Journal of Economic Geology (Apr 2015)
Geology, mineralogy and geochemistry of Ferezneh ferromanganese anomaly, east of Sangan mines complex, NE Iran
Abstract
Introduction The Ferezneh prospect area is one of the eastern anomalies of Khaf’s Sangan iron mine. The Sangan mines complex is located within the Khaf-Kashmar-Bardeskan volcano-plutonic and metallogenic belt in northeastern Iran. The Sangan mine is the largest Fe skarn in western Asia, having a proven reserve of over 1000 Mt iron ore @ 53% Fe (Golmohammadi et al., 2015) and consisting of three parts; western, central and eastern Sangan, each part including several anomalies. In this study, Ferezneh (North and West) prospect area which is an eastern anomaly of the Sangan iron ore is discussed. Ferezneh anomaly is located in 60°36'7" - 60°34'27"E and 34°30'47" - 34°29'46"N, 35 km south of the city of Taybad, 10 km southeast of Karat and 1.5 km southwest of Ferezneh village. The purpose of this study was to prepare a geologic map for separation and identification of the intrusions, determining their relationships with mineralization, distinguishing the type of mineralization, mineralogy, petrology and geochemistry of the mineral deposits, and finally their relationship with other major Sangan’s deposits. Materials and methods In order to achieve the objectives of the study: 1- 140 thin sections of the intrusive rocks, marble limestone and dolomite, as well as 40 polished sections of ore were taken in an area of 9.5 km2. Mineralogy and mineralization studies were performed in the Economic Geology Laboratory of Ferdowsi University of Mashhad. 2- A few samples were selected for X-ray diffraction analysis in order to ensure accuracy of mineralogical studies and were sent to Binalood Laboratory in Tehran. 3- In addition to major and minor elements geochemistry study of the ores, 10 samples were sent to East Amitis Laboratory in Mashhad for XRF analysis and also to Canada S.G.S Laboratory for ICP-MS analysis. Discussion and results Mineralization in the Ferezneh prospect area was limited to iron and manganese oxides in the form of massive and stratabound in recrystallized limestone that followed the structure pattern. Iron oxides often include goethite and hematite; while manganese oxides are pyrolusite, psilomelane and lesser amounts of cryptomelane. Small spots of rutile are rarely seen. The gangue minerals are dolomite, calcite and cryptocrystalline quartz. XRD analysis shows that iron and manganese oxides are the only metallic minerals. The geochemistry of mineralization was studied by ICP-MS and XRF analysis for major oxides, trace elements and REE. The range of Fe anomaly changes from 43.5 to 68% and Mn anomalies vary between 1.9 and 4.8 %. The range of Cu varies from 20 to 1063 ppm and the range of As differs between 20 and 1269 ppm, no Cu and As mineralization has been observed. Mn and Fe oxides uptake trace elements. In the Fe:Mn:Si ternary diagram, ten of the analyzed samples were plotted in the characteristic compositional field for Fe-rich hydrothermal. In the Fe:Mn:(Co+Ni+Cu)×10 ternary diagram, data were also plotted in hydrothermal fields. Minor and trace elements in the binary diagram of Ni+Co vs. Cu+Zn+Pb+Mo+V+As (Crerar et al., 1982) show samples within the field for hydrothermal deposits. REE pattern shows positive Eu anomaly and the Eu/Eu* ratio changes from 2 to 7, LREE/HREE ratio varies between 2.25 and 13.78, the mean being 6.94. Rare earth element contents show relatively low to moderate subtraction pattern. LREE have more variations than HREE values that have been fixed. Enrichment of LREE over HREE and positive Eu anomaly, are the key indications of hydrothermal origin for the ore deposits and low amounts of REE are the characteristic for hydrothermal deposits (Xu Bao et al., 2008). As, Cu, Pb, Zn and Sb act as trace indicator elements in reaching the hidden epithermal or hydrothermal sulfide deposit in depth. Although the type of mineralization in the main parts of Sangan is skarn (Karimpour and Malekzadeh Shafaroudi, 2006; Karimpour and Malekzadeh Shafaroudi, 2008; Golmohammadi et al., 2015), there is no evidence of limestone skarnification, skarn minerals and magnetite mineralization in the Ferezneh prospect area. Based on the listed data and interpretations, there is no relationship and similarity between Sangan mineralization and Ferezneh ferromanganese anomaly. This anomaly may be related to a younger mineralization and might be associated with the function of supersion fluid by leaching the sulfide hydrothermal deposits that form in the fault zones. References Crerar, D.A., Namson, J., Chyi, M.S., Williams, L. and Feigenson, M.D., 1982. Manganiferous cherts of the Franciscan Assemblage: I. General geology, ancient and modern analogues and implications for hydrothermal convection at oceanic spreading centers. Economic Geology, 77(3): 519-540. Golmohammadi, A., Karimpour, M.H., Malekzadeh Shafaroudi, A. and Mazaheri S.A., 2015. Alteration-mineralization, and radiometric ages of the source pluton at the Sangan iron skarn deposit, northeastern Iran. Ore Geology Reviews, 65(2): 545-563. Karimpour, M.H. and Malekzadeh Shafaroudi, A., 2006. Comparison of the geochemistry of source rocks at Tannurjeh Au-bearing magnetite and Sangan Au-free magnetite deposits, Khorasan Razavi, Iran. Iranian Journal of Crystallography and Mineralogy, 13(1): 3–26. (in Persian with English abstract) Karimpour, M.H. and Malekzadeh Shafaroudi, A., 2008. Skarn geochemistry – mineralogy and petrology of source rock, Sangan iron mine, Khorasan Razavi, Iran. Scientific Quarterly Journal of Geosciences, 17(65), 108–125. (in Persian with English abstract) Xu Bao, S., Yang Zhou, H., Tong Peng, X., Wu Ji, F. and Qiang Yao, H., 2008. Geochemistry of REE and yttrium in hydrothermal fluids from the Endeavour segment. Juande Fuca Ridge. Geochemical Journal, 42(4): 359–370.
