Journal of Economic Geology (Nov 2017)
Integration of geology, mineralization, geochemistry, and magnetic data in the Dehzaman apatite-bearing iron deposit in the Khorasan Razavi province
Abstract
Introduction The Dehzaman iron deposit is located in the Northeast of Kashmar- Kerman tectonic zone (KKTZ) (Ramezani and Tucker, 2003), southwest of Bardaskan in the Khorasan Razavi province. Mineralization are in two type: 1- Hematite ore (that is extracted for decades) 2- Magnetite ± Specularite and Magnetite - Specularite associated with apatite veins. Metarhyolite- Metarhyodacite units with low magnetic susceptibility are the most important host rocks in the study area. In the present paper, we provide an overview of the geological, alteration and mineralization characteristics, particularly the results of REE Geochemical data and Ground Magnetic data to explore the Magnetite ± Specularite veins. Identification of these characteristics can be used as a model for exploring this type of iron mineralization in the KKTZ specifically and elsewhere. Materials and methods Detailed field work was carried out in the Dehzaman study area. A total of 95 polished blocks and thin sections were prepared and studied from host rock, mineralization and altered zones, and geology, mineralogy and alteration maps were prepared by conventional petrographic and mineralogical methods at the Department of Geology of the Ferdowsi University of Mashhad. In addition, 9 samples from the ore zones (Magnetite ± Specularite and Magnetite – Specularite) were analyzed by ICP-MS for minor and trace elements and REE content at ACME lab, Canada. Also in order to determine the iron ore grade, 7 samples were analyzed by titration methods. Magnetic susceptibility of ore veins and host rocks was measured in order to determine the magnetic susceptibility contrast, and then ground magnetic survey was carried out with Geometrics G856. Total magnetic Intensity was measured at 2223 stations, processed and interpretation maps were prepared. Finally, magnetic anomalies in the eastern and central parts of the study area were interpreted. Results In the northeast of KKTZ, the outcrops of Precambrian to Neogene lithological units are observable. Metamorphosed volcano-sedimentary series of the Dehzaman mine area, all belong to the Upper Neoproterozoic- Lower Cambrian and are considered as low-grade regional metamorphism and deformation of high tectonic activity. Outcrop Rock units in the Dehzaman area consist of slate-phylite, Recrystallized carbonate units (Dolomite and limestone), Sericite schist, metavolcanic units, Mylonitic granite, Seynogranite. Metavolcanic units consist of Metarhyolite to metarhyodacite with porphyritic textures which hosts iron ore. Mineralization in the Dehzaman area consists of Magnetite and Specularite associated with apatite and lower amounts of chalcopyrite and Malachite. The structure of the area plays an important role in iron mineralization (Magnetite ± Specularite and Magnetite – Specularite) which occurs as vein and veinlet and multiple displacement of it are the result of this tectonic activity. Alteration is mainly limited to Magnetite ± Specularite and Magnetite – Specularite mineralized zone and is classified into chlorite, carbonate, silisification, biotite and tourmalinisation. Chip composite result from mineral veins show a high anomaly of REE (10.44 to 4827 ppm). Increase in rare earth elements is directly related to increasing microcrystals or inclusions of apatite in the Dehzaman iron ore. LREE is enriched into MREE and HREE in all samples. The amount of rare earth elements and their normalized pattern in the Dehzaman iron ore are similar with high rare earth elements in iron oxide ores that are usually known as Kiruna type which shows LREE enrichment relative to HREE (Frietsch and Perdahl, 1995). The higher magnetic susceptibility of magnetite ± Specularite and apatite-bearing Magnetite- Specularite in the center and east part respectively relative to volcanic host rocks has resulted in direct responses of mineralization from magnetic data. Integration of this data with geology, outcrop mineralization and filed survey delineated the trend, distribution and depth of magnetite mineralization. High anomaly of REE (in apatite) can also help us explore it indirectly from magnetic data. There is a weak magnetic response in mineral veins especially in the east and central parts of the deposit due to an increase of specularite. The result of ground magnetic survey in the eastern part of the veins shows an east-west anomaly in RTP image particularly at places which have no comparable outcrop. The width of mineralization is more than 20 meters in the northern and south eastern parts. Upward continued maps show the depth extension of the anomaly sources, mineralization to a depth of over 50 meters in the north and south of the eastern part. Based on magnetic anomalies and slope of veins, dip toward the east, 4 drilling locations to a maximum depth of 120 meters and at a vertical angle of 80 degrees in the hanging wall of faults associated with north and south magnetic anomalies are proposed in the eastern part of the Dehzaman deposit. Magnetic anomalies in the central part of the Dehzaman deposit show better correlation with surface outcrops because of higher concentration of magnetite in the veins. Anomalies here have an East-West trend with maximum width of 25 m in the central part. Upward continued images indicate that the depth of anomaly sources, mineralization, extend to over 50 meters. Anomaly discontinuities in the middle of the central part are due to two faults, located to the right and left of the center, which caused the displacement of mineral zone after mineralization. Based on magnetic anomalies and dip of the veins, two drilling locations to a maximum depth of 100 meters and at 80 degree angle are suggested in the eastern and western parts of central Dehzaman deposit. Acknowledgements This project is sponsored by the Ferdowsi University of Mashhad in connection with a research project dated 5.3.2015 No. 3/36972 that has been done. This research was made possible by the help of Opal Kany Pars Co. References Frietsch, R. and Perdahl, J.A., 1995. Rare earth elements in apatite and magnetite in Kiruna-type iron ores and some other iron ore types. Ore Geology Reviews, 9(6): 489–510. Ramezani, J. and Tucker, R., 2003. The saghand region, central Iran: U-Pb geochronology, pertrogenesis and implication for gondwana tectonics. American journal of science, 303(7): 622-665.
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