Study of the mineralization potential of the intrusives around Valis ( Tarom-Iran )

The study area is located in northwestern Iran in the central Iran zone, specifically the western Alborz sub-zone south of the Tarom-Hashtjin metallogenic zone. The exposed rock units in this area generally include Eocene volcanic rocks (lava flows and pyroclasts belonging to the Karaj formation) and Oligocene granitoid intrusive bodies. The intrusive bodies in the area have a petrographic composition of granite, syenite and monzonite and are mostly metaluminous. The dual characteristics of these intrusives (for example, the behavior of elements such as Rb, P, Ga/Al, Y/Nb, K/Na, and FeO/Fe2O3, the Rb/Nb ratios, the A/CNK molar ratios and the ACF and A/CNK-Fe2O3+FeO diagrams), some of which are consistent with the I nature and others with the S and A natures, show that the rocks are among hybrid granitoids and, in terms of the tectonic setting, lie within the WPG range. According to the Rb/Sr, Zr/Hf, K/Rb ratios, the granite melts that form the aforementioned bodies are not extremely evolved and have not undergone post magmatic activity, which would lead to mineralization. The Sm/Eu and Rb/Ba ratios and the behavior of Rb, Ba and Sr within the aforementioned granitoids show that the rocks are similar to average granitoids unrelated to Li, Be, Sn, W and Ta deposits; they fall within the range of barren granitoids but are partially fertile in Cu.

The study area is located in northwestern Iran in the central Iran zone, specifically the western Alborz sub-zone south of the Tarom-Hashtjin metallogenic zone.The exposed rock units in this area generally include Eocene volcanic rocks (lava flows and pyroclasts belonging to the Karaj formation) and Oligocene granitoid intrusive bodies.The intrusive bodies in the area have a petrographic composition of granite, syenite and monzonite and are mostly metaluminous.The dual characteristics of these intrusives (for example, the behavior of elements such as Rb, P, Ga/Al, Y/Nb, K/ Na, and FeO/Fe2O3, the Rb/Nb ratios, the A/CNK molar ratios and the ACF and A/CNK-Fe2O3+FeO diagrams), some of which are consistent with the I nature and others with the S and A natures, show that the rocks are among hybrid granitoids and, in terms of the tectonic setting, lie within the WPG range.According to the Rb/Sr, Zr/Hf, K/Rb ratios, the granite melts that form the aforementioned bodies are not extremely evolved and have not undergone post magmatic activity, which would lead to mineralization.The Sm/Eu and Rb/Ba ratios and the behavior of Rb, Ba and Sr within the aforementioned granitoids show that the rocks are similar to average granitoids unrelated to Li, Be, Sn, W and Ta deposits; they fall within the range of barren granitoids but are partially fertile in Cu.

