Geology
Wowo Gap is located at the south eastern end of the Papuan Ultramafic Belt, a complex of peridotite, pyroxenite and gabbro which form the prominent east-west trending Didana Range.
The Papuan Peninsular consists of a core of metamorphics with overthrust oceanic crust comprising ultramafics and basaltic rocks. The younger volcanics and sediments are associated with thrust structures, particularly to the east. Relatively recent basaltic and andesitic volcanism has occurred in the Didana Range and Group Mountains. Volcanoes, namely Mt Victory and Mt Trafalgar, occur to the east.
The mineralisation is hosted by a dissected peridotite breccia which forms a relatively flat, east-dipping plateau which is cut by narrow gullies at the eastern end of the Didana Range. Wowo Gap is the physiographic expression of the northeast trending Bereruma Fault.
The peridotite-bearing Sivai Breccia, has a total surface area of some 30 km2 in the three plateaux, with the Wowo Plateau being the largest. It is estimated that some 8 km2 of the original undissected plateau surface remains. The Sivai Breccia has been variously described as a fault scree or in-situ fractured and weathered deposit, rock glacier talus deposit, volcanic deposit, contemporaneous breccia deposit or primary tectonic breccia. A more recent interpretation is that the Sivai Breccia is a dislocation thrust at the top of the ultramafic slice. The breccia matrix consists of serpentinite and the peridotite clasts have been partially or wholly serpentinised. This breccia occurs as an apron along the eastern edge of the Didana Range sloping to the east.
To the west there are massive peridotite zones with linear tectonic breccias. These breccias would have provided easy access for fluids resulting in enriched zones.
The laterite profile of the Wowo Gap deposit from top to bottom comprises:-
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The laterite profile has developed over both rock types but appears to be better developed over the more permeable breccia. Soil and young volcanic ash overlies the limonite and saprolite-laterite profiles. The limonite zone 1 to 10 metres thick of yellow limonite ore. Commonly this material in the diamond core contains no boulders. At similar depths in the pits there are small weathered boulders, particularly at the bottom of the profile. The limonite is characterised by high iron and manganese contents. The nickel content is commonly 0.5 to 1.3%, with numerous sections averaging +1%. Individual samples assay up to 1.81% nickel and 0.68% cobalt.
The saprolite zone, which is typically 1 to 15 metres thick, consists of serpentine and garnierite with clay. This material also contains a significant amount of un-mineralised boulders. The boulders are interspersed within the saprolite material. This lower section of the profile has previously not been seen in the pits or wacker drilling, as this material was too hard to penetrate. The saprolite material is distinguished from the laterite material by lower iron and higher magnesium. This material contains significant nickel, but minor cobalt due to the reduction of manganese and its scavenging effect. Individual samples assay up to 2.85% nickel.
Project Geology
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