The Efemçukuru gold mine, an intermediate sulfidation epithermal vein deposit, is hosted in the center of a broadly NE-SW trending horst known as the Seferihisar Horst, which regionally exposes basement rocks of the Bornova Flysch in the Menderes Massif.

Local geology consists of intermediate sulfidation veins hosted by a low-grade metamorphic sequence of very fine-grained, black to dark grey shales to phyllite and schist that have been locally folded and intruded by rhyolite dikes. Mineralogy of the phyllites is fine-grained quartz, feldspar, muscovite, chlorite and rare biotite. The mineralogy of the schist is similar to the phyllite, comprising strongly deformed quartz, feldspar, chlorite and muscovite. A calc-silicate alteration, locally termed hornfels, occurs in a broadly NW-trending pattern in the center of the deposit area. The alteration commonly occurs as alternating dark green and tan-grey bands within meta-sedimentary rocks. The contact between calc-silicate alteration and phyllite is gradational. Rhyolite occurs throughout as 1 to 5 m-wide NW-striking dikes. Contacts of the rhyolite dikes with the flysch units are usually sharp.

Two major broadly NW-SE striking epithermal vein systems occur at Efemçukuru, namely Kestane Beleni and Kokarpinar, with strike extents of approximately 2 km and 4 km respectively. Both veins strike north-westerly (320°–340°), dip 60°E to 70°E, and can be traced on surface for strike lengths of over a kilometre. Both veins cut the rhyolite dikes, calc-silicate alteration and unaltered phyllite and schist. At surface, the veins are up to 5m wide and occur as multi-phase, brecciated, banded crustiform-colloform, and massive quartz-rhodochrosite veins. The individual epithermal veins within these vein systems contain multiple ore shoots with zoned mineral and metal distributions and a complex paragenesis.

The 2 km long Kestane Beleni vein hosts the major gold resource and reserve at Efemçukuru and comprises four ore shoots: South Ore Shoot (SOS), Middle Ore Shoot (MOS), North Ore Shoot (NOS) and Kestane Beleni Northwest (KBNW). The Kestane Beleni vein has a distinct mineralogical zonation with the proportions of Mn-silicate and carbonate and sulfide vein material varying across the vein system. Mn-rich vein assemblages are most abundant in the upper portions of the SOS, whereas the sulfide content of the MOS and NOS, particularly at depth, is much higher.

The SOS outcrops for 500 m and dips between 45° to 70° to the northeast. The shoot has a down dip extent of approximately 500 m. The southern half of the shoot consists mostly of a single vein whereas in the central part of the SOS, the vein splays at depth. A second larger splay develops nearer the surface, close to the mid-point of the SOS and continues for approximately 230 m to the north end of the shoot. Where the SOS consists of a single vein, its thickness generally ranges from 3 m to 5 m but can locally reach more than 10 m. Gold mineralization is not generally distributed across the whole vein, but more typically occurs as high grade (> 50 g/t x m) discrete zones within the vein that have a steep northerly dominant plunge and shallow to moderate southerly secondary plunge. Where the vein breaks into splays, the splays are generally narrower, with thicknesses of 1 to 2 m. Additionally, significant stockwork type mineralization is locally present between the vein splays where they cut hornfels. Limited amounts of stockwork mineralization occur where the vein hanging wall consists of phyllite, but are more restricted in size and continuity.

In the MOS area, the Kestane Beleni vein strikes 320° over approximately 230 m and has an average dip of 60° to 65° to the northeast. High grade gold mineralization in the MOS forms a steeply plunging shoot in the central part of the MOS and is hosted entirely within hornfels. The shoot has a narrow surface expression of ~3 m, but expands with depth to more than 20 m. A single splay diverges from the main vein in the central part of the shoot and an extensive zone of stockwork mineralization occurs between the two veins and extends into the hanging wall. The stockwork zone is best developed between 550 m and 600 m elevation with some extensions above and below these elevations, and is traceable along strike for approximately 75 m.

