Retrograde Solubility Research Articles

The Bingham Canyon Porphyry Cu-Mo-Au Deposit. III. Zoned Copper-Gold Ore Deposition by Magmatic Vapor Expansion

Fluid inclusion microthermometry and laser-ablation ICPMS microanalysis are combined with geological and textural observations to reconstruct the spatial and temporal evolution of magmatic fluids that formed the subvolcanic porphyry Cu-Au(-Mo) ore deposit at Bingham Canyon, Utah. The Bingham Canyon orebody is exposed over ~1.6 km vertically and has the shape of an inverted cup with distinct metal zoning. Fluid inclusions in the barren but highly veined and potassically altered deep center of the system have intermediate density (~0.6 g cm−3) and a salinity of ~7 wt percent NaCl equiv. They have subequal concentrations of Na, K, Fe, and Cu and contain minor CO2. The intermediate-density fluids were trapped as a single phase, mostly at >500°C and >800 bars. The Au-Cu-rich center near the top of the orebody contains low-density vapor inclusions (~0.2 g cm−3) coexisting with brine inclusions containing ~45 wt percent NaCl equiv. The vertical transition of different inclusion types indicates phase separation of the single-phase input fluid upon volume expansion associated with a pressure drop to 200 ± 100 bars. Mass-balance calculation based on all analyzed inclusion components indicates that the mass of the vapor phase exceeded that of the brine by ~9/1. The vapor contained Cu as its dominant cation (~1.5 wt %) and contributed about 95 percent of the total amount of copper transported to the base of the orebody. Bornite, chalcopyrite, and native gold were precipitated in a narrow temperature interval from 430° to 350°C, into secondary pore space created by local redissolution of vein quartz as a result of retrograde quartz solubility in the vapor-dominated fluid system. Intermediate-density fluid inclusions in the deepest parts of the peripheral copper ore zone have identical density and composition, including similar gold contents, as those in the deep center. Microthermometry and statistical estimation of phase proportions in the inclusions show that the vapor in the peripheral Cu-rich but Au-poor ore zone remained denser, and the separating brine was less saline (~36 wt % NaCl equiv), compared to vapor and brine in the central Au-Cu ore zone. This indicates that the peripheral fluids experienced a lower degree of phase separation, due to slightly higher fluid pressure at equivalent temperature, compared to more strongly expanding fluids in the center of the system. The systematic zoning of Au/Cu within the ore shell, despite compositionally similar input fluids, is interpreted to have resulted from slightly different pressure-temperature-density evolution paths of magmatic fluids. Copper was selectively precipitated in the peripheral ore zone, in contrast to complete coprecipitation of Au and Cu in the central upflow zone of the vapor plume. The formation of particularly rich Cu-Au ore in the center of the upward-expanding fluid plume is consistent with published experimental data, showing that the solubility of metals in hydrous vapor decreases sharply with falling pressure, due to destabilization of the hydration shell around metal complexes in expanding vapor. This interpretation supports the classic vapor plume model for porphyry copper ore formation but additionally emphasizes the role of sulfur-bearing complexes as a key chemical control on magmatic-hydrothermal metal transport and the deposition of Cu and Au in porphyry ores. Our interpretation of selective Cu ± Au precipitation as a function of vapor density can explain the more general observation that most gold-rich porphyry copper deposits are formed in shallow sub-volcanic environments, whereas deeper seated porphyry Cu-(Mo) deposits are generally gold poor.

Effects of host mineral re‐equilibration during uplift and cooling on the fidelity of primary hydrothermal fluid inclusions: a theoretical example using Mississippi Valley‐type ore fluids

