Regional Geology

The Cardinia Gold Project (CGP) areas (Mertondale and Cardinia – situated 20-40km NE of Leonora and Raeside – situated 10km SE of Leonora) are located within the North Eastern Goldfields, the easternmost subdivision of the Archaean Yilgarn Block on the Leonora (SH51-01) and Laverton 1:250,000 map sheets (SH51-02). The Eastern Goldfields Province comprises volcanic and sedimentary greenstone sequences of rocks of the Kurnalpi Terrain that were deposited around 2,700Ma. The greenstone sequence has undergone multiple folding events, metamorphosed to low or medium grade, extensively intruded by granitoids at about 2,680-2,660Ma and subjected to major faulting along northerly to north-north westerly trends. The greenstones can be further subdivided into four regional geological terranes generally separated by major terrain bounding faults or granitoids. The districts terranes from west to east are the Malcolm, Murrin, Laverton and Cosmo Newbery greenstone sequences.

The Cardinia Gold Projects sits upon greenstone rocks from the Minara Group, which is composed of the basal Welcome Well Formation, followed by the Minerie Formation and overlain by the Murrin Murrin Formation.

Figure 1. Schematic cartoon of the stratigraphy of the Minara Group from the Northern part of the Murrin Domain (From Groenewald et al. 2006).

The Welcome Well Complex is described as felsic lavas and agglomerate and breccia present in the Murrin Sector, a structural sector between the Keith-Kilkenny Tectonic Lineament in the west and the Celia Tectonic Lineament in the east. The Minerie Formation is classified as a tholeiitic basalt dominated sequence with compositions ranging from spinifex and cumulate-textured komatiitic basalt through to basaltic andesite, and displaying massive coherent flows, ponded doleritic flows, pillow lava and autoclastic facies. Intercalated crystal-vitric sandstone-siltstone turbidites record breaks in the tholeiitic activity in a deep submarine environment (Doyle et al., 2003). The overlying Murrin Murrin Formation is dominated by komatiitic basalt, komatiitic cumulate lavas and felsic vitric-crystal pumice-breccia sandstone facies.

Figure 2. Simplified geological map of the Kurnalpi Terrane in the Leonora – Murrin Murrin region.

Local Geology

The Cardinia Project lies almost entirely within the bi-modal volcanic sequence of the Minerie Formation.

The Minerie formation (Figure 3) comprises a sequence of at least 4 cycles of bimodal volcanism. Each cycle being made up of lower andesitic and basaltic (pillowed) lava flows with overlying felsic volcanic rocks, volcaniclastics and epiclastic sediments.

Figure 3. Schematic stratigraphic column for the Cardinia area highlighting stratigraphic levels where mineralisation exists.

Cardinia Mineralisation is shallow crustal with the understanding of a low sulphidation epithermal system developing. Gold mineralisation is very strongly associated with Silver, Arsenic, Bismuth, Antimony, Zinc and Tungsten and is within a large disseminated pyrite – silica – potassic alteration envelope.

The deposit mineralisation is generally made up of a fine grained, sulphide replacement system which has also flooded the rock with silica. Grades within the sulphide replacement system is in the order of 3 – 20 g/t Au with grades as high as 100 g/t Au present. This mineralisation is also anomalous in Silver, Arsenic, Bismuth, Copper, Tellurium, Antimony, Zinc and Tungsten.

This is often enveloped (but not always) by a larger alteration system of disseminated pyrite, which can at times include a broad zone of potassic alteration. This part of the mineralised system averages grades between 0.4g/t and 1.4 g/t gold with reduced associated metals present.

Figure 4. Drill core from the Lewis deposit.

A third style of gold mineralisation with limited exposure is quartz hosted, late stage, brittle cross-cutting veins. These veins can be very rich (>1000 g/t gold) and are usually narrow with as yet undefined continuity and strike extents. The understanding on the structural controls of this style of mineralisation is growing and becoming more prevalent.

Exploration is focused on identification of new areas of gold mineralisation with the potential to enhance the August 2019 PFS mine plan.

Figure 5. Cardinia geology with all drilling (maximum downhole grades (g/t)) and historical prospects

Mertondale mineralisation has similarities with Orogenic lode style deposits with large shear systems and brittle-ductile deformation events. The Mertondale area has two regional scale structures that host the deposits. The eastern structure lies within a basalt unit close to an upper intermediate volcaniclastic contact. The western structure lies within a schistose felsic volcanic that is isoclinally folded. The western structure has sheared the felsic volcanics and fine grain sediments.

The eastern structure mineralisation consists of an 8km long trend comprising the Merton’s Reward, Mertondale 2 and Mertondale 3-4 deposits and are a combination of brittle fractures in basalts with quartz veins being strongly mineralised, and ductile shearing involving porphyry intrusives.

The western structure is 15km in length and consists of a series of north trending, vertical dipping lodes, including the Mertondale 5, Tonto, Eclipse and Quicksilver deposits.  Mertondale West is a large shear structure that interleaves the felsic volcanic and fine grain sediments.