INTRODUCTIONWith a land area of approx. 1,000,000 km2 along the westernedge of the Sahara desert and 90% covered by gravel and sanddunes (Fig. 1, inset), the Islamic Republic of Mauritania maynot be on the top of many exploration managers’ lists ofplaces to expend their exploration budgets. The harsh desertclimate and lack of water keep most of the country’s popula-tion of 3 million confined to four or five cities along thePacific coast and Senegal River and ensure that transportationcorridors and infrastructure development in the interior ofthe country are limited. The flat topography of much of thecountry adds to the difficulty of exploration, as does the lackof experienced logistical and material providers. Territorialdisputes between neighbors to the north and Toureg uprisingsin Mali, Mauritania’s neighbor to the east, along with theperceived instability of the Mauritanian government thatunderwent a bloodless coup in 2008, are not likely to bolsterthe confidence of major companies lookingfor greenfields exploration frontiers.

† Corresponding author: e-mail, ctaylor@usgs.gov1 U.S. Geological Survey, Box 25046 Federal Center, MS-973, Denver,

CO 80225-00462 U.S. Geological Survey, 4200 University Dr., Anchorage, AK 997093 Université Laval, 1065, Avenue de la Médecine, Quebec City,

Quebec, Canada G1V 0A64 Unite de Coordination du Projet Minier, B.P. 5430, Nouakchott,

Mauritania5 Ministere du Petrole, Energy, et des Mines, B.P. 5430, Nouakchott,

Mauritania

SEGSEGwww.segweb.org

Advancing Science and Discovery

OCTOBER 2012 NUMBER 91

NEWSLETTER

to page 10 . . .

SEG

Whistler 2013: Geoscience for Discovery Society of Economic Geologists and SEG Canada Foundation

September 24–27, 2013 Whistler, BC

www.seg2013.org

Mauritania: A Greenfields ExplorationOpportunity in Northwestern AfricaC.D. Taylor,1,† E.D. Anderson,1 D.C. Bradley,2 G. Beaudoin,3 M.A. Cosca,1 R.G. Eppinger,1 G. L. Fernette,1 C.A. Finn,1M. J. Friedel,1 S.A. Giles,1 R. J. Goldfarb,1 J.D. Horton,1 G.K. Lee,1 E. Marsh,1 J. L. Mauk,1 H.A. Motts,2 M.Y. Ould El Joud,4S. Ould Soueidatt,4 A. Ould Taleb Mohamed,5 and B.W. Rockwell1

VIEWS (pg. 10-12)

Graham Brown

5° W

5° W

10° W

10° W

15° W

25° N

20° N

20° N

15° N

15° N

GuelbMhaoudatKediat

Idjil

Tasiast

GuelbMoghrein

..

..

....

Bia-652Conchita-Florence

Tabatanet

Tigsmat

Bir en Nar

Khnefissat

ElKhader

KaouatBou Naga

Kadiar Guelb En Naaj

Indice 78Bofal

GuidamakaDiaguili

GuelbTamagot

El Mheissat

Oued El MaA238(NW)

GuelbNichSud

El MrhaderEl Hajar

Sivé

Loubboira

Nouadhibou

Nouakchott

Zouerate

●

●

v

●

v

Nema

400 Kilometers

Mauritania

Senegal River

Fig. 3

Fig. 2

Inchiridistrict

Chami

Guelb er Richat

Sfariat Belt (Zednes fault zone)

Semsiyat dome

Hendrixshearzone

SebkhaN’Drhamacha

Tiris Complex

Tasiast-Tijirit terrane

Granites

Amsaga Complex

Rgueïbat Shield

Coastal Basin

Mauritanide Orogen

Tindouf Basin

Taoudeni Basin

Granites

Paleoproterozoic

Archean

Greenstone belts

v

MineExploration targetCity

..

Akjoujt

FIGURE 1. Map of Mauritania, showing major geologic provinces andlocations of features described in the text. Inset shows location ofMauritania on the African continent.

10 S E G N E W S L E T T E R No 91 • OCTOBER 2012

Nevertheless, prospective Archean,Paleoproterozoic, and Phanerozoic set-tings make Mauritania a highly favor-able target for a variety of commodities.

In 1999, the Mauritanian govern-ment, with assistance from the WorldBank and Islamic Development Bank,embarked on a program to promoteinvestment in its mineral industry. Theprogram, termed Projet de RenforcementInstitutionnel du Secteur Minier (PRISM),strives to improve the mining legisla-tion and the business climate, and toprovide baseline geoscientific data thatwill facilitate mineral exploration.

The U.S. Geological Survey (USGS) hasbeen engaged by the Mauritanian gov-ernment to synthesize all available geo-logical and resource data on a country-wide scale, and to produce a new1:1,000,000-scale geologic map of thecountry (Fig. 1). Additional country-wideproducts include (1) a geophysical syn-thesis of all available aeromagnetic andradiometric data flown mostly at a 1-km flight line spacing, which includes aderivative depth to basement map; (2) afull QA-QC evaluation, integration, anddisplay on approx. 325 separate mapsof >29,000 geochemical samples; (3) ahydrogeologic map; (4) complete LandsatTM coverage, both SRTM90 and ASTERDEMs for the entire country, and ASTERimagery for six high priority resourceareas; and (5) an updated database ofmineral deposits and occurrences. TheUSGS ground checked many of the moreimportant mineral occurrences and col-lected samples for geo chronologicalstudy to support the new mappingeffort and to provide absolute dates formineral deposit formation events.

