Summary:
The characteristics of the Gediktepe mineralization have been interpreted as a convex massive sulphide type deposit, which implies a syngenetic style of sulphide mineralization. Subsequent weathering and oxidation have been responsible for the development of oxide and gossan horizons.
Project geology
Upper Palaeozoic metamorphics are the most common units at Gediktepe, with a stratigraphic sequence, from top to bottom being: Dacite and pyroclastic; Calcschist; Feldspar-quartz schist; Chlorite-sericite schist; Quartz schist.
The second most common rocks are the Lower-Middle Miocene volcanics, observable around Karadikmen hill, southwest of Gediktepe, comprising altered dacites-rhyodacites, characterized by lava flows and pyroclastics.
The youngest units on the project are mineralized gossan and ferricrete, along with talus, colluvium and alluvium, being weathering products of the host rock.
Chlorite-sericite schist is the main host rock at Gediktepe, marked by gold and silver in the oxide zone, and copper-zinc-lead, with associated gold-silver, in the sulphide zone. The unit is observed at Findikalani Ridge, Çamdami Ridge, Karaismailöldügü, and northwest of Gögne Hill in the license area.
When disseminated pyrite in the chlorite-sericite schists exceeds 10% to 45% by volume, the unit is logged by Polimetal as transition zone (TR-Sulp) or disseminated sulphide. Disseminated pyrite minerals are aligned parallel to schistosity and appear as pyrite bands.
Petrographic analysis indicates that the rock has been intensely chloritized, epidote-altered, silicified, carbonatized, and mineralized. Fractures and spaces between individual crystals of cataclastic, structured epidote are filled with quartz, calcite and chlorite.
The feldspar-quartz schist is beige-light green in colour and is observable over a wide area at Gediktepe. It forms the primary unmineralized capping over the deposit, and generally contains virtually no sulphides.
The calc schist observed at Gediktepe in outcrop at Küçük Yellice hill and Findikalani Ridge is beige-light grey coloured, with low hardness and schistosity, and is reactive to HCI acid.
The dacites and pyroclastics, of the Lower-Middle Miocene volcanics, are the second largest geological unit at the Gediktepe project. The volcanics, located at southwest of Karadikmen Hill and Gasakdogrusu Hill, contain altered dacite to rhyodacite lava and pyroclastics.
Mineralization
The mineralization at Gediktepe is associated with greenschist facies schist units. The mineralization is thought to be deposited syn-genetically in sedimentary units, as an elongated NE-SW structure zone, and metamorphosed to schist. Greenschist minerals are generally actinolite + chlorite + albite + epidote (Alizade, 2013 – 2015, Çiftehan, 2015).
Massive sulphide-type mineralization occurs as lens shapes trending NW-SE and dipping approximately 20° to 40° to the north-west. Minerals include pyrite, sphalerite, tetrahedrite, tennantite, chalcopyrite, galena and magnetite, and the units are cut by later NW-SE trending post-mineralization structures. Within the oxidized zone, the sulphide mineralization has been completely leached out, leaving gold and silver relatively intact.
Potentially economic Au-Ag-Cu-Zn-Pb metals are present to varying degrees in the sulphide zone.
Reviews of interpretations revealed that, in the northern part of the deposit and in the vicinity of the enrichment zone, part of the sulphide zone shows high Au and Ag and low base-metal content (<0.1 % Cu and Zn).
Gossan (oxide mineralization)
The upper portions of the Gediktepe deposit have been weathered, leached, and oxidized by naturally-occurring acidic surface water and ground water. The natural acidity is due to the presence of sulphides, particularly pyrite, within the oxide zone, and the sulphide mineralization has been completely leached out, leaving gold and silver relatively intact. Relic “lenses” of high-gold mineralization remain in the oxide zone. There is some evidence that gold mineralization has been transported downwards, chemically or mechanically, as there is often an increase in gold grade just above the oxide sulphide contact.
The base of oxidation is generally abrupt, with rapid changes of metal grade in assay intervals across the boundary. Copper and zinc grades are typically less than 0.10% within the oxide zone, but increase to values typically around 1.4% Zn and 0.80% Cu immediately below the oxide horizon. Gold and silver follow the reverse trend, with Gold in the range of 3.0 g/t Au in the oxide zone and often less than 0.7 g/t Au immediately below in the sulphide zone.
Massive pyrite (MPy)
The massive pyrite zone consists of fine to medium-grained pyrite, with massive to banded, vuggy textures, and locally sandy textures near structural zones. The sphalerite-chalcopyrite-galena-and weak covellite are observed as vug-fracture fill, and replacement mineralization within a pyrite matrix. Locally, magnetite fragments are observed within massive pyrite. The massive pyrite zone hosts high Au and Cu mineralization (Çiftehan, H, 2015).
Massive pyrite magnetite (MPyMag)
Massive pyrite magnetite (MPyMag) has been distinguished based on magnetite contamination. It shows the same textures of the massive pyrite zone, and qtz-magnetite fragments can be seen conformable with the schistocity, or primary bedding structures within the massive pyrite. The MPyMag zone characteristically shows lower Au-Ag-Cu-Zn-Pb than the massive pyrite zone.
Enrichment zone (Enrch)
The enrichment zone consists of mainly chalcocite-covellite within fine to medium grained size pyritic mass. Due to occurring near or along the structure zone, most of the enrichment zone is intensely fractured, broken and fragmental. This zone contains higher grade Au-Ag-Cu-Zn mineralization than other sulphide mineralization.
Disseminated sulphide mineralization (Tr-Sulp)
A lower-grade sulphide mineralization (Au-Ag-Cu-Zn-Pb) is present within the rich disseminated (pyrite>10%) chlorite sericite schist. The total sulphide content in this zone exceeds 8.5%. Thick bands (1 cm to 50 cm) appear parallel to bedding, in host rock below and above the sulphide mineralization.