جستجوی مقالات مرتبط با کلیدواژه « manto-type » در نشریات گروه « زمین شناسی »

Hashemabad deposit is located in southeastern part of Esfahan province (Naein), in Central-Iran Zone and within Cretaceous-volcanic rocks. This system is a part of Naein-Ardestan basin which consists of Cretaceous sub-seafloor lava, volcano-sedimentary rocks, and ultrabasic-rocks which formed in extensional environment. This complex located in a tectonic zone (strike-slip fault) adjacent to Urumieh-Dokhtar magmatic arc. Main altered and metamorphosed rocks in this area include Middle-Upper Cretaceous basaltic-lava, andesite, basaltic-andesite, rhyolite and rhyolitic-tuff and younger subvolcanic masses which emplaced in relation to strike-slip faults. Andesite and basaltic andesite which well distributed in whole area are the main host of copper mineralization. Propylitic, argillic, sericitization, silicification, carbonatization and sulfidation are main alterations which well distributed along fault and fractures. However, the intensity of silicification and carbonatization increases in proximity of the mineralized zone. Ore mineralization generally is concomitant with bedding of host basaltic andesite lava in form of disseminated and lens shape and has observed with stratabound geometry along local and cross-cutting faults. Ore minerals have vein-veinlet, open space-filling, disseminated and replacement textures. Ore minerals include chalcocite, bornite, chalcopyrite and pyrite along with secondary minerals such as covellite, chalcocite, malachite, hematite, goethite and azurite. Geochemical studies proposed high potential and enrichment of copper (less Ag&Mo) in this area. The presence of relatively good amounts of gold in tuff units containing jasper as well as in the place of argillic-alteration is one of the unique features of this area. Considering the above evidences, this deposit could be considered as Manto type copper deposit.

The Gheshlagh Cu-deposit is located in the Tarom-Hashtjin metallogenic belt (THMB) of northwest Iran. The mineralization is hosted by Eocene volcanic and volcaniclastic rocks of the Karaj Formation at the subduction-related magmatic arc setting. The geochemistry and petrogenesis analysis confirmed the subduction setting and mineralogically- dominant plagioclase-pyroxene compositions of the host rocks. A good correlation between Al, Fe, Ca, Mg attests to the minerallogic composition, also a strong correlation between chalcophile elements like Pb, Zn, S, Cu and Ag shows sulfide mineralization in the rocks. Based on cross-cutting, the relationship of vein, textural relationship, mineral assemblage and fluid inclusion microthermometry show that alteration and mineralization in the Gheshlagh ore deposit occurred in the fourth main stages. The first stage (stage I) is accompanied by the propyllitic alteration and formation of pyrite (discontinuous) under reducing conditions in the seafloor and very shallow burial environment. The alteration is attributed to magmatic and seawater mixing, which with assuming of the δ18O ranges from 6-10 ‰ for the magmatic fluids and -0.8 to -0.9 ‰ for the Eocene seawater, supported by the values of δ18O quartz (2.1-6.5 ‰) corrected by homogenization temperature of 389 ºC of the related rocks. As the depth of burial increases (stage II), sediments have hardened and also tectonic and lithostatic stress, dykes and floods cause intraformational and magmatic fluids circulation by compaction and heat recharging. These high-temperature fluids are enriched in copper during circulation among volcanic units. Copper-rich fluids migrate upward and are reduced by entering the pyrite-rich andesitic-basaltic unit, and copper is deposited in sulfide forms such as chalcopyrite and chalcocite in the favorable sites. In deeper burial (stage III), the copper mineral formed in the previous stage would be replaced by bornite and digenite. At the supergene condition (stage IV), due to oxidizing conditions, weathering, and leaching, copper sulfides mostly appear as malachite in the joints and voids. According to the results, the mineralization model of the copper in the Qeshlaq deposit can be considered as manto type.

