Copper mineralization in Nahand-Ivand area, NW Iran, appears as disseminated copper sulfides alon... more Copper mineralization in Nahand-Ivand area, NW Iran, appears as disseminated copper sulfides along a redox boundary between gray sandstone and microconglomerate and hematitic sandstones, siltstones and shaly marl. Geochemical analyses of the Nahand-Ivand deposits show as much 35 wt.% Cu and 730 ppm Ag in the gray sandstone. Electron probe micro-analysis (EPMA) was used to determine the mineralogical composition and distribution patterns of copper and silver-bearing phases mainly in pyrite and Cu-bearing sulfides. The EPMA data were essential for evaluating the distribution and partitioning of potential economically-valuable components between co-existing minerals. Furthermore, they contribute to a better understanding of the genesis of the NahandIvand copper deposits and will guide further exploration in the region. The EPMA results from different types of pyrite reveal Cu contents as high as 0.32 wt.%, 1.10 wt.%, and 2.88 wt.% for framboidal pyrite (PyI), overgrowths on framboidal pyrite (PyII), and diagenetic pyrite (PyIII), respectively. This successive increase of copper from PyI to PyIII is attributed to a continuous supply of copper that replaces framboidal pyrite in turn by the more copper-rich digenetic pyrite. Because of hydrothermal overprinting, pyrite has been replaced by djurleite, roxbyite, and other nonstoichiometric Cu-S minerals that include covellite. The EPMA study indicates that covellite contains significant concentrations of Ag (locally N 1 wt.%). In contrast. only trace amounts of silver have been detected in pyrite and other copper sulfides, indicating that covellite is the major Ag-carrier in the ore. According to textural relationships, such open space filling, impregnation, and replacement textures, and the EPMA results, later stage copper-bearing fluids were responsible for the silver enrichment in the Nahand-Ivand deposits.
One of the most important ores for REE mineralization are iron oxide-apatite (IOA) deposits. The ... more One of the most important ores for REE mineralization are iron oxide-apatite (IOA) deposits. The Posht-e-Badam Block (PBB) is a part of the Central Iranian geostructural zone which is the host of most important Fe deposits of Iran. Exploration studies of the IOA deposits within the PBB (e.g. Esphordi, Gazestan, Zarigan, Lake -Siah, Sechahoun, Chahgaz, Mishdovan, Cheshmeh Firouzi and Shekarab) demonstrate that these deposits contain high contents of REE. Concentrations of ∑REE in the most important IOA deposits of the PBB include the following: the Esphordi deposit varies between 1.2 and 1.88%, the Gazestan deposit between 0.17 and 1.57%, the Zarigan deposit between 0.5 and 1.2% and the Lake -Siah deposit varies between 0.45 and 1.36%. Concentrations of ∑REE within the apatite crystals present within the IOA ores in the Esphordi, Lake -Siah and Homeijan deposits have ranges between 1.9-2.54%, 1.9-2.16% and of 2.55%, respectively. These elements are mainly concentrated in apatite crystals, but other minerals such as monazite, xenotime, bastnasite, urtite, alanite, thorite, parisite-syn-chysite and britholite have been recognized as hosts of REEs, as small inclusions within the apatite crystals , and in subsequent carbonate, hematite-carbonate and quartz veins and veinlets. Given the extent of this block and the presence of several IOA deposits within this block, and also the high grades of REEs within these deposits, one can reasonably state that it is obvious that there are significant resources of REEs in this part of Iran.
