scholarly journals Triple oxygen isotope variations in magnetite from iron-oxide deposits, central Iran, record magmatic fluid interaction with evaporite and carbonate host rocks: REPLY

Geology ◽  
2020 ◽  
Vol 48 (7) ◽  
pp. e504-e504 ◽  
Author(s):  
Stefan T.M. Peters ◽  
Narges Alibabaie ◽  
Andreas Pack ◽  
Seann J. McKibbin ◽  
Davood Raeisi ◽  
...  
Keyword(s):  
Iron Oxide ◽  
Oxygen Isotope ◽  
Central Iran ◽  
Magmatic Fluid ◽  
Host Rocks ◽  
Fluid Interaction

scholarly journals Triple oxygen isotope variations in magnetite from iron-oxide deposits, central Iran, record magmatic fluid interaction with evaporite and carbonate host rocks

Geology ◽  
2019 ◽  
Vol 48 (3) ◽  
pp. 211-215 ◽  
Author(s):  
Stefan T.M. Peters ◽  
Narges Alibabaie ◽  
Andreas Pack ◽  
Seann J. McKibbin ◽  
Davood Raeisi ◽  
...  
Keyword(s):  
Iron Oxide ◽  
Oxygen Isotope ◽  
Carbonate Rocks ◽  
Isotope Composition ◽  
Central Iran ◽  
Magmatic Fluid ◽  
Isotope Data ◽  
O Isotopes ◽  
Magmatic Fluids ◽  
O Isotope

Abstract Oxygen isotope ratios in magnetite can be used to study the origin of iron-oxide ore deposits. In previous studies, only 18O/16O ratios of magnetite were determined. Here, we report triple O isotope data (17O/16O and 18O/16O ratios) of magnetite from the iron-oxide–apatite (IOA) deposits of the Yazd and Sirjan areas in central Iran. In contrast to previous interpretations of magnetite from similar deposits, the triple O isotope data show that only a few of the magnetite samples potentially record isotopic equilibrium with magma or with pristine magmatic water (H2O). Instead, the data can be explained if magnetite had exchanged O isotopes with fluids that had a mass-independently fractionated O isotope composition (i.e., MIF-O), and with fluids that had exchanged O isotopes with marine sedimentary carbonate rocks. The MIF-O signature of the fluids was likely obtained by isotope exchange with evaporite rocks of early Cambrian age that are associated with the IOA deposits in central Iran. In order to explain the triple O isotope composition of the magnetite samples in conjunction with available iron isotope data for magnetite from the deposits, we propose that magnetite formed from magmatic fluids that had interacted with evaporite and carbonate rocks at high temperatures and at variable water/rock ratios; e.g., magmatic fluids that had been released into the country rocks of a magma reservoir. Additionally, the magnetite could have formed from magmatic fluids that had exchanged O isotopes with SO2 and CO2 that, in turn, had been derived by the magmatic assimilation and/or metamorphic breakdown of evaporite and carbonate rocks.

scholarly journals Absence of hydrothermal oxygen isotope variations in host rocks supports magmatic origin of the giant Grängesberg iron oxide–apatite (IOA) deposit, Central Sweden

2021 ◽  
Author(s):  
Franz Weis ◽  
Valentin R. Troll ◽  
Erik Jonsson ◽  
Karin Högdahl ◽  
Chris Harris ◽  
...  
Keyword(s):  
Iron Oxide ◽  
Oxygen Isotope ◽  
Large Scale ◽  
Country Rock ◽  
Isotope Composition ◽  
Northwestern Part ◽  
Magmatic Origin ◽  
Ore Body ◽  
Two Samples ◽  
Host Rocks

