Scientific Quarterly Journal of Geosciences

Scientific Quarterly Journal of Geosciences

Mineralogical and Geochemical Skarn Zoning across the Baba Ali Deposit and its Economic Geology Applications, Western Iran

Document Type : Original Research Paper

Authors
Hassan Zamanian 1
Bijan Yousefi Yeganeh 1
Seyed Aref Alavi 2
1 Department of Geology, Lorestan University, Khoram Abad, Iran
2 Azad Islamic University of Khoram Abad, Iran
Abstract
In the Baba Ali magnetite skarn deposit, the main load of magnetite ore body lies between the dioritic and quartz syenitic rocks of the batholith hosted mainly by meta-dioritic rocks. Petrographically from SE towards NW, eight zones with distinct mineral assemblage can be recognized. The geochemical distribution pattern of elements across the Baba Ali skarn zones is governed by the distribution pattern of the prograde and retrograde mineral assemblages. The presence of andradite, salite, actinolite, epidote, sphene and idocrase as the calc-silicate minerals, and the absence of minerals like tremolite, forsterite, phlogopite, talc, and humite  and also  minerals of manganoan skarns  in these skarn zoning allow the grouping of the Baba Ali skarn deposit as a calcic Fe-skarn deposit. The EPMa compositions of pyroxene and garnet also are consistent with the Fe-skarn deposits. The average S content in the Baba Ali ore body is < 1.5 %. The low content of sulfide in the Baba Ali allots Island Arc type calcic Fe skarn characteristics to this deposit. The high ratio of exsoskarn by endoskarn (Extensive exsoskarn facies) indicates a shallow depth” hypabyssal “(< 5 km) for formation of the Baba Ali skarn. EPMa analysis of magnetite from the Baba Ali deposit show a rather pure magnetite phase, devoid of impurities such as Mg, Mn, Zn, Ni, Ti, V, and Cr. The absence of these impurities indicates a low temperature for formation of magnetite. Replacement of the hydrothermal (retrograde) minerals by magnetite also shows a low temperature within the  green schist  facies conditions for magnetite mineralisation. Replacement of the prograde assemblage i.e. garnet and pyroxene which formed in the 500 –550º C range by hydrothermal minerals along with magnetite indicates that magnetite mineralisation occurred at relatively lower temperature. The inferred  temperature of Fe mineralisation at the Baba Ali deposit is  in the range of 350 –400o C.
Keywords
Magnetite
Baba Ali
Skarn
Island arc
West of Iran

Subjects

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Scientific Quarterly Journal of Geosciences
Volume 16, Issue 62
Winter 2007, vol. 16, no. 62
Winter 2007
Pages 194-203