This sample is from the Irwin Kennedy collection, and the locality is the Pan-American mine at Quiruvilca in Peru. The sample is 7x5x4 cm in size, 228 grams, and is composed largely of dark, pitted galena with a spray of white quartz prisms and some orangey-red orpiment, monoclinic As₂S₃. The sample also contains lesser dark brown (and so probably iron-rich) sphalerite and a trace of chalcopyrite.

"Rock of the Month # 99, posted for September 2009" ---

Galena (PbS) is the principal ore mineral of lead, while orpiment is one of the more readily identified arsenic-rich sulphides.

The Quiruvilca district, located in a Miocene metallogenic belt in northern Peru, has been mined for polymetallic veins of copper, lead, zinc, silver and gold (Hollister, 1977; Hermelin, 1986; Bartos, 1989, 1990; World Wide Books and Maps, 1996; Mineral Information Maps and Northern Miner, 2006; Baumgartner et al., 2008). It is a noted mineral locality (Crowley et al., 1997; Hyrsl and Rosales, 2003).

In 1996, the Quiruvilca mine produced 19,442 tonnes of Zn, 5,649 tonnes of Pb and 90 tonnes of Ag (Gurmendi, 1997). The mine has operated since the early 20th century, at 3,800 m elevation, 130 km inland from Trujillo. The year 200 saw record silver production of 3.6 million oz. The underground workings of the mine are extensive, over a 4x3 km area and down to a depth of 400 m, with over 100 working faces and an average mining width of 0.7 m (Robertson, 1998, 2001).

The district is noted for minerals such as bournonite, enargite, orpiment, pyrite, tetrahedrite-tennantite and wurtzite (Crowley et al., 1997 and [orpiment] Behnke, 1991). Some of the Quiruvilca ore is enargite-rich (Robinson and Harris, 1987; Noble and Vidal, 1994; Petersen and Vidal, 1996).

References

Bartos,PJ (1989) Prograde and retrograde base metal lode deposits and their relationship to underlying porphyry copper deposits. Econ.Geol. 84, 1671-1683.

Bartos,PJ (1990) Metal ratios of the Quiruvilca mining district, northern Peru. Econ.Geol. 85, 1629-1644.

Baumgartner,R, Fontbote,L and Vennemann,T (2008) Mineral zoning and geochemistry of epithermal polymetallic Zn-Pb-Ag-Cu-Bi mineralization at Cerro de Pasco, Peru. Econ.Geol. 103, 493-537.

Behnke,D (1991) Photomacrography of microminerals. Mineral.Record 22, 471-476.

Crowley,JA, Currier,RH and Szenics,T (1997) Mines and minerals of Peru. Mineral.Record 28 no.4, 1-98.

Gurmendi,AC (1997) Peru. USGS Mineral Industry Surveys, International Review - 1996, document 9519096, 8pp.

Hermelin,M (editor) (1986) Geografia Economica. Area de Recursos Minerales, Bolivia- Colombia- Chile- Ecuador- Panama- Peru- Venezuela. Instituto Internacional de Integracion, La Paz, Bolivia, 716pp. (in Sp.).

Hollister,VF (1977) Kinematics and regional tectonic implications of the east-trending fold belt of Peru. BGSA 88, 1749-1755.

Hyrsl,J and Rosales,Z (2003) Peruvian minerals: an update. Mineral.Record 34, 241-254.

Mineral Information Maps / Northern Miner (2006) Peru: mining and exploration activity. Northern Miner 91 no.48, 2-sided map supplement.

Noble,DC and Vidal,CE (1994) Gold in Peru. SEG Newsletter 17, 1,7-13.

Petersen,U and Vidal,CE (1996) Magmatic and tectonic controls on the nature and distribution of copper deposits in Peru. In `Andean Copper Deposits: New Discoveries, Mineralization, Styles and Metallogeny' (Camus,F, Sillitoe,RM and Petersen,R editors), SEG Spec.Publ. 5, 1-18.

Robertson,R (1998) Pan American finds silver lining. Northern Miner 84 no.14, 1,13,20.

Robertson,R (2001) Pan American Silver aims to double production. Northern Miner 87 no.14, 1-3.

Robinson,GW and Harris,DC (1987) A baumhauerite-like mineral from Quiruvilca, Peru. Mineral.Record 18 no.3, 199-201.

World Wide Books and Maps (1996) South America, North West. International Travel Maps, Vancouver, 1:4,000,000 scale map, 2nd edition.