Fluid Inclusion Investigations of the Masjed Daghi Copper-Gold Porphyry-Epithermal Mineralization , East Azerbaijan Province , NW Iran

The Masjed Daghi mineralization is located 30 km southeast of Jolfa city at the bank of Araxes River, northwest Iran. This area is situated in the AlborzAzarbaijan structural zone of Iran. The most widespread rocks in the mineralization area are andesite and trachyandesite, while there are rock units of latite tuff, andesitic agglomerate, and hornblende porphyry basalt in eastern hills and Eocene flysch in the southern part of the area. Several intrusive bodies are present in the study area, from which the dominant intrusive rock hosting the mineralization is diorite porphyry. The mineralized rock units of the area are cut by different diorite ad mafic dikes. The most prevalent texture of mineralization is dissemination, while open space filling textures including veins and veinlets, are common as well. Diverse types of alteration including potassic, phyllic, argillic, silicification, and a little of carbonatization were recognized in the field and microscopic observations as well as by XRD. In addition to thick silica veins and stockwork zones, some silica, barite, sulfide, and calcite veins and veinlets have occurred in the Masjed Daghi mineralization area. In this research, 26 doubly polished thin sections (wafers) were prepared and investigated. Four samples were taken from surface veins, while 22 samples were chosen from core samples (of 6 boreholes) of white and greywhite silica, and silica-barite veins. The fluid inclusion studies on 105 primary fluid inclusions indicated five phases for inclusions including: 1) liquid or gas, 2) liquid and gas, 3) liquid, gas, and solid, 4) liquid, gas, halite, and solid, and 5) liquid, gas, halite, and two types of solids. The data gained from fluid inclusions approved two mineralization fluids which caused porphyry and epiHow to cite this paper: Atalou, S., Nazafati, N., Lotfi, M. and Aghazadeh, M. (2017) Fluid Inclusion Investigations of the Masjed Daghi Copper-Gold PorphyryEpithermal Mineralization, East Azerbaijan Province, NW Iran. Open Journal of Geology, 7, 1110-1127. https://doi.org/10.4236/ojg.2017.78074 Received: February 15, 2016 Accepted: August 12, 2017 Published: August 15, 2017 Copyright © 2017 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/


Introduction
The Masjed Daghi mineralization, with general coordinates of 38˚52'40''N and 45˚56'25''E, is located 30 km southeast of Jolfa city at the bank of Araxes River, northwest Iran.The exploration of Masjed Daghi mineralization area was commenced in 2000 by the Geological Survey of Iran (GSI) by means of preparation of 1:3000 and 1:5000 geologic maps, rock sampling, and digging 18 exploration boreholes [1].By recognizing some gold-copper anomalies, the exploration was continued with the digging of 16 exploration boreholes with the total length of 1882 meters [2].So far some PhD and MSc theses as well as some individual investigations were performed on the Masjed Daghi mineralization [3] [4] [5] [6], but some crucial questions about the genesis of the fluids causing the mineralization remained open.Recent exploration by the National Iranian Copper Industries Company with 67 boreholes with the total length of 38,600 meters estimated 204 million tons of copper 0.3% and 20% million tons of gold 320 ppb [2].The age of porphyry mineralization of Masjed Daghi using Re-Os method on molybdenite present in silica stock works is 20.46 + 3.55 million years [7].
The fluid inclusion studies performed in this study revealed valuable data about the characteristics of the mineralization including temperature of the formation of minerals, the pressure dominating the environment during the mineralization, the fluid density forming the minerals, the source and chemical composition of mineralizing fluids, the occurrence of boiling in the course of mineralization, depth, and type of mineralization.There is little attention given to research on the mentioned topic, especially in Iran, which is the main reason to carry out this research; therefore, the present study tries to investigate fluid inclusion of the Masjed Daghi Copper-Gold Porphyry-Epithermal Mineralization, East Azerbaijan Province, NW Iran.

