The Gross deposit is a structurally controlled zone of potassic metasomatism, hosted by Proterozoic sandstones. Mineralisation is associated with iron and manganese oxides, that follow from primary sulphides, particularly pyrite. The main part of the mineralised zone is truncated by surface topography, strikes east-west for approximately 1 km, dips shallowly to the south with a down-dip extent of 1.5 km, and is up to 400 m thick.
The deposit is situated in the western part of the Aldan shield, in the southwestern corner of the Uguskiy Graben. The major regional structural features are: 1) the N-S striking Tokkinsky Fault Zone (along the western margin of the Uguskiy Graben); and 2) WSW-ENE striking faults of the Kondinsky Fault System, which cut across the Tokkinsky Fault Zone, and are broadly parallel to the southern margin of the graben.
Gross mineralisation is hosted by the Olonnokonskiy Formation, and in the project area this formation comprises up to 20-30 m of basal conglomerates and gravels, overlain by 300-400 m of fine to medium grained sandstones. The sediments are shallow-dipping to the north, northeast or east.
The Olonnokonskiy Formation host rocks have undergone multiple tectonic and magmatic activation events, dominated by deformation and metasomatism associated with the intrusion of Mesozoic dykes and sills.
The main part of the mineralisation is located between two major south-dipping reverse faults: the Bottom Thru ........