Mojgan Salehi Yazdi; Mansour Ghorbani; Nima Nezafati; Mansour Vossoughi Abedini
Abstract
Takab-Mahneshan's metallogenic area is essential in gold mineralization, and it is a part of the northern Urmia-Dokhtar magmatic belt. The northern Urmia-Dokhtar has two distinctive features. It contains the Precambrian basement, and the young Mio-Pliocene magmatism rocks overlie its Precambrian basement. ...
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Takab-Mahneshan's metallogenic area is essential in gold mineralization, and it is a part of the northern Urmia-Dokhtar magmatic belt. The northern Urmia-Dokhtar has two distinctive features. It contains the Precambrian basement, and the young Mio-Pliocene magmatism rocks overlie its Precambrian basement. Precambrian basement has two different compositions, oceanic and continental crusts (gneiss, granite, mica-schist, greenschist, amphibolite, serpentinite, marble). The Young rocks are composed of hyaloclastite, acidic tuff, andesitic-basaltic, acidic to intermediate intrusions (diorite, granite), limestone, and marl of Qom formation. We categorized the Young rocks into four phases based on their age and positions. The mutual effect of the basement and young magmatism --in the latest phase --creates hydrothermal solutions in the form of a heat engine. The heat engine has caused rotation and variety, increasing mineralization in the area. As a result, there are mines, deposits, gold indications, and some associated gold elements, including Tuzlar, Bayche Bagh, Baghcheh at Mahneshan area, Zarshuran, Agh-darreh, and Ay-Qalesi in Takab. The Tuzlar and Baghcheh deposits with gold mineralization are in a Silicic-argillic zone, including pyrite, gold-bearing silica, argillic and ferrous hydroxides minerals. The Ay-Qalesi polymetallic deposits often contain zinc and lead. The Zarshuran and Agh-darreh deposits are the gold types that the first one has a variety of mineralization of sulfides and sulfosalts. The second one has simple gold mineralization, and finally, the Bayche Bagh deposit with polymetallic type includes chalcopyrite, pyrite, rutile, arsenopyrite, sphalerite, bornite, smaltite, chloanthite, azurite, and malachite minerals.
Economic Geology
Behzad Hamamipour; H. A. Tajeddin; Leila Barahmand
Abstract
The Sebandoon gold deposit is located 40 km north of the Bardaskan in the northern part of the Central Iran. The rock units exposed in the area consist of upper Cretaceous volcano-sedimentary sequences of trachyte-trachyandesite, andesibasalt,tuff and carbonaceous shale which intruded by post Eocene ...
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The Sebandoon gold deposit is located 40 km north of the Bardaskan in the northern part of the Central Iran. The rock units exposed in the area consist of upper Cretaceous volcano-sedimentary sequences of trachyte-trachyandesite, andesibasalt,tuff and carbonaceous shale which intruded by post Eocene syenite-quartz monzonite subvolcanic intrusions and diabasic dikes. The main gold reservoir in the Sebandoon deposit has occurred in cone-shaped and mostly in the trachyte-trachyandesite lava with dimensions of 90×150 m in the surface which continue up to the depth of 70 m. The hydrothermal alterations occurred in the deposit area include silicic, sulphidic, partly argillic (supergen) and propylitic which two former contains most of the high grade gold ores. The main ore structures and textures in the deposit are vein-veinlets (stockwork) and breccia which consists of quartz, sulphide minerals and rare adularia. Primary ore mineral assemblages of the deposit are simple and consist of pyrite, sphalerite, chalcopyrite, bornite, galena, arsenopyrite and gold. Covellite, chalcocite and iron hydroxides are secondary minerals in the deposit. Gold grains with less of than 60 microns in size has been found as inclusion in pyrite and chalcopyrite, in sulfides rims and intergrowth with quartz. Fluid inclusion studies on ore-bearing quartz reveal that majority of primary inclusions are liquid-rich two-phase (LV). The studies indicate homogenization temperatures between 165 and 254°C and salinity between 0.9 to 7.8 wt% NaCl eq. Comparison of the main characteristics of the Sebandoon deposit with epithermal gold deposits reveals that the geology, alteration, ore mineralogy, geochemical characteristics and fluid inclusions of the Sebandoon gold deposit is similar to low to intermediate-sulphidation type epithermal deposits.
M.R Omidvar Eshkalak; A.A Mokhtari
Abstract
The studied area is located in the southeastern end of the Sahand- Bazman Magmatic Belt in the north of Bazman volcano. This area composed of Miocene volcanic rocks including andesitic to dacitic lavas along with tuffaceous sandstone, ignimbrite, agglomerate, tuff and siltstone that underwent propyilitic, ...
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The studied area is located in the southeastern end of the Sahand- Bazman Magmatic Belt in the north of Bazman volcano. This area composed of Miocene volcanic rocks including andesitic to dacitic lavas along with tuffaceous sandstone, ignimbrite, agglomerate, tuff and siltstone that underwent propyilitic, argillic, sericitic, carbonatic and silicified alterations. Predominant form of the mineralization is silica veins and hydrothermal breccia, which crop out within the alteration zones. The textures within the silica veins include coliform, vuggy, stratiform, banded and hydrothermal breccias. The results of sample analysis demonstrate that hydrothermal breccias have the highest grades of Au (up to 27.6 ppm), and the silica veins with banded texture and fine grained sulfide bearing silica veins are other important Au- bearing mineralization in the next orders. The geochemical investigations demonstrate good positive correlation between Au and Ag, Sb, As, Pb, Zn, Mo, Bi and Hg in the Au- bearing silica veins. The fluid inclusion studies on silica veins with banded texture indicate that the salinity of fluids is 1.22-7.77 W% NaCl, and homogenization temperature is 190-296◦C. Based on the field evidences along with mineralogy, textures and structures of silica veins, geochemical and fluid inclusion investigations, the Au mineralization in the north of Bazman can be classified as low sulfidation epithermal gold deposits.