The NOS is separated from the MOS by an inflection that coincides with an additional 25° westward bend in the strike of the Kestane Beleni vein. Here the vein strikes approximately 300° and vein flattens to a 45°dip. The NOS outcrops intermittently for approximately 200 m along this bearing before it pinches out. Another inflection occurs between the NOS and KBNW, with the latter striking nearly east west over a 300 metre strike length before reverting to a 300° strike orientation. KBNW is typically narrower than the other three main shoots (< 3 m) and comprises two vein splays for much of its length.

The majority of the gold is fine-grained (< 30 microns) occurring as free grains in quartz and rhodonite gangue, and within and in contact with pyrite, chalcopyrite and sphalerite, and to a lesser extent in galena. Higher gold grades, however, are not directly related to sulfide abundance. Silver content of the deposit is highly variable. The average silver grade for both the MOS and SOS is low (11.9 and 8.3 g/t), however, parts of the MOS shoot contain silver values in excess of 100 g/t.

Efemçukuru mine employs small-scale underground mechanized mining methods to exploit the narrow, high- grade, subvertical mineralization. The projected mine life is 7 years at current production rate of 510,000 tpa.

The current mine layout has the following features:

- Four declines (SOS, MOS, NOS and KBNW), each covering approximately 400 m strike extent.
- Two surface portals (south and north).
- One surface conveyor adit for conveying crushed ore to the surface crushed ore bins.
- Four primary ventilation surface exhausts (south, central, north and northwest) and one fresh air raise for NOS.
- Link drives connect declines and serve as a secondary egress from the mine.

Ore is mined using conventional mechanized cut and fill and longhole mining methods.

The mine plan is based on the combination of drift-and-fill and longhole-open-stoping methods. Both DAF and LHOS stopes are mined concurrently from multiple production blocks to fulfil production requirements. Overall, the production blocks are mined in a top-down sequence, but stopes within a production block are mined bottom-up (overhand).

The selection of DAF and LHOS mining methods is primarily based on the orebody geometry (width and dip) and the expected ground conditions determined through geotechnical assessment. Regular geotechnical assessments indicate that the current mining method, stope sizes, and mining sequence will not change significantly change over the LOM.

The mine design has been developed to allow flexible access to all of the shoots of the Kestane Beleni. Four spiral footwall ramps at each orebody provide access for moving men, equipment, and supplies underground. Advantages of the four-ramp system include increased stope availability, more robust ventilation with increased equipment and labour productivity. All declines are interconnected by link drives, which serve as a secondary egress from the mine, spaced vertically 80–100 m apart.

Ore is truck hauled to a central ore pass system above the underground crusher before being conveyed to surface via a 380 m belt conveyor. The orepass system provides 3,500 tonne surge capacity for underground production with a further 5,000 tonne capacity in bins on surface. Waste rock is hauled to surface via the South 672 Portal or North 656 Portal.

Paste backfill is used as a “free standing” structure to control stability of walls, dilution, and safety for the LHOS. In the DAF stopes, paste backfill is used as the working floor. The paste plant is located near the North 656 Portal.

The mine operates seven days a week and three shifts a day. This annual schedule is equivalent to 365 days per year of operation.

The Efemçukuru concentrator has been successfully processing ore from Efemçukuru mine since commissioning in mid-2011. The original process flowsheet was designed to produce gold doré from the gravity concentrate and from the gold-containing sulfide minerals flotation concentrate. However, the gravity concentration circuit was decommissioned in 2017. Production of gravity concentrate has been considerably lower than what was estimated in the feasibility study (expected 30 % recovery) and thus, the process flowsheet was revised in 2018 to produce only flotation concentrate for sale. This had no effect on overall recovery because gravity concentrate was recovered from the flotation concentrate.

The process plant produces a gold-containing bulk sulphide rich flotation concentrate. Major sulfide minerals comprise pyrite, sphalerite and galena. Small percentage of chalcopyrite is also present. Major gangue minerals consist of quartz and manganese minerals.

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