Materials and Methods
This research was performed in four main stages which include: 1) Field observations and sampling, 2) Sample preparation and making 26 doubly polished thin sections, 3) Petrography of the sections, and 4) Geothermobarometric studies and Raman laser spectroscopy measurements.From 26 doubly polished thin S. Atalou 1).The fluid inclusion studies on 105 primary fluid inclusions (50 multi-phase and 55 two-phase fluid inclusions) were conducted in the Iranian Mineral Processing Research Center (IMPRC) using a THMS600 heating-freezing Linkam stage installed on a ZEISS microscope with the thermal range between −196˚C and +600˚C.In order to recognize dubious minerals within fluid inclusions, 10 fluid inclusions were analyzed using Raman laser spectroscopy in the physics laboratory at the Tarbiat Modarres University of Tehran.

Geology and Mineralization of the Study Area
The Masjed Daghi area is located within the Alborz-Azerbaijan structural subdivision of Iran [8].Andesite and trachy-andesite are the most abundant rock units of the study area and demonstrate a porphyritic texture including phenocrysts of plagioclase, amphibole, and biotite.There are rock units of latite tuff,

Fluid Inclusions Studies of the Masjed Daghi Deposit
In order to study the 105 primary fluid inclusions in the samples, the following characteristics of the inclusions were considered and investigated (Sections 4-1, to 4-13).

Primary and Secondary Inclusions
One of the most principal works in petrography stage is to recognize the primary inclusions as the best sources for investigation from other inclusions.Since we cannot use secondary fluid inclusions and those that have necking down to rec-ognize the physico-chemical conditions of mineralizing fluids, in the present study we have disregarded the secondary and pseudo-secondary inclusions.

Solid phases of Fluid Inclusions
In multi-phase fluid inclusions of Masjed Daghi, the dominating solid phase is halite with surface morphological features (cubic form).Sylvite is smaller than halite and is dissolved in a lower temperature than halite.The opaque solid phase is hematite in two major forms; 1) hexagonal which is red in color or 2) masses in the dark red to brown color.In some cases, two solid phases were recognized in the inclusions.These were recognized-using Raman laser spectroscopy-to be rutile, magnetite, arcanite, cerussite, anhydrite, asphalerite, and anglesite.

The Classification of Fluid Inclusion Phases of Masjed Daghi
The fluid inclusions of Masjed Daghi deposit can be divided into three major phases which are described in the following: A) Single-phase fluid inclusions The Liquid (L) and gas (V) single phase fluid inclusions of Masjed Daghi are of two types that are described as follows: micrometer.The average homogenization temperature is 186˚C with a maximum of 289˚C.The maximum salinity is 9.41 wt% NaCl equivalent with an average of 6.23.The average density is calculated to be 0.92 g/cm 3 and the ice melting temperature is -3.8˚C in average with a maximum of -6˚C.The average eutectic temperature is -40.8˚C with a maximum of −47˚C.The samples were taken from the veins in the potassic and phyllic alteration zones of diorite.In two-phase fluid inclusions rich of liquid more than 70% of the volume of the inclusion is filled with liquid.In white silica veins of samples BH45-369, BH49-605a, BH45-831, BH52-414, and BH39-199 the primary two-phase inclusions are also rich in liquid.b) Two-phase liquid and gas, rich in gas (V + L): In this type of inclusions observed in white silica veins (in potassic alteration of diorite; samples BH49-801 and BH66-466), about 85% to 95% of the inclusion is filled with gas, while 5% to 15% of it is occupied by liquid phase.The homogenization temperature of two-phase inclusion (V + L − V) to gas phase is 416°C.Grey silica veins of these samples have lots of multi-phase fluid inclusions.C) Multi-phase liquid, gas, and solid (L + V + Ha + S1 + S2) fluid inclusions The multi-phase inclusions can be divided into three major groups based on their contents which can be liquid, gas, and solid (L + V + Ha + S1 + S2) containing 3, 4, or 5 phases.a) Three-phase inclusions of liquid, gas, and solid (LVS) including 4 types of i) liquid, gas, halite (L + V + Ha), ii) liquid, gas, hematite (L + V + S (Hematite)), iii) liquid, gas, solid1 (L + V + S1), and iv) gas, liquid, solid2 (V + L + S2).
The number of multi-phase fluid inclusions has been 52 and the highest number was allocated to 4-phases and the least ones were allocated to 5-phases.The average homogenization temperature of multi-phase inclusions was 343˚C, while the maximum temperature was 550˚C.The average homogenization temperature of halite was 465˚C with a maximum of 550˚C.The average salinity was 55 wt% NaCl equivalent with a maximum of 66.9.The average homogenization temperature of sylvite-which was mostly observed in five-multi-phase inclusions-, was 407˚C with an average salinity of 31.13 wt% KC1 equivalent.Most of the multi-phase inclusions of liquid, gas, and solid were present in the grey silica veins located in the potassic alteration zone of diorite (samples BH49-605, BH66-466, BH39-1011, BH49-801, BH52-817, and BH38-441).Only a few twophase and single-phase gas fluid inclusions can be observed in white silica veins of these samples.In most fluid inclusions, the dissolution temperature of salt phase is higher than the homogenization temperature of the vapor phase (Thsalt > Th1-v).The grey silica veins with multi-phase fluid inclusions are indicators of porphyry mineralization conditions, while the single-and two-phase inclusions in white silica and barite veinlets indicate the epithermal mineralization conditions.

