عنوان مقاله [English]
IntroductionLahrud is situated in NW Iran, between 47º 30´ to 48º longitudes and 38º 30´ to 39º latitudes, based on the structural units this area is part of the Eocene age trending Alborz-Azerbaijan magmatic belt .The volcanic rocks of Eocene age mainly comprise of alkaline series.Materials and Methods Fractal modeling has been widely used in various fields of earth sciences and mineral exploration since the 1980s. One of the most important methods is the Concentration-Number fractal method; this method is based on the inverse relationship between the concentration and the cumulative frequency of each concentration and higher concentrations. In 2003, about 600 samples of Lahroud 1: 100,000 sheet stream sediments were randomly sampled by the National Geological and Mineral Exploration Organization and analyzed by ICP-MS. In this study, classical statistics operations, factor analysis, fractal Concentration-Number of operations and element geochemical anomaly maps were prepared. Classical statistics have a structural weakness for not taking into account the spatial position of the data which causes systematic errors. Factor analysis is one of the most popular multivariate analyses, which is used as a powerful tool for visualizing large three-dimensional spatial data based on the variance and covariance matrices. In this method, a large set of geochemical variables are combined with several factors. The basis of the factor analysis work is, that after the initial stages of data preparation, at each stage, the elements that have a number higher than 0.6 should be selected and the rest of the elements should be removed.Results and Discussion Factor analysis was performed in SPSS software and had four stages; All disruptive elements (Mo, Be, Hg, Pb, Ag, Sr, Se, and Bi) were removed after four stages of factor analysis, and As, Sb, Sn, W, Co, Mn, Zn, Ti, Ba, Ni, Cr, Au, Cu and B were classified into five groups. Graph diagram of the C-N of invoice points was drawn and their values determined the maps of geochemical communities. The interpretation of airborne geophysical data is done both qualitatively and quantitatively. In interpreting this data, geological structures such as the location of intrusive masses, faults or hidden faults, contacts, special structures such as folds, various alteration zones and various lithologies and their changes are considered. The Oasis Montaj geophysical software offers a variety of filters and applications for analyzing and, interpreting aerial magnetic data. Geophysical surveys of the Lahrud area were performed on 48 flight lines, including longitude, latitude, and magnetic field for each point.ConclusionThe presence of Andesite and Andesite-basalt rocks on the surface (geological study of area) reinforces the possibility of the presence of dioritic intrusive mass. This, has caused some of the rocks around the intrusive mass and fractures to rise through the weak points around it, and it has flowed as lava on the earth's surface. Finally it has formed the Andesite rocks of the region. Due to the size, depth and alterations of the rocks around the southern intrusive mass of the region, this, type of rooted batolite was detected with a slope to the south. The presence of Sb in the southwestern region confirms the performance of a hydrothermal system; the system, rises through the existing faults and affects the alteration rocks, creating Alunitization, Kaolinitiezation and Silicification alterations in the southwest and center of the sheet. Most of the anomalies are around the intrusive mass south of the region, where hydrothermal fluids have caused alterations, followed by mineralization. Concentration-Number fractal calculations, step-by-step factor analysis, preparation of geochemical anomalies of Gold, Antimony and Copper elements, studies and preparation of geophysical maps indicate that the anomalies of the elements are significant. They correspond to alteration areas and intrusions. This, indicates a close and notable connection between the alterations, faults and, intrusive masses of the Lahrud 1:100,000 sheet with the anomaly of the elements, especially Au and Cu. Therefore, the best exploration items in this sheet are Gold and Copper.