Geology, Mineralography and geochemistry in 16 B Fe mineralization Bafq (Yazd)

Introduction
The XVI-B anomaly iron ore deposit is situated within the Central Iranian structural zone, specifically in the Bafq region. This region is notable for its lack of a direct association between specific tectonic periods and iron ore deposits. The Bafq area contains 39 iron ore deposits with an estimated total reserve of 2 billion tons, making it one of the most significant iron ore extraction regions in Iran.
 
Materials and Methods
Prominent iron ore deposits in the area include Sechahoon (117 Mt), Chadormalu (400 Mt), and Choghart (216 Mt). The Bafq anomaly iron ore deposit is located within the Central Iranian structural zone. This study involved the collection of drilling core samples for ICP-MS analysis (conducted at Karaj Laboratory), thin-polish and thin-section preparations (54 samples), and XRF analysis (5 samples, also conducted at Karaj Laboratory). According to the structural-sedimentary unit classification of Iran, the study area lies within the central Iranian zone (Nabawi, 1976). This zone contains some of the oldest metamorphic rocks in Iran, dating back to the Precambrian (Aghanbati, 2004). The Bafq mineral district, a subset of the central-eastern Iranian microplate, has experienced tectonic evolution influenced by the Katanga orogeny and related movements over the past 600 million years (Taghavi, 2015). The region's Neoproterozoic–Early Cambrian mass magnetite deposits are predominantly found in volcanic rocks associated with mantle diapirism along caldera margins. Notable deposits include Chaghez, Chadormalu, Choghart, and Sechahoon (Torab et al, 2007). The dispersed mineralization of iron and rare earth elements in the Bafq mining area is directly linked to intracontinental rifting. Volcanism, magmatism, and regional tectonics, influenced by rift dynamics, played a significant role in the mineralization of igneous rocks (Samani, 1993).
The XVI-B deposit is part of the Bafq mineral district, located within the central-eastern Iranian microplate. Stratigraphically, the area is divided into western, central, and eastern sections (Ramezani and Tucker, 2003). The oldest rocks (Neoproterozoic–Early Cambrian) are situated in the eastern part, while the youngest rocks (Eocene) are found in the west. Major faults, including the Nybaz-Chatak and Poshte-Badam faults, delineate these sections.
Results and Discussion
The region contains diverse igneous and metamorphic rocks. The igneous rocks include gabbro, diorite, syenite, quartz monzonite, granite, and highly altered basic rocks (metabasites). The metamorphic rocks are dominated by marble and skarn formations. The leucogranite, characterized by idiomorphic and graphic textures, contains plagioclase and sodic feldspar crystals alongside quartz, alkali feldspar, biotite, and secondary minerals such as sericite, clay minerals, epidote, and carbonates. Tectonic activity has resulted in cataclastic textures in some samples. Mineralization in the area is primarily associated with syenite, gabbro, and skarn rocks. The metallic minerals include magnetite, hematite, pyrite, and chalcopyrite, while non-metallic minerals such as quartz, actinolite, calcite, and epidote are also present.
Mineralization and Geochemical Characteristics
Iron mineralization predominantly occurs as magnetite, which is observed in massive, void-filling, and disseminated forms. Near the surface, magnetite undergoes oxidation, resulting in its transformation into hematite, goethite, and other iron oxides. Associated metallic minerals include pyrite and chalcopyrite, often found with quartz, actinolite, calcite, and epidote in host rocks, intrusive syenites, gabbros, and skarns.The total iron oxide content in the collected samples ranges from 25% to 75%, while silica content varies between 5% and 45%. Titanium concentrations are relatively low, between 0.1% and 0.5%, and exhibit a negative correlation with iron content. Potassium oxide levels range from 0.1% to 1.8%, and phosphorus content varies between 0.02% and 0.35%, indicating an absence of phosphate mineralization. Magnesium oxide levels range from 1% to 12%, largely attributable to the presence of ferromagnesian minerals such as amphibole and dolomite. Negative correlations between magnesium oxide and iron suggest minimal substitution of magnesium for iron in the mineral lattice. Aluminum and calcium oxides range from 2% to 12% and 2% to 26%, respectively. The ore samples contain cobalt (3–75 ppm), nickel (1–17 ppm), chromium (10–96 ppm), and vanadium (40–120 ppm). The behavior of rare earth elements (REEs) indicates hydrothermal alteration, with total REE content varying between 13.1 and 375.1 ppm. Enrichment in light REEs (LREEs) and depletion in heavy REEs (HREEs), alongside a positive Eu anomaly, are consistent with skarn-type deposits (Bea et al, 1996). This pattern suggests that REEs may substitute for elements in garnet, zircon, and magnetite structures.
 
Conclusion
The geological evidence indicates that the oldest rocks in the area are Precambrian metamorphic units, including gneiss, mica-schist, amphibolite, and migmatite, which form the bedrock of the mineralization anomaly. The deposit is covered by Tertiary and Quaternary sediments of the Bafq Basin. The alkaline diorite-syenite intrusive units play a significant role in hosting mineralization.The mineralization comprises a variety of igneous and metamorphic rocks, including gabbro, syenite, quartz monzonite, granite, marble, and skarn. Magnetite is the dominant iron oxide ore and is accompanied by pyrite and chalcopyrite. Oxidation near the surface leads to the formation of secondary iron oxides like hematite and goethite. The geochemical data suggest that the deposit is of hydrothermal origin, with characteristics aligning it with skarn-type deposits. Correlations among trace elements such as Co/Ni, Cr/Ni, and Cr/V, along with ratios like Al/Co and Sn/Ga, further support this classification. The REE patterns, including a positive Eu anomaly and LREE enrichment, are consistent with skarn-type mineralization and provide insights into the role of hydrothermal fluids in the formation process. This study highlights the skarn origin of the XVI-B anomaly iron ore deposit, emphasizing the significance of intrusive magmatic activity and hydrothermal processes in its formation. These findings contribute valuable insights for the geological modeling and economic evaluation of the deposit.