Journal of Economic Geology (Jul 2017)
Chemical Compositions of Fluid Inclusions in the Jalal –Abad iron oxide deposit, North West of Zarand, Using LA-ICP-MS Microanalysis
Introduction The Poshtebadam Bafq Zarand district in central Iran is a world class iron oxide province. This region contains over two billion tons of iron ore reserves within more than 34 major magnetic anomalies and deposits in an area of 7,500 km2 (Stosch et al., 2011). The Jalal-Abad iron ore deposit (200Mt at 45% Fe, 1.18% S and 0.08% P) is located 38 km northwest of Zarand, 16 km southeast of the Rizu town in the Kerman province, Iran. Iron ore deposits are hosted by the Early Cambrian Rizu Series, composed mainly of sedimentary, volcanic and volcaniclastic rocks which are dominated by dolomite, sandstone, shale, siltstone, tuff, ignimbrite and rhyodacite. The origin of the iron oxide deposits is controversial and various genetic models have been suggested. Some researchers believe in magmatic origins or Kiruna type, while others suggest metasomatic replacement from pre-existing rocks (Stosch et al., 2011). LA-ICP-MS has been used to characterize the multi element chemistry of the diverse fluid inclusions found in the Jalal–Abad iron oxide deposit. The aim of this investigation was to understand the genesis of the ore body and identify possible hydrothermal fluid sources in the Jalal-Abad district. Sampling and method of study About 100 samples from different types of ore were collected from surface outcrops and a drill core whose association with mineralization are well established. Thin sections, polished thin sections and polished sections were prepared. SEM studies (FEI 5900LV) and LA-ICP-MS analyses of fluid inclusions were carried out in the School of Earth and Environment, the University of Leeds, UK. Fluid inclusions were studied using a Linkam THM-600 heating-freezing stage mounted on Zeiss petrography microscope at the Iranian Mineral Processing Research Center. Result and discussion Jalal Abad deposit is hosted by the early Cambrian volcano-sedimentary rocks of the Rizu series. Stratabound mineralization occurs in a variety of forms being massive, disseminated, replacement, open space filling, veins and breccias. Immediate host rocks include sandy siltstone, acidic volcanic rocks and dolomite. The Jalal Abad deposit mainly consists of iron oxides (magnetite, hematite and goethite), pyrite, chalcopyrite, and malachite that occur in massive, brecciated, open space filling, disseminated and vein forms. Hematite mostly occurs close to the surface and along fractured zones, formed as a secondary mineral due to magnetite oxidation and it is rare at depth. Pyrite is the most important sulphide mineral and is associated with magnetite, calcite, quartz, talc, dolomite, actinolite and chlorite. Copper mineralization at shallow levels is mainly in oxides formed from sulphide oxidation and at deeper levels primary chalcopyrite is also associated with magnetite. Cu mineralization is formed as disseminated or in veins form. Native gold was detected as inclusions smaller than 50 µm in chalcopyrite. Common alteration minerals are goethite, pyrite, talc, actinolite, chlorite, tremolite, dolomite, quartz, calcite, albite and sericite. The earliest hydrothermal alteration includes Na-Ca alteration which is associated with actinolite, magnetite and pyrite. Multiphase fluid inclusions (L+V+S) in quartz are abundant and homogenization temperatures are in the range of 260 to 440◦C. Salinities vary between 30 to 52 wt% NaCl equivalents. The concentrations of Na and K are in the range 26906 to 140716 ppm and 2372 to 70484 ppm, respectively. Fe content varies from 576 to16076 ppm with an average of 6914 ppm and Cu contents vary from 51 to 3204 ppm with a mean of 792 ppm. The Na/Ca values for fluid inclusions vary from 0.38 to 37.51 with a mean of 3.79. The average content of Na is 61511 ppm which is in agreement with salinity of fluid inclusions measured by microthermometry techniques. Magmatic fluids normally yield K > Ca, with Ca/K ratios between 0.01 to 1, whereas non magmatic fluids are often richer in Ca with Ca/K between 1 to 100 (Yardley, 2005). The amounts of Fe and Cu in magmatic fluids are commonly above 10000 and 1000 ppm, respectively. However, it depends on chlorinity (Fisher and Kendrick, 2008; Gillen, 2010; Appold and Wenz, 2011). Mn concentrations are 424 to 3645 ppm, with an average concentration of 7581 ppm. Mn/Fe ratio is varied from 0.21 to 1.87 with an average of 0.60.The wide range of homogenization temperature (170 -450 °C) and salinity (31- 52 wt % NaCl equiv) of the fluid inclusions and ratios of K/Ca in fluid inclusions indicate different fluid sources with magmatic and basinal type fluids (Yardley, 2005). Mn/Fe ratios in fluid inclusions are in wide ranges (0.21 -1.87) which indicate the presence of both reduced type and oxidized type fluids (Fisher and Kendrick, 2008). Results In addition to iron oxide, economical Cu mineralization occurs in the Jalal Abad deposit with Au, Bi and As mineralzation with insignificant apatite. The K, Fe, Ca, Na and Cu concentrations in fluid inclusions are most probably related to the mixing of magmatic and basinal fluids. The mineralogical, microthermometry and chemistry of fluid inclusions data show that magmatic-hydrothermal metal bearing fluids, nonmagmatic hydrothermal fluids and mixing of them are responsible for iron-Cu-Au mineralization (IOCG) in the Jalal- Abad deposit. References Appold, M.S. and Wenz, Z.J., 2011. Composition of Ore Fluid Inclusions from the Viburnum Trend, Southeast Missouri District, United States: Implications for Transport and Precipitation Mechanisms. Economic Geology, 106(1): 55-78. Fisher, L.A. and Kendrick, M.A., 2008. 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