Journal of Economic Geology

131-151

Authors: Mohammad Ali Jazi; Jamshid Shahabpour

Nakhlak lead mine is located at the Nakhlak mountain 55 km NE of Anarak town in Isfahan province. The mineralogy is simple; galena and barite are the main primary minerals and cerussite is the main secondary mineral. Sphalerite, pyrite, chalcopyrite, tetrahedrite-tennantite and acanthite occur as minor and trace mineral inclusions in galena. Secondary minerals are anglesite, plattnerite, wulfenite and malachite. The host rock has undergone a pre-mineralization dolomitization process. Four types of dolomite have been identified which saddle dolomite is the most distinguished. Open space filling textures occur in the form of breccia, cockade, crustification and colloform. Analysis of the galena samples indicates presence of many trace elements in galena among which silver is the most important. Element pairs such as Ag-As, Zn-Cd, As-Cu and As-Sb are highly correlated. This correlation may be explained by the presence of inclusions. Ag-Sb-Bi ternary diagram indicates that galena samples from Nakhlak are rich in Ag and Sb and poor in Bi. Sb/Bi (3773) ratio in galena is suggestive of a low temperature of formation for the deposit. The Upper Cretaceous carbonate host rocks and their dolomitization, the stratabound and epigenetic mineralization, the absence of igneous activity, the open space filling texture, the simple mineralogy and geochemistry all point to a Mississippi valley type model for the Nakhlak Pb deposit.

167-189

Authors: Zahra Karimi Sayide Abadi; Seyed Ahmad Mazaher; Mohammad Hassan Karimpour

The Arghash area is located 45 km to southwest of Neyshabour. The subvolcanic rocks in the area consist of biotite hornblende quartz monzodiorite porphyry, hornblende biotite quartz monzodiorite porphyry, hornblende monzonite porphyry, biotite hornblende monzonite porphyry, monzodiorite porphyry and biotite quartz monzodiorite porphyry units. The volcanic rocks consist of hornblende biotite dacite, biotite hornblende dacite, and andesite and pillow lava. The plutonic rocks consist of hornblende monzodiorite, hornblende monzonite, quartz monzonite, hornblende quartz monzodiorite, biotite granodiorite, hornblende granodiorite, biotite hornblende granodiorite, biotite quartz diorite and pyroxene dolerite units. Five types of alteration including propylitic, carbonate, argillic, silicification and sericitic were recognized. Those are subdivided into twelve sub-zones based on the mineral abundances and intensity of alteration. Primary pyrite, 3-4%, is found mainly as disseminated. Secondary mineralization includes limonite, hematite and jarosite. Twenty rock chip and 8 stream sediment samples were collected for geochemical exploration. The samples were analysed for Cu, Zn, Pb, Ag and Sb using Atomic Absorbtion Spectrophotometric (AAS) method. In stream sediment samples, Cu abundance is 34-58 ppm, Zn 45-422 ppm, Pb 28-42 ppm and Ag 2-12 ppm; whereas in rock chip samples, Cu abundance is 8-1137 ppm, Zn 13-411 ppm, Pb 15-97 ppm and Ag 3-32 ppm.

199-215

Authors: Ali Imamalipour; Hossein Abdoli; Behzad Hajalilo

Two types of mineralization including porphyry copper and epithermal gold mineralization have occurred in relation with an intermediate volcano-plutonic complex in Masjeddaghi area. Different alterations including silica, advanced argillic, intermediate argillic and propylitic have been distinguished in relation with epithermal mineralization, which have a zonal pattern. Elemental mass gains and losses during alterations were calculated using Zr as an immobile monitor. Silica zone has enriched in SiO2 and relatively in Al2O3 and K2O, and has depleted in Na2O, MgO and CaO. Ba, Sr, Pb, Rb and Cu elements have also enriched. The advanced argillic zone shows enrichment in SO3, Al2O3, SiO2, K2O, MgO and L.O.I; and depletion in Fe2O3, CaO, Na2O, MnO and MgO. Barium, Cu, Sr and Zn have depleted in this zone. Propylitic zone has enriched in MgO, CaO, L.O.I and SiO2, and has depleted in Na2O and K2O. Geochemical and mineralogical evidences indicate that the hydrothermal leaching of mafic minerals in parent rocks and formation of quartz, kaolinite, sericite and alunite assemblage in advanced argillic zone; and chlorite, epidote and calcite assemblage in propylitic zone is responsible for the above mentioned chemical variations. It is likely that the gains and losses of elements have been controlled by agents such as water/rock ratios, temperature changes and chemistry of hydrothermal solutions. The CIA and MIA indicators in the altered rocks indicate the intensity of alteration in silica and advanced argillic zones in comparison with propylitic zone.

235-254

Authors: Tooba Salehi; Majid Ghaderi; Nematoolah Rashidnejad-Omran

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.

1-20

Authors: Behzad Mehrabi; Ghasemi Siani

The Cheshmeh Hafez polymetal deposit is located in Troud – Chahshirin mountain range in Southeastern Damghan. In this province, the volcanism and associated mineralization are closely related to major faults Anjilo and Troud with NW-SE trend. The exposed rocks in the study area consist of volcano clastic sequence of sandstone, tuff, volcano breccias and mostly andesitic and andesitic- basalt flows at Cheshmeh Hafez district. Alteration in Cheshmeh Hafez area is consisting of Proplilitization, Sericitization, Argillic alteration and Silicification. Mineralization occurred in three district stages; 1) quartz, carbonate with early pyrite and chalcopyrite assemblages; 2) the main stage of sulfide deposition, comprises early euhedral galena followed by galena and sphalerite, then galena, chalcopyrite, tetrahedrite, pyrite, bornite and digenite, and 3) quartz and calcite barren veins with minor pyrite and chalcopyrite. The average assays from 12 samples of Cheshmeh Hafez veins are; 0.15 g/t Au, 3.23 g/t Ag, 4.47 wt % Pb, 2.64 wt % Cu, and 1.73 wt % Zn. Fluid- inclusion homogenization temperatures (Th) in quartz fall within range of 140º-300º with salinities ranging from 4.7 to 18 wt. % NaCl equivalent. Comparison of Th versus final ice melting (Tmice) values indicates the occurrence of fluid mixing process. In order to evaluate extent of mineralization in depth, IP and RS techniques were used, which indicate the presence of mineralization in depth.