Rare earth elements in apatites in different ore types show characteristic patterns which are rel... more Rare earth elements in apatites in different ore types show characteristic patterns which are related to different modes of formation of the ores. Most of the apatite-bearing iron ores are associated with alkaline magmas with LREE/HREE fractionation varying from moderate to steep. Iron-apatite deposits of Bafq-Saghand district (Central Iran) have a high concentration of REE (ΣREE = 1000-18500 ppm), and show a strong LREE/HREE ratio with a pronounced negative Eu anomaly. Eu depletion indicates that magmas have undergone near-surface feldspar crystal fractionation. These REE patterns are different from sedimentary apatites (phosphorites) which have a low REE contents and Ce negative anomalies. The REE patterns of apatites, iron-apatite ores, greenstone host rocks and magnetite ores in each iron-apatite deposits of Central Iran are similar and only have different REE contents. This similarity indicates a genetic relation for these rocks. All of iron-apatite deposits of central Iran have similar REE patterns too, which in turn show a genetic relation for all of these deposits. The REE patterns of apatites from iron ores in Central Iran are comparable to the REE patterns of apatites in Kiruna-type iron ores in elsewhere of the world. This similarity indicates a similar origin and processes in their genesis. The REE patterns of apatites in different deposits of Central Iran iron ores and Kiruna-type iron ores show an affinity to alkaline to sub-alkaline magmas and rifting environment. The alkaline host rocks of Central Iran iron ores are clearly related to an exten-sional setting where rifting was important (SSE-NNW fault lines). A probable source for this large scale ore forming processes is relatively low partial melting of mantlic rocks. The ores have originated by magmatic differentiation as a late phase in the volcanic cycle forming sub-surface injections or surface flows. These ores have formed during magmatism as immiscible liquids (silicate and Fe-P-rich magmatic liquids) which separated from strongly differentiated magmas aided by a large volatile and alkali elements content. Within the iron-apatite deposits of central Iran the Esfordi, Gazestan, Zarigan and Lakeh-Siah deposits are the best areas for REE mineralization (ΣREE = 0.78-1.85 %). According to the spatial distribution of iron-apatite deposits in this region and REE content of these deposits, it can be expected significant resources of REE are being in Bafq-Saghand region.
Rare earth elements in apatites of different ore types show characteristic patterns which are rel... more Rare earth elements in apatites of different ore types show characteristic patterns which are related to different modes of formation of the ores. Most of the apatite-bearing iron ores are associated with alkaline magmas with LREE/HREE fractionation varying from moderate to steep. Iron-apatite deposits in Posht-e-Badam Block (Central Iran) have a high concentration of REE (more than 1000 ppm up to 2.5%), and show a strong LREE/HREE ratio with a pronounced negative Eu anomaly. This REE pattern is typical of magmatic apatite and quiet distinct from sedimentary apatites (phosphorites) which have a low REE contents and Ce negative anomalies. On the other hand, they are comparable to the REE patterns of apatites in Kiruna-type iron ores in different parts of the world. The REE patterns of apatites, iron-apatite ores and iron ores are similar and only have different REE contents. This similarity indicates a genetic relation for these rocks. Most of the iron-apatite deposits in Central Iran have similar REE patterns too, which in turn show a genetic relation for all of these deposits. This similarity indicates a similar origin and processes in their genesis. There are some small intrusions around some of the iron-apatite deposits that are petrographically identified as syenite and gabbro. These intrusions also have REE patterns similar to that of iron-apatite ores. This demonstrates a genetic relation between these intrusions and iron-apatite ores. The REE patterns of apatites in different deposits of Posht-e-Badam Block iron-apatite ores show an affinity to alkaline to sub-alkaline magmas and rifting environment. The alkaline host rocks of Central Iran iron-apatite ores are clearly related to an extensional setting where rifting was important (SSE-NNW fault lines). A probable source for this large scale ore forming processes is relatively low partial melting of mantle rocks. The ores have originated by magmatic differentiation as a late phase in the volcanic cycle forming sub-surface injections or surface flows. These ores have formed during magmatism as immiscible liquids (silicate and Fe-P-rich magmatic liquids) which separated from strongly differentiated magmas aided by a large volatile and alkali element content. Separation of an iron oxide melt and the ensuing hydrothermal processes dominated by alkali metasomatism were both involved to different degrees in the formation of Posht-e-Badam Block iron-apatite deposits. We proposed that the separation of an iron oxide melt and the ensuing hydrothermal processes dominated by alkali metasomatism were both involved to different degrees in the formation of Posht-e-Badam Block iron-apatite deposits.