M.R Hezareh; I Rasa
Abstract
In the western part of the Sistan & BaluchestanProvince (continuation of the Jebal- e BarezRange) in southeast Iran, the epithermal type (i. e. gold and associated elements) model is one of the anticipated metallogenic model. The studied area is one of the important targets of regional geochemical ...
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In the western part of the Sistan & BaluchestanProvince (continuation of the Jebal- e BarezRange) in southeast Iran, the epithermal type (i. e. gold and associated elements) model is one of the anticipated metallogenic model. The studied area is one of the important targets of regional geochemical exploration. In this regard, the mineral and geochemical geological map of 1/20000 was prepared in an area of 81 km2. After processing of the data and identifying the ore zones, 30 trenches drilled perpendicular to the veins and one sample was taken in every 5 meters. The results show that a tectonomagmatic event and large scale fracturing with strike of N30E led the hydrothermal solutions and caused an extensive alteration. This alteration caused a regional propylitization in andesites and development of a large argillic-silicious alteration in associated lavas and pyroclastics followed by formation of the thin silicious veins in strike of N30E with chalcedony, colloform, cockade and vesicular structures, having the quartz adularia paragenesis and are assumed to be the sources of gold genesis and the main phase of gold formation.
H. Eshraghi; E. Rastad; M. H. Emami; A. Asgari
Abstract
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 ...
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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.
Gh. R. Rastgoo Moghaddam; E. Rastad; N. Rashid Nejad Omran; M. Mohajel
Abstract
Zartorosht gold deposit is located in southeastern part of the Sanandaj-Sirjan zone. Rock units exposed in the area include mafic to intermediate volcanic series, metamorphosed volcano-sedimentary rocks and meta-basites intruded by basic to felsic dikes. These late ...
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Zartorosht gold deposit is located in southeastern part of the Sanandaj-Sirjan zone. Rock units exposed in the area include mafic to intermediate volcanic series, metamorphosed volcano-sedimentary rocks and meta-basites intruded by basic to felsic dikes. These late Paleozoic units have been metamorphosed under lower to medium green-schist facies. Due to several phases of intense deformation, rock sequence indicates new fabrics. The intensity and types of deformation are not the same in the area, so that rock units illustrate ductile-brittle to brittle shear zones.
Gold mineralization occurs in ductile-brittle and brittle shear zones. In ductile-brittle shear zones, gold mineralization occurs parallel to the foliation with lenticular geometry along the strike and dip of the foliation. Analysis of samples from silicified parts of this zone indicates 0.5 to 7.95 ppm Au. In these zones, deformation fabrics can be observed as primary mylonitization in marginal and middle parts, and brittle fabrics in central parts. Gold mineralization in brittle type shear zones has occurred mainly along N70W to E-W and southern dipping normal faults. This type of mineralization includes gold-bearing veins and siliceous-sulfidic bands and can be followed in a 1.5 km long zone. Au grade in samples from siliceous-sulfidic zone is 17.2 ppm and sometimes it reaches up to 35.7 ppm. Mineralized rock units in shear zones indicate different types of alteration including chloritization, epidotization, sericitization, carbonatization, argilization, silicification and sulfidization. Siliceous-sulfidic alteration corresponds to ore-bearing zones within the shear zones.
Studies suggested temporal and spatial relation between alteration and deformation. Spatial relation is explained by overlapping alteration and deformation zones. Foliation parallel open spaces (generated during ductile deformation and mineralization processes) and also micro-fractures in porphyroclasts (generated during grain cataclastic flow) have been filled with hydrothermal - stage quartz and pyrite indicating temporal correlation of alteration and deformation. Au grade changes have close relation with deformation and alteration intensity. This relation has been distinguished by analysis of samples taken from trenches and tunnels perpendicular or parallel to general foliation of rock units. High gold content is related to intensely deformed (mylonitic and ultracataclasite) siliceous and sulfidic parts and Au-bearing siliceous-sulfidic parts coinciding with the inner parts of alteration zones.
Ore-mineral assemblages in the area are relatively simple including pyrite, arsenian-pyrite, rarely galena and sphalerite. Based on microscopic studies, Au occurs as free grains and electrum. Also electron-microprobe and electron-microscope analysis indicate that at least some of Au grains are in sulfide minerals lattice. According to these studies, gold has been observed with both pyrite and arsenian-pyrite phases. Ag has also been detected in sulfide minerals lattice and siliceous gangue.
Controlling parameters for mineral concentration in Zartorosht deposit are shear zones (ductile-brittle and brittle) and alteration (silicification and sulfidization). Based on the comparison of Zartorosht main characteristics with orogenic gold deposits, Zartorosht has the most similarities with orogenic gold mineralization; therefore, it is considered to be of this type.