Summary:
The Uchucchacua mineral structures, which include the Uchucchacua and Yumpag mines, are hosted by Mesozoic limestone of the Jumasha Formation and are classified as a mesothermal polymetallic deposit of silver-lead-zinc with important contents of manganese. The main mineralized structures are veins and ore bodies with high-grade silver content.
The geology consists of sedimentary rocks from the Upper Cretaceous carbonate sequence. At the base, limestones from the Jumasha and Celendín formations exist; these sedimentary rocks have been strongly folded and faulted. On top of these units and in erosional unconformity, the red layers of Casapalca formation were deposited, and were eventually covered by Calipuy group volcanic rocks and Tertiary intrusives.
Yumpag area
The Yumpag mine consists of a folded and thrust Mesozoic sedimentary basin, which is intruded by granodioritic, dioritic and subvolcanic stocks of rhyolite-dacite-diorite composition that generate an aureole of skarn and marble on the periphery.
Yumpag consists of a series of intermediate-sulfidation veins, running predominantly northeast, tensional to the Cachipampa fault, which controls the mineralization in the Uchucchacua Mine. The most important structure to date is the Camila vein, which presents a bonanza-type silver-bearing mineralization, associated with the presence of silver sulfosalts with some lead-zinc credits and traces of gold. The deposit is very similarto Uchucchacua, and will be integrated into said production unit in the future via a tunnel at level 3850.
The Yumpag area is an epithermal silver-manganese deposit hosted by Cretaceous limestone. Mineralization is structurally influenced by the Cachipampa fault, which also influences significant areas of silver mineralization at the Uchucchacua mine.
To date, two parallel mineralized structures with a N60° direction of significant economic interest have been identified: Camila and Tomasa.
Uchucchacua area
Uchucchacua is a polymetallic epithermal deposit of veins (fracture filling) and metasomatic replacement, emplaced in carbonate rocks of the Jumasha Formation. Mineralization is complex, occurring in multiple stages or pulses, controlled by well-defined vein structures, replacement bodies or shoots and skarn.
Uchucchacua is a polymetallic deposit associated with replacement bodies and veins. Its mineralization (Ag, Zn, Pb, Fe and Mn) is located in a sequence of carbonate rocks of the Upper Cretaceous Jumasha Formation.
The Uchucchacua area is formed by veins and replacement bodies associated with structural systems, including the Uchucchacua, Socorro-Cachipampa, Rosa and Sandra faults, among others.
The mineralization processes at Uchucchacua have been complex and multiple, therefore its mineralogy is unusually varied. Among the main mineral groups are: Oxides, Silicates, Carbonates, Sulfides and Sulfosalts. Among the main ore minerals, we have: Galena, Proustite, Argentite, Pyrargyrite, Native Silver, Sphalerite, Marmatite, Jamesonite, Polybasite, Boulangerite, Chalcopyrite, Covellite, Jalpaite, Stromeyerite, Golfieldite. Gangue minerals include Pyrite, Alabandite, Rhodochrosite, Calcite, Pyrrhotite, Fluorite, Psilomelane, Pyrolusite, Johansonite, Bustamite, Arsenopyrite, Marcasite, Magnetite, Stibnite, Quartz, Orpiment, Realgar, Benavidesite, Tephroite and Gypsum.
The style of mineralization, in general, is given by fracture filling and metasomatic replacement.
It is important to mention that the silver mineralization with base metals is mainly embedded in rocks of the Jumasha Formation middle member, and occurs in different styles:
-Socorro Zone: mineralization mainly in the form of veins;
-Carmen Zone: veins and bodies in the form of replacement chimneys and mantles;
-Huantajalla Zone: veins and replacement chimneys;
-lomopampa zone: veins;
-Lucrecia Zone: replacement bodies and veins.
The Uchucchacua mine veins are located in three main systems:
-NW-SE system, which generally predominates in the Socorro area, bounded by the Uchucchacua and Cachipampa faults.
-E-W system with N 80° to E-W strike and quasi-vertical dips.
-NE-SW system dominating the entire southern part of the deposit.
Mineralized structures are mostly between 1 and 4 meters thick, with occurrences in some sectors with thicknesses in the order of 15 meters.
Hydrothermal alteration
The alteration halo surrounding the mineralized bodies by replacement and vein filling is restricted to a few centimeters and in some cases cannot be distinguished. For this reason, it is necessary to observe the veining of hydrothermal calcite, which, due to its intensity and composition determined by fluorescence, is one of the most important guides in the exploration of this type of deposits.
Fluorescence, in the case of hydrothermal calcite, is caused by the interaction of ultraviolet light with the different elements contained in the calcite structure, and this depends on its relative distance to the mineralized body or vein.
If to start in a point of fresh limestone with presence of non-fluorescent (NF) calcite, as we get closer to a vein or mineralized body (zone of higher temperature), calcite veins show a white (W) fluorescence due to the presence of beryllium, from there it changes to a yellow (Y) fluorescence because of the phosphorus, then to a light green (LG) fluorescence due to the presence of magnesium, and finally to an orange-red (OR) fluorescence caused by the presence of manganese.