origin and nature of the aluminium phosphate-sulfate minerals (aps) associated with uranium...

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Manuscrito aceptado Accepted manuscript

Autor(es) Author(s): Marfil, R.; La Iglesia, A. ; Estupiñán, J.

Título (original, EN): Title (original, EN):

Origin and nature of the aluminium phosphate-‐sulfate minerals (APS) associated with uranium mineralization in triassic red-‐beds (Iberian Range, Spain)

Título (traducido, ES): Title (translated, ES):

Origen y naturaleza de los minerales fosfato-‐sulfato alumínicos (APS) asociados a la mineralización de uranio en los red-‐beds triásicos (Cordillera Ibérica, España)

DOI: 10.3989/egeol.40879.176

Fecha de recepción: Received date: 02/12/2011

Fecha de aceptación: Accepted date: 22/02/2012

Publicación online: Published online: 19/02/2013

Puede citar este artículo como: You may cite this article as: Marfil, R.; La Iglesia, A. ; Estupiñán, J. (2013). Origin and nature of the aluminium phosphate-‐

sulfate minerals (APS) associated with uranium mineralization in triassic red-‐beds (Iberian Range, Spain). Estudios Geológicos [en línea], manuscrito aceptado, doi: 10.3989/egeol.40879.176

Marfil, R.; La Iglesia, A. ; Estupiñán, J. (2013). Origin and nature of the aluminium phosphate-‐sulfate minerals (APS) associated with uranium mineralization in triassic red-‐beds (Iberian Range, Spain). Estudios Geológicos [online], accepted manuscript, doi: 10.3989/egeol.40879.176

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Origin and nature of the aluminium phosphate-sulphate minerals (APS) associated with uranium mineralization in triassic red-beds (Iberian Range, Spain)

Origen y naturaleza de los minerales fosfato-sulfato alumínicos(APS) asociados a la mineralización de uranio en los red-bedstriásicos (Cordillera Ibérica, España)

R. Marfil,1 A. La Iglesia,2 J. Estupiñan,3

ABSTRACT

This study focuses on the mineralogical and chemical study of an Aluminium–phosphate–sulphate (APS)mineralization that occurs in a clastic sequence from the Triassic (Buntsandstein) of the Iberian Range. Thedeposit is constituted by sandstones, mudstones, and conglomerates with arenaceous matrix, which weredeposited in fluvial to shallow-marine environments. In addition to APS minerals, the following diageneticminerals are present in the clastic sequence: quartz, K-feldspar, kaolinite group minerals, illite, Fe-oxides-hidroxides, carbonate-sulphate cement-replacements and secondary uraniferous minerals. APS mineralswere identified and characterized by optical microscopy, X-ray diffraction, scanning electron microscopy, andelectron microprobe. Microcrystalline APS crystals occur replacing uraniferous minerals, associated withkaolinite, mica and filling pores, in distal fluvial-to-tidal arkoses-subarkoses. Given their Ca, Sr, and Ba con-tents, the APS minerals can be defined as a solid solution of crandallite-goyacite-gorceixite (0.53 Ca, 0.46Sr and 0.01 Ba). The chemical composition, low LREE concentration and Sr > S suggest that the APS min-eral were originated during the supergene alteration of the Buntsandstein sandstones due to the presenceof the mineralizing fluids which causes the development of U-bearing sandstones in a distal alteration areaprecipitating from partially dissolved and altered detrital minerals. Besides, the occurrence of dickite associ-ated with APS minerals indicates they were precipitated at diagenetic temperatures (higher than 80ºC), relat-ed to the uplifting occurred during the late Cretaceous post-rift thermal stage.

Keywords: APS minerals, U-bearing sandstones, Diagenesis, Triassic Buntsandstein, Iberian Range,Spain.

RESUMEN

Este trabajo se centra en el estudio de los minerales fosfato-sulfato alumínicos(APS) que se producenen una secuencia clástica del Triásico (Buntsandstein) de la Cordillera Ibérica. El depósito está constituidopor areniscas, lutitas y conglomerados con matriz arenosa, que fueron depositados en ambientes de fluviala marino somero. En la secuencia clástica además de los APS están presentes los siguientes minerales dia-genéticos: cuarzo,feldespato potásico, minerales del grupo de la caolinita, illita, óxidos-hidróxidos de Fe,cementos-reemplazamientos de carbonatos y sulfatos y minerales secundarios uraníferos. Los mineralesAPS fueron identificados y caracterizados por microscopía óptica, difracción de rayos X, microscopía elec-trónica de barrido, y microsonda electrónica. Los microcristales de APS reemplazan a minerales uraníferos,asociados con caolinita-dickita, mica y rellenando la porosidad de arcosas-subarcosas fluviales a marealesdistales. Dado su contenido en Ca, Sr y Ba, los minerales APS se pueden definir como una solución

1 Dpt. de Geoquimica, Petrología y Geoquímica, Facultad de Ciencias Geológicas, UCM, 28040 Madrid, Spain. E-mail: [email protected]

2 Instituto de Geociencias (CSIC, UCM), Facultad de Ciencias Geológicas, UCM, 28040 Madrid, Spain. E-mail: [email protected]

3 Dpt. de Ciencias de la Tierra, Facultad de Ciencias del Mar y Ambientales UCA, 11510 Cádiz, Spain. E-mail: jenny.estupiñ[email protected]

Estudios Geológicos

2013

ISSN:0367-0449

eISSN:1988-3250

doi:10.3989/egeol.40879.176


Facultad de Ciencias del Mar y




distales. Dado su contenido en Ca, Sr y Ba, los minerales asociados con caolinita-dickita, mica y rellenando la porosidad de arcosas-subarcosas fluviales a marealesdistales. Dado su contenido en Ca, Sr y Ba, los minerales

cementos-reemplazamientos de carbonatos y sulfatos y minerales secundarios uraníferos. Los mineralesAPS fueron identificados y caracterizados por microscopía óptica, difracción de rayos X, microscopía electrónica de barrido, y microsonda electrónica. Los microcristales de

cementos-reemplazamientos de carbonatos y sulfatos y minerales secundarios uraníferos. Los mineralesAPS fueron identificados y caracterizados por microscopía óptica, difracción de rayos X, microscopía elec

a marino somero. En la secuencia clástica además de los genéticos: cuarzo,feldespato potásico, minerales del grupo de la caolinita, illita, óxidos-hidróxidos de Fe,

por areniscas, lutitas y conglomerados con matriz arenosa, que fueron depositados en ambientes de fluviala marino somero. En la secuencia clástica además de los genéticos: cuarzo,feldespato potásico, minerales del grupo de la caolinita, illita, óxidos-hidróxidos de Fe,

Este trabajo se centra en el estudio de los minerales fosfato-sulfato alumínicos(APS) que se producenriásico (Buntsandstein) de la Cordillera Ibérica. El depósito está constituido

por areniscas, lutitas y conglomerados con matriz arenosa, que fueron depositados en ambientes de fluvial

Este trabajo se centra en el estudio de los minerales fosfato-sulfato alumínicos(APS) que se producen

APS minerals, U-bearing sandstones, Diagenesis, APS minerals, U-bearing sandstones, Diagenesis, T

of the mineralizing fluids which causes the development of U-bearing sandstones in a distal alteration areaprecipitating from partially dissolved and altered detrital minerals. Besides, the occurrence of dickite associ

APS minerals indicates they were precipitated at diagenetic temperatures (higher than 80ºC), relat

eral were originated during the supergene alteration of the Buntsandstein sandstones due to the presenceof the mineralizing fluids which causes the development of U-bearing sandstones in a distal alteration areaprecipitating from partially dissolved and altered detrital minerals. Besides, the occurrence of dickite associ

Sr and 0.01 Ba). The chemical composition, low LREE concentration and Sr > S suggest that the eral were originated during the supergene alteration of the Buntsandstein sandstones due to the presence

APS minerals can be defined as a solid solution of crandallite-goyacite-gorceixite (0.53 Ca, 0.46Sr and 0.01 Ba). The chemical composition, low LREE concentration and Sr > S suggest that the

kaolinite, mica and filling pores, in distal fluvial-to-tidal arkoses-subarkoses. Given their Ca, SrAPS minerals can be defined as a solid solution of crandallite-goyacite-gorceixite (0.53 Ca, 0.46

APS crystals occur replacing uraniferous minerals, associated withkaolinite, mica and filling pores, in distal fluvial-to-tidal arkoses-subarkoses. Given their Ca, Sr

, X-ray diffraction, scanning electron microscopyAPS crystals occur replacing uraniferous minerals, associated with

hidroxides, carbonate-sulphate cement-replacements and secondary uraniferous minerals. , X-ray diffraction, scanning electron microscopy

APS minerals, the following diagenetic, kaolinite group minerals, illite, Fe-oxides-

hidroxides, carbonate-sulphate cement-replacements and secondary uraniferous minerals.

APS minerals, the following diageneticAPS minerals, the following diagenetic, kaolinite group minerals, illite, Fe-oxides-

deposit is constituted by sandstones, mudstones, and conglomerates with arenaceous matrix, which wereAPS minerals, the following diagenetic

Aluminium–phosphate–sulphate (APS)riassic (Buntsandstein) of the Iberian Range. The

deposit is constituted by sandstones, mudstones, and conglomerates with arenaceous matrix, which were

Aluminium–phosphate–sulphate (APS)


3 Dpt. de Ciencias de la Tierra, Facultad de Ciencias del Mar y




asociados con caolinita-dickita, mica y rellenando la porosidad de arcosas-subarcosas fluviales a marealesdistales. Dado su contenido en Ca, Sr y Ba, los minerales distales. Dado su contenido en Ca, Sr y Ba, los minerales

trónica de barrido, y microsonda electrónica. Los microcristales de asociados con caolinita-dickita, mica y rellenando la porosidad de arcosas-subarcosas fluviales a marealesdistales. Dado su contenido en Ca, Sr y Ba, los minerales

APS fueron identificados y caracterizados por microscopía óptica, difracción de rayos X, microscopía electrónica de barrido, y microsonda electrónica. Los microcristales de asociados con caolinita-dickita, mica y rellenando la porosidad de arcosas-subarcosas fluviales a mareales

cementos-reemplazamientos de carbonatos y sulfatos y minerales secundarios uraníferos. Los mineralesAPS fueron identificados y caracterizados por microscopía óptica, difracción de rayos X, microscopía electrónica de barrido, y microsonda electrónica. Los microcristales de

genéticos: cuarzo,feldespato potásico, minerales del grupo de la caolinita, illita, óxidos-hidróxidos de Fe,cementos-reemplazamientos de carbonatos y sulfatos y minerales secundarios uraníferos. Los minerales

por areniscas, lutitas y conglomerados con matriz arenosa, que fueron depositados en ambientes de fluviala marino somero. En la secuencia clástica además de los genéticos: cuarzo,feldespato potásico, minerales del grupo de la caolinita, illita, óxidos-hidróxidos de Fe,

riásico (Buntsandstein) de la Cordillera Ibérica. El depósito está constituidopor areniscas, lutitas y conglomerados con matriz arenosa, que fueron depositados en ambientes de fluviala marino somero. En la secuencia clástica además de los

Este trabajo se centra en el estudio de los minerales fosfato-sulfato alumínicos(APS) que se producenriásico (Buntsandstein) de la Cordillera Ibérica. El depósito está constituido

APS minerals, U-bearing sandstones, Diagenesis,

APS minerals indicates they were precipitated at diagenetic temperatures (higher than 80ºC), relatduring the late Cretaceous post-rift thermal stage.


precipitating from partially dissolved and altered detrital minerals. Besides, the occurrence of dickite associAPS minerals indicates they were precipitated at diagenetic temperatures (higher than 80ºC), relat

eral were originated during the supergene alteration of the Buntsandstein sandstones due to the presenceof the mineralizing fluids which causes the development of U-bearing sandstones in a distal alteration areaprecipitating from partially dissolved and altered detrital minerals. Besides, the occurrence of dickite associ

Sr and 0.01 Ba). The chemical composition, low LREE concentration and Sr > S suggest that the eral were originated during the supergene alteration of the Buntsandstein sandstones due to the presenceSr and 0.01 Ba). The chemical composition, low LREE concentration and Sr > S suggest that the


Sr and 0.01 Ba). The chemical composition, low LREE concentration and Sr > S suggest that the

APS crystals occur replacing uraniferous minerals, associated withkaolinite, mica and filling pores, in distal fluvial-to-tidal arkoses-subarkoses. Given their Ca, Sr

hidroxides, carbonate-sulphate cement-replacements and secondary uraniferous minerals. , X-ray diffraction, scanning electron microscopy

APS crystals occur replacing uraniferous minerals, associated with

, kaolinite group minerals, illite, Fe-oxides-, kaolinite group minerals, illite, Fe-oxides-hidroxides, carbonate-sulphate cement-replacements and secondary uraniferous minerals.

