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The Siirt Madenköy copper deposit is located in SE Anatolia, ~30 km NE of the town of Siirt in southeastern Turkey, ~100 km north of the Syrian border and 810 km ESE of Ankara (#Location: 38° 5' 21"N, 42° 9' 5"E).
The Madenköy copper field has been known and exploited since ancient times. Following initial prospecting in 1947, 1958 and 1962, the deposit was discovered by the Turkish General Directorate of Mineral Research and Exploration (MTA) during exploration carried out in the early 1970s, followed by a drilling program between 1973 and 1977. On the basis of 18 500 m of drilling in 66 holes, Outokumpu and MTA prepared a joint feasibility study in 1981, based on a resource of 24 Mt @ 2.03% Cu. In 1985 the title was transferred to Etibank and development commenced under a joint venture that included Preussag (Germany), Alarko (Turkey) and Etibank (Turkey). The JV was terminated in 1989 and subsequently the project was put to tender by Etibank. A bid by Park Elektrik Üretim Madencilik AŞ, a Turkish company, was accepted in 2004, affective until 2037 and mining commenced in 2006.
The Siirt Madenköy copper field is located in a structurally complex, east-west aligned belt in the collision zone between the Eurasian Plate to the north and the Africa-Arabian Plate to the south. This collision zone sandwiches an intervening east tapering block known as either the Anatolian Plate of Anatolide-Tauride Platform, which near Siirt is ~100 to 200 km wide. The Anatolide-Tauride Platform is, in turn split into a number of smaller blocks, which immediately to the north of Siirt Madenköy includes the 30 to 60 x 500 km, east-west elongated Bitlis Metamorphic Massif. The latter massif is separated from the Arabian Plate by the regional arcuate Bitlis Suture Zone, a segment of the larger Bitlis-Zagros Suture Zone, which much further to the SE includes the Zagros and Oman ophiolites.
The Bitlis Suture Zone is also part of a south-directed imbricated thrust zone with thrust planes dipping 10 to 30°N. Its southern margin is occupied by the Arabian Platform which is mainly covered by Middle to Upper Eocene autochthonous marine and platform carbonates (Midyat Group) overlain by flysch of the Lice Formation. These units together form the Upper Autochtonous Succession. Beneath these, the Lower Autochthonous Succession is represented by platform carbonates (the Jurassic-Senomanian Cudi-Mardin Group) and the folded Bedinan-Sadan-Telbesmi formations resting on a basement of Palaeozoic to Proterozoic shallow marine sediments and volcanic rocks.
The two autochtonous successions are separated by a locally exposed Lower Allochthonous Succession which was thrust southward during the Late Cretaceous. This latter succession represents deposition in a foredeep following subsidence on the margin of the platform into with Maestrichtian terrigenous sediments of the Kastel Formation were deposited, overlain by a sedimentary mélange that represents a subduction accretion complex. These sedimentary rocks overlie
an ordered ophiolitic sequence (the Kizildag and Cilo ophiolites) which were obducted onto the platform carbonates of the Lower Autochthonous Succession along the southern margin of the Neotethyan Ocean during the latest Cretaceous Senonian. These ophiolites represent oceanic crust that formed the leading edge of the advancing Anatolian Plate/Anatolide-Tauride Platform.
North of the Arabian Platform and Bitlis Suture Zone, there is a narrow (1 to 5 km wide) zone of imbrication which consists of a number of south-vergent thrust slices overlying the Lice Formation and include Upper Cretaceous to Lower Miocene units. Rifting during the early Middle Eocene formed the
Maden Group Basin, followed by deposition of deep sea sediments. This rift was located behind the Helete volcanic arc, superimposed on the Arabian
Platform and represents a back-arc basin. These units are tectonically overlain by the obducted Berit and Yüksekova ophiolites. The Siirt Madenköy deposit is hosted by spilitic lavas in this zone of imbrication.
To the north of the imbrication zone a Nappe Belt was developed, where the Lower Palaeozoic to Upper Cretaceous Keban-Malatya metamorphic rocks of the Bitlis Metamorphic Massif have been structurally emplaced with a south vergence. These high-grade metamorphic schists and gneisses are surrounded by an envelope of low-grade slate, phyllite, marble and metacherts. These metamorphic rocks form an upper nappe and tectonically overlie the Berit and Yü̈ksekova ophiolites and the Maden Group which occupy the lower nappe north of the Bitlis-Zagros Suture Zone.
