Geochemical data from Precambrian meta-iron-formation and related rocks of the Keystone area, South Dakota

1981 ◽  
Author(s):  
William H. Raymond
Keyword(s):  
South Dakota ◽  
Iron Formation ◽  
Geochemical Data

scholarly journals Sedimentary mechanisms of a modern banded iron formation on Milos Island, Greece

Solid Earth ◽  
2018 ◽  
Vol 9 (3) ◽  
pp. 573-598 ◽  
Author(s):  
Ernest Chi Fru ◽  
Stephanos Kilias ◽  
Magnus Ivarsson ◽  
Jayne E. Rattray ◽  
Katerina Gkika ◽  
...  
Keyword(s):  
Large Scale ◽  
Carbonaceous Material ◽  
Iron Formation ◽  
Geochemical Data ◽  
Formation Mechanisms ◽  
Banded Iron Formation ◽  
Crystalline Quartz ◽  
Tectonic Processes ◽  
Iron Deposits ◽  
Amorphous Si

Abstract. An early Quaternary shallow submarine hydrothermal iron formation (IF) in the Cape Vani sedimentary basin (CVSB) on Milos Island, Greece, displays banded rhythmicity similar to Precambrian banded iron formation (BIF). Field-wide stratigraphic and biogeochemical reconstructions show two temporal and spatially isolated iron deposits in the CVSB with distinct sedimentological character. Petrographic screening suggests the presence of a photoferrotrophic-like microfossil-rich IF (MFIF), accumulated on a basement consisting of andesites in a ∼ 150 m wide basin in the SW margin of the basin. A banded nonfossiliferous IF (NFIF) sits on top of the Mn-rich sandstones at the transition to the renowned Mn-rich formation, capping the NFIF unit. Geochemical data relate the origin of the NFIF to periodic submarine volcanism and water column oxidation of released Fe(II) in conditions predominated by anoxia, similar to the MFIF. Raman spectroscopy pairs hematite-rich grains in the NFIF with relics of a carbonaceous material carrying an average δ13Corg signature of ∼ −25‰. A similar δ13Corg signature in the MFIF could not be directly coupled to hematite by mineralogy. The NFIF, which postdates large-scale Mn deposition in the CVSB, is composed primarily of amorphous Si (opal-SiO2 ⋅ nH2O) while crystalline quartz (SiO2) predominates the MFIF. An intricate interaction between tectonic processes, changing redox, biological activity, and abiotic Si precipitation are proposed to have collectively formed the unmetamorphosed BIF-type deposits in a shallow submarine volcanic center. Despite the differences in Precambrian ocean–atmosphere chemistry and the present geologic time, these formation mechanisms coincide with those believed to have formed Algoma-type BIFs proximal to active seafloor volcanic centers.

scholarly journals Geologic interpretation of aeromagnetic and chemical data from the Oaks Belt, Wabigoon subprovince, Minnesota: implications for Au-rich VMS deposit exploration

2016 ◽  
Vol 53 (2) ◽  
pp. 176-188 ◽  
Author(s):  
Michael D. Hendrickson
Keyword(s):  
Base Metal ◽  
Volcanic Rocks ◽  
Correlation Coefficients ◽  
Massive Sulfide ◽  
Iron Formation ◽  
Geochemical Data ◽  
Volcanic Complex ◽  
Sulfide Deposits ◽  
Massive Sulfide Deposits ◽  
Subvolcanic Intrusion

The Oaks Belt (OB) is a Neoarchean volcanic complex located in northwestern Minnesota, USA. It is part of the Wabigoon granite–greenstone terrane that hosts the world-class Rainy River gold deposit in nearby Ontario, Canada. Rocks in the OB form a north-dipping homocline in the fault-bounded pressure shadow of a sigma-shaped volcano-plutonic wedge that spans east–west for 220 km across the Minnesota, USA – Ontario, Canada border. Exploration drilling in the area delineated pyrrhotite–pyrite massive sulfide deposits, iron formation, chert, and semi-massive sphalerite mineralized zones. High-resolution aeromagnetic data indicate a large (∼60 km2) composite subvolcanic intrusion underlies these iron-rich strata in the OB. The position of this inferred intrusion elucidates the low base metal content of known massive sulfide deposits, as they were too far away (6–10 km) from a heat source to have been favorable sites for base metal deposition. The relative abundance of Au and Zn in the OB, alongside correlation coefficients between metals in massive sulfide deposits, iron formation, and chert, indicates the rocks were affected by a low-temperature hydrothermal system under relatively shallow water conditions (<1000 m). Negative correlation between Na2O and CaO in basalt, and their mutual moderate positive correlation with immobile corundum (Al2O3), implies alteration in the upper part of the volcanic pile did not result in substantial element mobility in most samples. Geochemical data from mafic and felsic volcanic rocks plot mainly in the calc-alkaline field. Thus, the OB is most prospective for hosting Au-rich VMS deposits and future exploration should focus on paleo-thermal corridors and favorable stratigraphic horizons near the newly inferred composite subvolcanic intrusion.

