Sulphur-isotope geochemistry of silver–selpnarsenide vein mineralization, Cobalt, Ontario

1986 ◽  
Vol 23 (10) ◽  
pp. 1551-1567 ◽  
Author(s):  
M. D. Goodz ◽  
D. H. Watkinson ◽  
V. Smejkal ◽  
Z. Pertold
Keyword(s):  
Isotopic Composition ◽  
Isotope Fractionation ◽  
Isotope Geochemistry ◽  
Wall Rock ◽  
Sulphur Isotope ◽  
Vein Formation ◽  
Metavolcanic Rocks ◽  
Isotope Study ◽  
Vein Deposits ◽  
Sulphur Isotopic Composition

The silver–sulpharsenide vein deposits of Cobalt, Ontario, crosscut basement Archean metavolcanic rocks, Proterozoic strata, and younger Proterozoic diabase sills. A petrographic and sulphur-isotope study of the metallic minerals was initiated to assess possible genetic models of vein formation. Discrete differences exist between the sulphur-isotope compositions of basement sulphides (δ34S = + 4.0‰), brecciated wall-rock sulphides (+ 3.5‰), and vein sulphides (+ 2.3‰). The δ34S values consistently increase with distance from the vein centres. Sulphur-isotope fractionation trends are similar for all the vein deposits studied. Sulphur-isotope data suggest that sulphides were deposited between 130 and 254 °C. Based on the assumption of equilibrium between chalcopyrite and galena, the initial δ34S of the fluid was between + 5.0 and + 11.0‰. The release of sulphur during the reaction of Archean pyrite with Proterozoic formational brines to form pyrrhotite is proposed to explain the heavy sulphur isotopic composition of the fluid. This process could also have provided the Ni, Co, and As, known to be concentrated in some pyrite, that was deposited in the silver veins. Interpretation of mineral paragenesis and geothermometry indicate that temperature decreased and aS2 increased as deposition proceeded.

scholarly journals Evaluation of the Gas Content in Archived Shale Samples: A Carbon Isotope Study

Geosciences ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 481
Author(s):  
Buzek Frantisek ◽  
Gerslova Eva ◽  
Gersl Milan ◽  
Cejkova Bohuslava ◽  
Jackova Ivana ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Isotope Fractionation ◽  
Vitrinite Reflectance ◽  
Gas Content ◽  
Hammer Mill ◽  
Archived Samples ◽  
Isotope Study ◽  
Initial Content ◽  
Gas Loss ◽  
Rock Eval

We examined 14 archived samples of shale for the chemical and 13C isotopic composition of residual gases produced as part of rock-crushing operations at a hammer mill. Results were compared with data on maturity from Rock-Eval pyrolysis and vitrinite reflectance measurements. The samples originated from three different formations (Mikulov Marls, Ostrava Formation, and Liteň Formation) located in the Czech Republic. For comparison, we examined a gas-prone shale sample from the Polish Silurian. We used changes in the chemical and isotopic composition of released gases to evaluate the isotope fractionation during gas loss and retroactively calculated the initial content of gas in the shale samples. The gas content estimates (in L of gas per ton of rock) correspond with the maturity parameters of the shales. Calculated isotope fractionation for the gas release was −3‰ for both methane and ethane. The archived samples primarily lost methane (up to 90%), with subsequent changes in the content of ethane and higher hydrocarbon levels.

scholarly journals Atmospheric composition and climate on the early Earth

2006 ◽  
Vol 361 (1474) ◽  
pp. 1733-1742 ◽  
Author(s):  
James F Kasting ◽  
M. Tazewell Howard
Keyword(s):  
Isotopic Composition ◽  
Isotope Fractionation ◽  
Atmospheric Composition ◽  
Early Earth ◽  
Geothermal Heat ◽  
Sulphur Isotope ◽  
Ocean Ridges ◽  
Early Atmosphere ◽  
Isotopic Records

Oxygen isotope data from ancient sedimentary rocks appear to suggest that the early Earth was significantly warmer than today, with estimates of surface temperatures between 45 and 85°C. We argue, following others, that this interpretation is incorrect—the same data can be explained via a change in isotopic composition of seawater with time. These changes in the isotopic composition could result from an increase in mean depth of the mid-ocean ridges caused by a decrease in geothermal heat flow with time. All this implies that the early Earth was warm, not hot. A more temperate early Earth is also easier to reconcile with the long-term glacial record. However, what triggered these early glaciations is still under debate. The Paleoproterozoic glaciations at approximately 2.4 Ga were probably caused by the rise of atmospheric O 2 and a concomitant decrease in greenhouse warming by CH 4 . Glaciation might have occurred in the Mid-Archaean as well, at approximately 2.9 Ga, perhaps as a consequence of anti-greenhouse cooling by hydrocarbon haze. Both glaciations are linked to decreases in the magnitude of mass-independent sulphur isotope fractionation in ancient rocks. Studying both the oxygen and sulphur isotopic records has thus proved useful in probing the composition of the early atmosphere.

