In-situ iron isotope analyses of pyrites from 3.5 to 3.2Ga sedimentary rocks of the Barberton Greenstone Belt, Kaapvaal Craton
Kazumi YoshiyaYusuke SawakiTakazo ShibuyaShinji YamamotoTsuyoshi KomiyaTakafumi HirataShigenori Maruyama
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Similarities between Proterozoic (~ 1.8-2.5 Gyr) and Archean (> 2.5 Gyr) banded iron-formations are probably more significant than their differences. The contrasts largely reflect differences in the tectonic settings of Proterozoic and Archean terrains. Archean banded iron-formations are not as thick nor laterally as extensive as the major Proterozoic iron-formations. Nevertheless, some Archean iron-formations have strike lengths of over 150-200 km and may have been quite extensive prior to the deformation that has affected most Archean terrains. Stratigraphic sequences in which iron-formations occur are highly variable and indicate that iron-formations formed in many depositional environments. Sedimentary textures in the iron-formations are dominated either by granules and oolites or laminations (including microbanding) reflecting differences in their physical conditions of deposition. Granular and oolitic textures are abundant in only three Proterozoic depositional basins and most Precambrian iron-formations are laminated. Despite differences in associated lithologies and sedimentary textures Precambrian iron-formations have similar bulk compositions and mineral assemblages, implying that the chemical conditions of iron-formation deposition were similar through much of the Precambrian. The formation of banded iron-formation appears not to have reached a maximum around 1.8-2.0 Gyr but to have been an important process over a long period in the Precambrian.
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Research Article| July 01, 2010 Paleoproterozoic Age Relationships in the Three Bluffs Archean Iron Formation-Hosted Gold Deposit, Committee Bay Greenstone Belt, Nunavut, Canada* T. Davies; T. Davies 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada Search for other works by this author on: GSW Google Scholar J.P. Richards; J.P. Richards † 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada †Corresponding Author: E-mail: Jeremy.Richards@ualberta.ca Search for other works by this author on: GSW Google Scholar R.A. Creaser; R.A. Creaser 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada Search for other works by this author on: GSW Google Scholar L.M. Heaman; L.M. Heaman 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada Search for other works by this author on: GSW Google Scholar T. Chacko; T. Chacko 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada Search for other works by this author on: GSW Google Scholar A. Simonetti; A. Simonetti 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada Search for other works by this author on: GSW Google Scholar J. Williamson; J. Williamson 2Committee Bay Resources Ltd., #220, 9797 45 Avenue, Edmonton, Alberta, T6E 5V8, Canada Search for other works by this author on: GSW Google Scholar D.W. McDonald D.W. McDonald 2Committee Bay Resources Ltd., #220, 9797 45 Avenue, Edmonton, Alberta, T6E 5V8, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information T. Davies 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada J.P. Richards † 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada R.A. Creaser 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada L.M. Heaman 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada T. Chacko 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada A. Simonetti 1Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada J. Williamson 2Committee Bay Resources Ltd., #220, 9797 45 Avenue, Edmonton, Alberta, T6E 5V8, Canada D.W. McDonald 2Committee Bay Resources Ltd., #220, 9797 45 Avenue, Edmonton, Alberta, T6E 5V8, Canada †Corresponding Author: E-mail: Jeremy.Richards@ualberta.ca Publisher: Canadian Institute of Mining, Metallurgy and Petroleum Received: 07 Oct 2009 Accepted: 31 Mar 2011 First Online: 02 Mar 2017 © 2011 Canadian Institute of Mining, Metallurgy & Petroleum Exploration and Mining Geology (2010) 19 (3-4): 55–80. https://doi.org/10.2113/gsemg.19.3-4.55 Article history Received: 07 Oct 2009 Accepted: 31 Mar 2011 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation T. Davies, J.P. Richards, R.A. Creaser, L.M. Heaman, T. Chacko, A. Simonetti, J. Williamson, D.W. McDonald; Paleoproterozoic Age Relationships in the Three Bluffs Archean Iron Formation-Hosted Gold Deposit, Committee Bay Greenstone Belt, Nunavut, Canada. Exploration and Mining Geology 2010;; 19 (3-4): 55–80. doi: https://doi.org/10.2113/gsemg.19.3-4.55 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyExploration