Analytical and Numerical Methods in Mining Engineering (Feb 2022)
3D Zonation model of primary haloes and geochemical prospecting pattern of Aliabad Cu-Mo deposit, Yazd, Central Iran
Abstract
Most hydrothermal ore deposits are controlled by geological structures. They are often a product of multistage hydrothermal activities, as a result, primary alteration haloes usually overlap in the vertical direction. By distinguishing the hydrothermal stages associated with ore-forming processes, one can determine the timings of hydrothermal activities and use the results as a method to identify blind mineralization. In order to explore probable blind mineralized zones of the Aliabad deposit, it is necessary to evaluate the element concentrations towards the depth or margins of the deposit. Modeling primary geochemical haloes could be useful in this stage. The Aliabad porphyry Cu-Mo deposit, located in the southern segment of Central Iran and adjacent to the northern border of the Urmia-Dokhtar volcanic belt and east of the Dehshir fault. Ore bodies at the Aliabad deposit are primarily controlled by structural features, which provide an opportunity to investigate the zonality in primary halos in this copper-molybdenum porphyry deposit. The primary geochemical characteristics of the mineral deposit were studied based on geochemical analysis of 1559 core samples from 24 drill holes. The formation of the primary geochemical haloes, which joins the ore body up to the surface, can be associated with hydrothermal fluid diffusion through fracture (fissures) zone developed in the rocks of the folding axis in the mining area. Along the vertical direction, the concentrations of Cu, Ag, and Fe shows an increasing trend from the surface to the ore body, at all boreholes; while the concentration of Pb, Mn, and Bi are decreased with depth at the same environment. A detailed zonality sequence of indicator elements is obtained using the variability index of these elements: Pb → (Bi, Mn, Mo) → Cr → Ni → (Sb, V, Zn) → (Ag, Co, Cu, Fe, S) → P. According to this zonality, indexes such as Vz4=Pb×Mn/Cu×Ag and Vz5=Pb×Mn/Cu×Ag×Co can be constructed and considered as a significant criterion for predicting the Cu potential at a particular depth. Studying the distribution of the zoning indexes at different levels revealed high values of proposed indexes in the northwest and south of the area. It can be concluded that copper mineralization will continue to deeper and unexplored parts of the deposit northwest of the study area. Consequently, it is suggested that further investigations concentrate on geophysical operations and it is highly recommended to drill additional boreholes at these areas. It is noteworthy that new drillings of the northwestern part must continue deeper than current boreholes (>150 m); because geochemical zonality indexes are extended to deeper parts. This extension is not observed for the southern part, so, additional drillings at the southern part can be shallower than 150 m.
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