Auriferous chert, banded iron formation, and related volcanogenic hydrothermal alteration, Atik Lake, Manitoba

1989 ◽  
Vol 26 (12) ◽  
pp. 2676-2690 ◽  
Author(s):  
Louis R. Bernier ◽  
Wallace H. MacLean
Keyword(s):  
Hydrothermal Alteration ◽  
Earth Element ◽  
Massive Sulfide ◽  
Iron Formation ◽  
Small Scale ◽  
Banded Iron Formation ◽  
Sulfide Deposits ◽  
Sea Floor ◽  
Facies Metamorphism ◽  
Altered Basalt

Small-scale alteration pipes and stratiform alteration in Archean glomeroporphyritic tholeiitic basalts at Atik Lake, Manitoba, stratigraphically underlie silicate-oxide banded iron formation (BIF) and auriferous sulfide-bearing chert. The auriferous chert is locally interbedded with graphitic argillite, indicating euxinic conditions during deposition. Cordierite–gedrite rocks formed by recrystallization of alteration assemblages during the lower amphibolite-facies metamorphism (T = 550 °C, P = 2.5 kbar). Al2O3, TiO2, Zr, and Nb, which were relatively immobile during alteration, have been used to monitor igneous differentiation and alteration. Volcanogenic hydrothermal alteration resulted in depletion of Ca, Si, Mg, Na, and Sr in the altered basalt and the addition of K, Fe, Rb, and Ba. This was accompanied by mass and volume losses of up to 25%. The mineralizing fluid was reducing and somewhat acidic. Rare-earth-element (REE) profiles of BIF and graphitic argillite, normalized to Archean shale, are less steep ((La/Lu)N = 0.51 and 0.49 respectively), than those of both mineralized chert ((La/Lu)N = 0.04) and recent sea-floor, siliceous, gold-enriched massive sulfides ((La/Lu)N = 0.11). REE profiles and Boström's plot suggest that the auriferous, sulfide-bearing chert formed by mixing of hydrothermal and detrital components. The overall chemical changes in the Atik Lake alteration system are comparable to those in Noranda-type massive-sulfide deposits. The trace-metal association in the auriferous chert is similar to that at some modern sea-floor hydrothermal sites.

scholarly journals Tsunami Deposits on a Paleoproterozoic Unconformity? The 2.2 Ga Yerrida Marine Transgression on the Northern Margin of the Yilgarn Craton, Western Australia

2021 ◽  
Author(s):  
Desmond Lascelles ◽  
Ryan J. Lowe
Keyword(s):  
Broad Band ◽  
Iron Formation ◽  
Yilgarn Craton ◽  
Banded Iron Formation ◽  
Marine Transgression ◽  
Sea Floor ◽  
Northern Margin ◽  
Fine Grained ◽  
Western Side ◽  
Cut Surface

Large blocks and boulders of banded iron formation and massive hematite up to 40 x 27 x 6 m and in excess of 10,000 metric tonnes were detached from outcrop of the Wilgie Mia Formation during the ca 2.20 Ga marine transgression at the base of the Paleoproterozoic Windplain Group, and deposited in a broad band on the wave-cut surface 900 to 1200 m to the east. At the same time sand and shingle was scoured from the sea floor, leaving remnants only on the western side of the Wilgie Mia Formation and on the eastern sides of the boulders. Evidence suggesting that the blocks were detached and transported and the sea floor scoured by a tsunami bore with a height of at least 40 m is provided by (1) the deposition of the blocks indicates transportation by a unidirectional sub-horizontal force, whereas the smaller boulders are randomly oriented (2) 900 -1200m separating the BIF outcrop and the blocks (3) the absence of the basal conglomerate between the blocks (4) the blocks and boulders rest directly on the wave-cut surface of deeply weathered amphibolites (5) the blocks and boulders are surrounded and overlain by fine-grained sandstone of the Windplain Group.