Introduction
The study area is located in northwestern Iran and is part of the Alborz mountain range.Alborz itself is affected by the Alp-Himalayan orogeny and generally trends northwest-southeast.This area is geographically located between the eastern longitudes of 48º 30ʹ to 48º 40ʹ and northern latitudes of 37º to 37º 5ʹ.In terms of Iran's structural division, this area is located in the western Alborz subzone in central Iran (Alavi, 1996) (figure 1), and from metallogenic point of view, it belongs to the multimetallic belt of Tarom-Hashtjin (Ghorbani, 2013).The Tarom-Hashtjin belt covers an area between Qazvin (west of Taleghan) and north-northwest of Mianeh; it is limited by the Manjil depression and Talesh Mountains to the north and by the Alborz-Zanjan-Mianeh axis to the south.In fact, this belt is structurally confined to the north by the Sefidrood fault, to the south by the continuation of the Tabriz-Soltanieh and Soltanieh-Takestan faults, and to the west by the Astara-Marivan fault (Ghorbani, 2013) (figure 1).
Almost the entire study area is composed of Cenozoic volcanic, intrusive, and sedimentary rocks.The rocks along the Tarom-Hashtjin axis, which are considered equivalent to the Karaj Formation, are different from those in central Alborz in terms of the lithology and chemical composition because the lava flows do not consist only of volcaniclastic rocks along this axis and their compositions are more basic.In fact, the rocks in the Karaj Formation in central Alborz are predominantly acidic tuffs, while their equivalents along the Tarom-Hashtjin axis are mostly andesites and basaltic andesites.The ancient rocks in the Tarom-Hashtjin belt are not exposed within the central parts (Ghorbani, 2013), and the basement is mostly composed of Tertiary magmatic rocks.The volcanic rocks in the Tarom area vary from rhyodacite and dacite to basalt.These rocks are observed in the form of lava flows, tuffs and sometimes tuffites.According to the conducted studies, the following volcanic rocks have been observed in this belt: basalt, basaltic andesite, andesite, trachyte, latite, trachyandesite, dacite and rhyodacite ignimbrite and acidic to intermediate tuffs.Among these rocks, andesites are the most voluminous.Moein-Vaziri (1985) believed that most volcanic rocks from the Tarom-Hashtjin are potassic-alkaline, while some are sodic-alkaline or calc-alkaline.Most of the andesites are shoshonitic.
The emplacement of Oligocene age acidic to intermediate intrusive bodies within the Eocene volcanic rocks and the existence of the mining indices of Zehabad, Barikabad, Khalifehlou, Aliabad and Golouje in the Tarom region along with vast alteration zones have caused this area to be geologically considered as a prime geological district for the detection and identification of metallic and non-metallic deposits (Ghorbani, 2013).The studies conducted by different researchers (Peyrovan H., 1992;Torkamani E., 1997;Moayyed M., 2001) show that the granitoid bodies in this zone are of the I type.Haj Alilou (2000) believed that the intrusive bodies have been emplaced at a depth between 1400 to 3000 m and their formation temperature ranged from 700 to 880 degrees centigrade.Because of the high water content and sulfur fugacity, the bodies managed to create very extensive hydrothermal alterations together with vein, veinlet and scattered mineralizations in tuffites and Eocene volcanic rocks.The magmatic series of these intrusive bodies are shoshonite and high K calc-alkaline and are of the I type (Ghorbani, 2013).Shallower bodies are observed in the form of prophyrite with the general composition of monzonite porphyry and occurred along with major bodies with important roles in mineralization and hydrothermal alteration.The structural geology features similar anticline and syncline axes, and faults trending east-west and northwest-southeast had important roles in the emplacement of intrusive bodies and the development of hydrothermal alteration areas.Sericitic, argillic (advanced, intermediate and weak), silicic, chloritic, propyltic, zeolitic and alunite alteration zones have been recognized along this axis.
The igneous bodies, which have economic concentrations of either genetic or paragenetic chemical elements, generally show specific geochemical patterns (Beus, 1968), the identification of which potentially distinguishes metalliferous geological units from barren types.When determining the mineralization potential of felsic intrusive bodies, it is important to recognize their nature, which generally accompanies special types of ore deposits.To achieve this purpose and determine the mineralization ability of the granitoid bodies around Valis, petrography, petrology, and geochemical ratios and the distribution of major and rare elements have been studied; in addition, this granitoid body was compared with the world's most well-known fertile and barren granitoid bodies.

Figure 1.
Location of the study area (red square) on Iran's structural divisions map (Alavi, 1996).This area is located in Alborz in the Tarom-Hashtjin metallogenic zone according to the structural zoning implemented by Ghorbani (2013).

Geological Setting
This area is separated from the Talesh Mountains by Manjil Basin and from the Soltanieh Mountains by the Zanjan-Abhar Plain.The rock units in the area mainly include Eocene volcanic rocks (lava flows and pyroclasts belonging to the Karaj formation) and Oligocene granitoid intrusive bodies (figure 2).The volcaniclastic succession lithology in Tarom, as in other areas in Alborz, consists of green tuffs and shaly and sometimes calcareous intercalations.The Eocene volcanic rocks in the area include volcaniclastic and extrusive rocks.The extrusive rocks in this area include andesite, basaltic andesite, quartz trachyandesite and basalt, though the bulk of these rocks are basaltic andesites and quartz trachyandesite.Many intrusive bodies have been injected into Eocene volcaniclastic assemblages, so these bodies are post-Eocene (most likely Oligocene) in age.One characteristic of the Oligocene intrusive bodies is the creation of alteration areoles in Eocene volcaniclastics, and their hydrothermal phases have been generally accompanied by the formation of elements such as epithermal gold, copper, lead, zinc and kaolin.The main body is exposed at the surface in the form of a prolate batholith trending northwestsoutheast.Subvolcanic bodies are mostly observed in dyke form.Most faults in the area generally trend northwest-southeast, but some faults trend northeastsouthwest.The aforementioned bodies were injected along the structures and longitudinal faults in the highs in Tarom.Most structures in this area follow the fault system so that a set of alteration zones occurs along the faults.