Changing the Characteristics of Fluid Inclusions by Increasing Depth and in Northern and Southern Parts of the Mineralization Zone
The overall changes of 104 fluid inclusions of 6 boreholes from five depth levels of 199, 414, 605, 817, and 1011 meters were investigated (Table 1).By increasing the depth, the maximum size, the number of two-phase fluid inclusions, the dissolution temperature of halite, and the ice melting temperature of fluid inclusions were reduced regularly, while the number of multi-phase inclusions, homogenization temperature, and the salinity and density of fluid inclusions were increased regularly.The study of features of fluid inclusions in the boreholes No. 49, No. 38, and No. 66 in northern part and boreholes No. 52, No. 39, No. 45 in southern part of the study area demonstrate that the diversity of phases of fluid inclusions, the average homogenization temperature, the salinity, the salts dissolution temperature, the ice melting temperature, and the presence of solid hematite and sylvite phases in northern part of the area were increased considerably compared to the southern part and therefore the function of mineralizing fluids in northern part has been stronger.

The Correction and Determination of the Pressure and Depth of Mineralization
Despite homogenization of some fluid inclusions into gas, some inclusions of samples BH49-605a, BH45-831, BH39-199, and BH52-414 were homogenized into liquid phase.Therefore, in order to know the real temperature of trapping we need to revise and correct the pressure.In this regard, the calculations of pressure correction of fluid inclusion in sample BH39-1011 (having only NaCl and homogenized to liquid phase under predetermined salinity and homogenization temperature) is presented as an instance.To calculate the depth of trapping of the fluid inclusions of Masjed Daghi the Haas diagram was used [12].In this regard, the trapping depth of an inclusion showing 7.36 wt% NaCl equivalent and 289˚C homogenization temperature was 813 m.The pressure of trapping of this inclusion was calculated to be 215 bar, while its density was 0.8 g/cm 3 based on the Wilkinson's diagram [13].The calculated pressure was corrected using Shepherd's (1985) pressure-temperature diagrams which revealed a trapping temperature of 315˚C with a 26˚C correction value.
In order to calculate the pressure and the depth of mineralization, the Gunter's diagram [13] was used, a diagram that is appropriate for inclusions with 30 to 80 wt% NaCl equivalent.The results were in a good agreement with the data obtained from Flincor software [14].The fluid inclusion studies on Masjed Daghi samples indicated that the inclusions with Th(halite) > Th(L-V) are the most abundant ones and therefore the A curve which gives a better estimate of trapping pressure (compared to B and C curves) was utilized.Based on the Th(L-V) data, the average homogenization temperature and salinity after pressure correction were 380˚C and 55 wt% NaCl equivalent, respectively.These could be, nevertheless, increased to 401˚C and 71 wt% NaCl equivalent.In this respect, the trapping pressure of inclusions and the depth of mineralization have been calculated to be 1150 bar and 4.34 km, respectively.

