The behavior of ore elements in oxidized heterophase chloride and carbonate–chloride–sulfate fluids of porphyry Cu–Mo(Au) deposits (from experimental data)

Available online at www.sciencedirect.com

ScienceDirect Russian Geology and Geophysics 56 (2015) 435–445 www.elsevier.com/locate/rgg

The behavior of ore elements in oxidized heterophase chloride and carbonate–chloride–sulfate fluids of porphyry Cu–Mo(Au) deposits (from experimental data) A.A. Borovikov a,*, T.A. Bul’bak a, A.S. Borisenko a,b, A.L. Ragozin a, S.V. Palesskii a a

V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia b Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia Received 13 September 2013; accepted 26 November 2013

Abstract The spatial coexistence and synchronous formation of magmatogene porphyry Cu–Mo mineralization and epithermal gold mineralization are due to the genetic relationship between their formation processes. This relationship might be due to the generation of metal-bearing fluids of different geochemical compositions by the porphyry ore-magmatic system, which then participate in the formation of magmatogene porphyry Cu–Mo(Au) and associated epithermal gold deposits. Synthesis of fluid inclusions in quartz was performed for experimental study of the behavior of Cu, Mo, W, Sn, Au, As, Sb, Te, Ag, and Bi in heterophase fluids similar in composition and aggregate state to natural ore-forming fluids of porphyry Cu–Mo(Au) deposits. We have established that at 700 ºC, a pressure decrease from 117 to 106 MPa leads to a significant enrichment of the gas phase of heterophase chloride fluid with Au, As, Sb, and Bi. The heterophase state of carbonate–chloride–sulfate fluids is observed at 600 ºC and 100–90 MPa. It characterizes the highly concentrated liquid carbonate–sulfide phase–liquid chloride phase–low-density gas phase equilibrium. A decrease in the pressure of heterophase carbonate–chloride–sulfate fluid leads to a noticeable enrichment of its chloride phase with Cu, Mo, Fe, W, Ag, Sn, Sb, and Zn relative to the carbonate–sulfate phase. The processes of redistribution of ore elements between the phases of heterophase fluids can be considered a model of generation of metal-bearing chloride fluids, which occurs in nature during the formation of porphyry Cu–Mo(Au) deposits, as well as a model of generation of gas fluids supplying Au, Te, As, and other ore elements to the place of formation of epithermal Au–Cu and Au–Ag mineralization. © 2015, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. Keywords: synthetic fluid inclusions; ore deposits; ore formation

Introduction Study of the behavior of elements in ore-forming fluids of porphyry Cu–Mo(Au) ore-magmatic systems is necessary for understanding the factors favoring the formation of porphyry Cu–Mo and associated epithermal Au–Cu and Au–Ag deposits and the concentration of gold in their ores. Two levels of formation of ore mineralization are recognized in porphyry Cu–Mo(Au) ore-magmatic systems: hypabyssal (depths 3.5–2.0 km), mainly with porphyry mineralization, and subvolcanic (depths to 1.5 km), with epithermal mineralization (Kovalenker et al., 2006). High-sulfide Cu–Au epithermal mineralization is localized near subvolcanic intrusions and porphyry Cu–Au ores, and low-sulfide

* Corresponding author. E-mail address: [email protected] (A.A. Borovikov)

Au–Ag mineralization occurs in peripheral zones. Ores of porphyry Cu–Mo deposits are formed by assemblages of simple sulfides and oxides (pyrite, magnetite, chalcopyrite, bornite, chalcosine, and molybdenite). The mineral composition of ores of epithermal deposits is more diverse: sulfides, selenides, tellurides, as well as sulfides and sulfosalts of Sb, As, and Bi. Epithermal mineralization usually occurs at a distance of up to few hundred meters from porphyry one. It is either localized directly above porphyry mineralization or is superposed with it. This regular arrangement of magmatogene porphyry and epithermal types of mineralization is due to the genetic relationship between their formation processes. One of the reasons for the relationship might be generation of metal-bearing fluids of different geochemical compositions and aggregate states by the porphyry ore-magmatic system. The fluids participate in the formation of magmatogene

1068-7971/$ - see front matter D 201 5, V.S. So bolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.rgg.2015.02.005

436

A.A. Borovikov et al. / Russian Geology and Geophysics 56 (2015) 435–445

porphyry Cu-Mo-(Au) and associated epithermal gold deposits. The processes of formation of porphyry ore-magmatic systems have been best studied at the depths where ore accumulation zones of porphyry Cu-Mo(Au) deposits are located. The generation of metal-bearing fluids can be caused by the liquid immiscibility in magma, detachment of supercritical fluid fractions from magmatic melts, and their transition into a heterophase state (Borisenko et al., 2006, 2011; Panina and Motorina, 2008). The heterophase state of fluids is typical of porphyry ore formation and is recognized in all porphyry Cu-Mo deposits, based on the data on fluid inclusions (Audétat and Pettke, 2003; Borisenko et al., 2006; Hanley et al., 2005; Heinrich et al., 1999, 2004; Klemm et al., 2007; Rusk et al., 2004; Sotnikov et al., 1977; Ulrich et al., 1999, 2001; William-Jones and Heinrich, 2005). Study of fluid inclusions showed that the ore-forming fluids in porphyry Cu-Mo(Au) deposits localized both in granitoids (Kal’makyr (Uzbekistan), Sora (Khakassia), Zhireken (Transbaikalia); Vykhodnoe, Chubachi, and Borgulikan (Amur Region); BayanUla and Erdenetyin (Mongolia); Alumbrera (Argentina), Grasberg (Indonesia), Bingham Canyon and Butte (USA), El Teniente (Chile); Baogutu, Duobaoshan, Xilamulun, and Wunugetu (China), etc.) and in alkaline massifs (Ryabinovoe, Samolazovskoe, etc. (Aldan); Kirganik (Kamchatka), etc.) have the following specific features (Audétat and Pettke, 2003; Borisenko et al., 2006, 2011; Borovikov et al., 2012; Dashkevich et al., 2012; Heinrich et al., 1992, 1999; Klemm et al., 2007; Naumov et al., 1995; Panina and Motorina, 2008; Prokof’ev and Vorob’ev, 1991; Rusk et al., 2004; Ulrich et al., 1999, 2001): (1) High redox potential corresponding to the values of the sulfide–sulfate equilibrium. (2) High temperature, which varies from 300 to 700 ºC and more when approaching the granite solidus temperature; the fluid pressure reaches 200 MPa. (3) In the deposits localized in granitoids, the water–salt fractions of fluids are predominantly chlorides with sulfate impurities, and in the deposits localized in alkaline massifs, they are predominantly sulfates. The gas phase consists mainly of CO2, N2, and H2S (±). (4) The aggregate state of fluids corresponds to the equilibrium between the highly concentrated water–salt solution and the gas phase for chloride fluids systems of the deposits localized in granitoids. For essentially sulfate fluids of deposits localized in alkaline massifs, not only the liquid– gas equilibrium exists but also liquid immiscibility (highly concentrated sulfate solution–lowly concentrated chloride solution with sulfate impurities) is possible at supercritical parameters of the water–salt system (Valyashko, 2009; Valyashko and Urusova, 2010). (5) The water–salt fractions of fluids of porphyry ore-magmatic systems are characterized by high concentrations of salts, reaching 30–60 wt.% in chloride fluids and even >70 wt.% in sulfate fluids. (6) The total content of major ore-forming metals (Cu, Fe, Mo) in highly concentrated water–salt fluids is rather high and