AbstractThe origin of Kiruna-type iron oxide–apatite ores is controversial, and debate presently centres on a ‘magmatic’ versus a ‘hydrothermal’ mode of formation. To complement recent investigations on the Grängesberg iron oxide–apatite ore deposit in the northwestern part of the Palaeoproterozoic Bergslagen ore province in central Sweden, we investigated the oxygen isotope composition of the host rocks of this large iron oxide–apatite ore body. As the metavolcanic and metagranitoid country rocks around the Grängesberg ore body either pre-date or are coeval with ore formation, they would be expected to record an extensive isotopic imprint if the ore body had formed by large-scale hydrothermal processes involving an externally sourced fluid. A direct magmatic formation process, in turn, would have produced localized alteration only, concentrated on the immediate vicinity of the ore body. Here, we test these two hypotheses by assessing the oxygen isotope variations in the host rocks around the main Grängesberg iron oxide–apatite ore body. We analysed oxygen isotopes in quartz from metavolcanic (n = 17) and metagranitoid host rocks (n = 14) from the vicinity of the ore body, and up to 2 km distance along and across the strike of the ore body. Remarkably, we find no significant variation in δ18O values with distance from the ore body, or any deviations in country rock δ18O from common magmatic and/or regional values. Only two samples show shifts to values more negative than the common magmatic range, indicating highly localized hydrothermal overprint only. As a large-scale, low-temperature hydrothermal origin of the ore body through voluminous fluid percolation would be expected to have left a distinct imprint on the oxygen isotope values of the country rocks, our results are more consistent with an ortho-magmatic origin for the Grängesberg iron oxide–apatite ore.

MAPPING THE MINERAL ZONATION AT THE ERNEST HENRY IRON OXIDE COPPER-GOLD DEPOSIT: VECTORING TO Cu-Au MINERALIZATION USING MODAL MINERALOGY

2022 ◽  
Vol 117 (2) ◽  
pp. 485-494
Author(s):  
Tobias U. Schlegel ◽  
Renee Birchall ◽  
Tina D. Shelton ◽  
James R. Austin
Keyword(s):  
Iron Oxide ◽  
Gamma Ray ◽  
Geochemical Data ◽  
Iocg Deposits ◽  
Mineral Mapping ◽  
Gamma Ray Spectrometer ◽  
Mineral Assemblages ◽  
Copper Gold ◽  
Host Rocks ◽  
Acid Alteration

Abstract Iron oxide copper-gold (IOCG) deposits form in spatial and genetic relation to hydrothermal iron oxide-alkali-calcic-hydrolytic alteration and thus show a mappable zonation of mineral assemblages toward the orebody. The mineral zonation of a breccia matrix-hosted orebody is efficiently mapped by regularly spaced samples analyzed by the scanning electron microscopy-integrated mineral analyzer technique. The method results in quantitative estimates of the mineralogy and allows the reliable recognition of characteristic alteration as well as mineralization-related mineral assemblages from detailed mineral maps. The Ernest Henry deposit is located in the Cloncurry district of Queensland and is one of Australia’s significant IOCG deposits. It is known for its association of K-feldspar altered clasts with iron oxides and chalcopyrite in the breccia matrix. Our mineral mapping approach shows that the hydrothermal alteration resulted in a characteristic zonation of minerals radiating outward from the pipe-shaped orebody. The mineral zonation is the result of a sequence of sodic alteration followed by potassic alteration, brecciation, and, finally, by hydrolytic (acid) alteration. The hydrolytic alteration primarily affected the breccia matrix and was related to economic mineralization. Alteration halos of individual minerals such as pyrite and apatite extend dozens to hundreds of meters beyond the limits of the orebody into the host rocks. Likewise, the Fe-Mg ratio in hydrothermal chlorites changes systematically with respect to their distance from the orebody. Geochemical data obtained from portable X-ray fluorescence (p-XRF) and petrophysical data acquired from a magnetic susceptibility meter and a gamma-ray spectrometer support the mineralogical data and help to accurately identify mineral halos in rocks surrounding the ore zone. Specifically, the combination of mineralogical data with multielement data such as P, Mn, As, P, and U obtained from p-XRF and positive U anomalies from radiometric measurements has potential to direct an exploration program toward higher Cu-Au grades.

