Summary:
The Soto Norte deposit is considered a high-sulphidation epithermal deposit, with gold, silver, and copper occurring mainly in sulphides. The deposit is related to Miocene aged porphyry stocks and dikes that crosscut older sedimentary, igneous, and metamorphic rocks. The hydrothermal source fluids flowed through fault related pathways, generating background propylitic and phyllic alteration of the local rocks during mineralization, followed by silicification and argillic alteration in the centre of the main veins, zoning outward to intermediate argillic and propylitic alteration that formed during the principal stages of mineral deposition.
Mineralization
Mineralization at the Property is hosted in gneisses of the Bucaramanga Complex and leucogranites of the Santander Plutonic Group, and mostly occur within tectonic-hydrothermal breccia bodies emplaced in a dilatant structural setting.
Mineralization at the Property comprises parallel anastomosing veins within the fault systems, with variable widths and characteristics. Veins at Mascota have open-space filling textures, with hydrothermal brecciation and brecciated fragments of wall rock. Veining in the Gigante structure is mostly characterized by more compact, less vuggy, and often banded textures and is characterized by more heavily altered wallrock and clay content. Aserradero is a smaller, lower grade deposit located to the southeast of Mascota and Gigante.
Gold and electrum have a strong relationship with fine, crystalline pyrite and occur either free with the gold, adhering to pyrite particles, or encapsulated within the pyrite crystal lattice. Copper sulphides appear to have a partial affinity for pyrite but have much less of an association with gold than pyrite. Gold also occasionally occurs within tellurides. Silver occurs as silver sulphosalts, pyrargyrite, and proustite, and sometimes as native silver in the shallower areas. Copper occurs principally as enargite and to a lesser extent as bornite, chalcopyrite, chalcocite, and tetrahedrite-tennantite.
The Mascota and Gigante vein trends cover a strike extent of 2.6 km and have been drilled to a depth of approximately 800 m below the surface. The width of the veins is variable depending on structures, and pinch and swell, and averages between 1 and 3 m. The mineralized structures extend to the surface and are open at depth and along strike, resulting in a high exploration potential for expansion from future underground drilling stations.
Alteration
Alteration is strongly related to the presence of the faults that host or cut the mineralization, including propylitic alteration that gives way to phyllic alteration dominated by sericite. At distances of 5 to 15 m from the centre of the fault zone, phyllic alteration is replaced by argillic alteration and intensifies particularly on the hangingwall side of much of the Mascota veins. Where veining is strongly developed, particularly where there are a few 1 to 5 m wide veins encapsulated within one wider structure, the wall rock between the veins, and often in the footwall and hangingwall, is dominated by a pervasive silica alteration. Small cavities in the silica alteration and the quartz veins contain white alunite. In some faults the wall rock alteration can be extensive and the fault will often be filled with rock flour that produces a soft clayey gouge. Clay minerals that may influence mineral processing include minor kaolinite which is present in an average concentration of 1 to 2% and illite, which is present in an average concentration of 4 to 6% and is the predominant clay mineral at Gigante. However metallurgical testwork on samples with high clay content well above the average returned positive recovery values, indicating the clay minerals may not influence metallurgical recovery.
Oxidation of the mineralization has an irregular depth and penetrates much deeper around major faults and fractures, and alters pyrite to hematite, goethite, and limonite. Very little of the material in the mine plan is affected by oxidation.