The Mechanisms of Sulphide Oxidation and Gossan Formation

Thornber, M.R.; Taylor, G.F.

doi:10.1016/b978-0-444-89095-5.50015-8

Cited by 17 publications

(5 citation statements)

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“…10H + + SO À + 8e À ), that Bowell and Bruce saw as essential, must also pertain at Ruatapu if the necessary activity gradients are to be preserved (cf. Thornber and Taylor, 1992). Only while the wallrocks are permanently saturated in condensate¯uid by immersion can effective electrical conductivity be assured and some separation of the appropriate anodic/cathodic reactions be sustained (Fig.…”

Section: Cave Poolsmentioning

confidence: 98%

The steam condensate alteration mineralogy of Ruatapu cave, Orakei Korako geothermal field, Taupo Volcanic Zone, New Zealand

et al. 2000

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Ruatapu cave has developed beneath a block of hydrothermally altered Quaternary vitric tuff in the active Orakei Korako geothermal field. The cave extends~45 m, with a vertical drop of 23 m, to a shallow pool of clear, sulfate-rich (~450 mg/g), warm (T = 43À488C), acid (pH = 3.0) water. Steam, accompanied by H 2 S, rises from the pool surface, from a second pool nearby, and from fumaroles and joints in the ignimbrite, to condense on surfaces within the cave. Oxidation of the H 2 S to H 2 SO 4 produces acid sulfate fluids which react with the surficial rocks to generate three principal and distinct assemblages of secondary minerals. Kaolinite + opal-A + cristobalite + alunite + alunogen dominate the assemblage at the cave mouth; the essential Al, K and Si are derived from the tuffs and Na, Ca, Fe and Mg removed. In the main body of the cave the highly limited throughflow of water results in the more soluble of the leached constituents, notably Na and K, being retained in surface moisture and becoming available to form tamarugite and potash alum as efflorescences, in part at the expense of kaolin, along with lesser amounts of alunogen, meta-alunogen, mirabilite, halotrichite, kalinite, gypsum and, possibly, tschermigite; the particular species being determined by the prevailing physico-chemical conditions. Heat and moisture assist in moving Fe out of the rock to the air-water interface but, unlike typical surficial acid alteration systems elsewhere in the TVZ, there is an insufficient flow of water, of appropriate Eh-pH, to continue to move Fe out of the cave system. Much becomes locally immobilized as Fe oxides and oxyhydroxides that mottle the sides and roof of the cave. Jarosite crusts have developed where acid sulfate pool waters have had protracted contact with ignimbrite wallrock coated with once-living microbial mats. Subsequent lowering of the waters has caused the porous jarositic crusts to alter to potash alum + akagane Âite or schwertmannite. Meteoric water, with chloride concentrations of up to 10,000 mg/g, seeping through the roof produces a white, semi-thixotropic slurry which when dried yields 5.7 wt.% chloride and consisted of tamarugite plus halite. Some of this chloride (and sulfate) eventually enters the pool waters which have Cl À concentrations of 200 mg/g. This implies that the pools are not necessarily fed by a neutral pH alkali chloride fluid ascending from the geothermal reservoir, but are perched waters heated by ascending steam and fed largely by steam condensate.

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Section: Cave Poolsmentioning

confidence: 98%

The steam condensate alteration mineralogy of Ruatapu cave, Orakei Korako geothermal field, Taupo Volcanic Zone, New Zealand

et al. 2000

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“…The relatively good preservation of the gossan-hosting chlorites can be attributed to the slightly acidic to neutral conditions of the oxidation zone due to the low S/Cu ratio of chalcopyrite and the presence of carbonate-rich gangue minerals [15,39,86]. This supports the restricted influence of the water table, as demonstrated by the δ 65 Cu values, so that the chlorite minerals are mostly preserved from hydrolysis reactions.…”

Section: Geochemical Evolution and Exploratory Implicationsmentioning

confidence: 59%

Geochemical and Isotopic Fractionation in the Hypogene Ore, Gossan, and Saprolite of the Alvo 118 Deposit: Implications for Copper Exploration in the Regolith of the Carajás Mineral Province