The Solidification of Fluid Inclusions
The study of solidification (freezing temperature) of fluid inclusions is considered as the best method to study the salinity of fluids because the freezing point of water is related to the amount and type of salt dissolved in the fluid.By using ice melting diagram the amount and type of salt can be calculated [15].By recognizing the temperature of the first freezing stage or the last ice melting point we can understand the dissolution amount of each salt type in water [15].One of the most important methods to identify the fluid composition is to use eutectic temperature or primary melting temperature that can show a schematic representation of the composition of cations and anions present in the fluid [16].Ice H 2 O-NaCl-KCl would be the most appropriate predictable salt compositions in fluid inclusions of Masjed Daghi according to Boriswnko (1977) (cited in [17]).

Chloride and Sulfide Complexes
Understanding the compositions of fluids is an important step to recognize the ligands carrying metals [17].Many researchers support the presence of ligands such as HS-or H 2 S, CL-, and OH-to transfer metals in the form of complex ions.To understand the ore genesis and the transfer medium of elementes like Cu, Fe, and Mo based on the fluid inclusion studies, the diagram presented by Large [18] Large (1988) [18], while the samples of white silica veins fall within the sulfide ligand area (area B) of epithermal deposits.porphyry copper deposits from USA reported by Roedder (1984) based on their KCI-NaCl-H 2 O phases.According to Roedder, the KCl content of the fluids in the deposits of Bingham, Naica, and Red Mount is high and has increased to as high as the NaCl contents in some cases.On the contrary, the NaCl content is much higher than the KCl content in the deposits of Panguna, Granisle Bell, Tintic, Endaco, and Rio Pisco [19].The Masjed Daghi fluid characteristics match the latter.The space-filling degree of multi-phase inclusions of Masjed Daghi is about 15% to 30%.This together with the presence of lots of halite and sylvite in the samples imply the dominance of H 2 O-NaCl and H 2 O-NaCl-KCI systems.

Evidence of Boiling in the Masjed Daghi Mineralizing Fluids
The occurrence of boiling and the temperature and pressure through which the boiling has happened can have a very important impact on the study of mineralizations.The boiling of mineralizing fluids is one of the most important factors in precipitation of mineralization in ore deposits [20].The evidence of the occurrence of boiling of mineralizing fluids in Masjed Daghi include: 1) presence of single-phase gas inclusions (in samples like BH66-466, BH49-605, and BH39-1011), 2) presence of single-phase liquid inclusions as well as liquid-rich twoand multi-phase inclusions [15] [20] (sample BH49-605), 3) large gas bubbles in samples of BH49-605 and BH49-801, (4) two-phase liquid and gas inclusions filling 85% to 95% of samples BH49-801 and BH66-466 homogenizing to gas phase.Based on the Raman laser spectroscopic investigations, only one sample (BH39-383) contained CO 2 [20].Nevertheless, the lack of gases like CH 4 , N 2 , H 2 , Ar, H 2 S, and CO 2 in the majority of inclusions of Masjed Daghi may imply the release of such gases when boiling has occurred [20].The diagram showing the homogenization temperature against halite dissolution temperature [15] was applied for halite-bearing multi-phase inclusions of samples BH49-605, BH52-817, BH49-801, and BH66-466.This indicated that the Masjed Daghi samples plot along the line in the middle which implies Th (L − V) = Tm and therefore the occurrence of boiling process [15].On the other hand, the presence of two groups of low temperature and low salinity inclusions (with average homogenization temperature of 186˚C and average salinity of 6.23 wt% NaCl equivalent) and high salinity and temperature (average homogenization temperature of 343˚C and average salinity of 55 wt% NaCl equivalent), low difference between the homogenization temperature and trapping temperature of fluid inclusions (26˚C), and the attribution of the greatest size of inclusions (18 micrometer) to two-phase liquid and gas inclusions (sample BH39-199) would also indicate the occurrence of boiling.