scholarly journals Unsupervised geochemical classification and automatic 3D mapping of the Bolshetroitskoe high-grade iron ore deposit (Belgorod Region, Russia)

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Andrey O. Kalashnikov ◽  
Ivan I. Nikulin ◽  
Dmitry G. Stepenshchikov
Keyword(s):  
Iron Ore ◽  
Geological Mapping ◽  
Iron Formation ◽  
Geochemical Data ◽  
High Grade ◽  
Banded Iron Formation ◽  
Raw Data ◽  
Ore Deposit ◽  
Iron Ore Deposit ◽  
Log Ratio

Abstract We stated and solved three successive problems concerning automatization of geological mapping using the case of the Bolshetroitskoe high-grade iron ore deposit in weathered crust of Banded Iron Formation (Kursk Magnetic Anomaly, Belgorod Region, Russia). (1) Selecting a classification (clustering) method of geochemical data without reference sampling, i.e., solution of an “unsupervised clustering task”. We developed 5 rock classifications based on different principles, i.e., classification by visual description, by distribution of economic component (Fe2O3), by cluster analysis of raw data and centered log-ratio transformation of the raw data, and by artificial neural network (Kohonnen’s self-organized map). (2) Non-parametric comparison of quality of the classifications and revealing the best one. (3) Automatic 3D geological mapping in accordance with the best classification. The developed approach of automatic 3D geological mapping seems to be rather simple and plausible.

Pickle Lake revisited: New structural, geochronological and geochemical constraints on greenstone belt assembly, western Superior Province, Canada

2006 ◽  
Vol 43 (7) ◽  
pp. 821-847 ◽  
Author(s):  
M D Young ◽  
V McNicoll ◽  
H Helmstaedt ◽  
T Skulski ◽  
J A Percival
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Tholeiitic Basalt ◽  
Pyroclastic Flows ◽  
Iron Formation ◽  
Geochemical Data ◽  
Superior Province ◽  
Isotopic Compositions ◽  
Isotopic Analyses ◽  
Two Samples

New field work, U–Pb ages, geochemical data, and Sm–Nd isotopic analyses have established the timing and determined the nature of volcanism, deformation, and tectonic assembly of the Pickle Lake greenstone belt in the Uchi subprovince of the western Superior Province of the Canadian Shield. The >2860 Ma Pickle Crow assemblage has been redefined to include the former Northern Pickle assemblage on the basis of stratigraphic continuity and similar volcanic geochemistry between the two units across a previously inferred fault contact. The Pickle Crow assemblage consists of tholeiitic basalt with thin, but laterally extensive, oxide-facies iron formation overlain by alkalic basalts and minor calc-alkaline andesites to dacites with primitive Nd isotopic compositions (εNd2.89 Ga = +2.1 to +2.4) suggestive of deposition in a sediment-starved oceanic basin. The ~2 km thick ~2836 Ma Kaminiskag assemblage (former Woman assemblage) consists of tholeiitic basalt interbedded with intermediate and rare felsic pyroclastic flows with primitive Nd isotopic compositions (εNd2.836 Ga = +2.4). Two samples of intermediate volcanic rocks interbedded with southeast-younging pillowed basalt, previously inferred to be part of the Pickle Crow assemblage, yielded U–Pb zircon ages of 2744 [Formula: see text] Ma and 2729 ± 3 Ma. These rocks are thus part of the younger Confederation assemblage, which consists of intercalated basalt and dacite (εNd2.74 Ga = +0.1 to +0.8) exhibiting diverse compositions probably reflecting eruption in a continental margin arc to back-arc setting. The contact between the Confederation and Kaminiskag assemblages is assumed to be a fault. The greenstone belt is intruded by late syn- to posttectonic plutons including the composite quartz dioritic to gabbroic July Falls stock with a new U–Pb zircon age of 2749 [Formula: see text] Ma, and the ~2741 to 2740 Ma trondhjemitic to granodioritic Ochig Lake pluton and Pickle Lake stock, as well as the ~2697 to 2716 Ma Hooker–Burkoski stock. The earliest recognized deformation (D1) is recorded by a local bedding-parallel foliation in the Pickle Crow assemblage. This foliation is truncated by the ~2735 Ma Albany quartz–feldspar porphyry dyke and is not recognized in the volcanic rocks of the Confederation assemblage. The early deformation event is attributed to overturning of the Pickle Crow assemblage prior to deposition of the ~2744 to 2729 Ma Confederation assemblage. Subsequent deformation and development of a regionally penetrative planar fabric (S2) postdates ~2729 Ma volcanism, pre-dates the intrusion of the ca. <2716 Ma Hooker–Burkoski stock and is host to gold mineralization.