The Saveh-Kashan-Qom copper belt, in the northern part of the Urumieh-Dokhtar Magmatic Arc (UDMA) consists of two of the oldest (gold and copper) zones in Iran (Samani, 1998; Rajabpour et al., 2017) where Upper Eocene-Oligocene Mard Abad-Bouin Zahra volcanic suite is situated. This volcanic suite hosts several copper deposits including Jarou, Gomosh Dasht, Ghezel Cheshme, Bidestan and Afshar Abad that are known as the "Kuh-e-Jarou Mining District". The Kuh-e-Jarou Mining District has a total potential ore reserve of 2 Mt Cu with an average grade of 3 wt.% (Zar-Azin Gostar Consultant Engineering Co., 2009). Upper Eocene volcanic and pyroclastic rocks of rhyodacite, trachyandesite, andesite, and trachytic tuff with high-K calc-alkaline to shoshonitic affinity consist of the main host rocks for Cu mineralization. These units are primarily intruded by post Eocene intrusive bodies.  The geochemistry and genesis of ore bodies have not been fully understood since most previous studies in this area have been focused on petrology of volcanic and intrusive rocks. Moreover, the main purpose of this study is to investigate mineralization style, geometry, and textural-structural features of orebodies, alterations, and fluid inclusions with implication for genesis of Jarou, Gomosh Dasht, Ghezel Cheshme, Bidestan and Afshar Abad copper deposits. In addition, this research provides more insight into understanding geology and mineralization conditions in the study area with an implication for future exploration.

Seventeen thin polished sections from the ores and the host rocks were prepared and they were studied by a transmitted/reflected polarizing microscope in the Iran Mineral Processing Research Center (Karaj, Iran). Five rock powdered samples were also analyzed using X-ray diffraction (XRD) spectrometry (X′ pert Philips) in order to identify the mineralogy of clay minerals in the mineralogy laboratory of Salamanca University (Spain). Fluid inclusion microthermometry was performed using a Linkam THMS600 heating-freezing stage (-190 to +600 °C) mounted on a ZEISS Axioplan2 microscope in the fluid inclusion laboratory of the Iranian Mineral Processing Research Center (Karaj, Iran). Salinities (wt.% NaCl eq.), density (g/cm3) and pressure (bars) were calculated using the FLINCOR v.1.4 (Brown, 1989) and FLUIDS (Bakker, 2012).

The orebody is controlled by a series of feather-like ruptures and faults and its dominant mineral compositions are chalcopyrite and chalcocite with minor amounts of pyrite, galena, bornite and sphalerite. The gangue minerals are quartz, barite, calcite and chlorite. Four types of hydrothermal alterations including chloritization, sulfidization, silicification and epidotization were recognized. Based on field and petrographic studies, three mineralization stages were distinguished including (1) the pre-ore mineralization stage characterized by fine-grained disseminated pyrites, (2) the main hydrothermal stage consisting of three substages: I) an early quartz-chalcopyrite ± bornite vein, II) middle bornite-chalcocite ± covellite breccia ore, III) late galena and sphalerite inclusions, and (3) late-stage barite and calcite veins.Based on petrographic studies, five types of aqueous fluid inclusions have been distinguished in the quartz-chalcopyrite ± bornite and barite veins including two-phase liquid-rich (LV), two-phase vapor-rich (VL), liquid monophase (L), vapor monophase (V) and minor halite-bearing liquid-rich fluid inclusions (LVS). The results show that parental fluids with a density of >1 g/cm3 and an approximate depth of 400 meters were formed and they were followed by fluid inclusions with a density of <1 g/cm3 and a depth of <300 meters due to fluid depressurization, faults. Moreover, introducing low temperature meteoric waters have caused fluid mixing and subsequently copper ore deposition (Henley et al., 2015; Cheng et al., 2019). Considering all geological mineralization styles, textures and structures of the orebody, types of alteration and fluid inclusions in copper deposits of the Kuh-e-Jarou Mining District, it can be suggested that these deposits have similarities with the Manto-type copper deposits in Chile or volcanic red beds in northern America.

