scholarly journals Indices De Minéralisations En Or Dans La Province Panafricaine Du Sud Maradi (Sud Niger)

2021 ◽  
Vol 17 (21) ◽  
pp. 238
Author(s):  
Souley Baraou Idi ◽  
Moussa Konaté ◽  
Yacouba Ahmed ◽  
Abdoulwahid Sani
Keyword(s):  
Gold Mineralization ◽  
Methodological Approach ◽  
Shear Zones ◽  
Metallogenic Province ◽  
Fire Assay ◽  
Modest Contribution ◽  
Pan African ◽  
Basement Rocks ◽  
Vibrating Table ◽  
Primary Gold

Le socle du Sud Maradi (Sud Niger) correspond à l’extrémité Nord du bouclier Bénino-Nigérian, appartenant à la zone mobile panafricaine à l’Est du Craton Ouest-Africain. Cette étude apporte une modeste contribution dans la caractérisation géochimique des minéralisations aurifères de cette province métallogénique panafricaine. A cet effet, l’approche méthodologique mise en oeuvre associe le dosage géochimique de l’or par absorption atomique (Au Fire Assay/AA) pour les roches saines, et la séparation des pépites d’or par l’utilisation de la table à secousse pour les altérites du socle et les sédiments (placers et paléoplacers). Les analyses géochimiques ont mis en évidence l’existence de deux types de minéralisations: primaires et secondaires. Les minéralisations primaires de l’or sont à l’état disséminé (faibles teneurs de 0.005 à 0.017 g/t) mais des teneurs relativement plus élevées (0.006 à 0.017 g/t) ont été enregistrées au voisinage des zones de cisaillement du socle. Tandis que la minéralisation secondaire, mise en évidence dans les altérites du socle, dans les alluvions (placers) et dans les grès du Crétacé (paléoplacers) présentent des teneurs en or plus élevées (5 à 30 g/t), dépassant largement les teneurs des minéralisations primaires observées dans les roches saines du socle. Ce grand écart de teneurs s’explique par un fort lessivage du socle, qui aurait permis une reconcentration de l’or dans les sédiments. The South Maradi (South Niger) basement corresponds to the northeastern part of the Benin-Nigerian Shield, belonging to the Pan-African mobile zone, which is located to the east of the West African Craton. This study brings a modest contribution to the geochemical characterization of gold mineralization in this Pan-African metallogenic province. For this purpose, the methodological approach implemented combines the geochemical determination of gold contents by atomic absorption (Au Fire Assay/AA) for basement rocks and physical separation of gold specks by using the vibrating table process for basement alterites and sediments (placers and paleoplacers). The obtained results showed two types of gold mineralization: primary and secondary. Primary gold mineralization is in a disseminated state (low contents of 0.005 to 0.017 g / t) but relatively the higher values (0.006 to 0.017 g / t) were recorded near the basement shear zones. While the secondary gold mineralization, highlighted in basement alterites, alluvium (placers) and Cretaceous sandstones (paleoplacers) present higher gold contents (5 to 30 g / t) than primary gold contents observed in basement rocks. This large difference in values can be explained by a strong alteration of the basement, which would have allowed a reconcentration of the gold in the sediments.

The Adola Fold and Thrust Belt, southern Ethiopia: a re-examination with implications for Pan-African evolution

1989 ◽  
Vol 126 (6) ◽  
pp. 647-657 ◽  
Author(s):  
W. H. “Beraki ◽  
F. F. Bonavia ◽  
T. Getachew ◽  
R. Schmerold ◽  
T. Tarekegn
Keyword(s):  
Shear Zones ◽  
Southern Ethiopia ◽  
Low Grade ◽  
Thrust Belt ◽  
Progressive Development ◽  
Detailed Structural Analysis ◽  
Pan African ◽  
Basement Rocks ◽  
Fold And Thrust Belt ◽  
Dominant Structure

