Source requirements for the Golden Mile, Kalgoorlie: significance to the metamorphic replacement model for Archean gold deposits

1987 ◽  
Vol 24 (8) ◽  
pp. 1643-1651 ◽  
Author(s):  
G. Neil Phillips ◽  
David I. Groves ◽  
Isobel J. Brown
Keyword(s):  
Greenstone Belt ◽  
Gold Mineralization ◽  
Source Area ◽  
Shear Zones ◽  
Gold Deposits ◽  
Source Rocks ◽  
Critical Parameters ◽  
Alteration Zones ◽  
Replacement Model ◽  
Golden Mile

The Golden Mile at Kalgoorlie represents a giant Archean hydrothermal gold system localized by ductile shear zones and hosted mainly by a differentiated tholeiitic sill. Chlorite, carbonate, and pyrite alteration zones cover the whole mineralized area (1 km × 3 km), and calculations suggest that for the Golden Mile (production around 1200 t Au), the amounts of components added to these alteration zones are 340 Mt CO2, 20 Mt K, and 5 Mt S. If one adopts a metamorphic-replacement model for gold mineralization in which all ore components derive from devolatilization of greenstones at amphibolite facies or above, these data suggest that a source area involving a 5 km thick greenstone slab of area 8 km × 8 km could produce the necessary CO2, K, S, H2O, and Au. This is considered a reasonable volume of greenstone belt, and under such a model the minimum spacing of large gold deposits would be approximately 20 km along strike.Neither special Au-enriched source rocks nor unreasonably large volumes of greenstone belt are required to produce a giant gold deposit. Instead, the most critical parameters are suitable structural environments providing focussing of fluids and multiple channelways through specific Fe-rich, low-tensile-strength host rocks to ensure efficient depositional mechanisms.

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

Minerals ◽  
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.

scholarly journals CLASSIFICAÇÃO DOS VEIOS QUARTZO-CARBONÁTICOS DE DEPÓSITOS AURÍFEROS NO LINEAMENTO CÓRREGO DO SÍTIO, QF, MG

2013 ◽  
Author(s):  
Marco Aurélio Sequetto Pereira ◽  
Lydia Maria Lobato ◽  
Carlos Alberto Rosière ◽  
Rosaline C. Figueiredo e Silva
Keyword(s):  
Greenstone Belt ◽  
Gold Mineralization ◽  
Mineralogical Composition ◽  
Shear Zones ◽  
Gold Deposits ◽  
Lode Gold ◽  
Free Gold ◽  
Quadrilátero Ferrífero ◽  
Lode Gold Deposits ◽  
Mineral Replacement

