Cadia-Ridgeway Mine

Cadia-Ridgeway Mine

Cadia-Ridgeway Mine

Location: Orange, New South Wales,is one of three gold mines Newcrest currently operates in Australia.

Products: Copper & Gold. A series of large underground and open-cut gold and copper mines

Ore Minerals: Ore minerals are native gold, chalcopyrite and bornite, mostly occurring within veins, but also disseminated.  Magnetite is a major accessory mineral in veins. Hydrothermal alteration associated with the strongest mineralisation is potassic: orthoclase, albite, actinolite, magnetite, biotite.  This is overprinted by later propylitic assemblages: epidote, chlorite, Fe-carbonate, calcite, hematite dusting. 

Geological setting: The Cadia deposits are part of a Late Ordovician – Early Silurian porphyry alteration-mineralisation system that extends over an area of at least 6 X 2 km within the Ordovician Molong Volcanic Belt of the Palaeozoic Lachlan Fold Belt (Newcrest Mining Staff, 1997).  The Molong Volcanic Belt comprises a suite of intermediate to basic volcanics, volcaniclastics, comagmatic intrusions, and limestones.  The suite is probably part of a subduction-related island arc disrupted by later tectonism (Glen et al, 1997).  In the Cadia area the volcanics and intrusions are shoshonitic (Blevin, 1998).

Mineralization: Sheeted quartz vein, stockwork quartz vein, disseminated and skarn, all of which are genetically related to a relatively small (3 X 1.5 km in outcrop) composite intrusion of predominantly monzonitic composition, with a monzodioritic to dioritic rind (Cadia Hill Monzonite).  The Cadia Hill Monzonite intruded Forest Reefs Volcanics (volcaniclastics, lavas, subvolcanic intrusions, and minor limestone) and Weemalla Formation (siltstone, mudstone, minor volcaniclastics).  Emplacement of the Cadia Hill Monzonite was probably facilitated and localised by the development of a major north-west (NW) to south-east (SE) trending dilational structural zone, which is well evident in magnetic data.