Summary:
Two mineral deposit models are proposed for La Parrilla: intrusion-related carbonate replacement deposits and mesothermal fault-veins.
Mineralization occurs as vein and replacement deposits, the locations of which are structurally controlled by pre-existing faults, fractures, and bedding planes. Veins can be either open space filling, forming massive sulphide and breccia veins, or fault-related, consisting of matrix-supported breccias or gouge containing disseminated sulphides and oxides. Gradations commonly occur between the two types in any vein system. Stockwork veining can occur at country rock/vein contacts. Replacement deposits occur as oblique or perpendicular splays to veins and faults, and as larger replacement deposits concordant with sedimentary bedding.
La Parrilla deposits contain primary sulphides such as galena, sphalerite, pyrite, pyrrhotite, arsenopyrite, chalcopyrite, covellite, acanthite, native silver, and silver sulphosalts (tetrahedrite freibergite- solid solution). Due to supergene oxidation, the primary sulphides in the upper parts of some deposits have been altered to cerussite, anglesite, hemimorphite, hydrozincite, jarosite, goethite, hematite, cervantite, malachite, chrysocolla, chalcanthite, and native silver.
The major mineralized zones are:
• Rosarios vein: strikes north 70 degrees (°) west on average, dips at 64° to the northeast (290°/64°) and has a known strike length of 2 kilometres (km). The mineralization extends vertically for 900 metres (m), with a variable thickness of 0.2–14 m.
• The C1100 vein strikes north 50° west on average, dips at 75° to the northeast (310°/75°) and has a known strike length of 500 metres. The vein is mineralized for a vertical extent of 430 metres, and its thickness varies from 0.5 to 1.5 m.
• San Marcos vein: strikes north 20° west on average, dips at 60° to the northeast (340°/60°), and has a known strike length of 650 m. The vein is mineralized for a vertical extent of 350 m, and its thickness varies from 0.5 to 17 m.
• Quebradillas N-S Vein: strikes north 45° west on average, dips at 71° to the northeast (315°/71°), and has a known strike length of 125 m. The vein is mineralized for a vertical extent of 465 m, and its thickness varies from 0.25 to 5.0 m.
• The Quebradillas Vein: strikes north 88° east on average, dips at 86° to the south (88°/86°) and has a known strike length of 280 m. The vein is mineralized for a vertical extent of 175 m and ranges in thickness from 1 to 2.5 m.
• Quebradillas Q-38: strikes north 7° west on average, dips at 68° to the northeast (353°/68°) and has a known strike length of 150 m. The zone is mineralized for a vertical extent of 180 m, and has a variable thickness of 0.3 to 8.7 m.
• Quebradillas 460 Replacement vein: strikes north 16° west on average, dips at 63° to the northeast (344°/63°), and has a known strike length of 425 m. The zone is mineralized for a vertical extent of 570 m, and ranges in thickness from 0.1 to 8.5 m.
• Quebradillas 550 Vein: strikes north 80° east on average, dips at 83° to the south (80°/83°) and has a known strike length of 315 m. The vein is mineralized for a vertical extent of 185 m and varies in thickness from 0.5 to 5.5 m.
• Quebradillas Tiro Vein: strikes north 60° west on average, dips at 56° to the northeast (300°/56°) and has a known strike length of 70 m. The vein is mineralized for a vertical extent of 120 m, and its thickness ranges from 0.50 to 4.0 m.
• Quebradillas Viboras Vein: strikes north 80° west on average, dips at 80° to the south (100°/80°) and has a known strike length of 700 m. The vein is mineralized for a vertical extent of 250 m, and its thickness varies from 0.3 to 3.5 m.
• Quebradillas El Recuerdo Vein: strikes north 80° west on average, dips at 70° to the northeast (280°/70°) and has a known strike length of 550 m. The vein is mineralized for a vertical extent of 150 m, and its thickness varies from 1.3 to 9.0 m.
• San Nicolas Vein: strikes north 25° west on average, dips at 70° to the northeast (335°/70°) and has a known strike length of 525 m. The vein is mineralized for a vertical extent of 470 m, and its thickness varies from 0.3 to 1.8 m.
• Vacas Replacement vein: strikes north 17° west on average, dips at 58° to the northeast (343°/58°), and has a known strike length of 200 m. The zone is mineralized for a vertical extent of 400 m, and its thickness varies from 0.2 to 18 m. This vein was mined out in 2016.
Mineralization at La Parrilla occurs in veins, breccias, stockworks and replacements that are hosted by the Cretaceous limestones and shales of the Indidura Formation and by the granodiorite–quartz monzonite intrusion. Contact metamorphism and metasomatism resulted in the development of marble, hornfels, skarnoid, and skarn at the intrusive contact. Because mineralization is related to the intrusive contact and skarn development, the deposits are proposed to be of the intrusion-related hydrothermal type and may represent mesothermal to epithermal environments.