The Ravensthorpe area covers three major Precambrian tectonic units. The southern margin of the Archaean Yilgarn Craton, which includes the Ravensthorpe greenstone belt, covers the northern portion of the area. To the south, the Archaean granite-greenstone association is overlain by metasedimentary rocks of the Proterozoic Mount Barren Group. Munglinup Gneiss covers much of the southeast and is part of the Biranup Complex. The northeast-trending Jerdacuttup Fault separates the Munglinup Gneiss from the Mount Barren Group and Archaean granite-greenstones.
Trilogy
The Trilogy deposit is hosted in the middle Proterozoic Mount Barren Group. The host sequence is dominated by black shale, with lesser quartzite units. The deposit is conformable with the lie of the regional stratigraphy.
A large siliceous alteration halo surrounds the mineralisation. In the sulphide zone the mineralisation is identifiable by silicification and significant sulphides. The typical sulphide assemblage is represented by pyrite - covelite - chalcopyrite - galena - sphalerite.
The deposit comprises three sub-parallel zones (A, B and C from footwall to hanging-wall) dipping to the southeast at an average of 30 degrees. The zones extend over an average strike distance of 300 metres and tend to be more copper and gold rich to the southwest and more lead and zinc rich to the northeast. Their thicknesses range from 10 metres to 30 metres and are separated by barren material varying from 5 metres to 30 metres in thickness.
The base of oxidation occurs at about 35-40 metres vertical depth. Above this level gold and silver mineralisation predominates, with some depletion of the base metals. The sulphide resource continues from approximately 40 metres below surface to a maximum currently defined depth of 200 vertical metres.
Kundip
The Kundip mineralization is hosted in the Archaean Annabelle Volcanics. Varieties of dacite dominate the geology, along with lesser andesite and granites. Bedding in the volcanics most likely trends north west/south east and dips steeply to the north east. Immediately to the south of Kundip, the Archaean basement is unconformably overlain by later Proterozoic sediments, which dip off at eight degrees to the south.
Outcrop in the area is rather limited and highly oxidised. An area of alluvial soil and sand cover extends across much of the western section of the lease.
The mineralization generally occurs as gold-copper bearing quartz reefs. The vein systems are structurally controlled. The high grade zones present as massive pyrite, grading to sulphide rich quartz veins occurring in a series of en echelon ore lenses along large shear structures. The reefs are typically 0.5 to 2.0 metres in thickness, reaching a maximum of 10 metres where structural intersections occurs. The strike length on the major shear surfaces are typically in the range of 800 to 900 metres.
The most common sulphide is pyrite followed by chalcopyrite and pyrrhotite. Sulphides occur as massive to semi-massive and as thin veinlets along fractures.
