Laser-Ablation ICP-MS analyses of melt inclusions from an ore-forming volcanic system suggest, that melts and fluids responsible for porphyry-type mineralisation are extracted from the boundary layer of a crystallising magma chamber. During boundary-layer fractionation, Cu is partitioned into a sulphide melt, which is later de-stabilised by a fluid phase.

Experiments were conducted to determine the extent and mechanism by which the composition of quartz-hosted silicate melt inclusions (SMI) and aqueous fluid inclusions (FI) can undergo post-entrapment modification via diffusion. Quartz slabs containing assemblages of SMI and FI were reacted with synthetic HCl bearing and metalliferous aqueous fluids at T=500–720°C and P=150–200MPa. SMI from the single inclusion assemblages were analyzed by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) and electron probe microanalysis (EPMA) before and after the experiments. Analyses revealed that rapid diffusion of the univalent cations Na+, Li+, Ag+, Cu+ and H+ occurred through the quartz from the surroundings, resulting in significant changes in the concentrations of these elements in the inclusions. Concentrations of other elements with an effective ionic radius larger than that of Ag+, or multiple valence states were not modified in the inclusions during the experiments. Our results warn inclusion‘‘ researchers that the interpretation of Na, Li, Cu and Ag concentrations from quartz-hosted SMI and FI should be treated critically.

Fluid iuclusions in the subeconomic porphyry Cu-Mo-Au system at Nevados de Famatina and closely associated high-sulfidation epithermal Cu-Au-(Ag-As-Sb-Te) veins at La Mejicana, northwest Argentina, were studied to reconstruct the evolution of hydrothermal fluids front their deep magmatic source to the shallow epithermal euvironment. Field geology vein petrography, fluid inclusion microthermometry, and single-inclusion microanalysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) were combined to determine the evolution of pressure, temperature, and ore metal concentrations in the fluids. Cathodoluminescence imaging complements transmitted light petrography to constrain the successive stages of quartz formation and the entrapment sequeuce of the fluid inclusion populations.Aqueous liquid inclusions of similar to 5 wt percent NaCl equiv salinity trapped in quartz-sericite-pyrite (QSP) veins between 360 degrees aud 325 degrees C contain unusually high concentrations of Cu (400-5,000 ppm), As (similar to 200 ppm), Sb aud Te (both up to 100 ppm), aud Au (several ppm) along with other ore-forming elements. These veins are paragenetically transitional between subeconomic porphyry copper mineralization exposed in the valley floor, and high-sulfidation epithermal veins with high Au grades, which are preserved along a high ridge adjacent to the porphyry, stock. Low-density vapor aud hypersaline liquid (i.e., brine) inclusions were trapped in early-formed quartz of the porphyry stockwork veins, between 450 degrees and > 600 degrees C. The brine contains lower Cu and Au concentrations than coexisting vapor inclusions and texturally even earlier inclusions of intermediate density that are trapped ill phenocrysts aud some stockwork veins; the latter may be equivalent to a parental fluid. The low- and intermediate-density fluids compositionally overlap in salinity with the aqueous liquids recorded by the later transitional quartz-sericite-pyrite veins.Fluid inclusions and geologic time relations indicate that the transitional quartz-sericite-pyrite veins were the channelways for metal-rich aqueous liquids that generated the high-sulfidation epithermal Cu-Au deposit. These mineralizing liquids are interpreted to have evolved by continuous density increase ("contraction") from a low-salinity, S-rich magmatic fluid of low to intermediate density. This vaporlike fluid was produced by exsolution from a magma that existed at greater depth during the late stages of cooling of the magmatic-hydrothermal complex, and probably underwent minor brine separation prior to reaching the present level of exposure. Epithermal mineral precipitation occurred upon dilution of the low-salinity magmatic fluid with meteoric water, which entered the hydrothermal system its it was cooled aud successively eroded during continued magmatic fluid ascent.

