H Hadizadeh; A.A Calagari; N Nezafati; H Mollaei
Abstract
The Neian area in northwest of the Lut block host a polymetallic (Pb-Zn-Cu-Au-Ag) vein system which was developed within a series of volcanic rocks ranging in composition from dacite through rhyo-dacite and andesite to trachy-andesite. These rocks were formed by two distinct stages of lava eruption. ...
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The Neian area in northwest of the Lut block host a polymetallic (Pb-Zn-Cu-Au-Ag) vein system which was developed within a series of volcanic rocks ranging in composition from dacite through rhyo-dacite and andesite to trachy-andesite. These rocks were formed by two distinct stages of lava eruption. The rocks hosting mineralization possess calc-alkaline and shoshonitic nature and were formed in an orogenic environment. The concurrent and opposite function of two major faults in two sides of the mining area caused the generation of tensional conditions in the middle of the block and led to the development of a series of minor faults with dip-slip and strike-slip components within the block. These fracture zones acted as suitable conduits for fluid infiltration and development of ore-bearing siliceous veins. The factors such as extensive fractures and existence of pyroclastic rocks with high permeability caused the development of widespread alteration zones within the host rocks. Three distinct types of alterations were developed in the Neian deposit: (1) silicified (quartz, chalcedony, adularia, calcite, illite, and sericite); (2) argillic (illite, smectite, quartz, kaolinite, adularia, chlorite, sericite, and zeolite); and (3) propylitic (chlorite, calcite, albite, epidote, quartz and smectite) which are accompanied by five stages of mineralization. These alterations were formed by the chloride-bearing solutions with pH ranging from neutral to very alkaline. Mineralization at Neian is in the form of vein, veinlet, and dissemination within the host rocks and is also associated with hydrothermal breccias. The most important ore minerals at Neian are pyrite, sphalerite, galena, chalcopyrite, marcasite, pyrrhotite, melnikovite, and hematite. The most important gangue minerals also include quartz (chalcedony), cristobalite, calcite, dolomite, siderite, barite, fluorite, and adularia. The evidences like (a) the association of mineralization with siliceous-carbonate veinlets, (b) the presence of adularia, illite, bladed calcite, and hydrothermal breccias, and (c) the presence of alteration minerals such as quartz, adularia, illite, albite, chlorite, interlayered illite-smectite, calcite, and pyrite in the Neian hydrothermal system indicate that these minerals were formed by chloride solutions with almost neutral to very alkaline pH in a low-sulfidation epithermal environment.
A. Maghsoudi; M. Yazdi; M. Mehrpartou; M. Vosooghi Abedini
Abstract
The Mirkuh Ali Mirza gold mineralization is located in north Sarab in the Western Alborz–Azerbaijan structural zone. Mineralization was formed in the form of a vein occurring in Neogene dacitic and rhyodacitic tuff along a series of NW–SE trending fault; Mineralization associated with quartz-sericite-adularia-calcite ...
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The Mirkuh Ali Mirza gold mineralization is located in north Sarab in the Western Alborz–Azerbaijan structural zone. Mineralization was formed in the form of a vein occurring in Neogene dacitic and rhyodacitic tuff along a series of NW–SE trending fault; Mineralization associated with quartz-sericite-adularia-calcite and pyrite(<1%) assemblages is a typical of low-sulfidation epithermal gold mineralization. The fluid inclusion data from quartz minerals indicate homogenization temperature of 161-260°C and salinities of 0.5 to 6.5 wt% NaCl equiv. The variation in gold grade in quartz vein is 270-3240 ppb. The highest gold content is in lattice and breccias quartz that can indicate direct relationship between boiling to gold deposition. The idea is supported by coexistence of vapor-dominant and liquid-dominant fluid inclusions.
M. H. Ahmadi; G.H Shamanian; H. Azmi
Abstract
The Motrabad vein system is located 30 Km southwest of Bajestan in the northern part of the Lut Block. The vein host rocks consist of intermediate to silicic volcanic rocks. The mineralization occurs as irregular veins, veinlets and hydrothermal breccias. Based on field geology and textural evidences ...
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The Motrabad vein system is located 30 Km southwest of Bajestan in the northern part of the Lut Block. The vein host rocks consist of intermediate to silicic volcanic rocks. The mineralization occurs as irregular veins, veinlets and hydrothermal breccias. Based on field geology and textural evidences four types of quartz veins (A, B, C and D) were identified. Hydrothermal alteration is developed around the veins and tends to be more intense in the vicinity of the veins. Hydrothermal alteration consists of silicic, sericitic, propylitic and argilic assemblages. The plot of the Ishikawa alteration index (AI) Vs. chlorite-carbonate-pyrite index (CCPI), known as alteration box plot, display the main alteration trends. The hydrothermal alteration assemblage of quartz, adularia, chlorite, illite, calcite, and pyrite that envelopes the Motrabad vein system formed from the upwelling of near-neutral to weakly alkaline chloride waters. The mineralogic, alteration and geochemical characteristics of the studied area and their comparison with epithermal ore deposits represent an epithermal system of the low-sulfidation type.
E. Ashrafpour; S. Alirezaei; K.M. Ansdell
Abstract
Arghash gold district is located in the eastern Sabzevar zone. The basement of this zone consists of Precambrian metamorphosed rocks and Paleozoic-Mesozoic epicontinental sediments. The basement is covered by Upper Cretaceous ophiolitic mélange and Tertiary magmatic and sedimentary rocks. Arghash ...
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Arghash gold district is located in the eastern Sabzevar zone. The basement of this zone consists of Precambrian metamorphosed rocks and Paleozoic-Mesozoic epicontinental sediments. The basement is covered by Upper Cretaceous ophiolitic mélange and Tertiary magmatic and sedimentary rocks. Arghash district includes five gold-bearing vein systems, Au-I–Au-V, and one Sb vein, occurring in Tertiary intermediate to silicic volcanic rocks, tuffs, granite, and diorite. Intensive alteration, dominated by clay minerals, is confined to 1 to 5 m from the veins. The intensive argillic alteration is bordered by irregular zones of moderate to weak argillic and propylitic alterations.
Mineralization is mostly confined to veins. Pyrite is the main sulfide mineral and includes four generations: 1) disseminated euhedral to anhedral, fine- to coarse-grained pyrite (Py-I), locally associated with minor chalcopyrite, marcasite, tetrahedrite-tennantite, and arsenopyrite; native gold grains occur in quartz associated with the pyrite; 2) framboidal pyrite (Py-II) which contains up to 960 ppm Au; 3) arsenian pyrite overgrowths (Py-III) which contain up to 1980 ppm Au; and 4) fracture-filling, anhedral, barren, late stage pyrite (Py-IV). Gold occurs as nanoparticles as well as unstable solid solutions in the framboidal and arsenian pyrite.
Homogenization temperature (Th) and salinity were measured on fluid inclusions in several quartz and calcite samples. Th varies from 186º to 357ºC, and 169º to 313ºC, and salinity from 0.2 to 5.3 and 0.7 to 1.9 wt. percent NaCl equiv. for quartz and calcite, respectively. The low salinity character of the ore forming fluid is consistent with the ore mineralogy and metal contents. The variation in salinity and Th could be explained by a combination of boiling and mixing (dilution) of a hotter and more saline fluid with a cooler and less saline fluid. These processes led to the deposition of gold in the veins. The ore mineralogy, textures, alteration, homogenization temperatures, and salinities, are typical of low-sulfidation epithermal precious metal deposits.
