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Xiomara Cazañas Pura Alfonso Joan Carles Melgarejo Joaquín Antonio Proenza Anthony Edward Fallick 《Mineralium Deposita》2008,43(7):805-824
The El Cobre deposit is located in eastern Cuba within the volcanosedimentary sequence of the Sierra Maestra Paleogene arc.
The deposit is hosted by tholeiitic basalts, andesites and tuffs and comprises thick stratiform barite and anhydrite bodies,
three stratabound disseminated up to massive sulphide bodies produced by silicification and sulphidation of limestones or
sulphates, an anhydrite stockwork and a siliceous stockwork, grading downwards to quartz veins. Sulphides are mainly pyrite,
chalcopyrite and sphalerite; gold occurs in the stratabound ores. Fluid inclusions measured in sphalerite, quartz, anhydrite
and calcite show salinities between 2.3 and 5.7 wt% NaCl eq. and homogenisation temperatures between 177 and 300°C. Sulphides
from the stratabound mineralisation display δ
34S values of 0‰ to +6.0‰, whilst those from the feeder zone lie between −1.4‰ and +7.3‰. Sulphides show an intra-grain sulphur
isotope zonation of about 2‰; usually, δ
34S values increase towards the rims. Sulphate sulphur has δ
34S in the range of +17‰ to +21‰, except two samples with values of +5.9‰ and +7.7‰. Sulphur isotope data indicate that the
thermochemical reduction of sulphate from a hydrothermal fluid of seawater origin was the main source of sulphide sulphur
and that most of the sulphates precipitated by heating of seawater. The structure of the deposit, mineralogy, fluid inclusion
and isotope data suggest that the deposit formed from seawater-derived fluids with probably minor supply of magmatic fluids. 相似文献
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3.
Distribution of platinum-group elements and Os isotopes in chromite ores from Mayarí-Baracoa Ophiolitic Belt (eastern Cuba) 总被引：1，自引：0，他引：1
F.?GervillaEmail author J.A.?Proenza R.?Frei J.M.?González-Jiménez C.J.?Garrido J.C.?Melgarejo A.?Meibom R.?Díaz-Martínez W.?Lavaut 《Contributions to Mineralogy and Petrology》2005,150(6):589-607
The Mayarí-Baracoa ophiolitic belt in eastern Cuba hosts abundant chromite deposits of historical economic importance. Among
these deposits, the chemistry of chromite ore is very variable, ranging from high Al (Cr#=0.43–0.55) to high Cr (Cr#=0.60–0.83)
compositions. Platinum-group element (PGE) contents are also variable (from 33 ppb to 1.88 ppm) and correlate positively with
the Cr# of the ore. Bulk PGE abundances correlate negatively with the Pd/Ir ratio showing that chromite concentrates mainly
Os, Ir and Ru which gives rise to the characteristic negatively sloped, chrondrite-normalized PGE patterns in many chromitites.
This is consistent with the mineralogy of PGEs, which is dominated by members of the laurite–erlichmanite solid solution series
(RuS2–OsS2), with minor amounts of irarsite (IrAsS), Os–Ir alloys, Ru–Os–Ir–Fe–Ni alloys, Ni–Rh–As, and sulfides of Ir, Os, Rh, Cu,
Ni, and/or Pd. Measured 187Os/188Os ratios (from 0.1304 to 0.1230) are among the lower values reported for podiform chromitites. The 187Os/188Os ratios decrease with increasing whole-rock PGE contents and Cr# of chromite. Furthermore, γOs values of all but one of
the chromitite samples are negative indicating a subchondiritc mantle source. γOs decrease with increasing bulk Os content
and decreasing 187Re/188Os ratios. These mineralogical and geochemical features are interpreted in terms of chromite crystallization from melts varying
in composition from back-arc basalts (Al-rich chromite) to boninites (Cr-rich chromite) in a suprasubduction zone setting.
