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ÌíæáÌíÇ ÔãÇá ÇáÌÒÇÆÑ

                                                                                   

GITOLOGY OF NORTHERN ALGERIA

Northern Algeria belongs to the mesogean alpine province, which covers the betic chain of the south of Spain and the North of Morocco. This province presents a very great number of mineralisations Pb-Zn and polymetallic. In Algeria of North, an ancient basis (Hercynien) shows on the surface as levels in the Solid masses of Large and Small Kabyly, Edough, and in the heart of the horsts of the field of the High Lands. Principal mineralisations are of Mississipi Valley (Pb-Zn) type stratiform, slickenside polymetallic of epithermal type, mesothermal or porphyry, or perished-grantic in the basis (skarns, greisen, etc).

Metallogenic Groups of Northern Algeria
The Zn-Pb Maghreb province, in septentrional edge of the Sahara platform, is made up of two under-provinces:

in the North, the Tellian sub-province, of continental bais margin's type, including Kabyly's solid masses, with volcanic appearances at the Tertiary's.This sub-province conceals approximately 47% of the layers and 40% of the potential Pb-Zn.  The layers are primarily slickenside, with complex mineral association:  Pb, Zn, Cu, pyrite, F, Ba (Ace, Sb, Hg, Ni, Ag, In), in boxing rather siliceous (gneiss, schists, marls, sandstone).  The seams, clusters and disseminations meet at the metamorphic basis, the series of cover, until the Miocene's post layers;

in the south, the meridian or saharian sub-province, with a folded or tabular continental platform type sedimentation, where volcanicity misses.  It conceals approximately 53% of the layers and 60% of the potential Pb-Zn.  The layers, of type MVT, are with dominant stratiform, or in filling of fractures, with a simple paragenesis:  Zn-Pb (Cd, Ga, Ge, pyrite, rare Cu, Sb, Hg).  Boxing are carbonated.  Their age decrease from West (Lias close to Oran), from East (superior Cretaceous in Ain Me Lila, Miocne in eastern Constantine).

The Tellian sub-province subdivides itself in:

field of the Kabyly's primary solid masses:  these crystalline solid masses level along the Mediterranean coast.  They were the location of sedimentary gaps ias and the Secondary, with significant volcanic signs from Oligocene to Pliocene and mainly in Miocene.  Mineralisations are of polymetallic slickenside type, epithermal to mesothermal, porphyry, Skarn and MVT (Pb-Zn);
autochthonous Tell field:  it is most septentrional with that of the primary solid masses that it surrounds.  It was strongly dislocated with the Cretaceous with chippings and discharges towards the South.  Polymetallic mineralisations (Pb-Zn-Cu-Hg) are of type slickenside, epithermaux or msothermaux (Wadi El Kebir, etc.)
intra-Tellian field:  it is the central part of the Tellain furrow, largely covered by the layers and affected by E-O folds.  Mineralisations with Pb-Zn, of slickenside type, concentrate especially in limestones neritic;
immigrant field tellien:  constituted of layers with Triassic sole, it is rather deprived of Pb-Zn deposits. 

Sub-Sahara province subdivides itself in:

pre-Saharan field of Oran Meseta:  this Jurassic tabular zone, resting on a primary substratum, was slightly folded by the alpine phase.  We can find MVT type of stratform deposits in Lias dolomies (El Abed, etc.) 
intermediate pre-Saharan field of the mole of An M'lila and its edge:  it presents neritic facies at the lower Cretaceous and Pb-Zn  mineralisations, mainly of MVT type, are located on the edge of the mole (Kherzet Youssef);
pre-Saharan field of the Eastern Atlas:  it is affected by two tectonic directions (NO-SE and OSO- ENE), with diapirism of Sorted and Mio-Pliocee.  The shallow waters of the lower Cretaceous reefs conceal the essence of mineralisation in the vicinity of the triassic diapirs (Mesloula). 

The richness of the metal potential of this Northern province of Maghreb is due to several factors:

In the metamorphic base

o Presence of mineralisations closely associated to the metamorphic base, in relation to one or more alpine ante metallogenic times (probably hercyniennes),including stratoid levels stratodes with:

    • polymetallic sulphides;
    • magnetite Sb, With;
    • skarns ;
    • lenses of chromites in mea-peridotites;
    • mea-greisen with Sn, W, Li.


In the post paleozoic coverage

o Existence of rocks " mothers " and "storages" for base metals (Pb-Zn primarily) in the series of coverage , in context of basin of back arc, not very deep. These rocks are localised on several stratigraphic levels; one distinguishes:
  • of the black marls:  medium anoxic favorable to the trapping of metals. They are inserted between carbonates, dolomites, on several stratigraphic levels - Jurassic (Bathonien, Oxfordien);  Cretaceous (Gault, Cnomanien, Luttien), Oligocene, etc.  These facies are the precursors of oil and constitute one of the traditional terms of the regressive sequences - dolomites, evaporites.  They also play a role of screen for the fluids released by the compaction of the sediments and tectonic stacking during alpine compressions.  They can produce significant base metal concentrations, noble metals (With, EGP) described well in Kupferschiefers Polish and Germanic, but little described in Algeria.  The presence of kerogens and chlorides in the associated fluids is favorable to the migration of metals;

  • of dolomites:  rock store easily impregnated by sulphides and/or carbonates of iron.  In addition to these potential tanks, the structural instability of the frame hercynien to Jurassic, the Cretaceous and Miocene, and the phenomena related on the halocinese and the great accidents of the tablecloths telliennes, reinforce the interest of this zone for exploration, thanks to:

    o of the paleorifts, preceding the transgression marinates Sorted.  These paleorifts creates structures favorable to the deposits of mineralisations either strata-bound, near the high funds, or secants, in pseudomorphoses of crushed or slickenside zones; 

    o of the paleokarsts, in relation to several surfaces of emergence (Aaleeo-bajocien, Bathonien, Aptien-Gault, Cnomanien...).  This allowed the installation of Pb-Zn concentrations of the type MVT (the Mississippi Valley Type) in carbonates and a secondary enrichment of the ores in the oxidized zone (mn,oxidized Cu);

    o of the structures in dome, due to the rise of the diapirs of Sorted, accentuated by alpine tectonics.  They are mtallotectes privileged for the development of layers with: 

    • Stratiform sulphides Pb-Zn or in cluster:  example of the Bahloul ceeanano-turonian forming which boxes the layer of Bou Grine in Tunisia; 

    • Barytine, fluorite, clestine, strontianite in the cavities of dissolutions;

    • Siderite (Ouenza), if the sulphuretted activity is weaker.

o the existence of a volcanic activity related to the operation of an insular arc in Miocene with a calc-alkali magmatism hypovolcanic.  This magmatism opens beautiful prospects for research for mineralisations of the type porphyry Cu-With-Mo, Skarn W-Mo, pithermal With-Sb-Hg.

 
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