APS minerals, the following diagenetic, kaolinite group minerals, illite, Fe-oxides-

riassic (Buntsandstein) of the Iberian Range. Thedeposit is constituted by sandstones, mudstones, and conglomerates with arenaceous matrix, which were

APS minerals, the following diagenetic

Aluminium–phosphate–sulphate (APS)riassic (Buntsandstein) of the Iberian Range. The

deposit is constituted by sandstones, mudstones, and conglomerates with arenaceous matrix, which were


(APS) asociados a la mineralización de uranio en los red-beds


3 Dpt. de Ciencias de la



3 Dpt. de Ciencias de la

asociados con caolinita-dickita, mica y rellenando la porosidad de arcosas-subarcosas fluviales a marealesdistales. Dado su contenido en Ca, Sr y Ba, los minerales

cementos-reemplazamientos de carbonatos y sulfatos y minerales secundarios uraníferos. Los mineralesAPS fueron identificados y caracterizados por microscopía óptica, difracción de rayos X, microscopía electrónica de barrido, y microsonda electrónica. Los microcristales de asociados con caolinita-dickita, mica y rellenando la porosidad de arcosas-subarcosas fluviales a marealesdistales. Dado su contenido en Ca, Sr y Ba, los minerales

Este trabajo se centra en el estudio de los minerales fosfato-sulfato alumínicos(APS) que se producenen una secuencia clástica del por areniscas, lutitas y conglomerados con matriz arenosa, que fueron depositados en ambientes de fluviala marino somero. En la secuencia clástica además de los genéticos: cuarzo,feldespato potásico, minerales del grupo de la caolinita, illita, óxidos-hidróxidos de Fe,cementos-reemplazamientos de carbonatos y sulfatos y minerales secundarios uraníferos. Los minerales

Este trabajo se centra en el estudio de los minerales fosfato-sulfato alumínicos(APS) que se producenEste trabajo se centra en el estudio de los minerales fosfato-sulfato alumínicos(APS) que se producenen una secuencia clástica del por areniscas, lutitas y conglomerados con matriz arenosa, que fueron depositados en ambientes de fluvial

Este trabajo se centra en el estudio de los minerales fosfato-sulfato alumínicos(APS) que se producen

APS minerals indicates they were precipitated at diagenetic temperatures (higher than 80ºC), relatduring the late Cretaceous post-rift thermal stage.


were identified and characterized by optical microscopyAPS crystals occur replacing uraniferous minerals, associated with


Sr and 0.01 Ba). The chemical composition, low LREE concentration and Sr > S suggest that the eral were originated during the supergene alteration of the Buntsandstein sandstones due to the presence

deposited in fluvial to shallow-marine environments. In addition to minerals are present in the clastic sequence: quartz, K-feldsparhidroxides, carbonate-sulphate cement-replacements and secondary uraniferous minerals. were identified and characterized by optical microscopy, X-ray diffraction, scanning electron microscopy

APS crystals occur replacing uraniferous minerals, associated with

This study focuses on the mineralogical and chemical study of an Aluminium–phosphate–sulphate (APS)riassic (Buntsandstein) of the Iberian Range. The

deposit is constituted by sandstones, mudstones, and conglomerates with arenaceous matrix, which weredeposited in fluvial to shallow-marine environments. In addition to APS minerals, the following diagenetic


Origen y naturaleza de los minerales fosfato-sulfato alumínicos(APS) asociados a la mineralización de uranio en los red-bedsOrigen y naturaleza de los minerales fosfato-sulfato alumínicos(APS) asociados a la mineralización de uranio en los red-beds

minerals (APS) associated with uranium mineralization in Origin and nature of the aluminium phosphate-sulphate minerals (APS) associated with uranium mineralization in

Introduction

Aluminium phosphate-sulphate (APS) mineralsoccur in a wide range of geological environments,ranging from superficial weathering through sedi-m e n t a r y, diagenetic, hydrothermal and metamorphicenvironments, to post-magmatic systems (Dill,2001). But, APS minerals have been neglected bygeologists and geochemists due to their extremelysmall sizes (< 0.1-10 µm) and their low concentra-tions, generally less than 0.05 wt % (Gaboreau et al. ,2007). Nevertheless, APS minerals are abundant inthe clay mineral host-rock alteration assemblagesassociated with some uranium areas in the middleProterozoic basins (Wilson 1985; Beaufort et al. ,2005; Gaboreau et al., 2005; Gaboreau et al., 2007)and complex APS minerals were identified by Spötl(1990) as an early diagenetic precipitation in theLate Permian sandstones of the Northern CalcareousAlps (Austria). The model proposed for their originsuggests the precipitation of APS minerals as a con-sequence of the dissolution of detrital apatite in lowpH environment. In an extensive review, Dill (2001)remarked that the precipitation of these mineralsindicates extreme acid and oxidising conditions atshallow depths, and describes that these are commonoccurrences in different geological settings. This ori-gin was also proposed by Benito et al., (2005) andGalán Abellán et al., (2008) who studied the A P Sminerals group in palaeosols from the southeasterncontinental Late Permian of the Iberian Range.According to these authors, APS mineral formationoccurred shortly after sedimentation, due to the cir-culation of acid meteoric groundwaters, and conclu-ded that the lack of carbonates and the presence ofAPS minerals at the base of the Triassic are a clearindication of extremely acid conditions during theP e r m i a n - Triassic transition in the studied area.

In Australian sedimentary formations of marinesandstones, Rasmussen (1996) described the presen-ce of authigenic APS minerals (florencite, crandalli-te, gorceixite) as volumetrically minor but widespre-ad components of Archaean to Cretaceous sandsto-nes. In these sediments trace quantities of crandalli-te and gorceixite, as well as florencite, occur withinpockets and linings of detrital clay and quartz surfa-ces. According to this author, the authigenic mine-rals were precipitated shortly after burial within thezone of sulphate reduction and methanogenesis. Inthe Permo-Triassic sandstones of Australia, theabove author described early-diagenetic REE-phos-phate minerals with crandallite and gorceixitecrystals lining cavities formed in the sandstonesafter grain dissolution. Phosphates were probablyformed by the release of P and REE to the porewaters of fluvio-marine sediments, but they couldalso be formed by the partial dissolution and altera-tion of detrital minerals (monazite, clay matrix,feldspars and mica). The above considerations con-firm that APS minerals are key minerals, and asGaboreau et al., (2005) asserted, there is a need ofmore systematic analysis in all types of environ-ments and particularly in siliciclastic sedimentarybasins. Similarly, few data is available on the A P Scompositional variations in relations to the uraniumdeposits (e.g. Quirt et al., 1991; Gaboreau et al. ,(2005). The presence of APS minerals in theBuntsandstein sandstones where the uranium mine-ralization is widespread (Castañon et al., 1981; Dela Cruz et al., 1987), is important because the timingof APS precipitation is clearly related to the compo-sition and circulation of the mineralizing fluids. T h estudy of the clays mineralogy of the Buntsandsteinin this area of the Iberian Range by SEM, XRD,DTG and DTA has recently been accounted byMarfil et al., (2012) and reveals the illite-dickite-

2 R. Marfil, A. La Iglesia, y J. Estupiñan,

Estudios Geológicos, postprint 2013, SSN:0367-0449. doi:10.3989/egeol.40879.176

sólida de crandallita-goyacita-gorceixita (0,53 Ca, 0,46 Sr y 0,01 Ba). La baja concentración en LREE y elcontenido de Sr>S, sugieren que los minerales APS se originaron durante la alteración supergénica de lasareniscas del Buntsandstein, debido a la presencia de fluidos mineralizantes que provocaron la formaciónde areniscas uraníferas en una zona de alteración distal. Además, la aparición de dickita asociada a losminerales APS, indica que éstos precipitaron a temperatura superior a 80ºC, relacionada con el levanta-miento que tuvo lugar durante la etapa post-rift del Cretácico Superior.

Palabras clave: Minerales APS minerals, areniscas uraníferas, Diagénesis, Triasico Buntsandstein,Cadena Ibérica, España.

indication of extremely acid conditions during theriassic transition in the studied area.

indication of extremely acid conditions during the

ded that the lack of carbonates and the presence ofAPS minerals at the base of the Triassic are a clearindication of extremely acid conditions during the

culation of acid meteoric groundwaters, and conclu-ded that the lack of carbonates and the presence of

According to these authors, APS mineral formationoccurred shortly after sedimentation, due to the cir-culation of acid meteoric groundwaters, and conclu-

According to these authors, APS mineral formationoccurred shortly after sedimentation, due to the cir-

minerals group in palaeosols from the southeasterncontinental Late Permian of the Iberian Range.continental Late Permian of the Iberian Range.

A P Sminerals group in palaeosols from the southeasterncontinental Late Permian of the Iberian Range.

(2005) andA P S

occurrences in different geological settings. This ori-(2005) and

basins. Similarly, few data is available on the compositional variations in relations to the uranium

ments and particularly in siliciclastic sedimentarybasins. Similarly, few data is available on the

more systematic analysis in all types of environ-ments and particularly in siliciclastic sedimentarymore systematic analysis in all types of environ-

tion of detrital minerals (monazite, clay matrix,dspars and mica). The above considerations con-

firm that APS minerals are key minerals, and as

also be formed by the partial dissolution and altera-tion of detrital minerals (monazite, clay matrix,

waters of fluvio-marine sediments, but they couldalso be formed by the partial dissolution and altera-

formed by the release of P and REE to the porewaters of fluvio-marine sediments, but they could

after grain dissolution. Phosphates were probablyformed by the release of P and REE to the poreafter grain dissolution. Phosphates were probablyformed by the release of P and REE to the pore

crystals lining cavities formed in the sandstonesafter grain dissolution. Phosphates were probably

phate minerals with crandallite and gorceixitecrystals lining cavities formed in the sandstones

the Permo-Triassic sandstones of Australia, theabove author described early-diagenetic REE-phos-phate minerals with crandallite and gorceixite

the Permo-Triassic sandstones of Australia, thethe Permo-Triassic sandstones of Australia, theabove author described early-diagenetic REE-phos-

zone of sulphate reduction and methanogenesis. Inthe Permo-Triassic sandstones of Australia, the

rals were precipitated shortly after burial within thezone of sulphate reduction and methanogenesis. In

ces. According to this author, the authigenic mine-rals were precipitated shortly after burial within the

pockets and linings of detrital clay and quartz surfa-ces. According to this author, the authigenic mine-

these sediments trace quantities of crandalli-te and gorceixite, as well as florencite, occur withinpockets and linings of detrital clay and quartz surfa-

ad components of Archaean to Cretaceous sandsto-these sediments trace quantities of crandalli-

te, gorceixite) as volumetrically minor but widespre-ad components of Archaean to Cretaceous sandsto-

ce of authigenic APS minerals (florencite, crandalli-te, gorceixite) as volumetrically minor but widespre-

riassic transition in the studied area.indication of extremely acid conditions during the

riassic transition in the studied area.

