Uranium Mineralization in Saraya Granite, Senegal

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Uranium mineralization associated with albitization in a Paleoproterozoic granite:
example of the Saraya granite, (Eastern Senegal, West Africa)
Moumar Dièye, Cheikh Ibrahima Faye, Mahamadane Diène, Michel Cuney, Marc
Brouand, Mamadou Guèye
PII: S1464-343X(25)00037-8
DOI: https://doi.org/10.1016/j.jafrearsci.2025.105570
Reference: AES 105570
To appear in: Journal of African Earth Sciences
Received Date: 18 September 2024
Revised Date: 7 February 2025
Accepted Date: 7 February 2025
Please cite this article as: Dièye, M., Faye, C.I., Diène, M., Cuney, M., Brouand, M., Guèye, M.,
Uranium mineralization associated with albitization in a Paleoproterozoic granite: example of the Saraya
granite, (Eastern Senegal, West Africa), Journal of African Earth Sciences, https://doi.org/10.1016/
j.jafrearsci.2025.105570.
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Title: Uranium mineralization associated with albitization in a Paleoproterozoic granite: 1
example of the Saraya granite, (Eastern Senegal, West Africa) 2
Moumar Dièye1, Cheikh Ibrahima Faye1, Mahamadane Diène1, Michel Cuney2, Marc Brouand3, and Mamadou 3
Guèye1 4
1 : Ecole Nationale Supérieure des Mines et de la Géologie, Université Cheikh Anta Diop de Dakar, Sénégal 5
2 : GeoRessources, Université de Lorraine, CREGU, Villers les Nancy, France 6
3 : Areva NC/Business Unit Mine, Tour Areva – 1, Place de la coupole, 92084 Paris la défense Cedex, France 7
Abstract 8
The uranium mineralization occurrences hosted within the Saraya episyenites (hydrothermally 9
altered granites) were discovered between 1985 and 1960 during an airborne regional survey 10
conducted by prospectors from the Commissariat à l'Energie Atomique (C.E.A). Following this 11
discovery, a strategic and tactical exploration program led by the Compagnie Générale des 12
Matières Nucléaires (COGEMA) was undertaken between 1974 and 1984, which significantly 13
contributed to the improved delineation of these occurrences. Recent investigations carried out 14
by AREVA from 2008 to 2010 have facilitated the collection of fresh materials from drill core 15
samples of mineralized zones, along with detailed petro-mineralogical and geochemical studies. 16
Our results show that the uranium mineralization developed from peraluminous leucogranitic 17
granites, initially characterized by albitization is associated with dequartzification during the 18
episyenitization phase. This dequartzification resulted in the formation of vugs that were 19
subsequently filled by chlorite, uranium minerals, including coffinite, uraninite, and other 20
uranium oxides, along with Ti-oxides (rutile and anatase). Post ore-stage alteration led to the 21
development of carbonate minerals and argillization, in association with the leaching of the 22
primary uranium mineralization, as well as the remobilization of carbonaceous matter. 23
Enrichment in Medium Rare Earth Elements (MREE) and Heavy Rare Earth Elements (HREE), 24
as well as in yttrium, was also observed within the mineralized facies. 25
This mineralization event is part of a broader event spanning from the Paleoproterozoic to the 26
Mesoproterozoic, which also affected other uranium provinces in central Ukraine, Canada, 27
China, Australia, India, southern Morocco, and Guyana (Cuney et al., 2008). 28
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the Saraya episyenites
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the Saraya episyenites
were discovered between 1985 and 1960 during an airborne regional survey
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were discovered between 1985 and 1960 during an airborne regional survey
conducted by prospectors from the Commissariat à l'Energie Atomique (C.E.A).
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conducted by prospectors from the Commissariat à l'Energie Atomique (C.E.A).