The Kamtal Intrusion is located in Eastern Azarbaijan province, northwestern Iran, near the Armen... more The Kamtal Intrusion is located in Eastern Azarbaijan province, northwestern Iran, near the Armenian border. This body consists of an acidic part of monzogranitic composition, and an intermediate-basic part which is composed of quartz-monzonite and gabbro. The gabbro forms lenses within the intermediate rocks. Monzogranite has been intruded into the quartz-monzonite. Both monzogranites and quartz-monzonites are high-K calk-alkaline and metaluminous in composition and can be classified as I-type granitoids, while the gabbro has tholeiitic affinity. Monzogranite and quartz-monzonite are characterized by LREE-rich patterns and high LREE/HREE ratios. The similarities of their REE patterns suggest a genetic relationship among these rocks. The geochemical characters of the gabbro types indicate two different patterns: a flat pattern with low LREE/HREE ratio, and a steep pattern with high LREE/HREE ratio. The former was probably produced by high melting ratio of a depleted mantle source, and the steep pattern probably was the result of a low melting ratio of this mantle source. Negative anomalies of Nb and Ti can be seen in all rock types of the Kamtal Intrusion, which is indicative of subduction zones. The comparison of trace element variations with granitoid rocks of different tectonic settings allows observing a similarity between the Kamtal Intrusion and Andean volcanic arc granitoids. The Kamtal body is related to the VAG tectonic setting and was probably produced as a result of Khoy back-arc basin subduction beneath the Azerbaijan continental crust.
The Pahnavar calcic Fe-bearing skarn zone is located in the Eastern Azarbaijan (NW Iran). This sk... more The Pahnavar calcic Fe-bearing skarn zone is located in the Eastern Azarbaijan (NW Iran). This skarn zone occurs along the contact between Upper Cretaceous impure carbonates and an Oligocene granodioritic batholith. The skarnification process can be categorized into two discrete stages: prograde and retrograde. The prograde stage began immediately after the initial emplacement of the granodioritic magma into the enclosing impure car-bonate rocks. The effect of heat flow from the batholith caused the enclosing rocks to become isochemically marmorized in the pure limestone layers and bimetasomatized (skarnoids) in the impure clay-rich carbonates. Segregation and evolution of an aqueous phase from the magma that infiltrated to the marbles and skarnoids through fractures and micro-fractures took place during the emplacement of magma. The influx of Fe, Si and Mg from the granodiorite to the skarnoids and marbles led to the crystallization of anhydrous calc-silicates (garnet and pyroxene). The retrograde stage can be divided, in turn, into two distinct sub-stages. During earliest sub-stage, the previously formed skarn assemblages were affected by intense hydro-fracturing; in addition, Cu, Pb, Zn, along with H 2 S and CO 2 were added. Consequently, hydrous calc-silicates (epidote and tremolite-actinolite), sulfides (pyrite, chalcopyrite, galena and sphalerite), oxides (magnetite and hematite) and carbonates (calcite) deposited the an-hydrous calc-silicates. The late-retrograde sub-stage was due the incursion of colder oxidizing fluids into the skarn system, causing the alteration of the previously formed calc-silicate assemblages and the development of fine-grained aggregates of chlorite, illite, kaolinite, hematite and calcite. The lack of wollastonite in the mineral assemblage, along with the garnet-clinopyroxene paragenesis, suggests that the prograde stage formed under temperature and O 2 conditions of 430-550 • C and 10 −26-10 −23 , respectively .