Os depósitos tipo lode-gold orogênicos Cachorro Bravo, Laranjeiras e Carvoaria, associados ao lineamento regional Córrego doSítio (CdS), estão localizados na porção leste do Quadrilátero Ferrífero, sudeste do cráton São Francisco. São hospedados em rochasmetassedimentares turbidíticas arqueanas do greenstone belt Rio das Velhas e controlados por zonas de cisalhamento NE-SW. Diques esoleiras metamáficos pré- a pós-deformacionais ocorrem intimamente associados à mineralização aurífera e constituem excelentes guiasprospectivos em lineamentos regionais como CdS. Cinco sistemas de veios, V1 a V5, são classificados de acordo com a composiçãomineralógica, textura, orientação, distribuição espacial e geometria. Dois tipos de quartzo ocorrem nestes veios, sendo o tipo 1predominantemente fumê, cedo-hidrotermal, e o tipo 2 leitoso, recristalizado. Apenas os veios V1 (fault-fill veins) são relacionados àmineralização aurífera através da paragênese arsenopirita+pirita+pirrotita+berthierita+ ouro livre; se desenvolvem concordantes à foliaçãomilonítica, S1m, e estão deformados. Veios V2 (oblique-extension veins) são associados temporalmente aos V1 e, embora não estejammineralizados nos depósitos estudados, são contemporâneos ao estágio mineralizador. Estes dois sistemas foram formados em regimedúctil-rúptil. Veios V3 (extension e breccia veins) são tardios à mineralização e representam um estágio posterior do fluido em regimedúctil-rúptil a rúptil; podem estar relacionados à mudança do campo de tensão regional e colocação dos diques tardios Db1. Os veios V4(extension veins) possuem reações de substituição mineral que marcam a hidratação do sistema e podem se associar ao relaxamento dasforças compressivas. Já os veios V5 (vein stockworks) ocorrem apenas em diques e soleiras metamáficos Db1 e estudos de inclusões fluidasindicam que esses contêm fluido diferente dos outros sistemas.Palavras Chave: Classificação de veios quartzo-carbonáticos, ouro orogênico, zonas de cisalhamento, diques e soleiras. ABSTRACTQUARTZ-CARBONATE VEIN CLASSIFICATION OF AURIFEROUS DEPOSITS IN CÓRREGO DO SÍTIO LINEAMENT, QF, MG. Theorogenic-type, lode-gold deposits Cachorro Bravo, Laranjeiras and Carvoaria, associated with the Córrego do Sítio (CdS) regional lineamentare located in the eastern portion of the Quadrilátero Ferrífero region, southern São Francisco craton, Brazil. They are hosted in Archeanmetaturbiditic rocks of the Rio das Velhas greenstone belt and controlled by NE-SW shear zones. Pre- to post-deformational dikes/sills areclosely related to gold mineralization and constitute excellent prospective guides in these regional lineaments such as CdS. Five veinsystems have been classified, V1 to V5, in accordance to their mineralogical composition, texture, orientation, spatial distribution andgeometry. Two types of quartz occur in these veins, with type 1 being predominantly smoky, early hydrothermal, and type 2 a milky,recrystallized quartz. Only V1 veins (fault-fill vein) are related to gold and have a paragenesis with arsenopyrite+pyrite+pyrrhotite+berthierite+ free gold; they develop along the mylonitic foliation S1m, and have been deformed. The V2 veins (oblique-extension veins) areassociated temporally with V1 and although non-mineralized, in the studied deposits they are contemporaneous to the gold stage. Thesetwo systems are formed under a ductile-brittle regime. The V3 veins (extension and breccias veins) are post gold and represent a late-stagehydrothermal fluid under ductile-brittle to brittle regime; they may be related to changes in the stress field and to the emplacement oflate-stage Db1 dikes. The V4 veins (extension veins) have mineral replacement reactions that represent hydration of the system associatedwith the relaxation of the compressive field. The V5 veins (stockwork style) are limited to metamafic Db1 dykes/sills and fluid inclusionstudies indicate that they contain a different fluid from the others systems.Keywords: Quartz-carbonate vein classification, orogenic gold, shear zones, dikes/sills

scholarly journals Gold in Paleoproterozoic (2.1 to 1.77 Ga) Continental Magmatic Arcs at the Tapajós and Juruena Mineral Provinces (Amazonian Craton, Brazil): A New Frontier for the Exploration of Epithermal–Porphyry and Related Deposits

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 714
Author(s):  
Caetano Juliani ◽  
Rafael Rodrigues de Assis ◽  
Lena Virgínia Soares Monteiro ◽  
Carlos Marcello Dias Fernandes ◽  
José Eduardo Zimmermann da Silva Martins ◽  
...  
Keyword(s):  
Gold Mineralization ◽  
Mineral Exploration ◽  
Shear Zones ◽  
Gold Deposits ◽  
Lava Flows ◽  
The South ◽  
Alteration Zones ◽  
New Frontier ◽  
Amazonian Craton ◽  
Low Sulfidation

