scholarly journals Chlorine Isotope Composition of Apatite from the >3.7 Ga Isua Supracrustal Belt, SW Greenland

Minerals ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 27 ◽  
Author(s):  
Alicja Wudarska ◽  
Ewa Słaby ◽  
Michael Wiedenbeck ◽  
Łukasz Birski ◽  
Richard Wirth ◽  
...  
Keyword(s):  
Secondary Ion Mass Spectrometry ◽  
Extreme Values ◽  
Isotope Composition ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Chlorine Isotope ◽  
Apatite Crystals ◽  
Metavolcanic Rocks ◽  
Supracrustal Belt ◽  
Imaging And Spectroscopy

The study of the oldest surviving rock suites is crucial for understanding the processes that shaped the early Earth and formed an environment suitable for life. The metasedimentary and metavolcanic rocks of the early Archean Isua supracrustal belt contain abundant apatite, the geochemical signatures of which may help decipher ancient environmental conditions. However, previous research has shown that secondary processes, including amphibolite-facies metamorphism, have reset the original hydrogen isotope composition (δD) of apatite from the Isua belt; therefore, δD values are not indicative of primary conditions in the Archean. Here, we report the first in situ chlorine isotope (δ37Cl) analyses by Secondary Ion Mass Spectrometry (SIMS) from Isua apatite, which we combine with information from transmission electron microscopy, cathodoluminescence imaging, and spectroscopy, documenting the micron-scale internal features of apatite crystals. The determined δ37ClSMOC values (chlorine isotope ratios vs. standard mean ocean chloride) fall within a range from −0.8‰ to 1.6‰, with the most extreme values recorded by two banded iron formation samples. Our results show that δ37Cl values cannot uniquely document primary signatures of apatite crystals, but the results are nonetheless helpful for assessing the extent of secondary overprint.

scholarly journals Early (3700 Ma) Archaean rocks of the Isua supracrustal belt and adjacent gneisses

1983 ◽  
Vol 112 ◽  
pp. 5-22
Author(s):  
A.P Nutman ◽  
D Bridgwater ◽  
E Dimroth ◽  
R.C.O Gill ◽  
M Rosing
Keyword(s):  
Amphibolite Facies ◽  
Iron Formation ◽  
Ultramafic Rocks ◽  
Banded Iron Formation ◽  
Sedimentary Structures ◽  
The North ◽  
Gneiss Complex ◽  
Supracrustal Belt ◽  
Silicate Rocks

A coherent stratigraphy is recognised in the highly deformed, amphibolite facies early Archaean Isua supracrustal belt. The supracrustal belt consists of layered rocks (in which sedimentary structures are locally preserved), ultramafic rocks and units of garbenschiefer (a massive Mg-Al rich, leucoamphibolite). The layered supracrustal rocks form two sequences, which are separated from each other tectonically. When folding is taken into account, these sequences are now less than 200 m thick. Sequence A forms most of the belt. In it there is a transition upwards from predominantly layered amphibolites with banded iron formation horizons to calc-silicate rocks, carbonates and layered felsic metasediments. Sequence B is restricted to the western edge of the eastern part of the supracrustal belt. It changes upwards from predominantly layered felsic metasediments to ferromagnesian mica schists. The supracrustal belt is regarded as a thin fragment from a thicker, more extensive volcanosedimentary pile. The early Archaean gneisses adjacent to the supracrustal belt consist of early multiphase tonalites which were first intruded by mafic dioritic dykes and then by granitic sheets. The granitic sheets were originaIly horizontal to gently inciined and form up to 40 per cent of the gneiss complex. Interdigitation of supracrustal rocks and gneisses in the Isukasia area is due to both the style of intrusion ofthe gneisses and to tectonic intercalation. Archaean basic dykes that cut the supracrustal belt and adjacent gneisses are ofseveral generations. Within and south of the supracrustal belt they are generally strongly deformed and have been recrystallised under amphibolite facies conditions; but in the north of the area they are generally better preserved. The dykes cut across several generations of structures in the supracrustal belt and the adjacent gneisses.

