Overview

Deposit type

• Vein / narrow vein
• Banded iron formation

Summary:

The Southern Cross deposit is located within one of the three granite-greenstone terranes, and is known as the Southern Cross Province. The geology of this region is dominated by the Marda-Diemals greenstone belt, which is divided into three layers including the lower greenstone belt which is comprised of mafic volcanics and BIFs, a felsic-intermediate volcanic layer and an upper sedimentary layer which dominated by calc-alkaline volcanics and clastic sedimentary rocks.

Gold mineralisation in the Southern Cross district typically occurs along the northwest/southeast trending Achaean Southern Cross Greenstone Belt. The Southern Cross Greenstone Belt is a highly deformed band which comprises tholeiitic and high-Mg basalts and komatiites together with BIF overlain by younger sequences of terrigenous sedimentary rocks.The Belt has been influenced by overlapping metamorphic, deformational and granitoid emplacement events.

The lode-gold deposits in this belt occur within the volcanic-dominated greenstones, with the most significant deposits being within the Fraser’s Corinthia shear zone. The major structures which are recognised for gold mineralisation are in the fold-hinge zones and the shear zones. Within the foldhinge zones, the most common host rock is BIF, while in the shear zones, the gold mineralisation is found primarily within the mafic and ultramafic volcanic rocks and micaceous schists.

Within these rocks, the ore is present as quartz rich and sulfide rich lodes. The quartz lodes are commonly developed as veins in tremolite hornblende biotite schists. The gold mineralisation is generally associated with sulfides such as pyrrhotite, pyrite, galena and sphalerite. The sulfide rich lode is developed within greenstones, which are commonly foliated schists consisting of biotite, quartz, plagioclase and carbonate with finely disseminated gold mineralisation occurring in association with sulfide within the quartz bands.

Gold mineralisation in the Southern Cross region is typically structurally controlled, and is primarily hosted by quartz veins which may be associated with interlayered high-Fe metabasalts, greenstone belts, and shear zones containing BIF and pelitic rocks. The dominant ore mineralogy consists of pyrrhotite, pyrite, arsenopyrite and other sulfarsenides (Knaak, et al., 1995). Gold mineralisation may also be associated with massive pyrrhotite and pyrite replacement in the BIF, which is associated with breccia zones and schist bands.

Mining Methods

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Comminution

Crushers and Mills

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Processing

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Production

Operational metrics

Metrics	2022	2017	2016	2015
Annual processing capacity	....	2.4 Mt	2.4 Mt
Tonnes processed	....		1,757,935 t	993,360 t