can exceed few percent. High concentrations of other metals (Au, As, Sb, Bi) typical of ores of epithermal Au–Cu and Au–Ag deposits are usually observed in the gas fraction: Au—up to 11, As—up to 220 (Grasberg), Sb—100, and Bi—up to 40 ppm (Bingham). We used these physicochemical parameters of heterophase ore-forming fluids of porphyry Cu–Mo deposits to choose the conditions for an experimental study of the behavior of Cu, Mo, W, Sn, Au, As, Sb, Te, Ag, and Bi in heterophase fluid systems (Borovikov et al., 2011). Methods To study the behavior of ore elements in heterophase fluids, experiments on synthesis of fluid inclusions in quartz were carried out in gold and platinum ampoules, following the autoclave technique (Balitskii, 2008; Kotel’nikova, 2008), in the Laboratory of Metamorphism and Metasomatism at the Institute of Geology and Mineralogy, Novosibirsk. Equipment. The experiments were performed in autoclaves made of heat-resistant nickel-based alloy 10 to 20 cm3 in volume. Distilled water was used as a medium venting the pressure on gold ampoules. The autoclave was heated in a vertical resistant furnace; the current in it was adjusted by PIT-3B high-accuracy temperature regulators. The temperature in the course of experiments was measured by chromel/alumel thermocouples armored with steel capillaries inserted into the channels, at the bottom and in the inner lock at the top of the autoclave. The accuracy of temperature measurement was ±2 ºC, and the accuracy of temperature maintenance by a thermal regulator was ±6 ºC. The temperature gradient along the quartz seed was 1.71 ºC/cm at 700 ºC. The experimental regime was established for 4 h 15 min, and cooling of the furnace to the room temperature, for 12 h. Experiments with chloride fluids. The starting seeds were colorless prismatic plates of synthetic quartz with a squared section, 35–40 mm in length and 2.2–3.4 g in weight. Optical examination confirmed the absence of inclusions from the quartz. The model aqueous solution for filling the Au ampoules was acidified with HCl and contained 20 wt.% NaCl and metals (ppm): Rb—440, Cs—430, Ba—560, Te—150, As—100, Sb—70, Bi—1000. Rubidium, barium, and cesium were added to the solution as probable internal standards to evaluate the contents of As, Sb, Bi, and Au from LA-ICP-MS data because determination of Na concentration in the inclusions was impossible. The model solution was prepared from chemical reagents H2TeO4⋅2H2O and Bi(ClO4)3 (both of special-purity grade) and preliminarily prepared HCl solutions of Sb and As. Gold got to the solution from the Au ampoule used in the experiments. To ensure excess silica, necessary for the growth of quartz during the experiment, a mixture of special-purity amorphous anhydrous SiO2 with Na2SiO3⋅9H2O (mass ratio 1:2) was used. A mixture of hematite with magnetite (fraction 0.5–0.25 mm) (1 : 1) was taken as a redox potential buffer. The ampoule filling. The quartz seed, SiO2, and Na2SiO3⋅9H2O were successively placed into the preliminarily

A.A. Borovikov et al. / Russian Geology and Geophysics 56 (2015) 435–445

437

Fig. 1. Types of fluid inclusions synthesized during the experiments in the chloride watersalt system. Inclusions lacking signs of combined intake: a, two-phase inclusion; b, three-phase inclusion with halite crystal; c, partly crystallized melt inclusion; d, combined inclusion containing gas, salt solution, halite crystal, and silicate melt.

annealed Au-ampoule (∅14 × 50 × 0.5 mm). The buffer mixture was also introduced into the ampoule. On the one hand, this increased the time of the buffer action and, on the other, ensured the presence of Fe in the fluid, which made it similar in composition to natural fluids of porphyry ore-forming systems. The volume of the solution poured then into the ampoule was determined from the free volume of the ampoule and from the coefficient of its filling with pure water, which provided the required pressure. All ampoules were subjected to electric welding under cooling with liquid nitrogen in air. Their leak-proofness was controlled by the constant weight before and after the experiment. Experiments with carbonate–chloride–sulfate fluids. The experiments were carried out by the above-described ampoule technique with excess Na2SO4, which reliably buffered the redox potential at the value corresponding to the sulfate–sulfide equilibrium. The mixture of Na2SO4 (71.4 wt.%), NaCl (14.3 wt.%), and NaHCO3 (14.3 wt.%) served as a charge material. Ore elements (Fe, Cu, Mo, W, Sn, As, Sb, Te, Ag, and Bi) were added to the charge as a powdered homogeneous mixture consisting of arsenopyrite, chalcopyrite, smaltite, antimonite, galena, sphalerite, wolframite, molybdenite, metallic Sn and Ag, and Te- and Bi-containing chemical reagents (all in equal portions). This “ore” mixture was 0.008–0.011 g in weight and of minimum volume (~0.2 mm3); the latter was ignored during the calculations of free volume. This rough method of introduction of ore components was used because it was impossible to prepare a homogeneous solution containing all ore elements necessary for the experiment. Analysis of the experimental products. Inclusions without visible signs of combined intake (Fig. 1) were analyzed for ore and rock-forming elements by LA-ICP-MS on Agilent 7500s ICP-MS and ELEMENT-2 FINNIGAN MAT mass spectrometers with a New Wave UP213 laser ablation system. The glass NIST-612 was used as an external standard, and Na was chosen as an internal standard, because it is present in the main salt components of the experimental fluids. Laser ablation of the sample was started from its surface and then penetrated into it with a rate of 1–2 μm/s, burning out the quartz above the inclusion, then the inclusion and part of the matrix, and finally the quartz below the inclusion. The obtained results of LA-ICP-MS analysis were presented as the graphical time dependence of the intensity of analytical signal (a.s.). One can clearly see the beginning of laser ablation and

