Hydrothermal evolution of the Sar-Cheshmeh porphyry Cu–Mo deposit, Iran: Evidence from fluid inclusions

Journal of Asian Earth Sciences 28 (2006) 409–422 www.elsevier.com/locate/jaes

Hydrothermal evolution of the Sar-Cheshmeh porphyry Cu–Mo deposit, Iran: Evidence from fluid inclusions Ardeshir Hezarkhani * Department of Mining, Metallurgical and Petroleum Engineering, Amirkabir University, Hafez Avenue No. 424, Tehran, Iran Received 8 June 2005; accepted 14 November 2005

Abstract The Sar-Cheshmeh porphyry Cu–Mo deposit is located in Southwestern Iran (w65 km southwest of Kerman City) and is associated with a composite Miocene stock, ranging in composition from diorite through granodiorite to quartz-monzonite. Field observations and petrographic studies demonstrate that the emplacement of the Sar-Cheshmeh stock took place in several pulses, each with associated hydrothermal activity. Molybdenum was concentrated at a very early stage in the evolution of the hydrothermal system and copper was concentrated later. Four main vein Groups have been identified: (I) quartzCmolybdeniteCanhydriteGK-feldspar with minor pyrite, chalcopyrite and bornite; (II) quartzC chalcopyriteCpyriteGmolybdeniteGcalcite; (III) quartzCpyriteCcalciteGchalcopyriteGanhydrite (gypsum)Gmolybdenite; (IV) quartzG calciteGgypsumGpyriteGdolomite. Early hydrothermal alteration produced a potassic assemblage (orthoclase-biotite) in the central part of the stock, propylitic alteration occurred in the peripheral parts of the stock, contemporaneously with potassic alteration, and phyllic alteration occurred later, overprinting earlier alteration. The early hydrothermal fluids are represented by high temperature (350–520 8C), high salinity (up to 61 wt% NaCl equivalent) liquid-rich fluid inclusions, and high temperature (340–570 8C), low-salinity, vapor-rich inclusions. These fluids are interpreted to represent an orthomagmatic fluid, which cooled episodically; the brines are interpreted to have caused potassic alteration and deposition of Group I and II quartz veins containing molybdenite and chalcopyrite. Propylitic alteration is attributed to a liquid-rich, lower temperature (220–310 8C), Carich, evolved meteoric fluid. Influx of meteoric water into the central part of the system and mixing with magmatic fluid produced albitization at depth and shallow phyllic alteration. This influx also caused the dissolution of early-formed copper sulphides and the remobilization of Cu into the sericitic zone, the main zone of the copper deposition in Sar-Cheshmeh, where it was redeposited in response to a decrease in temperature. q 2005 Elsevier Ltd. All rights reserved. Keywords: Porphyry; Sar-Cheshmeh; Potassic; Phyllic; Iran

1. Introduction There have been a few investigations of the porphyry copper style of mineralization in Iran and southern Asia. In Iran, all known porphyry copper mineralization occurs in the Cenozoic Sahand–Bazman orogenic belt (Fig. 1). This belt was formed by the subduction of the Arabian Plate beneath Central Iran during the Alpine orogeny (Bazin and Hu¨bner, 1969; Niazi and Asoudeh, 1978; Berberian and King, 1981; Pourhosseini, 1981) and hosts two major porphyry Cu deposits. The SarCheshmeh deposit is the only one being mined at present, and contains 450 million tones of sulfide ore, with an average grade of 1.13% Cu and w0.03% Mo (Waterman and Hamilton, 1975). The Sungun deposit in northwest Iran, which contains * Tel.: C98 21 64542968; fax: C98 21 6405846. E-mail address: [email protected].

1367-9120/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2005.11.003

O500 million tones of sulfide reserves grading 0.76% Cu and w0.01% Mo (Hezarkhani, 1997), is being developed currently. On the basis of the overall geological setting and alteration patterns, Waterman and Hamilton (1975) proposed that the Sar-Cheshmeh deposit is Cu porphyry. Shahabpour (1982) subsequently made a preliminary study of the igneous petrology and isotope geochemistry, and concluded that the overall characteristics of the deposit are very similar to those predicted by the generalized porphyry deposit model of Lowell and Guilbert (1970). However, these studies have not provided sufficient data to evaluate the evolution of the hydrothermal mineralizing system. The purpose of this paper is to illustrate the hydrothermal history of the Sar-Cheshmeh porphyry deposit and to identify the factors controlling CuGMo mineralization. In order to achieve this the author: (1) documents the alteration and vein mineral paragenesis by a combination of core logging and

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Southwestern Iran (Fig. 1). The stock is part of the Sahand– Bazman igneous and metallogenic belt, a deeply eroded Tertiary volcanic field, roughly 100 by 1700 km in extending from Turkey to Baluchistan in southern Iran, consisting mainly of rhyolite and andesite, with numerous felsic intrusions. The volcanics were laid down unconformably over folded and eroded Upper Cretaceous andesitic volcanic and sedimentary rocks (w500 m thick). Subduction and subsequent continental collision from the Paleocene to the Oligocene caused extensive alkaline and calc-alkaline volcanic and plutonic igneous activity (Etminan, 1978; Shahabpour, 1982; Berberian, 1983), including intrusion of a porphyritic calc-alkaline stock at Sar-Cheshmeh during the Miocene (Emami,, 1992). Bordering the belt to the southwest is a major zone of complexly folded, faulted, and metamorphosed Tertiary and Paleozoic sedimentary rocks which form the Zagros Mountains (Waterman and Hamilton, 1975). 3. Sar-Cheshmeh stock and peripheral intrusive rocks

Fig. 1. Geological map of Iran (modified from: Sto¨cklin, 1977; Shahabpour, 1994) showing major lithotectonic units as follows: Zagros Fold Belt: Paleozoic platform sediments overlain by miogeosynclinal Mid-Triassic to Miocene sediments, and syn-orogenic Pliocene–Pleistocene conglomerates; Sanandaj–Sirjan Zone: Mesozoic granodioritic intrusions and metamorphosed Mesozoic sediments; Sahand–Bazman Belt: Calc-alkaline volcanic and Quartz monzonite and quartz diorite intrusions of dominantly Miocene age, hosting Cu–Mo porphyry style mineralization; Central Iran: Paleozoic platform sediments disrupted by late Triassic tectonic activity, and including horsts of Precambrian crystalline basement and Cambrian to Triassic cover rocks; Lut Block: The Lut Block is considered to be an old stable platform (Sto¨cklin, 1977), covered by thick Mesozoic sediments and Eocene volcanics; Alborz and Kopeh Dagh zones: Eocene volcanic and volcanoclastic rocks in the Alborz segment and in the Kopeh-Dagh segment; Eastern Iran and Makran zones: Post-Cretaceous flysch-molasse sediments.

