J. Torres-Ruiz

Geochemistry of Spanish sepiolite-palygorskite deposits: Genetic considerations based on trace elements and isotopes☆☆☆

Sepiolite-palygorskite deposits in Spanish Tertiary basins were formed in lacustrine environments. The mineral associations present in the mineralised intervals are made up of neoformed phyllosilicates (sepiolite, palygorskite, stevensite), detrital silicates (quartz, feldspars, illite, interstratified smectite-illite, Al-smectite and kaolinite) and carbonates (calcite, dolomite). Opal-A, gypsum and halite may also appear sporadically. Two groups of chemical elements and minerals can be distinguished according to their origin: Al, Ti, Fe, Mn, K, REE and transition trace elements are almost exclusively included in the detrital Al-silicates; Mg, Ca, Cl, F and Li are concentrated in the minerals formed in the depositional basins. Si, Na, Sr and Ba are contained in both detrital and neoformed minerals. REE, transition trace elements, F and Li contents can be used to distinguish between phyllosilicates formed by chemical precipitation in the depositional basins, detrital phyllosilicates, and those formed by transformation of the latter during early diagenetic processes. These data, together with those on δ18O isotopic fractionation indicate the formation of sepiolite and Mg-smectite as chemical precipitates, whereas palygorskite would derive from diagenetic transformation of other inherited clay minerals. The values calculated for the α(sepiolite-water) and α(palygorskite-water) fractionation factors at 20°C are 1.031 and 1.027, respectively.

Platinum-group minerals in chromitites from the ojen lherzolite massif (Serrania de Ronda, Betic Cordillera, Southern Spain)

SummaryChromitites (Cr ores) of the Ojen lherzolite massif (Serranía de Ronda, Betic Cordillera, Southern Spain) were found to contain platinum-group minerals (PGM) as discrete inclusions in the chromite and in the associated silicates. The PGM mineralogy consists of sulfides [laurite, erlichmanite, malanite, unnamed (Ni-Fe-Cu)2 (Ir, Rh) S3, unidentified Pd-S], sulfarsenides (irarsite, hollingworthite, ruarsite, and osarsite), arsenides [sperrylite, unidentified (Pd, Ni)-As], one unidentified Pd-Bi compound, and native platinum group elements (PGE) consisting of Ru and Pt-Fe alloys. Textural considerations suggest that the PGE chalcogenides with S and As were formed in the high-temperature magmatic stages, as part of the chromite precipitation event (primary PGM), in contrast with the native PGE, which originated during the low-temperature serpentinization of the ultramafic host of the chromitites (secondary PGM).The primary PGM inclusions in the Ojen chromite are unusual compared with PGM inclusions in chromitites from tectonitic upper-mantle of ophiolites and other alpine-type complexes in that i) they display a great variety of mineral species sulfides, sulfarsenides and arsenides, and ii) comprise specific phases of all six PGE. The singularity of the primary PGM mineralization probably reflects high activities of both S and As during chromite precipitation at Serrania de Ronda to be related with particular physico-chemical conditions during uplifting of sub-continental, astenospheric mantle.The nature, composition, and paragenetic association of secondary PGM at Ojen confirm the relatively-high mobility of the PGE at low temperature, and indicate that remobilization can be selective under appropriate redox conditions causing separation and redistribution of the PGE in the rocks as a result of the alteration process.ZusammenfassungPlatingruppen-Minerale in Chromititen aus dem Ojen-Lherzolithmassiv (Serranía de Ronda, Betische Kordillere, Süd-Spanien) In den Chromititen (Cr-Erzen) aus dem Ojen-Lherzolithmassiv (Serranía de Ronda, Betische Kordillere, Süd-Spanien) warden Platingruppen-Minerale (PGM) als einzelne Einschlüsse im Chromit and in den begleitenden Silikaten gefunden. Die Mineralogie der PGM setzt sich aus Sulfiden [Laurit, Erlichmanit, Malanit, einem unbenannten (Ni-Fe-Cu)2 (Ir, Rh)S3 und einem nicht identifizierten Pd-S], Sulfarseniden (Irarsit, Hollingworthit, Ruarsit und Osarsit), Arseniden [Sperrylit, einem nicht identifizierten (Pd, Ni)-As], einer nicht identifizierten Pd-Bi-Verbindung sowie gediegenen Platingruppen-Elementen (PGE) bestchend aus Ru and Pt-Fe-Legierungen, zusammen. Texturelle Untersuchungen haben ergeben, daß die PGE-Chalkogenide mit S und As im Zuge der Chromitfällung (primäre PGM) in den hochtemperierten, magmatischen Stadien gebildet warden, während die gediegenen PGE während der niedriggradigen Serpentini sierung des ultramafischen Nebengesteins der Chromitite (sekundäre PGM) gebildet warden.Die primären PGM-Einschlüsse in den Ojen-Chromiten sind im Vergleich zu PGM-Einschlüssen in Chromititen aus dem tektonisierten oberen Mantel in Ophiolithen und anderen alpinotypen Komplexen ungewöhnlich: i) Einerseits zeigen sie eine große Vielfalt an Mineralarten aus der Gruppe der Sulfide, Sulfarsenide und Arsenide. ii) Andererseits enthalten sie spezifische Phasen aller sechs PGE. Die Einzigartigkeit der primären PGM-Mineralisation könnte hohe Aktivitäten von S and As während der Chromit-Fällung in Serranía de Ronda widerspiegeln, die mit besonderen physiko-chemischen Bedingungen während der Hebung des subkontinentalen, asthenosphärischen Mantels zusammenhängen.Die Art, die Zusammensetzung and die paragenetische Vergesellschaftung von sekundären PGM in Ojen bestätigen die relativ hohe Mobilität der PGE bei niedriger Temperatur und zeigen, daß die Remobilisierung unter geeigneten Redox-Bedingungen selektiv wirken kann, wodurch eine Trennung und Neuverteilung der PGE in den Gesteinen als Ergebnis des Alterationsprozesses bewirkt wird.

