Mineralogy relationship between oligists and quartzes of the Aghajari Formation and Hormuz Series in the Siahoo region, Hormozgan

Aghajari Formation as the last unit of Fars Group cropps out in Hormuzgan Province with a considerable thickness. This Formtion is composed of red sandstones and green to reddish grey silty marls. According to Kalantari (1992), this formation has the age range of Middle Miocene to Pliocene. The thickness of this formation reaches to 3000m in northern Bandar Abbas (Gholamalian, 2012). The great thickness, broad expansion, slothness (with attention to the calcareaus matrix) and presence of some amounts of Iron rich minerals as grains are charactristics of this formation mineralogical composition. Also, these rocks contain polycrystalline quartz, wavy extinction quartz, fossil fragments and some minor minerals such as moscuvite, chlorite, albite, orthoclase in addition to oligiste. In order to identify the origin of the mentioned minerals; several samples are studied by microscope and Some are processed
by chemical analysis. In addition, the origin of oligiste particles in was considered; so, some samples containing this mineral were collected from Hormuz Series of Siahoo, Anguran, Zendan and Hormuz salt diapirs.

The studied area is located in 74 km North of Bandar Abbas, near the Siahoo and Aghasin villages. We should Go 64 km northward from Bandar Abbas and then 10 km eastward in order to access the studied section. The studied section is approximately 4 km before the Aghasin village. Fifty samples were collected from Aghajari Formation and Hormuz Series for
 the sake of this study; 22 of them were for chemical analysis and 20 for microscopic thin and polished sections. Three oligiste samples are collected from salt domes for comparison to the Iron rich mineral grains of Aghajari Formation. Oxidic and elemental XRF analysis of samples performed on 22 samples. In addition, point analysis of microprobe exercises are done on the rock forming grains of Aghajari Formation and Hormuz salt plug oligisites with XRF method. Thin and polished sections are studied by polarizan and reflective micoscopes.

Microscopic investigations on the thin sections of Aghajari Formation Showed the mineralogical content of rocks. Average mineralogical component of grains in this sandstones includs %45 to %50 quartz (%20 wavy extinction quartz and %25 to %30 polycrystalline quartz), less than %10 albite and orthoclase, %3 to %5 black oligiste and %30 to %35 calcareous matrix.
Quartz is the main mineral in the grains. Polycrystalline and wavy extinction quartzes can generally form in metamorphic phases. On the other hand, angular to semi-rounded quartz Grains show short distance transportation. It seems these quartz grains are originated from the Sanandaj – Sirjan metamorphic belt rocks. Weak mineralogy and grain size sorting and high thickness of Aghajari Formation show fast sedimentation and short distance transportation of grains. On the other hand, comparison of microprobe spot XRF analysis of oligiste grains shows the chemical composition similarity of this mineral in Hormuz series and Aghajari Fomation sandstones. So, these mineral grains are transported from Hormuz series salt plugs to the sedimentary environment during deposition of Aghajari Fomation in the Late Miocene to the Pliocene.

Results of XRF analysis, microprobe and microscopic investigations prove the presence of Fe2O3 as oligiste grains in the Aghajari Formation sandstones. Results of point analysis of these particles are similar to those of Hormuz series; showing the probable origin of oligiste particles in the sandstones. A large amount of quartz is present in the Aghajari Formaion sandstones that cannot be transported from salt plugs, because there are a few amounts of this mineral in the Hormuz Series.
Wavy extinction quartz grains are abundant in the Aghajari Formation sandstones and have been originated from Sanandaj - Sirjan metamorphic belt.
Presence of some mineral particles such as: albite, moscuvite, and chlorite in the Aghajari sandstones prove short distance transportation, probably from the Sanandaj - Sirjan metamorphic belt.
In fact, Aghajari sandstone particles are synchronously transported from two main sources; Sanandaj - Sirjan metamorphic rocks are the origin of quartz grains and oligiste fragments are originated from the Zagros Range salt domes.