Mineralization at HPG is defined in 36 veins. The five largest veins, H17, H15, H15_1, H18 and H10_1, contain about 50% of HPG’s current mineral resources. Sampling in workings along these vein structures indicates that 27% to 50% or more of the vein material is mineralized, ranging from 0.30 m to 1.77 m in width, averaging 0.77 m.
The veins occur in relatively permeable fault-fissure zones and are extensively oxidized from the surface to depths of about 80 m. Within this zone, the veins show many open spaces with conspicuous box-work lattice textures resulting from the leaching and oxidation of sulphide minerals. Secondary minerals present in varying amounts in this zone include cerussite (lead carbonate), malachite (copper carbonate), and limonite (hydrous iron oxide). Beneath this oxide zone, sulphide minerals are mixed with secondary oxide minerals in the vein, with sulphides becoming increasingly abundant with depth until around 150 m, beyond which fresh sulphides are present with little or no oxidation. The dominant sulphides are galena, which typically constitutes up to 10% of the vein, together with a few percent sphalerite, pyrite, chalcopyrite, and freibergite-tetrahedrite. Other metallic minerals are found in much smaller amounts and include argentite, native silver, native gold, bornite, and various sulfosalts. The minerals occur in narrow massive bands, veinlets or as disseminations in the gangue, which consists of quartz, sericite, and carbonate in the form of dolomite and calcite with some ankerite.