مطالعه کانی سازی، میان بارهای سیال و شرایط رخداد کانسارهای فلوریت باقر آباد و دره بادام، جنوب شرق محلات

Introduction Fluorite ore deposits are classified into three main groups: (1) magmatic deposits, (2) structures related deposits, and (3) sedimentary deposits (Dill, 2010). More than 30 fluorite occurrences with approximately 1.35 million tons of reserves have been recognized in Iran (Miller, 2014). Bagher Abad and Darreh Badam fluorite ore deposits, located in the southeast of Delijan (Markazi province) occur between the central Iran structural zone from the north and the Sanandaj-Sirjan structural zone from the south. The geology of the area is dominated by folded and faulted structures of Jurassic carbonates and shales (Thiele et al., 1968). The main host rocks for fluorite mineralization in the studied area are the Lower-Upper Jurassic carbonates and shales of Shemshak and Badamu Formations. Materials and Methods In this study, 70 samples from the various rock types including fluorite veins, host rocks and related alterations were collected. 25 thin- and polished thin-sections were prepared and studied to explain the mineralogy and paragenetic sequence of the ore body. Eight double-polished sections were also prepared for micro-thermometric analysis. The micro-thermometric analyses were conducted on primary fluid inclusions using Linkam THM600 heating-freezing stage connected to a TMS94 temperature controller and a liquid nitrogen pump (LNP) cooling system. Results The main host rocks for fluorite mineralization in the studied area are composed of the lower Jurassic slate and phyllite (Shemshak Formation) and the Middle to Upper Jurassic dolomitic limestone and calcareous sandstone (Badamu Formation). The main alterations associated with fluorite mineralization are sericitization, silicification and argillization. According to the fluid inclusions data, fluorite mineralization in Bagher Abad and Darreh Badam deposits were precipitated because of pressure reduction of ore bearing fluids and mixing of a primary moderate-salinity brine with less saline meteoric water. Estimation of trapping pressure-temperature of the mineralizing fluid in Bagher Abad fluorite deposit using the intersecting CO2 and H2O isochors for aqueous, aqueous-carbonic and carbonic fluid inclusions indicated that fluorite mineralization occurred at 180-260°C and 1-2 kbar pressure. According to the present study, circulation and upward flow of hydrothermal fluids (containing H2O and CO2) that originated from underlying altered bedrock provided appropriate conditions for increasing the solubility of metals and formation of halide (Cl¯ and F¯) metal complexes. Reaction with wallrock and gradual decrease in temperature due to mixing and dilution of the above-mentioned fluids with low-salinity meteoric water resulted in fluorite mineralization in favorable structures such as veins. Discussion Bagher Abad and Darreh Badam fluorite ore deposits are examples of epigenetic mineralizations which are not related to igneous activities in Iran. The mineralization is formed in nearly vertical veins, which are relevant to local fractures hosted in the Lower-Upper Jurassic carbonates and shales with east-west trend. The main ore textures are open-space fillings, breccias, veins and cavities associated with sericitic, silicic and argillic alterations. Micro-thermometric measurements were carried out on primary fluid inclusions in fluorite, calcite and barite minerals from both Bagher Abad and Darreh Badam deposits. Three types of fluid inclusions were distinguished: (1) two phase aqueous fluid inclusions (LV), (2) liquid (L) or vapor (V) mono phase inclusions, and (3) aqueous-carbonic (L1+L2+V) fluid inclusions. The first ice melting temperatures (Te) of two phase aqueous inclusions (LV) in fluorite, calcite and barite from Bagher Abad and Darreh Badam deposits vary between -32 to -15°C and -35 to -24°C, respectively, which represents a H2O+NaCl±KCl multiphase fluid (Van den Kerkhof and Hein, 2001). The last ice melting temperatures (Tmice) vary between -10.5 to -2.3°C and -12.0 to -5.6°C which are equal to salinities of 5.6-14.7 and 8.3-15.2 wt% NaCl equivalent for Bagher Abad and Darreh Badam deposits, respectively. The final homogenization temperatures (Thtotal) vary between 127 to 188 °C and 176 to 270°C for Bagher Abad and Darreh Badam deposits, respectively. The CO2 melting temperatures (TmCO2) of aqueous-carbonic inclusions in fluorite, calcite and barite show a range of -58.3 to -56.6°C which suggests CH4 and/or N2 impurities (Burruss, 1981). The clathrate melting temperatures (Tmclath) ranging from -6.0 to +1.0°C represent salinities between 5.5 to 18.2 wt% NaCl equivalent for both Bagher Abad and Darreh Badam fluorite deposits. References Burruss, R.C., 1981. Analysis of phase equilibria in C–O–H–S fluid inclusions. In: L.S. Hollister and M.L. Crawford (Editors), Fluid inclusions: applications to petrology. Mineralogical Association of Canada Short Course Series, Ontario, pp. 39–74. Dill, H.G., 2010. The chessboard classification scheme of mineral deposits: mineralogy and geology from aluminum to zirconium. Earth-Science Reviews, 100(1): 1–420. Miller, M.M., 2014. Fluorspar. In: S.M. Kimball (Editor), Mineral commodity summaries 2014. U.S. Geological Survey, Reston, Virginia, pp. 56–57. Thiele, O., Alavi, M., Assefi, R., Hushmand-zadeh, A., Seyed-Emami, K. and Zahedi, M., 1968. Explanatory text of the Golpaygan quadrangle map, scale 1:250,000. Geological Survey of Iran, Geological quadrangle E7, Tehran, 24 pp. Van den Kerkhof, A.M. and Hein, U.F., 2001. Fluid inclusion petrography. Lithos, 55(1–4): 27–47.

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