Bournonite from Mina Pulacayo, Bolivia.

bournonite [70 kb]

This sample is from the Irwin Kennedy collection, and the locality is Mina Pulacayo in Bolivia. The sample is 10x14x2.5 cm in size, 978 grams, and the central crystal is 25x15x15 mm in size. The bournonite rests on pyrite with lesser chalcopyrite and quartz, on a very fine-grained argillically altered host (?) sedimentary rock.

"Rock of the Month # 96, posted for June 2009" ---

Bournonite (CuPbSbS3) is a sulphosalt of copper, lead and antimony, widely known in a variety of metallic mineral deposits across the world, in Europe and India, China and Australia, Africa and the Americas. It may be part of complex sulphosalt assemblages, as at Lengenbach (Switzerland) and Madoc (southeast Ontario, Jambor, 1968). Gold is often associated with bournonite, as in the Birimian of west Africa (Appiah and Norman, 1989). Bournonite was reported in various early studies of Archean lode gold deposits in northwest Ontario (e.g., Kindle, 1932; Bruce, 1935; Pye, 1951). Bournonite may occur with native gold, other sulphosalts, and tellurides (e.g., Stillwell, 1953).

Bournonite is well-known from the vein deposits of Cornwall in southwest England (Collins, 1892; Embrey and Symes, 1987; Bancroft and Weller, 1993). Famous specimens have come in particular from the Herodsfoot mine, Liskeard (Wilson et al., 2000; Cooper, 2007; Thompson, 2007; Wilson, 2009). More recently, China has produced some superb specimens (Wilson et al., 2000; Trinchillo, 2008).

Pulacayo is a silver-rich base-metal deposit on the western margin of the Cordillera Oriental of Bolivia. The cumulative production between the 1883 discovery and closure of the main mine in 1956 was about 5,000 tonnes of fine silver (Pinto-Vasquez, 1993). In later years, the Pulacayo deposit retained probable reserves quoted as 670,000 tonnes grading 488 ppm Ag, 7.8% Zn and 7.7% Pb (Anon, 1990). The deposit is one of many associated with volcanic domes in the region (Lyons, 1963; Cunningham et al., 1991; Kamenov et al., 2002). Most of the ore at Pulacayo was from a single vein, the Tajo vein. The metalliferous veins occur in Silurian shales and sandstones and overlying continental sedimentary and pyroclastic rocks of Tertiary age, near and within a dacitic volcanic dome. The main dome-hosted veins have wide argillic and sericitic alteration haloes. Sericitization affected mostly plagioclase and biotite, whereas argillic alteration mostly attacked the K-feldspar. The top of the dome has a pervasive quartz-alunite alteration cap (Pinto-Vasquez, 1993). The basal remnant of this lithocap at Pulacayo is barren quartz-alunite, unlike the rich Ag deposit of Potosi (Sillitoe et al., 1998). The Bolivian lithocaps may contain bulk-tonnage Ag targets with high-grade Sn veins at depth.


Anon (1990) Bolivian bet looks viable, says Sikaman. Northern Miner 76 no.39, 18, 03 December.

Appiah,H and Norman,DI (1989) Geology of Prestea goldfields, Ghana. GSA Abs.w.Progs. 21 no.6, Annual Meeting (St. Louis), 351.

Bancroft,P and Weller,S (1993) Cornwall's famous mines. Mineral.Record 24, 259-283.

Bruce,EL (1935) Little Long Lac Gold Area. ODM Ann.Rep. 44 part 3, 60pp. plus map.

Collins,JH (1892) A Handbook to the Mineralogy of Cornwall and Devon. D.Bradford Barton Ltd, 108pp. plus addenda and plates, reprint of 2nd edition in 1969.

Cooper,MP (2007) Robbing the Sparry Garniture: A 200-Year History of British Mineral Dealers. Mineralogical Record, 1st edition, 358pp.

Cunningham,CG, McNamee,J, Vasquez,JP and Ericksen,GE (1991) A model of volcanic dome-hosted precious metal deposits in Bolivia. Econ.Geol. 86, 415-421.

Embrey,PG and Symes,RF (1987) Minerals of Cornwall and Devon. British Museum (Natural History) / Mineralogical Record Inc., 154pp.

Jambor,JL (1968) New lead sulfantimonides from Madoc, Ontario. Part 3 - syntheses, paragenesis, origin. Can.Mineral. 9, 505-521.

Kamenov,G, Macfarlane,AW and Riciputi,L (2002) Sources of lead in the San Cristobal, Pulacayo, and Potosi mining districts, Bolivia, and a reevaluation of regional ore lead isotope provinces. Econ.Geol. 97, 573-592.

Kindle,LF (1932) Kowkash-Ogoki gold area, district of Thunder Bay. ODM Ann.Rep. 40 part 4 - 1931, 55-104 plus map.

Lyons,WA (1963) Structural geology of Pulacayo Mine, Bolivia. Econ.Geol. 58, 978-987.

Pinto-Vasquez,J (1993) Volcanic dome-associated precious and base metal epithermal mineralization at Pulacayo, Bolivia. Econ.Geol. 88, 697-700.

Pye,EG (1951) Geology of Errington township, Little Long Lac area. ODM Ann.Rep. 60 part 6, 140pp.

Sillitoe,RH, Steele,GB, Thompson,JFH and Lang,JR (1998) Advanced argillic lithocaps in the Bolivian tin-silver belt. Mineralium Deposita 33, 539-546.

Stillwell,FL (1953) Tellurides in Western Australia. In `Geology of Australian Ore Deposits' (Edwards,AB editor), Australasian Institute of Mining and Metallurgy, 1290pp., 119-127.

Thompson,WA (2007) Ikons: Classic and Contemporary Masterpieces of Mineralogy. Mineral.Record special supplement, 192pp.

Trinchillo,D (2008) The Marc P. Weill collection of fine minerals. Mineral.Record 39 no.1, supplement, 96pp.

Wilson,WE (editor) (2009) Private Mineral Collections in Texas. Mineral.Record 40 no.1, supplement, 180pp.

Wilson,WE, Van Pelt, H and Van Pelt,E (2000) The Joseph A. Freilich collection. Mineral.Record 31 no.1, 1-80.

Graham Wilson, 02 October 2009

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