The main aim of this paper is the recognition of type of copper mineralization in Rashtabad and Mesboulaghi ore deposits with regard to Hashjin area metallogeny in west Alborz-Azarbayjan.
These mines are situated in north Zanjan and within the Eocene volcanosedimentary complex (Karaj Formation). Green tuff, crystal tuff, lithic tuff, sandy tuff, latite andesite and basaltic andesite lava are important members of this complex. Quartz monzonite intrusives (probably Oligo-Miocene) are seen in this area and in view of the intense hydrothermal alteration observed, probably the mineralization is related to this intrusives.
The form of mineralization in both area is vein and veinlet and major mineral in Rashtabad is chalcopyrite and in Mesboulaghi is chalcopyrite and bornite. Major gangue at Rashtabad is quartz and calcite and in Mesboulaghi it is quartz.
70 doubly polished thin sections were prepared from quartz and calcite. On the basis of petrographic evidence, there are four types of fluid inclusion in this area. Type I: with moderate salinity and rich in liquid. Type II: rich in gas and low density. Type III: rich in salt and Type IV: saline with low density. Out of 136 fluid inclusions in Rashtabad and Mesboulaghi, 86 cases belong to type 1, 8 cases belong to type II, 3 cases belong to type III and 12 cases belong to type V. Mesboulaghi samples show inclusions ranging form 80-140 μm length. The average length of inclusions in Mesboulaghi mine is 41.4 μm and in Rashtabad mine is 33.4 μm. The daughter phases in these fluid inclusions are halite, sylvite, anhydrite and opaque minerals.
On the basis of thermometry study, the thermal range of fluid inclusions homogenization in Mesboulaghi is from 162 to 434° C and in Rashtabad mine is from 272 to 485° C. Higher thermal limit in Rashtabad mine is related to smaller distance from the center of mineralization phase in this area. The major phase of copper mineralization at Mesboulaghi is between 300 to 330°C and in the Rashtabad mine is between 280 to 340° C. Another phase of copper mineralization (weak and with iron mineralization) took place in Mesboulaghi with thermal range of 360 to 390 ° C and in Rashtabad with thermal range of 400 to 430 °C, Mineralographic study reveals three phase of chalcopyrite mineralization in this area. The first phase of mineralization from 450 to 490 C and probably tiny chalcopyrite in matrix of mineralization belongs to this phase. It is possible that traces of gold belong to this warm phase. On the basis of this evidence we can say that this mineralization was mesothermal and occasionally hypothermal.
Freezing study confirms that the maximum salinity of fluid inclusions in Mesboulaghi is 14eq. wt% NaCl and in Rashtabad almost 19eq. wt% NaCl. The salinity of major copper bearing fluid in this area is between 8 to 13eq. wt% NaCl. The Salinity of hot phase (450 to 490 °C) is between 17 to 19eq. wt% NaCl. This phase must be regarded as a target for future study of porphyry copper and gold mineralization.