scholarly journals The early Archaean to Proterozoic history of the Isukasia area, southern West Greenland

1986 ◽  
Vol 154 ◽  
pp. 1-80
Author(s):  
A.P Nutman
Keyword(s):  
Volcanic Rocks ◽  
Amphibolite Facies ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Stratigraphic Sequence ◽  
Supracrustal Belt ◽  
History Of ◽  
High Grade Metamorphism ◽  
Polyphase Metamorphism ◽  
Chemical Sediments

The c. 3800 Ma Isua supracrustal belt and associated smaller bodies of supracrustal rocks are intruded by >3600 Ma orthogneisses. A coherent stratigraphic sequence is recognised consisting of interlayered metabasic rocks, metasediments derived from volcanic rocks, chemical sediments, and metabasic and ultramafic intrusions. Despite repeated deformation and high-grade metamorphism sedimentary structures are locally preserved. The depositional environment was probably an immersed volcanic region remote from areas of significantly older crust. Conglomeratic structures in a metachert and banded iron formation unit suggest shoaling and shallow water conditions. Felsic sediments locally preserve evidence of deposition from turbidite flows. The Isua supracrustal rocks are regarded as thin fragments of a thicker, more extensive sequence. The orthogneisses that intrude the supracrustal rocks consist of 3750-3700 Ma multiphase tonalites (the grey gneisses) which were first intruded by the basic Inaluk dykes, then by abundant shallow-dipping swarms of c. 3600 Ma granite sheets (the white gneisses) and finally by c. 3400 Ma pegmatitic gneiss sheets. These early Archaean rocks were metamorphosed under amphibolite facies conditions and repeatedly deformed prior to intrusion of the Tarssartôq basic dykes in the mid Archaean. In the late Archaean (3100-2500 Ma) there was polyphase metamorphism up to amphibolite facies grade and two or more stages of deformation and local intrusion of granitic gneiss sheets and pegmatites. However, despite general strong deformation there is a large augen of low deformation preserved within the arc of the Isua supracrustal belt. During the Proterozoic there was intrusion of basic dykes, major faulting with associated recrystallisation under uppermost greenschist to lowermost amphibolite facies conditions, followed by heating and intrusion of acid dykes at c. 1600 Ma. No profitable mineralisations have been located.

Biological Fe oxidation controlled deposition of banded iron formation in the ca. 3770Ma Isua Supracrustal Belt (West Greenland)

2013 ◽  
Vol 363 ◽  
pp. 192-203 ◽  
Author(s):  
Andrew D. Czaja ◽  
Clark M. Johnson ◽  
Brian L. Beard ◽  
Eric E. Roden ◽  
Weiqiang Li ◽  
...  
Keyword(s):  
Iron Formation ◽  
Banded Iron Formation ◽  
West Greenland ◽  
Fe Oxidation ◽  
Supracrustal Belt ◽  
Controlled Deposition

scholarly journals A Fonte dos Metais da Mina de Ouro do Schramm, Santa Catarina: Evidências de Dados de Isótopos de Pb e Elementos Terras Raras

2005 ◽  
Vol 32 (1) ◽  
pp. 51
Author(s):  
FLÁVIO FRANÇA NUNES DA ROCHA ◽  
ARTUR CEZAR BASTOS NETO ◽  
MARCUS VINÍCIUS DORNELLES REMUS ◽  
VITOR PAULO PEREIRA
Keyword(s):  
Gold Mineralization ◽  
Isotope Composition ◽  
Shear Zones ◽  
Iron Formation ◽  
Gold Mine ◽  
Banded Iron Formations ◽  
Banded Iron Formation ◽  
Santa Catarina ◽  
Lead Isotope Composition ◽  
Ree Patterns