APS minerals at the base of the Triassic are a clearindication of extremely acid conditions during the

riassic transition in the studied area.

ded that the lack of carbonates and the presence ofAPS minerals at the base of the Triassic are a clear

culation of acid meteoric groundwaters, and conclu-ded that the lack of carbonates and the presence of

occurred shortly after sedimentation, due to the cir-culation of acid meteoric groundwaters, and conclu-ded that the lack of carbonates and the presence of

According to these authors, APS mineral formationoccurred shortly after sedimentation, due to the cir-culation of acid meteoric groundwaters, and conclu-

continental Late Permian of the Iberian Range.According to these authors, APS mineral formation

minerals group in palaeosols from the southeasterncontinental Late Permian of the Iberian Range.

., (2008) who studied the minerals group in palaeosols from the southeastern

occurrences in different geological settings. This ori-et al., (2005) and

., (2008) who studied the

shallow depths, and describes that these are commonshallow depths, and describes that these are commonoccurrences in different geological settings. This ori-

indicates extreme acid and oxidising conditions atshallow depths, and describes that these are common

remarked that the precipitation of these mineralsindicates extreme acid and oxidising conditions at

sequence of the dissolution of detrital apatite in lowpH environment. In an extensive review, Dill (2001)remarked that the precipitation of these minerals

Gaboreau

felfirm that APS minerals are key minerals, and as

also be formed by the partial dissolution and altera-tion of detrital minerals (monazite, clay matrix,feldspars and mica). The above considerations con-

waters of fluvio-marine sediments, but they couldalso be formed by the partial dissolution and altera-waters of fluvio-marine sediments, but they couldalso be formed by the partial dissolution and altera-

after grain dissolution. Phosphates were probablyformed by the release of P and REE to the porewaters of fluvio-marine sediments, but they could

crystals lining cavities formed in the sandstonesafter grain dissolution. Phosphates were probablyformed by the release of P and REE to the pore

phate minerals with crandallite and gorceixitecrystals lining cavities formed in the sandstones

above author described early-diagenetic REE-phos-above author described early-diagenetic REE-phos-phate minerals with crandallite and gorceixite

the Permo-Triassic sandstones of Australia, theabove author described early-diagenetic REE-phos-

zone of sulphate reduction and methanogenesis. Inthe Permo-Triassic sandstones of Australia, the

rals were precipitated shortly after burial within thezone of sulphate reduction and methanogenesis. In

ces. According to this author, the authigenic mine-rals were precipitated shortly after burial within the

pockets and linings of detrital clay and quartz surfa-ces. According to this author, the authigenic mine-

te and gorceixite, as well as florencite, occur withinpockets and linings of detrital clay and quartz surfa-


te and gorceixite, as well as florencite, occur within

te, gorceixite) as volumetrically minor but widespre-te, gorceixite) as volumetrically minor but widespre-ad components of Archaean to Cretaceous sandsto-

ce of authigenic APS minerals (florencite, crandalli-te, gorceixite) as volumetrically minor but widespre-ce of authigenic APS minerals (florencite, crandalli-

formations of marinesandstones, Rasmussen (1996) described the presen-

formations of marine


indication of extremely acid conditions during theP e r m i a n - T

culation of acid meteoric groundwaters, and conclu-ded that the lack of carbonates and the presence ofAPS minerals at the base of the Triassic are a clearindication of extremely acid conditions during the

According to these authors, APS mineral formationoccurred shortly after sedimentation, due to the cir-culation of acid meteoric groundwaters, and conclu-ded that the lack of carbonates and the presence of

gin was also proposed by Benito et al., (2008) who studied the

minerals group in palaeosols from the southeasterncontinental Late Permian of the Iberian Range.According to these authors, APS mineral formation

occurrences in different geological settings. This ori-occurrences in different geological settings. This ori-gin was also proposed by Benito

., (2008) who studied the

indicates extreme acid and oxidising conditions atshallow depths, and describes that these are commonoccurrences in different geological settings. This ori-gin was also proposed by Benito

sequence of the dissolution of detrital apatite in lowpH environment. In an extensive review, Dill (2001)remarked that the precipitation of these mineralsindicates extreme acid and oxidising conditions at

Proterozoic basins (Wilson 1985; Beaufort et aet al., 2007)

and complex APS minerals were identified by Spötl(1990) as an early diagenetic precipitation in theLate Permian sandstones of the Northern Calcareous

the clay mineral host-rock alteration assemblagesassociated with some uranium areas in the middle

et al. ,

above author described early-diagenetic REE-phos-phate minerals with crandallite and gorceixitecrystals lining cavities formed in the sandstones

rals were precipitated shortly after burial within thezone of sulphate reduction and methanogenesis. Inthe Permo-Triassic sandstones of Australia, theabove author described early-diagenetic REE-phos-

te and gorceixite, as well as florencite, occur withinpockets and linings of detrital clay and quartz surfa-ces. According to this author, the authigenic mine-rals were precipitated shortly after burial within the



te and gorceixite, as well as florencite, occur withinpockets and linings of detrital clay and quartz surfa-

sandstones, Rasmussen (1996) described the presen-ce of authigenic APS minerals (florencite, crandalli-te, gorceixite) as volumetrically minor but widespre-ad components of Archaean to Cretaceous sandsto-

these sediments trace quantities of crandalli-

In Australian sedimentary In Australian sedimentary sandstones, Rasmussen (1996) described the presen-ce of authigenic APS minerals (florencite, crandalli-

In Australian sedimentary formations of marine

APS, indica que éstos precipitaron a temperatura superior a 80ºC, relacionada con el levanta

riasico Buntsandstein,

APS se originaron durante la alteración supergénica de lasareniscas del Buntsandstein, debido a la presencia de fluidos mineralizantes que provocaron la formación

Además, la aparición de dickita asociada a losAPS, indica que éstos precipitaron a temperatura superior a 80ºC, relacionada con el levanta

kaolinite mineral assemblage. The purpose of thepresent study is to contribute to a better understan-ding of the origin of these APS minerals and theirrelationship to the uranium mineral alteration.

Geological setting

The Iberian Range is an intracratonic, foldedsegment of the Alpine chain that developed as a riftbasin between Permian and late Cretaceous times(Salas & Casas, 1993; Salas et al., 2001). The for-mer authors indicate that the Iberian Basin wasfilled with thick clastic sequences during two riftingcycles, the first spanning from Late Permian to LateTriassic, and the second from Late Jurassic to EarlyAlbian. During these active periods, sedimentationtook place mainly in alluvial to lacustrine environ-ments in a complex system of extensional basins.Both cycles gave way to periods of post-rift thermalsubsidence during which shallow-marine carbon-ates were deposited. The sedimentation of thePermian and Triassic red-bed sandstones and mud-stones took place during the first stage of rifting inhalf–graben basins. During Early Permian (Au-tunian) times, a series of half–graben, intermontanebasins become unfilled by alluvial fans, slope brec-cias and lacustrine deposits associated in theirlower part with volcaniclastic rocks of cal-alkalineaffinities, such as andesites with subordinate rhyo-lites and basalts (Muñoz et al., 1983).

The Buntsandstein sediments can be dividedinto two major successions that are not always bothpresent in the Iberian area: a lower one, comprisinglaterally restricted conglomerates and more wide-spread sandstones, and an upper one of irregulardistribution, comprising sandstones, sandstones andsiltstones and siltstones. The lower successionshows a marked fining –upward sequence interpret-ed as being of alluvial fan origin and forming anapron derived from an elevated SW margin of theriff basin. The overlying formation consists, of pinkto red bedded sandstones of sandy braided river ori-gin. These sandstones consist of amalgamate chan-nel deposits totally devoid of fine grained floodplain sediments and are interpreted as having beendeposited during a slow subsidence rate (Lopez-Gomez et al, 2011).

This study is based on core samples from bore-hole “Sigüenza 44-3” (drilled by the former Spa-nish Junta de Energía Nuclear (today CIEMAT) andby the Shell Company in 1978), with a depth of 999m. This borehole is located on the Sigüenza Highsome 110 km Northeast of Madrid (Fig. 1). Twolarge Buntsandstein units were sampled, a lowerunit (538 to 369 m) composed of conglomeratesand sandstones with sporadic interbedded mud-stones at the top, and an upper unit (369 to 300 m)constituted by sandstones and mudstones and occa-sional conglomerates with arenaceous matrix. Bothunits are red beds, separated by a 10 m-thick con-glomerate, and were sedimentologically distin-guished in the original survey logs (Fig. 1). TheGamma ray spectrometry shows a radioactiveanomaly at a depth between 340 and 345 m, whichis related to the presence of secondary uraniumminerals in grey mineralized zones. On the con-trary, in this area, exploration of Buntsandstein tar-gets has not been successful, despite the fact thatsurface oil seeps are present in the Sigüenza area(Marfil et al., 1996b).

Samples and methods

The mineralogical composition of the almost 50sandstones and mudstones selected from the twoBuntsandstein units was determined by modalanalysis (400 points per thin section) using a polar-izing microscope. X-ray powder diffraction (XRD)analyses were performed on the 2-20 µm and <2µmfractions. A Bruker D8 Advance diffractometer,equipped with a Sol-X detector was used. Theexperimental conditions were: measurement inter-val 2- 70º 2q, time per step1 s, and a step size of0.02º 2q. The mineralogical composition of thecrystalline phases was estimated following Chung´s(1975) method and using Bruker software (EVA).Selected sandstones and mudstones samples wereexamined using a JEOL JSM-6400 scanning elec-tron microscope equipped with a Link Systemsenergy-dispersive X-ray microanalyser (accelerat-ing voltage 15 KV, beam current 3nA) by second-ary electron (SE) and backscattered electron (BSE)modes. Finally, the chemical composition of theAPS minerals was determined using a JEOL JXA-

Origin and nature of the aluminium phosphate-sulfate minerals (APS)… 3

Estudios Geológicos, postprint 2013, ISSN:0367-0449. doi:10.3989/egeol.40879.176

deposited during a slow subsidence rate (Lopez-plain sediments and are interpreted as having beendeposited during a slow subsidence rate (Lopez-

nel deposits totally devoid of fine grained floodplain sediments and are interpreted as having been

These sandstones consist of amalgamate channel deposits totally devoid of fine grained flood

The overlying formation consists, of pinkto red bedded sandstones of sandy braided river ori

gin of theThe overlying formation consists, of pink

ed as being of alluvial fan origin and forming aned as being of alluvial fan origin and forming angin of the

shows a marked fining –upward sequence interpret-ed as being of alluvial fan origin and forming an

