جستجوی مقالات مرتبط با کلیدواژه "مغناطیس سنجی زمینی" در نشریات گروه "زمین شناسی"

The Kuh-Baba iron ore deposit is located in ~70 km south of Hashtroud, East-Azarbaidjan province, NW Iran. The lithologic units cropped out around this deposit include Oligo-Miocene volcanic-sedimentary rocks, Pliocene intrusive rocks, and Pliocene dacitic domes. The principal host rocks for the Fe mineralization include units of gabbro-norite, pyroxene hornblende gabbro-norite, and monzo-diorite. Remote sensing investigations (using Sentinel satellite images) display the presence of lineaments, NE-SW trending fault structures, and various alteration zones. The dominant hydrothermal alteration in inner parts of the deposit is mainly propylitic (epidote, chlorite, sericite) which gradually changes to argillic outward toward the peripheral parts. Based upon field relations and microscopic examinations, the ores show massive, vein/veinlet, brecciated, and disseminated textures. In the propylitic zone, magnetite is accompanied by epidote and actinolite. The geochemical studies revealed that the FeT content in the diamond drill core samples varies from 3.85 wt% to 63.2 wt%. Ground magnetic survey was conducted in the area and also, the maps of total magnetic field, reduced to pole magnetic, analytic signal, first vertical derivative, and upward continuation were prepared in an attempt to identify the potential deep and shallow subsurface mineralized zones. The obtained results show that two anomalies, one in the north and the other in the central parts of the study area, were recognized which almost correspond with the location of the intrusive bodies.

Summary: In this study, satellite images, and aeromagnetic and ground magnetic data were analyzed to explore the geothermal potential in Sirch-Golbaf area in Kerman province. Thermal anomalies and apparent thermal inertia images were studied using MODIS, Landsat and ASTER images. As a result, two thermal anomalies were obtained; one in the southeastern part of the study area and the other one in Jooshan location. Magnetic investigations also detected two anomalies; a deep magnetic anomaly in the southern part of the area and another magnetic anomaly near Jooshan hot spring in the northeastern part. These magnetic anomalies were correlated with thermal anomalies.
Remote sensing techniques are helpful reconnaissance tools for detecting surface temperature anomalies and identifying geothermal indicators (Calvin et al., 2005). Lu et al. (2008) used Landsat ETM thermal images to detect thermal anomalies strongly correlated with faults in certain scales in the Jiangshan-Shaoxing fault in the Zhejiang Province, China. They defined thermal anomalies as areas having temperatures higher than the temperature of the spatial background. In a geothermal resource exploration in Akita and Iwate prefectures, northern Japan, Noorollahi et al. (2007) showed that 95% of the production wells were located in a zone within 6000 m to the active faults and 4000 m to hot springs. Magnetic measurements are also generally used in geothermal exploration programs to locate hidden intrusive bodies and possibly estimate their depths. Moreover, they can be used to trace buried dykes and faults, and also to detect areas of reduced magnetization due to thermal activity (Georgeson, 2009). A variety of magnetic studies in geothermal exploration projects having different objectives can be found in the literature (e.g. Hojat et al., 2016; Gailler et al., 2014; Georgsson, 2009; Hunt, 1989; Palmason, 1975). The aim of this study is to analyze remote sensing and magnetic data (airborne and ground measurements) for evaluating the geothermal potential zones in an area east of Kerman Province.
Methodology and Approaches: The input data in this research include MODIS, MOD11_L2 005 (day and night) reflectance and LST products, for the year 2015, ASTER L1T night-time image on November 10, 2015, Landsat ETM day-time image on November 14, 2015, aeromagnetic data collected by Houston Texas Co., USA, in 1975-1977, and geomagnetic total intensity contour map of Gowk area having 1:50000 scale, which surveyed by Atomic Energy Organization of Iran. Ground magnetic survey is also carried out in an area around Joshan hot spring. A comparison of the day-time and night-time images can reveal surface thermal differences for detecting geothermal anomalies. Land surface temperature was calculated using generalized split-window algorithm for MODIS sensor (Wan and Dozier, 1996), emissivity normalization method for ASTER (Coll et al., 2007; Banerjee et al., 2014), and LST calculation method for Landsat sensor (Barsi et al., 2003; Barsi et al., 2005; Coll et al., 2010). Apparent thermal inertia of the three sensors was calculated using albedo and LST difference of day and night (Sabol et al., 2006; Scheidt et al., 2010; Chang et al., 2012; Qin et al., 2013). After removal of noise from the observed magnetic data, processing steps including main field removal using IGRF model of the proper period, reduction to the pole, and upward continuation were applied on the magnetic data. The processed magnetic data were finally interpreted in order to locate the hidden intrusive bodies and faults.