AbstractThe Adola Fold and Thrust Belt of Ethiopia is a late- Precambrian, north–south trending belt of volcanic-sedimentary and ophiolite–like units overlying ‘basement rocks’ (gneisses and granitic gneisses). Detailed structural analysis and data from microfabrics have documented two thrusting events (D1, D5) and three folding phases (F2, F3, F4). All deformations have affected both the rocks of the Adola Fold and Thrust Belt and the ‘older basement’. The structural history is recorded as follows: (1) formation of ductile shear zones (Dl); (2) progressive development of recumbent folds (F2); (3) a superimposed north-south trending, tight to isoclinal, upright penetrative folding phase (F3), which imparted the dominant structure of the region; (4) F3 was later gently affected, at right angles to F3, by the last folding event (F4). Metamorphic conditions during this deformational cycle reached highest greenschist to medium amphibolite facies conditions. Close to major thrust contacts imbrication produced metamorphic discontinuities. Marked retrograde metamorphism in narrow horizons indicates a continuation of minor movements along the major thrusts, postdating the metamorphic peak. Evidence of a second thrusting/faulting episode (D5) is only recorded at the mesoscale. This latter event was accompanied by very low to low grade metamorphic conditions. In accepting the previously reported age of 1030±40 Ma for the volcanic–sedimentary unit of the Adola Fold and Thrust Belt, and the interpretation of these units as an immature island arc, a possibly early Pan-African oceanic accretion is postulated.

scholarly journals Petrographic Characterization of Hydrothermal Gold Deposits in Adi Gozomo Area, Northwestern Tigray, Ethiopia

2019 ◽  
Vol 9 (2) ◽  
pp. 801-807
Keyword(s):  
Gold Mineralization ◽  
Tectonic Setting ◽  
Shear Zones ◽  
Gold Deposits ◽  
Sulfide Deposit ◽  
Alteration Zone ◽  
Petrographic Analysis ◽  
Metasedimentary Rocks ◽  
Quartz Veins ◽  
Basement Rocks

Gold mineralization in Adi Gozomo area in northwestern Ethiopia was studied through petrographic analysis from both surface and core rock samples. Mineralization is associated with Neoproterozoic basement rocks comprised of metavolcanic, metasedimentary rocks and intrusives. Four phases of deformation and development of NE-SW foliation and shear zones were some of the common geological structures. The hydrothermal gold deposit s cramped to shear zones, 2nd generation quartz veins, 4th phase of deformation, silisifed and carbonatized alteration zone. Based on decreasing order of abundance the ore assemblage of the area includes pyrite, chalcopyrite, sphalerite, pyrrhotite, arsenopyrite and gold. The petrographic data indicates that the deposit is hydrothermal vein related type and an island arc tectonic setting. The mineralization is comparable with other known orogenic sulfide deposit types of the country in particular and Arabian-Nubian Shield in general.

scholarly journals RECOGNITION OF GOLD MINERALIZATION FAVORABILITY ZONES THROUGH AIRBORNE GAMMA-RAY SPECTROMETRY AND MAGNETOMETRY IN BRUSQUE AND BOTUVERÁ REGION, SOUTHERN BRAZIL

2018 ◽  
Vol 36 (3) ◽  
pp. 1 ◽  
Author(s):  
Bruno Macchioni Pereira ◽  
Francisco Jose Fonseca Ferreira
Keyword(s):  
Hydrothermal Alteration ◽  
Gamma Ray ◽  
Gold Mineralization ◽  
Shear Zones ◽  
Magnetic Data ◽  
Gamma Ray Spectrometry ◽  
Southern Brazil ◽  
Santa Catarina ◽  
Index Overlay ◽  
Primary Gold

