Summary:
Mineralization
The district has many characteristics that are typical of epithermal veins in Mexico, particularly of the Ag-rich variety. Quartz veins are accompanied by adularia, barite, calcite, rhodochrosite of variable timing, as well as acanthite, freibergite, Ag sulfosalts and minor electrum, plus variable amounts of pyrite, honey-colored sphalerite, tennantite/tetrahedrite, chalcopyrite and galena, and supergene Fe and Mn oxides; the hypogene minerals are characteristic of intermediate-sulphidation deposits in Mexico. Mineralization is believed to be Tertiary in age both the LVS and UVS are mineralized, but the basalts are recent and not mineralized.
Petrographic studies of the veins in the Deposit find that multiple stages of silver and base metal mineralization are associated with repeated fluid boiling and mixing events, defined by crustiform banded fill/cement assemblages within a framework of intermittent and more significant fracturing/rupturing of wall rock and preexisting vein/cement assemblages. There is a repetition of common hydrothermal fill/cement mineralogy, including mineralized minerals, such that correlation of vein/cement assemblages/events between drillhole intersections would be difficult.
The occurrence of adularia and style of early quartz and chalcedonic quartz replacement amongst wall rock replacement and fracture-fill/cement assemblages confirms silver and base metal mineralization associated with low sulphidation, epithermal style systems developed on the Martha and Olin structures at the Project. Significant widths of mineralized quartz and carbonate dominated fracture-fill and breccia cement assemblages have developed as a result of extended episodes of hydrothermal fluid flow and repeated rupturing of wall rock and preexisting vein/cement assemblages. Internal crustiform banding within the different voluminous fill/cement assemblages represents incremental opening and filling of fractures/cavities between major rupturing events.
The Martha vein is the largest vein in the deposit by far, with at least three times the volume of the next largest vein, La Abundancia. Both veins are low angle, the Martha vein dips ~20-30°, following the southwest-dipping contact of volcaniclastic rocks overlying an immature conglomeratic unit (consisting mainly of polylithic clastsupported fragmental rock with angular to sub-rounded clasts) or the underlying schist.
Avino vein
The Avino Vein is 1.6 km long and 60 m wide on the surface. The Avino Vein is the most striking and important example of the epithermal mineralization of the district whose structures are normally weathered and leached in their upper section as a result of contact with atmospheric waters producing a band of oxide minerals and zones of supergene enrichment to a depth of about 70 m.
In the oxide portion of the Avino Vein, the common minerals encountered include hematite, limonite, anglesite, and copper carbonate in white or green, somewhat chloritized, quartz zones. The common primary and secondary minerals encountered are argentite, bromargyrite, chalcopyrite, chalcocite, galena sphalerite, bornite, native silver, free gold, and native copper. Other minerals present in mineralized areas include quartz, pyrite, chlorite, barite, arsenopyrite, pyrrhotite, and specularite.
Higher silver values are reported to decrease overall with depth, except at vein intersections and vein inflections, where higher values persist to depth. The same can be said for gold, although the higher values start just below the onset of silver mineralization, at or near the surface. In contrast, higher copper values coincide with vein intersections and may increase with depth. Sporadic, localized copper enrichment occurs toward the footwall contact and may represent a different phase of fluid emplacement. Despite the overall decrease in precious metal grade with depth, local increases in metal grades are apparent in the mine sampling and exploration drilling, possibly reflecting changes in boiling level with pressure variations in the epithermal system.
The Avino Vein has been followed longitudinally for more than 1,300 m and vertically for more than 600 m. It strikes north 66° east with an east-west splay, and dips to the south and southeast at 60° to 70°. Steeply dipping, high grade zones within the vein and stock-work zones are frequently found in the upper part of the vein, as well as at its intersections with a number of lateral veins. An example of a higher-grade area of mineralization encountered with major lateral vein intersecting the Avino was the El Hundido, which exceeded 40 m in thickness. In the lower areas of the vein and mine, mineralized cross-veins, branch-veins, and stockwork zones have been found in the footwall at San Luis and at El Hundido, and are assumed to persist with depth.
San Gonzalo vein
The San Gonzalo Vein is located approximately 1.4 km northeast of the eastern modelled extent of the Avino Vein. The San Gonzalo Vein system constitutes a strongly developed vein system over 25 m wide, trending 300° to 325°/ 80° northeast to 77° south. It is characterized by banded textures and open-space filling. The main vein has an average width of 2 m, but the silica-pyrite or iron oxide- sericite alteration with additional stock working extends across 300 m, south of the main San Gonzalo Vein to the Los Angeles Vein.
The San Gonzalo is a typical narrow vein precious metal deposit with some erratic values and extends approximately 2 km to the northwest to the Santa Ana-Malinche area (Gunning 2009).
Guadalupe Vein
The Guadalupe Vein is located approximately 0.7 km northeast of the Avino Vein. It consists of northwest-southeast and east-west striking steep-dipping vein sets. The geometry is similar to the San Gonzalo vein, but the base metal mineralization more closely resembles the Avino hanging wall breccia.
La Potosina Veins
The La Potosina Veins are located close to the northern margin of the caldera, approximately 7 km north of the Avino mine and processing plant. It consists of complementary northwest-southeast striking steep-dipping vein sets. The geometry is complex, with at least two ages of fault displacement.
Oxide and Sulphide Tailings
The Avino tailings deposit is adjacent to the processing plant, approximately 300 m westsouthwest of the mine offices. The tailings have been built up over several decades of mining and processing, and several units have been defined based on the oxidation of the tailings and metal content.
Due to the historical processing sequence, the oxide tailings are primarily derived from weathered and oxidized rocks close to the surface on the Property, whereas the sulphide tailings are predominantly derived from material sourced at depth from the underground workings below the weathered/leached zone.