M. R. Hosseini; S. Alirezaei; J. Hassanzadeh
Abstract
The Bahr Aseman volcanic-plutonic complex is located to the southeast of the Kerman magmatic belt. Unlike Kerman magmatic belt which formed and evolved during Cenozoic in a dominantly continental arc and post-collision tectonic setting, Bahr Aseman complex formed during Late Cretaceous in an oceanic ...
Read More
The Bahr Aseman volcanic-plutonic complex is located to the southeast of the Kerman magmatic belt. Unlike Kerman magmatic belt which formed and evolved during Cenozoic in a dominantly continental arc and post-collision tectonic setting, Bahr Aseman complex formed during Late Cretaceous in an oceanic island-arc setting. The complex is composed of andesitic and andesitic-basaltic lava flows and subordinate pyroclastic materials and carbonate interlayers, as well as abyssal tonalite to quartz-diorite and quartz- monzodiorite intrusive bodies and shallow dioritic intrusions. Vein- type copper deposits, iron skarn and copper skarn are the main ore deposit types in Bahr Aseman. Chalcopyrite is the main ore mineral in vein-type and skarn-type copper deposits; the mineral is converted to oxide copper ores at surface and shallow depths. Magnetite is the main commodity in skarn type iron deposit. Highly altered porphyritic bodies associated with copper oxide ore were identified that are comparable, in some aspects, with porphyry type copper deposits; subsurface data, however, is required for conclusive remarks. The various types of deposits are distinguished by distinct fluid inclusion characteristics. In the vein type copper deposits, fluids in association with mineralization represent dominant homogenization temperature (Th) of 150-220 ºC and salinity of 5-10 and 25-30 wt% NaCl. Fluids in the skarn type copper deposits represent 170-250 ºC and ranges of 5-15 and 27-35 wt% NaCl as dominant Th and salinity, respectively. The δ34S values in the vein-type copper deposits vary between +3.9 and +5‰, suggesting a magmatic origin for sulfur and probably metals (directly derived from magma or leached from magmatic rocks). Sulfur isotope ratios for two samples from Moka are +4.3 and +7.1‰, slightly different from typical magmatic δ34S ranges. Oxygen and hydrogen isotope ratios for the vein-type copper deposits, measured on quartz and fluids extracted from inclusions in the mineral, are -6.6 to +1.9‰ and -79.4 to -51.8‰, respectively. This values suggest mixing of magmatic and meteoric fluids and/or fluid-rock interactions at different ratios. It appears that larger deposits have more shares of fluids with magmatic origin. With regards to the island-arc tectonic setting, recognized deposit types and ore minerals paragenesis, finding new copper and iron and probably gold deposits are possible in the Bahr Aseman area.
S Hassanpour; S. Alirezaei
Abstract
The Masjeddgaghi Cu-Au deposit is located to the southeast of the Arasbaran zone, NW Iran, to the south of the Lesser Caucasus. Mineralization in Masjeddaghi is associated with an Eocene dioritic subvolcanic pluton intruded into older volcanic and sedimentary rocks. The Masjeddaghi intrusive body is ...
Read More
The Masjeddgaghi Cu-Au deposit is located to the southeast of the Arasbaran zone, NW Iran, to the south of the Lesser Caucasus. Mineralization in Masjeddaghi is associated with an Eocene dioritic subvolcanic pluton intruded into older volcanic and sedimentary rocks. The Masjeddaghi intrusive body is high-K, calc alkaline, and meta-aluminous, and formed in an island arc subduction/collision setting. Hydrothermal alteration is distinguished by a potassic core marked by secondary biotite and K-spar that grades outward into a chlorite-rich propylitic halo. The ore minerals include chalcopyrite, associated with minor chalcocite, bornite, tetrahedrite, and trace molybdenite. Pyrite and magnetite are common associates. The Masjeddaghi deposit is elliptical in plan view, 500 x 400 m in diameters, and mineralization has been traced for several hundred meters from surface exposures. 40Ar/39Ar geochronology on secondary biotite from potassic alteration zone indicates that mineralization, and by corollary, the emplacement and crystallization of the Masjeddaghi porphyritic intrusion, occurred in 54.07 ± 0.53 Ma. The Masjeddaghi ore deposit shows geology, mineralization and alteration characteristics comparable to those typical of island arc type porphyry Cu-Au systems. Masjeddaghi ore deposit shows geology, mineralization and alteration characteristics similar to island arc porphyry type systems.
E. Haghighi; S. Alirezaei; E. Ashrafpour
Abstract
The Cheshmeh Hafez deposit in Torud-Chahshirin Range, north-central Iran, consists of a polymetal vein mineralization in Cenozoic volcanic host rocks of dominantly basaltic andesite and dacite compositions. The main ore vein, 1800 m long and <1 – 5 m wide, occurs discontinuously in a north-south ...
