طوبی صالحی

The Tutak area (northeastern part of Shiraz city) located in Sanandaj-Sirjan metamorphic Zone (SSZ) was chosen as study area because of having two important resources of iron and copper. Two metamorphic complexes of SSZ namely Surian and Tutak are the main host of these resources. The algorithms of Spectral Information Divergence and Adaptive Coherence Estimator were used to detect and distinguish rock units and indicator minerals. Using spectra of field samples, the pixel-based algorithm of Spectral Information Divergence enhanced greenschist and marble lithological units because of their significant spectral differences in VNIR region. Overall accuracy and kappa coefficients resulted by using this algorithm for detection of rock units were 0.83 and 0.72, respectively. Using data of USGS spectral library, the outputs of the sub-pixel algorithm of Adaptive Coherence Estimator successfully identified pixels with high abundances of chlorite and ankerite. Results showed that chlorite areas with its abundances more than 50% overlapped greenschist units, and the areas with chlorite abundances above 75% had acceptable conformity with the copper deposits, most prominent of which is Mazaijan copper deposit. The areas with more than 50% ankerite overlapped the marble units, and its abundances above 75% indicated an increase of the abundances of this mineral compared to the minerals of calcite and dolomite in this rock unit with approaching iron mineralization. So, based on study results, the Adaptive Coherence Estimator technique can be suggested to accurately detect and distinguish the minerals of the mineralogical reservoirs in study area.

Gomish-Tappeh Zn-Pb-Cu (Ag) deposit is located in northwestern part of Urumieh-Dokhtar volcano-plutonic zone، 90 km southwest of Zanjan. Exposed rocks at the area include Oligo-Miocene volcano-sedimentary and sedimentary sequences as well as Pliocene dacitic subvolcanic dome، rhyodacitic volcanics and andesite porphyry dykes. The main mineralization at Gomish-Tappeh deposit has occurred in a steeply deeping normal fault and fracture system defined by NE-SW trend in three stages including hydrothermal breccias، silicic-sulfidic، silicic-sulfidic-carbonate veins and veinlets and late banded veins (rich in silica and specularite). Host rocks to mineralization include dacitic crystal lithic tuff، dacitic subvolcanic dome، and specifically acidic tuff. Paragenetic minerals at the deposit consist of pyrite، arsenopyrite، chalcopyrite، bornite، galena، low-Fe sphalerite، tetrahedrite، tennantite and specularite. The main alteration types at the area are silicic، silicic-sulfidic، sericitic، carbonate، argillic and propylitic. Based on element distribution and frequency patterns in the ore samples، among base metals، Zn، Pb، Cu and Ag show the highest concentrations. Average grades in the ore veins at Gomish-Tappeh deposit are: 6% Zn، 4% Pb، 2% Cu، 88 ppm Ag and 44 ppb Au. Fluid inclusion microthermometric studies on quartz crystals of the first and second stages of mineralization indicate homogenization temperatures of 260-367 °C، salinities of 9. 1-16. 9 wt% NaCl equiv.، and approximate mineralization depth of 956 m below the paleowater table. Considering high salinity fluids and base metal contents، it is likely that base metals and silver were transported by chloride complexes. Fluid inclusion studies، hydrothermal breccias، banded-colloform-crustiform textures and amorphous silica indicate that boiling is the main factor for instability of the complexes and eventually، ore deposition.

Gomish-Tappeh Zn-Pb-Cu (Ag) deposit is located 90 km southwest of Zanjan, in northwestern part of Urumieh-Dokhtar volcano-plutonic zone. Exposed rocks at the area include Oligo-Miocene volcano-sedimentary and sedimentary sequences as well as Pliocene volcano-plutonic sequence (andesite porphyry dykes, dacitic subvolcanic dome and rhyodacitic volcanics). Alteration in the deposit developed as silicic, silicic-sulfidic, sericitic, carbonate, argillic and propylitic. Main mineralization at the Gomish-Tappeh deposit is observed as veins occurring in a steeply-deeping normal fault defined by an NE-SW trend in host rocks such as dacitic crystal litic tuff, dacitic subvolcanic dome, specifically the rhyolitic tuff. Paragenetic minerals in the ore veins consist of pyrite, arsenopyrite, chalcopyrite, bornite, low-Fe sphalerite, galena, tetrahedrite and specularite. Gangue minerals accompanying the ores include quartz, calcite, chlorite, sericite and clay minerals. Based on geochemical data, average grades for samples from the ore veins at the Gomish-Tappeh deposit are: 4% Pb, 6% Zn, 2% Cu and 88 ppm Ag. Moreover, REE distribution patterns for altered samples of the dacitic subvolcanic dome and acidic tuff when campared with fresh samples, show enrichment in LREE, while HREE demonstrate various bahaviours. The negative Eu anomaly in chondrite-normalized REE patterns for these rocks is related to the increase in fluid/rock ratio and destruction of those grains of plagioclase enriched in Eu. REE distribution patterns for the silty tuff (footwall to the ore) campared with acidic tuff represent enrichment in all REE as well as positive Eu anomalies. However, the ore samples indicate more enrichment in LREE/HREE ratios and higher Eu contents when campared with wallrock of the ore veins (silty tuff). This is due to the influence of chloric magmatic-hydrothermal fluids that caused alteration along the ore zone, releasing LREE and Eu from the host rocks and finally, concentrating and transporting these elements in the ore fluid.