Silicate melt inclusions have been analyzed in co-crystallized plagioclase, olivine and clinopyroxene in a typical arc-reiated basaltic-andesite from the Villarrica volcano (Chile). The melt inclusions show identical compositions with respect to most major and trace elements in all host minerals. However plagioclase hosted melt inclusions are variably enriched in Cu (up to similar to 4800 ppm) and Ag (up to similar to 950 ppb). We interpret the elevated Cu and Ag concentrations to be the result of heterogeneous entrapment of silicate melt with a sulfur-rich, chlorine-poor high-temperature magmatic vapor phase in which Cu and Ag were strongly compatible. This assumption is supported by the presence of individual Cu-rich vapor inclusions in some plagioclase crystals. Such a magmatic vapor phase may play a significant role in the transport of S, Cu and Ag within or between magmatic reservoirs and, consequently, in the formation of porphyry-type ore deposits. (C) 2009 Elsevier B.V. All rights reserved.

Analyses of co-existing silicate melt and fluid inclusions, entrapped in quartz crystals in volatile saturated magmatic systems, allowed direct quantitative determination of fluid/melt partition coefficients. Investigations of various granitic systems (peralkaline to peraluminous in composition, log fO2 = NNO−1.7 to NNO+4.5) exsolving fluids with various chlorinities (1–14 mol/kg) allowed us to assess the effect of these variables on the fluid/melt partition coefficients (D). Partition coefficients for Pb, Zn, Ag and Fe show a nearly linear increase with the chlorinity of these fluid (DPb ∼ 6 ∗ mCl, DZn ∼ 8 ∗ mCl, DAg ∼ 4 ∗ mCl, DFe ∼ 1.4 ∗ mCl, where mCl is the molinity of Cl). This suggests that these metals are dissolved primarily as Cl-complexes and neither oxygen fugacity nor the composition of the melt affects significantly their fluid/melt partitioning. By contrast, partition coefficients for Mo, B, As, Sb and Bi are highest in low salinity (1–2 mol/kg Cl) fluids with maximum values of DMo ∼ 20, DB ∼ 15, DAs ∼ 13, DSb ∼ 8, DBi ∼ 15 indicating dissolution as non-chloride (e.g., hydroxy) complexes. Fluid/melt partition coefficients of copper are highly variable, but highest between vapor like fluids and silicate melt (DCu ⩽ 2700), indicating an important role for ligands other than Cl. Partition coefficients for W generally increase with increasing chlorinity, but are exceptionally low in some of the studied brines which may indicate an effect of other parameters. Fluid/melt partition coefficients of Sn show a high variability but likely increase with the chlorinity of the fluid (DSn = 0.3–42, DW = 0.8–60), and decrease with decreasing oxygen fugacity or melt peraluminosity.

By combining both isothermal and rate heating experiments, structural relaxation times were determined in the glass transition range with in situ, high-temperature Raman spectroscopy. The obtained relaxation times agree well with the shear relaxation times obtained from viscosity data. Thus, the time scale for viscous flow is the same as the time scale of the rearrangement of the silicate network structure toward chemical equilibrium. This demonstrates that Si---O bond breaking is the primary control on silicate melt viscosity.

The use of a Carr–Purcell–Meiboom–Gill (CPMG) echotrain to increase the 29Si NMR sensitivity in glasses was investigated. The echo intensity decay follows a stretched exponential behavior M(t)=M0 exp[−(t/t2)β] with values for the exponent β in the range of 0.41–0.65. The signal to noise in the spectra can be increased by a factor of up to 4 by taking the weighted sum of the spectra obtained from the individual echoes. However, differential T2 relaxation for the different Qn species is observed, with a shorter relaxation time for Q4 than Q3. Thus, summing of the echoes leads to distorted spectral intensities and quantitative information can no longer be obtained from the spectra. To circumvent the problem with differential T2 relaxation, an alternative approach is developed in which the spectral intensity for each chemical shift value is determined from the stretched exponential fit to its echo decay. With this approach, the sensitivity can be increased by a factor of up to 2.4, while quantitative information can still be obtained from the spectra. The increased sensitivity permitted the detection of five-coordinated silicon in a potassium silicate glass with natural 29Si abundance at ambient pressure.