the microscopic examination of polished thin sections; (2) conducted a fluid inclusion study; (3) evaluated mineral stabilities and solubilities. This information is then used to determine the conditions under which the deposit formed and to reconstruct fluid evolution related to the concentration of economic levels of Cu mineralization. 2. Geological setting of the Sar-Cheshmeh deposit The Sar-Cheshmeh porphyry copper deposit is hosted by a diorite to granodiorite stock (Waterman and Hamilton, 1975), located 65 km southwest of Kerman City, Kerman Province,

The Sar-Cheshmeh Stock is a complex intrusive body, which outcrops over an area of about 1.1 by 2.2 km, shown topcenter of Fig. 2. The stock consists of three igneous phases: (1) diorite to granodiorite; (2) dacitic and related pyroclastics; and (3) andesite and related dykes, listed in order of emplacement (Hezarkhani, 2004a,b). Diorite to granodiorite is volumetrically most important and includes most of the central and northern part of the intrusive complex at the current erosional surface. Dacitic porphyry is volumetrically the next most important and hosts part of the mineralization. These two phases are cut by andesitic dykes, which in the northern and western parts of the Sar-Cheshmeh stock, are also mineralized locally. Petrographic studies have shown that mineralized dykes are mainly andesitic and are related to the intrusion of the diorite to granodiorite. The diorite to granodiorite and unmineralized andesitic dykes contain mafic xenoliths, whereas mafic xenoliths are rare in the mineralized dykes. The Sar-Cheshmeh diorite to granodiorite intrudes Eocene (w500 m thickness) and lower Tertiary volcanic and related sedimentary rocks (w1000 to w1600 m thickness). The latter consist of andesitic to dacitic tuff and agglomerates, with intercalated marly tuff. Quaternary trachytic to andesitic lavas locally surround the diorite/quartz diorite stock. The SarCheshmeh Stock is highly altered, and metasomatic effects are also evident in the country rocks. 4. Stock petrography Petrographic observations of polished thin sections indicate that the main stock porphyry contains w50% by volume of phenocrysts, consisting mainly of zoned plagioclase (An12–37), (w30 vol.%,), highly altered hornblende (w10 vol.%), quartz and biotite (w10 vol.%). Hornblende was the earliest major mineral to crystallize and forms euhedral to subhedral phenocrysts. Quartz phenocrysts crystallized next, and are ubiquitously rounded or embayed, which indicates isothermal decompression of a water vapor-undersaturated magma

A. Hezarkhani / Journal of Asian Earth Sciences 28 (2006) 409–422

411

Fig. 2. Detailed geological map of the Sar-Cheshmeh area showing the distribution of different igneous suites (after Waterman and Hamilton, 1975).

(Whitney, 1989). Subhedral plagioclase phenocrysts formed shortly after the quartz phenocrysts and biotite phenocrysts (subhedral to anhedral) formed later (Hezarkhani, 2004a,b). The diorite to granodiorite groundmass is fine-grained, and consists mainly of quartz, plagioclase and K-feldspar, with

lesser biotite and amphibole. Apatite, zircon, titanite, and rutile are present in minor to trace amounts (less than 1% all together). Dacitic and related pyroclastic dykes are pervasively altered, and contain abundant feldspar and amphibole

Fig. 3. Detailed alteration map of the Sar-Cheshmeh deposit (modified after Waterman and Hamilton, 1975). SCP, Sar-Cheshmeh Porphyry; LFP, Latite Feldspar Porphyry.

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A. Hezarkhani / Journal of Asian Earth Sciences 28 (2006) 409–422

phenocrysts in an aphanitic groundmass. A small proportion of primary biotite is also present. The pre-alteration modal mineralogy of these mineralized dykes is estimated to have been 25% plagioclase (An17–30), 21% orthoclase, 38% quartz, and 16% ferromagnesian (biotite and amphibole) and accessory minerals. Andesite and related dykes consist mainly of plagioclase, K-feldspar, biotite, quartz and highly altered amphibole. Plagioclase occurs later in the groundmass and as phenocrysts, and more than 37% of the total volume of the rock. K-feldspar composes up to 40 vol.% of the rock and occurs both as phenocrysts and in the groundmass. Amphibole occurs only as phenocrysts, and comprises less than 29% of the rock. Apatite, quartz, and magnetite occur as inclusions in the plagioclase and K-feldspar crystals 5. Alteration and mineralization Hydrothermal alteration and mineralization at Sar-Cheshmeh are centered on the stock and were broadly synchronous with its emplacement (Figs. 3–5). Early hydrothermal alteration was dominantly potassic and propylitic, and was followed later by phyllic, silicic and argillic alteration.

Petrographic observations and microprobe analyzes indicate the presence of two compositionally distinguishable types of biotite within this alteration zone: Primary biotite, which is Feenriched, brown in color, and generally euhedral; Hydrothermal biotite, which is mainly pale-brown to greenish-brown in color and very ragged (Shahabpour, 1982). The hydrothermal biotite occurs interstitial to feldspar and quartz and locally replacing hornblende and primary biotite phenocrysts (Khayrollahi, 2003). Electron microprobe data indicate that some grains of potassium feldspar are rimmed by albite (An4–12), suggesting a later transition alteration event (Shahabpour, 1982). Relict crystals of secondary biotite are observed almost everywhere in the stock, suggesting that potassic alteration was initially very extensive, but has been overprinted subsequently and obliterated by the later stages of alteration. Whole rock chemistry indicates that the principal mass changes accompanying potassic alteration were an appreciable addition of K, a small addition of Si and large depletions of calcium and magnesium. These reflect the replacement of plagioclase and amphibole by K-feldspar and biotite, respectively (Hezarkhani, 2004a,b; Khayrollahi, 2003). 5.2. Propylitic alteration

5.1. Potassic alteration Potassic alteration is represented by mineral assemblages, developed pervasively and as halos around veins in the central parts of the Sar-Cheshmeh stock (Figs. 3–5). Potassic alteration is characterized by K-feldspar, irregularly shaped crystals of Mg-enriched biotite and anhydrite (Shahabpour, 1982).

There is a relatively sharp boundary between the propylitic and potassic alteration zones in the deeper parts of the deposit, but at shallow levels this contact is obscured by later phyllic alteration. Propylitic alteration is pervasive and is represented mainly by chloritization of primary and secondary biotite and groundmass material in rocks peripheral to the central potassic

Fig. 4. Detailed Mo mineralization map of the Sar-Cheshmeh deposit (modified after Waterman and Hamilton, 1975).