Mineralisation at Siirt Madenköy is located on the eastern end of the Bitlis Suture Zone where autochthonous Tertiary units are overlain by pillow lavas intercalated with Eocene flysch. These units, which are structurally overlain by allochthonous thrust sheets of Palaeozoic Bitlis Massif metamorphics as well as further gabbros and serpentinites, are only exposed to the west and southwest of the mineralised area. The deposit occurs within the pillow lavas, hosted by an east-west elongated zone of very intensely altered spilites that is 400 to 500 m long and 50 to 200 m wide. The Palaeocene to Lower Eocene flysch sequence below the thrust sheets and ophiolites includes sandstone, mudstone, marl and fossiliferous limestone that pass laterally into, or are overlain by the ophiolites. The ophiolitic sequence comprises gabbros at the base, followed by dolerite (including some sheeted or isolated dykes) spilitic pillow lavas and Middle to Late Eocene mudstone.
The Bitlis Massif metamorphics in this region comprise amphibolites and chlorite schists overlain, in turn, by quartzite and sericite schists, and then by recrystallised, brecciated, calcite-veined Permo-Carboniferous limestone with nodule lenses.
Some gabbro has been encountered in association with the pillow basalts in the immediate deposit area.
The host rocks of the sulphide ore are pillowed spilite and porphyritic spilite flows which may be up to 450 m thick and outcrop with an east-west trend. Together with zones of alteration, they are exposed in a tectonic window surrounded by recrystallized limestones of the Bitlis Massif. The mudstone and conglomerates interbedded with the basic lava flows are derived solely from volcanic rocks. Pillows are 25 to 250 cm across, and are amygdaloidal with ophitic textures. They have a 2 mm thick glassy crust, with coarser-grained inner zones, and commonly dip at 50 to 60°NE and show exfoliation. Lavas with a porphyritic texture, commonly due to the presence of 5 mm long feldspar crystals, are extensively developed to the south of the mineralised area. Contacts between porphyritic and ophitic textured spilites are either gradational, or discontinuous and sharp. The spilites also contain reddish jasper and fine-grained tuffaceous horizons. Middle Eocene fossils were reported from mudstone intercalations between pillows. Mudstones, closely associated with the pillow lavas, show vertical and lateral gradations or interfinger with conglomerates composed of recrystallized limestone fragments. Some sandy lenses are also common, but are not very extensive.
The sequence is cut by dolerite dykes, which contain small amounts of magnetite, hematite and leucoxene. These dykes are exposed to the north of the mineralised and altered area and are generally fine-grained. They occur as sheeted dykes in the SW of the area, although they are also found as closely spaced isolated dykes. They contain accessory hematite, rutile, ilmenite, calcite and quartz.
A near vertical, east-west trending major fault divides the mineralised and altered area into two blocks, and defines the footwall of a major ore lens that has been dislocated and displaced to the SW. The lens shaped orebody dips at 50 to 60°NE in cross sections, and on its western end is terminated by a NNW-SSE trending fault.
Mineralisation and Alteration
The sulphide mineralisation at Siirt Madenköy closely follows an extensive east-west trending alteration zone that has been traced over an interval of at least 10 km and closely follows the regional thrust/imbrication zone. The host pillow basalts are also extensively spilitised in the mineralised area, with the development of chloritisation, argillisation, silicification and sericitisation to varying degrees. Vesicles in the spilites are filled with secondary zeolite, quartz and calcite. Albitisation of feldspars and chloritisation of the mafic minerals is extensive, with local sericite and clay alteration. The alteration chemistry is very similar in both the normal and porphyritic spilites. Calcite, epidote, quartz and actinolite minerals are also formed. Primary magnetite is replaced by, or altered to hematite (martitisation) along cleavage planes, and maghemite is accompanied by ilmenite laths altered to leucoxene and rutile along crystal outlines. Other accessory minerals include chromite, Co and Ni-sulphides.