The chemistry of garnet can provide clues to the formation of skarn deposits. The chemical analys... more The chemistry of garnet can provide clues to the formation of skarn deposits. The chemical analyses of garnets from the Astamal Fe-LREE distal skarn deposit were completed using an electron probe micro-analyzer. The three types of garnet were identified in the Astamal skarn are: (I) euhedral coarse-grained isotropic garnets (10-30 mm across), which are strongly altered to epidote, calcite and quartz in their rim and core, with intense pervasive retrograde alteration and little variation in the overall composition (Adr 94.3-84.4 Grs 8.5-2.7 Alm 1.9-0.2) (garnet I); (II) anhedral to subhedral brecciated isotropic garnets (5-10 mm across) with minor alteration, a narrow compositional range along the growth lines (Adr 82-65.4 Grs 21.9-11.7 Alm 11.1-2.4) and relatively high Cu (up to 1997 ppm) and Ni (up to 1283 ppm) (garnet II); and (III) subhedral coarser grained garnets (N 30 mm across) with moderate alteration, weak diffusion and irregular zoning of discrete grossular-almandine-rich domains (Adr 84.2-48.8 Grs 32.4-7.6 Alm 19.9-3.5) (garnet III). In the third type, the almandine content increases with increasing grossular/andradite ratio and increasing substitutions of Al for Fe 3+. Almost all three garnet types have been replaced by fine-grained, dark-brown allanite that is typically disseminated and has the same relief as andradite. The Cu content increases while Ni content decreases slightly towards the rim of garnet II and garnet III. Copper in garnet II is positively correlated with increasing almandine content and decreasing andradite content, indicating that the almandine structure, containing relatively more Fe 2+ , is more suitable than andradite and grossular to host divalent cations such as Cu 2+. Nickel in garnet II is positively correlated with increasing andradite content, total Fe, and decreasing almandine content. This is because Ni 2+ substitutes for Fe 3+ in the Y (octahedral) position. There are unusual discrete grossular-almandine rich domains within andraditic garnet III, indicating the low diffusivity of Ca compared to Fe at high temperatures.
The Astamal Fe-LREE skarn deposit is the largest iron skarn in NW Iran. It is a unique case, as a... more The Astamal Fe-LREE skarn deposit is the largest iron skarn in NW Iran. It is a unique case, as a distal skarn deposit which crops out approximately 600 m from the associated Oligo-Miocene granodioritic pluton. This deposit formed in the south-southwest of the pluton where fractures and faults within the Upper Cretaceous volcano-sedimentary host rocks acted as conduits for the mineralizing fluids. The deposit contains three iron ore bodies: southern, northern and eastern. The main mineral assemblage within the ore zones is characterized by magnetite, pyrrhotite and pyrite, with lesser quantities of chalcopyrite, hematite, goethite and limonite. The skarn minerals predominantly comprise garnet, epidote, actinolite, calcite, quartz, clinopyroxene and chlorite (in order of abundance). Retrograde alteration is strongly developed in the skarn zone where most of the garnet has been pervasively altered to secondary minerals (e.g. epidote, calcite and quartz) both in the rims and the cores whereas the majority of the clinopyroxene has been replaced by a hydrous retrograde mineral assemblage (e.g. tremolite, actinolite and chlo-rite). Garnets with andradite-grossular compositions are the dominant mineral in the skarn zone, which are generally isotropic with a narrow compositional range along the growth lines (Adr 94.3-64.5 Grs 21.9-2.7 Alm 11.1-0.2). These garnets are Fe-rich and have high Fe/(Fe + Al) ratios (between 0.96 and 0.78). Cu and Ni are enriched in the garnets. This suggests that these elements were enriched in the hydrothermal fluids from which the garnet precipitated. This is supported by the presence of chalcopyrite and Ni-bearing massive magnetite in the study area, which also suggests that Cu and Ni were enriched in the late stage ore-bearing hydrothermal fluids. Clinopyroxene with a hedenbergitic composition is generally homogenous and has particularly high Fe/Fe + Mg ratios (between 0.99 and 0.86) and is poor in TiO 2 , MnO and Cr 2 O 3. High Zn concentrations were also detected in the clinopyroxenes (up to 1044 ppm), despite an absence of significant Zn mineralization (such as sphalerite) in the district. Therefore, it is believed that the proportion of Zn in the hydrothermal fluids decreased significantly from the time of clinopyroxene formation to the period of the sulfide deposition phase. Allanite and LREE-bearing epidotes are the main LREE bearing minerals in this deposit. The epidote is also Fe-rich with high Fe/(Fe + Al) ratios (between 0.32 and 0.44). Due to a lack of replacement texture between both garnet and clinopyroxene and garnet and actin-olite (which is formed by alteration of clinopyroxene), it is believed that these two minerals have grown simultaneously and are coexisting minerals. In the Astamal skarn, these minerals can be stable and coexisting at temperatures between 490 and 560 °C and LogƒO 2 = −16 to −31.
