In the Mesel sediment-hosted disseminated gold deposit, the spatial distribution of hydrothermal alteration is controlled
by steeply dipping faults and shallowly dipping lithologies. Hydrothermal alteration of carbonate rock is characterised by
decalcification, dolomitisation and silicification. Intense argillic alteration occurs in a laccolithic andesite intrusion
adjacent to decalcified and silicified carbonate units. Sulphide minerals (pyrite, realgar, orpiment, stibnite and cinnabar)
accompany hydrothermal alteration and precious metal mineralisation. The trace elements Ag, As, Sb and Hg are zoned
spatially throughout the deposit. Mesel contains a mineable gold reserve of 7.8 million tonnes at 7.3 g/t Au. Gold
mineralisation is preferentially localised in carbonate rocks adjacent to and beneath the andesite intrusion. The ore body
consists of a central, near-vertical, high grade "feeder" system flanked by tabular, inward dipping, moderate grade
"ouflow" zones. Mineralisation is controlled predominantly by two steeply dipping faults with high grade (>10 g/t) gold
zones centred about structural intersections and fault splays. Gold is submicron size and locked in very fine grained (<10>
microns), disseminated and fracture-controlled arsenical pyrite. The Mesel deposit developed where high angle faults
guided ascending, sulphidising fluids into reactive carbonate stratigraphy adjacent to and beneath the andesite intrusion
and during subsequent migration of the auriferous fluids along "outflow" channels. Early decalcification and
dolomitisation enhanced porosity and permeability prior to silicification and sulphidation. Gold deposition occurred late
in the genesis of the deposit.