بررسي تكوين زمين شناسي و فلززايي كانسار اسكارن انارگ و پديده هاي مرتبط با آن

Geologic Evolution and Metallogeny of the Anarg Skarn Ore Deposit with Related Phenomena

The Anarg Polymetallic skarn deposit ( Cu, Zn, Fe, Ag, Au) is located on the 15 km west of the Posht-e- Badam village in the northeastern part of the Yazd province in central part of Iran. This area is situated in geological domain of the central Iran within the Anarak - Sarcheshmeh - Kharestan copper belt]. The Anargʹs granitoid intruded within the center of north - south trending zone . The K/Ar radioisotope age of this granitoid body is middle Eocene, respectively. Litho logically of this granitoid body is composed of I- type granite, granodiorite, quartzmonzonite and less of tonalite and quartz diorite. There is one calcic type skarn around this intrusion. The most important country rock is calcic marble, related to the Posht -e- Badam complex. The exoskam mainly consists of garnet ( andradite- grossularite), clino - pyroxene (diopside - hedenbergite ), amphibole ( tremolite - actinolite), epidote, chlorite, calcite, quartz, magnetite, chalcopyrite, galena and sphalerite, where its high grade metamorphic facies is attamped to the primer pyroxen - hornfels facies. The endoskarn minerals assemblage is composed of grassularite, andradite, epidote, chlorite, calcite, tremolite, actinolite, which its thickness is varied between 1-3 meters. The ore minerals occurred in three different localities (anomalies) namely A,B and C. The major part of economic ores are located within the exoskam zone. This paragenesis not only is related to the composition of hosting, but also reflects the evolutionary processes of intrusion emplacement. The magma tic derived solutions resulted from fractional - crystallization of igneous melt, as well as their interaction with surrounding rock units participates to from the aforesaid polymetallic skarn - type deposit, by met somatic processes. Skarnification in the Anarg ore field has been occurred in three stages namely :l) , Prograde, II). Retrograde - Met somatic and III) Hydrothermal stages. The major ore mineralization has occurred during 2 nd stage. This deposit is a lenticular form body, accompanied by irregular massives and less amount of vein and vein lets. Their ores show massive, inclusion, disseminated and less amount replacement type textures. By considering the mineralogical peculiarities and their correlation with phase diagrams, it is concluded that the temperature of the mineral zone formations are as follows: -Pyroxen zone, 450-600 0C - Garnet zone , 380 -480 0C This skarn was formed by contact- infiltration of magmatic derived fluids. This process has been intensified by fracturing systems of both magma tic and surrounding bodies. Mineralogical investigation ( X.R.D and ore microscopy) show that the major ore minerals are chalcopyrite, magnetite, galena and sphalerite. The Cu-content is varied between 0.35 to 12% , which indicates a remarkable deposit for mining consideration. It has to be mentioned that this deposit is classified as polymetallic - skarn type deposit, by considering the ( Cu, Zn, Fe, Ag, Au,) metals in one formation, which is related to the continental margin - type low angle sub ducted zone .