Geology of the Aftabrou Polymetallic Deposit, Saveh, Iran

Aftabrou polymetallic prospect is located at the contact of Oligo-Miocene calcalkaline granodioritic to dioritic and Eocene andesitic to basaltic volcanic complex in middle section of Urumiyeh-Dokhtar volcanic arc in NW of Saveh city. Petrographic study indicated that the volcanic rocks are mostly: lava and tuff. Composition of lavas is mainly andesite and tuffs are mainly composed of dacite to rhyodacite. Major phenocrysts in these rocks are plagioclase, clinopyroxene, hornblende and opac minerals. Petrographic and geochemical studies indicated an I-type granitoid and, calcalkaline magmatism associated with continental margin of subduction zone. This study determined three mineralization subzones of 0.2% 5.3% Cu, 0.02 1.31 ppm Au and 1.2% 3.9% Zn. Fluid inclusion studies on quartzic veins associated with magmatism, demonstrated that homogenization temperatures of this mineralization fluid are between 170 ̊C to 330 ̊C, the salinity of the system is between 11.7 to 23.5 weight percent, density of this fluid is 0.8 1.1 g/cm and is occurred in depth of less than 1800 m of surface. Fluid inclusion studies suggested that formation of mineral deposit is simple cooling and mixing with atmospheric water and type of Aftabrou deposit is IOCG. In this base, it is assumed that this IOCG mineralization is occurred associate with magmatism that is formed as a result of Neo-Tethys oceanic subduction beneath the Central Iran zone which is replaced in the Orumieh-Dokhtar magmatic arc.


Introduction
The UDMA is a frontier region with high mineral potential [1] [2] [3] [4] for which a comprehensive and detailed research is required. Aftabrou is polymetallic deposit [5] [6] that formed in contact of calcalkaline volcanic-plutonic and alkaline sub-plutonic complex in central Iran on Uramieh-Dokhtar magmatic belt. It is located on northwestern of Saveh geological map of scale 1:100,000, in the province of Markazi, ~60 km northwest of the city of Saveh (Figure 1).
Aftabrou pluton containing of two part, plutonic and sub plutonic rocks [7] that by relatively age-dating, sub plutonic rocks are youngest unit in studied area [8]. Plutonic rocks are diorite and granodiorite but subputonic is diorite that both of them are formed from I-Type magma and related to continental margin of subduction zone [7]. Although, volcanic-plutonic-hosted-related polymetallic gold and/or copper and/or Zinc mineralization are known at Dalli [2] and Kahang ( Figure 1), research on geology and mineralization of Aftabrou is few. [5] [6] [9]. Yet, geochemical properties and style of mineralization, tenor of metal elements, properties of ore fluid, type of mineralization and more important, the relationship between mineralization and magmatism in Aftabrou area, are not studding, completely and exactly. In this study, we will consider above items, exactly.

Study Area
The study area is a sparsely vegetated, semi-arid, mountainous region located in central part of the UDMA in Iran (Figure 1). The UDMA is the most important volcanic arc of Iran that extends about 2000 km in an N-SE direction in the central part of the Tethyan metalorganic belt. This arc hosts volcanic and plutonic rocks with calcalkaline magma genesis, mainly that this is hosts some world class polymetallic mineralization deposits such as Sar-Cheshmeh, Songun, Meiduk, Kahang, Darezar, Drrreh-Zerreshk and Dalli [2] [10]. Most of these deposits are related to calcalkalin magmatism, mainly and sometimes to alkaline-calcalkaline magmatism [7] [11] and located in the southeast or northwest of the UDMA belt. The central UDMA is a frontier region with high mineral potential [1] [2] [3]. Aftabrou prospect is prominent polymetallic system in the central UDMA

Geologic Setting of Aftabrou
The Aftabrou polymetallic deposit is hosted by a Miocene [4] plutonic and sub plutonic rocks that outcrops of middle Eocene [8] volcanic complex that forms a range of small hills in an area~4 km across, flanked to the east and southeast by shallowly sloping tuff deposits ( Figure 2). Mineralization is seen mainly, in breccial zone between volcanic and plutonic-sub plutonic rocks. This breccial zone is 2500 m × 100 m. The margins of the complex to the south and southeastern slope gently below Quaternary alluvial deposits, such that precise outcrop limits are soft to constrain. Sub plutonic rocks is surrounded plutonic rocks and is least volume in this area [7]. All of those units are shown in one background of this area in Figure 3(a).

Research Methods
Our researches in this study consist of two main parts. For this purpose, unsystematic lithogeochemical samples that were altered and mineralized from breccia and silicified zone in contact of volcanic and plutonicsub plutonic rocks and toward volcanic, plutonic-sub plutonic, are selected. These studies are done with preparation polish and thin section in Isfahan University. In order to apply geochemical mineralization study, 22 unsystematic lithogeochemical samples were analyzed by XRF method. Results of this analyze is shown in Table 1 and Table 2. All of these analysis (in part 1 and 2) done in Zar Azma laboratory in Tehran. In order to determine mechanism of forming mineral and type of mineralization study of fluid inclusion of mineralization is done in Isfahan University. Result of this analyze are listed in Table 3. Finally, these analyses were processed by using Excel, GCDKit, Minpet, and Igpet programs.