This review paper aims to integrate geological, tectonic and metallogenetic data, including new data, and propose a regional model for the gold (and base metal) mineralization in the south Amazonian Craton to support the mineral exploration concerning magmatic–hydrothermal deposits. The Proterozoic evolution of the Amazonian Craton comprises the accretion of terrains to the Archean Carajás Mineral Province. In the Tapajós and Juruena mineral provinces, located at the south part of the Amazonian craton, a long-lived ocean–continent subduction event produced ca. 2.0 to 1.77 Ga continental magmatic arcs. Extensive lava flows, volcaniclastic, sedimentary, and plutonic rocks were originated during at least four major orogenic magmatic events (ca. 2.1, 1.9, 1.88, and 1.80 Ga) and two post- to anorogenic events (ca. 1.87 and 1.77 Ga). Gold mineralization occurs in: (i) alluvial/colluvial occurrences, (ii) orogenic carbonate–sulfide-rich quartz veins in shear zones, (iii) stockworks, veins, and dissemination in granites, (iv) contact of basic dikes, (v) well-preserved high-, intermediate- and low-sulfidation epithermal mineralization, and (vi) porphyry-like and intrusion-related gold systems associated with late- to post-orogenic epizonal granites. The estimated historical gold production, mainly in secondary deposits, is over 27 Moz at the Tapajós and 6 Moz at the Juruena provinces. A total resource of over 5 Moz Au is currently defined in several small to large primary gold deposits. Andesite to rhyolite, volcaniclastic, and clastic sedimentary rocks (1.96–1.88 Ga) host epithermal (high-, intermediate-, and low-sulfidation) Au–(Ag–Pb–Zn) mineralization, whereas Au–Cu and Cu–M–Au mineralization is hosted in sub-volcanic tonalitic to granitic plutons. Advanced argillic alteration (alunite, pyrophyllite, enargite) associated with high-sulfidation mineralization occurs in ring volcanoes around nested volcanic calderas. This zone grades outward to propylitic or chlorite alteration, often covered by silica caps with vuggy silica. Lava flows and volcaniclastic rocks within faults or associated with volcanic edifices and rhyolitic domes host low- and intermediate-sulfidation mineralization. Low-sulfidation alteration zones typically have adularia and illite or sericite. Chalcopyrite, sphalerite, galena, pyrite, digenite, and manganiferous calcite are related to intermediate-sulfidation gold mineralization. Late- to post-orogenic evolved oxidized I-type granitoids host alkalic-type epithermal and porphyry-like gold mineralization. Porphyry-style hydrothermal alteration is analogous to those of modern systems, with inner sodic and potassic (potassic feldspar ± biotite or biotite) alterations grading to propylitic, muscovite-sericite, chlorite–sericite, and chlorite alterations. Potassic alteration zones are the locus of Cu–Mo mineralization, and gold-rich zones occur in muscovite/sericite–quartz–pyrite alteration. The Paleoproterozoic epithermal and porphyry-like mineralization in these large provinces defines a new frontier for the exploration of world-class gold deposits in the worldwide Proterozoic arc-related magmatic terrains.

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.

Gold-bismuth-telluride-sulphide assemblages at the Viceroy Mine, Harare-Bindura-Shamva greenstone belt, Zimbabwe

2008 ◽  
Vol 72 (4) ◽  
pp. 953-970 ◽  
Author(s):  
T. Oberthür ◽  
T. W. Weiser
Keyword(s):  
Native Gold ◽  
Gold Mineralization ◽  
Close Association ◽  
Shear Zones ◽  
Gold Deposits ◽  
Orogenic Gold ◽  
Main Stage ◽  
Melting Temperatures ◽  
Native Bismuth ◽  
Gold Bearing

AbstractGold mineralization at the Viceroy Mine is hosted in extensional veins in steep shear zones that transect metabasalts of the Archaean Arcturus Formation. The gold mineralization is generally made up of banded or massive quartz carrying abundant coarse arsenopyrite. However, most striking is a distinct suite of Au-Bi-Te-S minerals, namely joseite-A (Bi4TeS2), joseite-B (Bi4Te2S), hedleyite (Bi7Te3), ikunolite (Bi4S3), ‘protojoseite’ (Bi3TeS), an unnamed mineral (Bi6Te2S), bismuthinite (Bi2S3), native Bi, native gold, maldonite (Au2Bi), and jonassonite (AuBi5S4). The majority of the Bi-Te-S phases is characterized by Bi/(Se+Te) ratios of >1. Accordingly, this assemblage formed at reduced conditions at relatively low fS2 and fTe2. Fluid-inclusion thermometry indicates depositional temperatures of the main stage of mineralization of up to 342°C, in the normal range of mesothermal, orogenic gold deposits worldwide. However, melting temperatures of Au-Bi-Te phases down to at least 235°C (assemblage (Au2Bi + Bi + Bi7Te3)) imply that the Au-Bi-Te phases have been present as liquids or melt droplets. Furthermore, the close association of native gold, native bismuth and other Bi-Te-S phases suggests that gold was scavenged from the hydrothermal fluids by Bi-Te-S liquids or melts. It is concluded that a liquid/melt-collecting mechanism was probably active at Viceroy Mine, where the distinct Au-Bi-Te-S assemblage either formed late as part of the main, arsenopyrite-dominated mineralization, or it represents a different mineralization event, related to rejuvenation of the shear system. In either case, some of the gold may have been extracted from pre-existing, gold-bearing arsenopyrite by Bi-Te-S melts, thus leading to an upgrade of the gold ores at Viceroy. The Au-Bi-Te-S assemblage represents an epithermal-style mineralization overprinted on an otherwise mesothermal (orogenic) gold mineralization.

