Summary:
The silver-bearing mineral deposits are alluvial and colluvial, unconsolidated sediments (the pallacos flanking Cerro Rico), high sulfidation deposits (Tollojchi) and intermediate sulfidation deposits (Alta Vista and Paca). The pallacos also contain tin. Cerro Rico is a prominent +4,700 meter (m) elevation mountain.
San Bartolomé
The mineral deposits at Cerro Rico are the source of the San Bartolomé pallacos and were formed by erosion and downslope accumulation of the in situ high sulfidation, epithermal deposits at Cerro Rico, composed of veins, stockworks, hydrothermal breccias and irregular bodies, hosted in a very altered resurgent dome of dacitic- to rhyodacitic-composition porphyritic intrusion emplaced in Middle Miocene time (approx. 14 mya). These deposits consist of an unsorted mixture of cobbles and boulders in a sandy clay matrix, accumulated down slope by colluvial and alluvial processes, filling depressions, gullies and low-gradient areas. The deposits have been grouped into three areas named Antuco, Huacajchi and Santa Rita. As of 1 December 2023, the pallacos had been nearly depleted.
Alta Vista
Mineralization at Alta Vista is hosted in epithermal veins of intermediate sulfidation character. Mineralization is controlled by multiple, epithermal veins with the main, Veta Rica vein. Gangue mineralization at Alta Vista consists largely of quartz and Fe-Mn oxides with lesser amounts of alunite and other alteration minerals.
Tollojchi
Silver mineralization in Tollojchi is hosted in veins, breccias and disseminated zones and is strongly associated with the presence of several NE-SW trending lithocaps. Tollojchi mineralization is high sulfidation in character, with pyrophyllite and vuggy silica present, typical of this geologic environment (Sillitoe, 1998).
Paca
Paca mineralization is intermediate sulfidation in character, occurring as disseminations, and consists in oxidized and sulfidic material, hosted within igneous and sedimentary rocks. In conglomerate, mineralization is mainly in matrix, which was replaced by barite-tetrahedrite; in andesite, minerals observed are disseminated and cavity fillings. The contact between both units is the main control of mineralization. On surface, Ag contents are dominant, while base metals increase at depth.
Development and Operations
Manquiri has developed and produced from pallacos at San Bartolomé from commencement of commercial production in 2008 until September 2023. During 2023, pallaco mineralization was largely depleted.
Fines Disposal Facility (FDF)
FDF is an impoundment of fine (-2.4-millimeter (mm), 8 mesh#) material that has been screened out of the pallacos at the plant crusher station and then stored since the operation started. The material in the FDF has been explored primarily through barge-supported sonic drilling. Extensive drilling has been implemented to characterize the geochemical and geotechnical characteristics of the FDF. Deposition of fines to the FDF was finalized in 2023, and no additional material has been added after December 2023. No additional exploration activities are planned for the FDF in 2024.