Read More
The Cheshmeh Hafez deposit in Torud-Chahshirin Range, north-central Iran, consists of a polymetal vein mineralization in Cenozoic volcanic host rocks of dominantly basaltic andesite and dacite compositions. The main ore vein, 1800 m long and <1 – 5 m wide, occurs discontinuously in a north-south direction, and includes chalcedony, fine- to coarse-grained quartz, and jasperoid, associated with galena and subordinate chalcopyrite, sphalerite, bornite, pyrite, tetrahedrite, specular hematite and siderite. Crustiform bands, consisting of grey chalcedony, jasperoid, milky quartz, and various ore minerals are common, and breccias and comb textures are locally developed, in the vein. Supergene processes led to the replacement of galena by cerussite, and of hypogene copper minerals (chalcopyrite and bornite) by covellite and malachite. The main ore vein is accompanied by several smaller quartz and calcite veins in NE-SW and E-W directions, respectively, where the calcite veins are barren. Alteration related to mineralization is restricted to thin halos bordering the vein, and consists of quartz, chlorite, calcite, kaolinite and sericite (illite). Fluid inclusions in quartz associated with ore minerals are studied. Most inclusions are two-phase, liquid-rich, at room temperatures; few are vapor-dominant, and few consist solely of liquid. Primary fluid inclusions display low to moderate homogenization temperatures (135-285) and salinities (1-13 wt% NaCl equivalents). The δ34S values for the ore fluids in equilibrium with the sulfide minerals fall in the range -1.6 to +4.1‰ and suggest a magmatic source for sulfur. The ore and gangue mineralogy, and the alteration assemblages, suggest that the ore fluids were reduced and near-neutral in nature. This, combined with the metal contents, Ag/Au ratio between 16 to 25, iron- poor sphalerite, the crustiform and colloform textures, and the Th and salinity values, imply that mineralization at Cheshmeh Hafez is of epithermal, intermediate- sulfidation, character. The alteration assemblage at Cheshmeh Hafez is indicative of a sub-type of intermediate- sulfidation epithermal deposits with a tendency towards low-sulfidation type
Ahmad Kazemi Mehrnia; I. Rasa; S. Alirezaei; H. Asadi Harooni; J. Karami
Abstract
The Saridoon porphyry system is located 3 km northeast of Sarcheshmeh copper mine. Alteration mapping of the area was carried out using PIMA (Portable Infrared Mineral Analyzer) analysis of 145 samples, ASTER satellite images, XRD analysis of 22 samples, field observations and petrographic studies. The ...
Read More
The Saridoon porphyry system is located 3 km northeast of Sarcheshmeh copper mine. Alteration mapping of the area was carried out using PIMA (Portable Infrared Mineral Analyzer) analysis of 145 samples, ASTER satellite images, XRD analysis of 22 samples, field observations and petrographic studies. The lithocap is characterized by an advanced argillic alteration assemblage. The alteration occurs at high topographic levels and on the flanks of the topographic heights. Despite extensive exposures, the alteration varies in intensity and occurs as patches or partially exposed. Pyrophyllite spectral feature is used as a measure of alteration intensity (pyrophyllite abundance).
Phyllic alteration occurs in the central part of the sampled area. This spectrally distinct alteration assemblage occurs at all elevations, and is partially overprinted by advanced argillic alteration. Intermediate argillic alteration occurs on the flanks of advanced argillic and phyllic alterations. The mineral assemblage might have been formed by supergene processes, or alternatively, by low temperature hydrothermal fluids. The PIMA and XRD samples were analyzed by ICP-MS for a number of metals and semi-metals. A comparison of data from Saridoon and those from three other porphyry systems in northwest Kerman belt (Darrehzar, Abdar, and Chah Firuzeh) shows lower contents of Cu and Mo, and higher contents of As, Sb, Pb in Saridoon. The extend alteration systems in Iranian magmatic arc with low frequency of Cu and Mo shall be checked for advanced argillic alteration mineral assemblage using modern spectrometry instrument (e. g. PIMA). This distribution pattern of elements, coupled with the widespread occurrence of advanced argillic alteration at surface, suggests that stripping of overlying rocks at Saridoon was not as deep and effective as in many other porphyry systems in the Kerman belt. These findings suggest that alteration systems with low Cu and Mo contents and mineral assemblages typical of advanced argillic alteration merit closer and deeper inspection.
