جستجوی مقالات مرتبط با کلیدواژه "هیرد" در نشریات گروه "زمین شناسی"

The Hired mining area south of Birjand, South Khorasan province has been identified as the center of mineral pollution accumulation and it has been attempted to map the soils of the study area from their geochemical and environmental map. The maximum concentrations of Arsenic and Antimony were 5550 and 910 ppm, respectively. The enrichment factor (EF) for Arsenic, Antimony and Cadmium are 1.89, 2.05 and 0.03, respectively. This indicates the average contamination of the two elements Arsenic and Antimony and the lack of contamination of the area with Cadmium. According to the I-geo index, the degree of contamination of Arsenic and Antimony elements was 1, indicating a moderate contamination of the two elements in the region and less than 1 for Cadmium. Pollution Index (PI) for the Arsenic and Antimony elements in the area was moderate and for the Cadmium element, indicating that the soils of the study area were classified as non-polluted to moderately contaminated and most of this contamination is in the adjacent soils of the mine. In general, the soils of the study area have high levels of trace elements (above the natural background value) and if not controlled in the future, the pollution will reach a critical level and cause many problems for the inhabitants of the area.

The Hired gold prospect area is located in the Southern Khorasan province and 140 Km south of the Birjand city. The Acidic to mafic intrusive bodies with gabbro to granite composition have intruded into the Tertiary volcano sedimentary sequences. Based on magnetic susceptibility, the intrusives are divided into two categories: magnetite (oxidized) and ilmenite (reduced) series. The important alterations recognized on land surface and bore holes consist of: 1) quartz-tourmaline-sericite alteration, 2) carbonation alteration, 3) skarnization, and 4) propylitic alteration. Au and accompany elements mineralization (W, Sn, Bi, As, Sb, Pb, Zn, Ag) have formed as replacement, disseminate, vein-veinlet, massive, breccias, and skarn related to reduced granitic-granodioritic intrusive bodies and with different distance as compared with the bodies. Geological, mineralization, petrographical, mineralogical and alteration studies of the Hired gold deposit and comparison with the characteristics of different types of gold mineralization in the world indicate that this deposit has the most similarity with reduced intrusion-related gold systems (RIRGS). Since In this system, the most of gold reserve is accompanied with sulfide minerals and they form in roof of the reduced granitoid stocks and adjacent hornfels rocks, The IP- RS geophysical methods on reduced granitoid intrusive body and near regions was executed with the aim of recognition of hidden parts. Combination of geophysics data (IP, RS) with geological, alteration, and mineralization studies shows well development mineralization in the east of intrusive body and the country rocks. In this relation, 6 anomalous regions has been defined with Chargeability up to 30 mv/v that on the whole, they can be divided into two groups: 1) anomaly with high induced polarization and low specific resistivity resulting from presence of much metallic sulfurs as disseminate, veinlet, and massive accompanied with high sericitic alteration, 2) anomaly with high induced polarization and medium-high specific resistivity resulting from presence of much metallic sulfurs as disseminate and very high carbonation-silicic alteration.

Hired area is located in the northeastern border of Lut zone and western vicinity of Sistan suture zone. Northern part of Sistan suture zone trending NW-SE with complicated structure is the locality of several considerable ore deposits. We have employed aeromagnetic data, satellite images and field observations to consider the relation of surface and subsurface structures to the significant superficial structural features of Hired mining area. Aeromagnetic data were processed by applying appropriate filters including Reduction to pole and First vertical derivative for proper distinguishing the magnetic features. In addition, highpass filters were used for edge sharpening of the ASTER images. Aeromagnetic data have shown two main N-S and NW-SE structural directions which follow the northern Sistan suture zone. Presence of mineralized and altered veins and brittle shear zones with the same trend around the fractures is noticeable. Moreover, fractures intersections and conjuncture places are dramatically compatible with mineralization areas. Another result from aeromagnetic data is identification of a circular structure in the east of study area. The gold mineralization has occurred in the west part of mentioned structure which is strongly affected by NNW striking features. Satellite images in addition to confirmation of aforesaid structural trends imply a third structural NE-SW strike. This structure is not vivid on the aeromagnetic map and has only an ambiguous trace on it. Our field measurements verify this new structural trend as well.

The Hired gold mineralization is located 140 km South of Birjand, Southern Khorasan, and north of Lut Block. In the area, the Jurassic and Cretaceous units are covered by Tertiary volcano-sedimentary sequences. Granite, granodiorite-quartzdiorite and gabbronorite bodies have intruded Tertiary sequences, and mineralization occurs within or at periphery of a subvolcanic granodiorite-quartzdiorite stock with porphyry texture. The existence of ilmenite within subvolcanic granodiorite-quartzdiorite bodies which the lack of magnetite and low magnetic susceptibility (1.5×10-4 SI Units) as well as low ratio of Fe2O3/FeO (<0.5), they are classified as ilmenite or reduced (low fO2) granitoid rocks.Mineralization in Hired area is divided into three main zones based on the distance from the stock. The mineralized zones are as follow: intrusion-hosted mineralization, proximal mineralization and distal mineralization. These three zones are different in host rock, mineralogy, alteration, structure, texture and metal assemblage. In the intrusion-hosted mineralization, the ore-bearing unit is subvolcanic granodiorite-quartzdiorite stock. Three types of major vein-veinlets observed within the stock, including vein-veinlets of tourmaline-quartz-sericite and sulfide (TQSS), quartz-calcite and sulfides (QCS) and quartz-calcite with rare sulfide (QC). The vein-veinlets include sheeted and stockwork arrays. The proximal mineralization occurs in volcano-sedimentary sequences. These sequences include tuff, andesite and conglomerate components. The sulfides occur as disseminated, vein-veinlet and massive textures. Stockwork and rarely sheeted vein-veinlets in this type of mineralization contain quartz, calcite and sulfides. Sericitization, silicification and carbonatization are the principal alterations associated with mineralization zone. The distal mineralization occurs in faults with low angle dips, trending NE-SW and NW-SE. These faults are filled with silica and carbonates, with iron oxides and hydroxides at the surface. The comparison of the most important characteristics of Hired mineralization (including tectonic setting, host rock, mineralogy, mineral paragenesis, ore content, structure, texture and alteration) with the characteristics of different types of gold mineralization suggests that the Hired gold mineralization shows most similarity with the gold mineralization related to reduced granitoid intrusion. This type of mineralization is reported for the first time from Iran

Exposed rocks at Hired gold-tin prospecting area are mainly Mesozoic and Paleocene sedimentary and Eocene volcanic rocks. Oligo-Miocene Granitoids are intruded the Eocene and older rocks. Based on petrology and physical characteristics of rocks, granitoids are two types: 1) S-type and 2) I-type. Mineralization is seen as stockwork, fault mineralized zone, skarn and in replacement. Stockwork mineralization is exposed in the eastern part of target (1) and it is found within S-type granite and silicified – tourmaline rich shale. Hypogene minerals are: pyrite, arsenopyrite, pyrrhotite, chalcopyrite, ± galena, ± sphalerite, tourmaline, quartz, chlorite, calcite and sericite. Gold is mainly found in veinlets contain sulfide, quartz and tourmaline. Based on S-type granite, stockwork mineralization, tourmaline alteration and Sn anomalies (581 ppm), Hired is a Tin – Gold mineralized system. Geochemical data from drill holes in target (1) and (3) indicate that the high value of Au, Ag, Cu, Zn, Pb, As and Sb are found mainly between depth of 50 to 100m in eastern part of target (1), therefore this area is close to the source of fluid. Tin – Gold mineralized system at Hired is associated with S-type granite.