Chromite crystallization occurs as a consequence of magma mixing and assimilation of preexisting gabbro sills at the mantle–crust
transition zone. Cr#, PGE abundances, and bulk Os isotopic composition of chromitites are determined by the combined effects
of mantle source heterogeneity, the degree of partial melting, the extent of melt-rock interactions, and the local sulfur
fugacity. Small-scale (μm to cm) chemical and isotopic heterogeneities in the platinum-group minerals are controlled by the
mechanism(s) of chromite crystallization in a heterogeneous environment created by the turbulent regime generated by successive
inputs of different batches of melt. 相似文献
4.
Xu Jingyao Melgarejo Joan Carles Castillo-Oliver Montgarri 《Mineralogy and Petrology》2018,112(2):569-581
Five compositional-textural types of ilmenite can be distinguished in nine kimberlites from the Eastern Dharwar craton of southern India. These ilmenite generations record different processes in kimberlite history, from mantle to surface. A first generation of Mg-rich ilmenite (type 1) was produced by metasomatic processes in the mantle before the emplacement of the kimberlite. It is found as xenolithic polycrystalline ilmenite aggregates as well as megacrysts and macrocrysts. All of these ilmenite forms may disaggregate within the kimberlite. Due to the interaction with low-viscosity kimberlitic magma replacement of pre-existing type 1 ilmenite by a succeeding generation of geikielite (type 2) along grain boundaries and cracks occurs. Another generation of Mg-rich ilmenite maybe produced by exsolution processes (type 3 ilmenite). Although the identity of the host mineral is unclear due to extensive alteration and possibility includes enstatite. Type 4 Mn-rich ilmenite is produced before the crystallization of groundmass perovskite and ulvöspinel. It usually mantles ilmenite and other Ti-rich minerals. Type 5 Mn-rich ilmenite is produced after the crystallization of the groundmass minerals and replaces them. The contents of Cr and Nb in type 2, 4 and 5 ilmenites are highly dependent on the composition of the replaced minerals, they may not be a good argument in exploration. The highest Mg contents are recorded in metasomatic ilmenite that is produced during kimberlite emplacement, and cannot be associated with diamond formation. The higher Mn contents are linked to magmatic processes and also late processes clearly produced after the crystallization of the kimberlite groundmass, and therefore ilmenite with high Mn contents cannot be considered as a reliable diamond indicator mineral (DIM) and kimberlite indicator mineral (KIM).
相似文献5.
E. Aprile K. Arisaka F. Arneodo A. Askin L. Baudis A. Behrens K. Bokeloh E. Brown J.M.R. Cardoso B. Choi D. Cline S. Fattori A.D. Ferella K.L. Giboni A. Kish C.W. Lam J. Lamblin R.F. Lang K.E. Lim J.A.M. Lopes T. Marrodán Undagoitia Y. Mei A.J. Melgarejo Fernandez K. Ni U. Oberlack S.E.A. Orrigo E. Pantic G. Plante A.C.C. Ribeiro R. Santorelli J.M.F. dos Santos M. Schumann P. Shagin A. Teymourian D. Thers E. Tziaferi H. Wang C. Weinheimer M. LaubensteinS. Nisi 《Astroparticle Physics》2011,35(2):43-49
Results of the extensive radioactivity screening campaign to identify materials for the construction of XENON100 are reported. This dark matter search experiment is operated underground at Laboratori Nazionali del Gran Sasso (LNGS), Italy. Several ultra sensitive High Purity Germanium detectors (HPGe) have been used for gamma ray spectrometry. Mass spectrometry has been applied for a few low mass plastic samples. Detailed tables with the radioactive contaminations of all screened samples are presented, together with the implications for XENON100. 相似文献
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J. Proenza F. Gervilla J. Melgarejo O. Vera P. Alfonso A. Fallick 《Mineralium Deposita》2001,36(7):658-669
The Potosí Mine is located in the Moa-Baracoa massif in the easternmost part of the Cuban Ophiolitic Belt. Chromite mineralization occurs within the mantle-crust transition zone. Two events of magma intrusion overprint the chromitite bodies: one gave rise to the crystallization of pegmatitic olivine-norite dikes, and the other produced pegmatitic gabbro dikes. Sulfide-poor chromite ores, brecciated chromite ores, and sulfide-rich chromite ores can be distinguished in the different chromitite bodies. Sulfide-poor ores represent more than 80 vol% of the chromitites. This type occurs far from the zones intruded by pegmatitic gabbro dikes and shows petrographic and chemical features