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Oued Amizour, Tala Hamza |
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Algeria |
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Zn Pb
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Super Porphyry Cu and Au
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The Oued Amizour district and Tala Hamza volcanic-hosted massive sulphide (VHMS) Pb-Zn deposit is located on the north coast of Algeria, 15 km west of the coastal Mediterranean Sea city of Bejaia in north Africa, 180 km west of the capital, Algiers.
The Tala Hamza deposit and related mineralisation is located within the Oued Amizour massif, a Miocene intrusive volcanic complex, within the Kabylian section of the Atlas mountain chain, which stretches along the Mediterranean Sea in NW Africa.
The tectonic setting of Algeria can be divide into two distinct domains separated by the major South Atlas fault: (i) the Saharan Platform to the south, a relatively stable block of low tectonic activity that covers much of the country; and (ii) Northern Algeria, a generally ENE-trending, 350 km wide domain of Tertiary Alpine orogenic activity, that comprises the Atlas mountain chain resulting from the collision between the African and Eurasian plates from the Late Jurassic, and contains a thick (5000 to 10 000 m) succession of sedimentary rocks deposited in a subsiding Mesozoic basin on the northern margin of the African plate that underwent tectonic inversion
from the late Eocene.
The Atlas mountain chain may be further divided into: (i) the Saharan Atlas, a mountain range of Alpine origin to the south, immediately to the north of the South Atlas fault which separates it from the Saharan Platform; (ii) the broad high plains of the Oran Meseta to the west and Ain Regada to the east; and (iii) the Tellian Atlas to the north (which includes Kabylia), bordering the Mediterranean Sea reflect the final stages of collision between the African and Eurasian plates. This collision was influenced by the contemporaneous opening of the North Atlantic.
The Oued Amizour massif and the Tala Hamza deposit are located within the Tellian Atlas, which comprises a complex area composed of a succession of north dipping thrusts and south trending nappes set in place during the Lower Miocene, continuous with the Rif in Morocco to the west. This zone of derformation represents the final pulse of convergence and tectonic deformation in the Western Mediterranean, accompanied by the reactivation of some localised subduction, and generated intracontinental tectonic events in the Pyrenees, the Iberian range and in the High Atlas. This final pulse followed a general distensional tectonic regime during the Oligoceneas a consequence both of the North Atlantic ocean opening to the west and of the collision of Africa and Eastern Europe to the east.
While the basement to the Sahara Platform is Ebrnian to the SW, and Panafrican below much of the remainder, Northern Algeria, and the Tellian Atlas in particular is underlain by local gneisses and mica-schists, overlain by conglomerate and graptolitic (Silurian) shales/schists, Devonian shales and minor limestone reefs, local Carboniferous shales, Triassic red sandstones, evaporites and limestones/dolomites with basic volcanic intercalations in the upper part of the succession. The Jurassic is characterised by the Liassic transgressive marine sequence, comprising ~200 m of dolomitic and oolitic limestones overlying the Triassic evaporitic lagoonal sediments, succeeded by ~2000 m of Dogger shaley-carbonates and the Malm regressive phase with deltaic sediments to the south in the High Atlas and marine sequences in the north.
Cretaceous sediments are found throughout the Saharan Atlas, occurring mostly as quartzose clastics, reaching a maximum thickness of 1200, in the Western Atlas. There are a number of transgressions and regression, with sections of the sequence being absent locally, and intercalated evaporites,reefal limestones, other carbonates and marls being intercalated through the stratigraphic column.
The overlying Eocene formations are significant for their areal coverage and thickness of deposition. In the Tellian Atlas they are represented by clays, micro-fauna rich marls and carbonates, overlain by a thich sequence of Oligocene clastic rocks. These are suceeded in turn by a Lower Miocene marine transgression, represented by a thick blue marl facies (>1000 m) which passes laterally into marine shaly sandstones, ending with a regression in the Upper Miocene, followed by a further transgression resulting in the deposition of black or blue marls, sands and sandstones, limestones, diatomites and gypsum. Marine to lagoonal conditions continued into the Pliocene and Quaternary.