Genesis and evolution of strontium deposits of the granada basin (Southeastern Spain): Evidence of diagenetic replacement of a stromatolite belt

Abstract There are important strontium deposits in the Granada Basin, the most noteable of which (Montevives) has an annual production of approximately 50,000 tons of almost pure celestite. Two types of mineralization can be recognized: a primary variety consisting of stromatolitic carbonate that has been partially replaced by celestite, and a secondary variety consisting of celestite-pebble karst deposits. Both are included in an evaporitic Messinian succession. The primary variety of mineralization is within carbonates that interfinger with, and prograde across, gypsum deposits. The development of these deposits can be interpreted in the context of the general evolution of the Granada Basin during Late Tortonian and Messinian times. Open marine conditions prevailed during the late Tortonian. During the transition from Tortonian to Messinian a restriction of the basin resulted in evaporite sedimentation, with stromatolites thriving at the basins margin. The stromatolites were distributed along a coastal belt that was limited on the east by the tectonically active Sierra Nevada with its local alluvial fans. Runoff from the Sierra Nevada produced a freshwater lens and surface salinities that permitted the development of stromatolites, rather than the accumulation of gypsum. The replacement of stromatolitic carbonate by celestite occurred within the mixing zone of the coastal aquifers during sedimentation and/or early diagenesis. An essentially marine origin is considered for the strontium. Supplementary influxes from continental weathering are also thought to have been produced. Further restriction of the Granada Basin led to complete desiccation and the deposition of a 20 m thick halite layer. Later, gypsum deposits were exposed, and resulting cavities (“dolinas”) were filled with celestite pebbles. The return of sediment accumulation within lakes buried and preserved these deposits.

