Summary:
Gold deposits in the CGP occur in three main mining centres – Cardinia, Mertondale and Raeside. Cardinia and Mertondale are located within the Minerie Greenstone Belt while the Raeside deposits occur in the Malcolm Greenstone Belt.
The CGP has approximately 45km of strike of the Minerie greenstone and is composed of four bi- modal, felsic-mafic volcanic flows. Gold mineralisation occurs in a number of styles: low sulphidation epithermal deposits, volcanogenic massive sulphide deposits, and orogenic style gold deposits. All mineralisation styles result in zones of supergene enrichment within the oxide profile above each deposit.
The Mertondale prospects extend over a strike length from Merton’s Reward in the south to Mertondale 5 (32.0koz mined in 1991) 12km to the north. Merton’s Reward (60.5koz previously mined), Mertondale 2 (2.7koz mined in 1987 and 2010) and Mertondale 3-4 (179.3koz mined between 1986 and 1993) are contained within the eastern branch of the Mertondale Shear Zone and extend over approximately 3km of strike. Quicksilver, Tonto, Eclipse and Mertondale 5 are all contained within the western shear zone and extend over approximately 9km of strike. The Mertondale area consists of an eastern mafic flow (mafic flow 3), a central felsic volcanic sequence which is overlain by a volcanoclastic sequence of rocks which include schists and carbonaceous shales, and topped by another mafic volcanic flow (mafic flow 4).
The Eastern shear is present on the contact of mafic flow 3 and the younger felsic volcanic, or within the mafic unit. These orebodies are typically orogenic lode style deposits and are related to brittle fracturing and quartz veining and porphyritic intrusions. The Western shear is present within the volcaniclastic sediments just below the base of mafic flow 4. Mineralisation appears to be related to late stage shortening (isoclinal folding) and shearing along this major structure. Merton’s Reward, Mertondale 2, 3 and 4, Tonto, Eclipse and Mertondale 5 are included in the Ore Reserve Estimate.
The Cardinia deposits occur within the younger sequence of intermediate-mafic and felsic volcanic lithologies and locally derived epiclastic sediments, and are related to mafic flows 1 and 2. Minor felsic porphyries and lamprophyre lithologies have been recognised within the project. At Lewis, these intrusive rocks are often associated with lithologically discordant structures. Primary gold mineralisation at Lewis is consistent with volcanogenic massive sulphide mineralisation and sulphidic sediments as well as later, cross cutting, low sulphidation epithermal mineralisation. Helens consists of sulphide replacement mineralisation in a slightly discordant structure and appears to be a deeper part of the mineralising system. Historic production within the Cardinia mineral field includes Eagle, Kyte, Bruno, Lewis, Pride of the North, Pelsart, English and Scottish, Nevertire, Black Chief, White Chief, Comedy King, Faye Marie, Helens, Fiona, Rangoon, East Lynn, Triangle and Hobby. All these historic workings were high grade gold producers and occur across all of the Minerie stratigraphy.
Mineralisation within the Raeside project is hosted by a mixed package of fine-grained sediments and a quartz dolerite unit. The dolerite is sill-like in nature, and roughly conforms to bedding. The dolerite is fine to medium grained and is extensively chlorite altered. The gold mineralisation is generally constrained within the dolerite and certain sedimentary horizons.