the unsealing of inclusion, which makes it possible to determine correctly the analytical signal of the unsealed inclusion and calculate the contents of elements in it (Fig. 2). The concentration of NaCl in the synthesized two- and three-phase fluid inclusions obtained during the experiments with a chloride fluid was determined by cryometry and thermometry from the temperature of ice melting and the temperature of dissolution of NaCl crystal. This permitted determination of NaCl content in the two-phase and some three-phase inclusions (Borisenko, 1977; Ermakov, 1972; Roedder, 1984). If the three-phase inclusions decrepitated so that the complete dissolution of NaCl crystal was impossible, the NaCl content was calculated based on volumetric measurements of the linear sizes of the individual phases of three-phase inclusions: halite, a gas bubble, and the inclusion vacuole. Then, the volume of the inclusion vacuole was evaluated by approximating the inclusion shape in a three-axis ellipse (Ishkov and Reif, 1990), as well as the volumes of halite crystals, gas bubble, and salt solution of the inclusion. The masses of these halite and salt solution were calculated using the known densities of halite (d = 2.168) and NaCl solution (d = 1.200) in equilibrium with it at 20 ºC (Kogan et al., 1970). The mass of NaCl in the solution was calculated from its concentration (26.4 wt.%) in the saturated solution at 20 ºC and from the earlier calculated mass of the salt solution

Fig. 2. Typical analytical signals of elements under laser ablation of quartz and three-phase fluid inclusion in it. For a correct quantitative analysis for elements in the inclusion, the pattern must have intervals of ablation of “pure” quartz (a), quartz site with inclusion (b), and quartz beneath the inclusion (c).

438

A.A. Borovikov et al. / Russian Geology and Geophysics 56 (2015) 435–445

Fig. 3. Contents of NaCl in two- and three-phase inclusions. Left of the critical curve, the intervals of NaCl contents (wt.%) in two-phase inclusions estimated by cryometry are shown on the 700 ºC isotherm. Right of the curve, there are experimental data on the NaCl contents (wt.%) in three-phase inclusions coexisting with two-phase ones at the same pressure and temperature, after Sourirajan and Kennedy (1962), with our supplement.

(Zdanovskii et al., 1961). Then, the total mass and content (wt.%) of NaCl in the inclusion (halite + NaCl in the solution) was determined (Table 1). Moreover, using the determined content of NaCl in the two-phase inclusions, whose composition corresponded to the composition of the gas phase in the autoclave, we estimated the concentration of NaCl in the liquid water–salt phase by extrapolation of the data obtained by Sourirajan and Kennedy (1962) (Fig. 3). Comparison of the contents of NaCl estimated by cryometry and thermometry as well as of the volumetric-measurement and extrapolation results shows their good agreement (Table 1). The average values of the determined parameters differ by no more than 5–6% from each other, which might indicate that the content of NaCl in the three-phase inclusions was determined correctly by these methods. When calculating the Na content of the internal standard in the inclusions, we used the average contents of NaCl determined by the extrapolation of the data of Sourirajan and Kennedy, since these data show a smaller scatter as compared with those obtained by the volumetric

method. The total content of salts (Na2SO4, Na2CO3, NaCl) in concentrated sulfate inclusions obtained during the experiments with sulfate–carbonate fluid at 600 ºC was evaluated at ~70 wt.% equiv. Na2SO4, using the T-X state diagram of the Na2SO4–H2O system (Valyashko, 2004). The content of Na in the concentrated sulfate inclusions was calculated from wt.% equiv. Na2SO4. The content of Na in the melt inclusions was determined by microprobe analysis (CAMECA). The procedure of calculation of element contents in the inclusions. The algorithm of calculation of element contents in the inclusion is derived from the known formula of Longerich et al. (1996) for processing the results of LA-ICPMS analysis. Applying this formula to such calculations from the results of LA-ICP-MS analysis with external and internal standards, we can present it as follows: Ciincl

std Cistd Iiincl INa = std ⋅ incl std , cr CNa CNa INa Ii

Table 1. Estimated contents of NaCl in two-phase and three-phase inclusions Experiment

Temperature of melting, °C

Content of NaCl (wt.%), from thermoand cryometric data

Content of three-phase inclusions (wt.%)

Ice in two-phase inclusions

Halite in three-phase inclusions

Two-phase inclusions Three-phase inclusions

Extrapolation (average) (Sourirajan and Kennedy, 1962)

Volumetric data (average)

10–1

–4.0 to –2.9

No data*

6.4–4.7

53.5–48.5 (51)

56.1–49 (52.6)

10–2

–6 to –4.8

No data*

9.2–6.4

No data

49–43 (46)

53.0–37.0 (45)

10–3

–7.5 to –5.2

335–385

10.5–7.8

45.1–41

46–41.7 (43.9)

46.5–36.6 (41.6)

10–4

–

4.3–3.9

–

26.3

–

–

* Partial dissolution of halite and decrepitation of inclusion at 600 °C.

No data

A.A. Borovikov et al. / Russian Geology and Geophysics 56 (2015) 435–445

where Ciincl is the content of element in the inclusion; Cistd is the content of element in the external standard NIST 612; std is the content of Na in the external standard NIST 612; CNa cr is the content of Na estimated by cryometry or other CNa method; Iiincl is the intensity (pulse/s) of the signal of element in the inclusion; Iistd is the intensity (pulse/s) of the signal of incl is the intensity element in the external standard NIST 612; INa std is the (pulse/s) of the signal of Na in the inclusion; and INa intensity (pulse/s) of the signal of Na in the external standard NIST 612. The intensity of the a.s. of element in the inclusion (Iiincl) was determined by the subtraction of the a.s. of the quartz background from the a.s. of the element in the interval of the inclusion unsealing (Fig. 3). The result was multiplied by the value equal to the ratio of the element content in the external std) to the intensity of the a.s. of the standard standard (CNa std (INa ). The results of this calculation are important because they reflect the quantitative ratios of elements at the site of ablation of quartz containing the inclusion and are actually multiple of the element contents in the inclusion. The contents of elements (in percentage and fractions of a percent) in the inclusion are derived by normalization of these results to the ratio between the Na content in the sample in the interval of the inclusion unsealing (Cincl i ) and the Na content in the cr ). This inclusion estimated by cryometry or other method (CNa algorithm of calculation of element contents in fluid inclusions from LA-ICP-MS data is given in many publications concerned with LA–ICP-MS analysis of fluid inclusions (Audétat et al., 1998; Günther and Heinrich, 1999; Günther et al., 1997, 1998; Heinrich et al., 2003; Ulrich et al., 2001). An LA–ICP-MS analysis of individual fluid inclusions has drawbacks, e.g., the results of analysis of even compositionally identical fluid inclusions always show a wide scatter of values and thus a great error. In our opinion, this is due to the following reasons: the uneven flow of the substance into the detector during the laser ablation of the inhomogeneous medium (fluid inclusion–mineral matrix system), the difference in the aggregate state between the fluid inclusion substance and the mineral matrix, the microscopic size of the fluid inclusions, and the necessity of the large amount of substance for LA–ICP-MS analysis. The results of analysis of similar fluid inclusions synthesized during our experiments also show a wide scatter, but the results of analysis of two-phase and polyphase inclusions differ, on the average, by more than an order of magnitude. This marks particular tendencies in the distribution of ore elements between the gas and liquid fractions of the experimental heterophase fluids as the pressure changes. The mineral phases in the newly formed quartz and the daughter phases in the polyphase fluid inclusions, obtained in the experiment with sulfate fluid, were identified by Raman spectroscopy on a Ramanor U-1000 (Jobin Yvon) spectrometer with a HORIBA JOBIN YVON detector and a Millennia Pro S2 laser (532 nm). The daughter phases of the polyphase inclusions were identified using the RRUFF Raman spectra base [http://rruff.info/].