Results and Two thermal anomalies were detected on the maps and charts obtained for the average temperature difference (day and night) and apparent thermal inertia. One anomaly was located in the Jooshan area and the other one was situated in the western part of Gowk fault and continues along it to the southeastern side. Gowk fault is an active fault with Jooshan (45 C) hot spring, and most earthquakes larger than magnitude 5 have occurred in this part. These might be evidences of a thermal anomaly. The results of magnetic interpretations confirmed thermal anomalies showing a deep magnetic anomaly in the southern part of the study area and another magnetic anomaly in the Jooshan hot spring.

Ground magnetometer surveys is one of the oldest geophysical exploration methods used in identifying iron reserves. The correct interpretation of ground magnetic surveys, along with geological and geochemical data will not only reduce costs but also to indicate the location, depth and dimensions of the hidden reserves of iron (Robinson and Coruh, 2005; Calagari, 1992). Kalateh Naser prospecting area is located at 33° 19ó to 33° 19óó 42" latitude and 60° 0' to 60° 9ó 35" longitude in the western side of the central Ahangaran mountain range, eastern Iran (Fig.1). Based on primary field evidences, limited outcrops of magnetite mineralization were observed and upon conducting ground magnetic survey, evidence for large Iron ore deposits were detected (Saadat, 2014). This paper presents the geological and geochemical studies and the results of magnetic measurements in the area of interest and its applicability in exploration of other potential Iron deposits in the neighboring areas.
To better understand the geological units of the area, samples were taken and thin sections were studied. Geochemical studies were conducted through XRF and ICP-Ms and wet chemistry analysis. The ground magnetic survey was designed to take measurements from grids of 20 meter apart lines and 10 meter apart points along the north-south trend. 2000 points were measured during a 6-day field work by expert geophysicists. Records were made by Canadian manufactured product Magnetometer Proton GSM19T (Fig. 2). Properties of Proton Magnetometer using in magnetic survey in Kalateh Naser prospecting area is shown in Table 1. Total magnetic intensity map, reduced to pole magnetic map, analytic single map, first vertical derivative map and upward continuation map have been prepared for this area.
The most significant rock units in the area are cretaceous carbonate rocks (Fig. 3). The unit turns to shale and thin bedded limestone in the central part and into red and white crystalline limestone towards the west, which sometimes can be referred as marble and skarn (Figs. 4, 5 and 6; Saadat, 2014). Iron mineralization is mostly observed in these units. Acidic to intermediate intrusive bodies consisting hornblende quartz monzonite, biotite granodiorite, pyroxene quartz diorite have outcrops in the north and northwestern part of the area (Fig. 3). Outcrops from andesite to dacite volcanic rocks in combination with ultra-mafic rocks can be seen in the southern part of the region.