0.02º 2crystalline phases was estimated following Chung´s

val 2- 70º 20.02º 2

experimental conditions were: measurement interval 2- 70º 2

equipped with a Sol-X detector was used. experimental conditions were: measurement inter

fractions. equipped with a Sol-X detector was used.

analyses were performed on the 2-20 µm and <2µmfractions. A

Buntsandstein units was determined by modalanalysis (400 points per thin section) using a polar

sandstones and mudstones selected from the twoBuntsandstein units was determined by modal

The mineralogical composition of the almost 50sandstones and mudstones selected from the two

The mineralogical composition of the almost 50

Samples and methodsSamples and methodsSamples and methods

surface oil seeps are present in the Sigüenza areasurface oil seeps are present in the Sigüenza areasurface oil seeps are present in the Sigüenza areagets has not been successful, despite the fact thatsurface oil seeps are present in the Sigüenza area

, in this area, exploration of Buntsandstein targets has not been successful, despite the fact that

is related to the presence of secondary uraniumminerals in grey mineralized zones. On the con

anomaly at a depth between 340 and 345 m,is related to the presence of secondary uranium

Gamma ray spectrometry shows a radioactiveanomaly at a depth between 340 and 345 m, which

guished in the original survey logs (Fig. 1). TheGamma ray spectrometry shows a radioactive

glomerate, and were sedimentologically distin-The

units are red beds, separated by a 10 m-thick con-glomerate, and were sedimentologically distin-

deposited during a slow subsidence rate (Lopez-1).

deposited during a slow subsidence rate (Lopez-plain sediments and are interpreted as having beendeposited during a slow subsidence rate (Lopez-

nel deposits totally devoid of fine grained floodnel deposits totally devoid of fine grained floodplain sediments and are interpreted as having been

to red bedded sandstones of sandy braided river oriThese sandstones consist of amalgamate chan

nel deposits totally devoid of fine grained flood


The overlying formation consists, of pinkto red bedded sandstones of sandy braided river ori

apron derived from an elevated SW marThe overlying formation consists, of pink

shows a marked fining –upward sequence interpreted as being of alluvial fan origin and forming an

siltstones and siltstones. The lower successionshows a marked fining –upward sequence interpreted as being of alluvial fan origin and forming an

spread sandstones, and an upper one of irregulardistribution, comprising sandstones, sandstones andsiltstones and siltstones. The lower succession

spread sandstones, and an upper one of irregularspread sandstones, and an upper one of irregulardistribution, comprising sandstones, sandstones and

laterally restricted conglomerates and more wide-spread sandstones, and an upper one of irregular

into two major successions that are not always bothpresent in the Iberian area: a lower one, comprising

izing microscope. X-ray powder difanalyses were performed on the 2-20 µm and <2µmfractions.

Buntsandstein units was determined by modalanalysis (400 points per thin section) using a polarizing microscope. X-ray powder dif

sandstones and mudstones selected from the twoBuntsandstein units was determined by modal

The mineralogical composition of the almost 50sandstones and mudstones selected from the two


Samples and methods


Samples and methods

., 1996b).., 1996b).surface oil seeps are present in the Sigüenza area

., 1996b).

gets has not been successful, despite the fact thatsurface oil seeps are present in the Sigüenza area

, in this area, exploration of Buntsandstein targets has not been successful, despite the fact that


, in this area, exploration of Buntsandstein tar


Gamma ray spectrometry shows a radioactiveanomaly at a depth between 340 and 345 m,is related to the presence of secondary uranium

guished in the original survey logs (Fig. 1). Gamma ray spectrometry shows a radioactive

glomerate, and were sedimentologically distin-glomerate, and were sedimentologically distin-guished in the original survey logs (Fig. 1).

units are red beds, separated by a 10 m-thick conglomerate, and were sedimentologically distin-units are red beds, separated by a 10 m-thick con

constituted by sandstones and mudstones and occasional conglomerates with arenaceous matrix. Both

at the top, and an upper unit (369 to 300 m)constituted by sandstones and mudstones and occa

plain sediments and are interpreted as having beendeposited during a slow subsidence rate (Lopez-Gomez et al, 201

These sandstones consist of amalgamate channel deposits totally devoid of fine grained floodplain sediments and are interpreted as having been

apron derived from an elevated SWThe overlying formation consists, of pink


nel deposits totally devoid of fine grained flood

siltstones and siltstones. The lower successionshows a marked fining –upward sequence interpreted as being of alluvial fan origin and forming anapron derived from an elevated SW

The overlying formation consists, of pink

spread sandstones, and an upper one of irregulardistribution, comprising sandstones, sandstones anddistribution, comprising sandstones, sandstones andsiltstones and siltstones. The lower successionshows a marked fining –upward sequence interpret

present in the Iberian area: a lower one, comprisinglaterally restricted conglomerates and more widespread sandstones, and an upper one of irregulardistribution, comprising sandstones, sandstones and

The Buntsandstein sediments can be dividedinto two major successions that are not always bothpresent in the Iberian area: a lower one, comprisinglaterally restricted conglomerates and more wide

half–graben basins. During Early Permian (Autunian) times, a series of half–graben, intermontanebasins become unfilled by alluvial fans, slope breccias and lacustrine deposits associated in theirlower part with volcaniclastic rocks of cal-alkaline

Samples and methods

surface oil seeps are present in the Sigüenza area(Marfil

minerals in grey mineralized zones. On the contrary, in this area, exploration of Buntsandstein targets has not been successful, despite the fact thatsurface oil seeps are present in the Sigüenza area

anomaly at a depth between 340 and 345 m,is related to the presence of secondary uraniumminerals in grey mineralized zones. On the con

, in this area, exploration of Buntsandstein tar

glomerate, and were sedimentologically distin-guished in the original survey logs (Fig. 1). Gamma ray spectrometry shows a radioactiveguished in the original survey logs (Fig. 1). Gamma ray spectrometry shows a radioactiveanomaly at a depth between 340 and 345 m,is related to the presence of secondary uranium

sional conglomerates with arenaceous matrix. Bothunits are red beds, separated by a 10 m-thick conglomerate, and were sedimentologically distin-guished in the original survey logs (Fig. 1). Gamma ray spectrometry shows a radioactive


at the top, and an upper unit (369 to 300 m)constituted by sandstones and mudstones and occasional conglomerates with arenaceous matrix. Bothunits are red beds, separated by a 10 m-thick con

unit (538 to 369 m) composed of conglomeratesand sandstones with sporadic interbedded mud


located on the Sigüenza Highsome 110 km Northeast of Madrid (Fig. 1).

ge Buntsandstein units were sampled, a lowerunit (538 to 369 m) composed of conglomerates

hole “Sigüenza 44-3” (drilled by the former Spagía Nuclear (today CIEMAT) andgía Nuclear (today CIEMAT) andgía Nuclear (today CIEMA

by the Shell Company in 1978), with a depth of 999located on the Sigüenza High



Fig. 1— Map of Spain showing the location of the Sigüenza High and borehole “Sigüenza 44-3”, as well as, the syn-thetic lithological section of the Triassic (Buntsandstein) sequence with logs (GR, SP, RS). Modified from Marfil etal., (1996b).

riassic (Buntsandstein) sequence with logs (GR, SPFig. 1— Map of Spain showing the location of the Sigüenza High and borehole “Sigüenza 44-3”, as well as, the syn

riassic (Buntsandstein) sequence with logs (GR, SPFig. 1— Map of Spain showing the location of the Sigüenza High and borehole “Sigüenza 44-3”, as well as, the syn

lithological section of the Fig. 1— Map of Spain showing the location of the Sigüenza High and borehole “Sigüenza 44-3”, as well as, the syn

lithological section of the Fig. 1— Map of Spain showing the location of the Sigüenza High and borehole “Sigüenza 44-3”, as well as, the syn

lithological section of the


Fig. 1— Map of Spain showing the location of the Sigüenza High and borehole “Sigüenza 44-3”, as well as, the synthetic lithological section of the al., (1996b).

Fig. 1— Map of Spain showing the location of the Sigüenza High and borehole “Sigüenza 44-3”, as well as, the syn

8900 electron microprobe (accelerating voltage 15kV, current 21.5 nA, beam diameter 5 µm and thecounting time 100s). The detection limits in ppmwere 250 for Al, 370 for Sr; 245 for Fe, 205 for P,135 for Ca, 240 for S, and 285 for Ba. For LREEthe detection limits were 222 for Nd, 90 for La, 60for Ce, 53 for Th and 158 for Pr. The followingstandard were used: For P apatite; for Ca augite; forSr CO3Sr; for Al sillimanite; for Fe almandine; forBa CO3Ba, for F apatite; for S chalcopyrite, and forLREE synthetic glass from PH developments.

Results

Bulk composition of the sandstones

Modal analyses indicated that the Buntsandsteinsandstones are mainly arkoses, subarkoses andquartzarenites (Table 1; Fig. 2) with coarse to me-dium grain (2.0 -1.0 mm and 1-0.5mm), and mode-rate sorting (Trask coefficient 1.2 - 1.4). Feldspars,mainly K-feldspars, appear to be commonly repla-ced by illite and kaolinite minerals. Ductile rockfragments consist of micaschists, argillites, and earlyeroded and transported (rip-up clasts). Mica includesmuscovite and subordinate amounts of biotite.Turmaline, apatite, rutile, anatase, sphene, malachi-te, ilmenite, monazite, torbernite and xenotime arecharacteristic accessory components. Frameworkgrains and the matrix are replaced by secondary ura-niferous minerals in green and grey sandstones beds.These secondary uraniferous minerals appear in dif-ferent associations: as cement (Fig. 3A), replacing

feldspars and illite epimatrix (Fig. 3B) and chert,filling microfractures of the quartz grains and theexfoliation planes of the mica. They also becomevisible as individual grains (Fig. 3C, D, E). Severalof these uraniferous mineral grains are replaced byAPS as the figures 3C and 3F show. Pyrite appearsto be associated with the development of anhydritenodules. Other cements include scarce K-feldsparo v e rgrowths, Fe and Ti oxides or oxyhydroxides (ascoatings and patches), dolomite and Fe-dolomi-te/ankerite. Occasionally, abundant calcite, anhydri-



Table 1.— Mineral compositions based on modal analyses of selected samples containing APS minerals. Q: cuarzo;K-F: K-feldspar; MRF: metamorphic rock fragments; VRF: Volcanic rock fragments; Q overg: Quartz overgrowth: Anh:anhydrite

Fig. 2.— Ternary plot of the framework minerals: quartz(Q), feldspars (F) and lithic rock fragments (Lt) forBuntsandstein sandstone samples from boreholeSigüenza SS-44-3.ferent associations: as cement (Fig. 3A), replacing

These secondary uraniferous minerals appear in dif-ferent associations: as cement (Fig. 3A), replacingThese secondary uraniferous minerals appear in dif-

grains and the matrix are replaced by secondary ura-niferous minerals in green and grey sandstones beds.These secondary uraniferous minerals appear in dif-

characteristic accessory components. Frameworkgrains and the matrix are replaced by secondary ura-

Turmaline, apatite, rutile, anatase, sphene, malachi-te, ilmenite, monazite, torbernite and xenotime arecharacteristic accessory components. Framework

Turmaline, apatite, rutile, anatase, sphene, malachi-te, ilmenite, monazite, torbernite and xenotime are

eroded and transported (rip-up clasts). Mica includesmuscovite and subordinate amounts of biotite.

fragments consist of micaschists, argillites, and earlyeroded and transported (rip-up clasts). Mica includesmuscovite and subordinate amounts of biotite.

