THE CALCULATION OF MASS CHANGES WITHIN THE ANDESITIC ROCKS AT SAR-CHESHMEH PORPHYRY SYSTEM

4th International Scientific Conference - SGEM2004, www.sgem.org, SGEM2004 Conference Proceedings/ ISBN: 954-918181-2, June 14-18, 2004, 25- 36pp

ABSTRACT

The Sar-Cheshmeh granodioritic stock, called “Sar Cheshmeh Porphyry”, is
intruded into the Eocene andesitic rocks. This intrusion has caused potassic (biotitic)
and propylitic alteration zones in peripheral rocks. Potassic alteration zone is
overprinted by a phyllic alteration zone, which is occurred by heated meteoric waters
that affected primary alteration zones. About half of the copper mineralization in Sar-
Cheshmeh has occurred in potassically and phyllically altered andesitic rocks. In this
paper, mass change calculations and element mobility in phyllic and potassic
alteration zones within the andesitic rocks have been calculated by isocon plot
methods. The results show that Nb, Zr and Y were relatively immobile during
hydrothermal alteration episodes and their mass conserved alteration. In potassic
(biotitic) alteration zone, andesitic rocks show enrichment of K, Fe, Ca, Mn, Mg, Na
and depletion of Si, Al. Because of occurrence of chalcopyrite and some bornite, the
Cu content of the rocks is added during this alteration zone. In phyllic alteration, an
obvious enrichment of Si and addition of Fe, Mn, Ca and depletion of Al, Mg, K, Na
is caused by widespread silicification of rocks and sericitization of alkali-feldspars
and destruction of ferrromagnesian minerals.

Key words : Mass Change, Isocon Diagram, Sar-Cheshmeh