439

Experimental results Experiments with chloride fluids. During the experiment, a heterophase medium appeared in the ampoule with a quartz seed (Fig. 4). The upper part of the ampoule was filled with the gas phase, and the lower part contained a thin layer of highly concentrated chloride solution with a silicate melt beneath it. Thus, the regeneration of quartz on the seed and the intake of inclusions proceeded in different media. In the upper part of the seed, mostly two-phase (gas + liquid) fluid inclusions were synthesized, which then homogenized into a gas phase. In the lower part, three-phase inclusions with halite were synthesized in the layer of highly concentrated chloride solution; below them, inclusions of combined phase composition were produced. During the experiments, the content of NaCl varied from 4.7 to 10.5 wt.% in the synthesized two-phase fluid inclusions and from 41.7 to 53.5 wt.% in the three-phase inclusions (Table 1). These data permit estimation of the pressure in the autoclave for the H2O–NaCl system at the moment of the inclusion intake at high pressures and temperatures (Sourirajan and Kennedy, 1962). According to the estimates, the interval of the intake temperatures might have been 700–690 ºC, and the experimental pressure was close to 109, 113, 117, and 123.5 MPa (Fig. 3). The medium was alkaline, as evidenced from the presence of aegirine among the newly formed phases. The contents of As, Sb, Te, Au, and Bi in the synthesized inclusions were determined by LA-ICP-MS (Table 2). At 700 ºC and a pressure decrease from 117 to 109 MPa, the behavior of As, Sb, and Au in the gas phase coexisting with highly concentrated chloride solution is similar: Their contents in the gas phase significantly increase (on the average, by two to three orders of magnitude). The contents of these elements in the water-salt phase, on the contrary, seriously diminish with decreasing pressure, as compared with the gas phase. The maximum contents of As (up to 870 ppm), Sb (up to 690 ppm), and Au (up to 640 ppm) are detected in the water-salt phase at 117 MPa, a near-critical pressure. In the experiments at 123 MPa, the supercritical state of the fluid phase was achieved, as evidenced from the synthesis of only two-phase fluid inclusions with 26.3% NaCl and from the absence of three-phase inclusions with halite. The supercritical chloride fluid had high contents of As (360 ppm), Sb (2250 ppm), Au (70 ppm), and Bi (340 ppm). Bismuth and tellurium show a somewhat different behavior. As the pressure decreases from 117 to 109 MPa, the content of Bi increases both in the gas (from 6 to 8730 ppm) and in the water-salt (from 70 to 550 ppm) fluid phases. The behavior of Te is especially unusual: Its contents in the gas and water-salt fluid phases increase with decreasing pressure, but its content in the silicate melt does not seriously change. This might be due to the intense (compared with other elements) interaction of Te with Au of the ampoule, which becomes more intense as the pressure grows, or due to the intense dissolution of Te in the relatively small volume of the silicate melt. The partition coefficients of elements between the solution and the gas phase (K = C in the solution/C in the gas

440

A.A. Borovikov et al. / Russian Geology and Geophysics 56 (2015) 435–445

Fig. 4. Experimental synthesis of inclusions with chloride fluids during the regeneration of quartz in the heterophase medium at 700 ºC and 109 MPa. On the left, there is the experimental scheme, with the shown ampoule contents during the experiment: quartz seed (Q), gas phase (1), highly concentrated chloride solution (2), silicate melt (3), and gold ampoule walls (4). On the right, there are photos of two-phase (a), highly concentrated three-phase (b), and melt (c) inclusions trapped by regenerated quartz in the corresponding medium. Arrows mark the localities of fluid inclusions on the 45 mm long quartz seed (Q).

phase) best reflect their behavior in the fluid system (Fig. 5). For As, Sb, Te, Au, and Bi at 700 ºC and a pressure decrease from 117 to 109 MPa, these coefficients vary as follows: for As—from 9.7 to 0.07; for Sb—from 125 to 0.1; for Te—from 1.4 to 0.03; for Au—from 3200 to 0.33; and for Bi—from 12 to 0.1. According to the probe microanalysis data, the silicate melt synthesized during the experiments contained (wt.%): SiO2— 73.2–67.6, FeO—16.2–4.0, NaO—6.1–0.5, Cl—1.1–0.4 (Table 2), and water, whose content was not determined. The content of FeO in the silicate melt in the presence of chloride solution and gas phase decreases from 16.2 to 4.0 wt.% as the pressure grows. Under supercritical conditions, the content of FeO again increases to 15.5 wt.%. The low content of Na in the melt is due to the mass formation of mineral phase similar in composition (FeO—31.2; NaO—13.9; SiO2—55 wt.%) and crystalline structure (data of X-ray diffraction analysis) to aegirine. The silicate melt shows no significant changes in As, Sb, Te, and Au contents with increasing pressure (Table 2). Experiments with carbonate–chloride–sulfate fluid. In the experiment with carbonate–chloride–sulfate fluid at 600 ºC

and 100 and 90 MPa, an equilibrium of two immiscible water–salt phases (essentially chloride and essentially carbonate–sulfate) was reached. This kind of equilibrium is specific for the Na2SO4–H2O system, in which two immiscible liquids differing in the concentration of the main salt component appear under supercritical PT-conditions (Valyashko, 2004, 2009). In our experiments, the liquid phase with the lowest concentration of Na2SO4 was enriched in NaCl. This is confirmed by the presence of not only primary gas inclusions but also primary two-phase liquid chloride inclusions with minor Na2SO4 in the regenerated quartz, as well as primary highly concentrated sulfate inclusions synthesized at 600 ºC and 100 and 90 MPa (Fig. 6). According to the Raman spectroscopy data, the highly concentrated inclusions contain burkeite Na6(SO4)(CO3)2 as the main solid salt phase, which dominates over the solution and gas by volume. These inclusions decrepitated on heating within 500–450 ºC. The total content of salts in the concentrated inclusions was roughly estimated from the T–X state diagram for the Na2SO4–H2O system at ~70 wt.% equiv. Na2SO4 (Valyashko, 2004).

