Summary:
The regional and local geology of the Project area is well understood having a long exploration and development history. Stratigraphically the oldest rocks are the Cambrian aged sequence containing locally the Tyndall Group, Central Volcanic Complex, Yolande River Sequence and andesitic volcanics and intrusives. These are overlain by the late Cambrian-Ordovician aged Owen group and Silurian aged Eldon Group. Quaternary/Tertiary deposits, including glacials, complete the regional geological sequence.
Prince Lyell -Deeps/North Flank/D Panel/Royal Tharsis
The footwall of the mineralisation at the Prince Lyell Deeps is defined by the Great Lyell Fault, which juxtaposes the Cambrian volcanic host rocks against a later Cambro-Ordivician sedimentary sequence. The Great Lyell Fault truncates the mineralisation at depth.
The mineralisation consists of disseminated to veinlet pyrite-chalcopyrite hosted within strongly altered and schistose volcanic rocks. Alteration consists of a chlorite-pyrite+/-magnetite core surrounded by a muscovite pyrite envelope. The North Flank/D Panel and Royal Tharsis mineralisation and alteration is similar to the Prince Lyell, however the former has a stronger stratigraphic control.
Dimensions:
Prince Lyell North Flank: the resource has dimensions of 490 m in height, 1,500 to 2,090 mRL (2,000 mRL represents sea level and the surface is approximately 420 m above sea level). The strike length of the resource is up to 300 m, and plan width is approximately 80 m.
Prince Lyell Deeps: the strike length of the resource is up to 260 m, and the plan width is approximately 100 m. The in situ resource is classified from 1,115 mRL to 1,315 mRL (2,000 mRL represents sea level and the surface is approximately 420 m above sea level).
Royal Tharsis/Prince Lyell Upper Remnants: the strike length is approximately 1,300 m. The acrossstrike extent is 450 m and has been modelled down to 825 m below the highest surface point. The deposit outcrops at surface. The mineralisation spans from 1,675 to 2,500 mRL.
North Lyall remnants
The high-grade mineralisation at North Lyell is predominately chalcopyrite-bornite. The massive assemblies are associated with hematite-barite-silica alteration. These deposits occur at or near the Mount Read Volcanic – Owen Group contact and are associated with intense pyrophyllite, paragonite and muscovite alteration. Numerous copper sulphides and other minerals are recognised including tetrahedrite, digenite, djurleite, covellite, mawsonite, linnaeite, sphalerite, stromeyerite, and hematite. The lower-grade mineralisation further to the north and east within the deposit tends more towards a disseminated style of chalcopyrite mineralisation. Numerous large faults and contacts control the distribution, intensity and trends in the mineralisation.
Dimensions: the strike length is approximately 900 m. The acrossstrike extent is 500 m and has been modelled down to 650 m below the highest surface point. The deposit outcrops at surface. The mineralisation spans from 1,980 to 2,630 mRL.
Western Tharsis
The project area is hosted by a sequence of northwest trending intermediate and felsic volcanics dipping steeply to the west. The copper mineralisation occurs in a horizon of recrystallised quartz sericite-pyritechalcopyrite-bornite schists within a broader pyritic sequence The mineralisation is broadly similar to that at Prince Lyell. However, there appears to be a more rapid drop-off in grade at the margins of the deposit than is observed at Prince Lyell.
Dimensions: the strike length is approximately 360 m. The acrossstrike extent is 60 m (at the widest point) and has been modelled down to 1,020 m below the highest surface point. The deposit outcrops at surface. The mineralisation spans from 1,420 to the 2,260 mRL.
Copper Chert
The project area is situated at the northern end of the Mount Lyell field at the conformable boundary between the Central Volcanic Complex and the Tyndall Group. The local rock package is sub-vertical striking in the northwest direction.
Mineralisation is within a high silica unit that exhibits massive to conglomeratic textures of variable size, intersticed with intense sericite zones. A phyllic sericite altered volcaniclastic unit completes the mineralisation package. Mineralisation is copper sulphides within breccias and phyllic zones of the units dominantly as fracture infill, disseminations and blebs. Pyrite is the most abundant sulphide mineral. Chalcopyrite, bornite and chalcocite form the main copper-bearing minerals of variable concentrations, but decrease in abundance, respectively. Galena and sphalerite are common also, but not always present. A later stage of mineralisation consisting of cross-cutting coarse quartz +/- sulphides (usually bornite or chalcocite) is also present representing potential remobilisation during deformation. Visible gold has been noted in these veins.
Dimensions: the strike length is approximately 365 m. The acrossstrike extent 80 m (at the widest point) and has been modelled down to -290 m below the highest mineralisation point. The mineralisation spans from 1,880 to 2,300 mRL.
Green Horn/Cape Horn
The project area is hosted by a sequence of north-northwest trending intermediate and felsic volcanics dipping steeply to the west. The copper mineralisation occurs in a horizon of recrystallised quartz-sericitepyrite-chalcopyrite-bornite schists within a broader pyritic sequence. The mineralisation is broadly similar to that at Western Tharsis and Prince Lyell. Two distinct mineralised structures are seen. The Cape Horn mineralisation is the easternmost structure. The Green Horn mineralisation is the westernmost structure.
Dimensions: the strike length is approximately 300 m for both pods. The across-strike extent is up to 50 m for each pod and has been modelled down to 710 m below the highest mineralisation point. The mineralisation spans from 385 to -290 mRL.
Mineralisation style summary
In summary the main mineralisation styles at the Mt Lyell Project are:
• disseminated chalcopyrite;
• massive pyrite-chalcopyrite;
• chalcopyrite-bornite.
In addition, there are two subordinate styles:
• banded sphalerite-galena;
• copper-cuprite.