Geology, mineralogy and geochemistry of Koodakan 2 prospecting area, South of Birjand, East of Lut Block

The study area is located in 180 kilometers at the South of the city of Birjand and at 4 kilometers North of the Qhaleh-Zari mine, within the Central Lut Block. According to Stocklin and Nabavi (1973), the Lut Block (Eastern Iran) extends over 900 km in a north-south trend and is 200 km wide in an East-West direction. It is confined by the Nayband fault and the Tabas Block on the west, Nehbandan Fault in the east, Doruneh Fault in the north, and the Jaz- Morian Basin in the south. The sixty- five percent of the exposed rocks within the Lut Block consist of volcanic and plutonic rocks (Karimpour et al., 2011). The extensive magmatism of the area has resulted from the west-dipping subduction of the Lut Block zone (Karimpour et. al., 2005). The Koodakan area is located in the north of the Qhaleh-Zari mine, and in fact, it is comprised of the continuation of Qhaleh-Zari mineralization type. In the study area, rock units include Tertiary volcanic, intrusive, subvolcanic, and pyroclastic rocks. The samples were collected from the study area focusing on the vein mineralization for preparing geology, mineralization and geochemistry maps. In addition, the dip and direction of the faults were measured for preparing structural map. Ten samples were analyzed for thirty six elements using Inductively- Coupled Plasma-Mass spectrometry (ICP-MS) in the Zar- Azma Laboratory, Mashhad, Iran. Petrographically, the rocks in the area consist of granodiorite, dioritic dikes, andesite and andesite- basalt. The volcanic rocks have extended throughout the study area and are mainly affected by various intensities of propylitic and/or carbonate alterations. The volcanic rocks are mainly andesitic in composition. Based on field observations and microscopic evidence, volcanic rocks can be subdivided into andesite, hornblende andesite, andesite- basalt and pyroxene andesite. Diorite porphyrtic dikes swarms are the youngest units in the area, and are not related to mineralization. Propylitic alteration comprises dominant alteration in the Koodakan 2 area and is characterized by epidote, chlorite and calcite mineral assemblages. Argillic alteration is locally present within the surface outcrops. Silicification is mainly cropped out in both adjacent to mineralized veins, and to a lesser amount, as pervasive silica. Mineralization is mainly controlled by a system of faults and joints. Three trends of faults are identified in the area including the a) NW-SE. b) NE-SW. c) E-W. The NE-SW trending mineralized veins represent a northeast dip ranging from 60- 70, and a width between 5 cm to 3 meters. In most cases, mineralization is hosted by pyroclastic units (especially agglomerate) or in the contact between agglomerate and andesitic rocks. At least three styles of veins were identified in the area. These are 1) quartz+ specularite+ chalcopyrite ± galena ± pyrite veins. The thickness of these veins varies from 2 cm to >1 m. The type 1 displays a dominant NW-SE strike. Quartz comprises of the most common mineral assemblage within the three types of veins forming uhedral to subhedral crystals with 1-10 cm long. Sulfide mineral dominantly includes chalcopyrite which is weathered to chalcocite at margins- together with galena, and pyrite. 2) quartz+ Fe oxides (limonite) veins range in thickness between 20 cm-1 m, and their ore mineral contents are not as important as types. 3) The NW-SE trending late carbonate veins mainly occurred in northern parts of the study area. These veins do not contain any ore minerals. Based on lithogeochemical studies, the concentration of Cu in mineralized veins ranges from 75-9928 ppm. The highest grade of Cu is related to quartz + malachite ± Fe oxide veins, and the lowest grade is related to silicified- Fe oxide veins. The geochemical abundances of Pb are similar to that of Cu and mainly vary from 7ppm to >3%.Highest concentrations of Zn are consistent with type 1 veins, and range from 25- 109285 ppm. Arsenic represents a widespread distribution of halos in the studied veins and its content varies between 5 and 424 ppm. Based on geology, mineralization, and geochemistry data, mineralization of the Koodakan 2 area is comparable with the veins in the Qaleh- Zari deposit and can be classified as IOCG deposit type. Detailed studies including the fluid inclusion, electron microprobe, and stable isotopic investigations can be further applied to examine the type of mineralization in the Koodakan 2 area.