Evaluation of geochemical data based on polarized geochemical system method, assesing favorability for copper associated ore mineralization in Milajerd prospecting area, Esfahan province

Document Type : علمی -پژوهشی


1 Department of Geology, Faculty of Natural Sciences, Lorestan University, Khoram Abad, Iran

2 Atomic Energy Organization of Iran, Tehran, Iran

3 Department of Geology, Faculty of Sciences, Bu-Ali Sina University, Hamedan, Iran


IntroductionThe Milajerd prospecting area is located within 100 km of western Ardestan and belongs to Naein-Natanz prospecting region. This area is one of the favorable target areas that have been defined by multidiscipline GIS-based metallogenic modellings for metallic resources. This area consists of two main zones with different geologic and geophysical (magnetic) characteristics. The first zone (on the west and south) presents sialic continental crust with Gondwana-type Paleozoic-Middle Triassic epi-platform sediments that is covered by Eurasian-type Upper Triassic to Lower Jurassic coal-bearing silici-clastic series of Nayband Formation. The Nayband Formation is overlaid by Cretaceous conglomerate -sandstone beds that are followed by limestone and marls upward.  The conglomerate and sandstone beds present angular unconformity with Nayband and older formations. The second zone on the east and north belongs to Molla-Ahmad-Karkas arc-type volcano-plutonic belt, which is composed of intermediate to acidic Eocene volcanic series that have been intruded by Late Eocene to Miocene granitodes.Material and methods   The Milajerd Pb-Zn±Au polymetallic prospecting zone in Naein-Qom Magmatic Zone is one of the favorable targets defined by multidisciplinary metallogenic modellings for gold and base metal resources. Ground controlling of the aforesaid target area has been carried out by coarse 1000*1000 m2 grid litho-geochemical surveying. A total of 176 rock-chips samples each weighting 1500gr were collected. Each of them was  assayed by ICP AES method  in Kanpazhuh Laboratory for  Au,As,Ag,Ba,Pb,Zn, Cu,Mo, Ni,Co,V,Ti,P,Bi,Cr,Fe,In,La,K,Na,Mg,Mn,S,Sb,Sc,Sr,Th,U,W,Zr.Results and Discussion The main approach for evaluating the favorability and mineral resources, was data processing and information analysis based on defining “Polarized Geochemical Systems (PGS) and related depleted, background and enriched zones. These zones are spatially forming unified systems referred to as” PGS” and present localities of ore deposit formation. According to the defined PGS, there are four systems with three expected types of ore mineralization; 1) porphyry Cu-Mo-(Au), 2) contact- halo Polymetal, and 3) epithermal gold ore formation. There is good correlation between lost copper in depleted zones and its concentrated amount in enrichments zones.ConclusionIt is estimated that the depleted value would be almost equal to 1,969,800 t that is probably accumulated in enrichment zones. The tonnage of enriched copper is estimated to be 2,063,500 t (probably originated from Eocene-Miocene volcano-plutonic rocks and the Crust), almost equal to depleted value. These values could be considered as the key criteria to assess the favorability of the prospecting area for aforesaid-types’ ore mineralization.