Writers : Zamanian.H , Yousefi Yeganeh.B ، Alavi.S. A
Refference : Geosciences Scientific Quarterly Journal,No.:62,P.:203
Publishing Year : 1385

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 `rn of elements across the Baba Ali skarn zones is governed by the distribution pattern of the prograde and retrograde min. assemblages. The presence of andradite, salite, actinolite, epidote, sphene and idocrase as the calc-silicate minerals, and absence of minerals like tremolite, forsterite, phlogopite, talc, and humite and also minerals of manganoan skarns in thes! irn zoning allow the grouping of the Baba Ali skarn deposit as a calcic Fe-skarn deposit. The EPMa compositions of pyroxcene and garnet also are consistent with the Fe skarn deposits. The average S content in the Baba Ali ore body is < 1.5 %. The v 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 A. karn. EPMa analysis of magnetite from the Baba Ali deposit show a rather pure magnetite phase, devoid of impurities such Mg, Mn, Zn, Ni, Ti, V. and Cr. The absence of these impurities indicates a low temperature for formation of magnet 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 -550° 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 of350 -400°C.
Subject List : Skarn