Santos,

Costa,

Roerdink

2023

Minerals

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In the Carajás Mineral Province, gossan formation and lateritization have produced numerous supergene orebodies at the expense of IOCG deposits and host rocks. The Alvo 118 deposit comprises massive and disseminated hypogene copper sulfides associated with gossan and mineralized saprolites. The hypogene reserves are 170 Mt, with 1% Cu and 0.3 ppm Au, while the supergenes are 55 Mt, comprised of 30% gossan and 70% saprolite, with 0.92% Cu and 0.03 ppm Au. The gossan includes goethite, malachite, cuprite, and libethenite zones. The saprolite comprises kaolinite, vermiculite, smectite, and relics of chlorite. In the hypogene mineralization, Ag, Te, Pb, Se, Bi, Au, In, Y, Sn, and U are mainly hosted by chalcopyrite and petzite, altaite, galena, uraninite, stannite, and cassiterite. In the gossan, Ag, Te, Pb, Se, and Bi are hosted by Cu minerals, while Au, In, Y, Sn, and U are associated with iron oxyhydroxides, in addition to Zn, As, Be, Ga, Ga, Mo, Ni, and Sc. As supporting information, δ65Cu values indicate that the gossan is immature and, at least partly, not affected by leaching. In the saprolite, Ga, Sc, Sn, V, Mn, Co, and Cr are associated with the iron oxyhydroxides, partially derived from the host rock weathering. The δ56Fe values indicate that hypogene low contribution of the hypogene mineralization to the saprolite iron content. The association of Al2O3, Hf, Zr, Th, TiO2, Ce, La, Ba, and Sr represents the geochemical signature of the host rocks, with dominant contributions from chlorites, while In, Y, Te, Pb, Bi, and Se are the main pathfinders of Cu mineralization.

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“…Anodic leaching can take place within the cracks, fissures, and open grain boundaries. The anodic weathering can be 100 m or more beneath the cathodic oxygen reduction at the water table (Thornberg and Taylor 1992). Eh decrease as a result of metal sulfide oxidation has also been observed in tailings (Armienta and others 2000).…”

Section: Arsenic Hydrogeochemistrymentioning

confidence: 94%

“…Lower Eh values do not rule out arsenopyrite oxidation. Self-potential reactions occurring in the oxidation of sulfide ore minerals can account for electrochemical dispersion of metals and Eh decrease at depth (Sivenas and Beals 1982;Rose and others 1990;Thornberg and Taylor 1992). This decrease may be explained by the higher electrical conductivity of sulfide ore minerals compared with silicates, most oxides, and carbonates.…”

Section: Arsenic Hydrogeochemistrymentioning

confidence: 95%

“…At the deep end of the orebody, reduced substances are oxidized by loss of electrons to the orebody. The lower end of the electrode becomes the anode (deficient in oxygen) and the upper end the cathode (more oxygen) (Sivenas and Beals 1982; Rose and others 1990; Thornberg and Taylor 1992 ). Anodic leaching can take place within the cracks, fissures, and open grain boundaries.…”

Section: Arsenic Hydrogeochemistrymentioning

confidence: 97%

See 1 more Smart Citation

Response to B. Morse (2001) on "The role of arsenic-bearing rocks in groundwater pollution at Zimapan Valley, Mexico" by Armienta and others, Environmental Geology 40(4/5)

Armienta¹,

Ongley²,

Rodríguez³

et al. 2002

Environmental Geology

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The Mechanisms of Sulphide Oxidation and Gossan Formation

Cited by 17 publications

References 0 publications

The steam condensate alteration mineralogy of Ruatapu cave, Orakei Korako geothermal field, Taupo Volcanic Zone, New Zealand

The steam condensate alteration mineralogy of Ruatapu cave, Orakei Korako geothermal field, Taupo Volcanic Zone, New Zealand

Geochemical and Isotopic Fractionation in the Hypogene Ore, Gossan, and Saprolite of the Alvo 118 Deposit: Implications for Copper Exploration in the Regolith of the Carajás Mineral Province

Response to B. Morse (2001) on "The role of arsenic-bearing rocks in groundwater pollution at Zimapan Valley, Mexico" by Armienta and others, Environmental Geology 40(4/5)

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