OREAS 42P

The multi-element reference material OREAS 42P is a composite standard produced from a range of oxidised materials including Blackwood greywacke (central Victoria), Bulong laterite (Yilgarn, Western Australia), Hilton North gossan and Mount Oxide ferruginous mudstone (Mount Isa region, Queensland). The dominant constituent, a gold-bearing greywacke, was obtained from the flank of a mineralised shear zone within Ordovician flysch sediments in the Blackwood area of central Victoria. The sedimentary succession hosting the shear zone consists predominantly of medium-grained greywackes together with subordinate interbedded siltstone and slate. Hydrothermal alteration in the vicinity of the mineralisation is indicated by the development of phyllite. The shear zone, in which gold grades attain a maximum, is manifested by foliated sericitic and chloritic fault gouge and goethitic quartz veins. The very homogeneous distribution of gold on a mesoscopic scale and uniform concentration gradient away from the ore zone suggests the gold is extremely fine-grained and evenly disseminated.