Summary:
The Gediktepe Project is a massive sulfide deposit hosted in schists. The sulfide zone is polymetallic with potentially economic values of zinc, copper, gold, and silver. The upper portions of the Gediktepe deposit have been weathered, leached, and oxidized by naturally occurring acidic surface water and ground water. The oxide zone hosts gold-silver mineralization, but is nearly devoid of base metals.
Mineralization at the Project is associated with greenschist facies units that are interpreted to represent massive sulfide deposition that was syngenetic with sedimentary units. These units are now elongated along a north-easterly trending structural zone that has been metamorphosed to schist. The massive sulfide-type mineralization occurs as lens-shaped units trending north-easterly and dipping at approximately 20° to 40° to the northwest. The major sulfide zone minerals are sphalerite and chalcopyrite. Pyrite is ubiquitous.
Disseminated pyrite mineralisation, or veins of massive sulphide in the host rock, have sometimes been referred to as transitional sulphide, only because the massive sulphide mineralisation abundance is diminishing to waste grades as a result of phenomena other than post-emplacement alteration of the minerals.
The tabular mineralised zones, particularly within the sulphide horizon, dip gently to the west. In the north-eastern portion of the deposit, mineralised zones may be shallower dipping. In several locations the overall trend is abruptly terminated, and the tabular mineralised zones are displaced downwards to the north-east, indicating post-mineralisation activity. Progressing south-west to north-east across the deposit, this displacement geometry has been identified three to four times, and these features have been recognised as abrupt breaks or offsets during interpretation of mineralised bodies.
Massive sulphide-type mineralisation occurs as lens shaped units trending north-east / south-west and dipping at approximately 20° to 40° to the north-west. Minerals include pyrite, sphalerite, tetrahedrite, tenantite, chalcopyrite, galena, and magnetite. The units are cut by later north-west / south-east trending post-mineralisation structures within the oxide zone, in which the sulphide mineralisation has been completely leached out, leaving gold and silver relatively intact. Potentially-economic gold–silver–copper–zinc mineralisation is present to varying degrees in the sulphide zone.
The mineralisation at Gediktepe has been is divided by Polimetal into five main types:
- Gossan;
- Massive Pyrite;
- Massive Pyrite–Magnetite;
- Enriched;
- Disseminated Sulphide.
Recent review of interpretations revealed that, in the northern part of the deposit and in the
vicinity of the enriched mineralisation, areas within the sulphide horizon show high gold and
silver and low base-metal (< 0.1% copper and zinc) concentrations.
Gossan (oxide)
The natural acidity is due to the presence of sulphides, particularly pyrite, within the oxide zone, and the sulphide mineralisation has been completely leached out, leaving gold and silver relatively intact. Relic ‘lenses’ of high-gold mineralisation remain in the oxide zone. There is often an increase in gold grade just above the oxide–sulphide contact.
Copper and zinc grades are typically less than 0.10% within the oxide zone but increase to values typically around 1.40% 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 in the oxide zone and often less than 0.7 g/t at the top of the sulphide zone.
The Gediktepe oxide-type mineralisation is characterised by yellow-to-red leached zones of intense iron oxide gossan material. Near surface, is a leached cap, locally containing elevated gold values.
Massive Pyrite
The massive pyrite zone consists of fine to medium-grained pyrite, with massive-to-banded, vuggy textures, and locally sandy textures near structural features. The sphalerite–chalcopyrite–galena and weak covellite are observed as vug fracture fill and replacement mineralisation within a pyrite matrix. Locally, magnetite fragments are observed. The massive pyrite zone hosts high gold and copper mineralisation.
Massive Pyrite–Magnetite
Massive pyrite–magnetite has been distinguished from massive pyrite based on the presence of magnetite. Massive pyrite–magnetite shows the same textures as the massive pyrite. Quartz– magnetite fragments can be seen conformable with the schistosity, or primary bedding structures, within the massive pyrite–magnetite. The massive pyrite–magnetite characteristically shows lower gold–silver–copper–zinc–lead grades than the massive pyrite.
Enriched
The enriched zone consists of mainly chalcocite–covellite within fine to medium-grained pyritic mass. Occurring near or along structural features, the enriched zone is generally intensely fractured. Relative to other sulphide mineralisation zones, the enriched zone contains higher grade gold–silver–copper–zinc mineralisation.
Disseminated Sulphide
A lower grade sulphide mineralisation (gold–silver–copper–zinc–lead) is present within the rich disseminated (pyrite > 10%) chlorite–sericite schist. The total sulphide content in this zone exceeds 8.5%. Bands of 1–50 cm thickness appear parallel to bedding in this host rock below and above the sulphide mineralisation.