Summary:
The Timok deposit is located within the central part of Timok Magmatic Complex (TMC), in the Bor District of northeastern Serbia. The project area is approximately five kilometres south of the mining municipality of Bor. The TMC comprises a series of andesitic to dacite-andesitic subvolcanic, volcanic and volcano-sedimentary sequences and plutonic intrusions (mainly monzonite to diorite and granodiorite compositions). The TMC is generally erosionally well-preserved when compared with both the Banat and Panagyurishte segment belts to the north in Romania and to the east in Bulgaria respectively. The largest porphyry and porphyry-epithermal deposits in the Timok segment are represented by the Majdanpek and Bor copper and gold deposits which are hosted within in Upper Cretaceous andesitic volcanic units.
The Cenomanian sedimentary rocks are conformably overlain by volcanic, volcaniclastics and sedimentary units of the Upper Cretaceous TMC. The TMC complex is dominated by Late Cretaceous (Turonian to Campanian) andesitic lavas, lava domes and shallow intrusions, volcaniclastic and epiclastic units and basaltic andesites, volcaniclastics and clastic sedimentary rocks that formed in an extensional rift basin.
The TMC andesite volcanic rocks are typically calc-alkaline in composition. Kolb et al. (2013) describe a geochemical signature similar to adakites, which are commonly associated with porphyry and epithermal copper and copper-gold deposits elsewhere in the world. The western and eastern borders of the TMC complex are structurally controlled by major faults. In the centre and southeast of the TMC, Miocene clastic sedimentary rocks unconformably overlie the Late Cretaceous units.
The Timok deposit comprises two different styles of copper-gold mineralization - the Upper Zone and the significantly larger Lower Zone. Upper Zone high sulphidation (HS) epithermal mineralization occurs at depths from 450 to 850 m below surface. Lower Zone porphyry style mineralization is found from 700 to 2,200 m below surface. To date, the deepest drill hole intercepting Lower Zone mineralization terminated in mineralization at 2,268 m below surface.
Timok Upper Zone
The Cukaru Peki Upper Zone is a copper-gold deposit located within the central zone (or Bor District) of the Timok Magmatic Complex, which represents one of the most highly endowed copper and gold districts in the world.
Timok Upper Zone (UZ) is a high-grade HS epithermal deposit typically associated with an advanced argillic alteration system with a discrete footprint.
The top-third of the HS epithermal mineralization of the UZ is characterized by a massive sulphide lens located on the top of a volcanic to volcaniclastic sequence. This lens has a variable but overall similar dip to the overlying stratigraphy. With increasing depth from the top of the UZ, the proportion of massive sulphide mineralization intruding or replacing the host rock reduces, as does the sulphide content and presence of fragmental volcanic units. With depth, the mineralization becomes more characterized by veins and stockworks hosted by more coherent andesite.
The massive sulphide comprises mainly pyrite and covellite and hosts the highest grades of copper and gold; multiple pyrite replacement phases are observed, which in some places comprise up to 95 wt% of the deposit. Locally, different pyrite phases can be recognized by cross-cutting relationships; however, in general they are difficult to distinguish. Covellite is interpreted to be later than pyrite and is observed transgressively cutting and brecciating massive pyrite; however, pyrite can also locally be observed cross-cutting covellite stringers or massive aggregates of covellite flakes intergrowing with alunite.
Pyrite with enargite is also present. Enargite is commonly observed rimmed and sometimes replaced by covellite and is therefore interpreted to represent an earlier phase of mineralization.
Mineralized hydrothermal breccias have also been locally observed in the UZ and at least two events have been recognized: an early syn-mineralization phase and an inter-mineral phase, hosting fragments of massive sulphide.
Gold mineralization is present in a number of forms, including tellurides such as calaverite (Au), sylvanite (Au-Ag) and kostovite (Au-Cu), altaite (Pb) and is mostly hosted in pyrite but also locally found encapsulated in bornite (Cornejo, 2017). Native gold is not common; however, where observed it is very fine, approximately 2 to 6 µm in diameter.
Low temperature galena and sphalerite as disseminations and in veins are noted in the peripheral zones of the UZ mineralization, mostly related to kaolinite-pyrite alteration fronts.
Timok Lower Zone
The Timok Lower Zone consists of lower grade porphyry copper-gold style mineralization comprising quartz-sulphide veins and disseminated sulphides and larger alteration footprint. The Lower Zone is situated approximately 200 m beneath the Upper Zone and extends from this point to the north of the Upper Zone, and most likely represents the source of fluids for the Upper Zone epithermal mineralization.
The Lower Zones constitutes a telescoped porphyry system related to multi-stage diorite intrusion, whereby the Lower Zone potassic zone with well-developed A-type vein stockwork is overprinted by quartz-sericite alteration (with classic D-type veinlets) and Upper Zone HS alteration and mineralization assemblages including alunite-dickite, covellite-pyrite and vuggy silica replacement.