AbstractAt the moment of its trapping as a primary fluid inclusion, a hydrothermal fluid is typically at or near equilibrium with multiple mineral species at depth and temperature. After trapping, however, the isolated inclusion fluid can re‐equilibrate only with its own host mineral species during later uplift and cooling to surface conditions. Because the solubility versus temperature behavior is unique for each host mineral species, identical inclusions trapped at the same time within different species may re‐equilibrate in a disparate manner upon cooling and become variably less representative of the original trapped fluid once they reach ambient temperature. To test the significance of this effect, a series of theoretical equilibrium reaction models was constructed in which a trapped hydrothermal fluid characteristic of Mississippi Valley‐type ore deposits is cooled in contact with silicate, sulfide and carbonate hosts, respectively, from 100 to 25°C. Dissolved base metal concentrations are predicted to decline by two to four orders of magnitude in inclusions in all hosts, due to the precipitation of optically undetectable masses of sulfide daughter minerals. Fluids in the calcite host show the greatest decline in dissolved base metals upon cooling, due to its retrograde solubility and consequent shift in the pH and aqueous C speciation of the fluid. δ13C values for CO2 in all hosts become depleted by 2–7‰ relative to the original trapped fluid, with depletions again being the greatest for the calcite host due to its retrograde dissolution. Analytical techniques that extract and analyze the complete contents of fluid inclusions at room temperature can account for the predicted precipitation of microscopic daughter minerals during cooling, but may not compensate for chemical changes caused by the retrograde dissolution of calcite. Such solubility effects are another reason to be cautious in using carbonate minerals for fluid inclusion studies, in addition to their undesirable physical properties of softness, deformability and perfect cleavage.

Controlling Low Temperature Aqueous Synthesis of ZnO. 1. Thermodynamic Analysis

A thermodynamic model based on published data is presented for calculating the solubility and speciation of ZnO in aqueous solutions as a function of pH, ammonia concentration, and temperature. These calculations are used to explain how solubility and speciation control nucleation and growth behavior from an aqueous solution. The nucleation and growth behavior, in turn, can lead to the different morphologies of epitaxial and particulate ZnO obtained experimentally using low temperature aqueous methods. The calculations indicate that the presence of the zinc amine complex, Zn(NH3)42+, causes ZnO to display a substantial decrease in solubility when the temperature is raised from room temperature to 90 °C. This retrograde solubility is the basis for a novel continuous circulation reactor for synthesizing ZnO, which is presented in part 2 of this series.

NMR study of the cataract-linked P23T mutant of human γD-crystallin shows minor changes in hydrophobic patches that reflect its retrograde solubility

The Pro23 to Thr (P23T) mutation in human γD-crystallin (HGD) shows several cataract phenotypes. We found earlier [A. Pande, O. Annunziata, N. Asherie, O. Ogun, G.B. Benedek, J. Pande, Decrease in protein solubility and cataract formation caused by the Pro23 to Thr mutation in human gamma D-crystallin, Biochemistry 44 (2005) 2491–2500] that the mutation dramatically lowers the solubility of P23T but the overall protein fold is maintained. Recently we observed that solutions of P23T showed liquid–liquid phase transition behavior similar to that of HGD but the liquid–protein crystal phase transition was altered, suggesting an asymmetric distribution of “sticky” patches on the protein surface [J.J. McManus, A. Lomakin, O. Ogun, A. Pande, M. Basan, J. Pande, G.B. Benedek, Altered phase diagram due to a single point mutation in human gammaD-crystallin, Proc. Natl. Acad. Sci. USA 104 (2007) 16856–16861]. Here we present high-resolution NMR studies of HGD and P23T in which we have made nearly complete backbone assignments. The data provide a structural basis for explaining the retrograde solubility of P23T by (a) identifying possible “sticky” patches on the surface of P23T and (b) highlighting their asymmetric distribution.

Using Laboratory Flow Experiments and Reactive Chemical Transport Modeling for Designing Waterflooding of the Agua Fria Reservoir, Poza Rica-Altamira Field, Mexico

Summary Waterflooding for enhanced oil recovery requires that injected waters must be chemically compatible with connate reservoir waters, in order to avoid mineral dissolution-and-precipitation cycles that could seriously degrade formation permeability and injectivity. Formation plugging is a concern especially in reservoirs with a large content of carbonates, such as calcite and dolomite, as such minerals typically react rapidly with an aqueous phase, and have strongly temperature-dependent solubility. Clay swelling also can pose problems. During a preliminary waterflooding pilot project, the Poza Rica-Altamira oil field, bordering the Gulf coast in the eastern part of Mexico, experienced injectivity loss after 5 months of reinjection of formation waters into Well AF-847 in 1999. Acidizing with hydrochloric acid (HCl) restored injectivity. We report on laboratory experiments and reactive-chemistry modeling studies that were undertaken in preparation for long-term waterflooding at the Agua Fría reservoir. Using analogous core plugs obtained from the same reservoir interval, laboratory core-flood experiments were conducted to examine the sensitivity of mineral-dissolution and -precipitation effects to water composition. Native reservoir water, chemically altered waters, and distilled water were used, and temporal changes in core permeability, mineral quantities, and aqueous concentrations of solutes were monitored. The experiments were simulated with the multiphase, nonisothermal reactive transport code TOUGHREACT™ (Lawrence Berkeley National Laboratory, Berkeley, California, 2004), and reasonable-to-good agreement was obtained for changes in solute concentrations. Clay swelling caused an additional impact on permeability behavior during coreflood experiments, whereas the modeled permeability depends exclusively on chemical processes. TOUGHREACT was then used for reservoir-scale simulation of injecting ambient-temperature water (30°C, 86°F) into a reservoir with initial temperature of 80°C (176°F). Untreated native reservoir water was found to cause serious porosity and permeability reduction because of calcite precipitation, which is promoted by the retrograde solubility of this mineral. Using treated water that performed well in the laboratory flow experiments was found to avoid excessive precipitation and allowed injection to proceed.