The source of the ore elements in the Schramm gold mine, localized in central part of Santa Catarina shield, has been constrained based on lead isotope composition of galena and sulfosalts, and the rare earth element (REE) patterns of the ore. The Pb207/ Pb206 model age obtained in galena and lillianite-gustavite series from the mineralization yields an age of 1.88 Ga. It is higher than the estimated age of the deposit (» 534 Ma). The Pb isotopic composition obtained in these minerals indicates that the age of Schramm mine source is similar to that of the galena of the Ribeirão da Prata mine (Pb-Zn-Cu-Ag). This mine is located 25 Km southwest of the Schramm gold mine witch is hosted in the tension fracture zone conjugated with the first order shear zone that contains the Ribeirão da Prata deposit. The similarities between Pb-isotope compositions of both deposits could indicate that they were contemporaneous and derived from the same regional lead source. The REE patterns of the ore samples of Schramm mine are similar to that of the pyroxenites and banded iron formations from the Archean Santa Catarina Granulitic Complex that host the Schramm gold mine. They present low REE contents with flat patterns and lack Eu anomalies. The comparison among the isotopic data from this mine with those from other places indicates that the banded iron formation and mafic-ultramafic granulitic gneisses are the source of the gold mineralization. This evidence agreed with the hypothesis that the ore fluids were derived from retrogressive metamorphism reactions of Santa Catarina Granulitic Complex in the shear zones during the final stage of Brasiliano orogenic cycle.

scholarly journals Invisible Gold in Pyrite from Epithermal, Banded-Iron-Formation-Hosted, and Sedimentary Gold Deposits: Evidence of Hydrothermal Influence

Minerals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 447 ◽  
Author(s):  
Yuichi Morishita ◽  
Napoleon Q. Hammond ◽  
Kazunori Momii ◽  
Rimi Konagaya ◽  
Yuji Sano ◽  
...  
Keyword(s):  
Secondary Ion Mass Spectrometry ◽  
Gold Deposits ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Field Range ◽  
Invisible Gold ◽  
Epithermal Deposits ◽  
As Relationship ◽  
Low Sulfidation ◽  
The Relationship

“Invisible gold” in pyrite is defined as an Au solid solution of the pyrite lattice, sub-microscopic Au nanoparticles (NPs) in the pyrite, or other chemisorption complexes of Au. Because the relationship between the Au and As concentrations in pyrite could indicate the genesis of the deposit, the purpose of this study is to assess the micro-analytical characteristics of the Au–As relationship in pyrite from epithermal and hydrothermally affected sedimentary Au deposits by secondary ion mass spectrometry. The Au and As concentrations in pyrite vary from 0.04 to 30 ppm and from 1 to 1000 ppm, respectively, in the high-sulfidation Nansatsu-type epithermal deposits; these concentrations are both lower than those of the low-sulfidation epithermal Hishikari deposit. The Au concentrations in pyrrhotite and pyrite reach 6 and 0.3 ppm, respectively, in the Kalahari Goldridge banded-iron-formation-hosted gold deposit, and Au in pyrrhotite may sometimes exist as NPs, whereas As concentrations in pyrrhotite and pyrite are both low and lie in a narrow range from 6 to 22 ppm. Whether Au is present as NPs is important in ore dressing. The Au and As concentrations in pyrite from the Witwatersrand gold field range from 0.02 to 1.1 ppm and from 8 to 4000 ppm, respectively. The shape of the pyrite grains might prove to be an indicator of the hydrothermal influence on deposits of sedimentary origin, which implies the genesis of the deposits.

