Rb—Sr and Sm—Nd geochronology of lower Proterozoic granite—greenstone terrains in French Guiana, South America

Gruau, Gérard; Martin, Hervé; Leveque, Bernard; Capdevila, R.; Marot, A.

doi:10.1016/0301-9268(85)90029-4

Cited by 88 publications

(39 citation statements)

References 23 publications

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“…Similar highgrade metamorphic rocks in Venezuela and Brazil have yielded Sm-Nd ages of 2.2 Ga (Teixeira et al, 1989; and in French Guyana have given ages of 2.23 Ga (U-Pb method on zircons; and 2.0 Ga (Rb-Sr method; Gruau et al, 1985).…”

Section: Regional Geologymentioning

confidence: 89%

“…4 Geological characteristics of the Omai deposit compared with other Paleoproterozoic and Late-Archean gold deposits. Principal references: 1- Bertoni et al (1991a); 2- 3-Norcross (1997);4-GebreMariam et al (1993);5-Hagemann et al (1994);6 -Tremlow (1984); 7- 8-Golding et al (1989); 9- ; 10- 11-Kent et al (1996); 12- Groves et al (1998);13-Anglin et al (1996);14-Milési et al (199214-Milési et al ( ,199515-Fouillac et al (1993);16-Oberthûr et al (1996) 148 CHAPTER IV Table 4.1 Ages of granite-greenstone terranes and gold deposits at Omai and in the Guiana Shield 169 Nd ample / 0.1967 chondrite ) -1; (d) e Nd calculated at T = 1999 Ma for scheelite, T = 2102 Ma for the Omai stock, T=2120 Ma for quartzfeldspar porphyry, and T = 2200 Ma for mafic volcanic rocks; ^ Data for Barama-Mazaruni volcanic rocks from ; ® Data for Cuyuni (Barama-Mazaruni) limestone from ; D ata for Paramaca Series, French Guiana, from Gruau et al (1985).. 173 Table 5.2 Comparison between the normative mineral calculations for bauxitic latérite from Fongo Tongo deposit, Cameroon, using the method of Nyobe (1991) and MINNOR; nc = not considered; (°) -Al-goethite has been calculated by Nyobe (1991) as goethite; * = normative minerals using the method of Nyobe (1991); ** = normative minerals using MINNOR 215 Table 5.3 Comparison between the mineralogical compositions of ironstones of the Gaoua area in Burkina Faso determined by semi-quantitative XRD method and normative mineralogical compositions using MINNOR. Sample names represent their iron content; n = number of analysed samples; (*) = mineralogical composition determined by semiquantitative XRD method (data from Boeglin and Mazaltarim, 1989, Table III); only the principal mineralogical phases are determined; (**) = normative mineralogical composition using MINNOR; only the same minerals determined by XRD method are shown 217 Table 5.…”

Section: Chapter IImentioning

confidence: 99%

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Géologie, géochimie et métallogénie du gisement d'or Omai, Bouclier Guyanais, Amérique du Sud =

