Geological Setting and Mineralization Regional Geology

Chelopech is classified as a high-sulphidation type epithermal copper-gold deposit. It is located in the Panagyurishte mining district that also hosts other epithermal gold-copper deposits as well as porphyry copper-gold deposits such as Elatsite, Assarel and Medet. The geology of the district is made up of a basement of Precambrian gneisses that is intruded by Palaeozoic granites and overlain by Late Cretaceous magmatic and sedimentary sequences.

At Chelopech, the gold-copper orebodies are hosted by the Late Cretaceous magmatic rocks. These form a multi-phase intrusive complex that is cut by vertical intrusion-related breccia bodies (phreatomagmatic breccias including diatremes and blind breccia pipes). The Chelopech orebodies were then preserved under 300-500 metres of younger sedimentary rocks and by later normal and thrust faults.

The distribution of the ore bodies is thought to be controlled by favorable breccia and host rock contact zones and structural intersections within the breccias. The orebodies are usually hosted by the phreatomagmatic breccias within a diorite intrusive body. The orebodies range from 40-200 metres in length, are 20-130 metres in thickness and can extend for up to 400 metres down plunge.

The high-sulphidation mineralization occurs as quartz-sulphide and sulphosalt-rich replacement zones surrounded by haloes of silica and advanced argillic alteration. The main ore minerals are tennantite, enargite-luzonite, chalcopyrite and pyrite. Gold occurs as a native element forming Au-Ag alloys, as well as micrometer-scale inclusions in sulphosalts and pyrite grains.

The main orebodies are generally found below 500 metres from surface and are spatially grouped into two mining areas. The Central zone consists of eight orebodies and the Western zone consists of ten orebodies.

Advanced argillic alteration related to Chelopech ore system extends towards the southeast, beneath the Chelopech thrust fault, and is associated with a blind breccia pipe zone that has a strike length of approximately 1,200 metres. This part of the system, known as the Southeast Breccia Pipe Zone, extends to the northeast to include Block 10 and is one of the main target areas for the current underground exploration program.