The ultimate goal of this programwas to produce a series of commodityand/or mineral deposit reports, identi-fying the permissive and favorable areasof the country for exploration. Reportsand maps that describe known occur-rences, exploration history, and permis-sive geology have been created formany metallic mineral deposit typesand a variety of industrial mineral com-modities. They will be published inearly 2013 and this article presentssome of the highlights of the effort.

GEOLOGIC SETTING OF MAURITANIAMauritania comprises four main geo-logic provinces (Fig. 1). The Rgueïbat

Shield is a NE-trending crustal blockthat is the exposed northern part of theWest African craton (WAC). It containsthe oldest rocks in the country andconsists of two major subdivisions sepa-rated by a crustal-scale shear zone repre-senting a major accretionary boundary(Lahondère et al., 2003; Pitfield et al.,2004; Schofield et al., 2012). The south-western part consists of Mesoarchean toPaleoproterozoic rocks that includehigh-grade granite-gneiss (Tiris andAmsaga Complexes) and greenstonebelt assemblages (Tasiast-Tijirit terrane).These rocks host the Tasiast gold depositand most of the iron deposits. Thenortheastern part of the Shield consistsof younger Paleoproterozoic (Birimian)to Neoproterozoic successions, whichhost many orogenic gold occurrences inthe WAC. This region is characterizedby a series of volcanosedimentary beltsand associated batholithic-scale graniticintrusive suites of different ages cut bymajor shear zones.

The NW-trending Mauritanide oro-genic belt, located along the westernmargin of the WAC and thought to bean African continuation of the Appala -chian orogenic belt, represents a fold-and-thrust belt with associated calc-alkaline volcanosedimentary sequencesand an ophiolite complex. These rockswere deformed episodically throughoutthe latest Neoproterozoic to earliestPaleozoic Pan-African assembly ofGondwana and again during the latePaleozoic Variscan orogeny (Pitfield etal., 2004). The Guelb Moghrein copper-gold deposit is hosted in the northernpart of the belt, which also has poten-tial for volcanogenic massive sulfide(VMS), orogenic Au, and magmatic Ni-Cu deposits.

The geology of the Mauritanide beltvaries from north to south. The north-ern Mauritanides extend from westernSahara to the Akjoujt area in Mauritaniaand are characterized by supracrustalnappes that are thrust to the east andnortheast onto the Archean Tasiast-Tijirit terrane (Maurin et al., 1997,Pitfield et al., 2004). In the Akjoujt area,there is a western inflection of the beltwhere it comes in contact with rocks ofthe Rgueïbat Shield and the frontalunits of the nappe stack are thrust ontothe Archean basement and the forelandof the Taoudeni basin (Pitfield et al.,2004). The southern Mauritanides,which extend from central Mauritania

into Senegal, consist of a N-S–trendingthrust pile of allochthonous andparautochthonous units juxtaposedagainst the Paleozoic rocks of theTaoudeni basin (Le Page, 1988). Withinthe belt are four parallel N-S–trendingzones separated by east-directed thrustscomprising, from east to west, an imbri-cated ophiolite, a continental margin-rift facies association, an eastern calc-alkaline igneous complex, and a westerncalc-alkaline igneous complex (Pitfieldet al., 2004; Lahondère et al., 2005).

The Taoudeni basin represents oneof the largest Mesoproterozoic toPaleozoic cratonic sedimentary basinsin Africa. It lies to the east of theMauritanide belt and, in part, forms theforeland basin to the Neoproterozoic-Paleozoic orogens. Consisting primarilyof many thousands of meters of conti-nental sandstones, as well as platformcarbonate rocks with lesser shales, itoccupies the central and eastern partsof Mauritania and has potential forpetroleum and sedimentary rock-hostedbase metal deposits. The ubiquitouspresence of Jurassic mafic sills and dikesthroughout the basin is the likelysource of Cu in widespread occurrencesand these represent theoretical loca-tions for conduit-type magmatic Ni-Cudeposits.

The Tindouf basin lies along thenorthern margin of the Rgueïbat Shieldand is a major pericratonic basinlocated primarily in Algeria, Morocco,and western Sahara. Two small areas ofmostly shallow water marine sedimen-tary rocks occur within Mauritania andare mainly unexplored. Low thermalmaturity of source rocks along thesouthern margin of the basin implypotential for hydrocarbons. Largedeposits of Phanerozoic oolitic iron-stones exist on both sides of the Algeriaborder (Malla and Takherist, 2000;Guerrak, 1988).

The Coastal basin lies to the west ofthe Mauritanide belt and represents apassive margin environment related tothe opening of the Atlantic Ocean. Thissedimentary sequence contains phos-phate, gypsum, and petroleum, both inMauritania and in other countries alongthe Atlantic seaboard, and also repre-sents an area permissive for sedimen-tary rock-hosted base metal deposits.