Figure 2.
Simplified geological map of the study area (Davis et al, 1972).

Methodology
The rock samples were collected from the intrusive bodies in the study area.Forty-five thin sections were prepared for petrological study.To study the chemical characteristics, 11 of the most representative rock samples taken from the intrusives were selected for whole rock major oxide, trace element, and REE analysis and sent to ACME Company in Canada and the Atomic Energy Organization of Iran.At the ACME Company, the samples were first dried and then crushed and pulverized to pass a 200 mesh sieve.A lithium borate fusion and dilute nitric acid digestion of a 0.2 g sample pulp followed by ICP emission spectrometry was used to carry out the whole rock analysis for 11 major oxides and some minor elements.The loss on ignition (LOI) was obtained by sintering at 1000°C.Two separate ICP-MS analyses were done to determine the trace elements.The rare earth and refractory elements were collected from a lithium borate decomposition (same as that used for the major elements) to determine the total abundances.The precious and base metals and their associated pathfinder elements were generated from an aqua regia digestion (table 1).At the Atomic Energy Organization of Iran, the pulverized samples were mixed with boric acid and then pressed and analyzed using the XRF method (table 2).The geochemical data were processed using the Minpet 2.02 software.Because iron has been reported in its unseparated form, Irvine and Baragar's (1971) method was used in this study to calculate the bivalent and trivalent iron.

Geochemistry and Tectonomagnetic Setting of the Intrusives around Valis
The petrographical studies and chemical classification diagrams show that the intrusive bodies in the study area have granite, syenite and monzonite (granitoid) compositions and are mostly metaluminous (figure 3).Contradictory features in the intrusives (such as the behavior of P, Rb, Ga/Al, Y/Nb, K/Na, and FeO/Fe 2 O 3 , the Rb/Nb ratios, the A/CNK molar ratios and the A/CNK-Fe 2 O 3 +FeO and ACF diagrams), some of which are consistent with the I nature and others with the S and A natures, show that the rocks are classified as hybrid granitoids (figures 4-7).(Chappell and White, 1992) and, b) Na2O versus K2O diagrams (Chappell and White, 1974).The data from the study area are consistent with both I and S granites.Plotting the data on the granitoid tectonomagmatic discrimination diagrams (figure 8) shows that they usually fall within the WPG fields.et al, 1984).These data usually plot in the WPG field.