ABSTRACT. The northeastern portion of Santa Catarina State, southern Brazil, bears important primary gold mineralization associated with granitic intrusions with potassic and phyllic hydrothermal alteration zones and a phase shear zone reactivation. Airborne radiometric and magnetic data were applied in the study area through the use of gamma-ray spectrometry (Total Count, K, eTh and eU) and suggestive parameters of hydrothermal alteration as Kd, Ud and F, in association with geological units, while magnetometry (RTP, THDR, TDR and Signum Transform) was applied in the definition of the structural framework. Geophysical data was interpreted and integrated to geological information, such as lithologic units, structures, shear zones and gold mineralization, using the knowledge driven and index overlay methods in order to define favorable targets. The geophysical and geological data exhibit good correlation, as seen in the gamma-ray spectrometric domains and magnetic lineaments, and the favorability map shows important target areas for primary gold mineralization. It was possible to observe in the geophysical maps that shear zones and faults have more influence in the occurrences than potassic and phyllic hydrothermal alteration related to granitic intrusions.Keywords: geophysical exploration, knowledge-driven, Dom Feliciano Belt.RESUMO. A porção nordeste do estado de Santa Catarina, sul do Brasil, possui importantes mineralizações auríferas primárias associadas a intrusões graníticas com zonas de alteração hidrotermal potássica e fílica e posterior fase de reativação de zonas de cisalhamento. Dados radiométricos e magnéticos aerogeofísicos foram aplicados na área de estudo através do uso de gamaespectrometria (Contagem Total, K, eTh e eU) e parâmetros sugestivos de alteração hidrotermal como Kd, Ud e Parâmetro F. Em associação com unidades geológicas, enquanto a magnetometria (RTP, GHT, ISA e Signum Transform) foi aplicada na definição do arcabouço estrutural. Os dados geofísicos foram interpretados e integrados às informações geológicas, como unidades litológicas, estruturas, zonas de cisalhamento e mineralizações de ouro, utilizando os métodos knowledge-driven e index overlay para definir alvos favoráveis. Os dados geofísicos e geológicos apresentam boa correlação, como visto nos domínios espectrométricos de raios gama e lineamentos magnéticos, e o mapa de favorabilidade mostra áreas-alvo importantes para a mineralização de ouro primária. Foi possível observar nos mapas geofísicos que as zonas de cisalhamento e as falhas têm mais influência nas ocorrências do que as zonas de alteração hidrotermal potássica e fílica relacionada às intrusões graníticas.Palavras-chave: exploração geofísica, knowledge-driven, Cinturão Dom Feliciano.

scholarly journals Decratonization by rifting enables orogenic reworking and transcurrent dispersal of old terranes in NE Brazil

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Carlos E. Ganade ◽  
Roberto F. Weinberg ◽  
Fabricio A. Caxito ◽  
Leonardo B. L. Lopes ◽  
Lucas R. Tesser ◽  
...  
Keyword(s):  
Shear Zones ◽  
Boundary Region ◽  
The North ◽  
Pan African ◽  
Juvenile Material ◽  
Oceanic Basin ◽  
Borborema Province ◽  
Isotopic Model ◽  
Late Neoproterozoic

AbstractDispersion and deformation of cratonic fragments within orogens require weakening of the craton margins in a process of decratonization. The orogenic Borborema Province, in NE Brazil, is one of several Brasiliano/Pan-African late Neoproterozoic orogens that led to the amalgamation of Gondwana. A common feature of these orogens is that a period of extension and opening of narrow oceans preceded inversion and collision. For the case of the Borborema Province, the São Francisco Craton was pulled away from its other half, the Benino-Nigerian Shield, during an intermittent extension event between 1.0–0.92 and 0.9–0.82 Ga. This was followed by inversion of an embryonic and confined oceanic basin at ca. 0.60 Ga and transpressional orogeny from ca. 0.59 Ga onwards. Here we investigate the boundary region between the north São Francisco Craton and the Borborema Province and demonstrate how cratonic blocks became physically involved in the orogeny. We combine these results with a wide compilation of U–Pb and Nd-isotopic model ages to show that the Borborema Province consists of up to 65% of strongly sheared ancient rocks affiliated with the São Francisco/Benino-Nigerian Craton, separated by major transcurrent shear zones, with only ≈ 15% addition of juvenile material during the Neoproterozoic orogeny. This evolution is repeated across a number of Brasiliano/Pan-African orogens, with significant local variations, and indicate that extension weakened cratonic regions in a process of decratonization that prepared them for involvement in the orogenies, that led to the amalgamation of Gondwana.