scholarly journals The Proterozoic Guanhães banded iron formations, Southeastern border of the São Francisco Craton, Brazil: evidence of detrital contamination

2017 ◽  
Vol 17 (2) ◽  
pp. 303 ◽  
Author(s):  
Vitor Rodrigues Barrote ◽  
Carlos Alberto Rosiere ◽  
Vassily Khoury Rolim ◽  
João Orestes Schneider Santos ◽  
Neal Jesse Mcnaughton
Keyword(s):  
Detrital Zircons ◽  
Iron Formation ◽  
Geochemical Data ◽  
Banded Iron Formations ◽  
Banded Iron Formation ◽  
Zircon Age ◽  
Shallow Marine ◽  
Eu Anomaly ◽  
Depositional Age ◽  
Iron Formations

The Guanhães banded iron formation (BIF) bearing succession occurs as tectonic slices, juxtaposed to Archean TTG granite-gneissic basement rock, developed during the Neoproterozoic-Cambrian Brasiliano collage. The succession has a maximum depositional age of ~2.18 Ga, from detrital zircons in quartzite, and consists of quartzites, schists, BIFs, gneiss and amphibolite, all metamorphosed under amphibolite facies conditions. The Guanhães BIF shows HREE enrichment and consistent positive Eu anomaly (PAAS-normalized REE+Y). Two types of contamination were observed in the samples. The first is contamination by an exotic detrital component, which resulted in low Y/Ho (<30) and Pr/Yb (SN) ratios. Evidence of such contamination, combined with inferred stratigraphic stacking data, indicates that the Guanhães BIFs were deposited on a shallow marine environment. The second type of contamination resulted in higher Eu-anomalies, positive Ce-anomalies, and higher REE+Y concentrations, possibly due to the interaction between later magmatic fluids and the Guanhães BIF. A strong Cambrian event is recorded in zircon age data. The uncontaminated samples display REE+Y distribution similar to other Precambrian BIFs, particularly those from the Morro-Escuro Sequence and the Serra da Serpentina Group, without true Ce-anomalies and Y/Ho close to seawater values (45). Geochronological and geochemical data presented in this paper strongly suggest a correlation between the Guanhães supracrustal succession and the Serra da Serpentina and Serra de São José Groups.

scholarly journals NOVAS EVIDÊNCIAS DE REMANESCENTES OCEÂNICOS NA FAIXA ARAÇUAÍ: AS ROCHAS META-ULTRAMÁFICAS DE SÃO JOSÉ DA SAFIRA

2000 ◽  
Author(s):  
Laurenn Wolochate Aracema ◽  
Ana Carolina Neves ◽  
Juliana Cristina Henriques Ferreira ◽  
Antônio Carlos Pedrosa-Soares ◽  
Lydia Maria Lobato ◽  
...  
Keyword(s):  
Silicate Rock ◽  
Iron Formation ◽  
Geochemical Data ◽  
Ultramafic Rocks ◽  
Mica Schist ◽  
Banded Iron Formation ◽  
Magnetic Oxide ◽  
Ophiolitic Mélange ◽  
Eastern Brazil ◽  
Minas Gerais State

Neoproterozoic oceanic slivers have been characterized in the Araçuaí Belt, eastern Brazil. Close to the SãoJosé da Safira town, Minas Gerais State, meta-ultramafic rocks consist of serpentinite with preservedperidotite cores, talc-anthophyllite schists, a diopside-rich rock, and tremolite schist. They are closelyassociated with banded iron formation (magnetic oxide, sulfide and silicate types), muscovite schist andgraphite schist. This rock assemblage is interpreted as an ophiolitic mélange emplaced by thrusts betweentwo different units. One of them, correlated to the Salinas Formation, consists of quartz-mica schist (withgarnet, staurolite, kyanite, and/or sillimanite), sedimentary-derived calc-silicate rock, and sparseorthoamphibolite. The unit correlated to the Capelinha Formation consists of orthoquartzite, hematite andmica quartzites. All described rocks were transported from NE to SW in response to a dextral, obliquethrustsystem. Geochemical data from metaultramafic rocks of São José da Safira indicate an ophioliticorigin. The comparison with data from other Neoproterozoic oceanic remnants (Abadiânia and Fuchuan)corroborates this interpretation.

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