Late Archaean Kenogamissi complex, Abitibi Subprovince, Ontario, Canada: doming, folding and deformation-assisted melt remobilisation during syntectonic batholith emplacement

2004 ◽  
Vol 95 (1-2) ◽  
pp. 297-307 ◽  
Author(s):  
Keith Benn
Keyword(s):  
Greenstone Belt ◽  
Shear Zones ◽  
Crystal Mush ◽  
Magmatic Differentiation ◽  
Late Archaean ◽  
Metavolcanic Rocks ◽  
Abitibi Subprovince ◽  
Crystalline Crust ◽  
Complex Structural ◽  
Highly Strained

ABSTRACTThe Kenogamissi complex represents a large exposure of folded Late Archaean crystalline crust exposed within the Abitibi Subprovince, Ontario, Canada. It is composed of an heterogeneous amphibolite-grade orthogneiss unit, and several generations of batholiths and plutons of tonalite, granodiorite and granite composition. Together, the various units represent granitic magmatism during the period from 2740 Ma to 2660 Ma. Structural mapping and petrographic studies were focused on the orthogneiss unit (2723 Ma), on the newly defined Roblin tonalitegranodiorite batholith (ca. 2713 Ma) and on the highly strained metavolcanic rocks within the deformation aureole that surrounds the Kenogamissi complex. Structural analysis indicates that the Kenogamissi complex was emplaced into the greenstones as a dome that caused severe flattening and recumbent F2 refolding of earlier F1 folds in the deformation aureole. Doming is interpreted to be caused by the emplacement and inflation of tonalite-granodiorite batholiths, such as the Roblin Batholith, into the actively folding Swayze greenstone belt. Continued regional folding resulted in F3 refolding of F1 and F2 in the deformation aureole. Continued regional folding also deformed and folded the Kenogamissi complex and resulted in further uplift and emplacement of the complex into the greenstone belt. The early-formed magmatic foliation and compositional layering in the Roblin Batholith were folded by F3 while the batholith was still a crystal mush, and an F3 axial-surface magmatic foliation was locally formed. Folding of the partially molten Roblin Batholith also resulted in the remobilisation of fractionated liquids into shear zones which formed on the limbs of the F3 magmatic folds. Similar structures are present in the orthogneiss unit and are interpreted to represent remobilisation of melts which intruded the orthogneiss at the time of emplacement of the Roblin Batholith. The formation of the dykes on sheared fold limbs may be attributed to increased dilatancy during localised shearing of the crystal mush. Deformation-assisted remobilisation and extraction of fractionated liquids, and the possible transport of the fractionated liquids to higher levels in the crystallising Roblin Batholith, may have played a role in its magmatic differentiation.

scholarly journals The geology, petrology, and geochronology of the Archean Côté Gold large-tonnage, low-grade intrusion-related Au(–Cu) deposit, Swayze greenstone belt, Ontario, Canada

2017 ◽  
Vol 54 (2) ◽  
pp. 173-202 ◽  
Author(s):  
Laura R. Katz ◽  
Daniel J. Kontak ◽  
Benoît Dubé ◽  
Vicki McNicoll
Keyword(s):  
Greenstone Belt ◽  
Thermal Ionization Mass Spectrometry ◽  
Ionization Mass ◽  
Low Grade ◽  
Metavolcanic Rocks ◽  
Volcanogenic Massive Sulphide ◽  
Abitibi Subprovince ◽  
Back Arc ◽  
Miarolitic Cavities ◽  
Subvolcanic Intrusion

The Archean Côté Gold Au(–Cu) deposit is the first large gold deposit discovered in the Swayze greenstone belt of the Abitibi Subprovince. The deposit is a low-grade, large-tonnage type with a combined indicated and inferred resource of 8.65 M oz Au (245.2 t Au). The deposit is hosted by the Chester intrusive complex (CIC), a multiphase, subvolcanic intrusion composed of low-Al tonalite, diorite, and quartz diorite, plus magmatic and hydrothermal breccia bodies. The age of the tonalite and dioritic phases is constrained at 2741–2739 ± 1 Ma using high-precision isotope dilution – thermal ionization mass spectrometry (ID–TIMS) U–Pb zircon geochronology. Although these phases are co-temporal and co-spatial, they appear to be petrogenetically unrelated. The CIC was emplaced into mafic metavolcanic rocks of the Arbutus Formation whose geochemistry reflects a back-arc environment. The tonalite of the CIC is coeval and co-genetic with the felsic to intermediate metavolcanic rocks of the Yeo Formation. Emplacement of the CIC into a shallow crustal level is inferred based on the incorporation of screens and inclusions of the Yeo Formation and is supported by the presence of textures in tonalite and dioritic rocks (e.g., granophyres, miarolitic cavities, and pegmatites), as well as Al-in-hornblende geobarometry results of ≤1.3 ± 0.6 kbars (1 kbar = 100 MPa). The CIC is petrologically similar to other subvolcanic, low-Al tonalite–trondhjemite–diorite intrusions that underlie volcanogenic massive sulphide (VMS)-type deposits and which themselves may contain syn-intrusion mineralization. Several geochemically unrelated dykes and deformation events crosscut and postdate the CIC.

