Ore solution chemistry; VII, Stabilities of chloride and bisulfide complexes of zinc to 350 degrees C

Abstract

The association constants for the dominant zinc chloride complexes were determined from solubility measurements of zincite (ZnO) and smithsonite (ZnCO3) in 0 to 5 m NaC1-CO2-H20 solutions from 100 ø to 350øC. For the important sphalerite solubility-controlling reactions: Zn +2 + CI-= ZnC1 +, Zn +• + 2C1-= ZnClø•, Zn +• + 3C1-= ZnCI•, Zn +• + 4C1---ZnCI• •, and ZnS(s) + 2H + --Zn +2 + H•S(aq), the respective logs of the equilibrium constants for temperatures (øC) equal to 100, 150, 200, 250, 300, and 350 are 1.2, 2., -1.7. The log K values for the last reaction were calculated here using free energy data for ZnS(s), Zn +•, and H•S(aq). The equilibrium constants for the dominant zinc bisulfide complexes were determined from solubility measurements of sphalerite (ZnS) in 0 to 4 m NaHS-H•S-H20 solutions from 100 ø to 350øC. The important solubility-controlling reactions are: ZnS(•) + H•O(t) = Zn(OH)(HS) ø, ZnS(,) + H2S(aq) --Zn(HS)•, ZnS(•) + H2S(aq) + HS-= Zn(HS)•, and ZnS(,) + H•S(aq) + 2HS-= Zn(HS)• •, and the respective logs of their equilibrium constants for temperatures (øC) equal to 100, 150,200,250, 300, and 350 areEnthalpies and entropies of complex formation derived from these data demonstrate the increasing importance of electrostatic effects in complex formation at higher temperatures. Good agreement was found between our measured and calculated solubilities of sphalerite from 100 ø to 350øC in an NaC1-H•S-H20 solution and in an NaC1-CaCI•-CO•-H•S-H•O solution in equilibrium with calcite. Therefore, the nine equilibrium constants provide confirmed resolution of sphalerite solubilities in ore solutions having chemistries quite different from those used in the solubility experiments. Sample calculations of sphalerite solubilities in Kuroko-type massive sulfide ore fluids are given which demonstrate the effectiveness of cooling in the temperature range of 250 ø to 300øC as a precipitation mechanism for sphalerite.

Hydrothermal Processes: The Development of Geochemical Concepts in the Latter Half of the Twentieth Century

“…The odyssey began with the Pearson intermediate-class metal, Zn, and measured solubilities primarily of sphalerite to investigate the transporting potential of chloride versus bisulphide complexing (Barnes, 1963) . Later together with Bill Bourcier, we improved the data set for Zn complexes (Bourcier and Barnes, 1987) . Solubility measurements from our Penn State lab also included ore minerals of copper (Crerar and Barnes, 1976), lead (Giordano and Barnes, 1979), silver (Gammons and Barnes, 1989), gold (Shenberger and Barnes, 1989), and mercury Barnes and Seward, 1997) .…”

Sulfide Ameliorates Metal Toxicity for Deep-Sea Hydrothermal Vent Archaea

“…Survival medium (pH 5) for the heterotrophs was prepared by adding 0.82 g of CH 3 COONa per liter, 0.80 mg of resazurin per liter, and 96 mg of Na 2 S · 9H 2 O per liter to Turk's Island artificial seawater (13). For the methanogen, DSMZ medium 282 seawater was supplemented with 1 mg of resazurin per liter, 9.75 g of MES [2-(N-morpholino)ethanesulfonic acid] buffer per liter, and 96 mg of Na 2 S · 9H 2 O per liter and set to pH 6.…”

“…c Zinc-free ion concentrations are calculated at room temperature by using stability constants for ZnS and Zn(HS) 2 (17,31) and for chloro complexes (NIST database [see above]). In parentheses, zinc-free ion concentrations are calculated by using stability constants determined at 100°C (3) for Zn chloro complexes and Zn(HS) 2 and Zn(HS) 3 Ϫ . The differences in results between temperatures are due to incomplete stability constant data for higher temperatures as well as more sensitive voltammetric methods for determining stability constants at room temperature.…”

Isotopic Studies of the Guerrero Composite Terrane, West-Central Mexico: Implications for Provenance of Crustal Rocks and Genesis of Ore Metals

“…Lead isotope compositions of sulfide minerals and rocks associated with an ore deposit can constrain the possible sources of metals in a hydrothermal system. This is because of the similar geochemical behavior of Pb, Cu, and Zn in hydrothermal fluids and the occurrence of Pb in the same paragenetic stages as Zn, Cu, Ag, and cadmium (Cd) (Bourcier and Barnes, 1987;Wood et al, 1987 with a few exceptions, they plot within the field defined by the sedimentary rocks from the Huetamo Sequence (Figure 4.6). This indicates that a substantial component of the Pb in these deposits might have been incorporated from continent-derived sediments.…”

“…Lead isotope compositions of sulfide minerals and rocks associated with an ore deposit can constrain the possible sources of metals in a hydrothermal system, because of the similar geochemical behavior of Pb, Cu, and Zn in hydrothermal fluids and the occurrence of Pb in the same paragenetic stages as Zn, Cu, Ag, and Cd (Bourcier and Barnes, 1987;Wood et al, 1987). Therefore, Pb reflects the geochemical behavior of ore metals in polymetallic deposits more accurately than radiotracers such as Sr and Nd (Macfarlane, 1989).…”