Pooneh Eshbak; Azadeh Malekzadeh Shafaroudi; Mohammad Hassan Karimpour
Abstract
Jalambadan area is located northwestern Sabzevar, Khorasan Razavi province, and southwestern Quchan-Sabzevar magmatic belt. Geology of the area includes of andesitic-trachyanesitic volcanic rocks, which is intruded by monzodioritic to dioritic subvolcanic intrusive rocks. The texture of igneous rocks ...
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Jalambadan area is located northwestern Sabzevar, Khorasan Razavi province, and southwestern Quchan-Sabzevar magmatic belt. Geology of the area includes of andesitic-trachyanesitic volcanic rocks, which is intruded by monzodioritic to dioritic subvolcanic intrusive rocks. The texture of igneous rocks is porphyry and the main minerals are plagioclase, alkali fldespar, pyroxene, hornblende, and magnetite. Age of intrusive rocks determined 44.7 to 45.2 Ma (Middle Eocene-Lutetian), using zircon U-Pb method. Geochemically, igneous rocks of the area are calc-alkaline and were formed at subduction zone. Relativelly, enrichment in LREE relative to HREE and enrichment of K, Rb, Cs, and Sr relative to Ti and Nb elements are observed in all of samples. Eu anomaly and Sr/Y ratios can be attributed to the presence of residual plagioclase and a few garnet in a source. (87Sr/86Sr)i (0.703708 to 0.704444), (143Nd/144Nd)i (0.512858 to 0..512933), and εNd I (5.42 to 6.88) values of intrusions and geochemical signatures of volcanic rocks indicate magma is drived from partial melting (7-5% for intrusions and 15-25% for volcanic rocks) of spinel lherzolite mantle wedge above subducted slab, which is assimilated slightly with upper continental crust very little.
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.