Voicu¹

1999

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IVdépôt de la minéralisation à Ornai (basse température, pression, salinité, et contenu en CO 2 , pH légèrement acide à neutre, fugacités modérées de l'oxygène et du soufre, fugacité élevée des tellurures), l'implication de l'eau de surface, la présence des structures hôtes de la minéralisation de nature essentiellement cassante et la localisation dans un terrain faiblement métamorphisé sont autant de critères permettant de classer Ornai dans la catégorie des gîtes épithermaux. D'autres caractéristiques majeures tels que: le style d'altération; le cadre géodynamique; l'emplacement tardi-orogénique/syn-à tarditectonique; la présence des fluides d'une source profonde et; de manière moins directe, la paragénèse minéralogique se rattachent à la définition des gîtes mésothermaux plus profonds. La superposition des caractéristiques épi-et mésothermales d'Omai correspond donc à la partie supérieure du "continuum model" proposé pour les gisements archéens de type "gold-only" et définie comme le domaine crustal dit épizonal. Ornai serait donc un premier exemple de gîte orogénique aurifère d'âge paléoprotérozoïque de type épizonal associé aux granitoïdes et aux roches vertes. Il représente un équivalent de ce type de gîte ayant été décrit uniquement dans certains cratons archéens (Yilgarn et Zimbabwe).Mots clé: Guyana, Paléoprotérozoïque, or, géochimie, métallogénie ABSTRACTThe Omai gold mine is located in the Barama-Mazaruni Supergroup, part of the Paleoproterozoic greenstone belt of the north-central Guiana Shield. The lithological sequence consists of mafic volcanic (and genetically related subvolcanic maficultramafic bodies) to felsic volcanic cycles with intercalated sediments. The volcanosedimentary unit was intruded by a quartz monzodiorite plug (the Omai stock) and several irregularly-shaped quartz-feldspar porphyry and rhyolite dikes. Postmineralization mafic dikes and sills were intruded discontinuously from Mesoproterozoic to Triassic. The Barama-Mazaruni volcano-sedimentary sequence has been metamorphosed to lower greenschist faciès. The local structure is relatively simple and consists of two deformational phases (Dl and D2). Dl phase resulted in the ESE-WNW trending/steeply dipping regional scale foliation and ductile shear zones, whereas the D2 event caused brittle± ductile fracturing with moderate dips, oriented perpendicularly to Dl shear zones. D2 structures provided the main pathways for the mineralizing fluids.The Omai deposit consists of two gold mineralized zones exploited in open pit operations referred to as Fennell and Wenot. Fennell mineralization is mainly hosted by the Omai stock and to a lesser extends by the volcanic rocks (tholeiitic basalts and calcalkaline andésites). Wenot mineralization is mainly hosted by tabular quartz-feldspar porphyry dikes as well as by strongly silicified rhyolite dikes, and subordinately by andésites and metapelites.The geological features and geochronological data of these ore zones suggest that they are genetically related and represent a contemporaneous metallo...

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Section: Regional Geologymentioning

confidence: 89%

Section: Chapter IImentioning

confidence: 99%

Géologie, géochimie et métallogénie du gisement d'or Omai, Bouclier Guyanais, Amérique du Sud =

Voicu¹

1999

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“…This monotonous area nevertheless features some isolated hills and inselbergs, with both tabular and linear relief. Most of these feature in three mountain chains that are parallel to the coast and frame three planer areas (see Paget, 1999 in Figure 3): (I) in the southern Tumuc Humac massif, inselbergs such as Mitaraka Mount reach an altitude of more than 650 m -detailed accounts of the geomorphology and geology of rock outcrops in this area are provided by Hurault (1963); (II) in the southern peneplain, rivers flow from the south through typical 'demi-orange' relief (Gruau, Martin, Leveque, Capdevilla, & Marot, 1985;Teixeira, Taasinari, Cordani, & Kawashita, 1989); (III) the Inini-Camopi Massif corresponds to the highest (up to 830 m) and is associated with river network deflexion to the east and west; (IV) the Central Massif (also called the central peneplain) runs from north of the fourth parallel to the Northern chain (V) and is associated with volcano-sedimentary rock often covered by lateritic duricrust that protect the highest relief of about 500 m (Choubert, 1957); and finally (VI), the coastal area which is a 15-to 20-km strip of lowland characterized by enlarged flat wetlands between lowered multiconvex reliefs. Inland areas are covered by almost continuous tropical rainforest that is one of the last of its kind to be almost undisturbed by recent human activity (Hammond, 2005).…”

Section: Study Areamentioning

confidence: 99%

Landform and landscape mapping, French Guiana (South America)

et al. 2013

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In this paper two geomorphologic maps (landform level and landscape level) are presented covering the French Guianan rainforest (84,000 km 2 ) using full-resolution Shuttle Radar Topography Mission (SRTM) data. The entire country was segmented into 224,000 landform units on the basis of an original object-oriented approach using a modified counting box algorithm. A Principal Components Analysis (PCA) followed by k-means clustering (Ward's method) identified 12 different landform types corresponding to theoretical elementary landforms. The landscape map was generated by analyzing the spatial distribution of the different landform types. The different maps and models were compared with topographic field data collected on 92 transects totaling 260 km in length. The object-focused approach is a very efficient method that preserves geomorphologic consistency and discriminates between landforms using simple descriptors that are easily understood by non-geomorphologists. Despite major noise in the data, the landform map proved to be reliable and provided a strong spatial structure for the definition of landscape units. We recommend using the landform map at scales 1: 100,000-1: 250,000. Landscape map, used on a 1:1,000,000-1:2,000,000 scale, enabled us to draw bio-geographical limits in this region and provides exhaustive relief information that usefully supplements the geological map.