Effect of Solvent on the Phase Diagram of a Simple Anisotropic Model of Globular Proteins

Anisotropic protein interactions play a role in globular protein phase transitions, including the shape of fluid-fluid coexistence curves and the formation of hemoglobin polymer fibers in sickle cell disease. Also, the solvent has been shown to play an important role in the phase behavior of some aqueous protein solutions, through the release or trapping of water molecules upon crystallization. Both anisotropy and solvent effects have been treated separately in earlier theoretical studies. Here we propose and analyze a simple, composite model that treats both anisotropy and solvent effects. We find that this model qualitatively explains some phase behavior that has been observed in protein solutions, including normal and retrograde solubility curves and lower critical points.

Seeded growth of GaN by the basic ammonothermal method

Two preliminary experiments are reviewed and seeded growth of GaN is updated in this paper. In a mineralizer study, it was shown that basic mineralizers promoted synthesis of wurtzite GaN. Through a dissolution study of polycrystalline GaN in basic supercritical ammonia, it was confirmed that GaN has retrograde solubility. A GaN film as thick as 45 μm was obtained in seeded growth from metallic Ga nutrient. Uniform growth of GaN over a 3×4 cm 2 oval-shaped seed crystal was also demonstrated. Seeded growth of GaN from polycrystalline GaN nutrient was attempted to avoid growth saturation problem in Ga nutrient. Extended growth up to 11 days was attained with increased mineralizer concentration. The cross-sectional TEM observation showed high density of voids and defects at the growth interface, although most of them did not propagate to the top surface. The estimated threading dislocation density was at the order of low–10 9 cm −2 and no evidence of basal plane stacking fault was observed.

Dissolution of biogenic ooze over basement edifices in the equatorial Pacific with implications for hydrothermal ventilation of the oceanic crust

Recent observations indicate that curious closed depressions in carbonate sediments overlying basement edifices are widespread in the equatorial Pacific. A possible mechanism for their creation is dissolution by fluids exiting basement vents from off-axis hydrothermal flow. Quantitative analysis based on the retrograde solubility of calcium carbonate and cooling of basement fluids during ascent provides an estimate for the dissolution capacity of the venting fluids. Comparison of the dissolution capacity and fluid flux with typical equatorial Pacific carbonate mass accumulation rates shows that this mechanism is feasible. By maintaining sediment-free basement outcrops, the process may promote widespread circulation of relatively unaltered seawater in the basement in an area where average sediment thicknesses are 300–500 m. The enhanced ventilation can explain several previously puzzling observations in this region, including anomalously low heat flux, relatively unaltered seawater in the basement, and aerobic and nitrate-reducing microbial activity at the base of the sediments.

TIM: a model protein for the study of crystal growth in space and gels

The understanding of the basic processes underlying the crystallisation of proteins requires the use of very well-characterised model systems, for which theory and models of crystal growth can be verified experimentally. Triose phosphate isomerase (Tm TIM) [1] can be produced in large amounts, and crystallises reproducibly. It has been used for experiments in microgravity and in gels, and it has been shown to produce crystals of marked improvement in these non-convective environments. It is thus an interesting model protein for studying the effect of convective mixing on protein crystallisation. We present here the phase diagrams for Tm TIM in function of temperature, protein, and precipitant concentration, and relate the results with the observed crystallisation behaviour. Solubility curves and the binodal curve in function of these tree parameters show that Tm TIM is a case of ‘retrograde solubility’. This phenomenon has been observed in many cases but only been described in detail in the case of human hemoblobin [2]. The phase diagrams form the basis for the understanding of the results from counterdiffusion experiments with Tm TIM, including improved crystal quality, and polymorfic variation in function of growth conditions.

