Summary:
Leonora Operations comprise of Gwalia, Admiral, Hub, Ulysses, Tower Hill and other deposits.
Gwalia mine
Gold mineralisation at Gwalia occurs in an array of en echelon, moderately east dipping lodes within strongly potassic altered mafic rocks and extends over a strike length of approximately 500 m and to a vertical depth of at least 2,300 m. Four primary mineralised zones (Main Lode, South West Branch, South Gwalia Series and West Lode) have been identified with each zone consisting of several individual lodes.
Mineralisation domains are defined by abundance of quartz and quartz/carbonate veining, the presence of distinctive laminated veining, strong potassic alteration, abundance of sulphides (commonly >3% pyrite) and elevated gold grade.
The Sons of Gwalia mineralised zone strikes 15 degrees east of true north over a distance of 500m and plunges 45 degrees to the southeast. The mineralised zone consists of several stepped or en echelon style foliation parallel lodes disposed in plan in a “horse-shoe” shape with the limbs converging at the southern end. The mineralised zone and individual lodes dip east at 35 to 45 degrees and are conformable with the foliation of the Mine Sequence mafic schists.
The individual lodes are a few metres to tens of metres thick defined by simple planar envelopes extensive along strike and down plunge. Gold mineralisation at Gwalia is associated with a proximal potassic alteration assemblage and pyritic, quartz-rich, laminated veins generally with low sulphide content.
Admiral Group
The Admiral Group of deposits lies within the Archaean-aged Norseman to Wiluna greenstone belt. Host rocks comprise a sequence of dolerite and basalt units. Gold mineralisation is associated with a strongly altered, distinctive assemblage of biotite-sericite-albite-pyrite±carbonate alteration and quartz veining located within regionally extensive NS trending shear zones which take the same name as the deposit they are located on. Depth of complete oxidation varies from 1m to 30m with depth to fresh rock varying from 5 to 50m.
Within the shear zones, discrete zones of mineralisation are typically 2-8m in thickness and dip at 30-50° to the east. A number of horizons of magnetic dolerite sills occur within the mafic stratigraphy at ABCDK. Where the main shear cuts through these units, local thickening and increased grade are evident. The zones are visually distinct and typically display sharp boundaries to the mineralisation.
On the northern contact of the dolerite sill with the pillow basalts at Admiral, Clark and Butterfly there is an intense zone of shearing which runs parallel to the lithological contact dipping at 50-60° to the north. This shear is mineralised over 1.5km strike from the Admiral deposit in the west through Clark to Butterfly in the east. The mineralisation on this contact is referred to as the Hercules shear.
Mineralisation within the Hercules Shear is typically 5m to 12m wide and hosted within highly foliated basalts with intense quartz/carbonate/sericite alteration and associated sulphides.
Drilling in the area extends to a maximum depth of 300m below surface. The mineralisation has been interpreted and estimated to that depth and the mineralisation remains open over much of the 1.5km strike length of the deposits.
Ulysses deposit
Ulysses is an orogenic, lode-style deposit hosted within mafic rocks of the Norseman-Wiluna greenstone belt. Host rocks comprise a sequence of dolerite and basalt units. Gold mineralisation is associated with a strongly altered, distinctive assemblage of biotitesericite-albite-pyrite ± carbonate alteration and quartz veining located within a regionally extensive WNW trending shear zone termed the Ulysses Shear. Depth of complete oxidation is approximately 30m to 40m with depth to fresh rock occurring approximately 45 to 60 metres below surface.
Within the Ulysses shear zone, discrete zones of mineralisation are typically 1-8m thick and dip at 30-50° to the northeast. Several horizons of magnetic dolerite sills occur within the mafic stratigraphy at Ulysses. Where the main shear cuts through these units, local thickening and increased grade are evident and form plunging shoots with good continuity of grade and thickness over considerable plunge lengths. These high-grade plunging shoots are visually identifiable due to the strong pyrite-albite-biotite. They have been separately modelled and estimated to properly reflect the observed the high-grade continuity.
Drilling at Ulysses extends to a maximum depth of 520m below surface. The mineralisation has been interpreted and estimated to that depth and the mineralisation remains open over much of the 2.7km strike length of the deposit.
Gold mineralisation occurs within a strong zone of shearing and biotite-sericite-pyrite alteration typically 5- 10m true width. High grade shoots have developed at the intersection of the Ulysses shear and magnetic dolerite sills within the mafic stratigraphy. The shear zone strikes east-west and dips 30-400 to the north.
Hub deposit
The Hub deposit is defined as a meso-thermal, lode gold deposit within the Mertondale Shear Zone, a splay fault zone off the regional Keith–Kilkenny Shear Zone. Mineralisation is hosted largely within Archaean-aged mafic schist and volcanosediment packages and intermediate mafic rocks. A mylonitic fabric is observable in the lithologies. Gold mineralisation generally occurs in northerly striking, sub-vertical to steep dipping zones associated with silica-sulphide-mica alteration and veining.
At Hub, most of the mineralisation is hosted in a narrow (~ 4 m wide) vertical to steep west dipping lode. Several minor subsidiary hanging and footwall lodes are present. The main lode has been cut by late dolerite and lamprophyre dykes which offset and disrupt the mineralisation in places. The depth of complete oxidation varies from between 50 m and 100 m below surface which is underlain by a transitional horizon typically 25 m thick.
Tower Hill
Gross stratigraphy at Tower Hill from west to east is represented by a granitic footwall (FW), followed by a strongly deformed and foliated ultramafic unit, through to a mafic hanging wall (HW). Gold mineralisation is hosted in a moderately (35-50º) east dipping quartz vein package that sits locally between the granitic FW and the ultramafic HW. Quartz veins trend north-north-west and extend over a 1km strike. The quartz veins range from 1m to nearly 50m in width at the widest point. Gold distribution within quartz veins is ambiguous and it is difficult to confidently distinguish between mineralised and un-mineralised veins. In general veins within the mineralized sequence have internal laminations, fractures, and sulphides.
The hydrothermal system at Tower Hill comprises two dominant alteration facies: the potassic alteration zone and the regional carbonation zone. The potassic alteration zone lies adjacent to, and encompasses, the granite–ultramafic contact. Immediately east of the potassic zone is the regional carbonation zone which is characterised by ultramafic comprising a talc–chlorite–carbonate assemblage. All auriferous veins lie within the potassic alteration zone.
Dimensions
Mineralisation at Tower Hill has continuity over 1.2km along strike, and currently >800m down dip. Mineralisation width ranges from ~1 to 50m across strike.