Uranium geochemistry and dating of Pacific island apatite

Roe, Kevin K.; Burnett, William C.

doi:10.1016/0016-7037(85)90263-7

Cited by 30 publications

(19 citation statements)

References 36 publications

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“…Another 2 grams were subjected to 0.2N K 2 CO 3 leaches at pH = 12 for 24 hours at 70°C (Weinberg and Cowart 2001). Previous leaching studies showed that apatite dissolution is not an important process (Roe and Burnett, 1985). The resulting analyzed phases of the phosphorites were designated as soluble (S), leachable (L), and solubleunleachable (F).…”

Section: Uranium and Uranium Isotopic Analysesmentioning

confidence: 99%

“…On the other hand even the purest francolite samples analyzed here and elsewhere do contain U, presumably somewhere in the lattice. That such U remains sensitive to the hydrologic environment is shown by the preponderance of +6 U in surficial island phosphorites (Roe and Burnett, 1985), and also in the oxidized groundwater of Florida (Upchurch and Randazzo, 1997;Weinberg and Cowart, 2001).…”

Section: U Adsorption In the Phosphoritesmentioning

confidence: 99%

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Secondary uranium in phosphorites and its relation to groundwater in Egypt

Dabous

2003

Geochem. J.

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The stratiform phosphorite deposits of Egypt, which are found in an east-west band between 24° and 27° north latitude, contain from 25 to 100 ppm uranium, a significant portion of which can be shown to have been secondarily adsorbed from groundwater. This fraction is readily leachable in 0.2 N K 2 CO 3 and in the Red Sea area has the same 234 U/ 238 U activity ratio, 1.3, as the U dissolved in the associated groundwater. Both the excess of 234 U and the deficiency of 230 Th relative to 238 U shows that the leachable U was adsorbed within the last 250 ky. Secondary U with the same 234 U/ 238 U activity ratio also occurs in the Western Desert phosphorite, indicating that it too has been adsorbed relatively recently, even though the groundwater table today is well below the phosphatic strata. On the other hand, the leachable U in the intervening Nile Valley deposits has an activity ratio near 1.0, suggesting that those strata have been above the groundwater table for the last million years. The adsorption of U may not be entirely associated with the principal phosphate mineral, carbonate-fluorapatite (francolite), Ca 5 (PO 4 ,CO 3 )(F,OH). Iron, organic and clay phases are also present in the phosphorite ore.A recent review by Sharafeldin (1999) has summarized the uranium occurrences as well as the clay mineralogy of the Egyptian deposits.

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Section: Uranium and Uranium Isotopic Analysesmentioning

confidence: 99%

Section: U Adsorption In the Phosphoritesmentioning

confidence: 99%

Secondary uranium in phosphorites and its relation to groundwater in Egypt

Dabous

2003

Geochem. J.

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“…At some point the limestone cap was above sea level for sufficient time for karstification to occur and for phosphatic material to accumulate over the karst. The origin of the phosphate material has not been confirmed; most authors (Power 1904, Hutchinson 1950, Roe and Burnett 1985 have suggested that the origin is avian guano that has been reworked as a result of the submergence and uplift of the island, but others (Owen 1923, Barrett 1988 have suggested (without much scientific evidence) alternative geochemical mechanisms. One criticism of the avian theory is the Holocene climate: Nauru is wetter than other areas where guano has been converted into high-quality apatite.…”

Section: Laboratory Studiesmentioning

confidence: 99%

“…The F concentration (1.7-3.0% [Roe and Burnett 1985]) is generally slightly below that required for pure fluoroapatite, with some hydroxy and carbonate groups incorporated into the apatite. Ca concentrations are around 37%, with Mg varying from 0.5 to 8%.…”

Section: Laboratory Studiesmentioning

confidence: 99%

“…The phosphate material has been shown to be very pure apatite (Roe and Burnett 1985, Morrison 1987, Commission of Inquiry 1988, with a P content averaging about 15% but ranging from 6 to 18%. The F concentration (1.7-3.0% [Roe and Burnett 1985]) is generally slightly below that required for pure fluoroapatite, with some hydroxy and carbonate groups incorporated into the apatite.…”

Section: Laboratory Studiesmentioning

confidence: 99%

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Pre-Mining Pattern of Soils on Nauru, Central Pacific

Morrison¹,

Manner²

2005

Pacific Science

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The environment of Nauru, a raised atoll located in the central Pacific Ocean (0 32 0 S, 166 56 0 W ), was devastated by mining of phosphate ''rock'' during the twentieth century. Some 100 million tonnes of phosphate material has been removed, leaving more than 80% of the island as a dolomite pinnacle-dominated karrenfeld. Based on fieldwork examining sites unmined at that time, laboratory studies on undisturbed profiles, aerial photographs, and old mining maps, a picture of what the soil pattern on Nauru was before mining has been developed. Four major soil associations were identified: the coastal fringe carbonate-dominated soils set on a recent fringing reef; deep and relatively deep phosphate-dominated soils free of substantial influence from the underlying dolomite pinnacles occurring on the NE, NW, SE, and SW sectors of the uplifted section of the island (known locally as ''Topside''); a complex set of soils found on Topside and on the scarp where the pinnacle influence is important but containing some deep soils where phosphate material accumulated between the pinnacles; and a complex set of soils in low-lying areas around the old lagoon at Buada. Distribution of soils is discussed and physical, chemical, and mineralogical properties of the soils are presented. Soils were basically AC profiles, with coarse textures, free drainage, and limited moisture-retention capacities. Organic matter accumulated to various depths from about 5 to 50 cm. Soil pH was generally above 6, cation exchange capacities were closely aligned to organic matter contents, but trace element deficiencies would have been common. Cadmium concentrations were relatively high in Nauru soils. The soils are likely to have been of limited fertility, with moisture being a major limitation in many years. Classification of the soils indicated a dominance of Ustropepts and Ustolls, with smaller areas of Ustipsamments and Ustorthents, and very small areas of soils showing aquic features. The postmining situation is also discussed; only very limited areas of three of the original soil associations remain (the relatively deep profiles free of pinnacle influence have completely disappeared). Limitations to rehabilitation are also briefly reviewed.

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Literature

Geyh¹,

Schleicher²

1990

Absolute Age Determination

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Uranium geochemistry and dating of Pacific island apatite

Cited by 30 publications

References 36 publications

Secondary uranium in phosphorites and its relation to groundwater in Egypt

Secondary uranium in phosphorites and its relation to groundwater in Egypt

Pre-Mining Pattern of Soils on Nauru, Central Pacific

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