Petro-Mineralogical and Geochemical Characterization of the Banded Irons Formations BIFs of the Nimba Range and its Western Extension (Nimba Region)

2019 ◽  
Vol 44 ◽  
pp. 99-134
Author(s):  
Mohamed Samuel Moriah Conté ◽  
Abdellah Boushaba ◽  
Ali Moukadiri
Keyword(s):  
Regional Metamorphism ◽  
Major Elements ◽  
Iron Formation ◽  
Banded Iron Formations ◽  
Banded Iron Formation ◽  
Metasedimentary Rocks ◽  
Republic Of Guinea ◽  
Metavolcanic Rocks ◽  
The Republic ◽  
Iron Formations

The Nimba Range and its western extension are located in the Nimba region on the borders of the Republic of Guinea, Liberia and Côte d'Ivoire. It is a mountainous region made up of metavolcanic and metasedimentary rocks. Metavolcanic rocks are gneisses, granites, amphibolites and quartzites, which constitute the lower part of Archean age. The upper part consists of Proterozoic rocks of metasedimentary origin. It contains important deposits of itabirites which occupy the top of the mountains and hills of the region. The petrographic study of the banded iron formations reveals the existence of silicate banded iron formations (SIF) and oxidized banded iron formations (OIF). The results of the scanning electron microscope (SEM) and metallogenic analyzes show the presence of iron minerals (magnetites, hematites, pyrites, goethites, martites and siderites). These analyzes also reveal the presence of the metamorphic index minerals associated with the banded iron formations, hence the existence of several types of ferriferous formations (silicate (SIF) and oxidized (OIF) banded iron formations). Overall, there is an increase in the degree of regional metamorphism from east to west of the Nimba region. The geochemical analysis of the banded iron formations reveals that with the exception of Na2O, all the major elements have a negative linear correlation although dispersed with Fe2O3. This correlation is explained by a decrease in quartz, garnet, micas (muscovite and biotite), amphibole, pyroxene, plagioclase, titanium and phosphorus contents. Conversely, there is an increase in iron ore content: magnetites, pyrites, hematites, goethite. But the alkali content remains constant in these banded iron formations. Then, the lower the Fe2O3content, the higher the FeO content, while those of SiO2and Al2O3are constant in all of these formations in the Nimba region except in the chlorite banded iron formation where both are anticorelated. Finally, the ratio SiO2/ Fe2O3vs MgO + CaO + MnO / Fe2O3of the banded iron formations of the Nimba region compared to the same formations of the whole world allows to give them Proterozoic age. Some itabirites have high levels of magnetite, hematite, and goethite (same feature as itabirites of Lac supérieur and Pic de fon) and only chlorite itabirite has a low to medium Mg-Si-BIF content.

scholarly journals Descriptive text to the Geological map of Greenland, 1:100 000, Kangaatisiaq 68 V.1 Syd and Ikamiut 68 V.1 Nord

2010 ◽  
pp. 1-41
Author(s):  
Adam A. Garde ◽  
Julie A. Hollis
Keyword(s):  
Sea Water ◽  
Ocean Floor ◽  
Iron Formation ◽  
Second Phase ◽  
Banded Iron Formation ◽  
Mafic Dykes ◽  
West Greenland ◽  
North East ◽  
Basement Rocks ◽  
Supracrustal Belt

