TY - BOOK

T1 - Isotopic and elemental distribution of copper between Cu-bearing minerals and aqueous fluids

T2 - Implications of an experimental study

AU - Qi, Dongmei

PY - 2019

Y1 - 2019

N2 - Transport and deposition of copper in the Earth’s crust are mainly controlled by the speciation of Cu and solubility of Cu-bearing phases in magmatic-hydrothermal fluids. In order to improve our understanding of mobilization of copper by hydrothermal fluids, we conducted experiments with Cu-bearing phases (metallic copper, Cu2O, CuCl) and aqueous solutions (H2O, NaClaq, KClaq, HCl, acetate solutions with/without pH buffer) at 25°C-800°C and 0.1 -200 MPa. The high temperature and high pressure (i.e., 800°C and 200 MPa) experiments were conducted in rapid heat/rapid quench argon cold seal pressure vessel using the synthetic fluid inclusion technique. The experimental charges Cu2Os ± CuCls + H2O ± NaClaq ± HClaq (chloride concentration: 0 to 4.3 mol/kg) were loaded in either Cu or Au capsules. Two types of quartz cylinders were used to trap in-situ hydrothermal fluids: (i) pre-cracked and (ii) intact prior to experiment. Fluid composition was subsequently determined by analyzing individual fluid inclusions using laser ablation inductively coupled plasma mass spectrometry. Two types of inclusions, i.e., fluid inclusion and Na-bearing silicate melt inclusion, have been formed exclusively in metallic Cu-NaCl system. Moreover, micron- to submicron-sized cuprite has been observed in both types of inclusions. In HCl±CuCl-bearing systems, fluid inclusion trapping potential nantokite (CuCl) is observed. The Cu content is strongly enhanced by initial chloride content, and can reach up to 4.3 wt% and 11 wt% in 4.3 m NaCl and 1.9 m HCl solutions, respectively. Fast cooling which is avoided by most researchers shows advantages of preservation of ample inclusions in Cu-NaCl system. In addition, the fluid inclusions after rapid quench (25 K/s) yields much smaller variation of Cu content in comparison to the usually favored slow quench process (0.5 K/s). The H-D exchange experiment demonstrates that only H2O is present in isolated, isometric inclusions whereas D2O has been measured in necking-down inclusions, implying isolated (and isometric) inclusions are well sealed and are representative of fluid present at run conditions. This study confirms that synthetic fluid inclusion is an effective method to preserve in situ hydrothermal fluid at high P-T conditions. Two coexisting phases, i.e. hydrothermal brine and silica-rich melt phases, may be responsible for Cu transport and enrichment. The moderate temperature and pressure (100-250°C, 5-30 MPa) experiments were conducted in a Parr autoclave allowing for in-situ sampling of liquid phase. The partitioning of Cu between cuprite and hydrothermal fluids (KClaq, H2O, pH buffered KClaq and H2O, where pH buffer refers to 0.2 m HAc/KAc) has been investigated from two aspects: Cu concentration and isotope fractionation. Experimental products are native copper and tenorite. Native copper is formed at 250°C and occurs in H2O and KCl-bearing runs and short-termed (≤24 hours) acetate-bearing runs. Tenorite formed in 150°C and 250°C long-termed (72 hours) acetate-bearing runs. Four competing reactions control the Cu partitioning, i.e., cuprite dissolution, Cu(I) disproportionation into Cu(II) and native Cu, decomposition of acetate into methane and carbon dioxide and oxidation of dissolved Cu(I) to Cu(II). It is worth noting that the last reaction exclusively occurs in Cu2O-acetate systems. During the cuprite dissolution stage (

AB - Transport and deposition of copper in the Earth’s crust are mainly controlled by the speciation of Cu and solubility of Cu-bearing phases in magmatic-hydrothermal fluids. In order to improve our understanding of mobilization of copper by hydrothermal fluids, we conducted experiments with Cu-bearing phases (metallic copper, Cu2O, CuCl) and aqueous solutions (H2O, NaClaq, KClaq, HCl, acetate solutions with/without pH buffer) at 25°C-800°C and 0.1 -200 MPa. The high temperature and high pressure (i.e., 800°C and 200 MPa) experiments were conducted in rapid heat/rapid quench argon cold seal pressure vessel using the synthetic fluid inclusion technique. The experimental charges Cu2Os ± CuCls + H2O ± NaClaq ± HClaq (chloride concentration: 0 to 4.3 mol/kg) were loaded in either Cu or Au capsules. Two types of quartz cylinders were used to trap in-situ hydrothermal fluids: (i) pre-cracked and (ii) intact prior to experiment. Fluid composition was subsequently determined by analyzing individual fluid inclusions using laser ablation inductively coupled plasma mass spectrometry. Two types of inclusions, i.e., fluid inclusion and Na-bearing silicate melt inclusion, have been formed exclusively in metallic Cu-NaCl system. Moreover, micron- to submicron-sized cuprite has been observed in both types of inclusions. In HCl±CuCl-bearing systems, fluid inclusion trapping potential nantokite (CuCl) is observed. The Cu content is strongly enhanced by initial chloride content, and can reach up to 4.3 wt% and 11 wt% in 4.3 m NaCl and 1.9 m HCl solutions, respectively. Fast cooling which is avoided by most researchers shows advantages of preservation of ample inclusions in Cu-NaCl system. In addition, the fluid inclusions after rapid quench (25 K/s) yields much smaller variation of Cu content in comparison to the usually favored slow quench process (0.5 K/s). The H-D exchange experiment demonstrates that only H2O is present in isolated, isometric inclusions whereas D2O has been measured in necking-down inclusions, implying isolated (and isometric) inclusions are well sealed and are representative of fluid present at run conditions. This study confirms that synthetic fluid inclusion is an effective method to preserve in situ hydrothermal fluid at high P-T conditions. Two coexisting phases, i.e. hydrothermal brine and silica-rich melt phases, may be responsible for Cu transport and enrichment. The moderate temperature and pressure (100-250°C, 5-30 MPa) experiments were conducted in a Parr autoclave allowing for in-situ sampling of liquid phase. The partitioning of Cu between cuprite and hydrothermal fluids (KClaq, H2O, pH buffered KClaq and H2O, where pH buffer refers to 0.2 m HAc/KAc) has been investigated from two aspects: Cu concentration and isotope fractionation. Experimental products are native copper and tenorite. Native copper is formed at 250°C and occurs in H2O and KCl-bearing runs and short-termed (≤24 hours) acetate-bearing runs. Tenorite formed in 150°C and 250°C long-termed (72 hours) acetate-bearing runs. Four competing reactions control the Cu partitioning, i.e., cuprite dissolution, Cu(I) disproportionation into Cu(II) and native Cu, decomposition of acetate into methane and carbon dioxide and oxidation of dissolved Cu(I) to Cu(II). It is worth noting that the last reaction exclusively occurs in Cu2O-acetate systems. During the cuprite dissolution stage (

U2 - 10.15488/4318

DO - 10.15488/4318

M3 - Doctoral thesis

CY - Hannover

ER -