and Mining Geology Search Advanced Search Abstract The Three Bluffs gold deposit is located in the Committee Bay greenstone belt, which forms part of the Rae domain of the western Churchill province, Nunavut, Canada. Gold mineralization is hosted by iron formation of the Neoarchean volcanosedimentary Prince Albert Group, and is associated with silicification (quartz veining) and sulfidation of magnetite and other Fe-rich minerals.Conventional U-Pb zircon dating of a conformable dacite unit within the volcanosedimentary host-rock sequence and a crosscutting diorite intrusion confirm a ~2.7 Ga age for deposition of the supracrustal package.U-Pb monazite dates and Pb isotopic analyses of sulfides were obtained by laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS). A subset of U-Pb monazite (1813.8 ± 8.7 Ma) and Re-Os arsenopyrite (1822 ± 21 Ma) dates, combined with a Pb-Pb secondary errorchron age for pyrite and arsenopyrite (1829 ± 77 Ma), suggest that gold mineralization associated with sulfidation of the iron formation occurred at ~1815 Ma, prior to high-grade (upper amphibolite facies) tectonometamorphism in the Three Bluffs area (D2TB/(M2TB).An ~1815 Ma age for deposit formation is broadly consistent with evidence from elsewhere in the western Churchill province and to the southwest in Manitoba and Saskatchewan for a late Trans-Hudson (1.9–1.8 Ga) gold mineralizing event. The majority of U-Pb monazite ages form a second population at 1780.6 ± 4.2 Ma, similar to the age of the majority of Re-Os arsenopyrite analyses (1763 ± 11 Ma). These dates are thought to reflect the timing of peak M2TB metamorphism. 40Ar/39Ar dating of amphibole, biotite, and muscovite yielded plateau ages ranging from 1723.8 ± 9.0 Ma to 1710 ± 17 Ma, which are interpreted to record the timing of postpeak metamorphic cooling to below the respective closure temperatures for Ar diffusion in these minerals. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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Two main hydrothermal mineral assemblages have been identified in the banded iron-formation-hosted gold mine at Nevoria. The earlier quartz ± garnet ± clinopyroxene ± calcite vein group formed pre- or synmetamorphic, and the later quartz ± pyrrhotite ± pyrite vein group appears to be postmetamorphic and related to gold mineralization. Fluid inclusion characteristics are obviously different in those two vein groups. Microthermometric analysis indicates that the fluids with metamorphic alteration are aqueous, CO2-rich or CO2-absent solutions; no or very small amounts of CH4 were involved in this fluid. Mineralizing fluids were a CH4-CO2-H2O solution. The initial auriferous fluids were CH4 dominant. Heterogeneous trapping, interaction of the hydrothermal fluid with graphite-bearing rocks, or fluid mixing may cause large variations of CH4/CO2 ratios or a XCH4 of CH4-CO2-H2O inclusions, particularly in mineralized quartz-pyrrhotite veins. Phase mixing or separating, resulting in an increase in pH and f O2, together with loss of reduced sulfur by mineral-fluid reactions and precipitation of sulfides, led to the breakdown of the gold-transporting complexes.
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The paper considers the results of a study of particles of carbonaceous substance and sulfur isotopes of associated sulfides in metapelites of the Neoarchean banded iron formation (BIF) of the Kostomuksha greenstone belt of Karelia (Karelian Craton of the Fennoscandian Shield). According to the petrographic observations, the carbonaceous matter occurs within and between silicate minerals’ grains, inside sulfides or at the grain boundaries, separating sulfide crystals from biotite or amphibole. Scanning electron (SEM) and atomic force (AFM) microscopy revealed the several types of the carbonaceous material varying in structure and carbon content. Raman spectra approved both well-structured graphite and weakly structured graphite (kerogen) components of the carbonaceous substance. The isotopic composition of total organic carbon is typical for biogenic processes. The obtained δ13Corg value within the range of –27,9– –30,6‰ is consistent with carbon fixation by photo- or chemoautotrophs. The sulfur isotopy of the associated sulfides is marked by positive Δ33S anomaly (up to +0.94‰) and negative δ34S values (–2.06‰ ─ –4.1‰). Positive Δ33S values indicate sulfur genetic association with photochemical elemental sulfur (S8) from the atmosphere, while negative δ34S values reflect isotope fractionation in bacterial-mediated processes. Based on these observations, we believe that the initial carbonaceous substance has mainly organic origin.
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