Mauritania: A Greenfields Exploration Opportunity in Northwestern Africa (Continued). . . from 1

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IRON ORES—MAURITANIA’SCASH COWHigh-grade hematitic iron ores, con-taining 60–65% Fe, have been mined inMauritania from Superior-type irondeposits since 1952. Depletion of thehigh-grade ores in recent years hasresulted in a number of new projectsfocused on lower grade magnetite oresin an Algoma-type banded iron forma-tion (BIF) containing 35% Fe. Mauritaniais the 15th largest iron producer in theworld and currently has about 1.1 billiontonnes (Bt) of crude iron ore reserves(USGS, 2012). Production is mainly con-trolled by Société National Industrielleet Miniere (SNIM), a parastatal com-pany that is 78% owned by the govern-ment. Iron ores account for about 50%of the export earnings of the country.About 11 million tonnes (Mt) per yearare shipped from three mines (Fig. 2),hosted in Mesoarchean (Guelb el Rhein)to Paleoproterozoic (Guelb Mhaoudatand the TO14 pit in the Kediat Ijil)rocks near Zouerate in the westernRgueïbat Shield, to loading facilities onthe Atlantic coast at Nouadhibou via a700-km-long railway constructed exclu-sively for the purpose. In 2001, SNIMformed a joint venture with Australia’sSphere Investments to study options foropen-pit mining and beneficiation ofthe magnetite deposit at Guelb El Aouj.The deposit has measured, indicated,and inferred resources of 701 Mt ofmagnetite ore with a grade of 36.3% Fe.Planned production is 7 Mt/yr of directreduction grade pellets (Mining Journal,2006).

In the major iron-producing regionsurrounding Zouerate, Algoma-typemagnetite-quartzite BIF deposits arehosted in the Mesoarchean Tiris Com -plex, which consists of high-gradegneisses and various granulite bodies.The magnetite quartzites are widespread,and are easily distinguished by theiraeromagnetic response and by theirtendency to form low ridges and guelbs(“guelb” is the Arabic word for “hill”)that crop out above the otherwise flattopography of the Tiris Complex.Individual iron-rich beds range from afew centimeters to 10 m in thickness(O’Connor et al., 2005). Economicdeposits form where thicker BIF unitsare doubled or tripled by thrust stack-ing or folding. Delineation of such tar-gets can be effectively accomplished byfiltering of the aeromagnetic data asdisplayed in Figure 2. Numerous targets,

both in outcrop and under shallowcover, remain to be prospected (Tayloret al., in press).

To the south of the Tiris Complex,Mesoarchean gneisses and granulites ofthe Amsaga Complex also containabundant small BIF-hosted deposits, asdo the Mesoarchean metavolcanic rocksin the greenstone belts of the Tasiast-Tijirit terrane to the west. Finally, LateArchean metavolcanic rocks of theInchiri district near Akjoujt also hostprospective BIFs. These rocks host theGuelb Tamagot and at El Khaderprospects currently being evaluated byan Indonesian company (PT BumiResources Minerals Tbk) that hasobtained an exploitation permit. ElKhader is unusual in that it consists ofa goethite cap to an IOCG prospect (see

below). A second project, ~45 kmsoutheast of Akjoujt, is being developedby TransAfrika Resources at theirKaouat project. They estimate aresource of 370 Mt at 30% Fe, based ondrilling, and about 1.2 Bt of in situ BIF,based on geologic mapping, gravity,and magnetic surveys (Taylor et al., inpress, and references therein).

PRECAMBRIAN GOLD IN THE NORTHERN WESTAFRICAN CRATONThe gold resources of Mauritania cur-rently identified include two importantdeposits and a series of poorly studiedprospects. The Tasiastdeposit, which came

OCTOBER 2012 • No 91 S E G N E W S L E T T E R 11

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Archean Tiris BIF Paleoproterozoic BIF Iron OccurrenceEdge of Taoudeni Basin

Buried extensionof Kediat Ijil

Buried extensionof Guelb Mhaoudat

Analytic Signal (masked to <1000m depth)

TAOUDENI BASIN

Guelb Mhaoudat

Kediat Ijil

Zouerate

T014

Guelb El RheinGuelb El Aouj

FIGURE 2. The Tiris complex near Zouerate in the western Rgueïbat Shield hosts irondeposits in Mesoarchean (Guelb el Rhein) to Paleoproterozoic (Guelb Mhaoudat andTO14) rocks. Geophysical targeting, using total field magnetic data above 0.75(green) over regions where the depth to magnetic basement is less than 1,000 m,identifies target areas where BIF is likely to be thickened by faulting or folding.

12 S E G N E W S L E T T E R No 91 • OCTOBER 2012

into production in 2007, is located inthe southwestern corner of the RgueïbatShield and is a world-class Paleoprotero -zoic(?) orogenic gold deposit. The pro-ducing Guelb Moghrein deposit occursalong a shear zone in Middle Archeanrocks at the bend in the northernMauritanides and is most commonlyclassified as an IOCG type of deposit(see next section). Both major depositsare surrounded by numerous prospectsthat show similar mineralization styles.