A structural reappraisal of the Beardmore–Geraldton Belt at the southern boundary of the Wabigoon subprovince, Ontario, and implications for gold mineralization

2004 ◽  
Vol 41 (2) ◽  
pp. 217-235 ◽  
Author(s):  
Bruno Lafrance ◽  
Jerry C DeWolfe ◽  
Greg M Stott
Keyword(s):  
Gold Mineralization ◽  
Shear Zones ◽  
Axial Plane ◽  
Superior Province ◽  
Southern Boundary ◽  
Gold Mines ◽  
Southern Margin ◽  
Ore Zones

The Beardmore–Geraldton Belt occurs along the southern margin of the Archean Wabigoon subprovince, Superior Province, Ontario. The belt consists of shear-bounded interleaved metasedimentary and metavolcanic units. The units were imbricated from 2696 to 2691 Ma during D1 thrusting and accretion of the Wabigoon, Quetico, and Wawa subprovinces. Post-accretion D2 deformation produced regional F2 folds that transposed lithological units parallel to the axial plane S2 cleavage of the folds. During D3 deformation, the folds were overprinted by a regional S3 cleavage oriented anticlockwise of F2 axial planes, and lithological contacts and S2 cleavage were reactivated as planes of shear within dextral regional shear zones that generally conform to the trend of the belt. D3 is a regional dextral transpression event that also affected the Quetico and Wawa subprovinces, south of the Beardmore–Geraldton Belt. Gold mineralization at the Leitch and MacLeod-Cockshutt mines, the two richest past-producing gold mines in the Beardmore–Geraldton Belt, is associated with D3 shear zones and folds, overprinting regional F2 folds. The plunge of the ore zones is parallel to F3 fold axes and to the intersection of D3 shear zones with F2 and F3 folds.

Geochemical evaluation of the in-situ regolith of Madengi hills of Dodoma, Tanzania. Implication on bedrock mapping and delineating gold mineralization target

2021 ◽  
pp. geochem2021-074
Author(s):  
Godson Godfray
Keyword(s):  
Gold Mineralization ◽  
Early Stage ◽  
Shear Zones ◽  
Soil Geochemistry ◽  
Residual Soils ◽  
Content Type ◽  
Geochemical Evaluation ◽  
Supplementary Material ◽  
Pathfinder Elements

Successful gold exploration projects depend on a piece of clear information on the association between gold, trace elements, and mineralization controlling factors. The use of soil geochemistry has been an important tool in pinpointing exploration targets during the early stage of exploration. This study aimed to establish the gold distribution, the elemental association between gold and its pathfinder elements such as Cu, Zn, Ag, Ni, Co, Mn, Fe, Cd, V, Cr, Ti, Sc, In, and Se and identify lithologies contributing to the overlying residual soils. From cluster analysis, a high similarity level of 53.93% has been shown with Ag, Cd, and Se at a distance level of 0.92. Au and Se have a similarity level of 65.87% and a distance level of 0.68, hence is proposed to be the most promising pathfinder element. PCA, FA, and the Pearson's correlation matrix of transformed data of V, Cu, Ni, Fe, Mn, Cr, and Co and a stronger correlation between Pb and U, Th, Na, K, Sn, Y, Ta and Be shows that source gold mineralization might be associated with both hornblende gneisses interlayered with quartzite, tonalite, and tonalitic orthogneiss. From the contour map and gridded map of Au and its pathfinder elements, it has been noted that their anomalies and target generated are localized in the Northern part of the area. The targets trend ESE to WNW nearly parallel to the shear zones as a controlling factor of Au mineralization emplacement.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5721965

Granitoid-hosted gold mineralization in Ikibzyaksky ore field: a new milestone in Baikal-Patom metallogenic province gold potential study

2021 ◽  
pp. 4-18
Author(s):  
ANATOLY IVANOV ◽  
YURI AGEEV ◽  
ALEXANDER MEZENTSEV ◽  
BASIL MOLOCHNY ◽  
VICTOR KONKIN
Keyword(s):  
Fault Zone ◽  
Gold Mineralization ◽  
High Grade ◽  
Metallogenic Province ◽  
Deep Fault ◽  
Potential Study ◽  
Plutonic Belt ◽  
Gold Sulfide ◽  
First Time ◽  
Deep Fault Zone

New data is provided on gold mineralization in the southern Baikal-Patom metallogenic province, Ikibzyakskoye ore field, located in Pravo-Mamakansky deep fault zone separating Patom fold area from Baikal-Vitim volcanic-plutonic belt. For the first time, the metallogenic province was found to comprise granitoid-hosted ore vein-stringer zones with high-grade economic gold sulfide-quartz mineralization. This mineralization is localized within fault shistosity zones manifesting intense beresitization and listvenitization (in metabasite xenoliths).

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.

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