The In Tifinar and Tidjerazraze centres comprise numerous volcanic plugs with some plutonic rocks extending in a north-south line over some 30 km with to the east a northeasterly orientated dyke swarm (Liegeois et al., 1991 and J.F. Sauvage, pers. comm., 1985).
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The Iforas (Adrar des Iforas) forms a southwestern promontory of the central saharan Hoggar shield (Black et al., 1979) and consists of metamorphosed Upper Proterozoic sediments and older basement rocks. Most of the alkaline rocks of Mali are located within this area (Fig. 167) and have been reviewed by Ba et al. (1985). Descriptions of rock types are given in the text accompanying the 1:500,000 map of the Adrar des Iforas (Fabre, 1982; Fabre et al., 1982). An outline of the general geology of the area including brief descriptions of some of the principal alkaline intrusions will be found in Black et al. (1979), and Liegeois et al. (1996) give a short account of the alkaline rocks and carbonatites of the Tadhak province of northwestern Iforas. Liégeois and Black (1984) review the geochronology of the igneous rocks of the Iforas and the same authors have also published a broader review (Liégeois and Black, 1987).
Tirkine is a nepheline syenite intrusion surrounded by sand that obscures outer contacts. It consists of an outer nepheline syenite ring displaying igneous lamination with a central nepheline syenite intrusion with no apparent directional fabric.
The northern part of this complex, which is 15 km from east to west, is obscured by Quaternary sediments. An outer incomplete ring and the arcuate disposition of some rock units are indicative of a ring-complex. The intrusion is emplaced in 2000 Ma Eburnean gneisses and granites.
These are three plugs up to 300 m in diameter one of which consists of phonolite and the other two of eudialyte-nepheline syenite intruding phonolite.
This is a 1.5 km diameter intrusion of rodbergite (hematite and ferrocarbonatite) that lies along a fault extending north from the Adiounedj (No. 105-00-006) complex. Another small such body is indicated on a map in Liegeois et al. (1991, Fig.
The major rock type of this very irregular complex is fenite with a substantial area of rodbergite and lesser areas of foid syenite and carbonatite (Sauvage and Savard, 1985). Dykes are numerous and widespread.
According to Sauvage and Savard (1985) this complex comprises an early alkaline intrusion which has been cut and strongly fenitized by later carbonatites. The alkaline rocks are predominantly ijolites and urtites with some nepheline syenites and pyroxenites.
An approximately circular complex 2 km in diameter, Anezrouf is composed dominantly of nepheline syenites with smaller intrusions of other igneous rocks scattered across and adjacent to it, including arcuate bodies of ijolite and pyroxenite close to the southern margin.
This small, circular complex is only 800 m in diameter. It consists of foyaite of two textural types. The first is homogeneous and consists of perthite, nepheline and pyroxene; the second is porphyritic with phenocrysts of nepheline several centimetres in diameter enclosing the other phases.
Tessalit is some 30 km in diameter, intruded into rhyolites and consists of four main, overlapping intrusive centres (Ba et al., 1985; Liegeois et al., 1996). Granite is the predominant rock type, with lesser areas of syenogranite and microsyenite, which vary widely in the degree of alkalinity.