Hydrothermal garnet in porphyry copper related skarn deposits, Ali-Abad, Yazd Province, Iran

Document Type: Regular Paper


1 Department of Earth Sciences, Faculty of Sciences, Shiraz University, Shiraz, Iran

2 Department of Geology, Faculty of Sciences, University of Isfahan, Isfahan, Iran

3 Department of Geology, Faculty of Sciences, Tehran University, Tehran, Iran


The Ali-Abad porphyry copper deposit is located in the Central Iranian magmatic belt. As a result of subduction
magmatism, Oligo-Miocene leucogranitoid rocks have intruded into conglomerates of lower Cretaceous age. Due
to contact metamorphism the following mineral assemblage has occurred in the altered conglomerate: Garnet
(andradite-grossular) + epidote+ quartz + calcite + pyrite Skarnification have only occurred in reactive carbonate
clasts of the conglomerates. Chemical composition of garnets and classic discrimination scheme imply the
porphyry copper related skarn-type mineralization. Garnets are characterized by abrupt chemical zoning area and
thin bands. REE pattern of skarn garnet and host granite have similar trends, so it is concluded that garnets are
hydrothermal in origin. The garnet mineralization episode occurred during skarnification, giving hydrothermal
fluid temperatures of 422-472 ºC, likely this episode corresponds to the fluid boiling and high
of garnet
forming processes in the skarn system. Probably, the temporal decrease of hydrothermal fluid pressure led to rapid
growths of andradite zones i.e., extensive hydrofracturing, porosity of conglomerate could be the dominant
conditions which led to boiling of hydrothermal fluids and precipitation of andradite garnet.