441

A.A. Borovikov et al. / Russian Geology and Geophysics 56 (2015) 435–445

Table 2. Contents of ore elements (ppm) in the gas and water–salt fluid phases and in silicate melt, from data of LA–ICP–MS study of individual fluid and melt inclusions synthesized at 700 and 109.0–123.5 MPa Element

Heterophase fluid (gas + one-salt solution) 109

Supercritical fluid

113

117

123.5

3

3

5

MPa Gas fluid phase 8 NaCl, wt.%

6.4–4.7

9.2–6.4

10.5–7.8

26.3

As, ppm

1230* (3090–185)

200 (305–60)

45 (60–30)

180 (470–95)

Sb

530 (1100–60)

64 (91–32)

5.5 (6.8–4.2)

2250 (9400–90)

Te

1430 (3300–190)

86 (154–44)

1.9 (2.3–1.5)

1.4 (25–0.5)

Au

66 (210–10)

7 (12–4.2)

0.2 (0.4–0.1)

66 (230–1.6)

Bi

8930 (19000–710)

570 (800–330)

6.0 (10–1.6)

340 (1140–13)

1

4

3

No three-phase inclusions

Water–salt fluid phase

NaCl, wt.%

53.5–48.5** (56.1–49)***

49–43 (53.0–37.0)

45.1–41()

–

As, ppm

90

175 (225–134)

436 (470–410)

N.d.

Sb

53

135 (173–94)

690 (2000–32)

N.d.

Te

47

21 (30–10)

2.7 (6.8–0.5)

N.d.

Au

22

105 (172–47)

640 (1890–1)

N.d.

Bi

545

198 (346–94)

70 (106–30)

N.d.

0.9–0.5

8.1–5.4

15.0–11.2

1.4–0.8

Silicate melt NaCl, wt.%

2

2

2

3

As, ppm

7.7 (14.7–0.7)

4.0 (5.6–2.3)

1.7 (1.9–1.6)

3.0 (4.4–1.1)

Sb

4.6 (8.8–0.3)

1.6 (2.9–0.3)

0.2 (0.3–0.2)

3.1 (5.5–0.1)

Te

0.005 (0.009–0)

0.003 (0.005–0.001)

0.001 (0.001–0)

0.03 (4.5–0.1)

Au

0.007 (0.005–0.008)

0.003 (0.003–0.002)

0.002 (0.003–0)

0.8 (2.5–0)

Bi

1.6 (8.8–0.3)

14 (15–12)

26 (31–21)

4.7 (12–0.06)

Note. Aalyses were carried out by LA-ICP-MS in the Laboratory of Isotope-Geochemical Methods of Analysis at the Analytical Center of the Institute of Geology and Mineralogy, Novosibirsk (analyst S.V. Palesskii). Bold numerals are the number of studied inclusions. * Average contents (ppm); parenthesized are the ranges of contents. ** Content of NaCl calculated from volumetric data. *** Content of NaCl estimated by extrapolation, using the data from Sourirajan and Kennedy (1962).

The two-phase inclusions contain a water–salt solution and gas. On cooling, crystallization of ice and the eutectic solution took place in them. The solutions of these inclusions are characterized by the temperatures of the eutectics melting close to that of the NaCl–H2O system, –22.4 to –24.8 ºC, and by the temperature of ice melting of 15.5 ºC (100 MPa) and 14.5 ºC (90 MPa). The decrease in the temperatures of the eutectics melting is due to the presence of minor NaHCO3 and Na2SO4 in the solutions. The main component of the eutectic solution of the four-component NaCl–Na2SO4– NaHCO3–H2O system is NaCl (22.8 wt.%), whereas Na2SO4 and NaHCO3 amount to 0.18 and 0.66 wt.%, respectively (Kogan et al., 1970). Thus, the solutions of the synthetic two-phase inclusions are mostly of chloride composition, with minor Na sulfate and Na hydrocarbonate. The content of NaCl in the solutions of the synthesized two-phase inclusions does not exceed 18.6–17.8 wt.%. Homogenization of the two-phase

inclusions to a liquid phase proceeds at 329 ºC (100 MPa) and 427 ºC (90 MPa); the liquid density varies from 0.89 to 0.74 g/cm3. The LA–ICP-MS analysis has revealed Co, Cu, Zn, As, Mo, Ag, Sn, Sb, and W in the two-phase and polyphase inclusions (Table 3). Though the experiments were carried out in gold ampoules, no Au was discovered in the fluids. At 100 MPa, the ore elements show the following partition coefficients (C in the carbonate–sulfate phase/C in the chloride phase): Fe—0.12, Co—12.2, Cu—6, Zn—2, As—0.42, Mo— 6.3, Ag—157, Sn—4.5, Sb—2.7, W—1.1, and Pb—2.8. Thus, at 600 ºC and 100 MPa, Ag, Co, Mo, Sn, Pb, Sb, Zn, and W accumulate in the highly concentrated sulfate phase, whereas Fe and As enrich the chloride phase (Fig. 7a). A pressure decrease from 100 to 90 MPa changes the distribution of elements between the chloride and sulfate fluid phases. The new partition coefficients are as follows: Fe—0.15, Co—2.8,

442

A.A. Borovikov et al. / Russian Geology and Geophysics 56 (2015) 435–445

Fig. 5. Change in the partition coefficient of elements (C in the liquid phase/C in the gas phase) between the liquid and gas phases. Pressure (MPa): a, 106; b, 113; c, 117.

Cu—0.1, Zn—0.07, As—2.9, Mo—0.11, Ag—0.26, Sn—0.7, Sb—0.7, W—0.7, and Pb—3.7. At 90 MPa, most of the ore elements (Zn, Cu, Mo, Fe, W, Ag, Sn, Sb) concentrate in the chloride phase, whereas the carbonate–chloride–sulfate phase coexisting with it becomes enriched in Co, As, and Pb (Fig. 7b). The LA–ICP-MS analysis revealed Cu, Zn, and As in the low-density gas inclusions.

Discussion Based on the performed experiments, we have drawn two important conclusions about the behavior of ore elements in oxidized heterophase chloride and carbonate–chloride–sulfate magmatic fluids with changing pressure. This can help to elucidate the possible conditions of generation of ore-forming fluids at the upper subvolcanic levels of the porphyry Cu–Mo ore-magmatic systems.

Fig. 6. Experiment with carbonate–chloride–sulfate fluids. View of the face of quartz synthesized on the seed; the face was not subjected to polishing. Primary fluid inclusions are localized above the quartz face. 1, highly concentrated sulfate–carbonate inclusion; 2, two-phase chloride inclusions of medium concentration.