Copper mineralization in Nahand-Ivand area, NW Iran, appears as disseminated copper sulfides alon... more Copper mineralization in Nahand-Ivand area, NW Iran, appears as disseminated copper sulfides along a redox boundary between gray sandstone and microconglomerate and hematitic sandstones, siltstones and shaly marl. Geochemical analyses of the Nahand-Ivand deposits show as much 35 wt.% Cu and 730 ppm Ag in the gray sandstone. Electron probe micro-analysis (EPMA) was used to determine the mineralogical composition and distribution patterns of copper and silver-bearing phases mainly in pyrite and Cu-bearing sulfides. The EPMA data were essential for evaluating the distribution and partitioning of potential economically-valuable components between co-existing minerals. Furthermore, they contribute to a better understanding of the genesis of the NahandIvand copper deposits and will guide further exploration in the region. The EPMA results from different types of pyrite reveal Cu contents as high as 0.32 wt.%, 1.10 wt.%, and 2.88 wt.% for framboidal pyrite (PyI), overgrowths on framboidal pyrite (PyII), and diagenetic pyrite (PyIII), respectively. This successive increase of copper from PyI to PyIII is attributed to a continuous supply of copper that replaces framboidal pyrite in turn by the more copper-rich digenetic pyrite. Because of hydrothermal overprinting, pyrite has been replaced by djurleite, roxbyite, and other nonstoichiometric Cu-S minerals that include covellite. The EPMA study indicates that covellite contains significant concentrations of Ag (locally N 1 wt.%). In contrast. only trace amounts of silver have been detected in pyrite and other copper sulfides, indicating that covellite is the major Ag-carrier in the ore. According to textural relationships, such open space filling, impregnation, and replacement textures, and the EPMA results, later stage copper-bearing fluids were responsible for the silver enrichment in the Nahand-Ivand deposits.
One of the most important ores for REE mineralization are iron oxide-apatite (IOA) deposits. The ... more One of the most important ores for REE mineralization are iron oxide-apatite (IOA) deposits. The Posht-e-Badam Block (PBB) is a part of the Central Iranian geostructural zone which is the host of most important Fe deposits of Iran. Exploration studies of the IOA deposits within the PBB (e.g. Esphordi, Gazestan, Zarigan, Lake -Siah, Sechahoun, Chahgaz, Mishdovan, Cheshmeh Firouzi and Shekarab) demonstrate that these deposits contain high contents of REE. Concentrations of ∑REE in the most important IOA deposits of the PBB include the following: the Esphordi deposit varies between 1.2 and 1.88%, the Gazestan deposit between 0.17 and 1.57%, the Zarigan deposit between 0.5 and 1.2% and the Lake -Siah deposit varies between 0.45 and 1.36%. Concentrations of ∑REE within the apatite crystals present within the IOA ores in the Esphordi, Lake -Siah and Homeijan deposits have ranges between 1.9-2.54%, 1.9-2.16% and of 2.55%, respectively. These elements are mainly concentrated in apatite crystals, but other minerals such as monazite, xenotime, bastnasite, urtite, alanite, thorite, parisite-syn-chysite and britholite have been recognized as hosts of REEs, as small inclusions within the apatite crystals , and in subsequent carbonate, hematite-carbonate and quartz veins and veinlets. Given the extent of this block and the presence of several IOA deposits within this block, and also the high grades of REEs within these deposits, one can reasonably state that it is obvious that there are significant resources of REEs in this part of Iran.