A 29Si NMR spectrum with high signal to noise ratio was collected from a well-characterized, isotopically-enriched SiO2 glass with a single scan after full relaxation of the magnetization. From the spectrum, the average Si–O–Si bond angle was estimated at 150° with a minimum fwhm of the bond angle distribution of 16°. The 29Si spin-lattice relaxation times were measured by saturation recovery and differential T1 relaxation was observed for the various Si environments.

In situ, high-temperature Raman spectroscopy was used to study the Qn speciation in binary Nasilicate glasses and melts. Over 300 Raman spectra in the compositional range from 25 to 40 mol% Na2O were collected at room and high temperatures between 800 and 1200 K. Quantitative information on the relative abundances of species in melts was obtained from the Raman spectra through a quantification procedure that does not require any a priori assumptions about the line shapes or external calibration of the Raman scattering efficiencies for the various Qn species. The ΔH° associated with the speciation reaction 2Q3 = Q4 + Q2 was found to be 20.3 ± 7.9 kJ/mol. For a given temperature, the speciation is more disordered in sodium than in potassium silicate melts. Because of the smaller temperature dependence of the speciation in the sodium silicate system, the difference in the speciation for the sodium and potassium silicate system decreases with increasing temperature. In addition to the speciation data, the partial Raman spectra for the different species were obtained. The experimentally observed variation of the partial Raman spectra with temperature, and, to a minor extent, with composition, should stimulate future theoretical studies on the vibrational properties of silicate glasses and melts.

In situ, high-temperature Raman spectroscopy was used to study the Qn speciation in binary potassium silicate melts. Over 300 Raman spectra in the compositional range from 20 to 38mol% K2O were collected at temperatures between 800 and 1200K. Quantitative information on the relative abundances of species in melts was obtained from the Raman spectra through a quantification procedure that does not require any a priori assumptions about the line shapes or external calibration of the Raman scattering efficiencies for the various Qn species. The ΔH0 associated with the speciation reaction 2Q3 =Q4 +Q2 was found to be 33.1±7.3kJ/mol.

A mathematical approach was developed to interpret Raman spectra of binary silicate glasses and melts without the necessity of external calibration, e.g., from NMR spectroscopy. The developed approach is based on Principal Component Analysis (PCA), linear combinations of partial Raman spectra and a linear optimization technique. In order to apply and to test this approach, we developed an experimental method to collect a large number of Raman spectra efficiently. We applied the quantification and the experimental approaches to investigate potassium silicate glasses with compositions from 17.4 to 38mol% K2O. The equilibrium constant for the reaction 2Q3⇄Q2+Q4 was found logK3=−2.37±0.07, in excellent agreement with NMR studies for the same glasses.

Many modern seafloor tectonic environments are host to hydrothermal systems and associated polymetallic sulfide deposits. Metal transport and precipitation are controlled by magmatic processes such as pre-eruptive degassing and the hydrothermal cycle. The original availability of Pb and other ore metals in a given setting is dependent on concentrations in the original magmatic source or additional enrichment processes. We have examined the Pb budget of melt inclusions from nine modern seafloor settings representing back-arcs, mid-ocean ridges and seamounts. Melt inclusions provide information on the characteristics of parental magmas, including insights into metal budgets. Trace element data in melt inclusions hosted in plagioclase, olivine and pyroxene were obtained by laser-ablation inductively-coupled mass-spectrometry. Results from back-arcs emphasize the impact of slab-subduction and dehydration processes on the chemical characteristics of generated magmas. Volatile- and fluid-mobile element-rich melt inclusions at Manus basin and Okinawa trough reflect a robust contribution of elements from the subducting slab as evidenced by relatively low Ce/Pb ratios. At Bransfield strait, on the other hand, melt inclusions are volatile poor, and fluid-mobile element ratios are similar to mid-ocean ridge values indicating little or no contribution from the slab. High Cu concentrations at Manus basin and Okinawa trough can be explained by fluxing of ferric iron from the subducting slab benefiting the production of sulfate over sulfide. Metal budgets for seamounts located on and nearby the axis of mid-ocean ridge segments appear to be independent of any input of mantle plume material. Results from the southern Explorer ridge (strong lower mantle influence, transitional- and enriched-MORBs), Pito and Axial seamounts (moderate lower mantle influence, transitional-MORBs) and a Foundation near-ridge seamount (little to no mantle influence, normal-MORB) show that, despite similar tectonic environments and varying contributions of mantle plume material, Cu, Zn and Pb values do not vary significantly between the enriched and non-enriched magma components of a given setting.

