جستجوی مقالات مرتبط با کلیدواژه "پهنه طارم-هشتجین" در نشریات گروه "زمین شناسی"

The Jizvan region with an area of ​​45 km2 is located about 70 km northwest of Zanjan town in the Tarom-Hashtjin metallogenic zone. The major rock units in the Jizvan area consist of a regular sequence of thin-layered tuff and breccia tuff with intermediate to basic compositions, interlayered with andesites and basalts. In addition, volcanic trachytic and porphyry andesitic rock units are also scattered in the region. Parts of the tuff and breccia tuff sequence are intruded by hypabyssal quartz monzonite, monzodiorite and syenite intrusions in the east of the region. As a result of this event, due to the presence of linear structures and the invasion of hydrothermal fluids, the above-mentioned rocks are affected by advanced argillic alteration. Carbonatic (malachite) and sulfidic (chalcopyrite, bornite, tetrahedrite-tennantite and chalcocite-covellite) copper mineralizations, along with pyrite, galena, sphalerite, arsenopyrite, quartz, calcite and goethite minerals are developed with a vein-veinlet texture in the above-mentioned units. Using the study of primary biphase fluid inclusions containing liquid and gas phases, homogenization temperatures from 95.6 °C to 268.9 °C with the highest frequency at 185 °C are recorded. The salinity of mineralizing fluids is between 4.65 and 23.8 wt% NaCl equivalent, while their density falls in the range from 0.77 to 1.08 g/cm3. Based on the fluid inclusion data, the mixing between magmatic and meteoric waters is the main cause for precipitation of metallic elements and the occurrence of mineralization in Jizvan area. These data overlap with the representative data of epithermal deposits.

The action of alteration processes on the Eocene tuffs has led to the formation of a spread argillic alteration zone in the Kamar district (south of Ardebil, Tarom-Hashtjin Zone). The aim of this study is to determine the factors controlling argillic alteration, using mineralogical studies and chemical alteration indices. Quartz, kaolinite, muscovite (sericite), rutile, anatase, illite, diaspore, alunite, albite, clinochlore, jarosite, gypsum, pyrite, orthoclase and dolomite are the mineral assemblage of this alteration zone. The mineralization of sulfides includes pyrite (predominantly), chalcopyrite, borneite, chalcocite, galena, and sphalerite. The chemical index of alteration (CIA) values are between 51.55 to 74.3 %, and the mineralogical index of alteration (MI) values vary from 8.22 to 48.3%. The mafic index of alteration (MIA(O)) ranges from 55.88% to 87.48%, Depletion of a large number of elements, including some immobile elements (Zr, Y, LREEs, Al2O3), the presence of minerals indicating acidic pH, such as jarosite and alunite, and high-temperature minerals such as rutile and anatase, the presence of the vuggy quartz in some altered regions, and concomitant enrichment of As, Sb and Mo, in the Kamar argillic zone, bear similarities to the hot fluid alterations of high-sulfidation epithermal deposits.

Intrusion of quartz-monzodioritic igneous bodies of Oligocene age into the Eocene lithic crystal tuffs and trachy-basalts resulted in occurrence of widespread argillic alteration zone in the Jizvan area (Tarom-Hashtjin zone). Mineralogical studies indicate that this alteration zone includes kaolinite, quartz, smectite, pyrophyllite, muscovite-illite, alunite, rutile, calcite, feldspar, chlorite, hematite and goethite minerals. Hypogene ore minerals within the silicic-carbonatic veins and veinlets of argillic alteration zone contain chalcopyrite, galena and pyrite accompanied by goethite, malachite and azurite of supergene origin. Mass changes calculations of elements with assumption of Al as a monitor immobile element indicate that elements such as Ti, P, Th, Nb, Ta, Y and Zr have suffered leaching during argillization of lithic crystal tuffs. This abnormal behaviour is in relation to low pH of altering solutions, high water/rock ratio, abundance of complexing ions and suitable drainage system. The distribution pattern of REEs normalized to chondrite shows differentiation and enrichment of LREEs relative to HREEs and occurrence of negative Eu and Ce anomalies during argillization of lithic crystal tuffs. Geochemical investigations reveal that occurrence of negative Ce anomaly (0.49-0.92) is in relation to the destruction of zircon by acidic-oxidizing fluids. Negative Eu anomaly (0.23-0.73) and mass loss of elements such as Si, Fe, K, Rb, Cs, Sr and Ba indicate destruction of plagioclase and hornblende by strongly acidic hydrothermal fluids and high oxygen fugacity of environment. The correlation coefficients between elements display the controlling role of Mn-oxides in distribution and concentration of REEs, Pb, Zn and Cu. Mineralogical and geochemical evidence such as presence of pyrophyllite, alunite and rutile, enrichment of LREEs relative to HREEs, low values of La৯, negative Ce anomaly and strong positive correlations between (LREEs/HREEs)N-LOI and (La/Lu)N-P suggest that the development and evolution of argillic alteration zone in the Jizvan area is affiliated to hypogene processes.