a strategic and tactical exploration program led by the Compagnie Générale des
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a strategic and tactical exploration program led by the Compagnie Générale des
was undertaken
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was undertaken
between 1974 and 1984, which
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between 1974 and 1984, which
delineat
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delineat
ion of
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ion of
these
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these
occurrences
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occurrences
by AREVA from 2008 to 2010 ha
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by AREVA from 2008 to 2010 ha
ve facilitated
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ve facilitated
samples of mineralized zones
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samples of mineralized zones
, along with
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, along with
that
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that
the
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the
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uranium mineralization developed from
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uranium mineralization developed from
, initially characterized by albitization
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, initially characterized by albitization
episyenitization phase. This dequartzification
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episyenitization phase. This dequartzification

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1. Introduction 29
The Saraya deposit represents a typical example of a uranium mineralization associated with 30
albitization and dequartzification within a highly fractionated peraluminous granite (Mouthier, 31
1988; Bassot, 1997). In the ‘70s and ‘80s COGEMA drilled 441 rotary and diamond holes at 32
the Saraya Prospect to depths of 80–100 m. The new exploration program conducted in 2009 33
by AREVA, which drilled 72 RC and diamond holes down to depths of 200 m has provided 34
access to fresh materials from core drillings, offering an opportunity for a comprehensive 35
reevaluation of the alteration and mineralization processes at Saraya, the granite being largely 36
covered by a several meter-thick laterites (Blot et al., 1976). Due to the recent increase of the 37
uranium prices, a new exploration project is being developed on the Saraya deposit by Haranga 38
Ressources (https://haranga.com/our-projects/saraya-uranium-project/). 39
This study is of particular importance due to the presence of uranium deposits associated with 40
sodium metasomatism in many other regions each side of the Atlantic Ocean which may be 41
linked to a common event, well before the opening of the Atlantic Ocean, such as Poli in 42
northern Cameroon (Oesterlen and Vetter, 1986), the Mayo-Kebbi in Chad (Mbaguedje, 2015), 43
Trimdrart in southern Morocco, all located in Western Africa, as well as Lagoa Real in Brésil 44
and Kurupung in Guyana beyond the Atlantic Ocean (Cinelu and Cuney., 2006; Cuney et al., 45
2008) (Fig. 1a). 46
The objective of this study is to present a detailed mineralogical and whole rock geochemical 47
study from both mineralized and non-mineralized rocks of the Saraya intrusion to enhance our 48
understanding of the sodium metasomatic alteration, dequartzification, and uranium 49
mineralization processes within this plutonic complex. Additionally, this paper aims to 50
delineate the various stages of mineralization and post-mineralization processes at the Saraya 51
deposit. A comparison will be also done with other uranium deposits associated with the same 52
type of alteration each side of the Atlantic Ocean. 53
2. Geological setting 54
Proterozoic domains of varying extension are known within most continents (Africa, America, 55
Australia, Eurasia, Antartica) (Dioh, 1995) (Fig. 1a). The term "Birimian", initially defined in 56
Ghana by Kitson in 1928, describes Paleoproterozoic formations of the West African Craton 57
(WAC). These Birimian formations, were formed between 2250 and 2000 Ma during the 58
Eburnian orogeny (Abouchami et al., 1990; Liégeois et al., 1991; Boher et al., 1992; Hirdes et 59
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Due to the recent increase of the
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Due to the recent increase of the
on the Saraya deposit by Haranga
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on the Saraya deposit by Haranga
uranium
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uranium
-
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-
project/)
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project/)
.
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.
due to the presence of
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due to the presence of
uranium deposits associated
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uranium deposits associated
each side of t
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each side of t
he Atlantic Ocean
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he Atlantic Ocean
well before the opening of the Atlantic Ocean