We have established that at 700 ºC, the water–salt phase of the heterophase chloride fluid system is the richest in ore-forming elements at the pressure close to the critical one. A pressure decrease (in our experiments, from 117 to 109 MPa) leads to a radical redistribution of As, Sb, Te, Au, and Bi into the gas phase. In particular, the partition coefficient (C in the solution/C in the gas phase) changes from 1.4 to 0.03 for Te and from 3200 to 0.33 for Au, which causes a significant enrichment of the gas phase with these elements. The above fact evidences that at the subvolcanic level of porphyry ore-magmatic systems, a drastic fall in pressure can result in the generation of gas fluids with elevated contents of As, Sb, Te, Au, and Bi. These fluids participate in the formation of epithermal gold mineralization on the periphery of Cu–Mo deposits. The above-described pressure-dependent behavior of ore elements can explain the different ratios of metal contents in the polyphase and gas fluid inclusions found in porphyry Cu–(Mo,Au) deposits at different depths. In the Bingham Canyon (USA) and Grasberg (Indonesia) porphyry Cu–Au deposits, the contents of ore-forming metals (in particular, Cu and Au) in gas inclusions are one or two orders of magnitude higher than those in water–salt inclusions (Heinrich et al., 1999; Landtwing et al., 2005; Ulrich et al., 1999). In the more deep-seated Bajo de la Alumbrera porphyry Cu–Mo deposit (Argentina), where the mineral formation pressure reaches 132 MPa and more (Heinrich et al., 1999; Ulrich et al., 1999, 2001), and in quartz of the Rito del Medio and Canada Pinabete granite-porphyry plutons (New Mexico, USA) (Audétat and Pettke, 2003), the contents of Fe, Cu, Zn, Rb, Cs, Sb, and Bi in water–salt inclusions are one or two orders of magnitude higher than those in coexisting gas inclusions. The same distribution of ore elements was established in the El Teniente porphyry Cu–Mo deposit (Chile) (Klemm et al., 2007). Thus, the results of the performed experiments with chloride fluids agree with the regular behavior of ore elements in natural heterophase oxidized chloride fluids. We have also established that at 600 ºC and 100–90 MPa, carbonate–sulfate–chloride fluids are in the heterophase state and are two immiscible liquid-like water-containing fractions of different compositions. One of them is rich in salts and is of essentially carbonate–sulfate composition, and the other has a medium content of salts and is of chloride (with sulfate impurities) composition. The fluid system also contains a

A.A. Borovikov et al. / Russian Geology and Geophysics 56 (2015) 435–445

443

Table 3. Contents of ore elements (ppm) and Na (wt.%) in the chloride and carbonate–chloride–sulfate fluid phases, from results of LA-ICP-MS study of individual fluid and melt inclusions at 600 °C Element

90 MPa

100 MPa

3

1

Chloride fluid phase

Content of NaCl*

18.6

17.8

Fe

18,000 (3,0000–4500)**

3100

Co

440 (960–370)

90

Cu

11,500 (18,000–3500)

30

Zn

690 (2,000–0)

90

As

420 (950–50)

120

Mo

970 (2900–40)

4

Ag

70 (220–0)

2

Sn

3850 (6300–1,000)

170

Sb

490 (630–430)

470

W

530 (1100–85)

55

Pb

160 (450–25)

100

Carbonate–chloride–sulfate fluid phase 4

3

Content of Na2SO4***

≈ 70

≈ 70

Fe, ppm

2800 (5400–20)

390 (740–180)

Co

1260 (2300–170)

1100 (2500–80 )

Cu

1160 (1500–800)

180 (300–120)

Zn

50 (100–0)

180 (280–90)

As

1240 (2300–140)

50 (100–40)

Mo

110 (220–0)

25 (70–10)

Ag

18 (40–0)

315 (540–150)

Sn

2700 (5300–280)

760 (1100–370)

Sb

350 (540–150)

1260 (3250–240)

W

90 (180–0)

60 (80–30)

Pb

590 (1100–60)

280 (400–20)

Note. Analyses were carried out by LA-ICP-MS in the Laboratory of Experimental Mineralogy and Crystallogenesis at the Institute of Geology and Mineralogy, Novosibirsk (analyst A.L. Ragozin). * Content of NaCl in two-phase inclusions determined by cryometry. ** Average content of element in the inclusion; parenthesized are the ranges of contents. *** Content of Na2SO4 in two-phase inclusions estimated from the diagram of the water–salt system Na2SO4–H2O (Valyashko, 2004).

low-density gas phase. This fluid state corresponds in the behavior to the so-called water–salt systems of type II, which are characterized by liquid immiscibility under supercritical PT-conditions (Valyashko, 2009; Valyashko and Urusova, 2010). Analysis of synthetic sulfate and chloride fluid inclusions showed that as the pressure decreases, most of the metals participating in the formation of ores of porphyry Cu–Mo deposits (Cu, Mo, Fe, Zn, Ag, Sn, Sb, and W) concentrate in the chloride fraction of heterophase carbonate–sulfide–chloride fluid. In nature, such fluids are generated by alkaline basic magmas and are effective concentrators of ore-forming metals and sulfur. This was established in studying of the fluid regime of the Aldan alkaline massifs (Borisenko et al., 2006, 2011; Borovikov et al., 2012; Naumov et al., 2008; Prokof’ev and

Vorob’ev, 1991). The liquid immiscibility, which is typical of such fluids in the supercritical conditions of their existence, causes the generation of a metal-bearing chloride fraction. The latter serves as an ore-forming fluid for the formation of porphyry Cu–Au mineralization in alkaline massifs. Metalbearing homogeneous chloride fluids of similar composition and salt concentrations were established as medium-density fluid inclusions at the subore levels of many porphyry Cu–Au deposits (Heinrich et al., 1999; Klemm et al., 2007; Landtwing et al., 2005; Ulrich et al., 1999, 2001). Porphyry Cu–Mo(Au) ore-magmatic systems form in granitoids with the participation of the mantle matter, which is proved by the manifestation of alkaline basic magmatism within porphyry Cu–Mo(Au) ore clusters and by isotope data (Berzina et al., 2013; Sotnikov, 2006). This permits carbonate–chloride–sulfate fluids separat-

444

A.A. Borovikov et al. / Russian Geology and Geophysics 56 (2015) 435–445

Fig. 7. Change in the partition coefficient of elements (C in the carbonate–sulfate phase/C in the chloride phase) between the carbonate–chloride–sulfate and chloride phases at 600 ºC. a, At 100 MPa; b, at 90 MPa.

ing from alkaline basic magmas to be considered as primary metal-bearing fluids of porphyry Cu–Mo(Au) ore-magmatic systems. Separation of these fluids into sulfate and chloride phases with decreasing pressure is a model of generation of oxidized chloride ore-forming fluids in porphyry Cu–Mo(Au) deposits.

formation of epithermal Au–Cu and Au–Ag mineralization associated with porphyry mineralization. We thank A.A. Tomilenko and V.B. Naumov for critical remarks and recommendations, which helped to improve the manuscript. This work was supported by grants 12-05-00618, OFI-m, and 13-05-12056 from the Russian Foundation for Basic Research.

