The gypsum-anhydrite equilibrium by solubility measurements

Innorta, G.; Rabbi, Ernesto; Tomadin, L.

doi:10.1016/0016-7037(80)90192-1

Cited by 46 publications

(33 citation statements)

References 3 publications

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“…It is also well known that gypsum occurs as efflorescences ("desert roses") by evaporation in the dry season, and is found as a gangue mineral in gold-quartz deposits (Lindgren 1928, Boyle 1979. The temperature of breakdown of gypsum to anhydrite + H 2 O in pure water is 49 ± 2.5°C (Innorta et al 1980), and is considerably lowered by the presence of NaCl (Blount & Dickson 1973). Therefore, gypsum is expected to be encountered only in low-temperature hydrothermal deposits or in the supergene zone (Holland 1967).…”

Section: Discussionmentioning

confidence: 99%

On the Association of Palladium-Bearing Gold, Hematite and Gypsum in an Ouro Preto Nugget

Cabral¹,

Lehmann²,

Kwitko-Ribeiro³

et al. 2003

The Canadian Mineralogist

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An ouro preto (black gold) nugget from Gongo Soco, Minas Gerais, Brazil, has a mineral assemblage of hematite and gypsum hosted by Pd-bearing gold. The hematite inclusion is microfractured and stretched. Scattered on the surface of the gold is a darkcolored material that consists partially of Pd-O with relics of palladium arsenide-antimonides, compositionally close to isomertieite and mertieite-II. The Pd-O coating has considerable amounts of Cu, Fe and Hg, and a variable metal:oxygen ratio, from O-deficient to oxide-like compounds. The existence of a hydrated Pd-O compound is suggested, and its dehydration or deoxygenation at low temperatures may account for the O-deficient Pd-rich species, interpreted as a transient phase toward native palladium. Although gypsum is a common mineral in the oxidized (supergene) zones of gold deposits, the hematite-gypsumbearing palladian gold nugget was tectonically deformed under brittle conditions and appears to be of low-temperature hydrothermal origin.Keywords: ouro preto, hematite-gypsum mineral assemblage, Pd-bearing gold, Pd-O coating, isomertieite, mertieite-II, Gongo Soco, Minas Gerais, Brazil. SOMMAIREUne pépite de ouro preto (or noir) provenant de Gongo Soco, Minas Gerais, au Brésil, contient l'assemblage hématite + gypse dans un hôte d'or palladifère. L'hématite en inclusion est microfissurée et étirée. La surface de la pépite est recouverte d'un matériau foncé qui correspond en partie à une gaine de Pd-O avec des reliques d'arséniures et d'antimoniures de palladium dont la composition ressemble à celles de isomertieïte et mertieïte-II. Cette couche à Pd-O contient des quantités importantes de Cu, Fe et Hg, et montre un rapport variable de métal à oxygène, allant de matériau déficitaire en oxygène à des composés ressemblant à des oxydes. A notre avis, il y a des indications d'un composé Pd-O hydraté, et sa déshydratation ou sa perte en oxygène à faibles températures rendrait compte des variétés riches en Pd et appauvries en O, que nous interprétons comme phases transitoires dans une progression vers le palladium natif. Quoique le gypse est un minéral répandu dans la zone oxydée (supergène) des gisements d'or, la pépite d'or palladifère à hématite-gypse a été déformée tectoniquement sous conditions cassantes, et semble avoir une origine hydrothermale à faible température.(Traduit par la Rédaction)

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Section: Discussionmentioning

confidence: 99%

On the Association of Palladium-Bearing Gold, Hematite and Gypsum in an Ouro Preto Nugget

Cabral¹,

Lehmann²,

Kwitko-Ribeiro³

et al. 2003

The Canadian Mineralogist

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“…The gypsum and anhydrite equilibrium point has been extensively studied by van't Hoff et al (1903), Partridge and White (1929), Posnjak (1938), Kelley et al (1941), Bock (1961), Hardie (1967), Blount and Dickson (1969), Innorta et al (1980), Freyer and Voigt (2003), Charola et al (2007), and Berdugo et al (2008), among others. The transition temperatures of gypsum-anhydrite and gypsum-hemihydrate in these studies vary mostly within the ranges from 42 to 60 C and 80 to 110 C, respectively.…”

Section: The Caso 4 -H 2 O Systemmentioning

confidence: 97%

Gypsum Soils—Their Morphology, Classification, Function, and Landscapes

Casby-Horton¹,

Herrero²,

Rolong³

2015

Advances in Agronomy

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“…However, due to the solubility of gypsum in water (0.208 g/100 g at 25 • C [5]), the gypsum void fraction is expected to increase when plasterwork is exposed to humidity (e.g., rain) or humidity rising by capillarity from support elements. It can therefore be concluded that, apart from the amount of water used in plasterwork manufacture, weathering from water also increases its porosity, weakening the material by decreasing its mechanical properties.…”

Section: Mechanical Strengthmentioning

confidence: 99%