Potential field methods have been used as a practical tool to do reconnaissance of the operation area and primary investigation. In these methods various filters such as different orders of horizontal and vertical derivatives and combination of them have been applied to locate the anomaly source and boundary of the geological structures. Derivatives of the potential field as the high-pass filters intensify high frequencies of the shallow anomaly sources and weaken low frequencies of the deep anomaly sources. These derivatives are sensitive to the noise level of data significantly and intensify the noises which are high frequency variations in data and cause decreasing the parameters of the signal such as signal-to-noise ratio and resolution. Although the first and second derivatives have been used routinely in interpreting potential field data, the non-integer or fractional orders can be applied to determine the most efficient order of derivatives. In this study, fractional order derivatives and application of them on the potential field data have been discussed. Results of the different fractional orders of horizontal and vertical derivatives and enhanced analytic signal of synthetic data have been shown to determine the efficiency of this method. Random noises have been added to some models to simulate the real cases. In addition, different fractional orders of enhanced analytic signal have been applied on real magnetic data of the Gazestan region. Results of this study show that optimizing quality and spatial resolution in qualitative interpretation of potential field data can be achieved by applying non-integer order derivatives to find the highest order of horizontal and vertical derivatives and enhanced analytic signal.

The Gazestan magnetite–apatite deposit is situated 78 km east of Bafq. The Gazestan deposit is located in Bafq-Poshtebadam subzone of Central Iran structural zone. The rock units in the area belong to the Rizu series and consist of carbonate rocks, shale, tuff, sandstone and volcanics. In addition to sedimentary and volcanic rocks, intrusive rocks in the form of stock and dyke outcrop as diorite gabbro, gabbro, diabase, quartz-monzonite and granite in various places. The green rocks with acidic to intermediate composition (trachyte and dacite demonstrate green color due to alteration) host iron and phosphate mineralization which in some localities, show subvolcanic facies. The alteration is more obvious in the volcanic rocks and includes chloritization, argillic, silicification, and also formation of mafic minerals such as epidote, tremolite and actinolite. The host rocks are strongly altered. Mineralization at the Gazestan deposit comprises a combination of iron oxides and apatite with various ratios accompanied by quartz and calcite, observed in different forms mainly within the trachytic-dacitic rocks and a small proportion in the rhyolites. Five forms of mineralization are distinguished in the area including massive iron ore with minor apatite, apatite-magnetite ore, irregular vein-veinlets (stockwork) in the brecciated green rocks, disseminated, and pure massive apatite veins. The host rocks in the Gazestan area plot on calc-alkaline field. Comparison of the most important characteristics of the Gazestan deposit (including tectonic setting, host rock, mineralogy, alteration, structure and texture) with those of various types of mineralization in the world suggest that the deposit is quite similar to the iron oxide - apatite deposits.

The Gazestan magnetite– apatite deposit is located 78 km east of Bafq, in the Bafq-Poshtebadam subzone of the Central Iran structural zone. The rock units in the area belong to the Rizou series and consist of carbonate rocks, shale, tuff, sandstone and volcanic rocks. Intrusive rocks in the form of stock and dyke crop out as granodiorite and granite in various places. Trachytic and dacitic rocks in the area are green due to chloritic alteration and host iron and phosphate mineralization. The main alteration types are chloritic and argillic, while sericitic, potassic, and silicic alterations as well as tourmalinization and epidotization are also found in the rock units. Five forms of mineralization are distinguished in the Gazestan deposit, including massive iron ore with minor apatite, apatite-magnetite ore, irregular vein-veinlets (stockwork) in the brecciated green rock and disseminated and monomineralic massive apatite veins. Fluid inclusion studies were conducted on the apatites of two stages. According to these studies, temperature and salinity values in the stage-I apatite are higher than those in stage-II apatite. Lower salinity values in the stage-II apatite could be due to contamination of magmatic fluids with meteoric waters during later stages of mineralization. Oxygen, hydrogen and carbon stable isotope composition of magnetite, quartz, apatite and calcite; and calculation of oxygen isotope composition in the fluid equilibrated with the oxide minerals suggest mixing the magmatic fluids with basin brines in mineralization of the Gazestan deposit.