Gold distribution in the Val-d'Or Formation and a model for the formation of the Lamaque–Sigma mines, Val-d'Or, Quebec

1991 ◽  
Vol 28 (5) ◽  
pp. 706-720 ◽  
Author(s):  
Mehmet F. Taner ◽  
Pierre Trudel
Keyword(s):  
Gold Mineralization ◽  
Regional Metamorphism ◽  
Analytical Techniques ◽  
Shear Zones ◽  
Gold Deposits ◽  
Mining District ◽  
Volcanic Complex ◽  
Geothermal Systems ◽  
Gold Mines ◽  
Geothermal Activity

Recent lithogeochemical studies by accurate analytical techniques (e.g., instrumental and radiochemical neutron-activation analyses) have been used to explore the possibility of using gold distribution in the research for new gold deposits; these show that anomalous gold distribution occurs in some parts of the Val-d'Or Formation in the Val-d'Or mining district of Quebec. Gold lithogeochemistry in the Val-d'Or Formation has shown that it is possible to distinguish: (i) background values (1.4–3.5 ppb Au); (ii) zones of primarily anomalous gold values around the Lamaque–Sigma mines (median: 15 ppb Au); (iii) enrichment halos around gold orebodies (median: 70 ppb Au); and (iv) secondary gold enrichment in shear zones. We conclude that the Val-d'Or Formation is auriferous, i.e., anomalously rich in gold at least in some of its parts and contains the Lamaque – Sigma gold mines, representing 68% of the total gold production in the district. The Val-d'Or Formation is part of a central volcanic complex within an island-arc system. The centre of this complex is located in the main Lamaque plug, and this environment may be compared to high-temperature active geothermal systems that are commonly responsible for the formation of epithermal gold deposits. Gold mineralization at Sigma and Lamaque is considered to be related to a late hydrothermal phase or a retrograde phase of regional metamorphism. For the formation of the gold deposits, two distinct and successive events are postulated: (i) a gold-rich synvolcanic geothermal activity and (ii) a late remobilisation from the host rocks followed by deposition of gold ore within favourable structures.

Gold Deposits of the ~15-Moz Ahafo South Camp, Sefwi Granite-Greenstone Belt, Ghana: Insights into the Anatomy of an Orogenic Gold Plumbing System

2021 ◽  
Author(s):  
Quentin Masurel ◽  
Paul Morley ◽  
Nicolas Thébaud ◽  
Helen McFarlane
Keyword(s):  
Rock Mass ◽  
Shear Zone ◽  
Gold Mineralization ◽  
Hanging Wall ◽  
Spatial Association ◽  
Sedimentary Rocks ◽  
Shear Zones ◽  
Gold Deposits ◽  
Orogenic Gold ◽  
Plutonic Rocks

