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Caldag Nickel

Turkey

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The Çaldag nickel laterite deposit is located within the Aegean region of Turkey, in the province of Manisa, ~70 km east of Izmir (#Location: 38° 32'N, 27° 48'E).

The Çaldag deposit is developed over a fragment of ophiolite situated on the northern edge of the Menderes Massif, which lies within the Aegean Graben. The ophiolite complex is 93±2 Ma oceanic crust that was tectonically obducted onto Triassic dolomites during the Late Cretaceous when the Neo-Tethys Ocean closed (Önen and Hall 2000). The deposit occurs within the West Anatolian extensional province, characterised by north-south extension that produced a framework of east-west trending horsts and deep sediment-filled grabens resulting from the response of the Anatolian plate to the collision between the Arabian-African, Indian and Eurasian plates.

The Çalda&gcaron; deposit was developed on a horst block to the north of the Gediz Graben, and covers an area of 9 km2, over a variably serpentinised ultramafic body. The deposit is partly overlain by Eocene sandstones, conglomerates and freshwater limestones, which protected the deposit from erosion, preserving it for the last ~55 My (Çagatay et al., 1981).

Weathering profile at Çaldag is both laterally and vertically variable, but can be divided into zones based on texture, mineralogy and thickness, although profiles across the deposit broadly display the same characteristics, namely: a limonite zone, which is the main ore zone, overlain by a redder, more hematitic horizon, which in the south of the deposit is capped by carbonate material and in the north by a siliceous horizon. Extensional faulting is common in the region with a number of profiles cut by normal faults with a displacement of up to 10 m. Although the profiles within the deposit are broadly similar, there are marked local variations in the three main pit areas.

In the South Pit, the unweathered serpentinite protolith is fine-grained, grey-green, and variably fractured, with anastomosing calcite and magnesite veins that dont penetrate into the limonite above. The overlying limonite zone is in sharp contact with the serpentinite, with small (<2 mm) veins of limonite penetrating up to 15 cm into the serpentinite. The basal sections of the limonite zone is banded, with varying amounts of goethite and asbolane, while the upper portions are disaggregated and contain limonite blocks cemented by calcite. The limonite passes up into a zone in which hematite dominates, containing blocks (<10 cm across) of dark grey silicified laterite as well as small (<2 mm) fragments of calcite commonly occuring as layers. The upper sections of this horizon are pervasively veined with calcite, forming a reticulate texture. The hematite zone is unconformably overlain by freshwater Eocene micritic limestone which contains bands of re-worked hematitic material, followed by by sparitic limestone.

In the North Pit, which is 500 m to the NNW of the South Pit, the underlying protolith is a grey-green serpentinite containing calcite veins which locally show a reticulate form. The overlying limonite horizon consists of disaggregated, predominantly limonitic blocks with calcite or silica cement, which higher in the profile takes on a red-brown colour suggesting a higher content of hematitic material compared to the main limonite zone. Within this upper zone thick (~20 cm) subvertical, continuous, veins of calcite are present. The uppermost horizon is yellow-brown soil which has a disaggregated appearance. Calcite is found throughout the zone acting as cement.

In the Hematite Pit, which is 1200 m to the north of the North Pit, the exposed protolith is light brown-green serpentinite containing brown goethite veins that form irregular circular patterns and cross-cut the contact between the serpentinite and limonite. The goethite veins also cross-cut rare white magnesite veins that are confined to the serpentinite. The boundary between the serpentinite and the the overlying limonite zone and is sharp, although relic serpentinite can be found within the limonite up to 40 cm above the contact. The limonite is generally fine-grained, yellow brown and contains irregular continuous goethite veins. Locally, the limonite is more competent and silicified, where it appear to be in situ, with gradational boundaries, and commonly bounded by goethite veins. Some 18 m above the unweathered serpentinite, the limonite zone becomes disaggregated and blocky,and is characterised by a lack of goethite veining. Some areas at the top of this horizon have a red colouration similar to that of the hematite zone within the south pit. An uppermost silica horizon has a gradational contact with the underlying limonite, while silica increases in abundance over a thickness of 20 m until the upper ~15 m of the profile is composed of up to 80% silica, where it has a distinct white colouration in the pit face.

The of the laterite profile in all three pits is composed of limonitic material without original igneous textures, in contact with the serpentinite beneath, and saprolite is not a significant component, and is rarely observed. The constituent lateritic minerals within the limonite zone vary little between the different pit profiles, with fine-grained goethite dominating. The exception is carbonate which is more common to the south. The main variations relate to the of the limonite zone. The southern profiles have distinct banding and blocky zones, whereas profiles further north have prominent goethite veins. The hematitic zone is best developed to the south where it has a banded structure and in some areas contains blocky calcite-rich material. The more northern profiles dont always have distinct hematitic horizons, although they do pass up into hematite associated "redder" coloured sections at the top of the limonite zone. The uppermost horizons of the South Pit profiles are composed of calcite-rich hematitic material, whilst the uppermost 20 m of the Hematite Pit profile is dominated by a siliceous horizon.

The resource of the deposits totals 33 Mt @ 1.14% Ni, 0.07% Co (Thorne, et al., 2009).

The most recent source geological information used to prepare this summary was dated: 2009.    
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.


  References & Additional Information
 References to this deposit in the PGC Literature Collection:
Thorne R, Herrington R and Roberts S,  2009 - Composition and origin of the Caldag oxide nickel laterite, W. Turkey: in    Mineralium Deposita   v.44 pp. 581-595


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