Granitoid intrusions cut the sequence detailed above during three main period, namely 455±19 Ma, 278±3 to 273±Ma (Peucat, 1996), and during the Miocene (Kolli, 2005).
The dominantly sedimentary geology outlined above is characteristic of Alpine Northern Algeria as a whole. The nappes and thrust terrane of the Tellian Atlas have introduced at least two and up to four para-allochthonous to allochthonous slices of Palaeozoic to Tertiary age rocks from further to the north and east with different geological characteristics (passive margin continental slope to deep ocean facies, which for example include Triassic rocks lacking the evaporites found in the autochthonous sequence), overlying autochthonous (shelf facies) rocks as young as Cretaceous and Paleocene, which were in turn thrust south over Mesozoic units (Saupe et al., 1995; Kolli, 2005). These slices are interpreted to have been deposited along the continental margin of a microplate in southern Europe, and tectonically transporteed to its present postion by progressive WSW movement to collide with, and overthrust onto the African plate during the Oligocene-Miocene to produce the Tell Atlas and Moroccan Rif (Petters, 1991).
The main compressive phase occurred during the Lower Miocene. This was followed by an interval of extension during the Middle Miocene, accompanied by acidic, calc-alkaline volcanism and plutonism, as well as mafic magmatism. Five volcanic pulses are known in sections of Kabylia, incuding mafic events dated at 15.1±0.6 and 19.1±1 Ma. The associated Miocene granitoids cut all of the allochthonous slices and autochthonous basement (Saupe et al., 1995). The Tala Hamza deposit and related mineralisation of the Oued Amizour massif is associated with this Miocene magmatism.
The Oued Amizour massif, within the Kabylia region of the Tellian Atlas contains a Miocene plutonic-volcanic complex which comprises granitoids, overlain by two or three volcanic and volcaniclastic series. The magmatic rocks belong to a potassic rich calc-alkaline series with ages that vary from 24.4 to 12.4 Ma. At Tala Hamza, the volcanics comprise a number of wide units of volcaniclastic and coherent rocks including breccias, lavas and sub-volcanic intrusives of andesitic and dacitic affinity.
The mineralisation occurs as a thick (from 40 to 300 m) zone with an overall shallow southerly dip. It covers an area of almost 750 x 750 m and is disconformable with the host volcaniclastic series. It is associated with strong hydrothermal alteration characterised by kaolinitisation, silicification, chloritisation, sericitisation and carbonatisation. Several generations of faults bound and offset the mineralisation with at least one set having a spatial association with high lead mineralisation and controlling the overall geometry (Terramin website).
The mineralisation has a number of features of low temperature, epithermal deposits including colloform textures in sphalerite and pyrite, Fe-poor honey-coloured sphalerite and low temperature potassic alteration (adularia).
The mineralisation styles range from massive through semi-massive, stockwork, breccia and disseminated sulphides. The breccias are often associated with replacement and infill vuggy textures. The ore mineralogy is simple and consists of pyrite, sphalerite and galena.
JORC reserves and resources are as follows (Terramin 2010), based on a 2.5% Zn eq. (Zn eq.% = Zn% + 0.591*%Pb) cut-off as at 19 Nov 2009, which formed the basis of the DFS.
Probable reserve - 38.1 Mt @ 4.78% Zn, 1.36% Pb, included within the following resource,
Measured resource - 30.6 Mt @ 5.74% Zn 1.59% Pb, with a higher grade core of 11.02 Mt @ 10.89% Zn and 3.04% Pb,
Indicated resource - 20.5 Mt @ 3.57% Zn 0.79% Pb,
Measured + Indicated resource - 51.1 Mt @ 4.87% Zn 1.27% Pb,
Inferred resource - 17.5 Mt @ 3.7% Zn 0.6% Pb,
Total resource - 68.6 Mt @ 4.6% Zn 1.1% Pb
The regional tectonic and geological setting is dominantly summarised from Askri et al., 1995, Geology of Algeria, except where attributed otherwise.
The most recent source geological information used to prepare this decription was dated: 2010.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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