Origin and petrogenetic implications of tourmaline-rich rocks in the Sierra Nevada (Betic Cordillera, southeastern Spain)

Tourmaline-rich rocks (up to 60% tourmaline) associated with low–medium grade metamorphic assemblages occur in the Sierra Nevada area (Betic Cordillera, southeastern Spain). Tourmaline appears in a variety of forms: (1) stratiform tourmalinites; (2) quartz–tourmaline nodules; (3) porphyroclasts in felsic orthogneisses; and (4) disseminations in psammopelitic metasediments and gneisses. Tourmaline within these lithologic groups exhibits textural and chemical variations that reflect complex premetamorphic growth under open-system conditions, and subsequent changes due to Alpine regional metamorphism. Microprobe analyses of the tourmalines reveal a wide compositional variation between schorl and dravite end members with variable contents of X-site vacancies (av. 0.084–0.225 apfu), Ca (av. 0.095–0.269 apfu), and excess of Al (up to 6.588 apfu) compared with the theoretical value of 6 in ideal schorl and dravite. The amount of Ca may be significant in porphyroclasts from the gneisses. Fe/(Fe+Mg) ratios for tourmalines in tourmalinites, metasediments, and gneisses range from 0.34 to 0.95, 0.16 to 0.92, and 0.28 to 0.97, respectively. Na/(Na+Ca) ratios are also variable, mostly ranging from 0.5 to 0.9. Many of the tourmalines have complex chemical and colour zoning patterns, including significant fluctuations in Al, Fe, Mg, Na, Ca, Ti, and F. Based on petrographic and chemical data, three generations of tourmaline have been established. The first generation corresponds to magmatic–postmagmatic tourmaline that is represented by tourmaline porphyroclasts within the orthogneisses. The second generation of tourmaline formed during tourmalinization of psammopelitic rocks giving rise to tourmalinites. The third generation of tourmaline is represented by cellular textures, pale reaction rims and overgrowths developed during the Alpine regional metamorphic overprint. D 2002 Elsevier Science B.V. All rights reserved.

Chemistry and genetic implications of tourmaline and Li-F-Cs micas from the Valdeflores area (Caceres, Spain)

Abstract Pervasive metasomatism that involved the formation of tourmaline-rich rocks and influx of Li. F. and Cs into Ordovician psammo-pelitic metasediments occurred in the Valdeflores area (Cáceres. Spain). Numerous Li- and Sn-bearing. mineralized, greisen-type veins also can be observed here, in the vicinity of geochemically specialized granites. Tourmaline- rich rocks appear as: (1) massive, fine-grained, dark green to black rocks: and (2) fine- scale tourmaline-rich laminae, which alternate with quartz-rich layers parallel to the bedding. Electron microprobe analyses indicate that the tourmaline lies mostly within the space defined by the exchange vectors from dravite: FeMg-1 (schorl), ⃞AlNa-1Mg-1 (foitite), AlOMg-1(OH)-1 (olenite), and CaMgNa-1Al-1 (uvite). The Fe/(Fe+Mg) ratio ranges mainly from 0.87 to 0.54 and increases with Al in the Y-site. Analytical results and substitutional relations show an insignificant elbaite component. Mica in the tounnalinized rocks is very fine-grained (mostly <50 μm). White mica ranges from lithian muscovite-phengite to lepidolite/zinnwaldite, containing up to 8.40 wt% F. 6.0 wt% Li2O, and 10.73 wt% FeO. Dark mica shows a variable color and has compositions characterized by relatively high contents of Cs2O (1.14-2.78 wt%) and F (1.94-8.08 wt%), with a deficit in K2O (5.75- 9.04 wt%). Log (fH₂O/fHF) of fluids in equilibrium with biotite in the tourmaline-rich rocks was 4.02-4.17 at T ≈ 400 °C. Log (fH₂O/fHF) values of fluids in equilibrium with topaz (XF ≈ 0.8) in country rock adjacent to contacts with veins, and in equilibrium with am- blygonite-montebrasite (Xamb = 0.2) in the veins were about 4.30-4.60 and 6.4-6.7, respectively. Tliese variations denote the existence of gradients in relative aHF more than differences of temperature during metasomatism. The lack of tourmaline in the veins is interpreted to reflect the alkalinity and low Fe-Mg contents in the fluids, which precluded the formation of tourmaline. Consequently, most of the boron was expelled into metasediments where tourmaline was produced as a result.