Conclusions The experimental studies of the behavior of ore elements in heterophase fluids, based on synthesis of fluid inclusions, yielded the following results: (1) At 700 ºC and 117–109 MPa, distribution of ore metals between the water–salt and gas phases takes place in the oxidized heterophase chloride water–salt fluids. When the pressure is slightly reduced relative to the critical one, the concentrated chloride phase has the maximum contents of metals. As the pressure radically decreases, the strong redistribution of ore elements (As, Sb, Te, Au, and Bi) into the gas phase occurs. At the subvolcanic level of porphyry Cu–Mo(Au) ore-magmatic systems, this process contributes to the generation of metal-bearing fluids forming epithermal Au–Cu and Au–Ag mineralization associated with porphyry mineralization. (2) At 600 ºC and 100–90 MPa, the oxidized carbonate– chloride–sulfate fluids are in the heterophase state. They are composed of a highly concentrated water–salt phase of essentially carbonate–sulfate composition (~70 wt.%), water– salt chloride phase of medium salt concentration (18.6– 17.8 wt.%), and low-density gas phase. A pressure decrease leads to the redistribution of ore elements Cu, Mo, Fe, and W, as well as Zn, Ag, Sn, and Sb, into the chloride phase. This process can be regarded as a model of generation of ore-forming oxidized chloride fluids in porphyry Cu–Mo(Au) deposits, which supply ore-forming elements during the

References Audétat, A., Pettke, T., 2003. The magmatic-hydrothermal evolution of two barren granites: a melt and fluid inclusion study of the Rito del Medio and Canada Pinabete plutons in northern New Mexico (USA). Geochim. Cosmochim. Acta 67, 97–121. Audétat, A., Günther, D., Heinrich, C.A., 1998. Formation of a magmatic-hydrothermal ore deposit: insights with LA-ICP-MS analysis of fluid inclusions. Science 279 (5359), 2091–2094. Balitskii, V.S., 2008. The mechanisms of formation and morphogenetic types of fluid inclusions in crystals of synthetic minerals, in: Proc. 13th Int. Conf. Thermobarogeochemistry and Fourth APIFIS Symp. [in Russian]. IGEM, Vol. 2, pp. 261–264. Berzina, A.P., Berzina, A.N., Gimon, V.O., Krymskii, R.Sh., Larionov, A.N., Nikolaeva, I.V., Serov, P.A., 2013. The Shakhtama porphyry Mo ore-magmatic system (eastern Transbaikalia): age, sources, and genetic features. Russian Geology and Geophysics (Geologiya i Geofizika) 54 (6), 587–605 (764–786). Borisenko, A.S., 1977. Study of the salt composition of solutions of gas-liquid inclusions in minerals by the cryometric method. Geologiya i Geofizika (Soviet Geology and Geophysics) 18 (8), 16–27 (11–19). Borisenko, A.S., Borovikov, A.A., Zhitova, L.M., Pavlova, G.G., 2006. Composition of magmatogene fluids and factors of their geochemical specialization and metal-bearing capacity. Russian Geology and Geophysics (Geologiya i Geofizika) 47 (12), 1282–1300 (1308–1325). Borisenko, A.S., Borovikov, A.A., Vasyukova, E.A., Pavlova, G.G., Ragozin, A.L., Prokop’ev, I.R., Vladykin, N.V., 2011. Oxidized magmatogene fluids: metal-bearing capacity and role in ore formation. Russian Geology and Geophysics (Geologiya i Geofizika) 52 (1), 144–164 (182–206). Borovikov, A.A., Bul’bak, T.A., Borisenko, A.S., Palesskii, S.V., 2011. Behavior of Au, Sb, Te, As, and Bi in heterophase chloride oxidized fluids

A.A. Borovikov et al. / Russian Geology and Geophysics 56 (2015) 435–445 at 700 ºC in the pressure range of 109–124 MPa: evidence from the study of synthetic inclusions. Dokl. Earth Sci. 437 (1), 349–351. Borovikov, A.A., Dashkevich, E.G., Borisenko, A.S., Gas’kov, I.V., Naumov, V.B., 2012. Metal-bearing magmatic fluids of the Ryabinovyi alkaline massif (Central Aldan), in: Proc. 15th All-Russ. Conf. Thermobarogeochemistry, Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Moscow, 18–20 September 2012 [in Russian]. Izd. IGEM RAN, Moscow, pp. 19–20. Dashkevich, E.G., Borovikov, A.A., Borisenko, A.S., Gas’kov, I.V., 2012. Composition of highly concentrated fluid inclusions in quartz from ore veins of the Samolazovskoe deposit (Central Aldan), in: Proc. 15th All-Russ. Conf. Thermobarogeochemistry, Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Moscow, 18–20 September 2012 [in Russian]. Izd. IGEM RAN, Moscow, pp. 31–32. Ermakov, N.P., 1972. Geochemical Systems of Inclusions in Minerals [in Russian]. Nedra, Moscow. Ishkov, Yu.M., Reif, F.G., 1990. Laser Spectral Analysis of Inclusions of Ore-Bearing Fluids in Minerals [in Russian]. Nauka, Novosibirsk. Günther, D., Heinrich, C.A., 1999. Enhanced sensitivity in laser ablation ICP–mass-spectrometry using helium–argon mixtures as aerosol carrier. J. Anal. Atom. Spect. 14, 1363–1368. Günther, D., Frischknecht, R., Heinrich, C.A., Kahlert, H.-J., 1997. Capabilities of an argon fluoride 193 nm Excimer laser for laser ablation inductively coupled plasma mass spectrometry microanalysis of geological materials. J. Anal. Atom. Spect. 12, 939–944. Günther, D., Audétat, A., Frischknecht, R., Heinrich, C.A., 1998. Quantitative analysis of major, minor and trace elements in fluid inclusions using laser ablation–inductively coupled plasma–mass spectrometry (LA–IC PMS). J. Anal. Atom. Spect. 13, 263–270. Hanley, J.J., Mungall, J.E., Spooner, E.T.C., 2005. Fluid and melt inclusion evidence for platinum-group element transport by high salinity fluids and halide melts below the J–M reef, Stillwater Complex, Montana, U.S.A., in: Ext. Abstr. Xth Int. Platinum Symp. Oulu, Finland, p. 94–97. Heinrich, C.A., Ryan, C.G., Mernagh, T.P., Eadington, P.J., 1992. Segregation of ore metals between magmatic brine and vapor: a fluid inclusion study using PIXE microanalysis. Econ. Geol. 87, 1566–1583. Heinrich, C.A., Günther, D., Audétat, A., Ulrich, T., Frischknecht, R., 1999. Metal fractionation between magmatic brine and vapor, determined by microanalysis of fluid inclusions. Geology 27, 755–758. Heinrich, C.A., Pettke, T., Halter, W.E., Aigner-Torres, M., Audétat, A., Günther, D., Hattendorf, B., Bleiner, D., Guillong, M., Horn, I., 2003. Quantitative multi-element analysis of minerals, fluid and melt inclusions by laser-ablation inductively-coupled-plasma mass-spectrometry. Geochim. Cosmochim. Acta 67, 3473–3497. Heinrich, C.A., Driesner, T., Stefánsson, A., Seward, T.M., 2004. Magmatic vapor contraction and the transport of gold from the porphyry environment to epithermal ore deposits. Geology 32 (9), 761–764. Klemm, L.M., Pettke, T., Heinrich, C.A., Campos, E., 2007. Hydrothermal evolution of the El Teniente Deposit, Chile: porphyry Cu-Mo ore deposition from low-salinity magmatic fluids. Econ. Geol. 102, 1021– 1045. Kogan, V.B., Ogorodnikov, S.K., Kafarov, V.V., 1970. Reference-Book on Solubility. Vol. 3: Ternary and Multicomponent Systems of Inorganic Compounds [in Russian]. Nauka, Leningrad. Kotel’nikova, Z.A., 2008. Method of synthetic fluid inclusions, in: Proc. 13th Int. Conf. Thermobarogeochemistry and Fourth APIFIS Symp. [in Russian]. Izd. IGEM, Moscow, Vol. 2, pp. 265–268. Kovalenker, V.A., Borisenko, A.S., Prokof’ev, V.Yu., Sotnikov, V.I., Borovikov, A.A., Plotinskaya, O.Yu., 2006. Gold-bearing porphyry-epithermal ore-forming systems: mineralogical composition of ores, fluid regime, and factors of large-scale concentration of gold, in: Topical Problems of Ore