The Thermometric Data of Fluid Inclusions
One of the useful methods to summarize and display the fluid inclusion data including salinity, density, depth, pressure, homogenization temperature, halite dissolution, melting point, and freezing point is using column histograms based on the variables.The histograms of final homogenization temperature-frequency for 100 fluid inclusions indicate two major temperature ranges of 155˚C and 515˚C for mineralization.The histogram of halite dissolution temperature against frequency indicates that the temperature of 505˚C has the highest frequency.The salinity histogram shows two individual mineralization phases based on salinity range (wt% NaCl equivalent); one from 2% to 10% and the other from 30% and 66%.The salinity of fluid inclusions is a useful guide to localize the main core of mineralization.In many types of ore deposits, the salinity of mineralizing fluids is greater at the primary stages of mineralization and as the mineralization proceeds, the salinity of the fluids would be reduced.Therefore, the inclusions with highest salinity degrees normally concentrate in the main body of the mineralization.Therefore, the presence of inclusions with high temperature and salinity in potassic zones can be correlated with the core of porphyry mineralizations.The most frequent ice melting temperature for 53 L + V inclusions from phyllic and potassic zones of Masjed Daghi is −4˚C which corresponds with 6.5 wt% NaCl equivalent.Based on the histograms, the salinity

Homogenization of Fluid Inclusions Based on Salt Contents
The fluid inclusions of the samples taken from Masjed Daghi were homogenized to gas and liquid phases, based on salinity percentage (without halite and undersaturated and saturated with halite).In the following the major outcomes of the studies on fluid inclusions of Masjed Daghi based on their salt content have been summarized: • The liquid and gas inclusions lacking halite (e.g.samples BH49-605-12 and BH49-801-3) were homogenized to gas.
• The liquid and gas fluid inclusions undersaturated with halite (with a salinity of less than %10 like samples BH45-831 and BH49-605a) were homogenized to liquid.Most of the undersaturated inclusions were of this type.
• The inclusions saturated with halite that were homogenized to liquid and gas phases can be divided into three groups: • 3-a-Halite dissolution has occurred after the dissolution of gas phase and the final homogenization has occurred with halite dissolution.Samples BH49-605, BH66-466, BH39-1011, BH-49-801, BH52-817, and BH38-441 were of this type and were located on the both sides of the halite saturation curve.
• 3-b-The dissolution of halite happened before gas phase dissolution and the final homogenization happened when there was gas phase dissolution, like the samples of BH49-605 and BH52-817 that were located in the upper part of the halite saturation curve.
• 3-c-The dissolution of halite happened concurrently with other phases and the final homogenization occurred as all phases were dissolved, like samples BH66-466, BH49-605, BH52-817, and BH49-801 that were located at the top of the halite saturation curve and formed the least number of samples saturated with halite.

Evidence for Porphyry Mineralization in Masjed Daghi
• Multi-phase fluid inclusions of L + V + S in Masjed Daghi have homogenization temperatures from 122˚C to 550˚C and salinities between 30.44 and 66.9 wt% NaCl equivalent with an average of 55.The maximum homogenization temperature of this group is 700˚C, while the maximum salinity is 84.5 wt% NaCl equivalent.
• Based on the Wilkinson diagram [20], all abovementioned samples are situated in the range of porphyry mineralization type (Figure 4).
• Based on the Raman laser spectroscopy investigations, the major daughter minerals of the inclusions include halite, sylvite, hematite, magnetite, anhydrate, rutile, and sphalerite.
• There is boiling evidence in the Masjed Daghi deposit.[20] showing the good match of fluid inclusions with both porphyry and epithermal mineralization types.
• Fluid inclusions in Masjed Daghi area contain halite and sylvite and have an average salinity of 44.57wt% NaCl equivalent, while an average salinity of 31.13 wt% KCl equivalent and regarding the phases of KCI-NaCl-H 2 O, demonstrate a similar trend of porphyry copper deposits like Panguna, Granisle Bell, Tintic, Endaco, and Rio Pisco.
• Based on the petrographic investigations, diorite is the major intrusive rock hosting the mineralization in Masjed Daghi, while intrusive bodies of quartzmonzonite, monzodiorite, quartzdiorite and granodiorite can be found at depth and amphibole diorite on the surface outcrops.The texture of all intrusive rocks is porphyritic.The alteration is pervasive in the mineralization area and based on field and petrographic observations and XRD analysis include potassic, phyllic, argillic, silicfication and carbonatization.
• The vast stockwork zones together with irregular and thick silica veins can be clearly observed in the area.The function of faults and fractures has been crucial to the setting of veins and dikes in the area.
• Dissemination is the most common form of mineralization, nevertheless, the open space fillings, especially in the form of veins and veinlets are present as well