Petrography of Aftabrou Rocks
Rocks in Aftabrou area are 3 groups of volcanic, plutonic and sub plutonic, that volcanics are highest volume and oldest, while, sub plutonics are lowest volume and youngest.  Volcanic rocks in Aftabrou are lava and tuff. The volume of lavas is more than tuffs. In more times lavas convert to tuffs, laterally ( Figure 3

Igneous Geochemistry of the Aftabrou Rocks
Calcalkaline, I-type magma formed plutonic rocks and alkaline magma formed sub plutonic rocks in Aftabrou area [7]. In this study, at first, we consider nature and type of magma former volcanic rocks.

Sample of Volcanic Rocks
12 samples of fresh igneous rocks from the Aftabrou volcanic complex were collected for whole-rock geochemical analysis. All of them were analyzed by ICP-

Classification of Volcanic Rocks
The

Nature of Former Magma of Volcanic Rocks
As is ploted in Figure 5(a), nature of this magma is subalkaline and calcalkaline ( Figure 5(b)).

Petrography of Mineralization in Aftabrou Area
In order to recognization of metal ore, petrography of mineralization in rock  In macroscopic study which rocks are in light gray-gray to light brown-brown color with fractures and vents that filled by iron hydroxides and carbonates ( Figure 6(a), Figure 6(b)). High hardness and its appearance defined it "silisic rock". This rocks in microscopic study, thin section, contain of auhedral to unhedral crystal of silica in different sizes from very fine grain to coarse grain ( Figure 6(d)). There are many fractures that filled with opac mineral ( Figure   6(d)). There are double generations of silica in this sample, that delay silica in comparision to once generation, have more coarse-grained. Primary texture in all of them is disappeared.
Polish section is shown a lot of auhedral to unhedral crystals of pyrite and deposit of malachite adminst them and many fine grain of single crystal of chal-copyrite ( Figure 6(c)). Pyrites, more time, completely, sometimes, slightly, convert to goethite (Figure 6(c)). In most of thin and polish sections extension joints in to pull-apart, are seen, that most filled with metal minerals.

Geochemistry of Mineralization in Aftabrou Area
In order to apply geochemical mineralization study, 22 unsystematic lithogeochemical samples were analyzed. Results of this analyze is shown in Table 2.
Location of this sampling point is shown in Figure 7. According to data from Table 2, three main anomalies are found in this area.

Copper Mineralization
According to data from Table 2

Gold Mineralization
According to data from Table 2

Zinc Mineralization
According to data from Table 2, Zinc concentration varies from 1.2% to 3.9%    Figure 13). This mineralization occurs in black color andesite-basaltic unit.

Fluid Inclusion Study of the Aftabrou
A total of 7 samples were collected from the different Levels of deposit as well as outcrop samples from the quartz veins related to mineralization (Figure 14), out of which fresher and unweathered samples were selected for fluid inclusion petrography and its micro thermometry. The advantages of using of quartz, are lack of cleavage and ability easy recrystallization that do it appropriate environment for protection of fluid inclusions [12]. Petrographic studies of the polished section and doubly polished thin sections (~100 μm thick) of quartz were carried  equation [13]. Whereas the equation of [14] was used to calculate salinity from halite-melting temperatures.

Micro Thermometric Studies
The b. Bubble of vapor is larger and less volume of liquid is form this (<25%). Samples of this is small and not studied (Figure 15(b)).
Histogram of homogenization temperature of fluid inclusion ( Figure 16) is shown that formation of available mineral in hydrothermal veins is occurred in more one stage of mineralization, but in medium and low temperature.
Freezing method: Freezing studies is used for salinity determination in waterrich fluid. In this case, the measurement of temperature of ice final melting  volume is shown range of salinity from 11.7% to 23.7%wt NaCl and medium salinity, 20. 24%wt. Lack of daughter phase may be in due to medium salinity [17] and mixing with atmospheric water [16].
Depth of fluid inclusion entrapment is determined less than 1800m of surface, by using the temperature of homogenization and pressure curve in diagram from ( Figure 17).
Density of mineralization fluid is determined from 0.8 -1. 1 gr/ cm 3 , by using the percentage weight of salinity vs. temperature homogenization in diagram from [15] (Figure 18).  Vapor pressure of fluid is determined less than 100 atmosphere, by using the percentage weight of salinity vs. temperature homogenization in diagram from ( Figure 19).
Determination of deposition formation and type of mineralization in Aftabrou deposit: Formation of mineral deposit is simple on the basis of obtained data. In the other words, decrease of fluid temperature is from fractures up to surface with atmospheric water mixing. According to presence of small vapor and medium salinity phases in samples, can point to fluid mixing. But, according to lack of CO 2 in samples and coexistence of vapor and liquid-rich fluid, cannot exact boiling occurrence [18]. So, trend of samples in diagram [15], deposit mechanism of mineral in veins, is simple cooling and mixing with atmospheric water ( Figure 20).
Aftabrou is in below range of deposit IOCG (from Cu-Au-Bi-Fe Oxide Type), on the basis of salinity-homogenization temperature diagram [15] (Figure 21).

