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Compositional zoning in Zn-chromites from the Cordillera Frontal Range, Argentina

Published online by Cambridge University Press:  05 July 2018

Ernesto A. Bjerg ,
Milka K. De Brodtkorb  and
Eugen F. Stumpfl
Ernesto A. Bjerg
Affiliation:
Institute of Geological Sciences, Mining University, 8700 Leoben, Austria Universidad Nacional del Sur, Dpto. de Geologia-CONICET, 8000 Bahia Blanca, Argentina
Milka K. De Brodtkorb
Affiliation:
CONICET, Paso 258-9 A, 1640 Martinez, Argentina
Eugen F. Stumpfl
Affiliation:
Institute of Geological Sciences, Mining University, 8700 Leoben, Austria
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Abstract

Serpentinised ultramafic bodies containing zoned chromite grains occur in the Cordillera Frontal Range, western Argentina. Chromites show Zn-rich Al-chromite cores (4.04 wt.% ZnO) surrounded by ferritchromite rims (1.3 wt.% ZnO) and outer Cr-magnetite rims. In intensely altered chromites which are spatially related to sulphide mineralisation, the primary chromite cores have been replaced by Zn-rich ferritchromit (7 wt.% ZnO) and they are rimmed by Cr-magnetite. In the Al-chromites the mean [Cr/(Cr + Al] ratio is 0.53 and the [Mg/(Mg + Fe)] ratio is 0.53; they plot in the field of Alpinetype intrusions. Ferritchromit has a mean [Cr/(Cr + Al)] ratio of 0.93 and [Mg/(Mg + Fe)] ratio of 0.4. In Cr-magnetites the mean [Cr/(Cr + Al) is 0.98 and the [Mg/(Mg + Fe)] ratio is 0. Ferritchromit is always surrounded by a Cr-magnetite rim and it was formed as a reaction product owing to the irreversible dissolution of primary chromite cores. The dissolution of these cores provided the essential components for ferritchromit growth. Zn was introduced into the chromite cores and ferritchromit rims during the formation of the latter. Step-scan profiles have shown that the Zn content in the cores increases from the centre to their outer border, where they show the highest Zn values. It is suggested that Zn was introduced by the fluid phase involved in the alteration process that affected the cores and lead to the formation of the zoned chromite grains. This alteration process was also responsible for the changes in [Cr/(Cr + Al)] and [Mg/(Mg + Fe)] ratios.

Keywords

chromitezoningferritchromitCordillera Frontal RangeArgentina
Type
Mineralogy
Information
Mineralogical Magazine , Volume 57 , Issue 386 , March 1993 , pp. 131 - 139
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1993

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References

Bevan, J. C. and Mallinson, L. G. (1980) Zincand manganese-bearing chromites and associated grossu-lar from Zimbabwe. Mineral. Mag., 43, 811–14.Google Scholar
Bjerge, E. A. (1984) Identificación de las fases monoclf-nica y hexagonal de la pirrotina de mina Salamanca. Su posible uso como geoterm6metro. IX Cong. Geol. Arg., 3, 269–74.Google Scholar
Bjerge, E. A. Gregori, D. A., Losada Calderón, A., and Labudfa, C. H. (1990) Las metamorfitas del Faldeo Oriental de la Cuchilla de Guarguaraz, Cordillera Frontal, provincia de Mendoza, Rev. Assoc. Geol. Arg. (in press).Google Scholar
Bliss, N. W. and MacLean, W. H. (1975) The paragenesis of zoned chromite from central Manitoba. Geo- chim. Cosmochim. Acta, 39, 973–90.Google Scholar
Brodtkorb, M. K. de (1970) La cobalto-pentlandita del yacimiento Salamanca, prov. de Mendoza, Rep. Argentina. Rev. Asoc. Geol. Arg., 25, 307–10.Google Scholar
Brodtkorb, M. K. de (1971) El Yacimiento Salamanca, ejemplo de dep6sito ‘hidrotermal’ de Cu-Ni. I. Cong. Hisp. Luso Am. Geol. Econ., 1001-11.Google Scholar
Droop, G. T. R. (1987) A general equation for estimating Fe3+ concentrations in ferromagnesian silicates and oxides from microprobe analysis, using stoichiometric criteria. Mineral. Mag., 51, 431–5.Google Scholar
Evans, B. W. and Frost, B. R. (1975) Chrome-spinel in progressive metamorphism—a preliminary analysis. Geochim. Cosmochim. Acta, 39, 959–72.Google Scholar
Groves, D. I., Barret, F. M., Binns, R. A., and McQueen, K. G. (1977) Spinel Phases Associated with Metamorphosed Volcanic-Type Iron-Nickel Sul-fide Ores from Western Australia. Econ. Geol., 72, 1224–44.Google Scholar
Groves, D. I., Barret, F. M., Binns, R. A., and McQueen, K. G. and Brotherton, R. H. (1983) Exploration significance of chrome-spinels in mineralised ultra-mafic rocks and nickel-copper ores. Spec. Publ. Geol. Soc. S. Aft., 7, 21–30.Google Scholar
Haller, M. J. and Ramos, V. A. (1984) Las ofiolitas famatinianas (Eopaleozoico) de las provincias de San Juan y Mcndoza. IX Cong. Geol. Arg., 2, 66–83.Google Scholar
Mogessie, A., Purtscheller, F., and Tessadri, R. (1988) Chromite and chrome spinel occurrences from meta-carbonates of the Oetztal-Stubai Complex (northern Tyrol, Austria). Mineral. Mag., 52, 229–36.Google Scholar
Moore, A. C. (1977) Zinc-bearing chromite (donathite?) from Norway: A second look. Ibid., 41, 351-5.Google Scholar
Polansky, J. (1972) Descripción geol6gica de la Hoja 24 a-b, Cerro Tupungato, provincia de Mendoza. Bol. Dir. Nac. Geol. Min., 128, 1–110.Google Scholar
Thayer, T. P., Milton, C., Dinnin, J., and Rose, H. (1964) Zincian chromite from Outokumpu, Finland. Am. Mineral., 49, 1178–83.Google Scholar
Villar, L. M. (1985) Las fajas ultrabásicas argentinas, tipos de ultramáificas. Metalogenia. IV Cong. Geol. Chil, 4, 610–33.Google Scholar
Villar, L. M. and Donnari, E. I. (1989) Asociaci6n peridotitagabro estratificado de la secci6n septentrional de la faja ultramáifica de la Cordillera Frontal de Mendoza. Reun. Geotrans. Am. Sur., 1, 45–9.Google Scholar
Weiser, T. (1967) Zinkund Vanadium-fiihrende Chromite von Outokumpu, Finnland. Neues Jahrb. Mineral., Mh., 234-43.Google Scholar
Wicks, F. J. and Whittaker, E. J. W. (1977) Serpentine textures and serpentinisation. Can. Mineral., 15, 459–88.Google Scholar
Wicks, F. J. and Whittaker, E. J. W. and Zussman, J. (1977) An idealised model for serpentine textures after olivine. 15, 446-58.Google Scholar
Wylie, A. G., Candela, P. A. and Burke, T. M. (1987) Compositional zoning in unusual Zn-rich chromite from the Sykesville district of Maryland and its bearing on the origin of ‘ferritchromit'. Am. Mineral., 72, 413–22.Google Scholar