Mineral chemistry of igneous rocks in the Lar Cu-Mo prospect, southeastern part of Iran: implications for P, T, and ƒO2

Abstract

The Lar Cu-Mo prospect is located 20 km north of Zahedan in Sistan and Baluchestan Province. This area is geologically situated in the Sistan Suture Zone. The Cu-Mo mineralization occurs as silicic veins in the Lar igneous rocks and includes hypogene chalcopyrite, bornite, and molybdenite mineralization. The syenite to monzonite host rocks occur as stock and dyke and display granular to porphyritic texture. In this study, mineral chemistry and petrographic examination of igneous rocks are used to constrain the crystallization conditions of the magma. The compositional range of plagioclase is relatively narrow (0.11%-26.05% An), whereas that of potassium feldspar is wide (11.80%-96.02% Or). Analyses of representative Lar biotite samples with electron microprobe analysis suggest that crystallization took place at average temperature of 731 °C. Amphiboles are calcic and compositionally range from pargasite to ferro-pargasite, edenite, actinolite, and magnesio-hornblende. Estimation of temperature and pressure using calcic amphibole geothermobarometry equations indicates that crystallization is estimated to have taken place at 831 °C and 7.65 kbar. Clinopyroxenes are mainly diopside and were crystallized in a magma chamber at an average temperature and pressure of 926 °C and 7.54 kbar, respectively. According to the mineral composition, the studied igneous rocks are calc-alkaline in magmatic series and were crystallized from a calc-alkaline oxidized magma. The whole-rock chemical data show that the study rocks are shoshonitic and high-K calc-alkaline.