The Yamaghan deposit is located in the southeast of Zanjan, within the Tarom subzone of Alborz magmatic belt in NW Iran. The rocks of the area are a collection of Eocene volcano-sedimentary units. Cu (Ag) mineralization in the deposit has occurred as stratabound in the mega porphyritic andesite unit. The main sulfide ores of chalcocite, bornite, chalcopyrite together with pyrite are seen as dissemination, open-space filling, vein-veinlet and replacement textures. Silver sulfide (acanthite) has also been identified based on microprobe studies. Propylitic and mineralization-related alteration types are observed in the deposit. The homogenization temperature of mineralizing fluids was measured in the range 230-390°C, average salinity being 15% NaCl equiv. The Yamaghan deposit formed in three main stages, the first stage occurred at temperatures lower than 100°C during diagenesis, forming framboidal pyrites in the host rock of mega porphyritic andesite. The second stage occurred at temperatures more than 300°C and caused the formation of copper sulfide minerals due to the replacement of pyrite in the first stage. During this replacement, excess iron in pyrite formed as hematite in the place of ores. In the third (or supergene) stage, secondary minerals such as secondary chalcocite, covellite, digenite and copper carbonate minerals such as malachite and azurite formed due to the influence of meteoric water. Based on the geology, host rock, mineralogy, structure and texture, and fluid inclusion data, the Yamaghan copper deposit is similar to Manto-type copper deposits around the world forming through hydrothermal processes.

The Manto-type copper deposits of the Qom-Saveh region are located in the central part of the Urumieh-Dokhtar magmatic arc and occurred in the Eocene volcano-sedimentary sequence. The most important deposits in the studied area are East Narbaghi, Khankishi, Veshnaveh, and Kahak. The geometry of mineralization is stratabound and hosted in the silty tuff, tuff breccia, andesite, lithic crystal tuff, and amygdaloidal andesite basalt. The hypogene ore minerals include chalcocite, bornite, and minor chalcopyrite with vein-veinlet, open space filling, disseminated, and replacement textures. Based on geological studies, two major stages are distinguished for hypogene mineralization. Disseminated and framboidal pyrite formed during the first stage of mineralization which occurred simultaneously with volcanism, sedimentation, and early diagenesis. The second stage of mineralization took place during late diagenesis when copper-bearing oxidized fluids entered into the reduced pyrite-bearing host rock, causing the replacement of the first stage pyrites by copper sulfides. The sulfur isotope composition of sulfide minerals from the East Narbaghi deposit varying from -10.2 to -4.4 ‰ (averaging -6.7 ‰VCDT) indicates the presence of a reduced environment resulting from activation of sulfate-reducing bacteria. The geology, ore mineralogy, alteration characteristics, and sulfur isotopic compositions suggest that the studied ore deposits may be classified as Manto-type mineralization.

The Kahak copper deposit occurs in the Eocene volcano-sedimentary sequence of Qom region, Urumieh-Dokhtar magmatic arc. The oldest rock unit in this sequence is a crystal tuff, overlain by tuff, andesite, sandstone, conglomerate, and limestone. Host rocks to the Kahak deposit include andesite and tuff, and the geometry of mineralization is stratabound. Mineralographical studies show that the ore minerals are pyrite, chalcopyrite, chalcocite, native copper, bornite, galena, covellite, digenite, and malachite accompanied by magnetite, and hematite. Based on mineralogical studies, two types of alteration are recognized in the volcanic rocks of the area, general alteration, and ore mineral alteration. The propylitic alteration is an indication of general alteration. The main alteration types in the mineralized zone of the deposit include carbonatization, silicification, chloritization, epidotization, and zeolitic. Dissemination, open space filling, vein-veinlet, pseudo-lamination, and replacement are the major textures and structures of the ore minerals at Kahak. Two major stages are distinguished for mineralization at the Kahak deposit. The first stage is volcanism and pyrite formation in the host rocks (andesite and tuff), producing reduction state. The second stage involves diagenesis and entering Cu-rich oxidant fluids replacing Cu for Fe in the pyrite and forming Cu-sulfides and hematite and mineralization. The Kahak copper deposit shows high similarities in geometry, host rock, mineralogy, texture and structure and genetic model with the Manto-type copper deposits worldwide.