445

Formation and Metallogeny. Abstr. Int. Meet., Novosibirsk, 10–12 April 2006 [in Russian]. Akadem. Izd. “Geo”, Novosibirsk, pp. 103–104. Landtwing, M.R., Pettke, T., Halter, W.E., Heinrich, C.A., Redmond, P.B., Einaudi, M.T., Kunze, K., 2005, Copper deposition during quartz dissolution by cooling magmatic-hydrothermal fluids: The Bingham porphyry. Earth Planet. Sci. Lett. 235, 229–243. Longerich, H.P., Jackson, S.E., Günther, D., 1996. Laser ablation inductively coupled plasma mass spectrometric transient signal data acquisition and analyte concentration calculation. J. Anal. At. Spectrom. 11 (9), 899–904. Naumov, V.B., Kovalenker, V.A., Myznikov, I.K., Salazkin, A.N., Mironova, O.F., Savel’eva, N.I., 1995. High-pressure fluids of hydrothermal veins of the Ryabinovyi alkaline massif (Central Aldan). Dokl. Akad. Nauk 343 (1), 99–102. Naumov, V.B., Kamenetsky, V.S., Thomas, R., Kononkova, N.N., Ryzhenko, B.N., 2008. Inclusions of silicate and sulfate melts in chrome diopside from the Inagli deposit, Yakutia, Russia. Geochem. Int. 46 (6), 554–564. Panina, L.I., Motorina, I.V., 2008. Liquid immiscibility in deep-seated magmas and the generation of carbonatite melts. Geochem. Int. 46 (5), 448–464. Prokof’ev, V.Yu., Vorob’ev, E.I., 1991. PT-conditions of formation of Sr–Ba-carbonatites, charoite rocks, and torgolites of the Murun alkaline massif (East Siberia). Geokhimiya, No. 10, 1444–1452. Roedder, E., 1984. Fluid Inclusions. Reviews in Mineralogy. Mineral. Soc. Am., Washington, D.C., Vol. 12. Rusk, B., Reed, M.H., Dilles, J.H., Klemm, L., 2004. Compositions of magmatic–hydrothermal fluids determined by LA–ICP-MS of fluid inclusions from the porphyry copper–molybdenum deposit at Butte, Montana. Chem. Geol. 210, 173–199. Sotnikov, V.I., 2006. Porphyry copper–molybdenum ore association: genesis, dimensions, and boundaries. Russian Geology and Geophysics (Geologiya i Geofizika) 47 (3), 355–363 (355–363). Sotnikov, V.I., Berzina, A.P., Nikitina, E.I., Proskuryakov, A.A., Skuridin, V.A., 1977. Copper–Molybdenum Ore Association (by the Example of Siberia and Adjacent Regions) (Trans. Inst. Geol. Geophys., SB RAS, Issue 319) [in Russian]. Nauka, Novosibirsk. Sourirajan, S., Kennedy, G.C., 1962. The system H2O–NaCl at elevated temperatures and pressures. Am. J. Sci. 260, 115–141. Ulrich, T., Günter, D., Heinrich, C.A., 1999. Gold concentrations of magmatic brines and the metal budget of porphyry copper deposits. Nature 388, 676–679. Ulrich, T., Günther, D., Heinrich, C.A., 2001. The evolution of a porphyry Cu–Au deposit, based on LA–ICP-MS analysis of fluid inclusions: Bajo de la Alumbrera, Argentina. Econ. Geol. 96, 1743–1774. Valyashko, V.M., 2004. Aqueous Systems at Elevated Temperatures and Pressures. Physical Chemistry in Water, Steam and Hydrothermal Solutions. Elsevier Acad. Press, London. Valyashko, V.M., 2009. Hydrothermal equilibria, layering, and heterogenization of supercritical fluids, in: Modern Problems of General and Inorganic Chemistry. Proc. Second Int. Conf., Moscow, 19–21 May 2009 [in Russian]. Izd. IONKh RAN, Moscow, pp. 491–500. Valyashko, V.M., Urusova, M.A., 2010. Heterogenization of supercritical fluids and nonvariant critical equilibria in ternary mixtures with one volatile (by the example of water–salt systems). Sverkhkriticheskie Flyuidy: Teoriya i Praktika, No. 2, 28–44. Williams-Jones, A.E., Heinrich, C.A., 2005. Vapor transport of metals and the formation of magmatic–hydrothermal ore deposits. Econ. Geol. 100 (7), 1287–1312. Zdanovskii, A.B., Solov’eva, E.F., Ezrokhi, L.L., Lyakhovskaya, E.I., 1961. Reference-Book of Experimental Data on Solubility of Salt Systems. Binary Systems, Elements of Group I and Their Compounds [in Russian]. Goskhimizdat, Leningrad, Vol. 3, pp. 1275–2224.

Editorial responsibility: A.E. Izokh