates that the deposition of native sulphur in the upper and central portions of the hydrothermal system was a result of the mixing of condensates of ascending magmatic gases and meteoric water giving rise to fluids which had lower pH (<3.5) and higher fugacities of oxygen and sulphur than the lead-zinc-depositing fluids at depth. The δ34S values of sulphide minerals from the lead-zinc veins (δ34S = −4.6 to 0.7‰) are much higher than the values of pyrite and native sulphur from the pyrite + native sulphur veins (δ34S = −12.9 to −20.1‰). This indicates that the fluids depositing native sulphur had higher sulphate/H2S ratios under higher fo2 conditions. Sulphur isotope compositions indicate an igneous source of sulphur with a δ34SΣS value near 0‰, probably the Noel Hill Granodiorite. Measured and calculated δ18O and δD values of the epithermal fluids (δ18Owater = −6.0 to 2.7‰, δDwater = −87 to −75‰) indicate that local meteoric water played an important role for formation of lead-zinc and native sulphur-bearing quartz veins.

Effect of the Grain Size on Electrochemical Corrosion Behavior of Cu60Ni20Cr20 Alloys in Solutions Containing Chloride Ions

2012 ◽  
Vol 476-478 ◽  
pp. 16-20
Author(s):  
Guo De Li ◽  
Jing Bian ◽  
Zhong Qiu Cao ◽  
Ke Zhang ◽  
Ya Jun Fu
Keyword(s):  
Grain Size ◽  
Corrosion Behavior ◽  
Electrochemical Corrosion ◽  
Chloride Ion ◽  
Chloride Ions ◽  
Coarse Grained ◽  
Protective Film ◽  
Ion Concentrations ◽  
Corrosion Rates ◽  
Electrochemical Corrosion Behavior

The two Cu60Ni20Cr20alloys with the different grain size were prepared by conventional casting (CA) and mechanical alloying (MA) through hot pressing. Effect of the grain size on electrochemical corrosion behavior of the two Cu60Ni20Cr20 alloys was also studied in solutions containing chloride ions. Results show that the free corrosion potentials of the two alloys move toward to negative values, corrosion current densities increase and therefore corrosion rates become faster with the increment of chloride ion concentrations. CACu60Ni20Cr20alloy and MACu60Ni20Cr20alloy have passive phenomena in 0.05mol/L Na2SO4 neutral solution, but passive phenomena become weak or disappear when the chloride ions are added. Corrosion rates of the nanocrystalline MACu60Ni20Cr20alloy become slower than those of the coarse grained CACu60Ni20Cr20alloy in solutions containing the same chloride ion concentrations because MACu60Ni20Cr20alloy is able to produce large concentrations of grain boundaries and passive elements is able to diffuse quickly to form the protective film.

Stratigraphy and depositional setting of the Sibley Group, Thunder Bay district, Ontario, Canada

1980 ◽  
Vol 17 (5) ◽  
pp. 633-651 ◽  
Author(s):  
J. M. Franklin ◽  
W. H. McIlwaine ◽  
K. H. Poulsen ◽  
R. K. Wanless
Keyword(s):  
Rift Valley ◽  
Lacustrine Environment ◽  
Saline Environment ◽  
New Name ◽  
Thunder Bay ◽  
Quartz Arenite ◽  
Lake Formation ◽  
Mud Flat ◽  
Depositional Setting ◽  
Red Bed

The Sibley Group is a Neohelikian (1339 ± 33 Ma, RbSr, 87Rb = 1.42 × 10−11 year−1) red bed sequence located in an elongate basin extending northward for 150 km from Nipigon, Ontario. The lowest unit, the Pass Lake Formation (new name), is 50 m thick and consists of quartz arenite, deposited primarily in a shallow, quiet lacustrine environment. It is overlain by the Rossport Formation (new name), a unit of 135 m thickness consisting of a lower arenaceous red dolomite member, central chert–carbonate and stromatolite member, and an upper argillaceous red dolomite member. The Rossport Formation was deposited in a shallow, highly saline environment, in a basin of fluctuating size. The Kama Hill Formation (new name) is 50 m thick, and consists of purple shale composed of smectite, authigenic microcline, and quartz. It was deposited in a periodically dry mud flat, and is characterized by desiccation cracks, evaporite casts, and mud-chip microbreccias.Both the Rossport and Kama Hill Formations have an increased arenite content near the basin margins. Breccias cut the Rossport Formation and consist of stoped blocks of Rossport and Kama Hill rocks; these breccias are cut by sandstone dykes. The Sibley Group is situated in, and was possibly deposited in, a "failed arm" which radiates from a paleo-plume in the Keweenawan rift valley.

scholarly journals The Los Llantenes Formation in the Precordillera of Jagüe (La Rioja Province) and the recognition of a rifting stage in the early evolution of the late Paleozoic basins in western Argentina.

2011 ◽  
Vol 38 (2) ◽  
pp. 245 ◽  
Author(s):  
Ricardo A. Astini ◽  
Federico Martina ◽  
Federico M. Davila
Keyword(s):  
Coarse Grained ◽  
Areal Extent ◽  
The South ◽  
Great Thickness ◽  
Basement Rocks ◽  
Upper Paleozoic ◽  
Basal Section ◽  
History Of ◽  
Low Efficiency ◽  
La Rioja

In the northern part of the Argentine Precordillera, northwestern La Rioja, the Upper Paleozoic is over 4,000 m thick. Very coarse conglomerates from the basal section have not been described nor adequately interpreted. This work analyses this unit in the context of a stratigraphic revision of the upper Paleozoic of the region, and interprets the conglomerate as a rift deposit. The thick (>1,000 m) and coarse purple conglomeratic succession, herein named ‘Los Llantenes Formation’, non-conformably rests on the basement rocks of the region and underlies deposits of the first glacial record associated with the Gondwanan glaciation. While its great thickness and restricted areal extent indicate localized subsidence, the crude stratification, poor sorting and abundance of >1-m boulders indicate an origin related to high-gradient, low-efficiency alluvial fans. Their composition and coarse-grained size indicate local provenance, abrupt relief and incipiently developed drainage systems and a highly compartmentalized and abrupt paleogeography. A complex glacial history generated deep ‘U’-shaped paleovalleys in the Los Llantenes Formation, developing paleovalleys that accommodated basal lodgment tills and glacial diamictites with sedimentologic features comparable to the Cerro Tres Condores Formation (Visean in age) exposed to the south. The age of the conglomerates of Los Llantenes Formation, clearly preglacial, can be stratigraphically bracketed between the Middle Devonian substrate cropping out to the south in the sierra de Las Minitas and the Middle Mississippian, age of the Cerro Tres Condores Formation. Consequently, Los Llantenes Formation may partly correlate with the Agua de Lucho Formation (Tournaisian-Vissean) that in the area of Rio del Penon, immediately to the south, underlies the glacigenic Cerro Tres Condores Formation. Mapping relationships with limited areal extent, together with the great thickness of Los Llantenes Formation and the local provenance, allow interpreting accommodation in extensional or pull-apart depocenters, conclusions that are relevant in order to reconstruct the history of the basin.

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