Mineralogical and geochemical studies on borate deposits from the Shahr- e - Babak playa (Khatoonabad and Robat - Marvast), Kerman province - Iran)

IntroductionBorate deposits are often important constituents of economic non - marine evaporates. They produce under arid climatic conditions in playa lakes (Floyd et al., 1998). In the south – western parts of the Kerman province, such as the Khatoonabad area (east of the city of Shahr –e –Babak) and Robat – Marvast basin (west of Shahr – e – Babak), there are several borate deposits. They can be seen mainly in Sanandaj – Sirjan depressions and they occur as borate bearing nodules beneath a thin layer of soil. In general, boron considerably reduces the thermal expansion of glass, provides good resistance to vibration, high temperatures and thermal shock, and improves its toughness, strength, chemical resistance and durability. It also greatly reduces the viscosity of the glass melt. These features, and others, allow it to form superior glass for many industrial and specialty applications (Garrett, 1998). In the past, the ancient residents used them as co-melting matters. Ulexite which is frequently found in the Khatoonabad playa (at 30 km South East of Shahr Babak) have Jewel properties (Ghaedi et al., 2014).
Materials and methodsAfter reviewing and Library Studies, geological field studies on the borate deposits were carried out from Shahr – e – Babak Playa. In order to take better samples, several pits were excavated with a depth of 30 cm to 1 meter so that borate minerals became apparent. X-ray diffraction analysis (IMIDRO, Karaj), and ICP AES (ALS CHEMEX, Canada) methods were carried out on representative samples taken from the studied area.
DiscussionField observations show that in the studied areas, borate bearing basins are fed by rivers which have originated from Sanandaj – Sirjan metamorphic rocks, Nain – Baft colored mélanges and igneous rocks of Urumieh – Dokhtar magmatic belt. Borate minerals also occur in fibrous aggregates and massive forms.
MineralogyXRD results show that the studied borate minerals mainly belong to the hydrated borates and contain ulexite, borax, gowerite, sassolite and inyoite. Geochemichal data indicate that the boron is the dominant constituent in the studied playa. Borate minerals are divided into two groups of hydrated and non-hydrated borate category (Palache et al., 1952.; Garrett, 1998). Both hydrated and non-hydrated borate minerals have been formed in the Shahr-e-Babak playa.
Hydrated borate in the study areas:Hydrated borates are those borates in which water molecules are involved (Garrett, 1998). In the studied area, the hydrated borate minerals include: Borax, Ulexite, Inyoite, Gowerite.
Non-hydrated borate in the study areas:In the Shahr-e-Babak playa, Sassolite non-hydrated borate minerals are abundant.
According to the XRD analyses performed on samples from the study areas, the hydrated borate minerals are more important minerals. The main economic valuable minerals include:1- Ulexite (NaCaB5O9.8H2O): Crystal Data: Triclinic. Point Group: 1 (Ghose et al., 1978). In the Shar – e - Babak playa, ulexite occurs as deposits with massive, cauliflower-like nodules and fibrous textures.
2- Borax (Na2B4O5(OH)4 •8H2O): Crystal Data: Monoclinic. Point Group: 2/m. Crystals are commonly short to long prismatic [001] (Levy and Lisensky, 1978). In the studied borate samples, it can be found in association with the other borate minerals, and often occurs in the form of salt marsh.
3- Gowerite (CaB6O8(OH)4 •3H2O): Crystal Data: Monoclinic. Point Group: 2/m (Erd et al., 1959). In the Khatoonabad samples, it was found as prismatic and spherical crystals along with ulexite.
4- Inyoite (CaB3O3 (OH)5 •4H2O): Crystal Data: Monoclinic. Point Group: 2/m (Christ, 1953). This mineral has been detected in the studied area by XRD.
Sassolite (H3BO3): Crystal Data: Triclinic. Point Group: 1 and as scaly pseudohexagonal crystals (Allen and Kramer, 1957). This mineral is found frequently in the Marvast Playa.
GeochemistryGeochemical data indicate that in the studied playa, boron is very abundant. Good correlation between the elements, such as B and Ca confirms the formation of Calcium bearing borate mineral in the studied areas.
OriginField observations show that in the studied areas, borate bearing basins are fed by rivers which have originated from the Sanandaj – Sirjan metamorphic rocks, Nain – Baft colored mélanges and igneous rocks of the Urumieh – Dokhtar magmatic belt.
ResultThe XRD results show that the studied borate minerals mainly are hydrated ones and contain ulexite, borax, gowerite, sassolite and inyoite. Geochemichal data confirm the frequency of boron in the playa. Good correlation between the elements such as B and Ca verifies the formation of Calcium bearing borate mineral in the studied areas.
AcknowledgementsThe authors wish to thank IMIDRO for performing XRD analyses.