similar to other chromitite bodies described in the Moa-Baracoa massif. Brecciated chromite ores occur within pegmatitic gabbro dikes. In this type, chromite crystals occur included within chromian diopside and plagioclase. These silicates often contain droplet-like sulfide aggregates. Sulfide-rich ores are spatially associated to the contacts between sulfide-poor chromite and pegmatitic olivine-norite dikes. These ores mainly consist of recrystallized (coarse) chromite with interstitial pyrrhotite, pentlandite, cubanite, and chalcopyrite. Chromite from sulfide-rich ores exhibits TiO2, FeO, V2O3, MnO, and especially, Fe2O3 contents, higher than those of chromite from brecciated ores and much higher than those of chromite from sulfide-poor ores. The sulfide-rich ores are PGE-rich (up to 1,113 ppb of total PGE), and show nearly flat chondrite-normalized PGE patterns, slightly above 0.1 times chondritic values. Mineralogical and chemical data indicate that the chromite ores of the Potosí Mine were modified by the intrusions of olivine-norite and gabbro dikes. The interaction between pre-existing sulfide-poor chromite ores and the intruding volatile-rich silicate melts produced strong brecciation, partial dissolution, and recrystallization (coarsening) of chromite. The sulfide assemblage formed by fractionation of the immiscible sulfide melt segregated from the volatile-rich silicate melt that generated the pegmatitic olivine-norite. The segregation of the sulfide melt can be interpreted as the consequence of chemical interaction between intruding melts and the host chromite. The variable extent of this interaction produced chromite ores with variable sulfide ratios. The magmatic nature of the sulfide mineralization is supported by sulfur isotope data, which range from -0.4 to +0.9. Sulfide melt collected incompatible PGE (Rh, Pt, Pd) to produce the typical flat chondrite-normalized pattern of sulfide-rich chromite ores. 相似文献
8.
Summary Four types of pegmatites comprise the zoned pegmatite field in the eastern sector of the Albera Massif. Type I is represented by barren pegmatites with graphic textures; type II comprises transitional varieties with Li-Fe-Mn phosphates, Be (chrysoberyl) and scarce Nb-Ta and U oxide minerals; type III consists of pegmatites with significant zones of replacement containing Li-Fe-Mn phosphates, beryl and more abundant Nb-Ta oxide minerals; and type IV, muscovite-quartz-albite pegmatites are highly mineralized with Be, Nb-Ta and HREE. REE mineralization is strongly related to abundance of graphite in the late pegmatite units and in the host-rock. The individual pegmatite types are distributed within four subparallel zones concentric around anatectic muscovite-biotite leucogranites, with type I within the granites or close to the contact, and type IV pegmatites in the outermost areas. The zoning from type I to type IV could relate to fractionation processes which generated the pegmatites and is characterized by an enrichment of Mn, Ta, Na, Li, P, Be and REE. According to the pegmatite distribution and their fractionation trends, we propose an origin by differentiation of a granitic melt.
With 5 Figures 相似文献
Résumé On a établi quatre types de pegmatites dans le champ pegmatitique zoné du secteur est du Massif des Albères (Pyrénées Orientales, France). Celles de type I sont des pegmatites non minéralisées avec des textures graphiques, celles de type II sont des variétés intermediaires avec des phosphates à Li-Fe-Mn, Be (chrysobéryl) et des rares oxides à Nb-Ta et U; celles de type Ill sont des pegmatites avec des zones de réplacement bien dévéloppées et qui contiennent des phosphates à Li-Fe-Mn, du béryl et des oxides à Nb-Ta plus abondants; celles de type IV sont des pegmatites bien minéralisées à Be, Nb-Ta et des T.R. La minéralisation à T.R. est liée à des phénomènes de graphitisation répandus dans les unités tardives de la pegmatite et dans l'encaissant. La distribution de chaque type de pegmatite correspond à quatre zones à peu près parallèles et concentriques autour des granites anatectiques à muscovite-biotite, avec le type I dans les granites ou prochain au contact, et les pegmatites à type IV dans la bande plus externe. La zonation serait due à des processus de fractionnement qui auraient généré les pegmatites et qui sont caracterisés par un enrichissement en Mn, Ta, Na, Li, P, Be et T.R. dès les pegmatites de type I vers celles de type IV. On propose un origine par différentiation des granites en vue de la distribution des pegmatites.