A. Hezarkhani / Journal of Asian Earth Sciences 28 (2006) 409–422

413

Fig. 5. Detailed Cu mineralization map of the Sar-Cheshmeh deposit (modified after Waterman and Hamilton, 1975).

zone. Epidote replaced plagioclase, but this alteration is less pervasive and less intense than the chloritization. 5.3. Argillic alteration Feldspar is altered locally to clay, down to a depth of 250 m, and within 100 m of the erosion surface the entire rock has been altered to an assemblage of clay minerals, hematite and quartz (Khayrollahi, 2003). The altered rocks are soft and white. XRD analysis indicate that the dominant clay mineral is kaolinite and that it is accompanied by illite (Khayrollahi, 2003). The shallow alteration is interpreted to represent a supergene blanket over the deposit and alteration of feldspar to clay at depth may have the same origin. However, the possibility cannot be excluded that the latter represents an argillic stage of the hypogene alteration. 6. Mineralization Hypogene copper mineralization was introduced during phyllic alteration and to a lesser extent during potassic alteration. It occurs as disseminations and in veinlets. During potassic alteration, the copper was deposited as chalcopyrite and minor bornite; later hypogene copper was deposited mainly as chalcopyrite (Hezarkhani, 2004a,b; Khayrollahi, 2003). Hypogene molybdenite was concentrated mainly in the deeper part of the stock, and is associated exclusively with potassic alteration, where it is found in quartz veins

accompanied by K-feldspar, anhydrite, sericite and lesser chalcopyrite (Hezarkhani, 2004a,b). The concentration of sulphide mineralization increases outward from the central part of the stock. The ratio of pyrite to chalcopyrite increases from 2:1 in the outer parts of the potassic alteration zone to 10:1 toward the margins of the stock. At the exposed surface of the deposit the rocks are highly altered; the only mineral, which has survived supergene argillization is quartz. Most of the sulfide minerals have been leached, and copper has been concentrated in an underlying supergene zone by downward percolating ground water. 7. Vein classification On the basis of mineralogy and cross-cutting relationships, it is possible to distinguish at least four main groups of veins representing four episodes of vein formation (Fig. 6): Group I. quartzCmolybdeniteCanhydriteGK-feldspar with sporadic pyrite, chalcopyrite and bornite; Group II. quartzCchalcopyriteCpyriteGmolybdenite; Group III. quartzCpyriteCcalciteGanhydriteGchalcopyriteGgypsumGmolybdenite; Group IV. quartzGcalciteGgypsumGpyrite. 7.1. Group I veins Group I veins are discontinuous, vary in thickness between 0.1 and 12 mm, and were formed during the early fracturing of the porphyry stock (Khayrollahi, 2003). Molybdenite is

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Group II and III veins appear to have a common origin, with Group III veins probably having formed by re-opening of Group II veins. As will be discussed in the section on fluid inclusions, primary saline fluid inclusions similar to those in Group II veins, are present in the centers of zoned quartz crystals in Group III veins (Hezarkhani, 2004a,b). The occurrence of chalcopyrite and other copper minerals in Group III veins suggests that they could have been leached by later fluid circulating in these veins.

Group I Qz + Ksp + Mo + Anh ± Py ± Cp Group II Qz + Cp ± Py ± Brn ± Mo Group III Qz + Py + Cal + Cp ± Anh (Gyp)

Volume % Occupation of Veins (Average)

Group IV Qz + Py ± Cal ± Gyp

15 Argillic Alteration

Phyllic Alteration

Potassic Alteration

"Fresh" Rocks

10

5

0 ~150

~350

~550

?

7.4. Group IV veins

Approx. Depth (m) Fig. 6. Diagram showing the volume proportions of the different vein Groups in each of the alteration zones.

the most important sulfide mineral, and occurs mainly along vein margins; K-feldspar, anhydrite, chalcopyrite, bornite and pyrite occur in the central part of the vein, and less commonly at the margins. Quartz makes up from 70 to 95% of the volume of the veins. The veins are surrounded by potassic, and less commonly phyllic and propylitic alteration haloes (Hezarkhani, 2004a,b). 7.2. Group II veins Group II veins generally cross-cut, and in places, off-set Group I veins. The most important characteristics of Group II veins are well-developed sericitic alteration haloes and the lack of K-feldspar. The volume ratio of chalcopyrite to pyrite is 4:1. Molybdenite contents vary from traces, to less than 17 vol.% of the vein. The alteration haloes are most obvious in the potassic alteration zone, where hydrothermal biotite in the halo was destroyed (Hezarkhani, 2004a,b; Khayrollahi, 2003). The sericitic alteration haloes have thicknesses varying between 3 and 19 mm. Vein quartz is relatively coarse-grained and tends to be oriented normal to the walls of the vein. Sulfide minerals are located mainly in a narrow discontinuous layer in the vein centers, but in some cases the sulphides are disseminated through the quartz. Group II veins occur in all alteration zones, but are concentrated mainly in the potassic alteration zone. Their thickness varies from 9 to 50 mm, and they are generally more continuous than Group I veins (Hezarkhani, 2004a,b). 7.3. Group III veins Group III veins are most abundant in the phyllic alteration zone, cross-cut both Group I and II veins and in some cases offset the earlier-formed veins. They are relatively continuous, layered, and vary in thickness from 9 to 42 mm. Quartz occurs mainly near the vein margins with anhydrite, calcite and sulfide minerals intergrown in the vein centers (Hezarkhani, 2004a). Quartz is relatively coarse grained, and locally shows optical zoning (overgrowths). Chalcopyrite is the only copper mineral, which occurs mainly as small blebs and inclusions in pyrite (Khayrollahi, 2003).

Group IV veins crosscut all the other vein groups and represent the youngest vein-forming event in the SarCheshmeh stock. They are very thick (up to 200 mm), and filled by quartzGcalciteGgypsum. Group IV veins are found mainly in the propylitic zone, but also occur locally in the phyllic and potassic alteration zones (Hezarkhani, 2004a,b). The only sulfide mineral is pyrite, which occupies w17 vol.% of these veins. Group IV veins are usually surrounded by zones of silicification up to 120 mm wide.

8. Fluid inclusion studies Fluid inclusions are abundant in quartz of all vein types, and range in diameter from 1 up to 25 mm. They are classified into three main types based on the number, nature and proportion of phases at room temperature: Type 1 (LV) inclusions consist of liquidCvaporGsolid phases (e.g. cubes of halite, !1 mm in length), with the liquid phase volumetrically dominant (O70%), and are common in all mineralized quartz veins. These are abundant in Group II and III veins. Vapor bubbles are variable in size, but constitute less than 27% of inclusion volumes. The inclusions homogenize to liquid. The distribution and volume of solid phases are irregular, (!2 to O12%), suggesting that they represent trapped solids rather than daughter minerals. Type 2 (VL) inclusions contain vapor (O65% of the inclusion volume)CliquidGsolid (a single solid phase which is either halite or an unidentified mineral phases). These inclusions mainly homogenize to vapor, rarely liquid, or by critical behavior. Type 3 (LVHS) inclusions are multiphase and consist of liquidCvaporChaliteCother solids. Based on the number and type of the solids, they are classified into three subtypes. Subtype S1 (haliteCchalcopyriteGanhydrite). Halite, anhydrite and chalcopyrite have consistent phase ratios and are interpreted to be daughter minerals. Vapor bubbles occupy !30% of the inclusion by volume. Subtype S2 inclusions contain sylvite in addition to the phases in S1 inclusions. The solid phases occupy w60% of inclusion volumes and the vapor bubbles w22%. Subtype S3 inclusions contain halite and hematite, but not chalcopyrite and sylvite. The volume of the solid phases is typically !40% of the inclusions and bubble volumes range between 20 and 60%.

