Mineralogical siting and distribution of gold in quartz veins and sulfide ores of the Ashanti mine and other deposits in the Ashanti belt of Ghana: genetic implications

Oberthür, Thomas; Weiser, Thorolf W.; Amanor, J. A.; Chryssoulis, S. L.

doi:10.1007/s001260050068

Cited by 94 publications

(50 citation statements)

References 11 publications

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“…Oberthür et al (1997) also reported that arsenopyrite crystals from different deposits in the Ashanti gold belt (Ghana) have an Au-rich rim and an Au-poor core. On the basis of spot analyses by secondary ion mass spectrometry with a beam 30 m in diameter, they noted an inhomogeneous Au distribution in crystals greater than 50 m in diameter.…”

Section: Review Of Recent Workmentioning

confidence: 91%

“…The existence of both visible native gold and chemically bound gold in sulfide and sulfarsenide minerals has been reported for many mesothermal gold deposits and may be regarded as the rule (Oberthür et al 1997). Oberthür et al (1997) also reported that arsenopyrite crystals from different deposits in the Ashanti gold belt (Ghana) have an Au-rich rim and an Au-poor core.…”

Section: Review Of Recent Workmentioning

confidence: 91%

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Chemical Speciation of Gold in Arsenopyrite

Cabri¹,

Newville

Gordon

et al. 2000

The Canadian Mineralogist

137

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The speciation of Au in gold-bearing arsenopyrite (FeAsS) from four gold deposits (Olympiada, Sentachan, São Bento and Sheba) was determined by micro-X-ray absorption near-edge structure (XANES) on grains well characterized microscopically and by electron-microprobe and secondary-ion mass spectrometry analyses and images. "Invisible" gold in arsenopyrite occurs in two apparently mutually exclusive chemical forms: chemically bound and elemental. Arsenopyrite from the Sentachan, São Bento and Sheba deposits contains chemically bound gold. With comparable constituent electronegativities and a white-line feature in the XANES indicating unoccupied Au 5d-states, but absorption-edge positions comparable to Au 1+ species, the bonding is interpreted as being covalent rather than ionic. The invisible gold in arsenopyrite from the Olympiada deposit, on the other hand, occurs as very small particles of Au 0 , probably less than a few nanometers in diameter. Micro-XANES data for the Olympiada and Sentachan arsenopyrite support earlier results obtained by 197 Au Mössbauer spectroscopy on arsenopyrite concentrates. In some arsenopyrite crystals, the gold concentration is closely related to growth zoning. This feature represents conditions during crystallization and does not correlate with the chemical form of the gold. Similarly, selenium, where present, correlates with gold in some deposits and not in others, irrespective of the gold speciation. The finding of two types of invisible gold in arsenopyrite from different deposits has beneficial implications for extractive metallurgy.

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Section: Review Of Recent Workmentioning

confidence: 91%

Section: Review Of Recent Workmentioning

confidence: 91%

Chemical Speciation of Gold in Arsenopyrite

Cabri¹,

Newville

Gordon

et al. 2000

The Canadian Mineralogist

137

View full text Add to dashboard Cite

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“…Gold mining in Ghana has been the largest foreign exchange earner since pre-independence, with gold export earnings rising from US$ 107.9 million to US$ 744.2 million between 1985and 1989(Obiri et al 2006. The main gold prospects in Ghana occur at Obuasi and Konongo in the Ashanti region, and at Tarkwa, Prestea and Bogosu in the western region (Oberthur et al 1997;Smedley 1996). The gold deposits in Obuasi and Prestea are locked in mineralised dyke and schist associated with arsenic and sulphur and, hence, extraction of the gold, which involves roasting, results in the release of airborne particles and large quantities of arsenic (Amonoo-Neizer and Amekor 1993).…”

Section: Introductionmentioning

confidence: 97%

Variations in Concentrations of Arsenic and Other Potentially Toxic Elements in Mine and Paddy Soils and Irrigation Waters from Southern Ghana

Adomako

Deacon

Meharg

2010

Water Qual Expo Health

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“…In the metasediments and metavolcanics gold is usually microscopic and is closely associated with sulfide minerals. Submicroscopic gold is detected in sulfides, particularly in arsenopyrite by secondary ion mass spectroscopy (Oberthür et al, 1997). The average ore grade in the metasediments and metavolcanics is about 20 g/t although up to 50 g/t is reported in some places (Oberthür et al, 1994).…”

Section: Mine Geologymentioning

confidence: 99%

“…Among others, Oberthür et al (1994Oberthür et al ( , 1997 studied the deposits from diverse approaches including mineralogy, stable isotope and fluid inclusion studies. Our studies are focused on the mineral chemistry that is incomplete or lacking in their works.…”

Section: Introductionmentioning

confidence: 99%

Ore Mineralogy and Mineral Chemistry of the Ashanti Gold Deposit at Obuasi, Ghana

1999

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Abstract:The gold deposit at Ashanti occurs in the Proterozoic Birimian formation of Ghana. Two main ore types mined from the deposit are gold-bearing quartz veins, and gold-sulfide disseminations in metasediments and metavolcanics. The main sulfide minerals in the gold-sulfide disseminated ores are arsenopyrite, pyrite and pyrrhotite, and to a very minor extent, sphalerite and tetrahedrite. Carbonate alteration and sericitization are prominent in the metavolcanics and the metasediments, respectively. In the quartz veins, pyrite and arsenopyrite commonly occur in small amounts, but gold mostly occurs in contact with tetrahedrite, chalcopyrite, galena, aurostibite, and sphalerite. Pyrrhotite is absent in the quartz veins.Microprobe studies indicate that As content of homogeneous arsenopyrite grains ranges from 27.0 to 31.7 atm%, and gives mineralization temperatures from 170 to 430ºC, although mostly from 300 to 400ºC. Chlorite geothermometry using temperature dependence of substitution of Al for Si in the tetrahedral site gives formation temeratures of 330 to 400ºC, comparable to the arsenopyrite temperatures. Applying sphalerite-pyrite-pyrrhotite geobarometry to sphalerite with FeS contents from 13.6 to 12.5 mol%, the pressure was estimated to be in a range from 5.9 to 7.0 kb at the stage of elevated temperatures.Mineralogical observations, especially absence of pyrrhotite in the quartz veins, together with microprobe data for gold and associated minerals suggest that the fluids having ascended through fissures in the Ashanti deposit were reduced by the reaction with carbonaceous materials in the metasediments during the declining stage of the regional metamorphism.

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Mineralogical siting and distribution of gold in quartz veins and sulfide ores of the Ashanti mine and other deposits in the Ashanti belt of Ghana: genetic implications

Cited by 94 publications

References 11 publications

Chemical Speciation of Gold in Arsenopyrite

Chemical Speciation of Gold in Arsenopyrite

Variations in Concentrations of Arsenic and Other Potentially Toxic Elements in Mine and Paddy Soils and Irrigation Waters from Southern Ghana

Ore Mineralogy and Mineral Chemistry of the Ashanti Gold Deposit at Obuasi, Ghana

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