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well before the opening of the Atlantic Ocean
northern Cameroon (Oesterlen and Vetter, 1986)
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northern Cameroon (Oesterlen and Vetter, 1986)
,
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,
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the
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the
Mayo
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Mayo
Trimdrart in southern Morocco, all located
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Trimdrart in southern Morocco, all located
in
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in
Western Africa,
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Western Africa,
beyond the Atlantic Ocean
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beyond the Atlantic Ocean
his
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his
study is to
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study is to
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present
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present
from both mineralized and non
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from both mineralized and non
the
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the
sodium metasomatic
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sodium metasomatic

3
al., 1992; Pawlig et al., 2006). The Kedougou Kenieba Inlier (KKI), situated southeast of 60
Senegal, marks the western most part of the WAC's Birimian domain, lying between the 61
Reguibat shield to the north and the Léo-Man shield to the south, and bordered by the Hercynian 62
Mauritanide belt to the west. The sedimentary formations of the Taoudeni intra-cratonic basin, 63
ranging from Neoproterozoic to Paleozoic, surround the KKI to the north, east, and south 64
(Gueye et al., 2007) (Fig. 1b). The KKI extends over approximately 16,000 km2 (Bassot (1966; 65
1987). Within this Inlier, distinguishes three supergroups arranged in parallel bands with a 66
general NNE-SSW trend the Mako supergroup to the west, and the Dialé and Daléma 67
supergroups to the east (Bassot, 1997). Recent work by Hirdes and Davis (2002), Lambert-68
Smith et al. (2015), and Masurel et al. (2016) subdivides the KKI formations into four Series, 69
which are, from west to east: the Mako Series (or Mako volcanic belt), the Dialé-Daléma Series 70
(Dialé-Daléma Basins), the Falémé Series (Falémé volcanic belt), and the Kofi Series (Kofi 71
Basin), (Fig. 1b). This last subdivision will be used in this document. 72
The Mako Series is characterized by extensive bimodal volcano-plutonism dominantly 73
tholeiitic (Bassot, 1997). It consists of pillowed or massive metabasalt flows interbedded with 74
banded cherts and associated with peridotites, metagabbros and metadolerites. This tholeiitic 75
basic-ultrabasic assemblage is overlain by carbonates, conglomerates, greywackes, and 76
sandstone-pelitic metasediments interbedded with acid to intermediate volcano-plutonism of 77
calc-alkaline affinity (Ngom, 1995; Ngom et al., 2011). The upper levels of the Mako series 78
consist of continental deltaic formations (Milési et al., 1986). The boundary between the Mako 79
Series and the Dialé-Daléma Series is tectonic and is marked by a regional shear zone, the MTZ 80
(Main Transcurent Zoone), oriented NE to SW, which rotates towards the NW beyond the 81
Falémé River in Mali (Milési et al., 1989b; Gueye et al., 2007), (Fig. 1b). 82
The Dialé-Daléma Series correspond to a single sedimentary unit intruded by the Saraya 83
Batholith (Bassot, 1997), which has been dated at 2079±2 Ma (Hirdes and Davis 2002, U-Pb 84
on zircon). The work of the Senegal-Soviet gold exploration mission in 1970 subdivided this 85
basin into a two groups. The lower group consists of 2000 to 3000 m thick alternating 86
sandstones or greywackes with some tourmalinized levels (Bassot, 1987; Dommanget et al., 87
1985), carbonate rocks (limestones or dolomites) and pelites sometimes rich in carbonaceous 88
material. The upper group consists of a thick sequence of more than 8000 to 10000 m, with 89
alternating sandstones, greywackes, shales, pelites and conglomerates (Bassot, 1997; Ngom et 90
al., 2011). The lower group is thought to be underlain by an ancient oceanic crust formed around 91
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supergroups to the east (Bassot, 1997). Recent work by Hirdes and Davis (2002), Lambert
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supergroups to the east (Bassot, 1997). Recent work by Hirdes and Davis (2002), Lambert
et al. (2015), and Masurel et al. (2016) subdivides the KKI formations into four Series,
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et al. (2015), and Masurel et al. (2016) subdivides the KKI formations into four Series,
which are, from west to east: the Mako Series (or Mako volcanic belt), the Dialé
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which are, from west to east: the Mako Series (or Mako volcanic belt), the Dialé
asins), the Falémé Series (Falémé volcanic belt), and the Kofi Series (Kofi
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asins), the Falémé Series (Falémé volcanic belt), and the Kofi Series (Kofi
subdivision will be used in this document.
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subdivision will be used in this document.
