Minerals of Bolivia
Bolivia, being the widest part of the Andes and its heartland in many respects, comes with an incredible mineral endowment that still remains to be fully appreciated. The country has the distinction of holding the world’s largest silver deposit at Cerro Rico overlooking the town of Potosi. Bolivia is the more prolific tin mineralized areas of the world. It also has one of the single richest silver veins at the Pulacayo mine east of Uyuni. Bolivia is the source of many fine mineral specimens for collectors.
Bolivia remains not well-developed across all measures, a fact largely due to irresponsible and corrupt governments, extreme geography, and the nation being landlocked thanks to Chile taking away part of their territory that once extended down to the coast at Antofagasta (an area that contains about 16% of Chile’s copper mineral wealth). The mining sector remains an important source of income for the country and its people, and yet since nationalization of the industry in 1952, the mining districts have largely been miss-managed (see Espinoza Morales, 2010). This is a country with a great number of mineral districts comprised of veins; nearly all exploitation is from underground mines. The country has only two open-pit mines. The currently active zinc mine of San Cristobal operated by Sumitomo, and the closed Kori Kollo gold mine that Newmont Mining Co. developed. There is room for more large-scale mining in Bolivia, but very few companies are willing to risk the unstable government policies, which includes excessively high taxation.
The Bolivian tin belt follows the grain of the Andes as it wraps around from northern Chile/Argentina and deflects into the regional northwest trend of Peru. The mineral camps are spaced out, and associated with Miocene dacitic dome complexes (Sillitoe et al., 1998) that are riddled by high-angle dipping veins. The early twentieth century mining monopolies on tin production (Loayza Portocarrero, 2006) along with poor practice labor relations and violent worker strikes precipitated the government nationalizing the industry. Although, mining held in the hands of the bureaucrats in practice is about access to the mineral wealth and personal enrichment through corruption than the greater good of the Bolivian population. Mining today in Bolivia is an odd mix of nearly defunct large-scale underground operations by the state miner Comibol (Corporación Minera de Bolivia), by highly organized mining cooperatives, small-scale miners that frequently operate with substandard working conditions or cross over into the activities of illegal mining, and a few international mining companies.
The largest tin mining camps include: Huanumi, Colquechaca, Tasna, Llallagua, Vilaco, Tatasi, Chorolque, Animas, Ubina, and Colavi. The major silver mining camps are at Porco, Potosi, and Pulacayo. A tract of generally weak copper mineralization runs through west-central Bolivia, a belt of sediment-hosted copper deposits, from which only the Corocoro mine has any modern production.
While mining remains important economic activity in Bolivia, very little in the way of mineral specimens make it to the international markets today. Most of the material available to the mineral collectors came from past decades with material located and exported by just a few individuals. The remainder of this summary discusses a few of the classic mineral localities, with the specimens shown having been purchased from Mineral Classics from Brian Kosnar.
Cassiterite – SnO2
Cassiterite is the most renowned mineral specimen from Bolivia, and once extremely abundant, today little remains on the market and it can fetch elevated prices. Fine specimens will have a metallic vitreous luster on well-developed crystals, which can be dark gemmy translucent. Recently at the Denver mineral show small plate of cassiterite was priced at US$8,000. The example we show here comes from the Viloco mine, Loayza province, of the La Paz department. The district consists of numerous narrow, almost sheeted, curvi-planar ENE-striking veins exposed from elevations of 4,600 meters up to 5,100 meters elevation. Associated minerals are chalcopyrite, molybdenite, scheelite, sphalerite, and wolframite. The Viloco mine discovery was in 1902. Most of the production from the district ended decades ago.
Cassiterite
Vivianite – Fe2+3(PO4)2 · 8H2O
Bolivia has yield fine collector-grade specimens of vivianite from the upper portion of the Siglo XX mine in Llallagua district that lies 75-km southeast of the Oruro city. Llallagua was discovered in 1872 while the Siglo XX mine was founded in 1903. Llallagua had large-scale production by Comibol using underground block cave methods. It is a classic world-class tin district hosted in ~20.5 Ma dacitic intrusion (Grant et al., 1979). The Llallagua district was mainly mined for tin from cassiterite (Ahfeld, 1931) but it also has the associated minerals of bismuthinite, stannite, wolframite, and sphalerite. The vivianite crystals from Siglo XX have a very deep translucent green color, and form large plates with sharp angled terminations. The contrasting light brownish-tan matrix material makes for nice displays. The crystals are dark translucent and when illuminated from behind make a fine deep green hue.
Bournonite – PbCuSbS3
Particularly excellent large euhedral crystals of bournonite come from the Mina Machacamarca, Viboras vein, Colavi, in the Potosi department of Bolivia. Colavi is positioned 40-km northeast of the Potosi city. The district has unusual occurrence of sandstone-hosted stratabound Cu-Sn-Pb-Sb-Zn replacements with quartz and pyrite. The mine first produced Pb-Ag-Sn starting in 1850. Associated minerals are argentite, bornite, cassiterite, chalcopyrite, freibergite, sphalerite, and pyrrhotite. Bournonite is often described as having a “cog wheel” habit, making the bournonite crystals distinct when large, but many mines in Bolivia also contain this mineral in fine-grained material that is difficult to distinguish from the silver sulfosalts.
