Structural analysis and metamorphism of the Barlow Fault Zone, Chibougamau area, Neoarchean Abitibi Subprovince: implications for gold mineralization

2020 ◽  
Author(s):  
Pierre Bedeaux ◽  
Antoine Brochu ◽  
Lucie Mathieu ◽  
Damien Gaboury ◽  
Réal Daigneault
Keyword(s):  
Fault Zone ◽  
Gold Mineralization ◽  
Structural Evolution ◽  
Amphibolite Facies ◽  
Fault System ◽  
Kinematic Evolution ◽  
Facies Metamorphism ◽  
Abitibi Subprovince ◽  
Northern Portion ◽  
Peak Metamorphism

Faults and deformation zones are important features of Archean terranes because of their significance for structural evolution and the formation of large gold districts. In the Chibougamau area, northeastern portion of the Abitibi Subprovince, an Apogee Metal Earth seismic reflection survey identified an association between an exceptional shallow-dipping subsurface reflector zone and the Barlow Fault Zone visible at the surface. This study aimed to reconstruct the kinematic evolution of the Barlow Fault Zone, determine its position within the structural setting of this section of the Abitibi Subprovince, and evaluate its importance for gold potential in the northern part of the Chibougamau area. Structural reconstruction and field observations are compatible with a reverse south-over-north movement related to a ductile north–south shortening event, which culminated with amphibolite metamorphism. Geothermobarometers indicate peak metamorphism conditions of 550 ± 50 °C and 6 ± 1.2 kbar. Results from this study suggest that amphibolite facies metamorphism covers a much wider area within the Chibougamau region than previously documented. The Barlow Fault Zone shares similar geometric characteristics and evolutionary history with other gold-bearing structures in the Abitibi Subprovince, but ultimately it was unable to provide optimal conditions for channelling fluid and precipitating gold. The Barlow Fault Zone is interpreted as a back-thrust fault that belongs to a more extensive south-dipping fault system encasing juxtaposed tectonic slivers. This system, with amphibolite facies metamorphism, is a defining feature of the northern portion of the Chibougamau area and developed during the accretion between the Opatica and Abitibi subprovinces.

scholarly journals Structural studies in the pre-Cambrian of western Greenland. Part III. Southern Sukkertoppen District

1962 ◽  
Vol 31 ◽  
pp. 1-46
Author(s):  
A Berthelsen
Keyword(s):  
Structural Evolution ◽  
Granulite Facies ◽  
Field Work ◽  
Amphibolite Facies ◽  
Alternative Theory ◽  
Low Grade ◽  
The North ◽  
Kinematic Evolution ◽  
Facies Metamorphism ◽  
Wrench Fault

This paper summarises several summers field work within the southern Sukkertoppen district. Since detailed mapping has only been carried out within smaller areas within the region, the remainder being covered by reconnaissance mapping along the coasts, the results should be considered as preliminary. The southern Sukkertoppen district can be divided into three tectonic units, the Nordland, the Finnefjeld, and the Alángua complexes, which, most probably, were formed during the Ketilidian cycle (E. Wegmann, 1938). The metamorphic complexes are traversed by postorogenic dykes and faults (Berthelsen and Bridgwater, 1960). The dykes and faults were seemingly formed before the Nagssugtôqidian revolution which affected the country further to the north (Ramberg, 1948). The northern Nordland complex is shown to have passed through a metamorphic and structural evolution very similar to that which recently has been described from a small area within the complex (see table 2). An original granulite facies rock assemblage has been exposed to two successive imprints of retrograde metamorphism: first an amphibolite facies metamorphism; next a postorogenic epidote-amphibolite to greenschist facies metamorphism in connection with the formation of the younger faults. Evidence is brought forward that the tectonic phases established from Tovqussap nunâ may also be traced within the remaining parts of the Nordland complex. In one case (see fig. 3) an analysis of the basement structures reveals that the post-orogenic faulting is of the wrench fault type. The Finnefjeld complex which is built up of homogeneous hornblende-biotite-bearing quartz-dioritic gneisses is believed to have been originally composed of granulite facies rocks. Subsequent strong penetrative movements accompanied by low grade amphibolite facies metamorphism were responsible for the formation of the present Finnefjeld gneisses. This idea is strongly supported by the facts that relic patches of hypersthene gneiss and transgressive, but deformed, more or less uralitised diorite bodies occur within the Finnefjeld gneiss. The Alangua complex comprises abundant pelitic and semipelitic schists, amphibolites, ultrabasics and skarn rocks in addition to gneisses which are considered to be of metasomatic origin. The ultrabasic rocks have been described by H. Sørensen (1952,1953, 1954, and 1955). The rocks of this complex can also be shown to have passed through two periods of metamorphism (see also H. Sørensen, 1952); an original medium to high grade amphibolite facies metamorphism was succeeded by a later low grade amphibolite facies metamorphism accompanied by granitisation, pegmatisation etc., indicating the presence of a volatile-rich dispersed phase. Although not studied in detail, the structures of the Alángua complex are sufficiently well-known to establish the kinematic evolution of this complex. The first amphibolite facies metamorphism seems to correspond to the Smalledal-Pâkitsoq phases of the Nordland complex, while the subsequent period of low grade amphibolite metamorphism can be matched with the posthumous phase. During this latter, the northern part of the Nordland complex, which locally was thrust over the Alángua rocks (thereby causing their refolding) was converted into the present Finnefjeld gneisses. This interpretation explains the present differences between the three com· plexes as being due to Stockwerk tectonics, fig. 16. An alternative theory which holds that the Alángua rocks are younger than those of the southern complexes does not seem to concur with the field relation known so far. No mineral deposits of economic interest were found during the survey, but traces of sulfides (see tables 1 and 3), magnetite, molybdenite, corundum, monazite, zircon, talc and soapstone have been met with at various localities.