Conclusion
Rocks in Aftabrou area were 3 groups of volcanic, plutonic and sub plutonic.
Volcanics involved of andesitic to dacitic tuff and lava that show porphyritic texture with glassy and fine grain microgranular to microgranular mesostasis.
The mineral is distinct and specified values of phenocrysts of quartz, alkalifeldespar, biotite, plagioclase, hornblende, clinopyroxen and opac minerals.
Copper mineralization with 0.2% -5.3% tenor are related to vein and veinlet (mainly malakite) and sulfidic (mainly chalcopyrite), in south eastern of Aftabrou pluton. Breccial and stockwork Gold mineralization with 0.02 to 1.31 ppm is occured in andesitic/granodoritic and tuffic rocks. Zinc mineralization with 1.2% to 3.9% occurs in black color andesite-basaltic unit. Field observations, petrographic and geochemical studies are shown that mineralization is more related to vein and veinlet of quartz.
Fluid inclusion studies of quartz two type of inclusion are shown, liquid, that is form major part (>50%) and vapor that is small and not studied (<25%).
Temperature of homogenization of this fluid is shown that available mineral occurd in more one stage of mineralization, but in medium and low temperature. By freezing method range of salinity from 11.7% to 23.7% wt, medium salinity, with density from 0.8 -1.1 gr/cm 3 and vapor pressure less than 100 atmosphere in depth less than 1800 m of surface are formed. Lack of daughter phase may be in due to medium salinity [17] and mixing with atmospheric water [16].
According to this information, formation of mineral deposit is simple. In the other words, decrease of fluid temperature is from fractures up to surface with atmospheric water mixing. According to presence of small vapor and medium salinity phases in samples, can point to fluid mixing. But, according to lack of CO 2 in samples and coexistence of vapor and liquid-rich fluid, cannot exact boiling occurrence [18]. So, trend of samples in diagram [15], deposit mechanism of mineral in veins, is simple cooling and mixing with atmospheric water [19].
Most IOCG deposits have mineral assemblages that imply the ore fluids were oxidized and sulfide poor, although host rocks locally appear to have influenced the formation of more reduced [19]. Fluid inclusions indicate that the ore fluids were saline and the overall impression is that these deposits formed from fluids with high Cl/S [20]. The geologic evidence presents a complex picture with key features including the following: IOCG deposits are associated with igneous rocks that range from diorites to granites [21]. Mineralization and associated alteration occurred at submagmatic temperatures [21]. There is generally strong, but not universal, evidence for coeval magmatism with different regions having different compositional intrusive suites [21]. For example, in Mantoverde system of Chilean IOCG deposits, as seen as, Aftabrou mineralization occured related to volcanic, volcanoclastic and locally intrusive host rocks from calcalkaline I-Type magmatism in volcanic arc setting with concentrations of Zn [22] and they are typically polymetallic, with one or more economic metals that may include various combinations of Fe, Cu, Au, Ag, U, Th, F, Co, Bi, W, rare earth elements (REE) and other metals.
Properties such as mineralization are associated with intermediate Cenozoic intrusive and semi intrusive [23], view of alteration and mineralization in a wide range [21]. Epigenetic mineralization, as seen as Aftabrou, in many other parts of the world such as Mantoverde IOCG system of Chilean [22], IOCG deposits in Canada [24], world's Mesozoic arc northern Chile and southern Peru [25], Iron Oxide Copper-Gold deposits (IOCG) are reported in frontier felsic to intermediate volcano-plutonic terrains [24]. On the other, Aftabrou is in below range of deposit IOCG (from Cu-Au-Bi-Fe Oxide Type), on the basis of salinityhomogenization temperature diagram [26].
On the other, in term of geodynamic setting, Aftabrou intrusion is classified as volcanic arc (VAG) and active continental margin (CAG) which have been formed as a result of Neotethys oceanic crust subduction beneath the Central Iran continental crust [7].
According to this, it is assumed that Aftabrou IOCG deposit is occurred associate with magmatism that is formed as a result of Neotethys oceanic subduction beneath the Central Iran zone which is replaced in the Orumieh-Dokhtar magmatic arc.
According to conducted research, genetic model(s), origin of fluids and processes of metal recharge and discharge during the alteration, brecciation and ore deposition processes that lead to IOCG(U) deposits remain poorly understood [24]. On the other, knowledge gaps can be partially attributed to the recent recognition of this deposit-type and the importance of pre-enrichment of their hosts to generate uranium-rich deposits. The nonsystematic geometry and the diversity of known deposits, the complexity of possible ore-forming processes, and the non-exposed nature of many IOCG(U) deposits (e.g., Olympic Dam) [24], are other than the need for further study of these reserves. Stable isotopes will be required in order to determine the accurate understanding of the origin of mineralizing fluid. IOCG deposits are currently viewed as the most challenging field of research in contemporary economic geology [21], it is suggested this deposit will be undergoing extensive exploration.