Lake Sediment Core Records of Sulphur Accumulation and Sulphur Isotopic Composition in Central Ontario, Canada Lakes

2006 ◽  
Vol 35 (1) ◽  
pp. 99-109 ◽  
Author(s):  
M. Catherine Eimers ◽  
Andrew M. Paterson ◽  
Peter J. Dillon ◽  
Sherry L. Schiff ◽  
Brian F. Cumming ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Lake Sediment ◽  
Sediment Core ◽  
Lake Sediment Core ◽  
Sulphur Isotopic Composition

Nature and evolution of metamorphic fluids associated with turbidite-hosted gold deposits: Hill End goldfield, NSW, Australia

1993 ◽  
Vol 57 (388) ◽  
pp. 423-436 ◽  
Author(s):  
P. K. Seccombe ◽  
J. Ju ◽  
A. S. Andrew ◽  
B. L. Gulson ◽  
K. J. Mizon
Keyword(s):  
Lead Isotope ◽  
Early Carboniferous ◽  
Gold Deposits ◽  
Source Rocks ◽  
Gold Deposition ◽  
Vein Quartz ◽  
Sulphur Isotope ◽  
Hydrous Minerals ◽  
Vein Formation ◽  
The Hill

AbstractThe Hill goldfield, NSW, Australia, is an example of a syntectonic, slate-belt gold deposit formed in a multiply deformed, Late Silurian slate-metagreywacke turbidite sequence. Gold is confined to bedding-parallel veins and discordant leader veins composed of as many as four generations of quartz, accompanied by phyllosilicates, carbonates and minor sulphides. Vein formation and gold deposition was apparently synchronous with Early Carboniferous metamorphism and deformation. Homogenisation temperatures (Th) for fluid inclusions in vein quartz demonstrate five groupings in the temperature intervals 350-280°C 280-250°C 250-190°C 190-150°C and 150-110°C corresponding to a variety of primary and secondary inclusions developed during four periods of vein quartz deposition under a generally declining temperature regime. Inclusion fluids are characterised by a low salinity of around 0.1 to 3.6 wt. % NaCl equivalent. The dominant gas phase present in the inclusion fluids varies from N2 in the early stages of the paragenesis, through CH 4 during the main episode of gold deposition, to CO2- rich fluids associated with late-stage mineralisation. δ18O values for vein quartz (range 15.1-17.1‰) and vein carbonate (range 11.3-13.4‰) are typical of metamorphic mineralisation. δD composition of hydrous minerals and inclusion fluids (range −53 to −138‰) suggest an influx of meteoric water in the later mineralising fluids. This conclusion is supported by δ13C data for vein calcite (range −2.5 to −9.7%0). δ34S composition of vein pyrrhotite and pyrite ranges from 6.9 to 7.8‰ early in the paragenesis, to lighter values (around 4.2 to 5.8%0) accompanying late gold deposition from more oxidising fluids. Sulphur isotope data imply a sulphur source from underlying turbidites and an increase in fluid oxidation state during mineralisation . Lead isotope measurements on vein pyrite, arseno py rite, galena and gold are characterised by two isotope populations with 207Pb/206Pb ratios of 0.862 and 0.860, which define two discrete mineralising events during vein formation. Consistency between data from vein minerals and lead isotope signatures for potential source rocks indicate that lead was derived from the sedimentary pile.

scholarly journals Silicon Isotope Geochemistry: Fractionation Linked to Silicon Complexations and Its Geological Applications