U–Pb garnet and titanite age for the Bristol Township lamprophyre suite, western Abitibi Subprovince, Canada

1990 ◽  
Vol 27 (11) ◽  
pp. 1451-1456 ◽  
Author(s):  
C. Tucker Barrie
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Fault Zone ◽  
Late Stage ◽  
Gold Mineralization ◽  
Light Rare Earth ◽  
Upper Limit ◽  
Abitibi Subprovince ◽  
Brittle Fractures ◽  
Light Rare Earth Elements

A U–Pb age of 2687 ± 3 Ma has been determined for a garnetite dike, using melanite garnet and titanite mineral separates. This is the first primary igneous U–Pb age reported using garnet. The garnetite dike is part of the Bristol Township lamprophyre suite, which is extremely enriched in large-ion lithophile elements and light rare earth elements and which is located within the Destor Porcupine fault zone of the western Abitibi Subprovince. The age represents an upper limit for late-stage gold mineralization found along brittle fractures that cut the lamprophyre suite and it coincides with regional transpression documented in several locations in the southern Superior Province.

Hydrothermal Alteration Mineralogy and Geochemistry of the Archean World-Class Canadian Malartic Disseminated-Stockwork Gold Deposit, Southern Abitibi Greenstone Belt, Quebec, Canada

2019 ◽  
Vol 114 (6) ◽  
pp. 1057-1094 ◽  
Author(s):  
Stéphane De Souza ◽  
Benoît Dubé ◽  
Patrick Mercier-Langevin ◽  
Vicki McNicoll ◽  
Céline Dupuis ◽  
...  
Keyword(s):  
Gold Deposit ◽  
Fault Zone ◽  
Hydrothermal Alteration ◽  
Greenstone Belt ◽  
Gold Mineralization ◽  
Amphibolite Facies ◽  
Alteration Zone ◽  
Gold Deposition ◽  
Abitibi Greenstone Belt ◽  
World Class