te/ankerite. Occasionally, abundant calcite, anhydri-coatings and patches), dolomite and Fe-dolomi-te/ankerite. Occasionally, abundant calcite, anhydri-

growths, Fe and Ti oxides or oxyhydroxides (ascoatings and patches), dolomite and Fe-dolomi-

nodules. Other cements include scarce K-feldsparnodules. Other cements include scarce K-feldspargrowths, Fe and Ti oxides or oxyhydroxides (as

to be associated with the development of anhydritenodules. Other cements include scarce K-feldspar

APS as the figures 3C and 3F show. Pyrite appearsto be associated with the development of anhydritenodules. Other cements include scarce K-feldspar

of these uraniferous mineral grains are replaced byAPS as the figures 3C and 3F show. Pyrite appears

visible as individual grains (Fig. 3C, D, E). Severalof these uraniferous mineral grains are replaced by

filling microfractures of the quartz grains and theexfoliation planes of the mica. They also becomevisible as individual grains (Fig. 3C, D, E). Several

feldspars and illite epimatrix (Fig. 3B) and chert,filling microfractures of the quartz grains and thefeldspars and illite epimatrix (Fig. 3B) and chert,

ferent associations: as cement (Fig. 3A), replacingThese secondary uraniferous minerals appear in dif-ferent associations: as cement (Fig. 3A), replacing

niferous minerals in green and grey sandstones beds.These secondary uraniferous minerals appear in dif-ferent associations: as cement (Fig. 3A), replacing

grains and the matrix are replaced by secondary ura-niferous minerals in green and grey sandstones beds.

characteristic accessory components. Frameworkgrains and the matrix are replaced by secondary ura-

te, ilmenite, monazite, torbernite and xenotime arecharacteristic accessory components. Frameworkgrains and the matrix are replaced by secondary ura-

Turmaline, apatite, rutile, anatase, sphene, malachi-te, ilmenite, monazite, torbernite and xenotime arecharacteristic accessory components. Framework

muscovite and subordinate amounts of biotite.Turmaline, apatite, rutile, anatase, sphene, malachi-

eroded and transported (rip-up clasts). Mica includesmuscovite and subordinate amounts of biotite.

ced by illite and kaolinite minerals. Ductile rockfragments consist of micaschists, argillites, and earlyeroded and transported (rip-up clasts). Mica includes

mainly K-feldspars, appear to be commonly repla-ced by illite and kaolinite minerals. Ductile rockfragments consist of micaschists, argillites, and early

rate sorting (Trask coefficient 1.2 - 1.4). Feldspars,rate sorting (Trask coefficient 1.2 - 1.4). Feldspars,mainly K-feldspars, appear to be commonly repla-

dium grain (2.0 -1.0 mm and 1-0.5mm), and mode-rate sorting (Trask coefficient 1.2 - 1.4). Feldspars,

quartzarenites (Table 1; Fig. 2) with coarse to me-dium grain (2.0 -1.0 mm and 1-0.5mm), and mode-

coatings and patches), dolomite and Fe-dolomi-te/ankerite. Occasionally, abundant calcite, anhydri-

growths, Fe and Ti oxides or oxyhydroxides (asgrowths, Fe and Ti oxides or oxyhydroxides (ascoatings and patches), dolomite and Fe-dolomi-

nodules. Other cements include scarce K-feldspargrowths, Fe and Ti oxides or oxyhydroxides (as

coatings and patches), dolomite and Fe-dolomi-

to be associated with the development of anhydritenodules. Other cements include scarce K-feldspar

APS as the figures 3C and 3F show. Pyrite appearsto be associated with the development of anhydrite

of these uraniferous mineral grains are replaced byAPS as the figures 3C and 3F show. Pyrite appearsof these uraniferous mineral grains are replaced by

exfoliation planes of the mica. They also becomevisible as individual grains (Fig. 3C, D, E). Several

feldspars and illite epimatrix (Fig. 3B) and chert,filling microfractures of the quartz grains and theexfoliation planes of the mica. They also become

feldspars and illite epimatrix (Fig. 3B) and chert,feldspars and illite epimatrix (Fig. 3B) and chert,

These secondary uraniferous minerals appear in dif-ferent associations: as cement (Fig. 3A), replacing

characteristic accessory components. Frameworkgrains and the matrix are replaced by secondary ura-niferous minerals in green and grey sandstones beds.These secondary uraniferous minerals appear in dif-

Turmaline, apatite, rutile, anatase, sphene, malachi-te, ilmenite, monazite, torbernite and xenotime arecharacteristic accessory components. Frameworkgrains and the matrix are replaced by secondary ura-

ced by illite and kaolinite minerals. Ductile rockfragments consist of micaschists, argillites, and earlyeroded and transported (rip-up clasts). Mica includesmuscovite and subordinate amounts of biotite.Turmaline, apatite, rutile, anatase, sphene, malachi-

mainly K-feldspars, appear to be commonly repla-mainly K-feldspars, appear to be commonly repla-ced by illite and kaolinite minerals. Ductile rockfragments consist of micaschists, argillites, and early

dium grain (2.0 -1.0 mm and 1-0.5mm), and mode-rate sorting (Trask coefficient 1.2 - 1.4). Feldspars,mainly K-feldspars, appear to be commonly repla-ced by illite and kaolinite minerals. Ductile rock

Modal analyses indicated that the Buntsandsteinsandstones are mainly arkoses, subarkoses andquartzarenites (Table 1; Fig. 2) with coarse to me-dium grain (2.0 -1.0 mm and 1-0.5mm), and mode-

LREE synthetic glass from PH developments.

o v e rgrowths, Fe and Ti oxides or oxyhydroxides (aso v e rgrowths, Fe and Ti oxides or oxyhydroxides (aso v e rcoatings and patches), dolomite and Fe-dolomi-te/ankerite. Occasionally, abundant calcite, anhydri-

APS as the figures 3C and 3F show. Pyrite appearsto be associated with the development of anhydritenodules. Other cements include scarce K-feldspar

growths, Fe and Ti oxides or oxyhydroxides (as

exfoliation planes of the mica. They also becomevisible as individual grains (Fig. 3C, D, E). Severalof these uraniferous mineral grains are replaced byAPS as the figures 3C and 3F show. Pyrite appears

feldspars and illite epimatrix (Fig. 3B) and chert,filling microfractures of the quartz grains and thefeldspars and illite epimatrix (Fig. 3B) and chert,filling microfractures of the quartz grains and theexfoliation planes of the mica. They also becomevisible as individual grains (Fig. 3C, D, E). Several

feldspars and illite epimatrix (Fig. 3B) and chert,filling microfractures of the quartz grains and the

K-F: K-feldspar; MRF: metamorphic rock fragments; VRF: Volcanic rock fragments; Q overg: Quartz overgrowth: K-F: K-feldspar; MRF: metamorphic rock fragments; VRF: Volcanic rock fragments; Q overg: Quartz overgrowth:



Fig. 3.—A) Photomicrograph (crossed nicols) showing secondary uranium minerals (U) replacing frame-work detritalgrains (possibly feldspars and illitized feldspars), as well as, quartz overgrowths. B) Photomicrograph (crossednicols) of the secondary uranium mineral (U) replacing feldspars and illite epimatrix. C) SEM image of the secondaryuranium mineral (U) partially replaced by small APS microcrystals (Table 4, analysis 67617-5). D) and E) SEMimages of secondary uranium mineral grains (U). E) U grain is replacing clay matrix composed by kaolinite. Theanalyses of these grains are in Table 4 (analysis 20492-1 and 67616-3). F) Several secondary uranium mineralphases (U) replaced by APS microcrystals. In the centre, remains of K-feldspar partially replaced by kaolinite (F-K toK) (Analyses 67616-4 of Table 4).able 4).

APS microcrystals. In the centre, remains of K-feldspar partially replaced by kaolinite (F-K toable 4).

able 4 (analysis 20492-1 and 67616-3). F) Several secondary uranium mineralAPS microcrystals. In the centre, remains of K-feldspar partially replaced by kaolinite (F-K to

images of secondary uranium mineral grains (U). E) U grain is replacing clay matrix composed by kaolinite. Theable 4 (analysis 20492-1 and 67616-3). F) Several secondary uranium mineral

uranium mineral (U) partially replaced by small images of secondary uranium mineral grains (U). E) U grain is replacing clay matrix composed by kaolinite. The

Fig. 3.—A) Photomicrograph (crossed nicols) showing secondary uranium minerals (U) replacing frame-work detritalgrains (possibly feldspars and illitized feldspars), as well as, quartz overgrowths. B) Photomicrograph (crossednicols) of the secondary uranium mineral (U) replacing feldspars and illite epimatrix. C) SEM image of the secondary

Fig. 3.—A) Photomicrograph (crossed nicols) showing secondary uranium minerals (U) replacing frame-work detritalgrains (possibly feldspars and illitized feldspars), as well as, quartz overgrowths. B) Photomicrograph (crossed

K) (Analyses 67616-4 of phases (U) replaced by K) (Analyses 67616-4 of T

images of secondary uranium mineral grains (U). E) U grain is replacing clay matrix composed by kaolinite. Theanalyses of these grains are in phases (U) replaced by APS microcrystals. In the centre, remains of K-feldspar partially replaced by kaolinite (F-K to

able 4).

uranium mineral (U) partially replaced by small images of secondary uranium mineral grains (U). E) U grain is replacing clay matrix composed by kaolinite. Theimages of secondary uranium mineral grains (U). E) U grain is replacing clay matrix composed by kaolinite. Theanalyses of these grains are in

nicols) of the secondary uranium mineral (U) replacing feldspars and illite epimatrix. C) SEM image of the secondaryuranium mineral (U) partially replaced by small images of secondary uranium mineral grains (U). E) U grain is replacing clay matrix composed by kaolinite. The

grains (possibly feldspars and illitized feldspars), as well as, quartz overgrowths. B) Photomicrograph (crossednicols) of the secondary uranium mineral (U) replacing feldspars and illite epimatrix. C) SEM image of the secondaryuranium mineral (U) partially replaced by small

Fig. 3.—A) Photomicrograph (crossed nicols) showing secondary uranium minerals (U) replacing frame-work detritalgrains (possibly feldspars and illitized feldspars), as well as, quartz overgrowths. B) Photomicrograph (crossednicols) of the secondary uranium mineral (U) replacing feldspars and illite epimatrix. C) SEM image of the secondary

Fig. 3.—A) Photomicrograph (crossed nicols) showing secondary uranium minerals (U) replacing frame-work detrital


analyses of these grains are in phases (U) replaced by K) (Analyses 67616-4 of

nicols) of the secondary uranium mineral (U) replacing feldspars and illite epimatrix. C) SEM image of the secondaryuranium mineral (U) partially replaced by small images of secondary uranium mineral grains (U). E) U grain is replacing clay matrix composed by kaolinite. Theanalyses of these grains are in phases (U) replaced by

Fig. 3.—A) Photomicrograph (crossed nicols) showing secondary uranium minerals (U) replacing frame-work detritalgrains (possibly feldspars and illitized feldspars), as well as, quartz overgrowths. B) Photomicrograph (crossednicols) of the secondary uranium mineral (U) replacing feldspars and illite epimatrix. C) SEM image of the secondaryuranium mineral (U) partially replaced by small images of secondary uranium mineral grains (U). E) U grain is replacing clay matrix composed by kaolinite. The

Fig. 3.—A) Photomicrograph (crossed nicols) showing secondary uranium minerals (U) replacing frame-work detrital

te and barite are common cement replacements. A P Sminerals are recognized at a depth between 365 mand 390m in core samples, corresponding to distalfluvial-to-tidal arkoses, near the boundary betweenthe upper and lower units of the studied sequence(Fig.1). Hydrocarbon (HC) impregnations weredetected in some grey Buntsandstein sandstones(Fig. 1); however, organic matter is rare and onlyappears in some anhydrite nodules.

