Summary:
Deposit Type
La Colorada Vein Mine is considered a typical hydrothermal polymetallic deposit located in a region with significant silver and base metal production from well-known vein and skarn deposits.
The La Colorada Vein Mine’s intermediate sulphidation epithermal vein model considered for exploration and mineral resource and reserve estimation transitions from silver-rich mineralization at surface to more base metalrich mineralization at depth.
Epithermal intermediate sulphidation Ag-Pb-Zn vein, CRD, and polymetallic skarn mineralization has been identified at the La Colorada Property. The upper portions of epithermal vein system have been the historic focus of the currently operating La Colorada Vein Mine, while the skarn and CRD mineralization is currently being defined and characterized by ongoing drilling and technical studies.
Epithermal Ag-Pb-Zn +/- Au intermediate sulphidation (IS) epithermal veins within the MSB are generally hosted in dacites of the LVC and in the underlying Cretaceous sedimentary sequences and tend to be older than 30 Ma (Ebner 2023). Polymetallic CRD and skarn mineralization replace the Cretaceous limestone units, appear similar in age and composition to the IS epithermal veins, and may be genetically related to them (Ebner 2023). Ongoing studies may corroborate this hypothesis or determine that they result from different events within the evolution of the hydrothermal system. Gold-rich low sulphidation (LS) epithermal deposits are also found in the MSB and these tend to be hosted in the UVS rhyolites (younger than 30 Ma) and are controlled by large-scale NNE- and NNW-striking extensional faults. The MSB also hosts additional volcanic-hosted massive sulphide, iron-oxide copper and gold, orogenic gold, carbonatite, pegmatite, tin vein and placer deposits (Ebner 2023).
Mineralization
Mineralization is related to multiphase hydrothermal and magmatic activity and occurs as various types, such as CRDs, breccia pipes and epithermal silver-lead-zinc systems. Some evidence for copper molybdenum porphyry mineralization demonstrate the full evolution of the hydrothermal system.
Mineralization is found in veins, replacement mantos, and skarn. The majority of the mineral resources and mineral reserves are sourced from the NC vein series, the HW vein series, Veta 3, the Amolillo vein system, vein and manto mineralization at the Recompensa system, with additional mineral resources from the undeveloped skarn deposit.
Most mineralized veins strike east to northeast and dip moderately to steeply to the south. Most of the mineralization of economic significance is located in quartz veins of the La Colorada mine that average 1 metre to 2 metres wide but may be significantly wider. Amolillo strikes over 1.5 km to the northeast and dips 60° to the southeast, for over 800 metres down dip. The average vein width is 2.2 metres. The NC vein series lies around 700 m to the southeast of Amolillo. The most significant of these veins, NC2, strikes around 1.2 km to the northeast and dips 75° to the southeast, for over 1 km down dip. The average vein width is 1.9 metres. The HW series is the western continuation of the NC series, strikes east-west, and dips 50° to the south, for over 600 m down dip. The average vein width is 1.8 metres. Veta 3 runs parallel to the HW and NC series, strikes for over 900 m to the northeast, and dips 75° to the northwest, for around 400 m down dip. The average vein width is 1.7 metres.
Manto style mineralization is found near vein contacts where the primary host rock is limestone.
Fractures and faults formed during the D1 to D3 deformation events acted as conduits for emplacement of epithermal vein mineralization. There are three ENE to E-W-trending principal vein structures which, from NW to SE, are named Recompensa, Amolillo and NC-HW. Each vein has second order sub-parallel splays and duplexes, and there are also several NW- to WNW-trending veins. In general, the principal veins are strongly brecciated, locally oxidized, and often exhibit irregular vein boundaries. Most of the mineralization of economic significance is located in quartz veins that average 1 metre to 2 metres wide, but may be significantly wider. The vein fillings consist of quartz, calcite, and locally barite and rhodochrosite. Galena, sphalerite, pyrite, native silver, and silver sulphosalts are present in unoxidized veins. The major mineralized veins are strongly brecciated and locally oxidized. Amolillo strikes over 1.5 km to the northeast and dips 60° to the southeast, for over 800 metres down dip. The average vein width is 2.2 metres. The NC series of veins lies around 700 m to the southeast of Amolillo. The most significant of these veins, NC2, strikes around 1.2 km to the northeast and dips 75° to the southeast, for over 1 km down dip. The average vein width is 1.9 metres. The HW series is the western continuation of the NC series, strikes east-west, and dips 50° to the south, for over 600 m down dip. The average vein width is 1.8 metres. Veta 3 runs parallel to the HW and NC series, strikes for over 900 m to the northeast, and dips 75° to the northwest, for around 400 m down dip. The average vein width is 1.7 metres. Well banded epithermal textures are rare. Vein breccias generally lack cohesiveness and consequently show very little surface expression. Veins typically occur as narrow feeders with massive sulphides in the upper portion of the system.
Emplacement of the intrusions fractured the sedimentary rocks and increasing porosity and permeability of the limestone host rocks which were metamorphosed were in contact with the hot fluids. Additional mineralogic changes resulted from cooling and infiltration of groundwater in the porous areas. Recrystallization and mineralization occur predominantly around intrusive bodies and is associated with intrusive sills, dykes or offshoots, and tends to follow the sedimentary bedding.
A skarn deposit was discovered in 2018 at depth and to the east of the NC2 vein. With increasing depth, mineralization styles transition from epithermal-style veins to manto-style mineralization in calcareous sediments, skarn, magmatic–hydrothermal breccia skarn, proximal skarn, epithermal veins overprinting porphyry, and copper–molybdenum–silver porphyry. Common minerals include galena and sphalerite, with quartz, carbonate, feldspar, pyroxene, and garnet. The deposit comprises several mineralized zones located between approximately 600 metres and 1,900 metres below surface, over an area of approximately 1,400 metres by 650 metres.