جستجوی مقالات مرتبط با کلیدواژه "هشجین" در نشریات گروه "زمین شناسی"

Tarazoj-Soushab tectonic window is located between Tarazoj and Soushab villages at the upper corner of the northeast of 1:100,000 Hashjin sheet. This area is a part of the West Alborz Tertiary magmatic belt. Mafic igneous rocks include basaltic pillow lava and gabbro bodies and felsic igneous rocks include granite and trachytic flows. The main minerals of the gabbroic and basaltic rocks are plagioclase, olivine and clinopyroxene and the main minerals of the granitic rocks include plagioclase, orthoclase and quartz, and the trachyte consists mainly of potassium feldspar. Gabbroic and basaltic rocks show calc-alkaline nature and granitic and trachytic rocks have shoshonitic nature. Examination of chondrite and primitive-mantle normalized spider diagrams in basalts and gabbros indicates enrichment of LREEs relative to HREEs. The LILE and LREE enrichment and HREE depletion in the pattern may indicate low melting rate, high fugacity of CO2/H2O in the magma formation environment or high depth of generation of basaltic and gabbroic magma. Examination of chondrite and ORG-normalized spider diagrams in granites and trachytes indicate enrichment of light rare earth elements (LREE) and incompatible elements relative to heavy rare earth elements (HREE). These patterns show a marked depletion of Eu (especially in granites). Gabbroic and basaltic rocks are located in an oceanic environment with E-MORB basalts tendency and the granites and trachites associated with this assemblage belong to anorogenic granitoids (A-type) and subgroup A1. These features indicate that the studied outcrops in the Tarazoj-Soushab tectonic window belong to the rift-related magmatism and opening of the Paleo-Tethys ocean (Paleo-Tethys II) in the northwest of Iran.

The study area is located about 20 km north-west of Hashjin, SW of Ardebil Province and is a part of Kejal-Shamsabad zone in the Tarom-Hashjin volcanic belt. Zeolite and associated minerals, such as quartz and calcite, are formed in cavities and fractures of trachy-andesitic country rock. Studies of zeolitic alteration zones show that stilbite is the main mineral and illite, sanidine, chlorite, calcite and, quartz are minor minerals. Based on petrographic studies, the main minerals of country rocks are plagioclase, k-feldspar, augite with volcanic glass and illustrate porphyritic texture. Geochemical studies and mass-changes calculations on the major and minor elements show that the elements such as Na, K, Ca, Mg, Fe and Mn depleted and Al and Si enriched in altered rocks relative to initial tracky-andesite. The rare-earth elements, except Eu and the HFS elements, have relatively similar behavior and show enrichment with increasing alteration whereas the LIL elements have different distribution patterns in altered and fresh rocks. Hydrothermal origin of zeolites are supported by evidences such as the euhedral crystals, open-space filling and amygdaloidal textures and the absence of main burial or contact metamorphic minerals. Stability field of zeolite is controlled by aqueous silica activity and temperature. Stilbite is stable in log (aSiO2) of -4.1 and forms at temperatures <100º C and pH of 8-9.

Barandagh quadrangle is located in northeast of Zandjan, and is a part of polymetallic region of Tarem-Zandjan. Field evidence and microscopic studies show an intimate relationship between geochemical anomalies and alteration zones in this area. Based on the field observations and mineralogical studis, these zones, in light of extent, locality, and constituent mineral assemblage, differ from one another, and are scattered along the main shear zone of the area and the margin of Ghezel-Ozan river. The major alteration zones in this area are affiliated with the shear zone, and can be categorized into two discrete alteration types: 1) hypogene acid-sulfate (e.g., silicified, alunitized, advanced argillic, sericitic, and propylitic zones) and 2) supergene acid-sulfate (characterized by minerals assemblage such as jarosite, alunite, goethite, gypsum, and native sulfur). Alteration zone along the margin of Ghezel-Ozan river consists of neutral-pH types of alterations (consisting mainly of argillic, calc-silicate-bearing, and zeolitic zones). In general, these alteration zones were developed by the function of a vast geothermal system during the late Oligocene to Mid-Miocene time. Date gathered indicate that the discrepancy in reaction rate between the fluids and the enclosing rocks caused the development of these two types of alterations. Note the type of alteration zones and the obtained results from geochemical exploration, show that this area possesses suitable potential for prospecting of Ag-Au epithermal and polymetallic (Cu, Pb, Zn, Au, Ag) deposits.