Rare earth elements in apatites in different ore types show characteristic patterns which are rel... more Rare earth elements in apatites in different ore types show characteristic patterns which are related to different modes of formation of the ores. Most of the apatite-bearing iron ores are associated with alkaline magmas with LREE/HREE fractionation varying from moderate to steep. Iron-apatite deposits of Bafq-Saghand district (Central Iran) have a high concentration of REE (ΣREE = 1000-18500 ppm), and show a strong LREE/HREE ratio with a pronounced negative Eu anomaly. Eu depletion indicates that magmas have undergone near-surface feldspar crystal fractionation. These REE patterns are different from sedimentary apatites (phosphorites) which have a low REE contents and Ce negative anomalies. The REE patterns of apatites, iron-apatite ores, greenstone host rocks and magnetite ores in each iron-apatite deposits of Central Iran are similar and only have different REE contents. This similarity indicates a genetic relation for these rocks. All of iron-apatite deposits of central Iran have similar REE patterns too, which in turn show a genetic relation for all of these deposits. The REE patterns of apatites from iron ores in Central Iran are comparable to the REE patterns of apatites in Kiruna-type iron ores in elsewhere of the world. This similarity indicates a similar origin and processes in their genesis. The REE patterns of apatites in different deposits of Central Iran iron ores and Kiruna-type iron ores show an affinity to alkaline to sub-alkaline magmas and rifting environment. The alkaline host rocks of Central Iran iron ores are clearly related to an exten-sional setting where rifting was important (SSE-NNW fault lines). A probable source for this large scale ore forming processes is relatively low partial melting of mantlic rocks. The ores have originated by magmatic differentiation as a late phase in the volcanic cycle forming sub-surface injections or surface flows. These ores have formed during magmatism as immiscible liquids (silicate and Fe-P-rich magmatic liquids) which separated from strongly differentiated magmas aided by a large volatile and alkali elements content. Within the iron-apatite deposits of central Iran the Esfordi, Gazestan, Zarigan and Lakeh-Siah deposits are the best areas for REE mineralization (ΣREE = 0.78-1.85 %). According to the spatial distribution of iron-apatite deposits in this region and REE content of these deposits, it can be expected significant resources of REE are being in Bafq-Saghand region.
Rare earth elements in apatites of different ore types show characteristic patterns which are rel... more Rare earth elements in apatites of different ore types show characteristic patterns which are related to different modes of formation of the ores. Most of the apatite-bearing iron ores are associated with alkaline magmas with LREE/HREE fractionation varying from moderate to steep. Iron-apatite deposits in Posht-e-Badam Block (Central Iran) have a high concentration of REE (more than 1000 ppm up to 2.5%), and show a strong LREE/HREE ratio with a pronounced negative Eu anomaly. This REE pattern is typical of magmatic apatite and quiet distinct from sedimentary apatites (phosphorites) which have a low REE contents and Ce negative anomalies. On the other hand, they are comparable to the REE patterns of apatites in Kiruna-type iron ores in different parts of the world. The REE patterns of apatites, iron-apatite ores and iron ores are similar and only have different REE contents. This similarity indicates a genetic relation for these rocks. Most of the iron-apatite deposits in Central Iran have similar REE patterns too, which in turn show a genetic relation for all of these deposits. This similarity indicates a similar origin and processes in their genesis. There are some small intrusions around some of the iron-apatite deposits that are petrographically identified as syenite and gabbro. These intrusions also have REE patterns similar to that of iron-apatite ores. This demonstrates a genetic relation between these intrusions and iron-apatite ores. The REE patterns of apatites in different deposits of Posht-e-Badam Block iron-apatite ores show an affinity to alkaline to sub-alkaline magmas and rifting environment. The alkaline host rocks of Central Iran iron-apatite ores are clearly related to an extensional setting where rifting was important (SSE-NNW fault lines). A probable source for this large scale ore forming processes is relatively low partial melting of mantle rocks. The ores have originated by magmatic differentiation as a late phase in the volcanic cycle forming sub-surface injections or surface flows. These ores have formed during magmatism as immiscible liquids (silicate and Fe-P-rich magmatic liquids) which separated from strongly differentiated magmas aided by a large volatile and alkali element content. Separation of an iron oxide melt and the ensuing hydrothermal processes dominated by alkali metasomatism were both involved to different degrees in the formation of Posht-e-Badam Block iron-apatite deposits. We proposed that the separation of an iron oxide melt and the ensuing hydrothermal processes dominated by alkali metasomatism were both involved to different degrees in the formation of Posht-e-Badam Block iron-apatite deposits.