Most of the Mesoarchean andPaleoproterozoic rocks of the RgueïbatShield in northern Mauritania are high-grade gneisses (e.g., Key et al., 2008;Schofield et al., 2012), which are notfavorable for gold resources. However,the metamorphic grade in the shieldappears to decrease to more favorablegreenschist facies to the east and definesan area with potential for orogenic golddeposits in Paleoproterozoic rocks. A fewsmall gold prospects (e.g., Conchita-Florence or Nsour, El Mheissat, Oued ElMa, and Bin-652), now being exploredby Drake Resources Limited (DrakeResources Limited, 2012), are recog-nized north of latitude 21oN, a regionthat includes most outcrops of ca. 2.1Ga Birimian rocks of the shield. DrakeResources Limited reports high-gradegold samples at Conchita-Florence,adjacent to a 140-km-long shear zonesystem of anomalous gold termed theHendrix shear zone. This zone also rep-resents the only distinct belt of volcani-clastic rocks defined to date in the east-ern part of the shield (e.g., Bradley etal., in press a). The high gold samplesalso have anomalous concentrations ofAg, Au, Mo, Sb, Te, and W, and areassociated with outcropping gold-bear-ing quartz veins in greenschist faciesmetapelites. Several 40Ar/39Ar dates onhydrothermal sericite from prospects tothe southeast along this trend (Bradleyet al., in press b) suggest that theseprospects are Paleoproterozoic in age.

Further assessment of the region willrequire detailed geochemical maps, re -gional metamorphic maps, and evalua-tion of existing regional structure. Ifpermissive areas exist for important goldresources in the Rgueïbat Shield, thensuch areas are likely to be broadlydefined as those of relatively low meta-morphic grade, mainly of greenschistfacies. They will likely be newly recog-nized metasedimentary rock belts similarto those that host the Conchita-Florence

occurrences. These favorable areas wouldinclude rocks of the Lower and UpperBirimian supracrustal rocks that arelocated east of the Zednes fault zone. Inaddition, the relatively NNW-trendingmajor faults cutting the eastern half ofthe shield are likely to be particularlypermissive hosts for gold ores wherepresent in lower grade metamorphicdomains; margins of igneous rocksshown along some of these faults in anylower grade exposures should be care-fully examined (Goldfarb et al., in press).

The far southwestern corner of theRgueïbat Shield (lat. 20°–21° and long.14°–16°) is the one area in the Meso -archean part of the shield with green-schist facies greenstone belts; the sevendefined belts (Bradley et al., in press a)trend N-S in the west (e.g., Chami) andNE-SW in the east (e.g., Tirijit). Thegreenstone belts are exposed in thesouthern part of the Tasiast-Tijirit ter-rane of Schofield et al. (2012). They arelocated within a basement of ca.3.1–3.0 Ga migmatitic gneisses thatwere metamorphosed at ca. 2.97 Ga;

the greenstone belts are likely of similarage to the gneisses. Younger, volumi-nous tonalities and granodiorites,which form the cores of dome-like fea-tures, surround the basement rocks andgreenstone belts (Key et al., 2008) andare dated at ca. 2.95–2.87 and 2.69–2.65Ga, respectively (Schofield et al., 2012).

The Tasiast gold deposit (Fig. 3) islocated along a N-S–trending shear sys-tem in the 70 × 15 km Chami green-stone belt. It has been mined since2008, first by Red Back Mining and cur-rently by Kinross Gold Corp. (2012).Kinross Gold Corp. reports a world-classreserve + resource of at least 21 Moz Auat 1.47 g/t. The mine produces just over200,000 oz Au per year. The Tasiastdeposit occurs as sheeted quartz-carbon-ate-albite-pyrrhotite veins, gold-bearingquartz-carbonate veinlets, and adjacentdisseminated gold, hosted in an uppergreenschist to lower amphibolite facies,magnetite-quartzite BIF and adjacentvolcaniclastic rocks. The orebodies arepresent within two parallel zones thatcontinue for 6 km along strike (Davis,

Mauritania: A Greenfields Exploration Opportunity in Northwestern Africa (Continued). . . from 11

0 20000 m

Mapped BIF Gold prospectMapped GreenstoneBelt

N’Derek

Tasiast

Rusty

C-23 Jurassic dikes

Mesoarchean (?) dike

Tijirit

Chami

Aoueouat

FIGURE 3. Reduced-to-pole aeromagnetic image of the southern Tasiast-Tijirit terrane, showing geo-physical extensions under cover of Mesoarchean greenstone belts and locations of orogenic golddeposits and prospects. Intersections of greenstone belts and possible Mesoarchean (?) lineamentsrepresent highly favorable targets for additional deposits. All linear NE-trending moderate amplitudeanomalies relate to Jurassic dikes.

2011). The brittle orebodies follow aseries of reactivated thrusts that includethe Tasiast and Piment fault zones.Anomalous W, As, Ag, and Sb arereported at the deposit. Altered rockincludes biotite, sericite, and chlorite(Davis, 2011). Reported K-Ar ages onhydrothermal sericite of 1.85 and 1.50Ga (Marutani et al., 2005) are unusual,as typically Mesoarchean rocks hostMesoarchean gold deposits and Paleo -proterozoic rocks host Paleoproterozoicdeposits. A major NW-striking aeromag-netic lineament (Finn and Anderson, inpress) intersects the Chami greenstonebelt in the Tasiast mineralized area andmay have important implications forexplorationists (Goldfarb et al., in press;Fig. 3 and see below).