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“…The dense pristine tropical rainforest is dominated by an isolated and partly denuded granitic inselberg, which emerges from a plateau of deeply weathered metavolcanic rocks of the Paramaca formation (Choubert, 1974). The inselberg bedrock is a 1.9 to 2.1 Ga old "Caribbean" granite (Depagne and Lelong, 1965;Gruau et al, 1985). This rock is a pinkish monzonitic-type granite.…”

Section: Study Sitementioning

confidence: 99%

Variation des rapports 87Sr/86Sr dans les sols et les plantes d’un inselberg tropical

Poszwa

Ferry²,

Pollie

et al. 2009

Ann. For. Sci.

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Abstract• From the summit downslope a granitic inselberg in French Guiana, soils and vegetation evolve from bare granite covered by cyanobacteria, to a savannah-type vegetation on thin patchy sandy accumulations, then to a low forest on shallow young soils and to a high forest on deep highly weathered ultisols.• We have used element budgets and Sr isotopic variations in soils and plants to investigate the mineral nutrient supply sources of the different plant communities.• Granite and atmospheric deposition have 87 Sr/ 86 Sr ratios of 1.3 and 0.71, respectively. The 87 Sr/ 86 Sr ratio of cyanobacteria (0.72) suggests granite weathering by cyanobacteria crusts. The 87 Sr/ 86 Sr ratio of the savannah-type vegetation is 0.73 and varies between 0.75 and 0.76 in the low and high forest leaf litter regardless of soil depth, age and degree of impoverishment.• These almost constant ratio suggest that forest Sr comes from rainwater and from the summit of this inselberg, where it is released and redistributed along the slope, by surface flow, lateral redistribution of litter, and mineral particles. However, because of its very low content in the rock and soils, Ca is supplied to plants by atmospheric deposition. • Du sommet vers la base d'un inselberg granitique (Nouragues, Guyane Française), les sols et la végétation évoluent depuis des savanes sur des ilots sableux entre les affleurements rocheux couverts de cyanobactéries, vers une forêt basse sur sols peu épais, riches en minéraux altérables puis une forêt haute sur sols très profonds et altérés. Mots• Les variations isotopiques du strontium des sols et des plantes ont été mesurées pour rechercher les sources de nutriments des différentes communautés végétales.• Les rapports 87 Sr/ 86 Sr du granite et des dépôts atmosphériques sont respectivement de 1,3 et 0,71. Le rapport 87 Sr/ 86 Sr des cyanobacteries (0,72) suggère une libération de Sr par altération du granite. Le rapport 87 Sr/ 86 Sr de la savanne est de 0,73 et varie entre 0,75 et 0,76 dans les litières de forêt basse et haute, quelle que soit la profondeur, et la richesse en minéraux altérables des sols.• La faiblesse et l'homogénéité surprenante de ces rapports suggèrent une alimentation en Sr des forêts essentiellement à partir de dépôts atmosphériques et des sols de la partie haute de l'inselberg, via des écoulements de surface, des redistributions latérales de litière et de particules minerales lors de crises érosives. Cependant, en raison de l'extrême pauvreté de la roche et des sols en calcium, le Ca des communautés végétales provient de la pluie.

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Rb—Sr and Sm—Nd geochronology of lower Proterozoic granite—greenstone terrains in French Guiana, South America

Cited by 88 publications

References 23 publications

Géologie, géochimie et métallogénie du gisement d'or Omai, Bouclier Guyanais, Amérique du Sud =

Géologie, géochimie et métallogénie du gisement d'or Omai, Bouclier Guyanais, Amérique du Sud =

Landform and landscape mapping, French Guiana (South America)

Variation des rapports 87Sr/86Sr dans les sols et les plantes d’un inselberg tropical

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