Petrogenesis and economic potential of the Obatogamau Formation, Chibougamau area, Abitibi greenstone belt

2020 ◽  
Author(s):  
Adrien Boucher ◽  
Lucie Mathieu ◽  
Michael A. Hamilton ◽  
Pierre Bedeaux ◽  
Réal Daigneault
Keyword(s):  
Greenstone Belt ◽  
Gold Mineralization ◽  
Massive Sulfide ◽  
Lava Flows ◽  
Economic Potential ◽  
Magmatic Differentiation ◽  
Mafic Lava ◽  
Abitibi Subprovince ◽  
Stratigraphic Position ◽  
Peak Metamorphism

Unravelling the petrogenesis and stratigraphy of Archean mafic lava flows is essential to our comprehension of the early geodynamic evolution and economic potential of greenstone belts. This study focuses on one of the oldest and thickest sequences of lava flows observed in the Neoarchean Abitibi Subprovince (greenstone belt), i.e., the Obatogamau Formation. The undated formation extends for more than 100 km in an E-W direction and consists mostly of aphyric and feldspar megacryst-bearing basaltic-andesite lava flows. These lava flows are tholeiitic, mostly Fe-rich and have nearly homogeneous chemistry. Petrogenetic modelling carried out using MELTS software points to limited magmatic differentiation as most samples of mafic lava flows did not reach Fe-Ti-oxide saturation. Zircon U-Pb dating establishes a crystallization age of 2726.2 ± 1.6 Ma for a felsic unit located at an intermediate stratigraphic position in the sequence of lava flows. Constraints from stratigraphically overlying volcanic units suggest that the Obatogamau Formation was likely emplaced rapidly, possibly within a few million years and as a consequence of frequent replenishment of shallow magma accumulations. High eruption rates are consistent with short episodes of volcanic quiescence deduced from field observations, indicating non-optimal conditions for volcanogenic massive sulfide systems. The pressure and temperature of peak metamorphism deduced from amphibole chemistry, however, points to favorable conditions for the release of metamorphic fluids. The study area may thus be prospective for orogenic gold mineralization, provided that fluids had access to a source of gold and that structural conduits allowed for the channeling of hydrothermal fluids.

Late Archaean clastic sedimentary rocks (Shamvaian Group) of the Zimbabwe craton: first observations from the Bindura-Shamva greenstone belt

2002 ◽  
Vol 39 (11) ◽  
pp. 1689-1708 ◽  
Author(s):  
A Hofmann ◽  
PH GM Dirks ◽  
H A Jelsma
Keyword(s):  
Greenstone Belt ◽  
Sedimentary Rocks ◽  
Sedimentary Facies ◽  
Shear Zones ◽  
Alluvial Fan ◽  
Sediment Supply ◽  
Turbidity Currents ◽  
Late Archaean ◽  
Facies Associations ◽  
Felsic Volcanic

The ~2.65 Ga old Shamvaian Group sedimentary rocks occur as a folded succession in the central part of the Bindura–Shamva greenstone belt of Zimbabwe. The strata comprise distinct, shear zone-bounded tectonostratigraphic units which may be stratigraphically arranged as follows. The lower part of the succession is represented by a transgressive, fining-upward sequence of alluvial fan conglomerate, overlain by fluvial braid-plain pebbly sandstone and marine shoreface sandstone. Detritus was derived from a mid-Archaean granitoid-gneiss terrain situated to the east. Sediment supply and subsidence rate must have been high. Shallow shelf sedimentation was followed by deep-water (sub-wave base) deposition by turbidity currents, giving rise to a thick succession of fine to coarse clastic material. The turbidite deposits were locally overlain by shallow-marine sandstone and fluvial to alluvial fan conglomerate. An upward increase in the abundance of intermediate and felsic volcanic clasts suggests an increase in the proximity of a volcanic terrain, such as a volcanic arc. Deposition was followed by layer-parallel shearing during thrust belt-style tectonism. Major shear zones developed preferentially along the contact between shallow- and deep-marine facies associations. Basin initiation may have been related to extensional tectonics, possibly on rifted continental crust, whereas later stages of basin history were characterized by compression, suggesting a foreland or fore-arc basin setting. Sedimentary facies, stratigraphy, and facies distribution are remarkably similar to some late Archaean sedimentary sequences of the Superior Province in Canada.