Other prospective areas within a fewtens of kilometers of the deposit couldinclude the Rusty prospect to the north-west of Tasiast, where auriferous quartzveins are identified in folded BIF andmafic volcanic rocks. At prospect C-23,north of Tasiast and in the Chamigreenstone belt, gold-bearing quartzveins occur along a sheared margin to agranodiorite body. To the south ofTasiast, in mainly sand covered areas,Drake Resources Limited reports goldanomalies from drill core from thesouthern part of the Chami greenstonebelt. The above-mentioned aeromag-netic anomaly of Finn and Anderson(in press) also crosses the adjacentgreenstone belts to the east and west ofthe Chami greenstone belt, and theselocations are marked by additional smallorogenic gold prospects. These intersec-tions of greenstone belts and the linea-ment, which is perhaps an ancient cra-ton margin boundary or fault parallel tothe boundary just inside the ancientmargin, are considered extremely favor-able targets for new resources (Goldfarbet al., in press; Fig. 3).

More detailed work in this south-western part of the shield is likely toidentify other large tonnage gold re -sources, because typically orogenic golddeposits do not occur as isolated singledeposits, but rather as clusters of de -posits. Similar orogenic gold depositsare probably present at Tijirit, which islocated in the Tijirit greenstone beltabout 120 km ENE of the Tasiast deposit.Evidence for potential in this area is aNNE-trending shear zone containingauriferous quartz veins that continuefor as much as 200 m along strike withinbasalt, gabbro, and schist (Goldfarb etal., in press).

GUELB MOHGREIN AND THE POTENTIAL FOR ADDITIONAL IOCGSThe Guelb Moghrein Cu-Au deposit inthe northern Mauritanides is consideredby many to be an iron oxide copper-gold (IOCG)-type deposit (Stricklandand Martyn, 2001; Kolb et al., 2008;Kirschbaum, 2011). It shares manycharacteristics with IOCG deposits,including economic Cu+Au, structuralcontrol, abundant breccias in the orezone, low Ti iron oxides, chalcopyriteand pyrrhotite as the dominant sul-fides, and a lack of quartz veining.However, no other IOCG deposits haveFe-rich carbonate host rocks, so in thatsense it is at least somewhat atypical ofIOCG deposits (Kirschbaum, 2011) andthere is a possibility that the mineraliz-ing fluids are of metamorphic origin(Sakellaris and Meyer, 2008).

Guelb Moghrein is located nearAkjoujt in the Inchiri district in westernMauritania. In addition, there are 19other copper and/or gold occurrences inthe Inchiri district, including the ElKhader gossan, where the goethite-richcap is currently being considered as asource of iron ore by PT Bumi ResourcesMinerals Tbk. Ancient copper workingsat Guelb Moghrein were noted by theFrench military in 1931 and sampled bythe Bureau Minier in 1946. Attempts tomine the deposit started in the 1950sand continued until the early 1990s,when General Gold International recov-ered five t Au (Gunn et al., 2004). FirstQuantum Minerals Ltd started commer-cial production in 2006. Mine produc-tion in 2011 was 3.61 Mt at an averagegrade of 1.4% Cu, with an additional1.1 t Au produced. Total proved andprobable reserves as of December 31,2011, were 3.2 Mt at 1.09% Cu and0.79 g/t Au. Measured and indicatedresources were 30.9 Mt of sulfide miner-alization at 1.18% Cu and 0.77 g/t Auand 0.12 Mt of oxide mineralization at1.58% Cu and 1.30 g/t Au (Fernette, inpress a, and references therein).

The Akjoujt area is situated at amajor bend in the Mauritanide belt,where it turns westward to follow thesouthern edge of the Rgueïbat Shieldand the rocks consist of a system ofoverlapping thrust sheets. The Akjoujtpackage is bounded to the north andeast by a sole-thrust contact with theArchean Amsaga terrane of the RgueïbatShield (Gunn et al., 2004). Supracrustalrocks in the Akjoujt area consist of

metabasalts and BIF, overlain withangular unconformity by the siliclastic(meta)sediments capped by a thick sec-tion of submarine basalts and dolerites.Partially migmatized leucogranite sheetsand pegmatites, which occur in areas ofoverthrust basement in the Akjoujt area,are the only intrusive rocks (Martynand Strickland, 2004).

Geochronological studies suggestthat whereas the host rocks at GuelbMoghrein are Archean, the ores areprobably earliest Paleoproterozoic. Twotypes of hydrothermal monazite andxenotime associated with primary sulfideore were dated by Meyer et al. (2006).Type I grains yielded an age of 2492Ma, which was concluded to be the ageof the mineralization. Type II grainsshowed an age of 1742 Ma, which wasinterpreted to indicate a later genera-tion of hydrothermal fluid flow.