Computer assisted analysis of diffuse electron diffraction of precipitates in GaAs

The single crystal growth of GaAs for epitaxial substrates is inseparably correlated with the formation of As precipitates of some nanometers in diameter due to retrograde solubility during cooling of the crystal to room temperature. These precipitates are the origin of diffuse scattering observed as weak lines in transmission electron diffraction (TED) pattern (see Fig. (A)). In order to thoroughly understand the structural characteristics of the precipitates computer simulations of the TED patterns were performed. Simulations were carried out via two different approaches. In a first simplified assumption 2-dimensional projections of the structure along [111] and [110] were considered. For the evaluation of the agreement between structure model and experimental findings the Fourier transform of the projected positions of the atoms was calculated. The regular positions of the atoms of the sphalerite structure are depicted as grey dots in Fig. (B). The Fourier spectrum clearly exhibits intensity maxima at positions expected for the perfect crystal (see Fig. (C)). In order to generate the diffuse lines in the Fourier spectrum interstitial atoms have to be incorporated. With respect to the ratio of its ionic radii, Ga and As are preferentially incorporated on a 4-fold coordinated site. But, an agreement is found only for the arrangement of interstitials as given in Fig. (B) as black dots. These positions are either the 3-fold or 2-fold coordinated ones which are not distinguishable in this projection. For visualization of the two-dimensional arrangement, the interstitial atoms were connected by lines not contributing to the Fourier spectrum. In addition to this first approach, simulations of the TEDpattern basing on three-dimensional models structurally relaxed by molecular dynamics calculations will be discussed. The findings of the computer simulations will be verified by comparison with results of high-resolution transmission electron microscopy (HRTEM) as well as high-angle annular dark-field scanning TEM (HAADF STEM).

Quantitative characterization of aperiodic nanostructures: the advantage of using electrons

The single crystal growth of GaAs for epitaxial substrates is inseparably correlated with the formation of As precipitates of some nanometers in diameter due to retrograde solubility during cooling of the crystal to room temperature. These precipitates are the origin of diffuse scattering observed as weak lines in transmission electron diffraction (TED) pattern (see Fig. (A)). In order to thoroughly understand the structural characteristics of the precipitates computer simulations of the TED patterns were performed. Simulations were carried out via two different approaches. In a first simplified assumption 2-dimensional projections of the structure along [111] and [110] were considered. For the evaluation of the agreement between structure model and experimental findings the Fourier transform of the projected positions of the atoms was calculated. The regular positions of the atoms of the sphalerite structure are depicted as grey dots in Fig. (B). The Fourier spectrum clearly exhibits intensity maxima at positions expected for the perfect crystal (see Fig. (C)). In order to generate the diffuse lines in the Fourier spectrum interstitial atoms have to be incorporated. With respect to the ratio of its ionic radii, Ga and As are preferentially incorporated on a 4-fold coordinated site. But, an agreement is found only for the arrangement of interstitials as given in Fig. (B) as black dots. These positions are either the 3-fold or 2-fold coordinated ones which are not distinguishable in this projection. For visualization of the two-dimensional arrangement, the interstitial atoms were connected by lines not contributing to the Fourier spectrum. In addition to this first approach, simulations of the TED pattern basing on three-dimensional models structurally relaxed by molecular dynamics calculations will be discussed. The findings of the computer simulations will be verified by comparison with results of high-resolution transmission electron microscopy (HRTEM) as well as high-angle annular dark-field scanning TEM (HAADF STEM).

Ammonothermal Synthesis of III-Nitride Crystals

Ammonothermal synthesis of nitrides is reviewed, with an emphasis on gallium and aluminum nitrides due to their important applications as direct wide band gap semiconductors. Since the crystallization process of nitrides involves the formation of some intermediate compounds during ammonothermal synthesis where a mineralizer is used, some ternary amides and ammoniates of aluminum and gallium with alkali metals or halides are also reviewed briefly. The ammonothermal crystallization of GaN and AlN bulk crystals, which is analogous to the hydrothermal growth of oxides, is introduced. Retrograde solubility, mineralizers, pressure−temperature−volume−concentration (PTVC) relations, phase relations, and transport growth of GaN in alkaline solutions are discussed in detail. Recent progress of GaN single-crystal growth by the ammonothermal technique is reported. We have grown GaN bulk single crystals up to 10 mm2 by 1-mm thick. Issues such as ammonia breakdown, impurity incorporation, and scale-up of the ammonother...