Petrography, mineralogy, and chemical characteristic of the APS minerals

Significant amounts of APS minerals were detec-ted in thin sections and SEM. APS minerals occur asvery small idiomorphic crystals filling secondarypores, stylolites and microfractures (Fig. 4 B). T h e s eminerals replace uraniferous grains or they areenclosed in the distorted and broken mica crystals



Fig. 4.— Comparison of the XRD patterns of the selected Buntsandstein sandstone samples containing APS miner-als from the upper unit (300 to 369 m) and the samples from the lower unit (369 to 538 m). Fraction 20-2µm. Thepeaks are labeled as c: crandallite, f: feldspar, il: illite, k: kaolinite, q: quartz

Table 2.— Mineralogical composition by XRD diffraction of selected sandstone samples (size fraction 2-20 µm). Mineralogical composition by XRD diffraction of selected sandstone samples (size fraction 2-20 Mineralogical composition by XRD diffraction of selected sandstone samples (size fraction 2-20 Mineralogical composition by XRD diffraction of selected sandstone samples (size fraction 2-20 Mineralogical composition by XRD diffraction of selected sandstone samples (size fraction 2-20 Mineralogical composition by XRD diffraction of selected sandstone samples (size fraction 2-20

enclosed in the distorted and broken mica crystalsminerals replace uraniferous grains or they areenclosed in the distorted and broken mica crystals

pores, stylolites and microfractures (Fig. 4 B). minerals replace uraniferous grains or they are

very small idiomorphic crystals filling secondarypores, stylolites and microfractures (Fig. 4 B). very small idiomorphic crystals filling secondaryted in thin sections and SEM. APS minerals occur asvery small idiomorphic crystals filling secondary

characteristic of the , mineralogy

characteristic of the , mineralogy

Fig. 4.— Comparison of the XRD patterns of the selected Buntsandstein sandstone samples containing als from the upper unit (300 to 369 m) and the samples from the lower unit (369 to 538 m). Fraction 20-2Fig. 4.— Comparison of the XRD patterns of the selected Buntsandstein sandstone samples containing als from the upper unit (300 to 369 m) and the samples from the lower unit (369 to 538 m). Fraction 20-2Fig. 4.— Comparison of the XRD patterns of the selected Buntsandstein sandstone samples containing

Mineralogical composition by XRD diffraction of selected sandstone samples (size fraction 2-20 Mineralogical composition by XRD diffraction of selected sandstone samples (size fraction 2-20 Mineralogical composition by XRD diffraction of selected sandstone samples (size fraction 2-20 Mineralogical composition by XRD diffraction of selected sandstone samples (size fraction 2-20 Mineralogical composition by XRD diffraction of selected sandstone samples (size fraction 2-20

(Fig. 1); however, organic matter is rare and onlydetected in some grey Buntsandstein sandstonesdetected in some grey Buntsandstein sandstones(Fig. 1); however, organic matter is rare and only

(Fig.1). Hydrocarbon (HC) impregnations weredetected in some grey Buntsandstein sandstones(Fig. 1); however, organic matter is rare and only

the upper and lower units of the studied sequence(Fig.1). Hydrocarbon (HC) impregnations were

Significant amounts of APS minerals were detec-ted in thin sections and SEM. APS minerals occur as

characteristic of the Petrographycharacteristic of the Petrography

als from the upper unit (300 to 369 m) and the samples from the lower unit (369 to 538 m). Fraction 20-2peaks are labeled as c: crandallite, f: feldspar, il: illite, k: kaolinite, q: quartz

Fig. 4.— Comparison of the XRD patterns of the selected Buntsandstein sandstone samples containing als from the upper unit (300 to 369 m) and the samples from the lower unit (369 to 538 m). Fraction 20-2

appears in some anhydrite nodules.

Mineralogical composition by XRD diffraction of selected sandstone samples (size fraction 2-20 Mineralogical composition by XRD diffraction of selected sandstone samples (size fraction 2-20 Mineralogical composition by XRD diffraction of selected sandstone samples (size fraction 2-20 Mineralogical composition by XRD diffraction of selected sandstone samples (size fraction 2-20

(Fig. 1); however, organic matter is rare and onlyappears in some anhydrite nodules.(Fig. 1); however, organic matter is rare and onlyappears in some anhydrite nodules.

(Fig.1). Hydrocarbon (HC) impregnations weredetected in some grey Buntsandstein sandstones(Fig. 1); however, organic matter is rare and onlyappears in some anhydrite nodules.

and 390m in core samples, corresponding to distalfluvial-to-tidal arkoses, near the boundary betweenthe upper and lower units of the studied sequence(Fig.1). Hydrocarbon (HC) impregnations were

Fig. 4.— Comparison of the XRD patterns of the selected Buntsandstein sandstone samples containing als from the upper unit (300 to 369 m) and the samples from the lower unit (369 to 538 m). Fraction 20-2peaks are labeled as c: crandallite, f: feldspar, il: illite, k: kaolinite, q: quartz

Fig. 4.— Comparison of the XRD patterns of the selected Buntsandstein sandstone samples containing



Fig. 5.— Photomicrographs (parallel nicols) of A) Abundant APS microcrystals lining pores and replacing distortedmuscovite and remains of others oxidized minerals; B) Abundant APS microcrystals lining pores and muscovite (M)and partially replacing oxidized grain of xenotime (X ). C) SEM image of aggregates of small APS euhedral crystalslining the planes of distorted muscovite and corroding quartz, and partially filling the pore space. D) SEM imageunder BSE mode of APS zoned microcrystals filling the porosity and corroding the quartz grains. E) SEM images ofsandstone showing kaolinite matrix and very rich in APS zoned crystals. Illite is rarely observed in this area wheremica is altered to kaolinite. F) SEM image showing zoned APS crystals between twisted kaolinite booklets andextremely broken quartz grains. extremely broken quartz grains. mica is altered to kaolinite. F) SEM image showing zoned extremely broken quartz grains.

sandstone showing kaolinite matrix and very rich in APS zoned crystals. Illite is rarely observed in this area wheremica is altered to kaolinite. F) SEM image showing zoned

APS zoned microcrystals filling the porosity and corroding the quartz grains. E) SEM images ofsandstone showing kaolinite matrix and very rich in APS zoned crystals. Illite is rarely observed in this area where

lining the planes of distorted muscovite and corroding quartz, and partially filling the pore space. D) SEM imageAPS zoned microcrystals filling the porosity and corroding the quartz grains. E) SEM images of

Fig. 5.— Photomicrographs (parallel nicols) of muscovite and remains of others oxidized minerals; B) and partially replacing oxidized grain of xenotime (X ). C) SEM image of aggregates of small

Fig. 5.— Photomicrographs (parallel nicols) of A) muscovite and remains of others oxidized minerals; B)

extremely broken quartz grains. mica is altered to kaolinite. F) SEM image showing zoned extremely broken quartz grains.

APS zoned microcrystals filling the porosity and corroding the quartz grains. E) SEM images ofsandstone showing kaolinite matrix and very rich in APS zoned crystals. Illite is rarely observed in this area wheremica is altered to kaolinite. F) SEM image showing zoned extremely broken quartz grains.

lining the planes of distorted muscovite and corroding quartz, and partially filling the pore space. D) SEM imageAPS zoned microcrystals filling the porosity and corroding the quartz grains. E) SEM images ofAPS zoned microcrystals filling the porosity and corroding the quartz grains. E) SEM images of

and partially replacing oxidized grain of xenotime (X ). C) SEM image of aggregates of small lining the planes of distorted muscovite and corroding quartz, and partially filling the pore space. D) SEM image

APS zoned microcrystals filling the porosity and corroding the quartz grains. E) SEM images of

muscovite and remains of others oxidized minerals; B) and partially replacing oxidized grain of xenotime (X ). C) SEM image of aggregates of small lining the planes of distorted muscovite and corroding quartz, and partially filling the pore space. D) SEM image

Fig. 5.— Photomicrographs (parallel nicols) of muscovite and remains of others oxidized minerals; B) and partially replacing oxidized grain of xenotime (X ). C) SEM image of aggregates of small

Fig. 5.— Photomicrographs (parallel nicols) of


sandstone showing kaolinite matrix and very rich in APS zoned crystals. Illite is rarely observed in this area wheremica is altered to kaolinite. F) SEM image showing zoned extremely broken quartz grains.

and partially replacing oxidized grain of xenotime (X ). C) SEM image of aggregates of small lining the planes of distorted muscovite and corroding quartz, and partially filling the pore space. D) SEM imageunder BSE mode of sandstone showing kaolinite matrix and very rich in APS zoned crystals. Illite is rarely observed in this area where

Fig. 5.— Photomicrographs (parallel nicols) of muscovite and remains of others oxidized minerals; B) and partially replacing oxidized grain of xenotime (X ). C) SEM image of aggregates of small lining the planes of distorted muscovite and corroding quartz, and partially filling the pore space. D) SEM image

Fig. 5.— Photomicrographs (parallel nicols) of

(Fig. 4 C). APS crystals (sizes ranging from 5 to 10µm) also appear filling cavities as cement thatsurrounds corroded quartz grains (Fig. 4 D). A P Sminerals are preferentially found among expandedmuscovite flakes which are totally twisted bymechanical compaction and altered to kaolinite (Fig.4E, F). The quartz present in these sandstones hassuturated and stylolitic contacts marked by iron oxi-des, indicative of pressure-solution processes.

