Summary:
Caballo Blanco deposit is located in the central part of the Eastern Cordillera, a thick sequence of Paleozoic marine siliciclastic and argillaceous sedimentary rocks deposited on the western margin of Gondwana and deformed in a fold-thrust belt.
The Caballo Blanco zinc, silver, lead mine, situated south of Potosi, is located in the Jayaquila – Victoria corridor, a 5-7 km north-south structural zone with three sectors, from north to south, the Colquchaquita, Reserva, and Tres Amigos mines. They are not described in the published literature. They are hosted by volcanic rocks of the Kari-Kari volcanic complex, with dimensions of 32 km north-south and 12 km wide, located on the SE side of the Los Frailes felsic volcanic field that covers an area of 8,500 km2 at altitudes of 4,000 – 5,200 masl. The history started with intrusion of small granitoids at about 25 Ma at Kumurana, at the southern end of the Kari massif, and Azanaques. These were followed by the formation of Kari at about 20 Ma that is interpreted to be a resurgent caldera with welded ignimbrite fill. Ash flows, domes and stocks formed in the Cebadillas episode at 17-10 Ma, including the Cerro Rico dome with Ag-Sn mineralization at 13.8 Ma (Zartman & Cunningham, 1995; Cunningham et al., 1996; Rice et al., 2005).
Deposit Type
The most important ore deposits of the Eastern Cordillera are polymetallic hydrothermal deposits mined principally for Sn, W, Ag and Zn, with sub-product Pb, Cu, Bi, Au and Sb. They are related to stocks, domes and volcanic rocks of Middle and Late Miocene age (22 to 4 Ma). Mineralization occurs in veins, fracture swarms, disseminations and breccias. The deposits of the Eastern Cordillera are epithermal vein and disseminated systems of Au, Ag, Pb, Sb, as that have been telescoped on to higher temperature mesothermal Sn-W veins and, in some cases, porphyry Sn deposits. The “telescoping” is a characteristic of these deposits and is the product of the collapse of a hydrothermal system, whereby younger lower temperature fluids overprint the alteration and mineralization developed by older higher temperature fluids. The systems show a fluid evolution from a high temperature, low sulfidation state to intermediate sulfidation epithermal and high sulfidation epithermal.
The rocks of the Kari complex are felsic, peraluminous, and rich in garnet, cordierite and tourmaline (Schneider, 1987).
Mineralization
Mineralization in its generality is characterized by being housed in philonian structures divided into four domain orientations:
1. Oriented at N 10°- 20° E, are Colquechaquita such as Karina, Viviana, Camila, and some Tres Amigos veins namely, Catalina, Milagros, Milagros Este, Tatiana and Central;
2. Oriented N 10°-30° W are the Reserve veins called Rosario, Wendy, Juanita and Blanquita, along with Ramo Catalina at Tres Amigos.
3. Corresponding to veins in the Porvenir region which have an N-S orientation, the Veta Rostia at Reserva the Milagros veins at Tres Amigos.
4. Oriented N 40°-45° W° is the Daniela vein at Tres Amigos.
General mineralogy is composed of quartz-pyrite-chalcopyrite and marmatite, sphalerite, galena, boulangerite as primary minerals in addition to accessory minerals such as siderite, calcite and ankerite at the trace amounts.
Reserva
The Rosario is a major Philonian type, mesothermal phase structure, it is split into a North Zone and South Zone, with a strike of N 10 ° W and dip of 65 ° to 70 ° extending 1,000 m in length from the intersection with the Wendy vein. The mineralization is composed of marmatite, sphalerite, galena and jamesonite in addition to pyrite, siderite and quartz.
The Wendy vein is a pre-mineral, fracture-filled brecciated unit that is oriented from North to South, with dip of 75° NE, and a strike length of 900 m with widths being on average 0.70 m. The Wendy vein is composed mainly of marmatite, sphalerite, galena and jamesonite with the addition of pyrite, siderite, marcasite and quartz.
The Porvenir Vein, located in the Porvenir area, is a secondary structure, with widths ranging between 0.20 to 1.50 m. The Porvenir extends for over 2.6 km, striking N-S and dipping 60° to 78° to the east. It has been developed for approximately 300 m on the +40 and +80 levels, where widths range between 0.25 to 0.50 m. On the surface it is recognized for its pervasive argillic alteration and oxidation, accompanied by faulted and fractured material. Mineralization is composed of sphalerite, galena, pyrite, quartz and siderite. It is not currently being explored or developed by the company.
Colquechaquita
Colquechaquita is a hydrothermal system where zinc, lead and silver minerals have filled fractures., sphalerite, galena, jamesonite are the predominant economic minerals, however pyrite, chalcopyrite, quartz, siderite and pyrrhotite, are present as gangue minerals. The system shows vertical zonation, which has been observed historically as the mine was originally according to historical data this mine is considered as a silver deposit in the in the upper levels however, at current mining levels such as Level -215, there is an increase in, sphalerite, marmatite, chalcopyrite, pyrrhotite.
The Karina Vein is a rosary-like hydrothermal Philonian fault filled structure. Distributed throughout two sectors, North and South, with strike of N10°W and dip of 80° to 90° to the northeast extending 450 m from the Triunfo headframe. The South zone is oriented N 10°-25° W, dipping 65° to 85° to the northeast, extends for 530 m. Economic mineralization is composed of sphalerite, marmatite, galena and jamesonite while the gangue is composed of pyrite, siderite and quartz. The predominant alteration minerals are siliceous, argillic, chloritization and sericitization. The average width of the vein is 1.5 m. The most relevant characteristic is the presence of kaolin associated with faulting and mylonite. The average width of the vein ranges from 0.50 to 2.0 m.
Three Amigos
A rosary-type Philonian structure, the ore corresponds to the filling of fault of Hydrothermal origin. Distributed in two sectors, North Zone and South Zone, the first with an average course N 25 ° E and 80 to 85 ° of inclination in se direction recognized and exploited along 750 m in length. The ore is composed of sphalerite, marmatite, galena and jamesonite. In addition, there is pyrite, siderite and quartz. The predominant alteration types are argillic, chloritic and sericitic. The average width of the vein is 0.50 m with the most predominant feature being the presence of kaolin within the fault and the argillic alteration anulus where the rock is fractured.
A Ramo de la Veta Catalina, in the area called Zona Sur Cuya. La Veta has a general course of North – South with 75° to 80° the SE, recognized along 750 m. The average width of the vein is 0.45 m. composed mainly of marmatite, galena, sphalerite and jamesonite with the addition of pyrite, siderite and quartz.
The Daniela vein is transverse to the Catalina vein, with general heading N49°W and widths of between 0.20 m to 0.8 m extending 500 m. It is mineralogically comprising of marmatite, galena, sphalerite, quartz and jamesonite.
The Miragros vein is an argentiferous vein that has a recognized extension of 2.0 km, varying in orientation where to the south it has a strike of N-S changing to 10° NW to the north, with dips that are also variable from between 60° to 80° E-NE, shifting to subvertical at depth. It has been traced to the -160 level with thicknesses varying between 0.3 to 0.75 m, however, at surface the thickness ranges between 0.20 to 1.20 m.