Evidence for Epithermal Mineralization in Masjed Daghi
• The two-phase fluid inclusions of L + V have had homogenization temperatures from 110˚C to 289˚C and salinities from 0.21 to 9.9 wt% NaCl equivalent.The average homogenization temperature of this group was 186˚C, while the average salinity was 6.23 wt% NaCl equivalent (Figure 4).• In the sample BH52-414, L + V inclusions were observed in quartz, sphalerite, and calcite which are characteristic of epithermal mineralization.
• According to the Raman laser spectroscopic investigations, only in one case CO 2 gas was recognized.Lack of gases like CO 2 , CH 4 , N 2 , H 2 , Ar, and H 2 S indicates the loss and release of such gases during boiling, which is one of the typical characteristics of epithermal mineralizations.
• Open space filling, dissemination, and vein and veinlets, are the most common textures observed in the samples.
• The sulfosalt minerals of tetrahedrate and tennantite which were abundantly observed in the samples are another characteristic of epithermal mineralization.
• The intrusion of plutonic bodies together with presence of volcanic rocks like andesite, trachyandesite, hornblende basalt, and dacite have provided the conditions required for circulation of mineralizing fluids.The free flow of Open Journal of Geology hydrothermal fluids with intermediate temperatures close to the surface have caused the occurrence of thick and long silica veins together with irregular veins of gypsum in the fractures of the rocks of the area.

Conclusions
The major intrusive rock hosting the mineralization in Masjed Daghi is diorite, while intrusive bodies of quartzmonzonite, monzodiorite, quartzdiorite and granodiorite can be found at depth and amphibole diorite on the surface outcrops.The texture of all intrusive rocks is porphyritic.Dissemination is the most common form of mineralization, nevertheless, the open space fillings, especially in the form of veins and veinlets are present as well.The alteration is pervasive in the mineralization area and based on field and petrographic observations and XRD analysis includes potassic, phyllic, argillic, silicification, and carbonatization.Potassic and phyllic alterations were observed from near surface to the depth of 1011 m.
In addition to thick silica veins and siliceous stockwork zones, the veins in mineralized area include mineralized grey silica veins, sulfide, silica-barite, white silica, gypsum, and calcite veins in order of their date of occurrence.Grey silica veins are the most abundant and the most ancient veins, while white silica veins are the youngest and calcite veins are the rarest veins.Some of samples contain both grey silica and younger white silicate veins.The white silica veins are observed in both parallel and intersecting forms to the grey silica veins.

The fluid inclusion studies on the abovementioned silica veins in Masjed
Daghi area demonstrate the presence of two mineralizing fluids, one with high temperature and salinity (multi-phase L + V + Ha + S with average homogenization temperature of 343˚C and the average salinity of 55 wt% NaCl equivalent), while the other fluid indicates a low temperature and salinity (two-phase L + V with average homogenization temperature of 186˚C and the average salinity of 6.23 wt% NaCl equivalent).All the low temperature-salinity samples are in a good agreement with an epithermal mineralization type, while the high temperature-salinity samples are in a good agreement with a porphyry type of mineralization.
Based on the geothermometric studies, the grey silica veins with multi-phase inclusions (3-phase, 4-phase, and 5-phase) all showed the characteristics of porphyry mineralization type, while the white silica veins and silica-barite veins with single-phase liquid or gas or two-phase liquid and gas inclusions repre-

Figure 1 .Figure 2 .
Figure 1.Location and number of boreholes in the study area.The sampled boreholes have been marked with a red circle.