The mine wastes and their environmental impact described in this paper are related to a skarn-type ore deposit, located in the Variscan crystalline basement of the Aiguilles Rouges Massive, Western Switzerland. The main minerals of the deposit are arsenopyrite, lollingite, hematite, scheelite, magnetite, pyroxene, amphibole and dolomite. The ore has been mined for arsenic and gold between 1900 and 1928, producing about 700 1 As and 55 kg An, and leaving mine dumps of several hundred in 3, situated on a relatively steep hill above the small Lake Ottans, at an altitude of 2200 m. This work was undertaken to determine the extent of the As-contamination, its environmental impact and to identify actual geochemical processes. Dump materials contain As and sulfur in the 10% range, contaminated soils contain between 50 mg/kg and several % As. Mine and dump percolating waters are weakly mineralized of the Ca-Mg-HCO3-SO4-type and have conductivities between 20 and 170 mu S/cm, pH values around 8, and As contents varying from 60 to 4000 mu g/l. Waters below the dump zone are of the same type and have slightly lower As-contents: in Lake Ottans, 200 m below the mine area, As is still between 100 and 160 mu g/l. Our results indicate that: (1) the contaminated area is limited to about 500 m in radius (1.2 km(2)) and that its environmental impact is rather limited, except for grazing cattle, (2) below the mine, the As decreases more rapidly in the soils than in the waters, (3) the distribution of the As seems to be determined by predominant alkaline pH in the surface and ground waters and by the distribution of the secondary solid phases (Fe-oxyhydroxides, clays, carbonate minerals, especially in the lower part). Transport by gravity creep or as suspended particles in water seems to be of secondary importance. (c) 2007 Elsevier B.V. All rights reserved.

The conventional model of leaching volcanic rocks as a source of metals in a seafloor hydrothermal systems has been tested by examining the behavior of Pb and other trace elements during hydrothermal alteration. ODP Leg 193 drill sites 1188 (Snowcap) and 1189 (Roman Ruins) on Pual Ridge in the eastern Manus Basin offshore eastern Papua New Guinea provide a unique three-dimensional window into an active back-are hydrothermal system. We investigate by means of a LA-ICP-MS microbeam technique the capacity of Pb to be leached from a host volcanic rock exposed to various types and intensities of alteration. Our results are in general agreement with previous studies that utilized bulk analytical techniques but provide a more detailed explanation of the processes.Fresh representative dacitic lavas from the Pual Ridge have an average whole rock Pb content of 5.2 ppm, an average interstitial glass Pb content of 5.6 ppm and an average plagioclase Pb content of 1.0 ppm. Altered matrix samples have highly variable Pb values ranging from 0 to 52.4 ppm. High Pb values in altered samples are associated with a low temperature chlorite and clay mineral assemblage, in some cases overprinted by a high temperature (up to 350 degrees C) silica-rich "bleaching" alteration. Only the most highly altered matrix samples have REE patterns that differ from the fresh Pual Ridge dacite. This may represent either different lava histories or alteration characteristics that have affected normally immobile REEs. Altered samples with the highest Pb values have similar REE patterns to those of the local unaltered lavas. They are compositionally similar to typical Pual Ridge dacites indicating a genetic relationship between the main regional volcanic suite and the sub-seafloor hydrothermally altered, Pb-enriched material.Relative loss/gain for Pb between the analyzed altered samples and a calculated precursor show a maximum relative gain of 901%. Samples with relative Pb gain from both drill sites are associated with lower temperature alteration mineral assemblages characterized by pervasive chloritization. The related lower temperature (220-250 degrees C) neutral to slightly acidic fluids have been ascribed by others to return circulation of hydrothermal fluids that did not interact with seawater. Because altered samples have a higher Pb content than the fresh precursor, leaching of fresh volcanic rocks cannot be the source of Pb in the hydrothermal systems. (C) 2007 Elsevier Ltd. All rights reserved.