scholarly journals Oxygen Fugacity and Volatile Content of Syntectonic Magmatism in the Neoarchean Abitibi Greenstone Belt, Superior Province, Canada

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 966
Author(s):  
Baptiste Madon ◽  
Lucie Mathieu ◽  
Jeffrey H. Marsh
Keyword(s):  
Oxygen Fugacity ◽  
Greenstone Belt ◽  
Inductively Coupled Plasma ◽  
Gold Mineralization ◽  
Gold Deposits ◽  
Hydrothermal Systems ◽  
Chemical Diversity ◽  
Temporal Association ◽  
Volatile Content ◽  
Abitibi Subprovince

Neoarchean syntectonic intrusions from the Chibougamau area, northeastern Abitibi Subprovince (greenstone belt), may be genetically related to intrusion related gold mineralization. These magmatic-hydrothermal systems share common features with orogenic gold deposits, such as spatial and temporal association with syntectonic magmatism. Genetic association with magmatism, however, remains controversial for many greenstone belt hosted Au deposits. To precisely identify the link between syntectonic magmas and gold mineralization in the Abitibi Subprovince, major and trace-element compositions of whole rock, zircon, apatite, and amphibole grains were measured for five intrusions in the Chibougamau area; the Anville, Saussure, Chevrillon, Opémisca, and Lac Line Plutons. The selected intrusions are representative of the chemical diversity of synvolcanic (TTG suite) and syntectonic (e.g., sanukitoid, alkaline intrusion) magmatism. Chemical data enable calculation of oxygen fugacity and volatile content, and these parameters were interpreted using data collected by electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry. The zircon and apatite data and associated oxygen fugacity values in magma indicate that the youngest magmas are the most oxidized. Moreover, similar oxygen fugacity and high volatile content for both the Saussure Pluton and the mineralized Lac Line intrusion may indicate a possible prospective mineralized system associated with the syntectonic Saussure intrusion.

scholarly journals Project SUPRASYD 1993 - granitic rocks and shear zones with possible gold potential, Julianehåb batholith, South Greenland

1994 ◽  
Vol 160 ◽  
pp. 28-31
Author(s):  
A.A Garde ◽  
H.K Schønwandt
Keyword(s):  
East Coast ◽  
Economic Assessment ◽  
Shear Zones ◽  
Geological Survey ◽  
Granitic Rocks ◽  
Significant Potential ◽  
Metavolcanic Rocks ◽  
Sulphide Deposits ◽  
Important Constituent

In 1992 the Geological Survey of Greenland (GGU) initiated the project SUPRASYD in order to carry out an economic assessment of the Ketilidian orogen in South Greenland, especially the supracrustal rocks in the southern and eastern parts of the orogen (see Dawes & Schønwandt, 1992). Geological investigations in the area east of Nanortalik and along the east coast of South Greenland as far as 62°N had previously indicated that acid metavolcanic rocks were an important constituent of the supracrustal rocks, and it was therefore expected that the region might have a significant potential for sulphide deposits.

A terrane interpretation of the Archaean Limpopo Belt

1993 ◽  
Vol 130 (6) ◽  
pp. 755-765 ◽  
Author(s):  
H. R. Rollinson
Keyword(s):  
Shear Zones ◽  
Kaapvaal Craton ◽  
Late Archaean ◽  
The North ◽  
Zimbabwe Craton ◽  
Marginal Zones ◽  
Limpopo Belt

AbstractThe Limpopo Belt is a zone of thickened Archaean crust whose origin is currently explained by a late Archaean continent-continent collision between the Kaapvaal and Zimbabwe cratons. This review shows that the two cratons have fundamentally different geological histories and that the Zimbabwe Craton was unlikely to have behaved as a stable ‘cratonic’ block at the time of the Limpopo Belt collision. The geological histories of the Zimbabwe Craton, the North Marginal, Central and South Marginal zones of the Limpopo Belt and the Kaapvaal Craton are shown to be sufficiently different from one another to warrant their consideration as discrete terranes. The boundaries between the five units outlined above are all major shear zones, further supporting a terrane model for the Limpopo Belt. The five units were all intruded by late- to syn-tectonic granites c.2.6 Ga, constraining the accretion event to c. 2.6 Ga.