Abstract The ~15-Moz Ahafo South gold camp is located in southwest Ghana, the world’s premier Paleoproterozoic gold subprovince. Major orogenic gold deposits in the camp include Subika, Apensu, Awonsu, and Amoma. These deposits occur along an ~15-km strike length of the Kenyase-Yamfo shear zone, a major tectonostratigraphic boundary juxtaposing metamorphosed volcano-plutonic rocks of the Sefwi belt against metamorphosed volcano-sedimentary rocks of the Sunyani-Comoé basin. In this study, we document the geologic setting, structural geometry, and rheological architecture of the Ahafo South gold deposits based on the integration of field mapping, diamond drill core logging, 3-D geologic modeling, and the geologic interpretation of aeromagnetic data. At the camp scale, the Awonsu, Apensu, and Amoma deposits lie along strike from one another and share similar hanging-wall plutonic rocks and footwall volcano-sedimentary rocks. In contrast, the Subika gold deposit is hosted entirely in hanging-wall plutonic rocks. Steeper-dipping segments (e.g., Apensu, Awonsu, Subika) and right-hand flexures (e.g., Amoma, Apensu) in the Kenyase-Yamfo shear zone and subsidiary structures appear to have represented sites of enhanced damage and fluid flux (i.e., restraining bends). All gold deposits occur within structural domains bounded by discontinuous, low-displacement, sinistral N-striking tear faults oblique to the orogen-parallel Kenyase-Yamfo shear zone. At the deposit scale, ore-related hydrothermal alteration is zoned, with distal chlorite-sericite grading into proximal silica-albite-Fe-carbonate mineral assemblages. Alteration halos are restricted to narrow selvages around quartz-carbonate vein arrays in multiple stacked ore shoots at Subika, whereas these halos extend 30 to 100 m away from the ore zones at Apensu and Awonsu. There is a clear spatial association between shallow-dipping mafic dikes, mafic chonoliths, shear zones, and economic gold mineralization. The abundance of mafic dikes and chonoliths within intermediate to felsic hanging-wall plutonic host rocks provided rheological heterogeneity that favored the formation of enhanced fracture permeability, promoting the tapping of ore fluid(s). Our interpretation is that these stacked shallow-dipping mafic dike arrays also acted as aquitards, impeding upward fluid flow within the wider intrusive rock mass until a failure threshold was episodically reached due to fluid overpressure, resulting in transient fracture-controlled upward propagation of the ore-fluid(s). Our results indicate that high-grade ore shoots at Ahafo South form part of vertically extensive fluid conduit systems that are primarily controlled by the rheological architecture of the rock mass.

Timing between granitoid emplacement and associated gold mineralization: examples from the ca. 2.7 Ga Harare–Shamva greenstone belt, northern Zimbabwe

1996 ◽  
Vol 33 (7) ◽  
pp. 981-992 ◽  
Author(s):  
M. L. Vinyu ◽  
H. A. Jelsma ◽  
R. Frei
Keyword(s):  
Greenstone Belt ◽  
Gold Mineralization ◽  
Time Frame ◽  
Gold Deposits ◽  
Isotopic Signatures ◽  
Ore Minerals ◽  
Granitoid Emplacement ◽  
Wide Scale ◽  
Temporal And Spatial ◽  
Favorable Conditions

Structurally controlled Late Archaean gold mineralizations associated with felsic plutons in the Harare–Shamva greenstone belt, Zimbabwe, are synchronous with the emplacement of their hosts. The ages of these mineralizations are identical to those reported from other mesothermal gold deposits elsewhere in the Zimbabwe Craton. The Pb and Nd isotopic signatures of the host plutons are compatible with a direct mantle or a short crustal residence period for the protoliths to the host intrusions. The coincidence of the Pb-isotope data from ore minerals with the whole-rock trends (errorchrons) of their host intrusives strongly suggests that the gold could have a magmatic, rather than a metamorphic, source. There is no evidence from the Pb isotopes of significant involvement of older basement in the genesis of gold deposits associated with felsic intrusions in the Harare–Shamva greenstone belt. On a craton-wide scale, the time frame around 2.65 Ga represents a period of significant crustal growth (through addition of mantle-derived magma), deformation, and metamorphism. The temporal and spatial coincidence of these three parameters has created favorable conditions for the emplacement of the largest class of Archaean gold mineralizations that are currently known in the country.

scholarly journals Virtual Structural Analysis of Jokisivu Open Pit Using ‘Structure-from-Motion’ Unmanned Aerial Vehicles (UAV) Photogrammetry: Implications for Structurally-Controlled Gold Deposits in Southwest Finland

2018 ◽  
Vol 10 (8) ◽  
pp. 1296 ◽  
Author(s):  
Mohammad Sayab ◽  
Domingo Aerden ◽  
Markku Paananen ◽  
Petri Saarela
Keyword(s):  
High Resolution ◽  
Unmanned Aerial Vehicles ◽  
Gold Mineralization ◽  
Regional Scale ◽  
Shear Zones ◽  
Gold Deposits ◽  
Open Pit ◽  
Conjugate System ◽  
Aerial Vehicles ◽  
D Model