Copper-gold mineralization at GuelbMoghrein occurs in discrete tabularbreccia zones developed parallel to D2

shear zones within metacarbonate rockcomposed of magnesite and dolomite.The mineralization and host metacar-bonate lie within a thrust zone thatseparates metarhyolite from metabasalt(Strickland and Martyn, 2001; Kolb et al.,2006). The ore consists of carbonate brec-cia with a matrix of mainly Fe-Mg clino-amphibole and magnetite, with lesserchalcopyrite, pyrrhotite, and other sul-fides. The massive sulfide-arsenide-goldmineralization formed at about 410°Cand 2–3 kbars (Kolb et al., 2006). Themetacarbonate host has been variouslyinterpreted as a metasediment (Kolb etal., 2006; Kirschbaum, 2011) and as ahydrothermal alteration product (Martynand Strickland, 2004). The wall rocksadjacent to the mineralized metacarbon-ate underwent albitization prior to andduring greenschist to amphibolite grademetamorphism, and this was followed bya potassic alteration event (Kirschbaum,2011). Factor analysis of rock geochemi-cal data show a strong ore-related corre-lation of Ag, As, Bi, Co, Cu, Ge, In, Ni,Se, Sn, Te, and Zn (JICA, 2005).

Reconnaissance fluid inclusion stud-ies of quartz veins from the footwallgreenschist at Guelb Moghrein showedpoly phase inclusions containing halitecrystals in gas-rich inclusions (JICA,2005). Homogenization temperaturesof the inclusions ranged from 240° to320°C and salinities from 33 to 39 wt %NaCl equiv. Sakellaris and Meyer (2008)indicate sulfide δ34S val-ues cluster near zero,

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14 S E G N E W S L E T T E R No 91 • OCTOBER 2012

corresponding to either magmatic ormetamorphic sulfur, and the δDfluid val-ues are typical of metamorphic waters.The combined oxygen and hydrogenisotope composition of the fluid plotsin the field of metamorphic waters,leading Sakellaris and Meyer (2008) toconclude that the sulfur and ore fluidare of metamorphic origin and that themost likely sources of metal were thehost metabasalt units.

Numerous workers (Gunn et al., 2004;Marutani et al., 2005, and referencestherein) suggest that there is potentialfor Guelb Moghrein-type Cu-Au miner-alization in the southern Mauritanides.They refer to specific prospects, includ-ing Kadiar, Indice 78, Guelb En Naadj,Diaguili, and Guidamaka as IOCG occur-rences. Kadiar is one of the most signifi-cant Cu prospects in the Mauritanidebelt and is currently being explored byOreCorp Mauritania SARL, which con-siders it a VMS target (OreCorp, 2012).The prospect consists of a siliceous gos-san with anomalous Cu and Au values,which overlies a lens of silicified ankeritewith malachite, chalcopyrite, and pyrite.Salpeteur (2005) notes that the onlyiron oxide present at Kadiar is hematiteand that magnetite is absent, and thushe questions whether Kadiar should beconsidered an IOCG-type occurrence.The Indice 78 prospect, originally iden-tified by soil sampling, consists of a 4.5-km-long zone of propylitic alterationcontaining disseminated copper sulfidesand numerous quartz veins, which islocalized along the contact betweenmeta-andesite and metarhyolite (Gunnet al., 2004). Within the alterationzone, carbonate occurs in veinlets andas irregular, coarsely crystalline patchesthat led Gunn et al. (2004) to suggestthat the Cu mineralization might besimilar to Guelb Moghrein; however,they conclude that the mineralization ismore likely of the VMS type.

The Cu ± Au occurrences in the south-ern Mauritanides are all associated withaccreted metamorphic rocks, which in -clude ultramafic bodies that mark suturezones. The lenses of intense carbonatealteration, silicification, and quartz vein-ing, often with associated Cr-rich micas,are typical “listwaenite” found at manyorogenic gold deposits. The southern Cuoccurrences, however, such as Diaguiliand Guidamaka, are also associated withjaspilite (red jasper) and hematite, andthere are podiform chromite occurrences

in the same area, features that are com-mon in Cyprus-type VMS deposits.Finally, the age of the country rocks inthe southern Mauritanides is Neopro -terozoic (Pitfield et al., 2004), in contrastwith the Archean age of the Akjoujt areasequence. Based on the above, it is con-cluded that the Cu ± Au occurrences inthe southern Mauritanides are not IOCG(Fernette, in press a; Taylor, in press a).

URANIUM EXPLORATIONMauritania is the site of active uraniumexploration and new discoveries arebeing made. There are currently at leastsix companies actively exploring foruranium in Mauritania. The countryhosts 80 known uranium occurrences,mainly in the Paleoproterozoic part ofthe Rgueïbat Shield, which include bothcalcrete and granite-hosted types. In fact,much of the northern shield is anoma-lous in U as shown by widespreadanomalies in airborne radiometric data.The granite-related occurrences are allwithin or proximal to major NW-trend-ing fault zones. The anomalous graniticrocks provide the source for the U inthe calcrete deposits (Fernette, in pressb, and references therein).

There are three granite-hosted andnine calcrete-type U deposits defined inthe northern shield in Mauritania. Thetotal combined resource of the depositsis 183.8 Mt, with an average grade of310 ppm U3O8. The calcrete depositstotal 138.3 Mt at 331 ppm U3O8 versus46.5 Mt at 248 ppm U3O8 for the gran-ite-hosted deposits. All of the depositsare held under license by either ForteEnergy or Aura Energy.