Wire silver – Ag
Wire or horn silver, which is native silver, forms in the supergene environment and can potentially be found in the upper near surface portion of many of Bolivia’s silver bearing veins. The example we have comes from the Porco district in the Potosi department. These mines lie some 33-km southwest from the city of Potosi. The veins at Porco are associated with the immense Miocene Frailes caldera, and they straddle the southern margin of the caldera rim (Cunningham et al., 1994). The Ag-Sn veins were mainly operated by Hochschild during the first half of the twentieth century until being nationalized in 1952. The USGS MRDS database lists the year of first production being 1542. The veins occur in two sets, which are northeast-striking and northwest-striking.
Stibnite – Sb2S3
If you plot up the stibnite occurrences in Bolivia one finds a belt of antimony running the length of the country that overlaps with both the tin and silver mining camps. Some locations are so endowed with stibnite that various attempts have been made to mine it just for the product of antimony. In 2018 a metric tonne of antimony oxide generally is valued at $8,200 dollars. The quality of the stibnite specimens yielded from Bolivia to date are lesser than the classic locality at Ichinokawa mine, Japan, and they do not compete on the market with fine and abundant material produced from China. However, given the importance of antimony in sulfides of Bolivian geology a good mineral collection on Bolivian minerals should include a specimen of stibnite, although, not much material is available on the market. Some clean small examples of stibnite come from the La Salvadora mine (Oruro department; at least 6 mines with this name are in Bolivia, other nearby Sb producer of the same name lies just NE across into the La Paz department. The USGS MRDS database shows La Salvador at -17.55, -67.183 which plots in a flat area with no mine diggings; whereas the La Paz department mine at -17.5, -66.917 also plots in a narrow valley devoid of mining activity. The location for the La Salvadora antimony mine clearly needs correction). The vein was discovered in 1850, but not placed into production for antimony until 1973. Some stibnite crystals from this location come with brilliant fine partial coatings of marcasite.
Native Copper– Cu
Bolivia’s Corocoro sediment-hosted copper mine has yielded fine large examples of copper pseudomorphs after euhedral aragonite crystals. The mine is one of the few copper-only producers in Bolivia, and the production dates back to over a hundred years of mining (Singewald and Berry, 1922). The USGS MRDS database lists the mine discovery as being 1540, but in truth native copper from the district was probably used by people in the Aymara culture. Ore minerals include bornite, chalcopyrite, chalcocite, covellite, cuprite, chrysocolla, and malachite (Entwhistle and Gouin, 1955). Corocoro mineralization appears related to basinal fluid flow and interaction with a regional unconformity. The deposit style is similar to the Central African copper belt in the Democratic Republic of Congo and Zambia. Host stratigraphic units are largly oxidized continental red beds that are locally disrupted by Oligocene or younger salt diapirs.
More exotic or lesser known minerals from Bolivia include pyromorphite, ferberite, valentinite, and ludlamite. The single most important mineral district in Bolivia is Cerro Rico at Potosi. Mineral specimens are difficult to obtain from this location. During a trip there the miners did not wish to sell any material, the stores in Potosi did not have any minerals for sale, and during the last Denver mineral show no material from Potosi was for sale. A fine specimen from Cerro Rico is the last thing we are searching for to complete our Bolivia mineral shelf. The country is certainly endowed with more minerals than covered here, but very little is being distributed among the world’s mineral collectors.
James M. Wise, December, 2018
References
Ahfeld, F., 1931, The tin ores of Unicia-Llallagua, Bolivia: Economic Geology, v. 3, p. 241-257.
Cunningham, C.G., Aparicio N., H., Murillo S., F., Nestor Jimenez Ch., N., Lizeca B., J.L., McKee, E.H., Ericksen, G.E., Tavera V., F., 1994, The relationship between the Porco, Bolivia, Ag-Zn-Pb-Sn deposit and the Porco caldera: U.S.G.S. Open-File Report 94-238, 19 p.
Entwhistle, L.P., and Gouin, L.O., 1955, The chalcocite-ore deposits at Corocoro, Bolivia: Economic Geology, v. 50, p. 555-570.
Espinoza Morales, J., 2010, Minería Boliviana su realidad: Impreso en Bolivia, La Paz, 453 p.
Grant, J.N., Halls, C., Avila Salinas, W., and Snelling, N.J., 1979, K-Ar ages of igneous rocks and mineralization in part of the Bolivian tin belt: Economic Geology, v. 74, p. 838-851.
Loayza Portocarrero, J.A., 2006, Simón el magnate del estaño: Impreso en Grafica J.V., Cochabamba, Bolivia, 460 p.
Sillitoe, R.H., Steele, G.B., Thompson, J.F.H., and Lang, J.R., 1998, Advanced argillic lithocaps in the Bolivian tin-silver belt: Mineralium deposita, v. 33, p. 539-546.
Singewald, J.T., and Berry, E.W., 1922, The geology of the Corocoro copper district of Bolivia: John Hopkins University studies in Geology v. 1, 117 p.
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