Mineralogy, geochemistry and genesis of Gozaldarreh iron deposit, southeast Zanjan

The Zanjan area hosts several iron deposits with small reserves which are currently active. This extended abstract describes the geology, mineralogy and geochemistry of the Gozaldarreh iron deposit located 44 km south of Zanjan. To further clarify the origin of Gozaldarreh mineralization, the associated Gozaldarreh granitoid intrusion and skarn were also subjected to detail petrography and geochemical studies including the granitoid type and genesis. During several field works, fifty-eight samples were collected from different rock types exposed in the area including granitoid intrusion, skarn unit and the iron ore body. Thirty-five thin, thin-polished and polished sections were prepared and studied in order to study the mineralogy, texture and paragenetic sequences. Based on the petrography and microscopy results, seen granitoid samples and eight ore samples were selected for chemical analysis. The major oxides were analysed by x-ray fluorescence (XRF) at the Geological Survey of Iran and the FeO was measured using wet chemical methods (titration). Trace elements and rare earth elements were measured by inductively coupled plasma mass spectrometry (ICP-MS) at the West Lab in Australia. The intrusion of the Gozaldarreh granitoid into the carbonaceous rocks of the Soltaniyeh and Barout Formations generated a contact methamorphism with a skarn developed and iron-oxide mineralization in the Gozaldarreh area. The Gozaldarreh granitoid is an I-type granite to grano-diorite and quartz-monzonite. The geochemistry of the Gozaldarreh granitoid suggests that this intrusion belongs to high-K calc-alkaline and shoshonite series of the volcanic arc of an active continental margin. The serisitic, argillic, silica-carbonate and chloritic alterations are the major alterations affected by the Gozaldarreh granitoid.
The garnet, clinopyroxene and wollastonite are the major minerals generated in the prograde skarn phase in the iron oxide mineralization area. The major iron-oxide mineralization stage has happened during the retrograde skarn phase along with epidote, tremolite-actinolite, chlorite, serpentine, talc, calcite and quartz. The iron-oxide mineralization is generally in the form of high grade irregular lenses and veins of magnetite with minor hematite, pyrite and chalcopyrite. A small volume of magnetite has also been deposited during the prograde skarn phase.
The evidences show that the Gozaldarreh ore mineralization took place in three stages: (1) intrusion of the Gozaldarreh granitoid and contact methamorphism of the carbonate host rocks and generating a marble with granoblastic texture and Ca-Mg silicates. The paragenetic sequence at this stage is garnet-wollastonite- calcite for carbonate rocks and garnet-clinopyroxene-calcite for dolomitic rocks, (2) metasomatism and replacement phase which created Ca-Mg silicates and minor magnetite as part of a prograde skarn phase, (3) the Gozaldarreh granitoid cooling stage and generation of the hydrothermal-magmatic system. This retrograde skarn phase has generated the main magnetite ore along with epidote, chlorite, tremolite-actinolite, serpentine, talc, calcite and quartz. The poor Ca-silicates, Fe-oxides, Fe-sulfides and carbonates were also generated as final stages of this retrograde phase. The later reactions and weathering affected these primary mineral assemblages and created the secondary minerals such as hematite, goethite, limonite, malachite and azurite. As a result of the intrusion of the Gozaldarreh granitoid into the carbonates of Soltanieh (PЄ-Єs) and Barout Formations (Єb), a skarn unit has developed at the contact metamorphic zone. The petrography of the Gozaldarreh granitoid shows a granular to micro-granular texture with alkali feldspar, plagioclase, quartz and biotite as major rock forming minerals and amphibole, zircon and sphene as accessory minerals. Epidot, calcite and chlorite are also present as secondary minerals. The sericitic, argilic, silica-carbonate and chlorite assembleges are presenting the major alterations of the Gozaldarreh granitoid. The analyses of the granitoid samples classify the intrusion as an I-type granite to grano-diorite and quartz-monzonite. The Y-Nb and (Nb+Y)-Rb plots (Pearce et al., 1984) suggest that the Gozaldarreh granitoid is part of the volcanic arc granitic intrusions. The Th-Co plot (Hastie et al., 2007) is placing Gozaldarreh granitoid in the high-K calc-alkaline and Shoshonite series.
The comprehensive field work shows that the iron mineralization in the Gozaldarreh area is spatially associated with the granitoid skarn zone. The exoskarn is well developed in the region and is the major host for Fe-mineralization. The endoskarn which is mainly exposed at the vicinity of the granitoid, is less developed and consists of clinopyroxene, epidote, chlorite, calcite and garnet. The clinopyroxene and garnet are recognized as prograde and epidote, chlorite and calcite are retrograde minerals. The exoskarn mainly consists of retrograde minerals such as epidote, chlorite, tremolite-actinolite, serpentine, talc, calcite, chrysotile and quartz. These retrograde minerals are mainly replaced the residue of prograde minerals such as clinopyroxene, garnet and wollastonite. The other major skarn-related phenomena in the area are the carbonate rocks recrystalization and pyrite-chalcopyrite-iron-oxide mineralization.
The Gozaldarreh iron ore exhibits different forms including massive, vein-type and disseminated iron-oxide mineralization. The ore bodies are mainly located in the exoskarn. Magnetite is the most abundant ore mineral followed by hematite, pyrite, chalcopyrite, limonite, malachite and azurite as minor minerals. The major gangue minerals are calcite, quartz, epidote, serpentine and chlorite.
The magnetite chemistry plot in the Ni/(Cr+Mn) vs Ti+V and Ca+Al+Mn vs. Ti+V diagrams (Dupuis and Beaudoin, 2011) showing the skarn origin for the Gozalarreh deposit. The TiO2-V2O5 diagram plot (Hou et al., 2011) for these samples also points to the skarn and hydrothermal origin.