a)
Liquid single-phase (L): In barite vein of sample BH39-199 and white silica veins of samples BH52-414 and BH45-831 the primary single-phase liquid inclusions are frequent and are present along with primary two-phase inclusions enriched in liquid.These inclusions are observed in the forms of elongated, regular polygonal, negative crystal, bar, and shapeless with 5 to 18 micrometers size and the salinity of 0.21 to 9.41wt% NaCl equivalent.b) Gas single-phase (V): The single-phase gas fluid inclusions are abundant in white silica veins of samples BH49-605, BH39-1011, and BH66-466.In grey silica veins, they are present along with two-phase and lots of multi-phase fluid inclusions.B) Two-phase liquid and gas fluid inclusions that are two types: a) Two-phase liquid and gas, rich in liquid (L + V): The most abundant fluid inclusions of Masjed Daghi with 52 cases belong to this type.This type is present at the depth of 199 to 831 meters in most of the samples.The size of the fluid inclusions varies between 5 and 18 micrometers with the average size of 9.8 melting point of 53 fluid inclusions in Masjed Daghi is between −0.3˚C and −6˚C with an average of −3.83˚C.The eutectic temperature in seven fluid inclusions in Masjed Daghi is equal to −30˚C to −47˚C with an average of −40.86˚C.Regarding the eutectic temperatures of −20.8˚C and −10.6˚C, respectively for H 2 O-NaCl and H 2 O-KCI, the presence of salts other than halite and sylvite in the fluids was necessary, in order to reduce the eutectic temperature to −47˚C.Based on the measured eutectic temperatures, compositions such as H 2 O-CaCl 2 , H 2 O-

Figure 3 .
Figure 3. Grey silica vein samples mostly fall within chloride ligand and Cu-Au porphyry deposits area (area A) of the diagram presented byLarge (1988) [18], while the samples of white silica veins fall within the sulfide ligand area (area B) of epithermal deposits.
of two-phase (L + V) inclusions of the final stages of mineralization has been very low compared to multi-phase inclusions.The histogram showing the distribution of homogenization temperature against dissolution temperature of salt in fluid inclusions indicate that most of the salt dissolution and homogenization temperatures have occurred from 350˚C to 550˚C, and from 110˚C to 550˚C, respectively.The fluid inclusions with high homogenization and salts dissolution temperatures correspond to the potassic zone of mineralization.The L + V inclusions with homogenization temperature lower than 290˚C compose the largest fluid inclusions of Masjed Daghi.The salinity and the salt dissolution temperature generally show a linear trend, although the sylvite-bearing inclusions do not follow this linear trend and show higher temperatures at the same salinity range.

Figure 4 .
Figure 4.The Wilkinson (2001) diagram[20] showing the good match of fluid inclusions with both porphyry and epithermal mineralization types.
sented the characteristics of epithermal mineralization type.Fluid inclusions with the characteristics of porphyry mineralization can be observed in all samples (except borehole 45) up to the depth of 1011 m.Fluid inclusions with epithermal characteristics are observed in the eastern part of the ore deposit up to the depth of 414 m and in northeast part up to the depth of 605 m.The depth of the epithermal mineralization reaches up to 831 m (in the western part of the area).In the northern part of the ore body, the characteristics of the fluid inclusions (e.g.homogenization temperature, salinity, number of phases, etc.) are more diverse than the southern part.As the depth increases, the maximum size, the number of two-phase fluid inclusions, the dissolution temperature of halite, and the ice-melt temperature of fluid inclusions would reduce regularly, while the number of multi-phase inclusions, homogenization temperature, and the salinity and density of fluid inclusions increased orderly.The mineralizing fluids in northern part of the deposit have functioned more strongly-especially with the depth increase-compared to the southern part.All the multi-phase and the sylvite-hematite-bearing inclusions were observed in the potassic alteration zone whose homogenization temperature and salinity reach up to 700˚C and 84.56 wt% NaCl equivalent, respectively.These high homogenization temperature and salinity might indicate the location of the core of the porphyry mineralization of the deposit.Based on the diagram presented by Large (1988), most of multi-phase inclusions of Masjed Daghi are situated in the range of porphyry copper-gold chloride ligands and only a few multi-phase inclusions together with the entire twophase inclusions are plotted within the sulfide complex ligand area.The ratio of wt% NaCl/KCI equivalent of the fluid inclusions of Masjed Daghi is comparable with porphyry type deposits of Panguna, Granisle Bell, Tintic, Endaco, and Rio Pisco.The pressure of trapping of the fluids has been 1150 bars and the depth of mineralization has been 4.34 kilometers.Based on the fluid inclusion studies, the boiling has occurred during mineralization in Masjed Daghi and the major mineralization has occurred in the temperatures of 155˚C and 515˚C.

Table 1 .
Changes in characteristics of fluid inclusions with depth increase.The porphyrymineralization features increase with depth.