Abstract
The Qozlou Fe skarn deposit is located at the Abhar–Mahneshan belt of the Central Iranian Zone. It is associated with Upper Eocene porphyritic granite that intruded into the Upper Cretaceous impure carbonaceous rocks. The Qozlou granite has high-K calc-alkaline affinity and is classified as subduction-related metaluminous I-type granitoids. Skarn aureole in the Qozlou is composed of endoskarn and exoskarn zones, with the exoskarn zone being the main skarn and mineralized zone. It includes garnet skarn, garnet-pyroxene skarn, pyroxene skarn, epidote skarn, and pyroxene-bearing marble sub-zones. The Qozlou Fe deposit is 300 m long and 5–30 m wide. Magnetite is the main ore mineral associated to pyrite, chalcopyrite, and pyrrhotite. Garnet, clinopyroxene, actinolite, epidote, calcite, and quartz occur as gangue minerals. Covellite, hematite, and goethite were formed during the supergene processes. The ore and gangue minerals have massive, banded, disseminated, brecciated, vein–veinlets, replacement, and relict textures. EPMA data indicate that garnets have andradite–grossularite compositions (Ad39.97–100–Gr0–49.62) and clinopyroxenes have diopsidic composition (En29.43–42.5–Fs14.31–20.99–Wo43.08–50.17). Based on mineralogical and textural criteria, skarnification processes in the Qozlou skarn can be categorized into three discrete stages: (1) isochemical (metamorphic–bimetasomatic), (2) metasomatic prograde, and (3) metasomatic retrograde. Anhydrous calc-silicate minerals (garnet and clinopyroxene) were formed during the prograde metasomatic stage, while ore minerals and hydrous calc-silicate minerals were formed during the retrograde ore-forming sub-stage. Temperature and ƒO2 conditions range between 430 and 550 °C and 10−26 and 10−23, respectively, for the metasomatic prograde stage. The retrograde metasomatizing fluids had likely ƒS2 = 10−6.5 and temperatures < 430 °C at the beginning of the ore-forming sub-stage.
Highlights
Skarn deposits are one of the more abundant ore types in the earth’s crust and formed in rocks of almost all ages (Einaudi et al 1981; Meinert et al 2005)
Fe skarn deposits in Iran were formed mainly during the Cenozoic (Nabatian et al 2017). These deposits are mainly located in the Alborz–Azarbaijan magmatic belt (AAMB), Urumieh–Dokhtar magmatic arc (UDMA), Sanandaj–Sirjan zone (SSZ), and Central Iranian zone (CIZ)
We present the first petrographic study of skarn zones, mineral chemistry, and formation condition of calc-silicate minerals from the Qozlou deposit
Summary
Skarn deposits are one of the more abundant ore types in the earth’s crust and formed in rocks of almost all ages (Einaudi et al 1981; Meinert et al 2005). Upper Cretaceous rocks are covered unconformably by Lower Oligocene red-colored, coarse-grained detrital deposits of the Lower Red Formation (LRF) (Lotfi 2001), which crop out in the northern part of the Qozlou Fe deposit (Fig. 2) They are composed of conglomerate at the base and alternation of red–brown sandstone, marl, and shale with about 800 m thickness. The Qozlou granitoid intruded into the Upper Cretaceous rocks and was covered unconformably by rock units of the LRF (Lotfi 2001; Shafaiepour et al in press) This intrusion led to the contact metamorphism and formation of the Qozlou Fe skarn deposit. The garnet–pyroxene skarn sub-zone is located near the contact of intrusion It contains clinopyroxene, garnet, actinolite, calcite, epidote, quartz, titanite, and opaque minerals. Chemical formulae and end-member proportions for the mineral analyses were calculated after Deer et al (1992) for pyroxenes, and Fe+3 was calculated based on ideal stoichiometric composition
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