Using Geochemical Features to Study the Mineralization Potential of the Intrusives around Valis
Determining the mineralization potential of felsic intrusive bodies is important because every specific type of granite is usually accompanied with a specific type of ore deposit.For example, palingenetic granites have mineralization potential for Cu, Au, Nb and minor amounts of Sn and W (Beus, 1968).High amounts of Li, Rb compared to K (lower K:Rb ratio) and Sr compared to Rb (high Rb:Sr ratio) are geochemical characteristics of magmatic production that can be used to study the separation of volatile substances and magmatic rare metals from magma, increasing the mineralization potential (Beus, 1968).
Special indicator minerals can indicate the economic concentrations of some metallic rare elements; for example, the existence of tourmaline and topaz in granitoid bodies can imply tin mineralization as cassiterite.In addition, pink, robellite type tourmalines are abundant in lithium bearing pegmatites (Rozendaal et al, 1995); therefore, the economic value and mineralization type of the pegmatites can be partially recognized according to the color of the existing tourmalines (Beus, 1968).Aplite can be seen in some granite bodies in the study area, especially in marginal zones or in the veins that form across the bodies.These aplites have tourmalines that are black in hand specimen.On the other hand, there is no sign of topaz; therefore, the mineralization of tin is unlikely.
Tungsten has different distributions in barren and fertile intrusives.In a few samples from barren igneous bodies, the W content is higher than 5 ppm, and no sample is observed with W content higher than 10 ppm.However, at least 10% of the samples from fertile bodies contain more than 10 ppm of tungsten (Jonasson and Boyle 1972).The intrusive bodies, which have been affected by post magmatic hydrothermal processes (Jonasson and Boyle, 1972).The amount of this element in the study area's intrusives ranges from 1.4 to 5.9; therefore, they are barren in terms of W.
The degree and type of differentiation and oxidation state of the magmas that formed granites are important to determine the potential and type of associated mineralization (Blevin, 2003).The K/Rb ratio is used to determine the transition state of granite melts; if the ratio is under 100, the granite is highly evolved (Rossi et al, 2011) (figure 9).This observation occurs because Rb tends to be differentiated in the melt during the segregation stage of aqueous liquid phases from the remaining silicate melts (Clarke, 1992).This ratio ranges from 142.8 to 271.4 in the study area's intrusives.The average value of K/Rb in the intrusives around Valis (table 3) is higher than all the values in table 4; according to this table, the greater the mineralization in the granitoid bodies the lower the ratio is, as Rb tends to remain in the melts and be differentiated among the silicate melts and aqueous liquids.Therefore, these granitoids are not strongly differentiated; in other words, the granite melts that created the intrusives in the study area are insufficiently evolved (table 4).Thus, the aforementioned bodies have not undergone sufficient post magmatic activity to cause mineralization.The value of K/Rb in the study area's intrusives is similar to the average for granitoids unrelated to Li, Be, Sn, W and Ta ore deposits, so the intrusives are classified as barren granites (table 4).The evolved nature of the granites is also recognizable using the Sr-Rb-Ba triangular diagram by El Bouseily & El Sokhary (1975) (figure 10).Most samples plot in the normal granite field, which shows that the intrusives in the study area are not completely evolved.
The ratio of compatible to incompatible elements (such as Sr/Rb) is also a useful tool to recognize the differentiation type of granite magmas (Blevin 2003, Ishihara and Tani 2004, Blevin and Chapell, 1992) (figure 11); in particular, the granite magmas in the study area have been slightly differentiated.Bea et al (2006) suggested another index to recognize the evolution of magmas; if Zr/Hf<20, strong magmatic hydrothermal alteration has occurred, while if Zr/Hf>20, magmatic hydrothermal alteration has not occurred.The Zr/Hf ratio in the study area's intrusives is between 33.8 and 44.4; therefore, magmatic hydrothermal alteration has not occurred.
The Sm/Eu and Rb/Ba ratios and amounts of Rb, Ba and Sr in the intrusives around Valis are higher than those of the S type granite source rocks of porphyry tin deposits around the world (Rongfupei and Dawei Hog, 1995;Lehmann et al, 1989) (table 5).Diagrams using the aforementioned parameters can show the fertility of the granitoids with respect to Sn (Karimpour, 1999); accordingly, the intrusives in the study area lack tin mineralization (figure 12a and b).
To discriminate granitoids and recognize their economic potential for tin, molybdenum or porphyry copper, the Rb/Sr and Ce/Yb ratios and color index (obtained from [CI=(SiO 2 +K 2 O+Na 2 O)/ (MgO+CaO+FeO)]) can be used (Karimpour et al, 1983) (figure 13a and b).Tin, high grade and low-grade molybdenum and porphyry copper deposits have been completely discriminated in these diagrams.The chemical data imply that the intrusives in the study area are barren in Sn and Mo but somewhat fertile in Cu (especially sample B7).
The geochemical behaviors of the copper and zinc in magnetic crystallization products are different.Unlike copper, which is found in the chalcopyrite phase, zinc replaces iron in iron and magnesium silicates.In intermediate rocks (with 52 to 60 wt% silica), the amount of zinc is fixed at approximately 85 ppm.In rocks with over 60% silica, the zinc amount decreases linearly with increasing SiO2.In rhyolite with 75% SiO2, the amount reaches 35 ppm (Wolf, 1975).Wolf believed that practically all rocks with total iron higher than 10% can be used in regional explorations of zinc.Considering prior research and using the SiO 2 versus Fe and Zn diagrams by Wolf (1975), we recognize the barren nature of the study area's intrusive bodies with respect to zinc (Figure 14).(Beus, 1968) compared to those in the intrusives around Valis.

Type of Granitoid K/Rb
Average of the granitoids Average of the granitoids unrelated to Li, Be, Sn, W and Ta deposits.
Average of the granitoids related to Li, Be, Sn, W and Ta deposits.
Average of the biotite granites related to Li, Be, Cs and Ta pegmatitic deposits.
The study area's intrusives are semi-evolved.(Wolf, 1975), and a plot of the data related to the study area.

