Summary:
The principal model for gold mineralization at the Agi Dagi and Çamyurt Gold Properties is a highsulphidation, epithermal gold deposit. Premier examples of this kind of deposit in the world are Yanacocha, Pierina and Alto Chicama in Peru. Most high sulphidation deposits are large, low-grade bulk-tonnage systems (Yanacocha), though vein-hosted high-sulphidation deposits also occur (El Indio).
At Agi Dagi, gold mineralization is associated with felsic volcanic rocks of Miocene age and a northeast trending silica cap rock about 4 km x 2 km in extent which forms a topographic high 700 to 900 m in relief. The gold mineralization is disseminated and associated with intensely silicified, vuggy, oxidized and brecciated rocks hosted in volcanic felsic to intermediate tuffs and occasionally phreatic breccia bodies. Hydrothermal-type breccias (crackle, jigsaw, hydrothermal) are most common in this siliceous alteration. Pyrite is by far the most abundant primary sulphide mineral associated with gold. Trace to minor amounts of enargite, covellite, galena and molybdenum are present locally.
Five main zones of gold mineralization are present at Agi Dagi: the Baba, Ayi Tepe, Fire Tower, Ihlamur and Deli Zones. The most important ones in term of resources and intensity of drilling are Baba and Deli. The Baba, Fire Tower and Deli zones are on the east side of the mountain top along a silicified dacite basin – phreatic breccia northeast-southwest trend. Gold mineralization is continuous between the south of Baba and Deli over 4 km although there are zones where gold mineralization is too deep or too low-grade to be considered for mining. The Ayi Tepe and Ihlamur zones are on a parallel trend the west side of the mountain. Mineralization does not appear as continuous in the Ayi Tepe – Ihlamur trend but it has been less recognized by drilling.
The north of the Baba hill is composed of phreatic breccias cutting through andesites and a half kilometre wide northeast trending basin composed of dacite flow and tuff. To the west, the Ayi Tepe hill is made up of the same geological assemblage, a dacite tuff basin over andesites cut by phreatic breccia pipes. These two basins are elongated towards the northeast and may be followed all across the Agi Mountain to Deli through Fire Tower.
Most of the gold mineralization in the Baba zone is spatially associated with the matrix-supported heterolithic phreatic breccia body cutting low-dipping dacite tuffs overlying andesite flows. Silicification (often vuggy and/or crackle-brecciated) appears to be related to this breccia and the dacite. The attitude of the gold mineralization as interpreted from drilling is dictated by the shape of the breccia body, which extends beyond in the dacite tuffs. Some lower grade mineralization also occurs in oxidized porphyritic andesite adjacent to the phreatic breccia. The bulk of gold mineralization occurs within the oxide zone.
The Deli hill is composed of a phreatic breccia pipe cutting through andesites and a kilometre wide basin composed of dacite flow and tuff. To the west in the Ihlamur extension, the northern edge of another basin of dacite is present. These two basins are elongated towards the southwest and may be discontinuously followed across the Agi Mountain to Baba and Ayi Tepe.
In Baba, the phreatic breccias and dacites are mostly silicified while alteration quickly falls to argillic in the underlying andesites. Vuggy silica appears coherent with a higher and a lower zone. Higher-grade gold mineralization is found in the upper part of the silicified zone while a lowgrade gold mineralization is common towards the bottom of the silica zone, coinciding with the bottom of the dacite or with phreatic breccia which is found at the dacite-andesite contact.
The Deli geochemical signature is that of a classical high-sulphidation epithermal model with elevated Au-Pb-As-Ag. The Deli zone is an intensely silicified package of dacite volcaniclastics overlying porphyritic andesites being intruded by elongated heterolithic phreatic/phreatomagmatic breccia bodies. The corridors (often faults) for the breccias in turn become fluid pathways where gold bearing fluid rises along sub-vertical feeder structures, flattening near surface and intersects crackleto jigsaw-brecciated and/or vuggy silica zones, and deposits gold within this rock package, much of which is subsequently oxidized.
At Agi Dagi, breccias are important as mineralization controls. Two main breccia families are present. These are the phreatic breccias and the hydrothermal breccias. But there are additionally other types of breccias.
Phreatic breccias include also phreatomagmatic breccias. These breccias are predominantly heterolithic, with a matrix of mostly rock flour (the phreatomagmatic variety also have a magmatic component but are less abundant than the phreatic breccia and were only identified at Deli). They are generally matrix-supported. These breccias have a mushroom shape with sub-horizontal to lowdipping near surface extensions away from the feeder pipe. The breccias and particularly their contacts with host rocks are important for providing pathways for later hydrothermal fluids. The phreatic brecciation mostly pre-dates mineralization.
The crackle and jigsaw breccias relate to stress and are a part of the continuum that ranges from fracture zones through intense fracturing (crackle), fracture with an element of clast rotation (jigsaw) and progress through to hydrothermal breccias which may even be matrix(cement)-supported and heterolithic depending on the amount and force of injection of the hydrothermal fluids.
Hydrothermal breccias are cemented by minerals that are derived from hydrothermal fluids (i.e. quartz-alunite-pyrophyllite-pyrite etc). Hydrothermal breccias are often directly related to mineralization, with higher grades coinciding with those whose matrix is more pyrite (or Fe-oxide) - rich. Hydrothermal brecciation overlaps and includes all other categories of breccias.