The geologic history of seawater oxygen isotopes from marine iron oxides

Science ◽  
2019 ◽  
Vol 365 (6452) ◽  
pp. 469-473 ◽  
Author(s):  
Nir Galili ◽  
Aldo Shemesh ◽  
Ruth Yam ◽  
Irena Brailovsky ◽  
Michal Sela-Adler ◽  
...  
Keyword(s):  
Iron Oxide ◽  
Oxygen Isotope ◽  
Iron Oxides ◽  
Isotope Composition ◽  
Geologic History ◽  
Temperature Dependent ◽  
Oxygen Isotope Fractionation ◽  
History Of ◽  
Sediment Cover

The oxygen isotope composition (δ18O) of marine sedimentary rocks has increased by 10 to 15 per mil since Archean time. Interpretation of this trend is hindered by the dual control of temperature and fluid δ18O on the rocks’ isotopic composition. A new δ18O record in marine iron oxides covering the past ~2000 million years shows a similar secular rise. Iron oxide precipitation experiments reveal a weakly temperature-dependent iron oxide–water oxygen isotope fractionation, suggesting that increasing seawater δ18O over time was the primary cause of the long-term rise in δ18O values of marine precipitates. The18O enrichment may have been driven by an increase in terrestrial sediment cover, a change in the proportion of high- and low-temperature crustal alteration, or a combination of these and other factors.

Uranium–lead ages of apatite from iron oxide ores of the Bafq District, East-Central Iran

2010 ◽  
Vol 46 (1) ◽  
pp. 9-21 ◽  
Author(s):  
Heinz-Günter Stosch ◽  
Rolf L. Romer ◽  
Farahnaz Daliran ◽  
Dieter Rhede
Keyword(s):  
Iron Oxide ◽  
Central Iran ◽  
East Central

Isotopic (K-Ar and oxygen) constraints on the extent and importance of the Liassic hydrothermal activity in western Europe

Clay Minerals ◽  
1996 ◽  
Vol 31 (3) ◽  
pp. 301-318 ◽  
Author(s):  
N. Clauer ◽  
H. Zwingmann ◽  
S. Chaudhuri
Keyword(s):  
Oxygen Isotope ◽  
Western Europe ◽  
Hydrothermal Activity ◽  
Gas Generation ◽  
Mineral Phases ◽  
Crystallization Conditions ◽  
Heat Pulses ◽  
Host Rocks ◽  
Hydrothermal Activities

AbstractThe K-Ar dates and oxygen isotope data of illite-to-mica mineral phases in Permian to Triassic sandstones from Germany and Libya have been compared to previously published results of similar minerals of Liassic ages taken from lithologically similar rocks in several sites in western Europe and northern Africa. The widespread Liassic age for the micaceous mineral phases can be related to abnormal heat pulses induced by pre-rifting conditions. The temperatures in most cases appeared to be in the 150–220°C range. Some of these hydrothermal activities were responsible for both gas generation and U and Pb-Zn concentrations.An approach combining K-Ar isotope dates and oxygen isotope signatures provides a framework for the characterization of the clay separates used in isotopic investigations and for depicting any crystallization conditions. The trend in decreases in δ18O values relative to increases in K-Ar dates, while the size of the clay fractions in a single sample increases, is indicative of detrital contamination. Varied trends in the δ18O values at constant K-Ar dates for clay fractions with increase in size might be indicative of changes in the pore volume of the host rocks.

Silicate melt inclusions from a mildly peralkaline granite in the Oslo paleorift, Norway

1990 ◽  
Vol 54 (375) ◽  
pp. 195-205 ◽  
Author(s):  
T. H. Hansteen ◽  
W. J. Lustenhouwer
Keyword(s):  
Fluid Inclusions ◽  
Melt Inclusions ◽  
Aqueous Fluid ◽  
Silicate Melt ◽  
Silicate Melts ◽  
Magmatic Fluid ◽  
Chemical Characteristics ◽  
Quartz Crystals ◽  
Fluid Interaction ◽  
Miarolitic Cavities

AbstractThe mildy peralkaline Eikeren-Skrim granite belongs to the Permian magmatic province of the Oslo rift, south-east Norway. Euhedral quartz crystals from the abundant miarolitic cavities contain primary inclusions of partly crytallized silicate melts and coexisting primary, aqueous fluid inclusions. Micro-thermometric measurements give maximum estimates for the granite solidus of 685–705°C. Quenched silicate melt inclusions are not peralkaline, have normative Or/Ab weight ratios of 1.15–1.44 (compared to 0.49–0.80 in whole-rock samples) and F and Cl contents of 0.1 and 0.21–0.65 wt. %, respectively. Coexisting magmatic fluid inclusions are highly enriched in Na, Cl, S and to some extent K. These chemical characteristics are the results of late-magmatic melt-mineral-fluid interaction in the miarolitic cavities.

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