Attempts to rationalize protein crystallization using relative crystallizability

Protein crystal growth (PCG) remains the bottleneck of crystallography despite many decades of study. The nucleation zone in the two-dimensional-phase diagram has been used to evaluate the relative crystallizability of proteins, which is expressed as a percentage over the phase area delineated by experimental protein and precipitating agent concentration ranges. For protein-salts which are subject to a direct temperature effect on solubility, as represented by Egg Lysozyme, a decrease in temperature augments the nucleation zone percentage whereas for those with retrograde solubility as a function of temperature, for example fructose-1,6-bisphosphatase in the presence and absence of AMP, an increase in temperature can significantly enhance the relative crystallizability. These results have been confirmed by the number of “hits” using PEGs as precipitating agents in Sparse Matrix Screen experiments for different proteins and are in excellent agreement with the relative crystallizability. The relationship between solubility dependence, relative crystallizability and crystallization success, has been evidenced. Such crystallizability can become a guide to identify efficient crystallization regions, providing a rational approach to PCG and structural biology.

High-pressure phase equilibria in binary and ternary mixtures with one near- or supercritical and one high-molecular component. New insights for application and theory

In this work we report on two different high-pressure phase equilibria. The first is the solubility of a low-volatile solid in a supercritical phase. These are two anthraquinone dyes 1,4-bis-(hexadecylamino)-9,10-anthraquinone and 1,4-bis-(dodecylamino)-9, 10-anthraquinone dissolved in CO2 and N2O. Secondly, the partition of an infinitely diluted high-molecular biocompound between coexisting high-pressure liquid phases in a ternary system consisting of a nearcritical gas, water, and an organic solvent, that is a fully miscible with water at standard conditions, is investigated. The high-molecular compounds are two cardiac glycosides digoxin and digitoxin, which occur in the foxglove plant. The corresponding ternary phase-forming system consists of CO2, water, and 1-propanol. The binary solubilities are determined within 310 and 340 K and up to 180 MPa where retrograde solubility is observed. The partitioning experiments are done at 313 and 333 K and at pressures, where a three-phase liquid-liquid-gas equilibrium with one water-like and one propanol-like phase exists. Experimental data are listed and discussed. Additionally, the correlation of the solubility data with a recently developed Carnahan-Starling-van der Waals type equation of state extended for the nearcritical region are discussed. The partitioning data with a hybrid model that combines the Peng-Robinson equation of state with an excess Gibbs energy approach based on UNIQUAC are outlined briefly and the results interpreted.

Modeling of ammonothermal growth of gallium nitride single crystals

Ammonothermal growth of GaN crystals with a retrograde solubility has been modeled and simulated here using fluid dynamics, thermodynamics and heat transfer models. The nutrient is considered as a porous media bed and the flow in the porous charge is simulated using the Darcy-Brinkman-Forchheimer model. The resulting governing equations are solved using the finite volume method. For the case of retrograde solubility, the charge is put above the baffle. The temperature difference between the dissolving zone and growth zone is found smaller than that applied on the sidewall of autoclave. The baffle opening has a strong effect on the nutrient transport and supersaturation of GaN species in the growth zone.

GaN single crystals grown on HVPE seeds in alkaline supercritical ammonia

Ammonothermal growth (synthesis in supercritical (sc) ammonia fluid) has the promise of producing large low defect gallium nitride crystals through the application of techniques similar to those used in hydrothermal growth. Retrograde solubility of GaN greater than 5% by weight using group I amides as mineralizers is demonstrated in high nickel content autoclaves at pressures of one to three kilobars and temperatures between 300 to 600°C. The above conditions were optimized to grow single-crystal GaN at rates up to 40 μm per day on one cm2 seeds. Gallium nitride Hydride Vapor Phase Epitaxy (HVPE) seeds are placed in the higher temperature zone below the nutrient basket employing the same configurations used in reverse gradient hydrothermal growth of berlinite (AlPO4). GaN single crystals grown by the ammonothermal technique were characterized by X-ray diffraction, photoluminescence, scanning electron microscopy (SEM), atomic force microscopy (AFM), and chemical etching. The nitrogen-terminated face tends to exhibita flatter surface morphology than the gallium-terminated face, which is made up of a series of hexagonal columns. Major impurities in the crystal include potassium from the mineralizer, metals from the autoclave, and oxygen. The nitrogen-terminated face incorporated a lower level of metallic impurities in comparison with the gallium-terminated face. Finally, several process phenomena such as ammonia decomposition, parasitic nucleation of GaN on the autoclave walls, impurity incorporation, and defect generation in single-crystal GaN layers grown on HVPE seeds are identified and their possible mechanisms are discussed.