The geochemical results indicated F2O3 value range of %31 to %96. P2O5 of maximum %0.45 was observed and TiO2 varied from %0.02 to %0.54 (Tables 2 and 3 and Figs 7, 8 and 9). The highest values of iron and copper are found in the northern part, titanium and phosphorus are located in the southern part and manganese and vanadium are placed in the central sector. According to the obtained results, the highest magnetic susceptibility was associated with the skarn units and was measured at 34000*10-5 SI which is related to the mineralization of Iron in the area. Magnetic susceptibility of limestone crystalline units were close to 50*10-5 SI and marble was less than 10* 10-5 SI which highlights the influence of iron mineralization in the carbonates rocks. This value was around 80*10-5 SI for intrusive rocks such as hornblende quartz monzonite in the area (Table 4). Ground magnetic studies suggest minimum of 40000 nT and maximum of 70000 nT total magnetic intensity in the area (Fig. 10-A; Ryahei, 2013). Utilizing the Reduced to Pole Magnetic Filter is to locate the anomalies in the study area (Fig. 11-A). Since magnetic declination causes a degree of deviation between the source and magnetic anomalies, the said filter is applied to magnetic data and ultimately, analysis is done based on the magnetic data transferred to the pole (Nakatsuka and Okuma, 2006; Clark, 1997). The results of reduce to pole magnetic map for this area yielded three large and two small magnetic anomalies (Figs 12-A and 12-B). The upward continuation maps were taken with 5m, 10m, 20m, 30m, 40m, and 50m. Smaller anomalies tend to disappear more comparing the 5m to 20m continuation maps respectively, and a homogenous large anomaly starts to form in the 50m map (Fig. 13). Large and clear anomalies continue to be present in the 50m continuation map and only two smaller anomalies are disappeared from the west of the area (Ryahei, 2013).
The results of geological, geochemical and magnetic susceptibility measurements indicate that magnetic anomalies in the Kalate-Naser area is related to the iron mineralization in this area. Lower amount of magnetic susceptibility in intrusive mass outcrops also indicate that these intrusive rocks did not play the main role in iron mineralization and were in fact have been weakly altered. It can only be concluded that the intrusive mass that led to mineralization sits beneath, at a higher depth.
The initial geophysical survey results are closely comparable to the powder drilling trials that confirm magnetite mineralization to the named depth (Saadat, 2014). Thus far, 1.5 Million ton of Iron ore deposits have been confirmed in the area and exploration continues during production. The obtained results once again highlight the importance of ground magnetic surveys that combined with other exploration methods can reduce costs, increase efficiency and simplify the exploration process. Methodology and results of the magnetic measurements conducted in Kalateh Naser can help to better understand the magnetite bodies in the neighboring areas.

Roudgaz prospect area is a Cu، Sn، Pb، Zn، and Au polymetal vein system located to the southeast of Gonabad and in the northeast of Lut block. Oxidan subvolcanic Tertiary rocks with monzonite to monzodiorite porphyry composition intruded the metamorphic rocks of middle Jurassic. The majority of intrusive bodies are affected by carbonation، argillic، sericitic، and silicification-tourmaline alteration. Mineralization in the area is controlled by fault and is present as vein with domination of NW-SE direction and 85-90º dip. Primary minerals are quartz، tourmaline، chalcopyrite، pyrite، and secondary minerals are malachite، azurite، and goethite. Geochemical sampling using chip composite method indicated high anomalies of Cu، Sn، Pb، and As (up to 10000 ppm)، Zn (up to 5527 ppm)، and Au (up to 325 ppb). Broad gossan zone is present in the area and is related to the oxidation of sulfide minerals. IP/RS survey was performed over the geochemical anomalies for identification of the location and extension of sulfide mineralization at depth. Generally، chargeability increases in gossan zones، veins، old workings and geochemical anomalies. Resistivity over the quartzite unit and also in locations where mineralized vein is associated with quartz has a high anomaly of up to 425 ohm-m. Due to high geochemical anomaly of Sn and its relation with reduced subvolcanic intrusives، ground magnetic survey was performed to identify the location of magnetite (oxidant) and ilmenite (reduced) series at depth. Variation of Total Magnetic Intensity (TMI) is 335. 1 Gamma in the TMI map. The highest magnetic anomalies in the RTP map are located to the north of the survey area which is related to magnetite series (hornblende biotite monzodiorite porphyry) and extend to the south at depth. The lowest magnetic anomaly is located to the center of the survey area and particularly to the east of the Roudgaz village correlating the highest chargeability and geochemical anomaly. Based on coincidence of geochemical and chargeability anomalies، two holes were drilled in the area and 24 samples were collected from the core drills for geochemical analyses. The highest anomalies are accompanied by silicification and chlorite alteration and locations of extension of secondary Fe oxides.