The XRD patterns of the 2-2-20µm fraction ofthe richest samples in APS minerals (Fig. 5) show acomposition of: crandallite 25%, quartz 13%, K-feldspar 7%, mica-illite 29%, kaolin minerals 25%and hematite 1% (Table 2). Crandallite with values

less than 10%, was also detected by XRD analysesin the <2 µm size-fraction. The chemical compositions of the APS mineralsand the structural formulae calculated on the basisof 2 moles of (XO4) and 6 moles of (OH) per for-mula unit, following Scott´s method (1987), aregiven in Table 3. According to the criteria of thisauthor, the analysed minerals belong to the plumbo-gummite group since trivalent anions are >1.5moles, divalent cations in A-sites are dominant andAl>Fe in B-sites. The results of the analyses areplotted on Scott’s diagram (Fig. 6). The calculatedaverage value of (XO4)3- is 1.51, which fits withinthe plumbogummite field. Considering the contents



Table 3.— Electron microprobe analyses and structural formulae of APS minerals from the Buntsandstein sandstones

Fig. 6.— Scott´s diagram: trivalent anions in XO 4 sites vs. divalent ± trivalent cations in A sites for APS minerals. Fig. 6.— Scott´s diagram: trivalent anions in XO 4 sites vs. divalent ± trivalent cations in Fig. 6.— Scott´s diagram: trivalent anions in XO 4 sites vs. divalent ± trivalent cations in

the plumbogummite field. Considering the contentsaverage value of (XO4)the plumbogummite field. Considering the contents

s diagram (Fig. 6). The calculatedaverage value of (XO4)3-

s diagram (Fig. 6). The calculated3-

The results of the analyses ares diagram (Fig. 6). The calculated

A-sites are dominant andThe results of the analyses are

, the analysed minerals belong to the plumbogummite group since trivalent anions are >1.5

A-sites are dominant and

, the analysed minerals belong to the plumbo, the analysed minerals belong to the plumbogummite group since trivalent anions are >1.5

According to the criteria of this, the analysed minerals belong to the plumbo

mula unit, following Scott´s method (1987), areAccording to the criteria of this

) and 6 moles of (OH) per formula unit, following Scott´s method (1987), are

and the structural formulae calculated on the basis) and 6 moles of (OH) per for

APS mineralsand the structural formulae calculated on the basis

less than 10%, was also detected by XRD analysesless than 10%, was also detected by XRD analyses

Fig. 6.— Scott´s diagram: trivalent anions in XO 4 sites vs. divalent ± trivalent cations in Fig. 6.— Scott´s diagram: trivalent anions in XO 4 sites vs. divalent ± trivalent cations in Fig. 6.— Scott´s diagram: trivalent anions in XO 4 sites vs. divalent ± trivalent cations in

the plumbogummite field. Considering the contentsthe plumbogummite field. Considering the contents

plotted on Scott’average value of (XO4)the plumbogummite field. Considering the contents

plotted on Scott’average value of (XO4)

moles, divalent cations in Al>Fe in B-sites.

gummite group since trivalent anions are >1.5gummite group since trivalent anions are >1.5moles, divalent cations in

, the analysed minerals belong to the plumbogummite group since trivalent anions are >1.5

According to the criteria of this, the analysed minerals belong to the plumbo

mula unit, following Scott´s method (1987), areAccording to the criteria of this

) and 6 moles of (OH) per formula unit, following Scott´s method (1987), are

) and 6 moles of (OH) per for

The chemical compositions of the and the structural formulae calculated on the basis

less than 10%, was also detected by XRD analyses

The chemical compositions of the

less than 10%, was also detected by XRD analyses

Fig. 6.— Scott´s diagram: trivalent anions in XO 4 sites vs. divalent ± trivalent cations in

the richest samples in APS minerals (Fig. 5) show acomposition of: crandallite 25%, quartz 13%, K-feldspar 7%, mica-illite 29%, kaolin minerals 25%

able 2). Crandallite with values

plotted on Scott’average value of (XO4)the plumbogummite field. Considering the contents

gummite group since trivalent anions are >1.5moles, divalent cations in Al>Fe in B-sites.

mula unit, following Scott´s method (1987), aregiven in Table 3. Table 3. Tauthor, the analysed minerals belong to the plumbogummite group since trivalent anions are >1.5

The chemical compositions of the and the structural formulae calculated on the basisof 2 moles of (XOmula unit, following Scott´s method (1987), are

less than 10%, was also detected by XRD analysesin the <2 µm size-fraction. less than 10%, was also detected by XRD analysesin the <2 µm size-fraction. The chemical compositions of the and the structural formulae calculated on the basis

less than 10%, was also detected by XRD analysesin the <2 µm size-fraction.

of Ca, Sr, and Ba, these APS minerals can be defi-ned as a solid solution of crandallite-goyacite-gor-ceixite (Ca 0.53, Sr 0.46, Ba 0.01). The LREE (La,Ce, Pr, Nd and Th) contents are very low; in thecase of La and Ce the average value is 282 ppm and434 ppm, respectively. The content of Pr, Nd andTh in all the analyzed APS minerals was usuallybelow the detection limit. Table 4 shows the chemi-cal composition of the selected sand grains contai-

ning high values in UO3. Their values in Cu, As andP suggest an uranyl phosphate arseniate, of theautunite group, specifically torbernite-zeuneriteserie: Cu(UO2)2(PO4, AsO4)2.10H2 O.

Discussion

The geochemical conditions in the Triassic basinduring the APS mineral precipitation were oxidi-sing and slightly acid, as indicated by the presenceof the paragenesis formed by kaolinite-illite-quartzand hematite. Furthermore, the red sandstones bedsare bleached and mottled corresponding to hemati-te dissolution caused by repeated process of acidifi-cation as described by Hoeve & Quirt (1984) andKister et al., (2006). According to Rasmussen(1996), the critical factor controlling the APS mine-ral precipitation is the availability of Al. In theBuntsandstein sandstones, enough Al for the preci-pitation of APS minerals was supplied by the alte-ration of feldspars, mica or kaolinite. The Sr con-tent of the APS minerals could be related to the pre-sence of celestite and strontianite in the interbeddedmudstones and sandstones (Morad et al. 1992).Consequently, the compaction of the interbeddedmudstones could have released the Sr and S neededfor the APS mineral precipitation in the mostporous sandstones. Another S source may be thesulphates present in fluids expelled from overlyingevaporitic formations (Keuper facies). Such condi-tions are more likely to be associated with the intro-



Fig.7.— Reciprocal diagram based on Sr, S, and LREEelectron microprobe analyses for APS minerals from thestudied Buntsandstein uraniferous sandstones comparedto the APS compositions from the Kombolgie Formation(Gaboreau et al., 2005). Distal alteration zone (1); inter-mediate alteration zone (2); and zone of proximal alter-ation (3).

Table 4.— Representative microanalyses by scanning electron microscopy, in %, of the uraniferous grains in threeAPS bearing samples corresponding to SS-21, SS-23 and SS-24.APS bearing samples corresponding to SS-21, SS-23 and SS-24.

Representative microanalyses by scanning electron microscopyAPS bearing samples corresponding to SS-21, SS-23 and SS-24.


sulphates present in fluids expelled from overlyingevaporitic formations (Keuper facies). Such condi

porous sandstones. sulphates present in fluids expelled from overlying

for the APS mineral precipitation in the mostporous sandstones.

mudstones could have released the Sr and S neededfor the APS mineral precipitation in the most

, the compaction of the interbeddedmudstones could have released the Sr and S needed

, the compaction of the interbeddedmudstones could have released the Sr and S needed

mudstones and sandstones (Morad , the compaction of the interbedded

of celestite and strontianite in the interbeddedmudstones and sandstones (Morad

ration of feldspars, mica or kaolinite. The Sr conAPS minerals could be related to the pre

of celestite and strontianite in the interbedded

ration of feldspars, mica or kaolinite. The Sr conration of feldspars, mica or kaolinite. The Sr conAPS minerals could be related to the pre

APS minerals was supplied by the alteration of feldspars, mica or kaolinite. The Sr con

Buntsandstein sandstones, enough Al for the preciAPS minerals was supplied by the alte

(1996), the critical factor controlling the ral precipitation is the availability of

., (2006). According to Rasmussen(1996), the critical factor controlling the

by Hoeve & Quirt (1984) and., (2006). According to Rasmussen

te dissolution caused by repeated process of acidifiby Hoeve & Quirt (1984) and

are bleached and mottled corresponding to hematite dissolution caused by repeated process of acidifi

and hematite. Furthermore, the red sandstones bedsare bleached and mottled corresponding to hemati

APS bearing samples corresponding to SS-21, SS-23 and SS-24.Representative microanalyses by scanning electron microscopy

APS bearing samples corresponding to SS-21, SS-23 and SS-24.

cal composition of the selected sand grains contai-

Representative microanalyses by scanning electron microscopy

sulphates present in fluids expelled from overlyingevaporitic formations (Keuper facies). Such conditions are more likely to be associated with the intro

porous sandstones. sulphates present in fluids expelled from overlying

for the APS mineral precipitation in the mostporous sandstones. for the APS mineral precipitation in the most

Consequentlymudstones could have released the Sr and S neededfor the APS mineral precipitation in the most

mudstones and sandstones (Morad Consequentlymudstones could have released the Sr and S needed

of celestite and strontianite in the interbeddedmudstones and sandstones (Morad

APS minerals could be related to the preAPS minerals could be related to the preof celestite and strontianite in the interbedded

ration of feldspars, mica or kaolinite. The Sr conAPS minerals could be related to the pre

APS minerals was supplied by the alteration of feldspars, mica or kaolinite. The Sr con

Buntsandstein sandstones, enough APS minerals was supplied by the alte

(1996), the critical factor controlling the ral precipitation is the availability of Buntsandstein sandstones, enough

(1996), the critical factor controlling the

by Hoeve & Quirt (1984) and., (2006). According to Rasmussen

(1996), the critical factor controlling the

te dissolution caused by repeated process of acidifiby Hoeve & Quirt (1984) and

are bleached and mottled corresponding to hematiare bleached and mottled corresponding to hematite dissolution caused by repeated process of acidifi

and hematite. Furthermore, the red sandstones bedsare bleached and mottled corresponding to hematiand hematite. Furthermore, the red sandstones beds

sing and slightly acid, as indicated by the presenceof the paragenesis formed by kaolinite-illite-quartz

APS mineral precipitation were oxidising and slightly acid, as indicated by the presence


APS bearing samples corresponding to SS-21, SS-23 and SS-24.

cal composition of the selected sand grains contai


ned as a solid solution of crandallite-goyacite-gorThe LREE (La,

Th) contents are very low; in thecase of La and Ce the average value is 282 ppm and

, Nd and

can be defi-ned as a solid solution of crandallite-goyacite-gor-

ration of feldspars, mica or kaolinite. The Sr content of the sencemudstones and sandstones (Morad

ral precipitation is the availability of Buntsandstein sandstones, enough pitation of ration of feldspars, mica or kaolinite. The Sr con

Kister (1996), the critical factor controlling the ral precipitation is the availability of Buntsandstein sandstones, enough

are bleached and mottled corresponding to hematite dissolution caused by repeated process of acidification as describedte dissolution caused by repeated process of acidification as described

et al., (2006). According to Rasmussen(1996), the critical factor controlling the

of the paragenesis formed by kaolinite-illite-quartzand hematite. Furthermore, the red sandstones bedsare bleached and mottled corresponding to hematite dissolution caused by repeated process of acidifi

by Hoeve & Quirt (1984) and

APS mineral precipitation were oxidiAPS mineral precipitation were oxidising and slightly acid, as indicated by the presenceof the paragenesis formed by kaolinite-illite-quartz

The geochemical conditions in the APS mineral precipitation were oxidi

sing and slightly acid, as indicated by the presence

suggest an uranyl phosphate arseniate, of theautunite group, specifically torbernite-zeunerite

O.

duction of oxidising meteoric waters during anuplift event in intra-formational unconformities inthe Iberian Basin.

