Is skarnization the cause of mineralization? a case study, Sanandaj Sirjan zone, west Iran

Abstract

The skarn type mineralization has long been accepted as an interaction of magma and the host carbonate rocks. Most researchers have considered the iron deposits in the northern Sanandaj Sirjan zone (Kurdistan area) as skarn-type mineralization which has been generated during the injection of the granitoid bodies into the host carbonate. The calculation of normative minerals from the mixed composition of granite and host dolomite shows that normal reactions cannot produce a large volume of Fe or Mn mineralization in northwest Iran as skarn deposits. One of the iron deposits which is known as the Saheb skarn deposit, 33 km east of Saqqez, NW Iran was selected for this study. The normative minerals from this deposit were calculated for a mixed composition based on 100 grams of Saheb granite and 50 grams of host dolomite. The results show the iron oxides don't extend into the last stages of magma crystallization to provide the Fe-Mn mineralization in the host rocks. Occasionally, in the contacts of plutons, various types of mineralization appear, however, they are not the result of a magma and carbonate interaction. They are probably the results of the hydrothermal fluids in the late stages of magma crystallization. The magma fluids and fossil water in the host rocks that were heated during the magma injection, leaching the Fe-Mn from the granitoid bodies and surrounding rocks. As follows, Fe-Mn-rich fluids move towards fractures and caves, finally precipitating as ore deposits into the host rocks. The skarnization phenomenon causes the reduction of volume due to the release of CO2 gas and also the crystallization of relatively dense minerals such as garnet. This process, make a partiality space for the precipitation of Fe-Mn-rich hydrothermal fluids. Our findings show that skarnization only makes space for the precipitation of the Fe from the hydrothermal fluids.