The Kamtal Intrusion is located in Eastern Azarbaijan province, northwestern Iran, near the Armen... more The Kamtal Intrusion is located in Eastern Azarbaijan province, northwestern Iran, near the Armenian border. This body consists of an acidic part of monzogranitic composition, and an intermediate-basic part which is composed of quartz-monzonite and gabbro. The gabbro forms lenses within the intermediate rocks. Monzogranite has been intruded into the quartz-monzonite. Both monzogranites and quartz-monzonites are high-K calk-alkaline and metaluminous in composition and can be classified as I-type granitoids, while the gabbro has tholeiitic affinity. Monzogranite and quartz-monzonite are characterized by LREE-rich patterns and high LREE/HREE ratios. The similarities of their REE patterns suggest a genetic relationship among these rocks. The geochemical characters of the gabbro types indicate two different patterns: a flat pattern with low LREE/HREE ratio, and a steep pattern with high LREE/HREE ratio. The former was probably produced by high melting ratio of a depleted mantle source, and the steep pattern probably was the result of a low melting ratio of this mantle source. Negative anomalies of Nb and Ti can be seen in all rock types of the Kamtal Intrusion, which is indicative of subduction zones. The comparison of trace element variations with granitoid rocks of different tectonic settings allows observing a similarity between the Kamtal Intrusion and Andean volcanic arc granitoids. The Kamtal body is related to the VAG tectonic setting and was probably produced as a result of Khoy back-arc basin subduction beneath the Azerbaijan continental crust.
The Pahnavar calcic Fe-bearing skarn zone is located in the Eastern Azarbaijan (NW Iran). This sk... more The Pahnavar calcic Fe-bearing skarn zone is located in the Eastern Azarbaijan (NW Iran). This skarn zone occurs along the contact between Upper Cretaceous impure carbonates and an Oligocene granodioritic batholith. The skarnification process can be categorized into two discrete stages: prograde and retrograde. The prograde stage began immediately after the initial emplacement of the granodioritic magma into the enclosing impure car-bonate rocks. The effect of heat flow from the batholith caused the enclosing rocks to become isochemically marmorized in the pure limestone layers and bimetasomatized (skarnoids) in the impure clay-rich carbonates. Segregation and evolution of an aqueous phase from the magma that infiltrated to the marbles and skarnoids through fractures and micro-fractures took place during the emplacement of magma. The influx of Fe, Si and Mg from the granodiorite to the skarnoids and marbles led to the crystallization of anhydrous calc-silicates (garnet and pyroxene). The retrograde stage can be divided, in turn, into two distinct sub-stages. During earliest sub-stage, the previously formed skarn assemblages were affected by intense hydro-fracturing; in addition, Cu, Pb, Zn, along with H 2 S and CO 2 were added. Consequently, hydrous calc-silicates (epidote and tremolite-actinolite), sulfides (pyrite, chalcopyrite, galena and sphalerite), oxides (magnetite and hematite) and carbonates (calcite) deposited the an-hydrous calc-silicates. The late-retrograde sub-stage was due the incursion of colder oxidizing fluids into the skarn system, causing the alteration of the previously formed calc-silicate assemblages and the development of fine-grained aggregates of chlorite, illite, kaolinite, hematite and calcite. The lack of wollastonite in the mineral assemblage, along with the garnet-clinopyroxene paragenesis, suggests that the prograde stage formed under temperature and O 2 conditions of 430-550 • C and 10 −26-10 −23 , respectively .