Idiomorphic APS crystals grow between thecollapsed mica, which is partially altered to kaolini-te fans and dickite (Marfil et al., 2012). Thisimplies that APS minerals postdate the mechanicaland chemical compaction, indicating that APS wereformed during diagenesis. Constraints placed byvitrinite reflectance deduced temperatures from theassociated organic matter in the underlying Permianshales of 135 to 159ºC around 900 m depth (Marfilet al., 1996 a, b). In addition, K/Ar age determina-tions of the associated fibrous illite, indicate that theepisode of illitization in the Buntsandstein occurredaround 199.6 ± 4.3 M.a. during Lower and MiddleJurassic (Marfil et al., 1996 a). These ages coincidewith the period of the most intensive extensionaltectonics in this basin coeval with volcanic events(Salas & Casas, 1993). Thus, the above mentionedfacts support the hypothesis of a diagenetic originand high temperature for the APS minerals, similarorigin as for these minerals in the Athabasca basinin Canada (Gaboreau et al., 2007). The assemblageof the APS minerals and dickite implies as wellhigh diagenetic temperature rates. According toEhrenberg et al., (1993) and Mcaulay et al. (1994)the transformation kaolinite-dickite occurs at tem-peratures between 80 and 130ºC. Thus, the minera-lizing fluids, related to tectonic events that occurredduring the late Cretaceous post-rift thermal stage,were meteoric waters that transported the uraniuminto the buried red Buntsandstein sandstones. Thefluids were enriched in uranium by circulatingthrough granitic and gnessic rocks of the SpanishCentral System (Castañon et al., 1981; De la Cruzet al., 1987), or even through Permian volcanicrhyolitic rocks. In this area of the Iberian Range sig-nificant Permian deposits composed by rhyoliticrocks (Peña et al., 1977. Muñoz et al., 1985) cropout. However, the time of the uranium mineraliza-tion and the origin and timing of migrating fluids inthe Buntsandstein are not yet fully understood. The low content in LREE of the APS crystals is notindicative of a clear relationship with the uraniummineralization detected in the studied arkosicsandstones. However, the Gamma ray spectrometry(Fig. 1) shows a radioactive anomaly located at a

depth of around 340 m, due to the presence of ura-nium minerals (Marfil et al., 1996b) Nevertheless,in agreement with the origin proposed by Gaboreauet al. (2005), APS minerals in the Triassic Bunt-sandstein facies could be related to the U-bearingarkosic sandstones in a distal alteration area, asshown in figure 7. Plotting the chemical analyses ofthe studied APS on the Gaboreau et al.( 2005) dia-gram, they fit in the area of distal alteration orbarren areas. The above authors explain that thechemical variation in APS minerals is influenced bythe host-rock lithology. For an equivalent alterationzone, the APS minerals formed in basement rocksare systematically enriched in P and LREE compa-red with those formed in the sandstones of thebarren areas. Monazite (Ce) in the gneissic weathe-ring profiles of the Leucogia area (Papoulis et al.,2004), is partially altered to a Th-silicate with verylow concentration of LREE. Likewise, the aboveauthors found that monazite in hydrothermaly alte-red rhyolitic rocks of Kos Island, were altered to P-bearing crandallite–goyazite and during this altera-tion process LREE are depleted. The alteration pro-cesses that occurred in the studied U-bearing sands-tones could be similar to those described by theabove mentioned authors.

Conclusions

In the studied Triassic sequence, several levelsof the Buntsandstein sandstones contain importantconcentrations of APS minerals deposited in sec-ondary pores formed by dissolution of the frame-work grains, mainly feldspars and uraniferous min-erals. They appear as well replacing kaolinite-illitematrix, inside microfractures of the quartz grainsand between the exfoliation planes of the mica.

APS minerals were precipitated under diagenet-ic conditions related to the uplifting occurred dur-ing the late Cretaceous post-rift thermal stage athigh diagenetic temperatures, suggested by thepresence of dickite in the studied samples

APS minerals occurred in barren sandstones inzones of distal alteration with low LREE contents,and related to some tectonic event responsible forthe introduction of meteoric and mineralizingwaters into the buried sediments.



(Fig. 1) shows a radioactive anomaly located at a, the Gamma ray spectrometry

(Fig. 1) shows a radioactive anomaly located at a

mineralization detected in the studied arkosic, the Gamma ray spectrometry

indicative of a clear relationship with the uraniummineralization detected in the studied arkosic

The low content in LREE of the APS crystals is notindicative of a clear relationship with the uranium

tion and the origin and timing of migrating fluids inthe Buntsandstein are not yet fully understood. tion and the origin and timing of migrating fluids in

., 1985) crop., 1985) crop, the time of the uranium mineraliza

nificant Permian deposits composed by rhyolitic., 1985) crop

and between the exfoliation planes of the mica. matrix, inside microfractures of the quartz grainsand between the exfoliation planes of the mica.

erals. matrix, inside microfractures of the quartz grains

work grains, mainly feldspars and uraniferous minerals. They appear as well replacing kaolinite-illite

ondary work grains, mainly feldspars and uraniferous min

concentrations of pores formed by dissolution of the frame

In the studied

above mentioned authors. above mentioned authors. tones could be similar to those described by theabove mentioned authors.

cesses that occurred in the studied U-bearing sandstones could be similar to those described by the

bearing crandallite–goyazite and during this alteration process LREE are depleted. The alteration processes that occurred in the studied U-bearing sands

bearing crandallite–goyazite and during this alterabearing crandallite–goyazite and during this alteraThe alteration pro

red rhyolitic rocks of Kos Island, were altered to P-bearing crandallite–goyazite and during this altera

authors found that monazite in hydrothermaly altered rhyolitic rocks of Kos Island, were altered to P-

Th-silicate with verylow concentration of LREE. Likewise, the above

ring profiles of the Leucogia area (Papoulis Th-silicate with very

barren areas. Monazite (Ce) in the gneissic weathering profiles of the Leucogia area (Papoulis et al

red with those formed in the sandstones of thebarren areas. Monazite (Ce) in the gneissic weathe

are systematically enriched in P and LREE compared with those formed in the sandstones of the

APS minerals formed in basement rocksare systematically enriched in P and LREE compa-

(Fig. 1) shows a radioactive anomaly located at a, the Gamma ray spectrometry

(Fig. 1) shows a radioactive anomaly located at a

mineralization detected in the studied arkosic, the Gamma ray spectrometry

indicative of a clear relationship with the uraniumindicative of a clear relationship with the uraniummineralization detected in the studied arkosic

the Buntsandstein are not yet fully understood. The low content in LREE of the APS crystals is notindicative of a clear relationship with the uranium

the Buntsandstein are not yet fully understood. The low content in LREE of the APS crystals is not

tion and the origin and timing of migrating fluids inthe Buntsandstein are not yet fully understood.

, the time of the uranium mineralization and the origin and timing of migrating fluids in

nificant Permian deposits composed by rhyoliticet al., 1985) crop

, the time of the uranium mineraliza

In this area of the Iberian Range significant Permian deposits composed by rhyolitic

., 1985) crop

., 1981; De la Cruzor even through Permian volcanicIn this area of the Iberian Range sig

., 1981; De la Cruz., 1981; De la Cruzor even through Permian volcanic

through granitic and gnessic rocks of the Spanish., 1981; De la Cruz

Buntsandstein sandstones. Thefluids were enriched in uranium by circulating

of the Buntsandstein sandstones contain importantconcentrations of ondary

In the studied of the Buntsandstein sandstones contain important

ConclusionsConclusions

above mentioned authors. tones could be similar to those described by theabove mentioned authors.

cesses that occurred in the studied U-bearing sandstones could be similar to those described by the

tion process LREE are depleted. tion process LREE are depleted. cesses that occurred in the studied U-bearing sands

bearing crandallite–goyazite and during this alteration process LREE are depleted.

red rhyolitic rocks of Kos Island, were altered to P-bearing crandallite–goyazite and during this altera

authors found that monazite in hydrothermaly altered rhyolitic rocks of Kos Island, were altered to P-

2004), is partially altered to a low concentration of LREE. Likewise, the aboveauthors found that monazite in hydrothermaly alte

Th-silicate with verylow concentration of LREE. Likewise, the above

barren areas. Monazite (Ce) in the gneissic weathering profiles of the Leucogia area (Papoulis

Th-silicate with very

red with those formed in the sandstones of thebarren areas. Monazite (Ce) in the gneissic weathe

are systematically enriched in P and LREE compaare systematically enriched in P and LREE compared with those formed in the sandstones of the

APS minerals formed in basement rocksare systematically enriched in P and LREE compa

APS minerals formed in basement rocks

chemical variation in APS minerals is influenced by. For an equivalent alteration

The above authors explain that thechemical variation in APS minerals is influenced by

mineralization detected in the studied arkosicsandstones. However(Fig. 1) shows a radioactive anomaly located at a

The low content in LREE of the APS crystals is notindicative of a clear relationship with the uraniummineralization detected in the studied arkosic

, the time of the uranium mineralization and the origin and timing of migrating fluids inthe Buntsandstein are not yet fully understood. The low content in LREE of the APS crystals is notindicative of a clear relationship with the uranium

In this area of the Iberian Range significant Permian deposits composed by rhyolitic

., 1977. Muñoz , the time of the uranium mineraliza

tion and the origin and timing of migrating fluids in

(Castañon or even through Permian volcanicor even through Permian volcanicIn this area of the Iberian Range sig

nificant Permian deposits composed by rhyolitic

fluids were enriched in uranium by circulatingthrough granitic and gnessic rocks of the Spanish

et al., 1981; De la Cruzor even through Permian volcanic

were meteoric waters that transported the uraniumBuntsandstein sandstones. The

fluids were enriched in uranium by circulatingthrough granitic and gnessic rocks of the Spanish

APS minerals and dickite implies as wellAccording to

et al. (1994)the transformation kaolinite-dickite occurs at tem-

Thus, the minera

above mentioned authors.

bearing crandallite–goyazite and during this alteration process LREE are depleted. cesses that occurred in the studied U-bearing sandstones could be similar to those described by the

authors found that monazite in hydrothermaly altered rhyolitic rocks of Kos Island, were altered to P-bearing crandallite–goyazite and during this altera

ring profiles of the Leucogia area (Papoulis 2004), is partially altered to a low concentration of LREE. Likewise, the aboveauthors found that monazite in hydrothermaly alte

are systematically enriched in P and LREE compared with those formed in the sandstones of thebarren areas. Monazite (Ce) in the gneissic weathered with those formed in the sandstones of thebarren areas. Monazite (Ce) in the gneissic weathering profiles of the Leucogia area (Papoulis 2004), is partially altered to a

the host-rock lithology. For an equivalent alterationAPS minerals formed in basement rocks

are systematically enriched in P and LREE compared with those formed in the sandstones of thebarren areas. Monazite (Ce) in the gneissic weathe



. For an equivalent alterationAPS minerals formed in basement rocks

APS on the Gaboreau gram, they fit in the area of distal alteration or


to the U-bearingarkosic sandstones in a distal alteration area, asshown in figure 7. Plotting the chemical analyses of

et al.( 2005) dia

., 1996b) Nevertheless,in agreement with the origin proposed by Gaboreau

riassic Buntto the U-bearing

The intergranular clay matrix composed ofkaolinite, illite and the feldspars constituted themain Al source, whereas secondary uranium miner-als and apatite were the most probable P sources.Fluids migrating from the Permian evaporitic for-mations, or, more probably, from the overlyingKeuper evaporitic facies can account for the Ca, Sand Sr contents.

Based on their chemical composition, the APSminerals have been defined as a solid solution ofcrandallite-goyacite-gorceixite.

ACKNOWLEDGMENTS

This work was supported by projects CCG07-UCM/AMB-2299 and GR35/10-A. Grupo 910404. We wish to acknowled-ge and thank the Shell Spain Company and the former Junta deEnergía Nuclear of Spain for giving us access to their samplesand data and the authorization to publish this work. We are alsoindebted to Da Berta de la Cruz from the CIEMAT for theirhelpful comments of some aspects of the paper and to check theEnglish version. We thank Alfredo Fernández Larios for perfor-ming the electron microprobe analyses of the APS minerals,and Eugenio Baldonedo Rodríguez for his valuable help withthe SEM analyses. We are grateful to D. X Arroyo for assistan-ce with SEM studies of the uraniferous minerals. Criticalreviews and comments by the two reviewers are gratefully ack-nowledged.

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Recibido el 2 de diciembre de 2011

Aceptado el 22 de febrero de 2012

Publicado online el 19 de febrero de 2013



Publicado online el Publicado online el

Recibido el 2 de diciembre de 201

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