The two adjacent Kangaatsiaq and Ikamiut map sheets cover a coastal area of central West Greenland in the northern part of the Palaeoproterozoic Nagssugtoqidian orogen. The map area is part of the Aasiaat domain, which almost entirely consists of Neoarchaean orthogneisses with intercalated metamorphosed volcano-sedimentary belts. The Aasiaat domain was partially reworked during the Nagssugtoqidian orogeny, but Palaeoproterozoic components are restricted to mafic dykes, the ≤1904 ± 8 Ma (2σ) Naternaq supracrustal belt east of Kangaatsiaq, and remnants of a c . 1850 Ma Palaeoproterozoic ocean-floor – arc-trench association on small islands north-east of Aasiaat. Undated, lithologically similar rocks occur on Hunde Ejlande north of Aasiaat. The Archaean volcano-sedimentary belts are up to 2 km thick and comprise fine-grained mafic and minor, intermediate amphibolite of ex- and intrusive origin, gabbro, leucogabbro-anorthosite, and biotite-garnet schist with common sillimanite pseudomorphs after andalusite. The c . 2.8 Ga Archaean orthogneiss is largely tonalitic besides minor dioritic and granodioritic components, and preserves intrusive relationships with some of the supracrustal belts. Sheet-like bodies of late-kinematic crustal melt granites are up to about 10 km in length and 2 km thick. One of these has yielded a zircon Pb-Pb age of 2748 ± 19 Ma (2σ). Up to kilometre-thick units of quartzo-feldspathic and locally garnet-bearing paragneisses also occur, some of which are younger than the orthogneisses. The Aasiaat domain has undergone two Archaean orogenic episodes, separated by injection of mafic dykes and sedimentation at its margins. Archaean deformation resulted in kilometre-scale, tight to isoclinals folds refolded by upright to overturned folds, and its southern part reached granulite facies P–T conditions with widespread partial melting. The Aasiaat domain also underwent heating during the Nagssugtoqidian orogeny, but only its northern part was tectonically reworked, resulting in an intense E–W- to NNE–SSW-trending structural grain associated with subhorizontal extension lineation. The Palaeoproterozoic Naternaq supracrustal belt in the eastern part of the Kangaatsiaq map area has a complex synformal structure and displays a prominent structural discordance against the underlying Archaean rocks; the belt also contains a second phase of SE-plunging, overturned folds. The Palaeoproterozoic ocean-floor – arc trench association on islands north-east of Aasiaat comprises pillow lava, manganiferous chlorite schist, chert, banded iron formation, graded aluminous schist, and siliceous sandstone, and points to the existence of a palaeosuture in this area. A Palaeogene picritic sill complex and a small exposure of sandstone form the c . 15 km long island group of Kitsissunnguit / Gronne Ejland in the north-eastern Ikamiut map area. Two contem-poraneous, N–S-trending mafic dykes were emplaced into the basement rocks south-west of the islands. One of these was hydraulically chilled and fractured during its emplacement, presumably due to contact with meteoric or sea water. Widespread hydrothermal alteration occurs along faults and joints in the basement rocks in the northern archipelago. The alteration may have been caused by circulation of magmatically heated meteoric or sea water during the development of the Cretaceous–Paleocene basalt province in West Greenland. No deposits of economic interest have been found in the Archaean rocks within the map area. A massive sulphide deposit in the Naternaq supracrustal belt was discovered and explored in the 1960s by Kryolitselskabet Oresund A/S, and a VHMS-style copper-gold-zinc mineralisation was reported in 2004 from Kitsissuarsuit / Hunde Ejlande by a local inhabitant. The potential for ornamental rocks is largely unexplored.

Earth’s Middle Ages: What Came after the GOE

2017 ◽  
Author(s):  
Donald Eugene Canfield
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Middle Ages ◽  
Atmospheric Oxygen ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Dissolved Iron ◽  
Great Oxidation Event ◽  
Low Levels ◽  
Substantial Rise

This chapter considers the aftermath of the great oxidation event (GOE). It suggests that there was a substantial rise in oxygen defining the GOE, which may, in turn have led to the Lomagundi isotope excursion, which was associated with high rates of organic matter burial and perhaps even higher concentrations of oxygen. This excursion was soon followed by a crash in oxygen to very low levels and a return to banded iron formation deposition. When the massive amounts of organic carbon buried during the excursion were brought into the weathering environment, they would have represented a huge oxygen sink, drawing down levels of atmospheric oxygen. There appeared to be a veritable seesaw in oxygen concentrations, apparently triggered initially by the GOE. The GOE did not produce enough oxygen to oxygenate the oceans. Dissolved iron was removed from the oceans not by reaction with oxygen but rather by reaction with sulfide. Thus, the deep oceans remained anoxic and became rich in sulfide, instead of becoming well oxygenated.

Sign in / Sign up

Export Citation Format

Share Document