Results
Based on the information obtained from field studies and the petrography and analysis results of the intrusives around Valis, the following results are determined: 1 -These intrusives have granite, syenite and monzonite petrographic compositions (granitoid) and are mostly metaluminous.
2 -Contradictory features in the intrusives (such as the behavior of P, Rb, Ga/Al, Y/Nb, K/Na, and FeO/Fe2O3, the Rb/Nb ratios, the A/CNK molar ratios and the A/CNK-Fe2O3+FeO and ACF diagrams), some of which are consistent with the I nature and others with the S and A natures, show that the rocks are classified as hybrid granitoids.
3 -In terms of the tectonomagmatic setting, the rocks are classified as WPG granitoids.
4 -Based on the K/Rb ratio, these granitoids are not strongly differentiated and have not undergone post magmatic activity, which would lead to mineralization.The amount of K/Rb in the study area's intrusives is similar to the average of granitoids unrelated to Li, Be, Sn, W and Ta deposits, classifying the intrusives as barren granites.
6 -The Sm/Eu and Rb/Ba ratios and the behavior of Rb, Ba and Sr in the intrusives around Valis are completely different compared to the S type granite source rocks of porphyry tin deposits around the world and are barren in terms of tin.
7 -The chemical data (Rb/Sr, Ce/Yb ratios and color index) imply that the intrusives in the study area are barren in terms of Sn and Mo but are somewhat fertile in Cu.
8 -The changes in Zn and Fe versus SiO2 show the barren nature of these intrusives.

Figure 3 .
Figure 3. Plot of chemical data from the intrusives around Valis on a) chemical rock classification(Cox et al, 1971) and b) aluminum saturation index(Maniar and Piccoli, 1989) diagrams.

Figure 4 .
Figure 4. Plot of chemical data from the intrusives around Valis on a) ACF(Chappell and White, 1992) and, b) Na2O versus K2O diagrams(Chappell and White, 1974).The data from the study area are consistent with both I and S granites.

Figure 5 .
Figure 5.The chemical data from the intrusives around Valis plot in the S field on the ACNK-Fe2O3+FeO diagram (Pearce et al, 1984).

Figure 6 )
Figure 6) Plot of chemical data from the intrusives around Valis on a) normative corundum versus Rb and b) P2O5 versus Rb diagrams for I (solid squares) and S type (hollow circles) granites related to the Lachlan Fold Belt in Australia (Pearceet al, 1984).The data from the study area are consistent with both I and S granites.

Figure 7 .
Figure 7. Plot of chemical data from the intrusives around Valis on a) Rb/Nb versus Y/Nb (Eby, 1992) and b) Ga/Al *10000 versus Nb diagrams (Whalen et al, 1987).The data are plotted in the A type granite field.

Figure 8 .
Figure 8. Plot of chemical data from the study area's intrusives on a) Rb-(Y+Yb) and b) Nb-Y diagrams (Pearce et al, 1984).These data usually plot in the WPG field.

Figure 10 .
Figure 10.Plot of the study area's samples on Sr, Rb and Ba triangular diagram (El Bouseily and El Sokhary, 1975).

Figure 11 .
Figure 11.Diagram of Rb/Sr versus SiO 2(Blevin, 2003) and a plot of the study area's samples.

Figure 13 .
Figure 13.The discrimination source rock diagrams of Cu, Sn and Mo porphyry deposits using a color index and ratios of a) Rb/Sr and b) Ce/Yb(Karimpour, 1999), and a plot of the study area's samples.

Figure 14 .
Figure 14.The relationship between changes in a) Fe and b) Zn versus SiO2 in barren and fertile granites(Wolf, 1975), and a plot of the data related to the study area.

Table 1 .
Representative whole rock major oxides (wt %), trace elements (ppm) and rare earth elements (ppm) for samples from the intrusives around Valis (ICP-AES and ICP-MS) (implemented by the Acme Laboratory).

Table 2 .
Representative whole rock major oxides (wt %) and trace elements (ppm) for samples from the intrusives around Valis (XRF) (implemented by the Atomic Energy Organization of Iran).

Table 3 .
Average of the rare and major elements in the intrusives around Valis.

Table 4 .
K/Rb ratios of barren and fertile granites

Table 5 .
Amount and ratios of some rare elements in S type granites around the world that contain tin compared to the intrusives in the study area (Not Analyzed = NA).