The Chelopech deposit is located within the Panagyurishte metallogenic district in the central part of the Srednogorie zone, a volcano-intrusive zone that formed during the Late Cretaceous magmatic evolution in Bulgaria The Panagyurishte mineral district is defined by a NNW alignment of porphyry-copper (Elatsite, Assarel and Medet) and epithermal Cu-Au (Chelopech) deposits, which is oblique to the east-west orientation of the Srednogorie belt. Alluvial (Topolnitza and Luda Yana) and vein-hosted (Svishti Plas) gold mineralization is also known in the area and has been previously exploited on a small scale.
The geology of the Panagyurishte mining district comprises a basement of Precambrian granitoid gneisses intruded by Palaeozoic granites and overlain by Late Cretaceous magmatic and sedimentary sequences. In some parts of the district, these rocks are overlain by Late Cretaceous flysch and by Palaeogene and Neogene molasse.
The basement rocks form a series of uplifted horst-anticlinal structures between which a series of three north to east trending sub-parallel grabens contain the Cretaceous sequences. To the north and towards Chelopech, the Srednogorie massif forms the basement.
The Chelopech area consists of pre-mineral and post-mineral sequences, separated by a Late Turonian erosional surface. The pre-mineral formation consist the following units (from older to younger):
The post-mineral formation consist the following units (from older to younger):
The overall structural complexity of the Chelopech area is interpreted as a result of pre-existing fabrics, faults and weak structural zones in the basement that were intermittently reactivated. Recent detailed structural mappings on surface and section reinterpretations suggest that the Chelopech imbricate thrust is a significant post-mineral structure that splits the entire sequence into a structurally less complex autochthon in the footwall of the thrust complex, and a complex allochthon in the hangingwall of the thrust complex. Recent mapping and structural interpretation confirmed syn-sedimentary faults in post-mineral cover sequence and numerous late – N-S and E-W striking – normal faults. The Petrovden fault is one of the main E-W striking normal fault, and juxtapose pre-mineral phyllic-altered rocks of the deeper part of the Chelopech intrusive complex in the north against unaltered post-mineral epiclastic rock units and sedimentary cover in the south. This implies a normal vertical dislocation of several hundred of meters.
Current interpretations show that several mineralization types occur within the Chelopech-Vozdol area, including porphyry stockwork Cu-Au-Mo, base-metal-Au-Ag veins and breccia hosted epithermal Au-Cu mineralization. These mineralization types are potentially genetically related, but their exact relationships are still unclear. As a general criterion it is agreed that the Petrovden fault (and other associated syn-sedimentary normal faults) played a key role in the preservation of the economically most interesting epithermal Au-Cu mineralization (Chelopech and Sharlo Dere deposits).
Key features of the Chelopech high-sulphidation type Au-Cu mineralization are summarized below:
Earlier models have interpreted that the Chelopech deposit is located within the Chelopech andesitic strato-volcanic sequence with complex structural and laterally correlatable stratigraphic control. Continuous effort to improve this model and as the result of two year re-logging program a new geological model is being developed. The main implication of new model is that the ore-hosting magmatic environment at Chelopech belongs to an intrusive system. The high-sulfidation hydrothermal system in the upper part of the structure developed within a shallow intrusive porphyritic diorite/microdiorite rock-body pierced by a number vertically-extended intrusion-related breccias bodies of blind breccias-pipe and surface-reaching maar-diatreme (i.e. phreatomagmatic explosive). The diatreme hosting the bulk of Chelopech deposit is one large body hosted by unbrecciated remnants of the single large pre-diatreme diorite. The diatreme is related to a granodiorite phase that also has porphyry Cu-Mo-Au stockwork and potassic-phyllic alteration (in Petrovden area), distal base metal sulfide veins (Petrovden and Vozdol areas), and the high-sulfidation Cu-Au system including the ore is localized in an overprinting hydrothermal breccia related to porphyry dikes (Chelopech and Sharlo Dere areas). The high-sulfidation system is localised within the diatreme by structures that have been intruded by porphyry dikes, so an understanding of the geometry of these structures and the dikes is a predictive tool for near mine exploration.
The shift of paradigm from volcanic to intrusive with respect the host environment of the mineralization processes, in particular the lithological control on ore deposition at Chelopech, radically changes both the perspectives of, and the strategies to be followed by, further exploration endeavors.
Geological interpretation and modelling of re-logged drill core has defined a new target area known as the SE Breccia Pipe Zone located between and to the southeast of Blocks 10 and 103. The SE Breccia Pipe Zone is approximately 650-700 metres in length, 100-150 metres in width and is separated from the main Chelopech diatreme by a 250-600 metre screen of coherent diorite (at the 400 level). The target area was defined using the new geological model and alteration and metal zoning patterns around Chelopech suggest the system is still open and untested below the Chelopech thrust in the area of the SE Breccia Pipe Zone. Drilling to test the SE breccia with underground and surface drill holes is expected to start in September 2016.
Also in 2016, two diamond drill holes were drilled at the Sharlo Dere prospect located approximately 900 metres east of the Central ore blocks. Both holes intersected intervals with clasts and blocks of mineralization in a sedimentary breccia that is interpreted to overlie the intrusive complex. One of the holes intersected a zone within the breccia that averages 0.31% copper and 1.23 g/t gold over 35 metres from a down hole depth of 616 metres (400 metres from surface) including 7.0 metres averaging 0.73% copper and 2.13 g/t gold from 621 metres. It is not known if the mineralized clasts at Sharlo Dere are derived from the upper parts of known ore blocks at Chelopech or were sourced from elsewhere.
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Dundee Precious Metals Inc. is a Canadian based, international gold mining company engaged in the acquisition, exploration, development, mining and processing of precious metals.