The structure of 21 binary potassium, rubidium and cesium silicate glasses (in the range 15–50mol% alkali oxide) was analyzed by 29Si single quantum and double quantum MAS NMR spectroscopy. Their glass transition temperatures (Tg) were measured by calorimetry. The chemical shifts and the relative abundance of Qn species correlate with the cationic field strength (Z/r) of the network modifier. A correlation is observed between Tg and the inverse of the entropy of mixing of the different Qn species, which is explained in the framework of the Adam–Gibbs relaxation theory. At high alkali content, up to 44% of the SiO4 tetrahedra are part of three-membered rings. At a given alkali content, the abundance of these rings increases with increasing cation size. The abundance of three-membered rings in K-silicate melts correlates with a temperature and a non-linear composition dependence of the heat capacity. It is also a possible cause for the anomalous volumetric behavior of potassium silicate glasses.

Olivine-clinopyroxenite xenoliths exhumed in alkali basalts (sensu lato) in the Nograd-Gomor Volcanic Field (NGVF), northern Hungary, contain abundant silicate melt inclusions. Geothermobarometric calculations indicate that these xenoliths crystallized as cumulates in the upper mantle near the Moho. These cumulate xenoliths are considered to represent a Period of Moho underplating by mafic alkaline magmas prior to the onset of Late Tertiary alkaline volcanism in the Carpathian-Pannonian region. The major and trace element compositions of silicate melt inclusions in olivine display an evolutionary trend characterized by a strong decrease in CaO/Al2O3. The parental melt of the cumulates was a basanite formed by low-degree (similar to 2%) partial melting of a garnet peridotite source. The compositional trend of the silicate melt inclusions, textural features, and modelling with pMELTS show that the parental melt evolved by major clinopyroxene and minor olivine crystallization followed by the appearance of amphibole simultaneously with significant resorption of the earlier clinopyroxene and olivine. The resulting residual melt was highly enriched in Al2O3, alkalis and most incompatible trace elements. This type of melt is likely to infiltrate and react with surrounding mantle peridotite as a metasomatic agent. It might also form high-pressure pegmatite-like bodies in the mantle that might be the source of the amphibole and sanidine megacrysts also found in the alkali basalts of the NGVF. Preferential remelting of the later formed (i.e. lower temperature) mineral assemblage (amphibole, sanidine, residual glass) might have significantly contaminated the host alkaline mafic lavas, increasing their Al2O3 and total alkali contents and, therefore, reducing their MgO, FeO and CaO content.

In this paper we study a real-world optimization problem in mineralogy which contains a large number of parameters and several objective functions. The problem has been described through a thermodynamic model for which the parameters have to be quantified. Due to non-linear chemical reactions and the characteristics of the problem, we developed a Bilevel Optimization approach in which the parameters that need to be determined can be split in two levels. The lower level contains three non linear equations and two linear charge and mass balance constraints. We use Linear Multi-Objective Particle Swarm Optimization (LMO PSO) to solve this problem for a general case. We then use the results in the upper level. This Bilevel Optimization has been used to find the thermodynamic parameters of the Na2O-SiO2 system. The results are analytically analyzed and compared with the reference data. This shows that the thermodynamic model is accurate and that the termination of thermodynamic properties using a Bilevel Optimization method based on PSO algorithms is reliable and efficient.