Abstract The Canadian Malartic stockwork-disseminated gold deposit is an Archean world-class deposit located in the southern Abitibi greenstone belt. It contains over 332.8 tonnes (t; 10.7 Moz) of Au at a grade of 0.97 ppm, in addition to 160 t (5.14 Moz) of past production (1935–1981). Although the deposit is partly situated within the Larder Lake-Cadillac fault zone, most of the ore occurs up to ~1.5 km to the south of the fault zone. The main hosts of the mineralized zones are greenschist facies turbiditic graywacke and mudstone of the Pontiac Group (~2685–2682 Ma) and predominantly subalkaline ~2678 Ma porphyritic quartz monzodiorite and granodiorite. These intrusions were emplaced during an episode of clastic sedimentation and alkaline to subalkaline magmatism known as the Timiskaming assemblage (<2680–2670 Ma in the southern Abitibi). The orebodies define two main mineralized trends, which are oriented subparallel to the NW-striking S2 cleavage and the E-striking, S-dipping Sladen fault zone. This syn- to post-D2 ductile-brittle to brittle Sladen fault zone is mineralized for more than 3 km along strike. The ore mainly consists of disseminated pyrite in stockworks and replacement zones, with subordinate auriferous quartz veins and breccia. Gold is associated with pyrite and traces of tellurides defining an Au-Te-W ± Ag-Bi-Mo-Pb signature. The orebodies are zoned outward, and most of the higher-grade (>1 ppm Au) ore was deposited as a result of iron sulfidation from silicates and oxides and Na-K metasomatism in carbonatized rocks. The alteration footprint comprises a proximal alteration envelope (K- or Na-feldspar-dolomite-calcite-pyrite ± phlogopite). This proximal alteration zone transitions to an outer shell of altered rocks (biotite-calcite-phengitic white mica), which hosts sub-ppm gold grades and reflects decreasing carbonatization, sulfidation, and aNa+/aH+ or aK+/aH+ of the ore fluid. Gold mineralization, with an inferred age of ~2664 Ma (Re-Os molybdenite), was contemporaneous with syn- to late-D2 peak metamorphism in the Pontiac Group; it postdates sedimentation of the Timiskaming assemblage along the Larder Lake-Cadillac fault zone (~2680–2669 Ma) and crystallization of the quartz monzodiorite. These chronological relationships agree with a model of CO2-rich auriferous fluid generation in amphibolite facies rocks of the Pontiac Group and gold deposition in syn- to late-D2 structures in the upper greenschist to amphibolite facies. The variable geometry, rheology, and composition of the various intrusive and sedimentary rocks have provided strain heterogeneities and chemical gradients for the formation of structural and chemical traps that host the gold. The Canadian Malartic deposit corresponds to a mesozonal stockwork-disseminated replacement-type deposit formed within an orogenic setting. The predominance of disseminated replacement ore over fault-fill and extensional quartz-carbonate vein systems suggests that the mineralized fracture networks remained relatively permeable and that fluids circulated at a near-constant hydraulic gradient during the main phase of auriferous hydrothermal alteration.

P–T conditions of Grenville-age eclogite facies metamorphism and amphibolite facies retrogression of the Glenelg–Attadale Inlier, NW Scotland

2005 ◽  
Vol 142 (5) ◽  
pp. 605-615 ◽  
Author(s):  
C. D. STOREY ◽  
T. S. BREWER ◽  
S. TEMPERLEY
Keyword(s):  
Tectonic Evolution ◽  
Amphibolite Facies ◽  
Geodynamic Evolution ◽  
Broad Agreement ◽  
Grenville Orogeny ◽  
Basement Rocks ◽  
Facies Metamorphism ◽  
Uplift Rates ◽  
Peak Metamorphism ◽  
Eclogite Facies

Peak and retrograde P–T conditions of Grenville-age eclogites from the Glenelg–Attadale Inlier of the northwest Highlands of Scotland are presented. Peak conditions are estimated as c. 20 kbar and 750–780°C, in broad agreement with previous work. The eclogites subsequently followed a steep decompression path to c. 13 kbar and 650–700°C during amphibolite facies retrogression. Peak eclogite facies metamorphism occurred > 1080 Ma and retrogression at c. 995 Ma, suggesting fairly sluggish uplift rates of < 0.3 km/Ma and cooling rates of < 1.25°C/Ma, when compared with other parts of the Grenville orogeny and/or modern orogens. However, current poor constraints on the timing of peak metamorphism mean that these rates cannot be used to interpret the geodynamic evolution of this part of the orogen. The P–T–t data, together with petrology and the field relationships between the basement rocks of the Glenelg–Attadale Inlier and the overlying Moine Supergroup, mean that it is difficult to support the currently held view that an unconformable relationship exists between the two. It is suggested that more data are required in order to re-interpret the Neoproterozic tectonic evolution of the northwest Highlands of Scotland.

scholarly journals The role of oroclinal bending in the structural evolution of the Central Anatolian Plateau: evidence of a regional changeover from shortening to extension

2011 ◽  
Vol 62 (4) ◽  
pp. 345-359 ◽  
Author(s):  
Erman Özsayin ◽  
Kadir Dirik
Keyword(s):  
Fault Zone ◽  
Structural Evolution ◽  
Shear Zones ◽  
Fault Zones ◽  
Fault System ◽  
Western Boundary ◽  
Southeastern Part ◽  
Anatolian Plateau ◽  
Isparta Angle

