Articles

 

BOLETÍN DE LA SOCIEDAD GEOLÓGICA MEXICANA

Vol 62, Núm. 1, 2013, P. 161-171

Platinum group minerals in chromitite bodies of the Santa Elena Nappe, Costa Rica: mineralogical characterization by electron microprobe and Raman–spectroscopy

Minerales de platinoides en cuerpos de cromitita de la nappe de Santa Elena, Costa Rica: caracterización mineralógica por microsonda electrónica y espectroscopía Raman

Federica Zaccarini1*, Ronald J. Bakker1, Giorgio Garuti1, Thomas Aiglsperger1, Oskar A. R. Thalhammer1, Lolita Campos2, Joaquin A. Proenza3, John F. Lewis4

1 Department of Applied Geosciences and Geophysic, University of Leoben, Peter Tunner Str. 5, 8700 Leoben, Austria. *E–mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

2 Escuela Centroamericana de Geologia, University of Costa Rica, San Pedro de Montes de Oca, 240–2060 UCR, San Jose, Costa Rica

3 Departament de Cristallografía, Mineralogia i Dipòsits Minerals. Facultat de Geologia, Universitat de Barcelona, C/ Martí i Franquès s/n, E–08028 Barcelona, Spain

4 Department of Earth and Environmental Sciences, The George Washington University, 2029 G St. NW, Washington, D.C. 20052, U.S.A.

 

Abstract

Forty–seven grains of platinum group minerals (PGM) associated with small chromitite bodies of the Santa Elena ultramafic Nappe (Costa Rica) were mineralogically investigated with electron microscope, electron microprobe and Raman spectroscopy. The mineralogical assemblage includes sulfides of the laurite–erlichmanite series (RuS2–OsS2), irarsite (IrAsS), osmium, Ir–Rh sulfides containing relevant amounts of Ni, Fe and Cu, and a Ru–As–S compound, possibly ruarsite (RuAsS). Most platinum group element (PGE) sulfides and sulfarsenides represent primary magmatic phases entrapped in chromite at high temperatures, whereas native osmium is probably formed by subsolidus exsolution. The lack of primary PGE alloys suggests relatively high S–fugacity in the chromite forming system. This investigation emphasizes the efficiency of Raman spectroscopy in the identification of PGM of extremely small size, and shows how this technique can be used in revealing distinctive compositional differences among PGM of the laurite–erlichmanite series and irarsite.

Keywords: Platinum–group minerals, chromitite, electron microprobe, Raman spectroscopy, Costa Rica.