Forte Energy’s first exploration targetwas the Bir en Nar area (Fig. 1), whereuranium mineralization was discoveredby Cogema in the 1970s (Marot et al.,2003). A recent estimate for the Bir enNar deposits includes an indicated andinferred resource of 1.33 Mt at 704 ppmU3O8. The granite-hosted deposits con-sist of three NW-trending mineralizedzones that dip moderately to the north-east. “Red” alteration is common inmineralized granite, although anoma-lous U values are also present in unal-tered granitic rock. Syenite and episyen-ite pods within the shear zone also hostmineralization (Fernette, in press b).

The A238 and A238 NW deposits arelocated 135 km northwest of Bir enNar, along the same shear zone. The

deposits were discovered by follow-upof an airborne radiometric anomaly thatlocated uraniferous calcrete. Drillingintercepted uranium mineralization in ashear zone below the calcrete zone. Bothdeposits are located within cataclasticzones along the mylonitized contactbetween two granitoid bodies. A largearea of unmineralized silica-hematitealteration and smaller areas of silicifica-tion occur to the northeast of the A238deposit. The A238 NW deposit occurs ona splay of the main shear zone to thenorthwest of the A238 deposit (Fernette,in press b, and references therein).

PHOSPHATE AND GYPSUMPhosphate deposits occur in outcrops ofphosphatic limestones, mudstones, andsandstones of Eocene age exposed alongthe northern bank of the Senegal River,about 300 km from the coast. Twodeposits have been extensively studied,one at the village of Bofal and anotherdeposit at Loubboira.

Reserves at Bofal are 70 Mt with anaverage thickness of 1.7 m, an averagegrade of 21% P2O5, and an averageoverburden of 8 m. In comparison,Loubboira has 29 Mt of reserves with anaverage thickness of 2 m, an averagegrade of 19% P2O5, and an averageoverburden of 7 m. These resources areopen to the north at Bofal and to thesoutheast at Loubboira; total probablereserves could exceed 100 Mt (Gunn etal., 2004). Resources were also identi-fied in several other zones to the south,which are less well known than the twoprincipal areas. The deposits continue100 km farther to the southeast intoSenegal at Matam, where a depositexceeding 36 Mt at 28.7% P2O5 hasbeen identified. On the opposite bankof the river from Matam, at Sivé inMauritania, resources of about 150,000t have been identified, where phos-phate rock beds average 26–28% P2O5.These deposits have potential for use asdirect application fertilizer and localfarmers are extracting phosphate rockfor this purpose (Gunn et al., 2004;Langer, in press).

Additional occurrences of sedimen-tary phosphate deposits are widespreadin the Taoudeni basin, although avail-able information suggests those discov-ered to date are small and low grade(Gunn et al., 2004). Furthermore, theirremote locations, far away from areas of

Mauritania: A Greenfields Exploration Opportunity in Northwestern Africa (Continued). . . from 13

farming and food production, suggestthat they are unlikely to be high-prior-ity exploration targets. The host rocksare mainly late Neoproterozoic. Thepotential of these strata to host eco-nomic phosphate deposits remainsunknown, but the Neoproterozoic–EarlyCambrian time period is an importantdepositional interval, with significantresources of this age occurring in sev-eral countries in West Africa (Langer, inpress).

Possibly one of the largest gypsumdeposits in the world occurs at SebkhaN’Drhamcha, 50 to 100 km north-northeast of Nouakchott. Both beddedevaporate- and dune-type deposits arepresent. The bedded gypsum depositscrop out chiefly along the eastern flankof the Sebkha N’Drhamcha, an evapora-tive pan just inland of the coast thatwas cut off from the ocean by a coastalsand belt, which formed within thepast 4,000 years (Pitfield et al., 2004).The thickness of the deposits is greatesttoward the center of the sebkha,decreasing to the west and north. Thereare several hundred million tonnes ofresources, of which about 140 Mt areproven reserves (Gunn et al., 2004).Resources identified in dune depositsoccur about 55 km from the highwaythat connects Nouakchott and Akjoujt.Limited sampling of these deposits,which are secondary accumulations inboth active and indurated dunes, indi-cated grades of 92–93% CaSO4•2H2Owith about 1.5% SiO2 (Pitfield et al.,2004). A provisional resource estimatesuggested about 2 Mt in one small areaof dunes. Extraction rates have been ashigh as 100,000 t/yr for plaster andcement production. The favorable loca-tion, close to the main road, togetherwith the high grades and limited thick-ness of overburden make these depositsattractive for exploitation. They arecapable of meeting Mauritania’s domes-tic requirements for plaster and derivedproducts (Langer, in press).

REE, CRITICAL METALS, AND DIAMONDS IN ALKALINEROCKS, CARBONATITES, AND KIMBERLITESResources of U, Th, Nb, Ta, Be, rare earthelements (REE), and fluorite associatedwith alkaline rocks, pegmatites, and car-bonatites are known in Mauritania andhave been exploited in the past at theBou Naga alkaline igneous complex.

