Amulsar, in the south of Armenia, is a low grade,high tonnage gold deposit with a current total combined CIM compliant resource of 5 million ounces gold and is currently open in all directions. The deposit lies within silicified host rocks along the crest of a 2800m high mountain ridge and the silicified rocks are underlain by, and partly interleaved with, a large volume of highly visible pale clay-altered volcanogenic rocks dominated by porphyritic andesite. A number of small plutons and subvolcanic intrusives lie just to the west of the alteration system, and contain currently sub-economic alenachalcopyrite veins.
Amulsar is a true ‘greenfields’ discovery. Although the alteration had been mapped in early Soviet times for a silica resource, and later Soviet exploration had been carried out for silica, gold was not reported until a reconnaissance trip by Lydian geologists in 2005 recognised the potential for epithermal-style gold mineralisation in rocks beside the highway.
Multiple panels of clay-altered porphyritic andesite are interleaved throughout the silicified upper volcanosedimentary sequence and these panels have complex fold geometries. The origin of most of the andesite panels is probably intrusive, but the interleaving is also at least partly structural. Prior to mineralisation several generations of thrusts had produced a large dissected fault-fold structure. Subsequent deformation, possibly dextral wrenching, produced structures that overprinted and refolded the older structures. An abundance of both systematic and non-systematic faults and linking fractures accommodated the resultant geometrical incompatibilities associated with the refolding, and it is these brittle structures that host mineralisation. Later oblique normal faults further segmented the system.
Gold, hematite, and silica occur within fractures, narrow oxide-filled breccia zones, and a few larger hydrothermal breccia zones. The alteration history at Amulsar is complex, reflecting the complex structural history. The early alteration patterns have elements of high to medium sulfidation models (silica±alunite and argillic alteration). However, the very strong hematitesilica alteration that accompanies gold deposition, and the high statistical association of Fe,Cu, Au, As, Sb, Bi, and Pb gives the deposit a strong IOCG signature for the Au, rather than either ‘epithermal’ or ‘orogenic’ models, although the epithermal alteration may be associated with polymetallic deposits elsewhere in the area.