Vancouver Campus

Structural, stratigraphic and temporal constraints of gold mineralization in the Bigar Hill deposit, Timok region, Serbia

The Timok Magmatic Complex (TMC) is a well-endowed mineral district in Serbia that hosts world-class Cu-Au porphyry (Majdanpek, Veliki Krivelj, Borska Reka) and high-sulfidation deposits (Bor, ÄŒukaru Peki). Recent exploration activities on the northwestern margin of the TMC have led to the discovery of the Bigar Hill sediment-hosted disseminated gold deposit (SHDG). It represents a previously unrecognized style of gold mineralization within the TMC and the Cretaceous metallogenic province of the western Tethyan orogenic belt – although they share many characteristics with the Carlin-type and distal disseminated gold deposits of Nevada, US. Gold distribution at Bigar Hill and associated hydrothermal mineralogical, geochemical and stable isotope alteration features were examined to reconstruct the structural and stratigraphic controls on hydrothermal fluid flow. The Bigar Hill stratigraphy encompasses Late Jurassic to Early Cretaceous limestone unconformably overlain by a calcareous clastic sedimentary sequence (unit S1). Late Cretaceous volcanic detritus-rich sandstone package (unit S2) unconformably overlies unit S1. Primary sparry carbonate cement, mainly ferroan calcite is characteristic features of both S1 and S2 units. Marl lies conformably over the S2 unit, and the andesitic sill intruded it. Gold mineralization is principally stratabound, located along two stratigraphic contacts. The contact zone between units S1 and S2 is a major mineralized horizon. The other mineralized corridor lies along the unconformable contact between limestone and the S1 siliciclastic rocks. Acidic hydrothermal fluids likely exploited the enhanced porosity and permeability of preserved weathering crusts, brecciated zones, and karst along the unconformities, further creating secondary porosity by dissolving host rock carbonate cement. Although stratigraphic features are considered highly influential on the spatial distribution of ore, the regional structural framework and syn-mineralization faults reactivations are thought to be necessary to allow mineralizing fluids to permeate favorable stratigraphic horizons. A 3D spatial analysis of stratigraphic contacts and changes in the thickness of sedimentary packages suggests that the controls of the ore body geometry are previously unrecognized sub-vertical structures that channeled upwelling metal-bearing fluids. Fluids then spread laterally along the contact zones between the sedimentary packages. Two recognized structural trends, NW and NE match the major gold mineralization trends.