Pegmatites and pegmatitic veins are rec-ognized in several areas of the Archeanand Paleoproterozoic parts of theRgueïbat Shield and are prospective forcritical element and REE resources. Morethan 150 beryl pegmatites are known inthe Khnefissat area of the Chami green-stone belt, and additional concentra-tions of pegmatites are known at GuelbNich Sud in the Sebkhet Nich green-stone belt and in the northeastern partof the Amsaga complex (Gunn et al.,2004). Owing to the small size of thesedeposits, they are unlikely to be eco-nomic unless additional value can begained by processing contained miner-als for industrial use. Vein and stock-work deposits containing anomalous Thand REE, as well as the above men-tioned U, are present particularly in thePaleoproterozoic rocks of the RgueïbatShield. The small mafic alkaline com-plex at Tabatanet is associated withmagnetic and radiometric anomaliesand consists of a probable vein-typedeposit that extends for 500 m. Thehyperalkaline granite at Tigsmat mayhave REE enrichments in associatedplacers, but appears to be of low eco-nomic potential. Two other areas, at elMrhader and at el Hajar, have indica-tions of resource potential based ongeophysical data and high scintillome-ter readings (Taylor, in press b).

Another possibility for U, Th, REE,and associated element enrichmentsexists in association with carbonatitecomplexes in Mauritania. Studies sug-gest the presence of a carbonatite at

Guelb er Richat (Woolley et al., 1984;O’Connor et al., 2005), also known asthe Eye of Africa; it is a distinctive land-mark visible from space and was used assuch during the Apollo missions (Fig.4). It is marked by a coincident high Thgeophysical anomaly. The location ofGuelb er Richat in an area of prominentENE-trending structures that are coinci-dent with two swarms of kimberliteintrusions suggests a deep-seated struc-ture is present in the sub-Taoudeni cra-tonic basement, which could localizethe emplacement of additional carbon-atite (and kimberlite, see below) bodies.A feature referred to as the Semsiyatdomal structure is also located alongthis lineament and may represent anadditional carbonatite intrusion at depth.For the most part, most occurrences ofTh, REE, and associated elements arepoorly described, poorly understood,and underexplored.

Diamond exploration was extensivein the late 1990s and was continuing ata lesser pace by Rio Tinto in the north-eastern Rgueïbat Shield and northernmargin of the Taoudeni basin at the timeof the 2007 USGS field survey (TalebOuld Abdival, Rio Tinto, oral commun.,2007). Gunn et al. (2004) discuss the RexDiamond project area to the east andnortheast of Zouerate. They also notethat De Beers worked with Rex DiamondMining Corp on the Akchar Permit areain the southwestern Rgueïbat Shieldand that De Beers ceased active explo-ration in late 2002. RexDiamond Mining

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to page 16 . . .

SEMSIYAT STRUCTURE

THE ADRAR ESCARPMENT

FIGURE 4. SRTM digital elevation model of the Geulb er Richat structure. Note smaller Semsiyat dometo the southwest.

16 S E G N E W S L E T T E R No 91 • OCTOBER 2012

Corporation was reported to have dis-covered a potential kimberlite area inthe Tasiast-Tijirit terrane. Gunn et al.(2004, based on Rombouts, 2003) statesthere are two kimberlite provinces on aNNE-trending lineament within theTaoudeni basin that also localizes theGuelb er Richat and Semsiyat domalfeatures thought to be carbonatiteintrusions at depth. The western clusteris located near the Guelb er Richatdome. The poorly located eastern clus-ter contains 21 kimberlites, of which 7are diamondiferous (Rombouts, 2003).

CONCLUSIONSAs a result of the aggressive developmentof the exploration and mining sectors ofthe economy by the Mauritanian gov-ernment through programs of dataacquisition and synthesis such as thosedescribed above, Mauritania now canprovide a greenfields exploration oppor-tunity supported by a wealth of readilyusable state of the art geoinformation.Additionally, the presence of geologicalenvironments that include Archean cra-ton, Paleoproterozoic metasedimentarybelts, Pan African orogenic belts, andmajor cratonic and coastal sedimentarybasins, as well as the presence of severalworld-class ore deposits, should get theattention of any explorationist. We havesummarized some of the more excitingpotential areas for gold, IOCG, iron,uranium, gypsum, phosphate, REEs, crit-ical metals, and diamonds in Mauritania.But we have not even touched on themore speculative potential for sedimen-tary rock-hosted base metals, VMS,shoreline placer titanium, or a variety ofindustrial minerals that, owing to theirproximity to the Zouerate-Nouadihbourailway, may represent additional eco-nomically viable commodities. The rawdata packages are available through theMinistry of Petroleum, Energy, andMines in Nouakchott. The derivativemaps and reports described will soonbe available on the USGS MineralResources Program website (accessibleat: http://minerals.usgs.gov/).

ACKNOWLEDGMENTSDennis Cox, Daniel Knepper, WilliamLanger, and David Leach all partici-pated in the early phases of the USGS-Mauritania project and are thanked fortheir contributions. Reviews by Karen

Kelley and Andrew Killick greatly im -proved the manuscript. The MauritanianMinistry of Petroleum, Energy, andMines is acknowledged for their permis-sion to publish this paper.

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