The Little Joe Lake South showing is located on a prominent north-facing cliff, 1.2 kilometres south of the Silver Pick prospect (093L 125).
The area is underlain by volcanic rocks of the Upper Cretaceous Kasalka Group.
Sulphide bearing quartz-ankerite veins are exposed along the ridge escarpment for more than 250 metres within massive to foliated porphyritic andesite and tuff of the Upper Cretaceous Kasalka Group. The foliated rocks strike northwest and dip steeply to moderately southwest or northeast. Within the area of extensive quartz veining, the host rocks are schists and phyllites speckled with fine-grained ankerite (or limonite after ankerite). In contrast to similar vein deposits nearby, rhyolite and other intrusions are not in evidence.
The quartz veins are generally 2 to 10 centimetres wide and are exposed along strike for an average of 3 to 5 metres along the face of the escarpment. The thickest and most sulphide-rich vein is 25 centimetres wide and is exposed intermittently for 20 metres. Vein quartz is massive and milky white to slightly banded or blotchy with respect to the distribution of sulphides and ankerite (or pockets of limonite after ankerite). Cockscomb quartz and vuggy textures are present but not common. Ankerite (and limonite) veinlets and slices of ankeritized wallrock subparallel to the vein walls give an impression of poorly development ribbon texture.
Metallic minerals within the veins include: galena, sphalerite, tetrahedrite, boulangerite, chalcopyrite, specularite and pyrite, and occur as irregular concentrations several millimetres to 2 centimetres in size. The vein assemblages are similar to those at the Cronin mine (093L 127), but the abundance of metallic minerals within the veins is much less than at Cronin.
Aside from a generally pervasive ankeritic component to the host phyllite, alteration adjacent o the veins is negligible; small amounts of chlorite (+/- sericite) are present along or close to the vein margins, but seem to be part of the vein rather than a product of wallrock alteration.
The quartz veins have variable morphology, and their relationships with the host phyllites indicate that there are several generations of veins, each related to intervals of progressive structural deformation. Veins that comprise the west part of the Little Joe Lake South showing are almost all concordant with host phyllite and are variably deformed. The thickest and most sulphide-rich vein is also approximately concordant within the phyllite, but is internally drag folded and probably thickened. Fold structures within the vein, defined by the alignment of acicular boulangerite, probably formed during shearing and dilation along foliation.
Other veins that closely follow the foliation of the host rocks are planar to slightly warped. They contain irregular clots of sphalerite and galena, and have irregular margins, but are generally not internally deformed. These veins were probably emplaced during the latest stages of shearing and dilation along the foliation.
Veins that comprise the east part of the prospect are largely discordant to foliation. Many are flat to gently north-dipping and occur in regularly spaced vein sets within the phyllites. The veins, which are generally undeformed and have sharp contacts, occupy planar dilations perpendicular to the foliation of the host rocks. Blebs of galena and sphalerite, one to two centimetres in diametre, are common within veins. Many of which are less than 5 centimetres wide. Veins in similar structural settings are slightly warped or folded and the host phyllites deformed. Drag-folding in the phyllites suggests down-dip, or normal movement along fractures (now occupied by quartz veins); movement was probably synchronous with vein emplacement.
Quartz veins also occupy crescent-shaped fractures where slip along foliation has induced shear folding and accompanying dilation perpendicular to the foliation direction. Veins that occupy these dilation zones are irregular in width and continuity, but are commonly widest in the fold crests. Quartz concentrations of this type, which reach widths of up to 50 centimetres, are riddled with irregular blebs and veinlets of sphalerite, galena and chalcopyrite.
The largest vein contains up to 104 grams per tonne silver and 8.25 per cent lead, whereas other veins contain up to 26 grams per tonne silver (Fieldwork 1991, page 99).
