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Ore solution chemistry; V, Solubilities of chalcopyrite and chalcocite assemblages in hydrothermal solution at 200 degrees to 350 degrees C

D. A. Crerar and H. L. Barnes
Ore solution chemistry; V, Solubilities of chalcopyrite and chalcocite assemblages in hydrothermal solution at 200 degrees to 350 degrees C
Economic Geology and the Bulletin of the Society of Economic Geologists (July 1976) 71 (4): 772-794

Abstract

Solubilities of the assemblages chalcopyrite (CuFeS (sub 2) ) + pyrite (FeS (sub 2) ) + bornite (Cu (sub 5) FeS (sub 4) ) and copper + chalcocite (Cu (sub 2) S) have been measured in subcritical aqueous solutions of NaCl and NaHS + H (sub 2) S under the following conditions: 200 degrees to 350 degrees C; a range of pH within 2.5 of neutral in sulfide solutions, and 1.5 of neutral in chloride solutions; up to 10.4 m NaCl and 2.85 m HS (super -) ; and from 15 to 256 atm total pressure. Sulfur fugacity was fixed by univariant sulfide assemblages; oxygen fugacity and pH were controlled in NaCl solutions by the graphite-CO (sub 2) buffer. The pale yellow color of high temperature solutions, plus optical absorption spectra at 25 degrees C, indicate that cuprous complexes predominate with this assemblage at temperatures to above 350 degrees C. The important solubility-controlling reactions and logs of their equilibrium constants are:200 degrees C 250 degrees C 300 degrees C 350 degrees C1/4 Cu (sub 5) FeS (sub 4) + HS (super -) + 1/2 H (sub 2) S(g) = 1/4 CuFeS (sub 2) + Cu(HS) (super -) (sub 2) -2.3 + or - 0.7 -2.3 + or - 0.7 -2.3 + or - 0.7 -2.3 + or - 0.71/4 Cu (sub 5) FeS (sub 4) + HS (super -) + 3/2 H (sub 2) S(g) = 1/4 CuFeS (sub 2) + Cu(HS) (sub 2) (H (sub 2) S) (super -) -- -3.8 + or - 0.7 -3.3 + or - + or - 0.7 -3.1 + or - 0.75CuFeS (sub 2) + 2H (super +) + 1/2 CO (sub 2) (g) = Cu (sub 5) FeS (sub 4) + 3FeS (sub 2) + 1/2 C (graph.)+ H (sub 2) O(l) + Fe (super 2+) 3.1 + or - 0.5 3.6 + or - 0.5 4.7 + or - 0.5 5.0 + or - 0.5Fe (super 2+) + Cl (super -) = FeCl (super +) 0.67 + or - 1.0 1.0 + or - 1.0 1.2 + or - 1.0 1.8 + or - 1.0CuFeS (sub 2) + H (super +) + 1/4 CO (sub 2) (g) + Cl (super -) = FeS (sub 2) + 1/4 C (graph.)+ 1/2 H (sub 2) O(l) + CuCl(aq) -1.2 + or - 0.5 -0.14 + or - 0.5 0.79 + or - 0.5 1.9 + or - 0.5Cu(c) + H (super +) + 1/4 Co (sub 2) (g)= 1/4 C (graph.)+ 1/2 H (sub 2) O(l) + Cu (super +) -1.6 + or - 0.3 -1.2 + or - 0.3 -0.29 + or - 0.3 0.46 + or - 0.3Cu (super +) + Cl (super -) = CuCl(aq) 2.2 + or - 0.6 2.4 + or - 0.6 2.2 + or - 0.6 2.7 + or -0.6 Iron bisulfide complexes are apparently unstable under the above conditions and could not be detected at the 0.5 to 10 ppm level. At neutral pH and Cl (super -) activity = 0.1, cuprous bisulfide complexes predominate for sulfur activities Sigma S > or = 1.0 (at 350 degrees ) and Sigma S > or = 0.03 (at 250 degrees C); the species CuCl predominates for lower Sigma S. At 350 degrees C with Sigma S < 0.1, under the near-neutral to weakly acidic conditions probably characteristic of porphyry copper ore-forming fluids, approximately 1,000 ppm Fe and Cu dissolve in 1.0 m NaCl as the species CuCl, Fe (super 2+) , and FeCl (super +) . Under similar conditions at 250 degrees C, solubilities fall to roughly 100 ppm Fe and 10 ppm Cu. Simultaneous transport of Fe and of Cu as bisulfide complexes above 200 degrees C is geologically unlikely. Where chloride complexed, Cu-Fe sulfides may be deposited by dilution of hydrothermal solutions, by increasing pH or Sigma S, and by decreasing temperature or oxygen fugacity.


ISSN: 0361-0128
EISSN: 1554-0774
Coden: ECGLAL
Serial Title: Economic Geology and the Bulletin of the Society of Economic Geologists
Serial Volume: 71
Serial Issue: 4
Title: Ore solution chemistry; V, Solubilities of chalcopyrite and chalcocite assemblages in hydrothermal solution at 200 degrees to 350 degrees C
Affiliation: Pa. State Univ., Ore Dep. Res. Sect., University Park, Pa., United States
Pages: 772-794
Published: 197607
Text Language: English
Publisher: Economic Geology Publishing Company, Lancaster, PA, United States
Accession Number: 1977-003701
Categories: Geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. tables
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Society of Economic Geologists
Update Code: 1977
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