Molecules ◽  
2019 ◽  
Vol 24 (7) ◽  
pp. 1415 ◽  
Author(s):  
Wang ◽  
Wei ◽  
Jiang ◽  
Liu ◽  
Lei ◽  
...  
Keyword(s):  
Chemical Weathering ◽  
Isotope Fractionation ◽  
Isotope Geochemistry ◽  
Ore Deposits ◽  
Silicon Isotope ◽  
Core Formation ◽  
Silicon Isotopes ◽  
Silica Precipitation ◽  
Geological Processes ◽  
Biological Uptake

The fundamental advances in silicon isotope geochemistry have been systematically demonstrated in this work. Firstly, the continuous modifications in analytical approaches and the silicon isotope variations in major reservoirs and geological processes have been briefly introduced. Secondly, the silicon isotope fractionation linked to silicon complexation/coordination and thermodynamic conditions have been extensively stressed, including silicate minerals with variable structures and chemical compositions, silica precipitation and diagenesis, chemical weathering of crustal surface silicate rocks, biological uptake, global oceanic Si cycle, etc. Finally, the relevant geological implications for meteorites and planetary core formation, ore deposits formation, hydrothermal fluids activities, and silicon cycling in hydrosphere have been summarized. Compared to the thermodynamic isotope fractionation of silicon associated with high-temperature processes, that in low-temperature geological processes is much more significant (e.g., chemical weathering, biogenic/non-biogenic precipitation, biological uptake, adsorption, etc.). The equilibrium silicon isotope fractionation during the mantle-core differentiation resulted in the observed heavy isotope composition of the bulk silicate Earth (BSE). The equilibrium fractionation of silicon isotopes among silicate minerals are sensitive to the Si–O bond length, Si coordination numbers (CN), the polymerization degrees of silicate unites, and the electronegativity of cations in minerals. The preferential enrichment of different speciation of dissoluble Si (DSi) (e.g., silicic acid H4SiO40 (H4) and H3SiO4− (H3)) in silica precipitation and diagenesis, and chemical weathering, lead to predominately positive Si isotope signatures in continental surface waters, in which the dynamic fractionation of silicon isotope could be well described by the Rayleigh fractionation model. The role of complexation in biological fractionations of silicon isotopes is more complicated, likely involving several enzymatic processes and active transport proteins. The integrated understanding greatly strengthens the potential of δ30Si proxy for reconstructing the paleo terrestrial and oceanic environments, and exploring the meteorites and planetary core formation, as well as constraining ore deposits and hydrothermal fluid activity.

Reactions between uranium veins and their host rocks in Vendée and Limousin (France)

1981 ◽  
Vol 44 (336) ◽  
pp. 417-423 ◽  
Author(s):  
M. Cathelineau ◽  
J. Leroy
Keyword(s):  
Structural Characteristics ◽  
Wall Rock ◽  
Structural Features ◽  
Gangue Mineral ◽  
List Type ◽  
Vein Formation ◽  
Wall Rock Alteration ◽  
Rock Alteration ◽  
Host Rocks ◽  
Basic Rocks

AbstractHydrothermal uranium veins, associated with the Hercynian leucogranites show important variations in their mineralogical, chemical and structural features in relation to the host rock lithology. These are described with particular reference to the Chardon deposit, Vendée where the veins cut granite, basic lithologies, and shales. The following features are described: 1Changes in the thickness of veins near to contact zones, particularly those between granites and basic lithologies, lamprophyres, and shales.2Changes in the gangue mineral assemblage with the preferential development of carbonate in veins cutting basic lithologies, and of silica in veins which cut granite.3Paragenetic zoning in the veins in passing from granites to their metamorphic aureoles.Comparisons between deposits of Vendée, Limousin, and Erzgebirge allow the following generalizations to be made: 1Open faults and subsequent mineralization are concentrated at boundaries between competent and more plastic lithologies.2Mineralizing fluids cause wall-rock alteration characterized by the removal of Si from granite and of Ca, Mg, Fe from metamorphic and basic rocks.3The chemical and structural characteristics of wallrocks are important controls on the mineralization but in acid lithologies the main controls on the pitchblende vein formation are the structural characteristics of the wallrock.

Sulphur isotope fractionation in modern microbial mats and the evolution of the sulphur cycle

Nature ◽  
1996 ◽  
Vol 382 (6589) ◽  
pp. 342-343 ◽  
Author(s):  
Kirsten S. Habicht ◽  
Donald E. Canfield
Keyword(s):  
Isotope Fractionation ◽  
Microbial Mats ◽  
Sulphur Isotope ◽  
Sulphur Cycle
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