Gold Remobilization: Insights from Gold Deposits in the Archean Swayze Greenstone Belt, Abitibi Subprovince, Canada

2020 ◽  
Vol 115 (2) ◽  
pp. 241-277 ◽  
Author(s):  
Evan C.G. Hastie ◽  
Daniel J. Kontak ◽  
Bruno Lafrance
Keyword(s):  
Greenstone Belt ◽  
Inductively Coupled Plasma ◽  
Native Gold ◽  
Gold Deposits ◽  
Coarse Grained ◽  
High Grade ◽  
Northern Ontario ◽  
Inductively Coupled ◽  
Abitibi Subprovince ◽  
Plasma Mass Spectrometry

Abstract Recognizing if and how Au is remobilized, in solid, melt, or fluid state, is critical for understanding the origin of high-grade ore zones in Au deposits. When evidence for Au remobilization can be demonstrated, then primary versus secondary processes can be distinguished, resulting in a more complete understanding of Au deposit formation. To address this, samples from two Au deposits, Jerome and Kenty, in the Archean Swayze greenstone belt of northern Ontario, Canada, together with archived samples from 39 high-grade Au deposits from the Abitibi greenstone belt across Ontario and Quebec, were geochemically characterized using integrated scanning electron microscopy-energy dispersive spectroscopy and electron microprobe imaging and analyses in addition to laser ablation-inductively coupled plasma-mass spectrometry elemental mapping. These data provided the basis to develop a model for Au remobilization and upgrading of Au that is widely applicable to orogenic gold settings. Data for the Jerome deposit indicate that Au uptake into early pyrite was not due to pulsing of different fluids, but instead was predominantly controlled by S availability, whereby the oscillatory/sector zoning in pyrite resulted from the substitution of As into S sites during rapid growth due to local chemical disequilibrium. In addition, Au-bearing pyrite from both the Jerome and Kenty deposits records textures, such as porosity development coincident with the presence of native gold and accessory sulfide phases, that are strongly suggestive of coupled dissolution-reprecipitation (CDR) reactions that liberated Au and associated elements from earlier auriferous (100–5,000 ppm Au) pyrite. During the remobilization process, Au and Ag were decoupled, which resulted in (1) a change in Au/Ag ratios of 0.5 to 5 in early pyrite to ≈9 in the new native gold (900 Au fineness) and (2) incorporation of Ag into cogenetic secondary mineral phases (e.g., chalcopyrite, tetrahedrite, and galena). Evidence for an association of low-melting point chalcophile elements (LMCE; Hg, Te, Sb, and Bi) with Au at the Jerome, Kenty, and many (>50%) of the 39 historic deposits sampled, along with native gold filling structurally favorable sites in vein quartz in all samples, indicates a fluid might not have been the only factor contributing to remobilization. This systematic Au-LMCE association strongly supports a model whereby Au is released by CDR reactions and is then remobilized by fluid-mediated, LMCE-rich melts that began to form at 335°C and/or by local, nanoparticle (nanomelt?) transport during deformation and metamorphism. Conclusions drawn from this study have implications for Au deposits globally and can account for the common presence of coarse-grained, commonly crystalline, native gold filling fractures in quartz and the paragenetically late-stage origin of gold in veins. They can also better explain the inability of Au in solution remobilization models to account for locally high gold grades, given the relatively low solubility of Au in hydrothermal fluids.

The Kostomuksha greenstone belt, NW Baltic Shield: remnant of a late Archaean oceanic plateau?

Terra Nova ◽  
1997 ◽  
Vol 9 (2) ◽  
pp. 87-90 ◽  
Author(s):  
I. S. Puchtel ◽  
A. W. Hofmann ◽  
K. P. Jochum ◽  
K. Mezger ◽  
A. A. Shchipansky ◽  
...  
Keyword(s):  
Baltic Shield ◽  
Greenstone Belt ◽  
Late Archaean ◽  
Oceanic Plateau

Pre-Caledonian granulite and gabbro enclaves in the Western Gneiss Region, Norway: indications of incomplete transition at high pressure

2000 ◽  
Vol 137 (3) ◽  
pp. 235-255 ◽  
Author(s):  
M. KRABBENDAM ◽  
A. WAIN ◽  
T. B. ANDERSEN
Keyword(s):  
High Pressure ◽  
Shear Zones ◽  
Granulite Facies ◽  
Amphibolite Facies ◽  
Ultrahigh Pressure ◽  
Western Gneiss Region ◽  
Ultrahigh Pressure Metamorphism ◽  
Mountain Belts ◽  
Orogenic Cycle ◽  
Highly Strained

