R. Samadi; M. V. Valizadeh; H. Mirnejad; A. A. Baharifar; S. J. Sheikh Zakariaee
R. Monazzami bagherzadeh; H. Mirnejad; P. Eshback; M. H. Karimpour
Abstract
Listvenites or ophiocarbonates are considered important for exploration of precious and base metlas particularly Au, Ag, Cu, As and Hg. These rocks, which crop-out dominantly in ophiolite-mélange zones and in the vicinity of main faults and shear zones, have formed as the result of hydrous ...
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Listvenites or ophiocarbonates are considered important for exploration of precious and base metlas particularly Au, Ag, Cu, As and Hg. These rocks, which crop-out dominantly in ophiolite-mélange zones and in the vicinity of main faults and shear zones, have formed as the result of hydrous and carbonic alteration of ultramafic rocks. Listvenites occur extensively in eastern Iran. Based on petrography, Hangaran listvenites are grouped into three major types: 1. Carbonatic listvenite (type I), 2. Silicic listvenite (type II), and 3. Sulfie-bearing silicic listvenite with brecciated texture (type III). Gold contents of listvenites is generally low and the highest concentration (290 ppb) has been found in type III. Studies of mineral concentrates from stream sediments reveal the presence of gold, pyrite, chalcopyrite, cinnabar and native copper. Gold grains reach to a maximum sizes of 80 microns, and they are often associated with pyrite. Electron microprobe analyses on several sulfides and carbonates in Hangaran listvenites show that sulfide minerals are mainly pyrite, marcasite, bravoite and to a lesser amount chalcopyrite, and that many pyrite grains have been altered to marcasite. Important carbonated minerals are magnesite and dolomite. The presence of obiquitous bravoite zonation that results from alternations in Ni content indicates periodic changes in the physicochemical conditions of the hyrdorthemal solution. Petrographic studies and paragenetic sequence of minerals show that magnesite and dolomite formed prior to the mineralization stage, which was then followed by the formation of sulfides (mainly pyrite). Studies on the oxygen and carbone isotopes in 3 dolomite samples (δ18OSMOW = 9.353- 9.982 ‰, δ13CPDB =1.57- 1.67 ‰ ) show that oxygen and carbone can originate from oceanic waters, and that dolomite has formed due to the circulation of this water in ultramafic rocks and their subsequent alteration. Considering the variation in marcasite-pyrite paris from Hangaran silicic listvenite (δ34SCDT value 5.7-7.9 ‰ ), it seems that sulfur has originated from granitic rocks in south of the study area. Taking into accout the extentive outcrops of serpentinized ultramafic rocks and granite in the region can considered the source of Au, Ag and base elements such as Cu, Pb, Zn, Hg, As, Sb in related to granite masses, and Cr, Ni, Ti and Fe in related to serpentinized ultramafic rocks. Fluid inclusion studies on mineralized quartz in Hangaran listvenites show that the hydrothermal fluid affecting the host rocks was low salinity and had a maximum temperature of 280ºC.
N. Fatehi Gelab; H Mirnejad; R Mathur
Abstract
The Darrehzar and Parkam deposits in Kerman province are two examples of porphyry type copper deposits in the Cenozoic Urumieh- Dokhtar magmatic arc. Volcanic rocks in the study areas are dominantly composed of andesite, trachyandesite and basalt. The Darrehzar quartzmonzonite stock consists of phenocrysts ...
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The Darrehzar and Parkam deposits in Kerman province are two examples of porphyry type copper deposits in the Cenozoic Urumieh- Dokhtar magmatic arc. Volcanic rocks in the study areas are dominantly composed of andesite, trachyandesite and basalt. The Darrehzar quartzmonzonite stock consists of phenocrysts of plagioclase, hornblend, quartz and biotite, andconstituent minerals of diorite-microdiorite porphyry in Parkam include plagioclase, alkali-feldspar, amphibol, biotite and quartz. The thickness of oxide zone in Darrehzar deposit is few meters and in many well cores it cannot be obsereved at all, while the the thickness of leached zone varies between 2 and 80 m. Supergene zone in the center of this deposit has the greatest thickness (120 m). The depth of hypogene zone from Darrehzar is 400 m. The thickness of leached zone from Parkam is around 20 m. The average thickness of supergene zone in this deposit is 15 m and its maximu depth is 64 m. The depth of hypogene zone in some cores is around 500 m. Evalutating the Cu isotope ratios from leached, supergene and hypogene zones in these two deposits show that the magnitude of Cu isotopic fractionation and Cu concentrations are mainly controlled by the weathering processes. The average δ65Cu values of copper in the leached, supergene and hypogene zones in Darrehzar deposit are, respectively, -6.16‰, +2.52‰ and +0.79‰, and those in the Parkam are -4.33‰, +4.82‰ and +0.34‰. Therefore, weathering of Cu sulfide minerals generated isotopically lighter residual minerals and dispersed the heavy isotope to the percolating groundwaters. It is thus expected that the copper isotope ratios of the leached zones in various porphyry copper deposits to be linked with the extent of leaching and the supergene enrichment processes. Microscopic studies and mineralogical studies shows that hematite in the Darrehzar’s leached zone in more abundant than that in the Parkam, while Parkam’s leached zone contain higher goethite content relative to that of the Darrehzar. The amount of chalcosite, and pyrite–chalcopyrite in the supergene and hypogene zones, respetively, from Darrehzar, are more abundant compared to those in the equivalent zones in Parkam.
Ramin Samadi; M. V. Valizadeh; H. Mirnejad; H. Kawabata
Abstract
Metamorphic rocks of Dehnow area mainly consist of gray to black fine-grained schists. Garnet schists are closer to the tonalitic body than the garnet chloritoid schists. There is a thin layer of staurolite and andalusite bearing hornfels between these schists and the Dehnow tonalitic body. Garnet schists ...
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Metamorphic rocks of Dehnow area mainly consist of gray to black fine-grained schists. Garnet schists are closer to the tonalitic body than the garnet chloritoid schists. There is a thin layer of staurolite and andalusite bearing hornfels between these schists and the Dehnow tonalitic body. Garnet schists and garnet chloritoid schists of Dehnow area are mineralogically comprised of quartz, biotite, muscovite, garnet, chlorite, chloritoid, tourmaline and ilmenite. Geothermobarometry results indicate that hornfels (550oC, 4.3 kbar) and garnet chloritoid schist (486-497oC) have formed in lower equilibrium condition in comparison with garnet schist (569oC, 5.3 kbar).