The Gazestan iron oxide-apatite deposit, is locted 78 km east of Bafq at the Posht-e- Badam- Bafq block. Different kinds of lower Cambrian volcanic and subvolcanic rocks ranging from basic to felsic, outcrop in Gazestan area. Felsic volcanic rocks mainly are associated with orogenic phase and considered as an arc magmatism. In Gazestan deposit, host rocks display extensive alteration that can be classified into six groups including Sodic-calcic, potassic, sericitic, carbonates, silicic, chlorite ± actinolite ± epidote and tourmaline alterations. Chlorite ± actinolite ± epidote alteration is well developed throughout the Gazestan deposit.The ore body is mainly magnetite-apatite with less sulfides (Pyrite-Chalcopyrite) and REE minerals (allanite-monazite) which occur as breccia, banded, massive, stockwork and vein in altered volcanic rocks. Three generations of apatite are recognized which the second generation is usually enriched in REE minerals (monazite). The homogenization temperature of apatite (III) was calculated between 130-200 °C. The REE pattern of apatites show strong LREE enrichment with negative Eu and HREE anomaly. Magmatic fluids with high amounts of P, Fe and REE are responsible for the ore formation at the first stages. At the final stage of mineralization, meteoric (marine) waters mixed with the magmatic fluids, causing decrease in temperature and precipitation of late apatite and gangue minerals (calcite and quartz). The Gazestan deposit share many similarities with the Kiruna-type deposits (one of the subgroup of IOCG deposits).

The Gazestan magnetite-apatite deposit is hosted within an upper Proterozoic-lower Cambrian volcanic-sedimentary sequence, known as Rizu series, in the Bafq district, Central Iran. The Gazestan deposit occurred in intensely altered felsic-intermediate subvolcanic and volcanic host rocks. Field observations, drill core logging, petrographic studies, as well as geochemical and XRD data are indicative of differences in alterations assemblages and temporal/spatial distribution of the alteration products, compared to other iron oxide-apatite deposits in the Bafq district. Unlike many other Bafq district iron deposits, sodic alteration is only locally developed. Similarly, Ca+Fe or actinolitic alteration is poorly developed in Gazestan. Chloritic and sericitic alterations are most closely associated with ore formation in Gazestan. Chlorite commonly associated with magnetite, quartz and calcite in the altered host rocks. The chemical composition of chlorite falls in pycnochlorite and clinochlore fields. Calculated temperature for chlorite formation varies between 324-236 º C. Sericite occurred both as a proximal alteration in ore zones, and as a distal alteration product in the volcanic and subvolcanic host rocks. Calcic-iron alteration is poorly developed in Gazestan. Potassic alteration marked by development of K-as well as biotite is only locally developed in Gazestan. Boron metasomatism occurs as quartz-tourmaline bands and disseminated grains in altered rocks. The scarcity and local nature of sodic (albitic) and calcic-iron (actinolitic) alterations, and the widespread and proximal chlorite alteration suggest that, compared to most other iron deposits of the Bafq district, Gazestan formed at relatively lower temperatures and possibly shallower depths.

The traditional approaches of modeling and estimation of highly skewed deposits have led to incorrect evaluations, creating challenges and risks in resource management. The low concentration of the rare earth element (REE) deposits, on one hand, and their strategic importance, on the other, enhances the necessity of multivariate modeling of these deposits. The wide variations of the grades and their relation with different rock units increase the complexities of the modeling of REEs. In this work, the Gazestan Magnetite-Apatite deposit was investigated and modeled using the statistical and geostatistical methods. Light and heavy REEs in apatite minerals are concentrated in the form of fine monazite inclusions. Using 908 assayed samples, 64 elements including light and heavy REEs from drill cores were analyzed. By performing the necessary preprocessing and stepwise factor analysis, and taking into account the threshold of 0. 6 in six stages, a mineralization factor including phosphorus with the highest correlation was obtained. Then using a concentration-number fractal analysis on the mineralization factor, REEs were investigated in various rock units such as magnetite-apatite units. Next, using the sequential Gaussian simulation, the distribution of light, heavy, and total REEs and the mineralization factor in various realizations were obtained. Finally, based on the realizations, the analysis of uncertainty in the deposit was performed. All multivariate studies confirm the spatial structure analysis, simulation and analysis of rock units, and relationship of phosphorus with mineralization.