Unmanned aerial vehicles (UAVs) are rapidly growing remote sensing platforms for capturing high-resolution images of exposed rock surfaces. We used a DJI Phantom 3 Professional (P3P) quadcopter to capture aerial images that were used to generate a high-resolution three-dimensional (3-D) model of the Jokisivu open-pit gold deposit that is located in southwestern Finland. 158 overlapping oblique and nadir images were taken and processed with Agisoft Photoscan Pro to generate textured 3-D surface models. In addition, 69 overlapping images were taken from the steep faces of the open pit. We assessed the precision of the 3-D model by deploying ground control points (GCPs) and the average errors were found minimal along X (2.0 cm), Y (1.2 cm), and Z (5.0 cm) axes. The steep faces of the open pit were used for virtual structural measurements and kinematic analyses in CloudCompare and ArcGIS to distinguish the orientation of different fracture sets and statistical categorization, respectively. Three distinct fracture sets were observed. The NW-SE and NE-SW striking fractures form a conjugate geometry, whereas the NNW-SSE striking fractures cut the conjugate fracture set. The orientation of conjugate fractures match well with the resource model of the deposit and NW- and NE-trending segments of regional-scale anastomosing shear zones. Based on the conjugate geometry of fracture sets I and II, and the regional pattern of anastomosing shear system lead us to interpret an origin of gold mineralization in two stages. An early N-S or NNW-SSE crustal shortening, corresponding to the regional D4 (ca. 1.83–1.81 Ga) or pre-D4 (ca. 1.87–1.86 Ga) Svecofennian tectonic event(s) that produced anastomosing shear zones. Subsequent E-W directed D5 contraction (ca. 1.79–1.77 Ga) partly reactivated the anastomosing shear zones with the formation of conjugate system, which controlled the migration of fluids and gold mineralization in SW Finland.

Geology, lithogeochemistry, and significance of porphyry intrusions associated with gold mineralization within the Timmins–Porcupine gold camp, Canada

2019 ◽  
Vol 56 (4) ◽  
pp. 399-418 ◽  
Author(s):  
Peter J. MacDonald ◽  
Stephen J. Piercey
Keyword(s):  
Partial Melting ◽  
Greenstone Belt ◽  
Deformation Zone ◽  
Gold Mineralization ◽  
Gold Deposits ◽  
Crustal Thickening ◽  
Abitibi Greenstone Belt ◽  
Crustal Structures ◽  
Intrusive Rocks ◽  
Intrusive Suite

The Timmins–Porcupine gold camp, Abitibi greenstone belt, is host >60 Moz of Au with many gold deposits spatially associated with porphyry intrusions and the Porcupine–Destor deformation zone (PDDZ). Porphyry intrusions form three suites. The Timmins porphyry suite (TIS) consists of high-Al tonalite–trondjhemite–granodiorite (TTG) with calc–alkalic affinities and high La/Yb ratios and formed during ∼2690 Ma D1-related crustal thickening and hydrous partial melting of mafic crust where garnet and hornblende were stable in the residue. The Carr Township porphyry intrusive suite (CIS) and the granodiorite intrusive suite (GIS) also have high-Al TTG, calc-alkalic affinities, but were generated 10–15 million years after the TIS; the CIS were generated at shallower depths (during postorogenic extension?) with no garnet in the crustal residue, whereas the GIS formed during D2 thrust-related crustal thickening and partial melting where garnet was stable in the residue. Gold mineralization is preferentially associated with the TIS, and to a lesser extent the GIS, proximal to the PDDZ. Intrusions near mineralization have abundant sericite, carbonate, and sulphide alteration. These intrusions exhibit low Na2O and Sr, and high Al2O3/Na2O, K2O, K2O/Na2O, Rb, and Cs, (i.e., potassic alteration); sulfide- and carbonate-altered porphyries have high (CaO + MgO + Fe2O3)/Al2O3 and LOI values. Although porphyries are not genetically related to gold mineralization, they are spatially related and are interpreted to reflect the emplacement of intrusions and subsequent Au-bearing fluids along the same crustal structures. The intrusive rocks also served as structural traps, where gold mineralization precipitated in dilatant structures along the margins of intrusions during regional (D3?) deformation.

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