39-49

Authors: Majid Hashemi Tangestani; Mooslem Azizi

Esteghlal fireclay mine, northern Abadeh, with dominant composition of kaolinite and pyrophyllite, and annual production of over a million tons, is one of the largest sedimentary deposits in Iran. Linear Spectral Unmixing (LSU) and Mixture Tuned Matched Filtering (MTMF) processes were applied on the VNIR + SWIR dataset of ASTER for identifying the frequency fraction and distribution of clay minerals in this mine. Sub-pixel frequency assessment of ASTER data showed that distribution of pixels with higher fractions belong to the kaolinite and pyrophyllite, outcropped in two different parts of the mine. Comparison of LSU and MTMF output results showed that MTMF is more reliable to determining the relative fraction of clay minerals at the study area.

61-75

Authors: Robabeh Jafari; Moosa Noghreeian; Mohammad Makizadeh

Nezam-Abad area is located in southwest of Shazand (Arak) which is a part of Sanandaj-Sirjan zone. Major intrusive rocks of Nezam-Abad are quartz diorite and minor amount of granodiorite. Leucogranitic, pegmatite dykes and quartz-tourmaline veins were intruded the quartz diorite. Quartz diorites are mainly composed of plagioclase, hornblende, biotite, quartz and pyroxene as major minerals. Major minerals of leucogranite are microcline, orthoclase, albite, quartz, biotite and muscovite. Accessory minerals consist of apatite, zircon, sphene, epidote, allanite, tourmaline and opaque. The presence of hydrous minerals like hornblende and biotite in these rocks indicate that the corresponding magma initially contained >3 wt% H2O (wet magma). The occurrences of garnet and andalusite minerals suggest assimilation process. Primary textures in these rocks are granular, granophyre, and poikilitic. Secondary textures are perthite, myrmekite, sericitization, chloritization and kaolinitization. Later hydrothermal activities and tectonic strains are factors for presence of perthite texture in leucogranite. K amount for sericitization of feldspars come from the K-feldspars and chloritization of biotite. Transformation of biotite to muscovite indicates the act of K rich fluid in later stages. On the basis of chemical analysis on the intrusive rocks, it is shown that the magma was calc-alkaline, metaluminous-peraluminous and medium-K to high-K. Study of major elements in Harker diagrams indicates Al2O3, FeO, Fe2O3 and CaO decrease with increasing of SiO2 and K2O and Na2O increase indicating that fractional crystallization may have played an important role in the formation of granitoid rocks from Nezam-Abad.

97-121

Authors: Hossein Ali Tajeddin; Ebrahim Rastad; Abdol Majid Yaghubpour; Mohammad Mohajjel

Barika gold (and silver) rich massive sulfide deposit is located 18 km east of Sardasht, north western part of Sanandaj-Sirjan metamorphic zone. Rock units outcropped in this area are Cretaceous metamorphosed volcano-sedimentary rocks in green schist facies, and include association of meta-andesite, meta-tuffite, phyllite and slate rocks, where the meta-andesitic unit (Kmv1) is host rock to the deposit. Barika deposit is composed of stratiform ore and stringer zone. Stratiform part contains massive and banded sulfide and barite associated with subordinary silica bands underlain by stringer silicic zone. The massive and banded ore is surrounded by an extensive zone of silicic stringer veins and disseminated mineralization within strongly altered and deformed andesitic volcanic rocks. Ore mineral assemblages in stratiform part of the deposit are quite variable and consist of pyrite, sphalerite, galena, stibnite, a variety of sulfosalt minerals and gold (electrum). Ore mineral assemblages in silicic veins in the stringer zone are simpler and consist of pyrite, galena, sphalerite, tetrahedrrite and trace chalcopyrite. Average gold and silver grades in stratiform ore are 8.3 and 420 g/t respectively and in silicic stringer veins are 0.7 and 30 g/t. Base metal content in both parts of the deposit are less than 1%. Based on our research, Barika is an immature Kuroko type massive sulfide deposit, which contains only black ore. The Barika deposit underwent low-grade metamorphism and high grade deformation after the ore deposition event. Geologic processes appear to control the mode of occurrence of gold in the deposit. In synvolcanism stage, deposition of a gold–bearing low temperature (140-200°C) and low salinity (1-9.6 wt% NaCl) hydrothermal fluid formed a Kuroko black ore type deposit. In the stage of mineralization, invisible gold was concentrated in framboidal pyrite and other sulfide minerals. The main effect of progressive metamorphism (D1) on gold mineralization is recrystallization of the framboidal pyrite and migration of submicroscopic gold to the crystal boundary to form electrum under low to moderate strain. Highly strain and deformation (D2) on the deposit caused the remobilization of gold and accompanied َAs, Sb, Ag, and Pb minerals and continued to form coarse-grained electrum (up to 3 mm) in open space fractures. The formation of barren silica veins (D3) and high angle normal faults (D4) are the results of retrograde metamorphism.