Structural evolution of the Hemlo greenstone belt in the vicinity of the world-class Hemlo gold deposit

A complex history of volcano-sedimentary deposition, polyphase strain, multiple intrusive events, and various stages of porphyroblastesis is indicated for the Hemlo gold deposit area within the Hemlo greenstone belt. Structural elements can be assigned to at least six stages of development (D1D6). D1 generated small-scale folds and low-angle faults (thrusts?) with no planar fabric, except within strain aureoles around the earliest intrusions. D2 was a progressive event resulting from northeast-directed compression, which generated regional, predominantly S-shaped folds (early D2); penetrative planar and linear fabrics, overturned stratigraphy, and formation of an inflection in the strike of the greenstone belt (mid-D2); and development of high-strain zones with dominant sinistral and local dextral shear sense (late D2). D3 was a distinctly separate progressive event resulting from northwest-directed transpression, which generated variably penetrative east- to northeast-striking foliation (S3), ductile dextral shear fabrics, and small-scale Z-shaped folds (early D3), followed by brittleductile to brittle development of cataclasite and pseudotachylite in layer-parallel zones (late D3). D4 resulted in contractional kinks and brittle fractures, locally in conjugate sets. D5 and D6 are represented by brittle to brittleductile faults, which overprint Paleoproterozoic and Mesoproterozoic dikes, respectively. Four granitoid magmatic events span the interval 27202677 Ma, with emplacement mainly during D2, between ca. 2690 and ca. 2684 Ma. A protracted period of regional medium-grade metamorphism likely spanned the D2D3 stages. The Hemlo gold deposit was emplaced during mid-D2 and was largely controlled by D2 structural elements and competency contrast between rock units.

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Deformation history of the Marmara Granitoid and implications for a dextral shear zone in NW Anatolia

10.5194/egusphere-egu2020-9231 ◽

2020 ◽

Author(s):

Salim Birkan Bayrak ◽

Işıl Nur Güraslan ◽

Alp Ünal ◽

Ömer Kamacı ◽

Şafak Altunkaynak ◽

...

Keyword(s):

Shear Zone ◽

Boundary Migration ◽

Microstructural Analysis ◽

Structural Data ◽

Ductile Deformation ◽

Brittle Deformation ◽

Deformation History ◽

Shear Sense ◽

History Of ◽

Dextral Shear

Marmara granitoid (47 Ma) is a representative example of the Eocene post-collisional magmatism which produced several granitic plutons in NW Anatolia, Turkey. It is a W-E trending sill-like magmatic body which was concordantly emplaced into the metamorphic basement rocks of Erdek Complex and Saraylar Marble. The granitoid is represented by deformed granodiorite which displays well-developed lineation and foliation in meso-scale defined by the elongation of mica and feldspar crystals and recrystallization of quartz however, in some places, magmatic textures are preserved. Deformed granodiorite is broadly cut by aplitic and pegmatitic dikes and contains mafic enclaves which display the same deformation indicators with the main granitoid.Microstructural analysis shows that the solid-state deformation of the Marmara granitoid is classified as ductile deformation with high temperatures and ductile-to-brittle deformation with relatively lower temperatures. Evidence for the ductile deformation of the granitoid is represented by chessboard extinction of quartz, grain boundary migration (GBM) and subgrain rotation recrystallisation (SGR) which exhibits that the deformation temperature changed from 600 oC to 400oC. Bulging recrystallization (BLG), grain size reduction of amphibole, biotite and plagioclases and microcracks on plagioclases were considered as overlying ductile-to-brittle deformation signatures which develop between 300-<250 oC temperatures.All of these field and micro-structural data collectively suggest that the shear sense indicators such as micafish structures and &#948; type mantled porphyroclasts displayed stair-steppings pointing out to a right lateral movement, indicating that the structural evolution and deformation history of Marmara granitoid was controlled by a dextral shear zone.

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Geology, structural evolution, and hydrothermal alteration of the Island gold deposit, Michipicoten greenstone belt, Ontario

10.4095/323671 ◽

2020 ◽

Author(s):

T J Ciufo ◽

K Jellicoe ◽

C Yakymchuk ◽

S Lin ◽

P Mercier-Langevin ◽

...

Keyword(s):

Gold Deposit ◽

Hydrothermal Alteration ◽

Greenstone Belt ◽

Structural Evolution

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

Economic Geology ◽

10.5382/econgeo.4674 ◽

2019 ◽

Vol 114 (6) ◽

pp. 1057-1094 ◽

Cited By ~ 4

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.