Origin and internal evolution of the Li-F-Be-B-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian Zone, Zamora, Spain)

Abstract The Li-F-Be-B-P bearing Pinilla de Fermoselle (PF) pegmatite occurs in the apical part of a leucogranite body. It shows a clear non-symmetrical vertical zoning from the contact with the leucogranite to a contact with the metamorphic country rocks. The pegmatitic facies evolve upward from (1) the undifferentiated Lower Border Zone (LBZ), with quartz, feldspars, muscovite, biotite, and black tourmaline, through (2) the Intermediate Zone (IZ), with quartz, muscovite, zinnwaldite, black tourmaline, and Fe-Mn phosphates, to (3) the highly evolved Upper Border Zone (UBZ), with quartz, albite, lepidolite, zinnwaldite, elbaite, and beryl. The composition of the pegmatite-forming minerals suggests that a residual melt become progressively enriched in F and Li until the crystallization of the apical UBZ, whereas P partitions in the melt only until the intermediate levels of differentiation attained in the IZ. Chemical variations in the mica and tourmaline as well as in the feldspar and Fe- Mn phosphate minerals are consistent with an internal evolution by crystal fractionation processes. A plausible model for the crystallization of the PF pegmatite involves a rapid, in situ, bottom-up crystallization from significantly undercooled liquids. The lack of metasomatic effects in the metamorphic host-rock and the estimated P content of the initial leucogranite melt suggest that the PF pegmatite mainly crystallized under closed system conditions.

Mineralogy and geochemistry of micas from the Pinilla de Fermoselle pegmatite (Zamora, Spain)

The highly fractionated, Li-F-Be-B-P-bearing Pinilla de Fermoselle (PF) pegmatite crops out in the westernmost part of the Zamora province (Spain). This body appears as a cupola over the PF leucogranite, displaying a non-symmetrical internal zonation with a complete sequence from a barren pegmatitic facies near the granite, to a highly evolved zone in the uppermost part of the body. Representative samples of micas from the different pegmatite zones have been studied. Based on textural and chemical criteria, the micas may be grouped into two assemblages: Al-rich micas and Fe-rich micas. In general, Al-rich micas show a continuous evolution from muscovitic to lepidolitic compositions from the leucogranite to the most evolved zone. Fe-rich micas range from Fe-biotite in the leucogranite and in the least evolved pegmatite zones, to an intermediate composition between zinnwaldite and trilithionite in the most evolved pegmatitic facies. The incorporation of Li into micas appears to be controlled by the substitutions Si 2 LiAl -3 ,a nd Li3Al-1-2, AlLiR-2 ,S iLi 2R-3 ,a nd SiLiAl -1R-1, where R = (Fe 2+ + Mg + Mn). Paragenetic relationships and chemical variations in micas from different zones making up the PF pegmatite suggest that the pegmatitic system derived from a granitic melt and evolved upwards by fractionation processes. Evidence in support of this model comes from: (i) the gradual enrichment in Li, Rb, Cs and F, parallel to the decrease in Mg and Ti; (ii) the convergent evolutionary trends towards lepidolite showed by the Al- and Fe-micas; and (iii) the parallel decrease in the K/Rb ratio in micas.

Chromian tourmaline and associated Cr-bearing minerals from the Nevado-Filábride Complex (Betic Cordilleras, SE Spain)

Abstract Chromian tourmaline, in association with other Cr-bearing minerals (amphibole, mica, epidote, chlorite, titanite, rutile and chromian spinel), occurs in fine calc-schist levels within metacarbonate rocks from the Nevado-Filábride Complex, SE Spain. Electron microprobe analyses of tourmaline and coexisting minerals document both chemical differences dependent on the host-rock type and an irregular distribution of Cr at grain scale. Tourmaline is Na-rich dravite, with average Mg/(Mg+Fe) ratios of 0.83 and 0.63 a.p.f.u. and Cr contents of 0.32 and 0.18 a.p.f.u., in dolomitic and ankeritic marbles, respectively. Tourmaline contains small but significant concentrations of Zn (av. 0.01 a.p.f.u.) and in ankeritic marble it also contains Ni (av. 0.04 a.p.f.u.). Zn-rich chromian spinel appears as small relict inclusions in silicates, with average Cr, Fe, Al and Zn contents of 1.201, 1.241, 0.411 and 0.107 a.p.f.u., respectively. Amphibole, epidote, mica and chlorite show average Cr contents of 0.088, 0.138, 0.115 and 0.267 a.p.f.u., respectively, in dolomitic marbles, and 0.103, 0.078, 0.065 and 0.185 a.p.f.u., respectively, in ankeritic marbles. Cr-silicates formed through metamorphic reactions involving detrital Cr-rich spinel, in addition to clay minerals and carbonates. The B necessary to form tourmaline was probably derived from the leaching of underlying evaporitic rocks.