A stylised vertical mineralogical zoning comprises, from bottom to top:
• Massive magnetite flanked below and on its margins by chloritised and argillised country rock containing disseminated pyrite and fracture-fill magnetite. K-rich argillised rocks occur immediately outboard of the massive magnetite, followed by chloritised and then more weakly argillic alteration. This zone passes upward into,
• Massive chalcopyrite + pyrite, the main ore zone, which in places is altered to secondary copper minerals such as chalcocite and covellite and is also accompanied by tetrahedrite-tennantite, bornite and with some linneite, sphalerite (with some chalcopyrite inclusions), galena and native silver. Gangue minerals include quartz, siderite, calcite, dolomite, marcasite, pyrrhotite, limonite, malachite, maghemite, hematite, ilmenite, rutile, leucoxene, chromite, Cr-spinel, chlorite, sericite, barite and titanite. The massive pyrite-chalcopyrite is partially flanked by, and passes upwards into,
• Disseminated pyrite, which occurs as euhedral and subhedral grains with some small magnetite, chalcopyrite, sphalerite and rutile inclusions, and is replaced along fractures by chalcopyrite and gangue minerals. Barite and zinc are enriched across the transition to the orebody. This mineralisation is flanked laterally by argillised pillow lavas, but passes upwards into K-rich argillised rocks, followed by chloritised and then more weakly argillic alteration, mirroring the zonation at the base of the deposit.
The K-rich argillised rocks in these zones are sericitised and are associated with massive pyrite lenses or pyrite disseminations, with illite, montmorillonite, kaolinite and quartz-bearing rocks. They represent the alteration formed nearest to the orebody and show a distinct K- enrichment relative to silicified rocks.
The chloritised rocks are either light green with argillised pillow forms (consisting of plagioclase, chloritised pyroxene, and are calcite-bearing with disseminated pyrite and limonite concentrated along fractures), or dark green to green-black chlorite-rich rocks with sericitised plagioclase, calcite and pyrite and/or magnetite disseminations. Compared with reasonably fresh spilites in the mineralised area, the chloritised rocks are depleted in Si, Ca and Na, but enriched in Fe and Mg. These chloritised rocks, with pyrite/magnetite disseminations, pass laterally and vertically into variably argillised spilite with a decrease in the chlorite and magnetite contents.
The outer argillised rocks are composed of kaolinite and montmorillonite, and are enriched in Si and K, but depleted in Fe and Mg when compared with the chloritised rocks.
Silicified rocks, found below the massive pyritic zone or at the surface, are grey and quartz, sericite and montmorillonite-bearing with pyrite disseminations.
Mineralisation occurs entirely within the pillow lavas of the sequence. The spilites surrounding the main ore zone contain varying amounts of sulphide disseminations and veinlets, mainly composed of pyrite though in places, partly oxidised chalcopyrite is present. Ore lenses appear to represent either complete replacement of the lavas or are due to direct discharge of hot sulphide fluid into the cold sea bottom between lava flows.
Zn contents range up to 2.75 wt.%, Pb up to 0.3%, Cu from 0.3 to 8.55% and Cd from 5 to140 ppm.
Ore Reserves and Mineral Resources
Akinci (2009) quotes a Proved Ore Reserve of 20 Mt @ 2.33% Cu, 0.67% Zn, 0.059% Pb.
The following Mineral Resource is quoted in Mining and Earth Sciences Magazine, Mining Turkey, 2013:
Measured Resource - 31.182 Mt @ 2.26% Cu;
Indicated Resource - 6.433 Mt @ 2.79% Cu;
Measured + Indicated Resource - 37.615 Mt @ 2.34% Cu;
Inferred Resource - 2.206 Mt @ 2.79% Cu;
TOTAL Resource - 39.821 Mt @ 2.40% Cu.
This summary is mostly drawn from Akanci 2009,
The most recent source geological information used to prepare this summary was dated: 2013.
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.
Akinci, O.T., 2009 - Ophiolite-hosted Copper and Gold Deposits of Southeastern Turkey: Formation and Relationship with Seafloor Hydrothermal Processes: in Turkish Journal of Earth Sciences, v.18, pp. 475-509.|
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