A. Hezarkhani / Journal of Asian Earth Sciences 28 (2006) 409–422

8.1. Solid phases in fluid inclusions Halite and sylvite in the inclusions were identified by their cubic and sub-cubic shapes and optical isotropy. Sylvite was distinguished from halite by its rounded edges and lower relief; it also dissolves at lower temperatures. Halite crystals are generally larger and more common than those of sylvite, and have a well-defined habit. Chalcopyrite was identified on the basis of its optical characteristics (opacity and triangular cross section). Anhydrite forms transparent anisotropic prisms. Hematite was easily identified by its red color, hexagonal shape, extremely high index of refraction and high birefringence. 9. Distribution and petrography of fluid inclusion types The Sar-Cheshmeh intrusions like other types of Iranian porphyry systems (e.g. Reagan, Bam-Kerman; Sungun, AharAzarbaijan) have undergone repeated episodes of fracturing and healing, with multiple generations of fluid inclusions representing the evolution of hydrothermal fluids and the corresponding alteration and mineralization. Type 1 inclusions are found in all vein Groups, but occur in variable proportions. They are most abundant in the Group II and III veins, but rare in Group I veins (Fig. 10). Most LV inclusions are distributed along healed fractures, and are secondary. Type 2 inclusions are found in Group I, II and III quartz veins. Some of these inclusions occur in growth zones in Group I and II quartz veins, where they are accompanied by LVHS fluid inclusions, indicating that at least some of them are primary. VL inclusions are generally elongate and have rounded ends, but some have negative crystal shapes. Some of the VL inclusions have variable liquid–vapor ratios, and seem to be formed from the necking-down of LVHS inclusions. LVHS inclusions up to 15 mm in diameter are found in all veins, from the deepest, potassically altered part of the stock (Group I and II veins) through to shallow level veins. At shallow levels (Group III veins), most of the LVHS inclusions are of subtype S3, but at deeper levels (mainly Group I and II veins), subtypes S1 and S2 predominate. Up to seven solid phases have been observed in a single LVHS inclusion. The coexistence of LVHS inclusions and vapor-rich inclusions (Type 2) with consistent phase ratios in the growth zones of quartz grains from potassic and phyllic alteration zones suggests a primary origin, and co-existence of two immiscible aqueous fluids. 9.1. Fluid inclusion population I LVHS1, LVHS2 and VL fluid inclusions occur in Group I and II quartz veins from the mainly potassic and lesser lowerphyllic altered zones (350–500 m below the present surface), but are rare at shallow levels (in the upper-phyllic alteration zone). In Group I veins, LVHS1 and LVHS2 fluid inclusions commonly form isolated clusters in the cores of quartz grains. VL inclusions commonly occur along microfractures, but they

415

are also present in clusters with LVHS1 fluid inclusions. LVHS1, LVHS2 and VL fluid inclusions that have been identified in quartz from Group II and III veins in phyllic alteration zones at shallow levels may be relics of earlier potassic alteration. These three fluid inclusion types are interpreted to represent the earliest episode of fluid entrapment. 9.2. Fluid inclusion population II At shallower levels, mainly in the phyllic alteration zone, there is a close spatial association in the deposit of solid-rich LVHS3 and VL fluid inclusions. They are found together in growth zones, but occur mainly along healed fractures. This population of inclusions is spatially associated with LV inclusions, especially in Group III veins, although clearly the latter must have been trapped separately from the LVS3 inclusions, if the halite is a daughter mineral. 9.3. Fluid inclusion population III LV fluid inclusions occur in all vein Groups, but are most common in Group II and III veins from phyllic and propylitic alteration zones. They are clearly located along fracture planes, and are secondary in origin. LV inclusions seem to represent a later stage fluid that circulated in the intrusion. The average homogenization temperature of this type of inclusion is low (see below). 10. Fluid inclusion microthermometry Microthermometric studies were carried out on 20 samples of quartz from Group I, II and III veins. Temperatures of phase changes in fluid inclusions were measured with a Fluid Inc. USGS-type gas-flow stage which operates by passing preheated or precooled N2 gas around the sample (Werre et al., 1979). Stage calibration was performed using synthetic fluid inclusions. Accuracy at standard reference temperatures was G0.2 8C at K56.6 8C (triple point of CO2), G0.1 8C at 0 8C (melting point of ice), G2 8C at 374.1 8C (critical homogenization of H2O), and G9 8C at 573 8C (alpha to beta quartz transition). The heating rate was approximately 1 8C/ min near the temperatures of phase transitions. 10.1. Low temperature phase changes The temperatures of initial (Te) and final melting of ice (Tm ice) were measured on types LV, VL and LVHS fluid inclusions. In the case of type VL inclusions, Te was difficult to determine, because of the high vapor/liquid ratios. Clathrate formation was not observed in any of the inclusions, which rules out the presence of significant CO2. The crushing of quartz under anhydrous glycerine confirmed this conclusion; the vapor bubble collapsed during crushing in all but a few inclusions, and in these the bubble size was unchanged or increased slightly, indicating that the maximum pressure of incondensable gases was w1 bar.

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14

24 20

12

16

8

12

4

8 4

0 -64

-56

-48

-40

-32

-24

-16

-8

-4

0 -32

-64

-56

-48

-40

-32

-24

-16

-8

-28

-24

-20

-16

-12

-8

-4

12

28

8

24 20

4

16

0

12

-4

8 4

16 12

0 -32

-28

-24

-20

-16

-12

-8

-4

8

24

4

20 16

0 -64

-56

-48

-40

-32

-24

-16

-8

12 8 4

-4

Fig. 7. Histograms of eutectic temperatures for LV, VL and LVHS fluid inclusions from mineralized quartz veins.

