Tungsten Mineralization Associated With Granitoid Rocks in Southwest of Arak, Iran

The NezamAbad-Malmir intrusion is located 45 km southwest of Shazand, Arak. It is trending southeast-northwest and is a part of the Sanandaj-Sirjan zone of the metamorphic belt of Iran. The intrusion is composed of some huge composite bodies with an area of 180-200 km². It is related to Alpine orogeny and intrudes metasediments of upper Triassic-Jurassic. The latter rocks consist of phyllites, micaschists, quartzites, metamorphosed cherty limestones and metamorphic acidic and basic tuffs. Two types of tungsten mineralization accompany the NezamAbad-Malmir intrusion: 1. Stratabound type, 2. Quartz-tourmaline vein type. Stratabound type is seen at Bamsar. In this area, six ore-bearing horizons have been identified. Country rocks are mainly calcareous schists in which ore minerals occur in laminas and layers. Ore paragenesis includes scheelite, chalcopyrite, arsenopyrite, sphalerite, pyrite, cassiterite, chalcocite and covellite. Vein type mineralization is hosted by tonalite-quartzdiorite intrusions at Revesht, NezamAbad and Fizaneh that are located 3, 7 & 8 km away from Bamsar. Ore paragenesis in these mineralized tourmaline and quartz veins consists of euhedral to anhedral scheelite and chalcopyrite. The NezamAbad-Malmir intrusion shows a range in composition from tonalite to alkali-granite. These plutons are texturally medium-grained granular but include some porphyritic textures. In thin section, the granophyre and myrmekite are observed. Pegmatite-aplite veins and dykes are fairly abundant. XRF analyses for 2 aplites (near tungsten mineralization) and a pegmatite sample show 3, 8 and 23 ppm tungsten, respectively. The tungsten content of the intrusion samples range from 15 to 45 ppm. The rock sample with the highest tungsten content (45 ppm), is a tonalite situated near the contact with metasediments. It is suggested that at Revesht, NezamAbad and Fizaneh, the NezamAbad-Malmir intrusion provided the tungsten deposited in quartz-tourmaline veins. The Bamsar occurrence is however, sedimentary-diagenetic in origin, subsequent concentration happening through Late Kimmerian regional metamorphism and deformation.