Other
Scientific paper
Sep 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998gecoa..62.2949x&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 62, Issue 17, pp.2949-2964
Other
8
Scientific paper
The solubility of Cu phases was measured in vapor-saturated aqueous HCl/NaCl solutions at temperatures ranging from 40 to 300°C, total chloride concentration from 0.01 to 1 m, and pH from 0 to 3.5. For temperatures up to and including 150°C, CuCl (s) was used as the solid reactant. At higher temperatures, foils of metallic Cu and Ag were used. Silver was added as a redox sensor, as the equilibrium constants describing dissolution of this metal as chloride complexes are already known to high precision. Copper was found to dissolve primarily as CuCl (aq) , CuCl 2 - , and CuCl 3 2- . Data collected from the experiments were regressed to determine the following equilibrium constants as functions of temperature (K): Cu ( s ) +1/4O 2( g ) +H + +Cl - =CuCl ( aq ) +1/2H 2 O ( l ) , log K 1 =0.1316*(1000/ T ) 2 +2.865*(1000/ T )+4.4243, R 2 =0.9958; Cu ( s ) +1/4O 2( g ) +H + +2Cl - =CuCl 2 - +1/2H 2 O ( l ) , log K 2 =1.0981*(1000/ T ) 2 -2.2961*(1000/ T )+12.916, R 2 =0.9896; Cu ( s ) +1/4O 2( g ) +H + +3Cl - =CuCl 3 2- +1/2H 2 O ( l ) , log K 3 =2.2704*(1000/ T ) 2 -8.7646*(1000/ T )+20.643, R 2 =0.9941. These equations can be used to calculate equilibrium constants at temperatures up to 350°C and vapor saturated pressure. %Our results at T < 150°C agree well with those published by other researchers, but the agreement is variable for results at T > 150°C. At higher temperatures, our data for CuCl 2 - are in accord with those of , whereas our data for CuCl (aq) deviate significantly from the results of . The agreement with published theoretical estimates of the formation constants for Cu(I) chloride complexes is not good, especially at T > 200°C. The solubility of chalcopyrite was calculated for a variety of conditions. For unit activity of Cl - , pH between 3 and 5, and oxygen and sulfur fugacity buffered by the assemblage pyrite-pyrrhotite-magnetite, Cu is transported mainly as CuCl 2 - , and has a solubility of 212 moles/kg (13.5 ppm) at 350°C and pH = 3. Chalcopyrite will deposit in response to an increase in pH, or decreases in a Cl - , temperature, and oxygen fugacity. Calculations of the solubility of chalcopyrite in seafloor hydrothermal systems show that the Cu-rich zones in volcanogenic massive sulfide deposits form at temperatures > 250°C and that cooling and/or pH increase are the most likely depositional controls. Below 250°C, chloride brines are incapable of transporting significant quantities of Cu unless conditions are unusually oxidized.
Gammons Christopher H.
Williams-Jones Anthony E.
Xiao Zhifeng
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