With 5 Figures 相似文献
9.
Nb-Ta-minerals from the cap de creus pegmatite field,eastern Pyrenees: distribution and geochemical trends 总被引：2，自引：0，他引：2
P. Alfonso Abella J. -C. Melgarejo i Draper M. Corbella i Cordomi 《Mineralogy and Petrology》1995,55(1-3):53-69
Summary Internal structure and mineralogy facilitate distinction of four main pegmatite types at the eastern end of the Pyrenees. Three main trends in compositional variations in Nb-Ta-Sn-REE-Ti minerals have been established: a regional trend, with Ta/(Ta + Nb) ratio increasing towards the more evolved pegmatites, Mn/(Mn + Fe) being relatively low and increasing only slightly; a single-body trend, with similar enrichment toward the late pegmatite units; a single-crystal trend, with zoning related to both Ta/(Ta + Nb) and Mn/(Mn + Fe) ratios and a tendency toward Ta-enrichment in the late growth stages. The regional geochemical enrichment trends in the Mn/(Mn + Fe) ratios and Ta/(Ta + Nb) are those expected for a beryl-columbite pegmatite type. In a single pegmatite, the evolution depends on the simultaneous growth of other mineral species. Three factors seem to control the development of zoning in columbite-tantalite crystals: availability of Mn, Ta, Fe, Nb, significant differences in solubility between mineral group end members and re-equilibria with late pegmatite fluids.
With 6 Figures 相似文献
Nb-Ta-Minerale aus dem Pegmatit-Feld vom Cap de Creus, östliche Pyrenäen: Verteilung und geochemische Trends
Zusammenfassung Am Ostrand der Pyrenäen können anhand des inneren Aufbaus und der Mineralogie vier Haupttypen von Pegmatiten unterschieden werden. Die Zusammensetzungen von Nb-Ta-Sn-SEE-Ti-Mineralen folgen drei Haupttrends: einem regionalen Trend, bei dem das Verhältnis Ta/(Ta + Nb) zu den höher entwickelten Pegmatiten hin zunimmt, während Mn/(Mn + Fe) relativ niedrig ist und nur leicht zunimmt; einem lokalen (auf das jeweilige Vorkommen beschränkten) Trend mit einer ähnlichen Anreicherung zu den spätpegmatitischen Einheiten hin; einem auf Einzelkristalle bezogenen Trend mit Zonierung in bezug auf die Verhältnisse Ta/(Ta + Nb) und Mn/(Mn + Fe) und einer Tendenz zur T a-Anreicherung in den späten Wachstumsphasen. Die regionalen geochemischen Anreicherungstrends in den Mn/(Mn + Fe)- und Ta/(Ta + Nb)-Verhältnissen entsprechen jenen, wie sie für den Beryll-Columbit-Pegmatit-Typ erwartet werden. In einem einzelnen Pegmatit hängt die Entwicklung vom gleichzeitigen Wachstum anderer Mineral-Spezies ab. Drei Faktoren scheinen die Ausbildung einer Zonierung in Columbit-Tantalit-Kristallen zu kontrollieren: das Angebot an Mn, Ta, Fe und Nb, deutliche Unterschiede in der Löslichkeit der Endglieder von Mineralgruppen und die Iteequilibrierung mit spätpegmatitischen Lösungen.
With 6 Figures 相似文献
10.
Van Lichtervelde Marieke Grand’Homme Alexis de Saint-Blanquat Michel Olivier Philippe Gerdes Axel Paquette Jean-Louis Melgarejo Joan Carles Druguet Elena Alfonso Pura 《Mineralogy and Petrology》2017,111(1):1-21
Mineralogy and Petrology - The Cap de Creus granitic pegmatites in the eastern Catalan Pyrenees were dated using in situ U-Pb geochronology by laser ablation ICP-MS on zircon and columbite-group... 相似文献
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