The temperature of first ice melting (Te) of most LV fluid inclusions was between K20 and K17 8C (Fig. 7), suggesting that NaClGKCl are the principal salts in solution (like other known porphyry systems in Iran). The Tm ice values for these inclusions range from K1 to K12 8C (Fig. 8), corresponding to salinities of 1.7–17 wt% NaCl equivalent, respectively (Sterner et al., 1988). A small proportion of LV inclusions in quartz phenocrysts in shallow dykes have Te between K23 and K40 8C, suggesting the presence of appreciable CaCl2, FeCl2, or MgCl2, in addition to NaCl and KCl. The Tm ice values for LV fluid inclusions in Group I quartz veins range from K2.1 to K9.2 8C, corresponding to a salinity of 3.1 to 10.2 wt% NaCl equivalent (Sterner et al., 1988); in Group II quartz veins they range from K1.3 to K12.5 8C, corresponding to a salinity from 2.3 to 15.5 wt% NaCl equivalent; and in Group III quartz veins they range from K2.4 to K14.3 8C corresponding to a salinity from 3.8 to 17.2 wt% NaCl equivalent (Table 1). The salinity data discussed above does not take account of a small number of LV inclusions which contain cubes of halite that are interpreted to have been entrapped with the fluid. The Te value of VL fluid inclusions ranges from K49 to K20 8C with a mode of wK28 8C suggesting that Na and K are the dominant cations in the solution, but that there are significant concentrations of divalent cations (Sterner et al., 1988; Nast and Williams-Jones, 1991). The Tm ice value for

0 -32

-28

-24

-20

-16

-12

-8

-4

Fig. 8. Histograms of final ice melting and hydrohalite dissolution temperatures for fluid inclusions from mineralized quartz veins.

these inclusions varies from K0.4 to K16.1 8C, which corresponds to a salinity between 0.9 and 19.3 wt% NaCl equivalent. The low Te (K33 to K47 8C) for some of the VL inclusions in Group I and II veins could indicate that these inclusions are the product of necking down of LVHS inclusions or heterogeneous entrapment (see below). Owing to the small volume of liquid in LVHS fluid inclusions, it is difficult to measure Te and the melting temperature of hydrohalite (Tm HH). The eutectic temperatures that could be measured in Group I and II veins (LVHS1 and LVHS2) range from K33 to K65.0 8C, suggesting important concentrations of Fe, Mg, Ca, and/or other components in addition to Na and K in this type of inclusion (Sterner et al., 1988). Eutectic temperatures for the CaCl2–H2O, NaCl– CaCl2–H2O, and FeCl3–H2O systems are K45.1, K53 and K55 8C, respectively (Linke, 1965), and could explain the low first ice melting temperatures observed for some of the LVHS inclusions. Tm HH values vary between K3 and K38 8C in LVHS inclusions. LVHS fluid inclusions (subtype LVHS3) in Group III vein quartz yield distinctly different microthermometric data from

Table 1 Sar-Cheshmeh fluid inclusion microthemometric data Samplea

Stageb

Originc

Typed

Te (8C)

Tm ice (8C)

Range I

p

VL

H-Z-5

I

s

LV

H-Z-6

I

p

LVHS2

H-Z-6

I

ps

LVHS1

H-Z-3

I

p

LVHS2

H-Z-4

I

p

LVHS3

H-Z-1

I

s

LV

H-Z-2

I

p

LVHS1

H-Z-4

I

ps

VL

H-Z-5 H-Z-5

I I

s s

LVHS2 VL

H-Z-7 H-Z-7

II II

s s

LV VL

H-Z-7

II

s

LVHS3

H-Z-8

II

p

VL

H-Z-9

II

p

LVHS1

H-Z-7

II

p

LVHS1

H-Z-7

II

p

LVHS2

H-Z-7

II

p

LVHS3

H-Z-7

II

ps

LV

H-Z-7

II

ps

LVHS3

H-Z-11

II

ps

LV

H-Z-11

II

ps

VL

H-Z-11

II

s

LV

H-Z-12

II

p

LVHS2

K14.7 K23.3 K23.0 K40.1 K41.0 K62.4 K41.1 K43.3 K45.1 K53.0 K40.0 K61.0 K17.0 K20.0 K33.0 K65.0 K20.0 K49.0 K49.8 K15.9 K49.1 K34.1 K14.1 K49.4 K45.0 K31.7 K21.0 K22.5 K44.3 K40.0 K39.3 K65.0 K31.4 K45.0 K58.0 K48.0 K18.0 K23.0 K54.2

to (5) to (6) to (10) to (6) to (7) to (19) to (7) to (11) to (12) (1) to (13) (3) to (11) to (10) to (5) to (9) to (12) to (9) to (2) to (4) (7)

K22.1 K26.2 K20.7 K23.1 K16.5 K19.0 K57.1 K48.9

to (4) to (3) to (4) to (8)

Range

K21.7

K4.0 to K13.2 (5) K1.9 to K13.1 (6) K5.7 to K26.0 (10) K7.9 to 11.3 (6) K11.1 to K24. 2 (7) K3.2 to K31.0 (19) K1.0 to K12.0 (7) K6.1 to 23.9 (11) K0.4 to K16.1 (12) K8.4 (1) K1.9 to K6.1 (13) K6.19 (3) K2.0 to K5.9 (11) K16.8 (10)

K34.6 K54.0 K41.8 K55.0 K51.3 K22.1 K50.1 K28.0

K28.1

K29.2

K21.9 K47.1 K50.1 K34.8 K52.5 K21.5

K23.2 K22.4 K17.3 K55.3

K0.3 to K13.2 (5) K12.1 to K28. 0 (9) K4.9 to K22.3 (12) K3.1 to K7.3 (9) K12.0 to K118.0 (2) K1.0 to K7.7 (4) K11.2 (7) K4.2 to K8.4 (4) K0.9 to 8.2 (3) K1.6 to K3.1 (4) K9.1 to K15.2 (8)

Tm HH (8C) Avg.

Range

Tm Halite (8C) Avg.

Range

Tm Sylvite (8C) Avg.

Range

Th L-V (8C) Avg.

K6.9 K4.1 K13 K8.4 K16.0

2.5 to 7.0 (2)

6.3

K13.1

13.3 to 5.1 (11)

6.9

442.0 to 245.0 (10) 402.0 to 301.3 (6) 449.0 to 311.0 (7) 281.0 to 443.0 (19)

342.1

93.1 to 60.5 (10)

79.9

353.0 372.7 372.4

60.5 to 90.1 (5) 78.4 to 72.0 (3)

72.3 76

K3.3 K13

3.0 to 16.3 (5)

8.1

443.0 to 322.0 (11)

381.1

K7.2 280.0 (1)

61.0 (1)

K3.5

K3.3 265.0 (1) K5.7 K18.4 K11 K5.7 K13.1

K3.3 to K12. 9 (9)

421.0 to 291.0 (9) 441.0 to 373.0 (12) 359 to 381.0 (9) 434.1 to 300.0 (2)

360.0 414.1 371.0 349.0

K3.1 321.4 (7) K7.1 K4.3 K2.1 K11.1

488.3 to 441.7 (8)

463.2

129.0 to 95.4 (8)

99.7

Salinity

Range

Avg.

