Summary:
The Orcopampa mine consists of an epithermal gold telluride deposit, hosted into lava flows and domes of Sarpane complex (calcalkaline to high potassium), of early Miocene to Holocene, which forms part of the tertiary metallogenic belt of Southern Peru (Au-Ag).
Deposit Types
The Chipmo mineralization is of hydrothermal type with quartz infill. This deposit can be classified as epithermal Au-Ag veins associated with tellurides, with intermediate and low sulfidation. These structures are located in calc-alkaline rocks that are rich in potassium (Sarpane Volcanic). Veinhosting faults appear to be deep and crustal (Villon, 2011)The major recognized structures are the Prometida, Nazareno and Pucara Sur veins and correspond to the N60°E system.
Mineralization
In general terms, mineralization in the area of Orcopampa is associated to calderas with subvolcanic intrusives, dikes in Miocene tuffs (Swanson, 1998); in the Ocoruro-Jaspe area, mineralized structures are related to the Sarpane complex, faults, and possibly to subvolcanic bodies with more than one event or pulses of mineralization.
Mineralization in Chipmo deposit is dominated by the occurrence of gold tellurides, mainly calaverite in high levels; petzite and hessite and native gold can be found in the central part. Copper sulfosalts and other gold-silver and bismuth tellurides occur subordinately. In general, mineralization is characterized by high Au/Ag ratios (>3) and low base metal concentrations, which are evident in the deep levels to the east. Its mineralogy is mainly composed of quartz in breccia, banded and replacement textures; there are also sulfides such as pyrite (leached), barite, gypsum, anhydrite and calcite. Alteration minerals include alunite, dickite, pyrophyllite, diaspore, kaolin, illite, smectite, chlorite, pyrite, etc.
Types of Mineralization
Mineralization in veins (Fracture Filling)
The fractures originated through tectonism and movements of regional and local faults; they have been filled by hydrothermal solutions of rosary-type with irregular shapes and mineralogical filling, most of which is composed of sulfides, silicates in some sections of the veins, strands and tension fractures. Additionally, cavities (geodes) or open fractures are present, which allowed the percolation of meteoric waters that oxidized part of the mineralization. Mineralization is also found in shoots of different lengths and widths at the interception of veins or strands (sigmoids). Veins are persistent in trend and reach decametric to kilometric lengths. In some cases, outcrops are not continuous; they narrow to centimeters (rosary-type) and are also covered by Quaternary material. Structures are oriented and controlled by three main structural systems:
E-W system, Lola, Florencia, Fresia structures (Jaspe Oeste Zone); Jaspe, Jaspe Sur structures (Jaspe Zone); Vanesa, Amparo, Ana 1, Paula, Irene, Aydé structures (Emilia Zone); Belinda, Blanca structures (San Jose Zone).
NE system, the following structures belong to this system (anti-Andean): Ana, Olenka, Valeria 1 (Emilia Zone); Claudia, Carmín, Jossie structures, (Jasper Este Zone); Liliana structure (Huaylla Zone); Valeria, Vania, Escondida, Señal Chipmo structures (San Jose Zone); Estrella, Ada, Dorita, Sophia structures, Úrsula, Elizabeth, Paty, Esperanza, Prometida Norte, Prometida structures (Prometida Zone).
NW system, part of the Andean system and belong to the strands of Jaspe vein (Jaspe Zone); Amelia, Alicia, Amparo structures (Jaspe Este Zone); Ocoruro Body with veinlets (Ocoruro Zone); Lorena Structure, (Chaqui Norte Zone); Karol, Dolly structures (Huaylla Zone).
Mineralization in veinlets
In the main structures, we have observed veinlets parallel to the main structures; others bifurcate from the main structure to the hanging wall and footwall; in the sigmoids there is evidence of tension veinlets between strands and between two main veins with a tendency to join; therefore, there are multidirectional stockwork-type veinlets filled with manganese oxides, calcite and in some cases, iron oxides.
Mineralization in veinlets
These are millimetric structures filled with gray quartz and calcite; they represent another stage of mineralization and may be related to gold mineralization.
Mineralization in breccia bodies
The mapped area shows evidence of breccia bodies formed by rounded or angular fragments from the same host rock (monomictic) or from foreign rocks, cemented with iron and manganese oxides with remnants of leached pyrite, quartz veinlets and presence of iron oxides (hematite).