The chemistry of garnet can provide clues to the formation of skarn deposits. The chemical analys... more The chemistry of garnet can provide clues to the formation of skarn deposits. The chemical analyses of garnets from the Astamal Fe-LREE distal skarn deposit were completed using an electron probe micro-analyzer. The three types of garnet were identified in the Astamal skarn are: (I) euhedral coarse-grained isotropic garnets (10-30 mm across), which are strongly altered to epidote, calcite and quartz in their rim and core, with intense pervasive retrograde alteration and little variation in the overall composition (Adr 94.3-84.4 Grs 8.5-2.7 Alm 1.9-0.2) (garnet I); (II) anhedral to subhedral brecciated isotropic garnets (5-10 mm across) with minor alteration, a narrow compositional range along the growth lines (Adr 82-65.4 Grs 21.9-11.7 Alm 11.1-2.4) and relatively high Cu (up to 1997 ppm) and Ni (up to 1283 ppm) (garnet II); and (III) subhedral coarser grained garnets (N 30 mm across) with moderate alteration, weak diffusion and irregular zoning of discrete grossular-almandine-rich domains (Adr 84.2-48.8 Grs 32.4-7.6 Alm 19.9-3.5) (garnet III). In the third type, the almandine content increases with increasing grossular/andradite ratio and increasing substitutions of Al for Fe 3+. Almost all three garnet types have been replaced by fine-grained, dark-brown allanite that is typically disseminated and has the same relief as andradite. The Cu content increases while Ni content decreases slightly towards the rim of garnet II and garnet III. Copper in garnet II is positively correlated with increasing almandine content and decreasing andradite content, indicating that the almandine structure, containing relatively more Fe 2+ , is more suitable than andradite and grossular to host divalent cations such as Cu 2+. Nickel in garnet II is positively correlated with increasing andradite content, total Fe, and decreasing almandine content. This is because Ni 2+ substitutes for Fe 3+ in the Y (octahedral) position. There are unusual discrete grossular-almandine rich domains within andraditic garnet III, indicating the low diffusivity of Ca compared to Fe at high temperatures.
The Astamal Fe-LREE skarn deposit is the largest iron skarn in NW Iran. It is a unique case, as a... more The Astamal Fe-LREE skarn deposit is the largest iron skarn in NW Iran. It is a unique case, as a distal skarn deposit which crops out approximately 600 m from the associated Oligo-Miocene granodioritic pluton. This deposit formed in the south-southwest of the pluton where fractures and faults within the Upper Cretaceous volcano-sedimentary host rocks acted as conduits for the mineralizing fluids. The deposit contains three iron ore bodies: southern, northern and eastern. The main mineral assemblage within the ore zones is characterized by magnetite, pyrrhotite and pyrite, with lesser quantities of chalcopyrite, hematite, goethite and limonite. The skarn minerals predominantly comprise garnet, epidote, actinolite, calcite, quartz, clinopyroxene and chlorite (in order of abundance). Retrograde alteration is strongly developed in the skarn zone where most of the garnet has been pervasively altered to secondary minerals (e.g. epidote, calcite and quartz) both in the rims and the cores whereas the majority of the clinopyroxene has been replaced by a hydrous retrograde mineral assemblage (e.g. tremolite, actinolite and chlo-rite). Garnets with andradite-grossular compositions are the dominant mineral in the skarn zone, which are generally isotropic with a narrow compositional range along the growth lines (Adr 94.3-64.5 Grs 21.9-2.7 Alm 11.1-0.2). These garnets are Fe-rich and have high Fe/(Fe + Al) ratios (between 0.96 and 0.78). Cu and Ni are enriched in the garnets. This suggests that these elements were enriched in the hydrothermal fluids from which the garnet precipitated. This is supported by the presence of chalcopyrite and Ni-bearing massive magnetite in the study area, which also suggests that Cu and Ni were enriched in the late stage ore-bearing hydrothermal fluids. Clinopyroxene with a hedenbergitic composition is generally homogenous and has particularly high Fe/Fe + Mg ratios (between 0.99 and 0.86) and is poor in TiO 2 , MnO and Cr 2 O 3. High Zn concentrations were also detected in the clinopyroxenes (up to 1044 ppm), despite an absence of significant Zn mineralization (such as sphalerite) in the district. Therefore, it is believed that the proportion of Zn in the hydrothermal fluids decreased significantly from the time of clinopyroxene formation to the period of the sulfide deposition phase. Allanite and LREE-bearing epidotes are the main LREE bearing minerals in this deposit. The epidote is also Fe-rich with high Fe/(Fe + Al) ratios (between 0.32 and 0.44). Due to a lack of replacement texture between both garnet and clinopyroxene and garnet and actin-olite (which is formed by alteration of clinopyroxene), it is believed that these two minerals have grown simultaneously and are coexisting minerals. In the Astamal skarn, these minerals can be stable and coexisting at temperatures between 490 and 560 °C and LogƒO 2 = −16 to −31.
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