The origin of Quaternary placer using remote sensing and geochemical investigation in Zavarian area, SW of Qom, Central Iran

Epithermal deposits are usually found in association with near-surface magmatic-hydrothermal environments with volcanic rocks. According to studies, their formation depth is less than 1.5 km and the temperature for their formation is less than 300 ° C. Epithermal deposits are usually rich in gold to gold-silver and rich in silver and include low sulfide, medium sulfide and high sulfide types. One of the anomalous areas for mineralization of epithermal type gold is located in the area of Zavarian in Qom, central Iran. The following article is about some results of our research about origin of Quaternery placer in the area of Zavarian.

The collected samples were chosen from samples which are associated with mineralization and host rock for geochemical studies. Samples were selected after field and petrographic studies. ICP-OES and Fired-Assay analize measurements were made on 120 samples and ICP-MS analize were made on 8 samples. Aster images were analized with ENVI for remotesinsing study.

Petrographic studies show that the basement rocks of the area include volcanic units of Miocene- Pliocene (MPb), volcanic andesite units of Miocene- Pliocene (MPan), volcanic- pyroclastic units of Miocene- Pliocene (MPVP), pyroclastic units of Miocene- Pliocene and recent alluvium. The plutonic rocks of the area are granodiorite-tonalite. The intruded dykes are subdivided to andesite dykes (DY1) and dacite dyke (DY2). The main alterations are advanced argillic, alunitization, propylitic, sericitic and silicification. Gold mineralization has been occurred in andesite and dacite dykes. Au-mineralization are mostly vein, breccia and replacement type. Ore minerals include magnetite, hematite, Fe-hydro-oxides, chalcopyrite, purite and bornite which are host of Au. The results of remote sensing and geochemical investigation suggest that the origin of hematite, magnetite, Purite, chalcopyrite and galena are volcanic- pyroclastic units of Miocene- Pliocene in quaternary placers. The results of ICP-OES and ICP-MS show that the average grade of gold in the study area is 1.36 ppm, which is 194 times richer than the average of earth crust (0.007 ppm). The maximum gold grade in the mineralization zone is 10.76 ppm. The average grade of silver is 2.69 ppm, which is 44.8 times richer than the average of earth crust (0.06 ppm). The average grade of copper is 1236 ppm and it is 40.19 times richer than the average of earth crust (30 ppm). The average grade of iron is 175707.9 ppm and it is 3.51 times richer than the average of earth crust.

Zavarian gold deposit is located 60 km SW of Qom and in Central Iran geotectonic zone. Gold mineralization has been occurred in andesite and dacite dykes which are associated with advanced argillic, alunitization, propylitic, sericitic and silicification. Au-mineralization are mostly vein, breccia and replacement type. Ore minerals include magnetite, hematite, Fe-hydro-oxides, chalcopyrite, purite and bornite which are host of Au. Geochemical data show that the average content of Au is 1.98ppm. Mineralogical, geochemical, alteration data show that gold mineralization in the area is epithermal high sulfide type. Also, the presence of chalcopyrite, bornite, Au-Cu-As- Ag- Pb, advanced argillic-alunitization, vague quartz texture, vein-veinlet-breccia and replacmente mineralization type support this idea too. The results of remote sensing and geochemical investigation suggest that the origin of hematite, magnetite, Purite, chalcopyrite and galena are volcanic- pyroclastic units of Miocene- Pliocene in quaternary placers.