scholarly journals Channelized CO2-Rich Fluid Activity along a Subduction Interface in the Paleoproterozoic Wutai Complex, North China Craton

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 748
Author(s):  
Bin Wang ◽  
Wei Tian ◽  
Bin Fu ◽  
Jia-Qi Fang
Keyword(s):  
Phase Equilibrium ◽  
Subduction Zone ◽  
North China Craton ◽  
Hydrothermal Fluid ◽  
North China ◽  
Hydrothermal Fluids ◽  
Iron Formation ◽  
Banded Iron Formation ◽  
Facies Metamorphism ◽  
Chlorite Schist

Greenschist facies metabasite (chlorite schist) and metasediments (banded iron formation (BIF)) in the Wutai Complex, North China Craton recorded extensive fluid activities during subduction-related metamorphism. The pervasive dolomitization in the chlorite schist and significant dolomite enrichment at the BIF–chlorite schist interface support the existence of highly channelized updip transportation of CO2-rich hydrothermal fluids. Xenotime from the chlorite schist has U concentrations of 39–254 ppm and Th concentrations of 121–2367 ppm, with U/Th ratios of 0.11–0.62, which is typical of xenotime precipitated from circulating hydrothermal fluids. SHRIMP U–Th–Pb dating of xenotime determines a fluid activity age of 1.85 ± 0.07 Ga. The metasomatic dolomite has δ13CV-PDB from −4.17‰ to −3.10‰, which is significantly lower than that of carbonates from greenschists, but similar to the fluid originated from Rayleigh fractionating decarbonation at amphibolite facies metamorphism along the regional geotherm (~15 °C/km) of the Wutai Complex. The δ18OV-SMOW values of the dolomite (12.08–13.85‰) can also correspond to this process, considering the contribution of dehydration. Based on phase equilibrium modelling, we ascertained that the hydrothermal fluid was rich in CO2, alkalis, and silica, with X(CO2) in the range of 0.24–0.28. All of these constraints suggest a channelized CO2-rich fluid activity along the sediment–basite interface in a warm Paleoproterozoic subduction zone, which allowed extensive migration and sequestration of volatiles (especially carbon species) beneath the forearc.

scholarly journals Tsunami Deposits on a Paleoproterozoic Unconformity? The 2.2 Ga Yerrida Marine Transgression on the Northern Margin of the Yilgarn Craton, Western Australia

2021 ◽  
Vol 9 (2) ◽  
pp. 213
Author(s):  
Desmond F. Lascelles ◽  
Ryan J. Lowe
Keyword(s):  
Broad Band ◽  
Iron Formation ◽  
Banded Iron Formations ◽  
Banded Iron Formation ◽  
Marine Transgression ◽  
Sea Floor ◽  
Northern Margin ◽  
Fine Grained ◽  
Western Side ◽  
Cut Surface

Large blocks and boulders of banded iron formations and massive hematite up to 40 × 27 × 6 m3 and in excess of 10,000 metric tonnes were detached from an outcrop of the Wilgie Mia Formation during the ca 2.20 Ga marine transgression at the base of the Paleoproterozoic Windplain Group and deposited in a broad band on the wave-cut surface 900 to 1200 m to the east. At the same time, sand and shingle were scoured from the sea floor, leaving remnants only on the western side of the Wilgie Mia Formation and on the eastern sides of the boulders. Evidence suggesting that the blocks were detached and transported and the sea floor scoured by a tsunami bore with a height of at least 40 m is provided by the following: (1) the deposition of the blocks indicates transportation by a unidirectional sub-horizontal force, whereas the smaller boulders are randomly oriented; (2) 900–1200 m separates the banded iron formation (BIF) outcrop and the blocks (3) there is an absence of the basal conglomerate between the blocks; (4) the blocks and boulders rest directly on the wave-cut surface of deeply weathered amphibolites; (5) the blocks and boulders are surrounded and overlain by fine-grained sandstone of the Windplain Group.

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