E. Ashrafpour; K. M. Ansdell; S. Alirezaei
Abstract
Arghash gold district includes five gold-bearing vein systems, (Au-ItoAu-V) and one antimony-rich vein hosted by intermediate to silicic volcanic rocks, tuffs, granite, and diorite. Pyrite is the main sulfide mineral consisting of four generations (Py-ItoPy-IV). Py-I toIII are intimately ...
Read More
Arghash gold district includes five gold-bearing vein systems, (Au-ItoAu-V) and one antimony-rich vein hosted by intermediate to silicic volcanic rocks, tuffs, granite, and diorite. Pyrite is the main sulfide mineral consisting of four generations (Py-ItoPy-IV). Py-I toIII are intimately associated with gold; however, Py-IV is barren. The δ34S values of pyrites in conventional bulk analyses fall into two groups, one highly enriched in 34S (δ34S= +9.3 to +21.8‰), and the other less enriched to slightly depleted in 34S (δ34S= +5.1 to -4.3‰). In-situ laser probe experiments were carried out to characterize various generations of pyrite. The results indicate a relatively narrow range for Py-I to Py-III (δ34S= -5.8 to +0.1‰) consistent with a magmatic source for sulfur. Py-IV is highly enriched (δ34S= +8.9 to +23.7‰), implying contributions of sulfur from sources enriched in 34S, like evaporites. The high δ34S values in the enriched group can be attributed to a significant occurrence of Py-IV in this group.
The δ34S values of two stibnites from Sb ore (-18.8 and -14.4‰) suggest a different sulfur, and possibly metal source, and/or radical changes in the physicochemical conditions of the fluid during deposition of stibnite. Metasedimentary basement rocks could contribute sulfur and metal to the circulating fluids. δ13CPDB values of vein calcites are near 1 per mil suggesting a sedimentary source for carbon. Carbonate units and interlayers in the area are a suitable source for CO2 in the ore fluids. The stable isotope data suggest that hydrothermal fluids experienced a complex history of water/rock interaction and that ore components, were derived, at least partly, from country rocks.
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 ...
Read More
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.
S. Ebrahimi; Y. Pan; S. Alirezaei; M. Mehrpartou
Abstract
The Sharafabad auriferous epithermal vein system is located in the Alborz-Azarbaijan magmatic assemblage in northwestern Iran. The veins are hosted by Eocene andesitic volcanic and pyroclastic rocks and tuffs. Wall rock alteration includes an inner silicic zone often bordered by argillic and propylitic ...
Read More
The Sharafabad auriferous epithermal vein system is located in the Alborz-Azarbaijan magmatic assemblage in northwestern Iran. The veins are hosted by Eocene andesitic volcanic and pyroclastic rocks and tuffs. Wall rock alteration includes an inner silicic zone often bordered by argillic and propylitic zones. Mineralization is mainly restricted to silica and silica-carbonate veins and veinlets in faults and fault zones. A total of 18 ore-bearing veins have been identified. The veins vary from 10 -1000 meters in length and 0.5-10 meters in width, respectively. Pyrite is the main sulfide, commonly associated with subordinate chalcopyrite, sphalerite, and galena. Gold occurs as scattered microscopic grains in quartz and pyrite, and along the grain boundaries of the sphalerite, galena and chalcopyrite. Silica occurs as gray quartz, white quartz, clear quartz, opal, chalcedony, and minor amethyst. On the basis of crosscutting relationships and mineral paragenesis, four stages can be distinguished: (I) pre-mineralization, (II) mineralization, (III) post-mineralization and (IV) supergene. The gold and the base metals sulfides occurred in the mineralization stage. Fluid inclusion data have been obtained from the ore-stage gray quartz and sphalerite, carbonates, and the late clear quartz and amethyst. The fluid inclusions from the gray quartz indicate homogenization temperatures of 170-270 ºC and salinities of 1 to 8.7 wt% NaCl equiv. The fluid inclusions in the sphalerite indicated homogenization temperatures of 215-265 ºC, and salinities of 10.8-15.3 wt% NaCl equiv. The carbonates formed at lower temperatures, between 160-250 ºC, from fluids of low salinities, at 1.5-3.8 wt% NaCl equiv. Amethyst from final stages of vein formation, not associated with sulfides and gold was deposited at 173-203 ºC from fluids containing 3.5 to 9.5 wt% NaCl equiv. The coexistence of vapor-dominant and liquid-dominant inclusions in quartz and sphalerite suggests that boiling occurred during the evolution of the ore fluids. The occurrence of boiling is supported by hydrothermal breccias, bladed calcite, and adularia. Fluid inclusion data suggest that ore was deposited at an average depth of about 400 m below the paleosurface. Considering the intermediate argillic alteration, association of gold with base metal sulfides, and the moderate salinities, the Sharafabad district can be classified as an intermediate-sulfidation epithermal system.