The Western Gneiss Region of Norway is a continental terrane that experienced Caledonian high-pressure and ultrahigh-pressure metamorphism. Most rocks in this terrane show either peak-Caledonian eclogite-facies assemblages or are highly strained and equilibrated under late-Caledonian amphibolite-facies conditions. However, three kilometre-size rock bodies (Flatraket, Ulvesund and Kråkenes) in Outer Nordfjord preserve Pre-Caledonian igneous and granulite-facies assemblages and structures. Where these assemblages are preserved, the rocks are consistently unaffected by Caledonian deformation. The three bodies experienced high-pressure conditions (20–23 kbar) but show only very localized (about 5%) eclogitization in felsic and mafic rocks, commonly related to shear zones. The preservation of Pre-Caledonian felsic and mafic igneous and granulite-facies assemblages in these bodies, therefore, indicates widespread (∼ 95%) metastability at pressures higher than other metastable domains in Norway. Late-Caledonian amphibolite-facies retrogression was limited. The degree of reaction is related to the protolith composition and the interaction of fluid and deformation during the orogenic cycle, whereby metastability is associated with a lack of deformation and lack of fluids, either as a catalyst or as a component in hydration reactions. The three bodies appear to have been far less reactive than the external gneisses in this region, even though they followed a similar pressure–temperature evolution. The extent of metastable behaviour has implications for the protolith of the Western Gneiss Region, for the density evolution of high-pressure terranes and hence for the geodynamic evolution of mountain belts.

Archean mafic metavolcanics from the Rouyn–Noranda district, Abitibi Greenstone Belt, Quebec. 1. Mobility of the major elements

1982 ◽  
Vol 19 (12) ◽  
pp. 2258-2275 ◽  
Author(s):  
Léopold Gélinas ◽  
Michel Mellinger ◽  
Pierre Trudel
Keyword(s):  
Greenstone Belt ◽  
Great Depth ◽  
Major Elements ◽  
Chemical Degradation ◽  
Type I ◽  
Calc Alkaline ◽  
Calcium Leaching ◽  
Abitibi Greenstone Belt ◽  
Metavolcanic Rocks ◽  
Metamorphic Facies

In a suite of Archean mafic pillows from the Rouyn–Noranda region of Quebec's Abitibi Greenstoné Belt, including both tholeiitic and calc-alkaline varieties spanning the prehnite–pumpellyite to upper greenschist metamorphic facies, three types of alteration can be defined: (I) chlorite–epidote–actinolite; (II) chlorite–epidote; and (III) chlorite ± sericite; the number of mineral phases decreases as a result of progressive hydration from type I to type III alteration. Albitization, resulting from substitution of [Formula: see text], in calcic plagioclase, is highly variable in type I alteration, but in types II and III the plagioclase is totally albitized and in some cases silicified. Chloritization is closely linked to increasing hydration and Ca leaching with MgO and FeO substituting for CaO in ferromagnesian minerals.Calcium was mobilized and carried by solutions, as evidenced by the variable concentration of epidote at the margins of pillows. This calcium leaching generated an excess of Al2O3 with respect to the combined molecular proportions of Na2O, K2O, and CaO, and is shown by the presence of corundum in CIPW norm calculations. In some pillows showing substitution of [Formula: see text], the fo2 of the invading fluid appears to have remained constant, being buffered by the pillow composition; this would be favored by a low water/rock mass ratio. As a result, the initial pillow Fe2O3/FeO ratio remained constant. In other pillows, the fo2 appears to have been imposed by the invading fluid rather than by the mineral assemblage: the FeO/MgO ratios are thus no longer representative of the magmatic composition whereas the ΣFeO/MgO is still representative of the pristine magmatic value.Two types of substitution of CaO by FeO and (or) MgO have been observed: (1) preferential substitution restricted to type I alteration, of FeO over MgO, similar to low-temperature substitution in modern-day sea-floor alteration; and (2) the more common substitution in type II and III alterations in which MgO predominates over FeO, similar to the high-temperature substitution taking place at great depth on the ocean floor.Although the samples were collected to test mineral heterogeneities caused by chemical degradation, more than 40% of the pillows sampled retained their pristine ΣFeO/MgO ratios. The various alteration patterns are independent of the initial tholeiitic or calc-alkaline lineage; this was confirmed using rare earth elements (REE) and inert trace elements such as Zr, Y, and Ti. The chemical changes in the mafic metavolcanic rocks do not obliterate their tholeiitic or calc-alkaline chemical affinities.

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