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Gold deposits of Suriname: geological context, production and economic significance

Netherlands Journal of Geosciences – Geologie en Mijnbouw ◽

10.1017/njg.2016.40 ◽

2016 ◽

Vol 95 (4) ◽

pp. 429-445 ◽

Cited By ~ 2

Author(s):

Nicole M. E. Kioe-A-Sen ◽

Manfred J. van Bergen ◽

Theo E. Wong ◽

Salomon B. Kroonenberg

Keyword(s):

Greenstone Belt ◽

Gold Deposits ◽

Point Of View ◽

Open Pit ◽

Small Scale ◽

Ore Formation ◽

Economic Significance ◽

History Of ◽

Greenstone Belts ◽

Available Information

AbstractGold has been a major economic asset for Suriname for more than a century. The long history of gold mining, concentrated in large parts of a greenstone belt in the northeast of the country, began with small-scale artisanal extraction activities and has recently seen the development of major open-pit operations. Despite the range of mining activities, Suriname's gold deposits and occurrences are under-explored from a scientific point of view. Primary gold mineralisations in the greenstone belt occur in multiple forms, and although their origin is commonly related to the Palaeoproterozoic Trans-Amazonian orogeny, the controls of ore formation in specific cases often remain obscure. This contribution presents an abridged overview of currently available information on the geological setting and characteristics for some of the main deposits where gold is extracted. In view of the consistent link between gold metallogeny and granitoid–greenstone belts in the northern Guiana Shield, the mineralised settings in Suriname are discussed in a regional context.

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Fluid signature of the shear zone–controlled Veio de Quartzo ore body in the world-class BIF-hosted Cuiabá gold deposit, Archaean Rio das Velhas greenstone belt, Brazil: a fluid inclusion study

Mineralium Deposita ◽

10.1007/s00126-019-00941-0 ◽

2020 ◽

Vol 55 (7) ◽

pp. 1441-1466 ◽

Cited By ~ 2

Author(s):

Carolin Kresse ◽

Lydia M. Lobato ◽

Rosaline C. Figueiredo e Silva ◽

Steffen G. Hagemann ◽

David Banks ◽

...

Keyword(s):

Fluid Inclusion ◽

Gold Deposit ◽

Shear Zone ◽

Greenstone Belt ◽

Fluid Inclusion Study ◽

Ore Body ◽

The World ◽

Inclusion Study ◽

World Class

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Structural Evolution of the Rio das Velhas Greenstone Belt, Quadrilátero Ferrífero, Brazil: Influence of Proterozoic Orogenies on Its Western Archean Gold Deposits

Minerals ◽

10.3390/min10110983 ◽

2020 ◽

Vol 10 (11) ◽

pp. 983

Author(s):

Orivaldo Ferreira Baltazar ◽

Lydia Maria Lobato

Keyword(s):

Greenstone Belt ◽

Gold Mineralization ◽

Structural Evolution ◽

Shear Zones ◽

Gold Deposits ◽

Normal Faults ◽

Small Scale ◽

Crenulation Cleavage ◽

Quadrilátero Ferrífero ◽

Tectonic Transport

The Quadrilátero Ferrífero region is located in the extreme southeast of the Brasiliano São Francisco craton, Minas Gerais state, Brazil. It is composed of (i) Archean TTG granite-gneaissic terranes; (ii) the Archean Rio das Velhas greenstone belt; (iii) the Proterozoic metasedimentary and metavolcano-sedimentary covers. The Rio das Velhas rocks were deposited in the synformal NW–SE-directed Nova Lima basin. The Archean deformation converted the Nova Lima basin into an ample synclinorium with an eastern inverted flank. Archean orogenic gold mineralization within the Rio das Velhas greenstone belt rocks is controlled by NNW–SSE-directed, Archean regional shear zones subparallel to the strata of the Nova Lima synclinorium borders. Transamazonian and Brasiliano orogenies are superposed onto the Archean structures that control gold mineralization. In the eastern domain, Brasiliano fold-and-fault belts prevail, whereas in the western domain Archean and Transamazonian structures abound. The present study focus mainly is the western domain where the Cuiabá, Morro Velho, Raposos, Lamego and Faria deposits are located. Gold orebodies plunge to the E–NE and are tectonically controlled by the Archean D1–D2 deformation. The D3 Transamazonian compression—Which had a SE–NW vector sub-parallel to the regional mineralized Archean foliation/bedding—Buckled these structures, resulting in commonly open, synformal and antiformal regional folds. These are well documented near the gold deposits, with NE–SW axial traces and fold axes plunging to E–NE. Such folds are normal to inverted, NW-verging, with an axial planar foliation dipping moderately to the SE. The Transamazonian compression has only been responsible for the reorientation of the mineralized Archean gold ores, due to coaxial refolding characterized by an opposite tectonic transport. It has therefore not caused any other significant changes. Thrust shear zones, sub-parallel to the strong Transamazonian foliation, have given rise to localized metric segmentation and to the dislocation of gold orebodies. Throughout the region, along the towns of Nova Lima to Sabará, structures pertaining to the Brasiliano Araçuaí orogeny are represented only by gentle folding and by a discrete, non-pervasive crenulation cleavage. Thrust-shear zones and small-scale normal faults have caused, at most, metric dislocations along N–S-oriented planes.

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