Geology & Mineralisation
Kharmagtai consists of multiple co-genetic gold-rich porphyry copper centres and tourmaline breccia pipes occurring within the Carboniferous Kharmagtai Igneous Complex. The Kharmagtai Igneous Complex consists of a series of intrusive bodies ranging between diorite through monzodiorite, quartz-monzodiorite to monzonite and granodiorite compositions. This cluster of intrusives is interpreted to be formed from a very large fractionating magma chamber at depth. The extents of this magma chamber can be seen in the recent gravity survey (see geophysics section).
There are three styles of mineralisation at Kharmagtai; porphyry style stock work Cu-Au mineralisation, tourmaline breccia style Cu-Au mineralisation and epithermal gold associated with carbonate base metal veins.
Porphyry mineralisation at Kharmagtai consists of chalcopyrite as disseminations and within high-density stock work quartz-sulphide veins. This is a very common style of Cu-Au mineralisation and forms the basis of the largest copper deposits in the world. At Kharmagtai porphyry mineralisation represents the larger portion of the defined resources (see resources section).
Tourmaline Breccia mineralisation at Kharmagtai consists of chalcopyrite-tourmaline- pyrite as infill to hydrothermal breccia’s that overprint the younger porphyry style mineralisation. The tourmaline breccia Cu-Au mineralisation at Kharmagtai is a new style of mineralisation for Mongolia, although elsewhere in the world this type of mineralisation represents a significant source of copper and is currently being mined at Anglo American’s Los Sulfatos deposit in Chile. At Kharmagtai, tourmaline breccia mineralisation was discovered by Xanadu beneath the porphyry stockwork zones at Stockwork Hill in 2015.
Epithermal gold mineralisation at Kharmagtai at hosted by carbonate-pyrite-chalcopyrite-sphalerite-galena veins controlled by late NW trending faults. Gold grades within these veins can range up to 190g/t Au. This style of mineralisation has not been a focus for exploration at Kharmagtai, although significant potential exists for a high-grade gold resource from epithermal veins on the lease.