A New Density Model of Quartz Solubility in H2O-CO2-NaCl Ternary Systems up to High Temperatures and High Pressures

A novel density model for computing quartz solubility in H2O-CO2-NaCl hydrothermal fluids applicable to wide ranges of temperature and pressure is proposed. Based on the models of Akinfiev and Diamond (2009) and Wei et al. (2012), the effective partial molar volume of water ( V H 2 O ∗ ) is replaced by the partial molar volume of water ( V ¯ H 2 O ) by implementing an empirical correction, and water molar fraction ( x H 2 O ) is modified with water activity ( a H 2 O ), in addition to a series of changes to the model coefficient forms. The absolute values of averaged relative deviation of this model compared to the experimental data sets in pure water, H2O-CO2, and H2O-NaCl solutions are 5.74%, 6.69%, and 7.09%, respectively, which are better than existing models in the literature. The model can be reliably used for computing quartz solubilities in pure water from 0°C to 1000°C, from 0 bar to 20,000 bar, and in CO2- and/or NaCl-bearing solutions from 0°C to 1000°C, from 0 bar to 10,000 bar (with slightly lower accuracy at 5000-10,000 bar in H2O-NaCl systems) in the single liquid region. Moreover, the trends and overall ranges of this model may probably be more accurate in the H2O-CO2-NaCl fluid mixtures compared to the limited experimental data. In addition, a bisection algorithm for deriving the isopleths of quartz solubilities based on this new model is first proposed, and application perspectives are discussed for various geologic settings including subduction zone, lower crust-upper mantle, migmatite, pegmatite, porphyry, and orogenic deposits.

Auriferous Quartz Veining Due to CO2 Content Variations and Decompressional Cooling, Revealed by Quartz Solubility, SEM-CL and Fluid Inclusion Analyses (The Linglong Goldfield, Jiaodong)

Quartz is the most common gangue mineral in hydrothermal veins. Coupled with capacities of hosting fluid inclusions and recording varieties of microtextures, its solubility behavior may provide unparalleled insights into hydrothermal processes. In this study, the Linglong goldfield in Jiaodong is targeted to investigate gold-producing quartz veining process. Scanning electron microscope (SEM)-cathodoluminescence (CL) imaging uncovered three episodes of quartz deposition, intervened by an episode of quartz dissolution. Based on newly-developed quartz solubility diagrams and CL-aided fluid inclusion microthermometry, it is proposed that precipitation of the earliest quartz (Qz1) was controlled by CO2 content increase and subordinately affected by decompressional cooling, leading to the formation of the early thick gold-barren veins (V1); the second generation of quartz (Qz2a) was formed by the same fluids that may have been diluted and cooled by meteoric water, leading to a greatly reduced quantity of quartz and the deposition of pyrite and gold; and the third generation of quartz (Qz2b) was deposited along with polymetallic sulfides, due to fluid cooling following a quartz dissolution event likely induced by cooling in retrograde solubility region and/or CO2 content decrease. This research may elucidate gold formation processes in orogenic intrusion—related deposits, and points to imperative CL-based in situ analyses for future studies.

Study of Hydrolization and Sedimantationin Acid Compositions Based on Sulfaminic Acid

This article presents the results of a study of the hydrolysis of sulfamic acid and the elaboration of acidic compositions that are characterized by reduced sedimentation compared to mud acid. The effect of complexing compounds on the hydrolysis of sulfamic acid is considered, the hydrolysis of sulfamic acid and sulfamates is compared, and the secondary sedimentation of sulfamic acid and mud acid compositions is compared using the formation of hexafluorosilicates. The hydrolysis intensity of sulfamic acid and ammonium sulfamate was determined by the mass of sediments formed during the reaction of hydrolysis products with calcium chloride. The mass of calcium sulfate formed is proportional to the rate of hydrolysis of sulfamic acid. The process of dissolution of the quartz component of the terrigenous formation was studied using the gravimetric method. Differences in influence of EDTA, HEDP, and NTP on sedimentation prevention of the products of sulfamic acid hydrolysis were studied by the example of reactions with Ca2+. It was shown that compositions with NTP are characterized by a lower sediments formation. The ratio of NTP concentration and the hydrolysis rate of sulfamic acid is shown. Differences in the hydrolysis rate of compositions based on sulfamic acid and sulfamates were determined at a temperature of 80°C. It was shown that sulfamates are characterized by a lower rate of hydrolysis. Differences in quartz solubility were determined for compositions based on sulfamic and sulfuric acids, differences in the reactions kinetics were shown. It has been established that acid compositions based on sulfamic acid are characterized by less sedimentation rate being compared with acid compositions based on hydrochloric acid by the example of hexafluorosilicates formation.

The Influence of CO2 on the Solubility of Quartz in Single-Phase Hydrothermal Fluids: Implications for the Formation of Stockwork Veins in Porphyry Copper Deposits

Porphyry copper deposits consist of low-grade stockwork and disseminated sulfide zones that contain characteristic vein generations formed during the evolution of the hydrothermal systems. The present contribution examines the influence of variable CO2 concentrations on the solubility of quartz in single-phase hydrothermal fluids forming stockwork veins in porphyry deposits at temperatures of 150° to 550°C and pressures ranging from 100 to 2,000 bar at concentrations up to 8 mol % CO2. The calculations demonstrate that quartz solubility in hydrothermal fluids decreases with increasing CO2 content. Retrograde quartz solubility is less pronounced in CO2-bearing fluids and is not observed in single-phase fluids having CO2 concentrations exceeding 6 mol %. Despite the effects of CO2, retrograde quartz solubility plays an important role in the formation of porphyry stockwork veins that contain little or no quartz as a gangue mineral. At high temperatures and lithostatic pressure conditions below 900 bar, early biotite veins can form as a result of quasi-isobaric cooling of single-phase hydrothermal fluids under conditions of retrograde quartz solubility or near-constant quartz solubility. Stock-work veins consisting of molybdenite or hypogene copper sulfide minerals lacking quartz could form at temperatures of up to 450°C under hydrostatic pressures ranging from ~250 to 900 bar. In the presence of CO2, retrograde quartz solubility is shifted toward slightly lower temperatures at constant pressure. At temperatures below ≾375°C, quartz is precipitated during quasi-isobaric cooling irrespective of CO2 content of the hydrothermal fluids, resulting in the formation of late porphyry quartz veins.