Range

Avg.

576.0 to 420.0 (5) 433.9 to 249.0 (6) 600.0 to 241.0 (10) 291.0 to 520.0 (6) 361.0 to 500.0 (7) 441.0 to 279.0 (19) 287.0 to 249.0 (5) 381.0 to 243.2 (11) 622.0 to 401.0 (12) 373.0 (1) 400.0 to 411.2 (9) 277.0 (3) 400.0 to 423.1 (11) 221.0 to 400.0 (10) 434.0 to 372.0 (5) 272.0 to 480.0 (9) 400.0 to 269.0 (12) 381.0 to 293.0 (9) 311 to 291.2 (2) 291.2 to 253.0 (4) 281.0 to 294.0 (7) 257.0 to 350.0 (4) 583.0 to 600.0 (3) 320.0 to 316.6 (4) 492.0 to 430.0 (8)

500.0

13.1 to 9.1 (5)

12.7

317.1

4.9 to 17.1 (6)

8.2

423.0

51.9 to 39.2 (10) 45.71 to 38.0 (6) 39.0 to 55.1 (7)

42.1

53.6 to 41.0 (19) 17.0 to 1.7 (7)

43.7

45.5

496.1

52.0 to 42.7 (11) 9.0 to 19.3 (12)

12.8

403.1

33.6 (1) 9.7 to 2.1 (13)

4.8

410.1

11.9 10.0 to 1.9 (11)

400.3

36.6 to 40.8 (10) 13.1 to 1.2 (5)

6.0

339.2

41.5 to 31.7 (9)

44.8

311.1

48.7

341.0

50.3 to 41.7 (12) 42.1 to 45.0 (9)

44.1

141.5

51.5 to 31.0 (2)

44.1

251.5

3.93 to 2.70 (4)

350.7 407.6 334.9 273.6 303.1

42.6 45.1

7.8

A. Hezarkhani / Journal of Asian Earth Sciences 28 (2006) 409–422

H-Z-1

Avg.

35.2 to 33.1 (7) 282.0

9.0

590.5

10.0 to 0.7 (3)

5.6

311.2

5.2 to 1.9 (4)

4.3

461.8

56.2 to 51.3 (8)

54.6

(continued on next page) 417

418

Table 1 (continued) Stageb

Originc

Typed

H-Z-10

II

p

LVHS1

H-Z-9

II

p

LVHS2

H-Z-9

II

s

VL

H-Z-10

II

p

LV

H-Z-10

II

p

LVHS2

H-Z-8 H-Z-15

II III

s ps

LVHS3 LV

H-Z-16

III

p

LVHS3

H-Z-17

III

ps

LVHS3

H-Z-18

III

s

LVHS3

H-Z-19 H-Z-13 H-Z-14

III III III

ps ps p

LV LVHS3 VL

H-Z-14

III

p

LV

H-Z-15

III

p

VL

H-Z-19

III

s

VL

Te (8C)

Tm ice (8C)

Tm HH (8C)

Range

Avg.

Range

Avg.

Range

K41.3 to K59.9 (5) K37.0 to K58.3 (9) K17.0 to K45.3 (21) K19. 7 to K37.1 (9) K43.1 to K56.2 (5) K51.9 (1) K29.1 to K32.7 (6) K36.4 to K59.0 (9) K31.1 to K47.2 (7) K30.8 to K52.0 (5) K44.0 (1) K55.0 (2) K9.2 to K33.1 (6) K21.4 to K30.5 (12) K29.8 to K33.1 (9) K53.2 (1)

K49.7

K11.0 to K30. 0 (5) K5.2 to K18.7 (9) K1.7 to K14.2 (21) K1.6 to K7.3 (9) K6.7 to K21.0 (5) K36.4 (1) K2.9 to K8.2 (6) K3.1 to K11.3 (9) K5.1 to K14.1 (7) K5.5 to K10.1 (5) K9.3 (1) K19.9 (2) K9.3 to K17.9 (6) K2.6 to K10.7 (12) K1.5 to K12.1 (9) K7.1 (1)

K17.0

10.7 (1)

K54.2 K26.4 K22.4 K47.1

K25.0 K48.1 K33.9 K50.0

K29.5 K25.1 K25.9

Tm Halite (8C) Avg.

K15.3

Tm Sylvite (8C)

Range

Avg.

Range

227.0 to 400.0 (5) 469.0 to 271.0 (9)

333.3

81.0

344.2

100.0 to 52.3 (5)

K7.9 K3.5 451.0 to 301.0 (3) 302.0 (1)

K15.3 9.2 (1)

363.0

K5.5 K7.1 K9.1 K6.7

K18.9 to K27.2 (7)

K21.9

510.0 to 413.0 (9) 471.0 to 229.2 (7) 399.0 to 283.0 (5) 255.6 (1) 373.1 (2)

K16.0 K7.6 K8.1 259.0 (1)

441.9 363.0 361.3

92.0

Th L-V (8C) Avg.

76.1

Salinity

Range

Avg.

Range

Avg.

243.0 to 355.0 (5) 431.0 to 320.0 (9) 340.0 to 510.0 (21) 283.0 to 391.0 (9) 402.0 to 275.7 (5) 298.0 (1) 267.0 to 342.0 (6) 372.0 to 343.0 (9) 310.0 to 232.0 (7) 319.0 to 322.0 (5) 291.0 (1) 200.0 (2) 381.0 to 542.0 (6) 362.0 to 255.3 (12) 600.0 to 401.0 (9) 299.2 (1)

323.5

29.8 to 48.3 (5)

40.6

400.1

54.1 to 32.7 (9)

41.2

411.4

1.9 to 14.9 (21)

8.9

315.5

6.2 to 7.3 (9)

4.9

327.6

50.8 to 34.1 (5)

282.0

34.8 (1) 9.5 to 3.5 (6)

346.5

61.1 to 42.5 (9)

55.8

271.0

43.3 to 32.0 (7)

44.9

312.2

44.3 to 41.0 (5)

42.7

374.3

11.5 41.3 21.2 to 9.8 (6)

13.6

285.3

14.3 to 3.2 (12)

9.2

453.6

14.1 to 2.1 (9)

10.3

Number of inclusions measured is given in parenthesis. Te, eutectic temperature; Tm, ice melting temperature; Tm HH, ice melting temperature for hydrohylite; Th, homogenization temperature; Avg, average. a Numbers before dash identify drill holes and those after the dash indicate the depth. b Stage of mineralized quartz veins. c Fluid inclusion origin. P, primary; S, secondary; Ps, pseudosecondary. d Types of fluid inclusion.