The role of oroclinal bending in the structural evolution of the Central Anatolian Plateau: evidence of a regional changeover from shortening to extensionThe NW-SE striking extensional Inönü-Eskişehir Fault System is one of the most important active shear zones in Central Anatolia. This shear zone is comprised of semi-independent fault segments that constitute an integral array of crustal-scale faults that transverse the interior of the Anatolian plateau region. The WNW striking Eskişehir Fault Zone constitutes the western to central part of the system. Toward the southeast, this system splays into three fault zones. The NW striking Ilıca Fault Zone defines the northern branch of this splay. The middle and southern branches are the Yeniceoba and Cihanbeyli Fault Zones, which also constitute the western boundary of the tectonically active extensional Tuzgölü Basin. The Sultanhanı Fault Zone is the southeastern part of the system and also controls the southewestern margin of the Tuzgölü Basin. Structural observations and kinematic analysis of mesoscale faults in the Yeniceoba and Cihanbeyli Fault Zones clearly indicate a two-stage deformation history and kinematic changeover from contraction to extension. N-S compression was responsible for the development of the dextral Yeniceoba Fault Zone. Activity along this structure was superseded by normal faulting driven by NNE-SSW oriented tension that was accompanied by the reactivation of the Yeniceoba Fault Zone and the formation of the Cihanbeyli Fault Zone. The branching of the Inönü-Eskişehir Fault System into three fault zones (aligned with the apex of the Isparta Angle) and the formation of graben and halfgraben in the southeastern part of this system suggest ongoing asymmetric extension in the Anatolian Plateau. This extension is compatible with a clockwise rotation of the area, which may be associated with the eastern sector of the Isparta Angle, an oroclinal structure in the western central part of the plateau. As the initiation of extension in the central to southeastern part of the Inönü-Eskişehir Fault System has similarities with structures associated with the Isparta Angle, there may be a possible relationship between the active deformation and bending of the orocline and adjacent areas.

scholarly journals Structural evolution of a crustal-scale seismogenic fault in a magmatic arc: The Bolfin Fault Zone (Atacama Fault System)

2021 ◽  
Author(s):  
Simone Masoch ◽  
Rodrigo Gomila ◽  
Michele Fondriest ◽  
Erik Jensen ◽  
Tom Mitchell ◽  
...  
Keyword(s):  
Fault Zone ◽  
Large Scale ◽  
Damage Zone ◽  
Structural Evolution ◽  
Crystalline Basement ◽  
Fault System ◽  
Fault Mechanics ◽  
Seismogenic Fault ◽  
Magmatic Arc ◽  
Atacama Fault System

&lt;p&gt;The nucleation and evolution of major crustal-scale seismogenic faults in the crystalline basement as well as the process of strain localization represent a long-standing, but poorly understood, issue in structural geology and fault mechanics. Here, we addressed the spatio-temporal evolution of the Bolfin Fault Zone (BFZ), a &gt;40-km-long exhumed seismogenic splay fault of the 1000-km-long strike-slip Atacama Fault System. The BFZ has a sinuous fault trace across the Mesozoic magmatic arc of the Coastal Cordillera (Northern Chile). Seismic faulting occurred at 5-7 km depth and &amp;#8804; 270 &amp;#176;C in a fluid-rich environment as recorded by extensive propylitic alteration and epidote-chlorite veining. The ancient (125-118 Ma) seismicity is attested by the widespread occurrence of pseudotachylytes both in the fault core and in the damage zone. Field geological surveys indicate nucleation of the BFZ on precursory geometrical anisotropies represented by magmatic foliation of plutons (northern and central segments) and andesitic dyke swarms (southern segment) within the heterogeneous crystalline basement. Faulting exploited the segments of precursory anisotropies that were favorably oriented with respect to the long-term stress field associated with the oblique ancient subduction. The large-scale sinuous geometry of the BFZ may result from linkage of these anisotropy-pinned segments during fault growth. This evolution may provide a model to explain the complex fault pattern of the crustal-scale Atacama Fault System.&lt;/p&gt;

scholarly journals Structural evolution of the El Salvador Fault Zone: an evolving fault system within a volcanic arc.

2014 ◽  
Vol 40 (3) ◽  
Author(s):  
Carolina Canora ◽  
José J. Martínez-Díaz ◽  
Pilar Villamor ◽  
Alejandra Staller ◽  
Kelvin Berryman ◽  
...  
Keyword(s):  
El Salvador ◽  
Fault Zone ◽  
Structural Evolution ◽  
Fault System ◽  
Volcanic Arc

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.

scholarly journals Structural evolution of a crustal-scale seismogenic fault in a magmatic arc: The Bolfin Fault Zone (Atacama Fault System)

2021 ◽  
Author(s):  
Simone Masoch ◽  
Rodrigo Gomila ◽  
Michele Fondriest ◽  
Erik Jensen ◽  
Thomas Matthew Mitchell ◽  
...  
Keyword(s):  
Fault Zone ◽  
Structural Evolution ◽  
Fault System ◽  
Seismogenic Fault ◽  
Magmatic Arc ◽  
Atacama Fault System
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