Vapor pressure scanning of non-stoichiometry in Cd 0.9Zn 0.1Te 1±δ and Cd 0.85Zn 0.15Te 1±δ

Vapor pressure was measured for the quasi-binary section Cd 1− x Zn x Te of the phase diagram of the ternary system Cd–Zn–Te with x = 0.1 0 and 0.15. From this experiment, P–T– X (pressure–temperature–composition) space arrangement of the solidus was derived, and the vapor pressure scanning method was applied for high-precision determination of non-stoichiometry in Cd 0.9Zn 0.1Te 1± δ and Cd 0.85Zn 0.15Te 1± δ . The solidus volume was shown to be of pronounced asymmetrical shape with retrograde Te solubility. The stoichiometric 50 at% Te plane is contained in the Cd 0.9Zn 0.1Te 1± δ solidus volume, while being completely outside the Cd 0.85Zn 0.15Te 1± δ solidus, on the metal side of it. Phase equilibrium is presented in T– X and P( i)– T projections ( i = Cd , Zn, Te 2) of the phase diagram. These data are crucial for preparation technology of Cd 1− x Zn x Te 1± δ with strictly controlled composition and for high-precision analysis of the matrix elements. From the isoplethal ( X S = const ) sections of the solidus, partial sublimation enthalpies of the main vapor species were estimated.

Ammonothermal growth of GaN crystals in alkaline solutions

A method for the growth of GaN bulk crystals under ammonothermal conditions is described. Gallium nitride is shown to have a retrograde solubility in ammonobasic solutions. Using polycrystalline GaN as nutrient and hydride vapor phase epitaxy GaN templates as seeds, the crystals were grown in the hot zone. The ammonothermal growth experiments were carried out in ammonobasic solutions in high nickel content autoclaves for up to 3 weeks. Growth rates up to 50 μm/day were achieved and single crystals of GaN up to 10×10×1 mm 3 were obtained. The ammonothermal crystals are of high quality, as characterized by optical microscopy, scanning electron microscopy, high-resolution X-ray diffraction and photoluminescence measurements.

Solubility of Lithium Nitrate in Solutions of Lithium Halides

Solubility isotherms in LiNO3 – LiX – H2O (X = Cl, Br, I) systems at 298.15 K were measured for the first time with special regard to the retrograde solubility of lithium nitrate trihydrate. The compositions of solutions used as media in absorption refrigerators and heat pumps were compared with the results and subsequently discussed.

Mechanical graphite transport in fault zones and the formation of graphite veins

AbstractThis paper describes a vein-shaped graphite occurrence in which, for the first time, the geological, mineralogical and isotopic evidence support its formation by physical remobilization of previously formed syngenetic graphite. The deposit studied is located in the Spanish Central System and it occurs along the contact between a hydrothermal Ag-bearing quartz vein and a graphite-bearing quartzite layer. The characteristics of this occurrence differ from those of fluid-deposited vein-type graphite mineralization in that: (1) graphite flakes are oriented parallel to the vein walls; (2) graphite crystallinity is slightly lower than in the syngenetic precursor (graphite disseminated in the quartzite); and (3) the isotopic signatures of both types of graphite are identical and correspond to biogenic carbon. In addition, the P-T conditions of the hydrothermal Ag-bearing quartz veins in the study area (P <1 kbar, and T up to 360°C) contrast with the high degree of structural order of graphite in the vein. Therefore, physical remobilization of graphite can be regarded as a suitable alternative mechanism to account for some cases of vein-shaped graphite deposits. Such a mechanism would require a previous concentration of disseminated syngenetic graphite promoted, in this case, by the retrograde solubility of quartz. This process would generate monomineralic graphite aggregates enhancing its lubricant properties and permitting graphite to move in the solid state along distances in the range of up to several metres.