11.8

45.0

7.1

A. Hezarkhani / Journal of Asian Earth Sciences 28 (2006) 409–422

Samplea

A. Hezarkhani / Journal of Asian Earth Sciences 28 (2006) 409–422

those of LVHS1 and LVHS2 inclusions in Group I and II veins. The eutectic temperatures vary from K31.4 to K45 8C and the hydrohalite melting temperature varies between K3.3 and K12.9 8C.

419

LVtype VLtype LVHS1 type LVHS2 type LVHS3 type

14 12

10.2. High temperature phase changes

Group I Veins

24 20

8 6 4 2 0 0

10

20

30

40

50

60

12 Group II Veins

10 Frequency

LV fluid inclusions homogenize to liquid (Th LCV/L) at temperatures between 257 and 350 8C, with a well defined mode at Th L of w282 8C for Groups I and II, and 320 8C for Group III mineralized quartz veins (Fig. 9). Almost all VL inclusions homogenize to vapor (Th VCL/V) between 340 and 510 8C. VL inclusions from Group III veins homogenize at temperatures between 381 and 542 8C, but some of the VL inclusions from Group II veins exhibit no changes until the temperature is within w32 8C of the homogenization tempera-

Frequency

10

8 6 4 2

16

0 0

12

10

20

30

40

50

60

12

8

Group III Veins

10

0 180

240

300

360

420

480 540

24

Frequency

4

8 6 4 2

20 0 0

16

10

20

30

40

50

60

Salinity- wt % NaCl Equivalent 12

Fig. 10. Histograms of salinities (wt% NaCl equivalent) from microthermometric data for LV, VL and LVHS fluid inclusions, in mineralized quartz veins.

8 4 0 180

240

300

360

420

480

540

180

240

300

360

420

480

540

24 20 16 12 8 4 0

Fig. 9. Histograms of homogenization temperatures for LV, VL and LVHS fluid inclusions from mineralized quartz veins.

ture; the vapor then rapidly expands to fill the inclusion, indicating a fluid near-critical density (cf. Cloke and Kesler, 1979; Roedder, 1984). The liquid and vapor phases in LVHS1 and LVHS2 inclusions from Group I veins homogenize to liquid at temperatures between w291 and w520 8C (Fig. 9) and between w272 and w480 8C in Group II veins. The liquid– vapor homogenization temperature for LVHS3 inclusions is from w210 to w411 8C in Group I and II veins and w221 to w400 8C in Group III veins (Fig. 9). The first mineral to dissolve in LVHS2 inclusions is sylvite, at temperatures between 61 and 100 8C (Group I and II veins). Salinities based on the halite dissolution temperature range from 39 to 61 wt% NaCl equivalent (Sterner et al., 1988) (Fig. 10). The halite dissolution temperatures for LVHS3 inclusions are 229– 471 8C in Group I and II quartz veins. The halite dissolution temperatures (Tm Halite) in LVHS3 inclusions in Group III quartz veins are 200–350 8C which correspond to salinities of

420

A. Hezarkhani / Journal of Asian Earth Sciences 28 (2006) 409–422

32–44 wt% NaCl equivalent with an average of 35 wt% NaCl equivalent (Table 1). Most LVHS1 inclusions (Group I and II veins) and LVHS3 inclusions in Group I and II veins homogenized by vapor disappearance. By contrast LVHS2 inclusions (Group I and II veins) homogenized mainly by halite dissolution. LVHS3 inclusions in Group III veins homogenized by other vapor disappearance or by halite dissolution. Anhydrite and chalcopyrite did not dissolve on heating to temperatures in excess of 600 8C. 10.3. Decrepitate compositions Residues from decrepitated fluid inclusions were analyzed using the procedures of Haynes et al. (1988). Three cleaned, doubly polished thin sections were heated rapidly to a temperature of 450 8C, which was sufficient to cause most inclusions to decrepitate and low enough to avoid significant loss of volatile components. The sections were analyzed using a JEOL JSM-840A scanning electron microscope equipped with a Tracor Northern energy dispersive X-ray spectrometer in raster mode. Analyzes in which the sum of cation charges differed by !15% from the sum of anion charges were considered reliable and are reported in Table 2. The following elements were present in appreciable concentrations in the residues: Na, Ca, K, Fe, Mg, Cl and S. Only Cl, however, was consistent in its concentration among the various residues analyzed. Other elements (e.g. Na) varied by at least a factor of two, and in some cases (e.g. Ca), ranged from 0 to O19 wt%. Copper is present only in residues from LVHS2 inclusions. In general, NaC is the dominant cation in residues from all three solid-bearing inclusion types. However, in LVHS3 decrepitates the atomic proportion of Ca2C approaches, and in some cases exceeds that of NaC. Next to

NaC, Ca2C is the most important cation in LVHS1 inclusions and has high but variable concentrations in LVHS2 inclusions. The concentration of KC, as expected, is highest in LVHS2 inclusions and among the other cations is exceeded only by that of NaC. In these inclusions the K/Na ratio ranges from 0.06 to 0.59 and has a mean value of 0.37. Element molalities of the above were calculated, with the aid of microthermometrically estimated salinities, and are presented in the Table 2. Of particular interest is the unusually high molality of S, which varied from 0.35 to 0.44 in LVHS1, 0.32 to 0.34 in LVHS2 and 0.62 to 1.35 in LVHS3 inclusions. However, even inclusions with little or no Ca contain up to 0.7 m S. The molality of Cu varied from 0.04 to 0.07, and compares favorably with estimates of 0.03–0.06 m obtained by relating the volume of the daughter mineral to the volume of fluid in some LVHS2 inclusions. 11. Alteration and mineralization The presence of molybdenite and anhydrite in Group I veins, chalcopyrite and anhydrite in Group II veins and chalcopyrite and anhydrite in LVHS1 and LVHS2 inclusions from vein Groups I and II suggests that Fluid I was responsible for the transport and eventual deposition of Mo, Cu, Fe and S. Molybdenite formed at the margins of the Group I veins, where its deposition was probably controlled by temperature decreasing from w510 to w460 8C (Fig. 11, Group I). If Mo was transported as the complex KMoO04 , it is also possible that deposition occurred due to destabilization of this complex as a result of the transfer of KC to the surrounding potassic alteration haloes (Nast and Williams-Jones, 1991). The cooling (and KC transfer) stabilized K-feldspar at the expense of plagioclase, and biotite at the expense of hornblende; the K/Na ratio was approximately 0.2. The rarity of chalcopyrite in

Table 2 Composition of decrepitate residues from different types of fluid Inclusions No.

