Document Type : Original Research Paper
Authors
1 Ph.D. Student, Department of Geology, Ferdowsi University of Mashhad, Mashhad, Iran
2 Associate Professor, Department of Geology, Ferdowsi University of Mashhad, Mashhad, Iran
3 - Associate Professor, Department of Economic Geology, Tarbiat Modares University, Tehran, Iran
Abstract
The Senjedak-I prospect area is one of the six eastern anomalies of Sangan iron mine. Geologic units in the area consist of Jurassic shales and sandstones, skarn rocks and Tertiary biotite monzonite and biotite syenogranite intrusive rocks. Due to the severe alteration of biotite monzonite porphyry intrusive, geochemical studies have focused on the biotite syenogranite.
This granular intrusive consists of alkali feldspar, plagioclase, quartz, biotite and accessory minerals such as zircon, sphene, apatite and magnetite, with weak sericitic, argillic and silicic alteration. Biotite syenogranite rock is rich in silica (68.7 to 77.2 wt.%) and is chemically peraluminous and has generated by fractional crystallization from an I-type granitic magma poor in P (average 0.1% P2O5). This intrusive rock falls in the range of I-type granites and is oxidized. REE values indicate negative Eu anomaly, mild enrichment of LREE, a positive pattern close to flat HREE, negative anomalies of Ba, Sr, La, Ce, Ti, and Eu. On the basis of Rb, Nb, Yb, Hf, and Ta, tectonic setting of samples fall in Volcanic Arc Granite (VAG) and Post Collision Granite (post-COLG) divisions.
The most important event in Senjedak-I area is the penetration of Fe-bearing fluids in carbonate rocks, their recrystallization, skarnification (prograde and retrograde), and iron ore deposition that could be explained by the occurrence of calc-silicate minerals.
The skarn has been separated into 4 zones on the basis of abundance of the calc-silicates: garnet skarn, phlogopite skarn, epidote skarn, and amphibole skarn.
According to Electron Probe Micro Analysis (EPMA), the composition of garnets is andradite-grossular (An 100-42.6 Gr 0-55.32 Sps 0-1.39) and pyroxenes are diopside-hedenbergite (Di 63-92 Hd 4-35 Jo 0.5-3.9).
Mineralization in this prospect area formed as stratabound and massive bodies in the carbonate rocks. The main ore mineral is magnetite (40%) with minor amounts of pyrite. Secondary minerals are hematite and malachite. The FeO in the magnetite is 91.7% and the S content is 0.03%. The Senjedak-I anomaly places along the eastern part of Dardvay deposit (in central division of Sangan mine) and the geochemical similarities of intrusive rocks, chemistry of skarn minerals, and pyroxene and garnet composition confirms that the Senjedak-I is a part of Dardvay, which is separated by a main fault with southeast-northwest trend.
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