Tourmaline as a petrogenetic monitor of the origin and evolution of the Berry-Havey pegmatite (Maine, U.S.A.)

Abstract The Berry-Havey pegmatite (Oxford pegmatite field, Androscoggin County, Maine, U.S.A.), enriched in Li, F, B, Be, and P, is intruded in hornblende-rich amphibolite, with minor biotite or diopside. The pegmatite has a complex internal structure, with four texturally and compositionally different zones that show an increasing degree of evolution inward: wall zone, intermediate zone, core margin, and core zone. The main minerals are quartz, feldspars, Al-micas, tourmaline, with minor Fe-micas, garnet, beryl, amblygonite-montebrasite, Fe-Mn phosphates, and apatite. Tourmaline is present in all zones of the pegmatite, showing different textures: black anhedral crystals in the wall and intermediate zones; black prisms of up to 40 cm in length in the intermediate zone; black tapered prisms, surrounded by a pseudo-graphic intergrowth of quartz or albite with black ± green/bluish tourmaline, and constituting a continuous layer under the core zone; multicolored and “watermelon” zoned crystals in the core zone; and gemmy deep green and color-zoned “watermelon” tourmaline prisms, up to 15 cm length, inside the pockets. A complete chemical evolution from Mg-rich schorl in the wall zone to elbaite with an important deprotonation in the pockets inside the core zone is observed. The most plausible exchange vectors for this chemical evolution are FeMg-1, YAlWO[YR2+W(OH)]-1 and Al[X]X(R2+Na)-1 (where R2+ = Fe2++Mg2++Mn2++Zn2+), for the tourmalines from the wall and intermediate zones. In the core margin, tourmaline composition evolves from schorl toward Li-rich species through the substitution (YAlYLiYR2+-2). Later, during the crystallization of the core zone, this exchange vector combined with the substitution ([X] YAl0.5XNa-1YLi-0.5). Finally, the gemmy tourmalines from the pockets show a deprotonation related to the exchange vector YAlWO2YLi-1W(OH)-2 and may be classified as darrellhenryite. These substitutions may reflect an increase in oxygen fugacity and a decrease in Li and F related to the crystallization of lepidolite and amblygonite-montebrasite in the core zone adjacent to or within the pockets. The crystallization of these minerals would reduce the availability of Li and F for the very latest tourmaline crystals, growing inside the pockets, where the deprotonation becomes important. Chemical and textural variation in tourmaline is consistent with a fractional crystallization process for the internal evolution of the Berry-Havey pegmatite. Crystallization of the tourmaline layer under the core zone may be related to the exsolution of the fluid phase implied in the formation of pockets.

TOURCOMP: A program for estimating end-member proportions in tourmalines

Abstract A Visual Basic program (TOURCOMP) has been written to recast the tourmaline composition into end- member components from electron microprobe data or more complete tourmaline analyses. TOURCOMP is a program based on a linear algebraic model that directly calculates the end-member proportions of tourmalines from their structural formulae. The program is developed for IBM- compatible personal computers running under the Windows™ operating system. The source code has been also translated and compiled in order to run on an Apple computer. Analytical problems, uncertainties concerning site occupancies, and the normalization procedure to determine the structural formula are the main error sources. However, the method of recalculating tourmaline end-members presented in this paper is considered to provide reasonably good results, bearing in mind the chemical complexity of tourmaline.