The Mako Series is characterized by extensive bimodal volcano
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The Mako Series is characterized by extensive bimodal volcano
. It consists of pillowed or massive metabasalt flows interbedded with
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. It consists of pillowed or massive metabasalt flows interbedded with
banded cherts and associated with peridotites, metagabbros and metadolerites. This tholeiitic
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banded cherts and associated with peridotites, metagabbros and metadolerites. This tholeiitic
ultrabasic assemblage is overlain by carbonates, conglomerates, gr
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ultrabasic assemblage is overlain by carbonates, conglomerates, gr
pelitic metasediments interbedded with acid to intermediate volcano
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pelitic metasediments interbedded with acid to intermediate volcano
alkaline affinity (Ngom, 1995; Ngom et al., 2011). The upper levels
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alkaline affinity (Ngom, 1995; Ngom et al., 2011). The upper levels
consist of continental deltaic formations (Milési et al., 1986). The boundary
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consist of continental deltaic formations (Milési et al., 1986). The boundary
Series and the Dialé
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Series and the Dialé
-
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-
Daléma Series is tectonic and is marked by a regional shear zone,
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Daléma Series is tectonic and is marked by a regional shear zone,
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(Main Transcurent Zoone)
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(Main Transcurent Zoone)

4
2200 Ma, the western extension of which forms the basis of the Mako Series (Dia, 1988; 92
Abouchami et al., 1990), (Fig. 1b). 93
The Falémé Series lies to the east of the Dialé-Daléma Series. They were identified as a separate 94
entity from the Dialé-Daléma Series by Hirdes and Davis (2002) and Lawrence (2010). They 95
form a NNE-trending volcano-plutonic complex (consisting of syn-tectonic granitoids, 96
rhyolites, and andesites), as well as sedimentary, detrital, and carbonate rocks (Ndiaye et al., 97
1997; Hirdes and Davis, 2002; Dabo and Aïfa, 2011; Lawrence et al., 2013a), approximately 98
80 km long and 16 km wide (Lambert-Smith et al., 2016a). The Falémé Series is bounded to 99
the east by the SMSZ (Senegal-Malian Shear Zone), which represents the contact with the Kofi 100
sedimentary series in Mali, (Fig 1b). 101
The Kofi Series consists of sandstone, mudstone, carbonate rocks, and minor proportions of 102
sodium-boron-bearing evaporites, which host syn-tectonic peraluminous biotite granitoids 103
(Lawrence et al., 2013a). These different series have been affected by several alteration 104
processes including albitisation, tourmalinisation, chloritization, and epidotization (Bassot, 105
1987, 1997; Ndiaye, 1994; Dabo and Aifa, 2011). 106
107
2.1. Geodynamic context 108
The geodynamic evolution of the KKI is interpreted differently depending on geochemical and 109
lithostructural constraints. Bassot (1966), Dioh (1986), Fabre (1987), and Zonou (1987) 110
propose a geodynamic context corresponding to a mid-oceanic rift for the Mako Series. Dia 111
(1988), Boher et al. (1992), Diallo (1994), Dia et al. (1997), and Pawlig et al. (2006) are in 112
favor of an island arc context with continuous evolution from the initial tholeiitic volcanism of 113
the Mako Series followed by the calc-alkaline volcanism of the Daléma-Falémé and Kofi 114
Series. Other authors favor two distinct events with initial bimodal, tholeiitic, and calc-alkaline 115
volcanism in the Mako Series, followed by calc-alkaline volcanism in the Daléma-Falémé and 116
Kofi Series (Bassot, 1987; Pouclet et al., 1996; Ngom et al., 2007; Ngom et al., 2010). 117
According to Abouchami et al. (1990), Birimian tholeiitic volcanism in the WAC is associated 118
with oceanic plateaus derived from mantle plumes, whereas calc-alkaline volcanism in the 119
basins is associated with transcurrent tectonics (Bassot, 1987; Fabre and Morel 1993; Pouclet 120
et al. 1996). 121
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, which represents the contact with the Kofi
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, which represents the contact with the Kofi
The Kofi Series consists of sandstone, mudstone, carbonate rocks, and minor proportions of
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The Kofi Series consists of sandstone, mudstone, carbonate rocks, and minor proportions of
tectonic peralum
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tectonic peralum
eries have been affected by several alteration
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eries have been affected by several alteration
processes including albitisation, tourmalinisation, chloritization, and epidotization (Bassot,
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processes including albitisation, tourmalinisation, chloritization, and epidotization (Bassot,
1987, 1997; Ndiaye, 1994; Dabo and Aifa, 2011
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1987, 1997; Ndiaye, 1994; Dabo and Aifa, 2011
).
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).
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The geodynamic evolution of the KKI is interpreted differently depending on geochemical and
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The geodynamic evolution of the KKI is interpreted differently depending on geochemical and
lithostructural constraints. Bassot (1966), Dioh (1986), Fabre (1987), and Zonou (1987
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lithostructural constraints. Bassot (1966), Dioh (1986), Fabre (1987), and Zonou (1987
geodynamic context
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geodynamic context
(1988), Boher et al. (1992), Diallo (1994), Dia et al. (1997), and Pawlig et al.
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(1988), Boher et al. (1992), Diallo (1994), Dia et al. (1997), and Pawlig et al.