Types

Ca wt %

Na wt %

K wt %

Fe wt %

Mg wt %

Al wt %

Cl wt %

S wt %

Mn wt %

Cu wt %

SZC

SZK

SZC– SZK

K/Na Ration

1 2 3 4 5 6 7 8 9

LVHS1 LVHS1 LVHS1 LVHS2 LVHS2 LVHS2 LVHS3 LVHS3 LVHS3

0.61 9.21 7.97 3.01 2.32 1.83 17.99 19.11 7.54

11.03 22.01 21.56 17.23 23.43 24.12 12.14 10.81 17.01

1.32 1.42 2.02 10.11 6.34 5.34 1.91 1.72 1.37

19.92 1.97 1.12 2.98 3.77 2.33 2.89 2.67 3.14

0.00 1.85 1.88 1.96 1.34 1.59 1.99 1.46 1.81

0.95 1.90 1.86 0.00 0.34 0.58 1.16 0.23 3.12

60.11 65.00 61.51 59.51 63.68 60.37 61.21 60.34 58.02

1.11 1.31 1.41 1.09 2.32 1.03 4.12 4.32 1.98

1.86 0.30 0.27 0.03 1.00 0.00 0.01 0.00 0.00

0.00 0.00 0.00 0.00 0.00 0.00 0.03 0.00 0.00

17.70 19.17 18.19 17.51 19.11 17.75 18.89 17.85 16.85

K17.73 K19.20 K18.22 K17.55 K19.11 K17.78 K18.92 K18.73 K17.38

K0.03 K0.03 K0.03 K0.04 K0.00 K0.03 K0.03 K0.87 K0.52

0.12 0.06 0.09 0.59 0.27 0.22 0.16 0.16 0.08

No.

Types

Mol. Ca

Mol. Na

Mol. K

Mol. Fe

Mol. Mg

Mol. Al

Mol. Cl

Mol. S

Mol. Mn

Mol. Cu

1 2 3 4 5 6 7 8 9

LVHS1 LVHS1 LVHS1 LVHS2 LVHS2 LVHS2 LVHS3 LVHS3 LVHS3

0.16 2.39 2.07 0.76 0.58 0.46 4.51 4.79 1.89

4.80 9.58 9.38 7.50 10.19 10.49 5.28 4.70 7.40

0.33 0.36 0.51 2.58 1.62 1.36 0.49 0.44 0.35

3.56 0.35 0.20 0.53 0.67 0.41 0.51 0.47 0.56

0.00 0.76 0.77 0.81 0.55 0.65 0.82 0.60 0.74

0.37 0.74 0.72 0.00 0.13 0.22 0.43 0.09 1.17

17.25 18.66 17.65 16.79 17.96 17.03 17.27 17.02 16.37

0.35 0.41 0.44 0.34 0.72 0.32 1.29 1.35 0.62

0.34 0.05 0.05 0.01 0.18 0.00 0.00 0.00 0.00

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

SZC, Sum of cation charges; SZK, Sum of anion charges.

A. Hezarkhani / Journal of Asian Earth Sciences 28 (2006) 409–422 700

421

700

600

600 750

750

600 500 400

500

600 500 400

500

300

400

300

400

200

200

100

300

100

300

50

200

50

200 Group I Veins.

Group II Veins.

100

10

0

30

20

40

50

60

70

100 0

10

30

20

40

50

60

70

700 700 Vapour pressure curves

TEMPERATURE (˚C )

Critical curve

600

LVHS1 Type

Vapour

LVHS2 Type

750

Liquid 300

400

200

LV

Type

VL

Type

600 500 400

500

300

400

100

300

750

LVHS3 Type

600 500

500

600

200

NaCl + Liquid

50

100

300

200

50

NaCl saturation curve

100

0

10

20

30

40

50

60

70

200 Group III Veins.

wt % NaCl equivalent 100 0

10

20

30

40

50

60

70

Fig. 11. Liquid–vapour homogenization temperature vs. salinity plotted on a section from the NaCl–H2O system (halite saturation and critical curves from Chou, 1987).

Group I veins and its abundance in Group II veins indicates that physico-chemical conditions became appropriate for bulk Cu deposition only during the formation of Group II veins, i.e. after some evolution of the hydrothermal system. The occurrence of anhydrite in the hypogene mineral assemblage can be explained by the hydrolysis of SO2 upon cooling. The breakdown of SO2, which is believed to occur around 400 8C (Burnham and Ohmoto, 1980; Burnham, 1981), is a possible source for both sulfate (to form anhydrite) and sulfide (to form molybdenite, pyrite, and chalcopyrite). Fluid II of mainly mixed meteoric and magmatic origin circulated later in the central part of the stock, at temperatures up to 440 8C (Fig. 11, Group II). Late fractures, or reopened veins, provided the pathways for this fluid to circulate in the system. It is proposed that the low K/Na ratio (!0.2) and relatively high temperature of this fluid caused destabilization of the previously formed K-feldspar in the potassic alteration zone, and its replacement by albite. The fluid also dissolved earlier formed copper sulfide minerals (higher fo2) and remobilized Cu which was transported to the upper levels of the intrusion. It caused extensive sericitization and silicification, and the reprecipitation of the Cu as chalcopyrite, all in response to the resultant cooling. During potassic alteration and

main stage Cu–Mo mineralization (360 up to 510 8C), the peripheral part of the stock was altered propylitically at lower temperatures (230–440 8C). The circulation of Fluid III, which did not penetrate into the hotter central part of the intrusion, caused this propylitic alteration zone (Fig. 11, Group III). This fluid also may have caused some of the argillic alteration, in which almost all the feldspars were altered to kaolinite and other clay minerals. This conclusion is based on the decrease in salinity from 18 down to 1 wt% NaCl equivalent (Fig. 11) in LV fluid inclusions and the corresponding decrease in homogenization temperature. 12. Conclusions The following conclusions can be derived from this study: 1. Multiple intrusions of dioritic and granodioritic rocks at Sar-Cheshmeh indicate a long-lived intrusive episode associated with repeated fracturing and hydrothermal activity. 2. Based on mineralogical and fluid inclusion analyzes from the deposit, three distinct hydrothermal fluids have been recognized as follows:

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A. Hezarkhani / Journal of Asian Earth Sciences 28 (2006) 409–422

2.1 The first hydrothermal fluid (Fluid I) caused potassic alteration and CuGMo mineralization. This fluid was magmatically derived and characterized by high temperatures and moderate to high salinities, which caused the wide distribution of Group I and II mineralized quartz veins and the main Cu deposition. 2.2 The second hydrothermal fluid (Fluid II) was formed mainly by the mixing of magmatic fluid, at moderate to low temperatures, with a predominantly meteoric fluid (Fluid III). 2.3 The latest fluid was responsible for the sericitic alteration zones in the lower and upper portions of the stock and also remobilized a huge amount of Cu upwards from the potassic to the phyllic alteration zone. 2.4 The third hydrothermal fluid (Fluid III) consisted of low temperature, low to moderate salinity, meteoric water, which was responsible for peripheral propylitic alteration in a zone outside the core of potassically altered rock, and possibly argillic alteration when it penetrated into the stock.

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