Com una roca carbonàtica pot esdevenir magatzem de petroli?

Les roques calcàries es poden transformar en dolomies, un tipus de roca amb una suficient porositat com per acollir aigua, mineralitzacions o hidrocarburs en aquests espais buits. Bona part de les reserves naturals de petroli i gas es troben en aquest tipus de roca, a força profunditat, de manera que és difícil poder-les estudiar. A la zona de Benicàssim hi ha afloraments de calcàries i dolomies similars a les que contenen hidrocarburs a l'Orient Mitjà, que han estat estudiades i de les quals s'ha recreat el procés de dolomitizació amb simulacions per ordinador.Las rocas calcáreas se pueden transformar en dolomías, un tipo de roca con una suficiente porosidad como para acoger agua, mineralizaciones o hidrocarburos en estos espacios vacíos. Buena parte de las reservas naturales de petróleo y gas se encuentran en este tipo de roca, a bastante profundidad, por lo que es difícil poderlas estudiar. En la zona de Benicasim hay afloramientos de calizas y dolomías similares a las que contienen hidrocarburos en Oriente Medio, que han sido estudiadas y de las que se ha recreado el proceso de dolomitización con simulaciones por ordenador

Pyrrhotite nano-inclusions in apatite from Les Guilleries lamprohyres (NE Iberian Peninsula)

Apatite is ubiquitous in most types of rocks but in trace amounts, and can form by a variety of processes. Apatite is of great interest because it is an important carrier of volatiles (F, Cl, and OH) and rare-earth elements (REEs), and can be used to reconstruct petrogenetic processes in different environments (e.g., [1]). However, very few studies are dedicated to understanding apatite microstructures (e.g., [2]). Here, we explore apatite in Les Guilleries lamprophyre dykes to gain insights into the parental melt and potential processes of re-mobilization of REEs. The studied dykes are calc-alkaline and represent upwelling of deep lithospheric mantle material (least modified magmas) that emplaced at the end of the Hercynian orogeny in a variety of igneous rocks [3]. The texture and composition of apatites were examined in two thin sections of the least altered dykes, numbered GUI-40 and GUI-41, using SEM/EDS, EPMA, and FIB-TEM. Our results show that apatites in GUI-40 are REE-depleted, mostly rounded, subhedral, and range from ~5 to ~35 μm in size. Their average X-site occupancy is F=78, Cl=2, and OH=20 (mol%). Apatites in GUI-41 are highly acicular (~3-10 μm wide and up to ~120 μm long), REE-enriched compared to GUI-40, and their average X-site occupancy is F=64, Cl=5, and OH=31 (mol%). TEM work on an apatite grain in GUI-40 reveals the presence of abundant nano-inclusions, ~10-60 nm in size, with euhedral, hexagonal shapes in the apatite core (Fig. 1). The nano-inclusions are (i) fully occupied by pyrrhotite, (ii) half occupied by pyrrhotite, or (iii) completely empty. The data suggest that apatites in GUI-40 are primary and their microstructure reflect immiscibility of liquids, interpreted as a characteristic inherited from the primary lamprophyre melt. The presence of Fe in the magma and/or the reducing conditions likely prevented S to form ellestadite domains within the apatite structure. This study also demonstrates that slight REE re-mobilization did occur during a secondary, hydrothermal event

Autoaprenentatge i autoavaluació en el reconeixement de minerals i de jaciments (Geologia)

Hem emprat l'eina d'autoavaluació del Campus Virtual en dues assignatures de la llicenciatura de Geologia relacionades amb minerals, amb la idea de reforçar l'aprenentatge de la part més teòrica en una i la part més pràctica l'altra. En totes dues vam crear uns repositoris de preguntes multiresposta: a l'assignatura de Jaciments Minerals cobrien el temari teòric i, en canvi, a l'assignatura de Mineralogia, les preguntes complementaven el material de pràctiques de laboratori (identificació de minerals, en mostra de mà i al microscopi petrogràfic). En aquest darrer cas, es van construir a més, 8 tests d'avaluació automàtica, que s'obrien als alumnes durant uns dies per tal que poguessin contestar-los fora d'hores de classe, amb ajut d'apunts si volien, durant un temps limitat establert per nosaltres. En vista dels resultats i les opinions dels alumnes, creiem que val la pena fer l'esforç de crear repositoris de preguntes i utilitzar l'eina d'autoavaluació, i més encara per a l'avaluació de la part pràctica, on solen tenir més dificultats per a jutjar el propi aprenentatge al llarg del curs

Allanite in Variscan Post-Collisional Lamprophyre Dykes from Les Guilleries (NE Iberia) as a Part of Rare Earth Elements Recycling in Collisional Orogens

Recent studies of Late Permian calc-alkaline lamprophyre dykes located in the Les Guilleries Paleozoic massif of the Catalan Coastal Range have revealed that allanite is present as the main REE-bearing accessory phase, which is the object of this study. The lamprophyre dykes are amphibole-plagioclase-dominated spessartites with a wide variety of accessory phases, including titanite, ilmenite, allanite, fluorapatite, spinel, zircon, and sulfides, and show complex alteration textures related to secondary albite, chlorite, epidote, titanite and calcite. The allanite crystal composition, analyzed by SEM-EPMA and LA-ICP-MS, evidences the solid solution between epidote and allanite with a ferriallanite component, similar to what is found in Variscan post-collisional granitoids from western Europe. However, heterogeneity in crystal shapes, sizes, type of zoning, dissolution embayment textures, growth of epidote coronas, mineral paragenesis, and the unique geochemical characteristics of allanite crystals suggest multiple crystallization events. At least two types of allanite-epidote composite grains have been identified: allanite Type I, with regular allanite-epidote core-to-rim zoning and a secondary allanite rim; and allanite Type II, with anhedral allanite cores surrounded by epidote coronas. Additionally, irregular zoning, complex dissolution textures and REE redistribution suggest the occurrence of deuteric and/or post-magmatic processes, which are also common in Variscan post-collisional plutons from the Catalan Coastal Range and nearby Paleozoic massifs. Multivariate statistical analyses of major elements in allanite-epidote composite grains show a relationship between major textural and geochemical variations for three out of ten principal components, mainly related to cationic substitutions between ferriallanite-(Ce) and epidote, but also involving Mn and Ti(REE + Fe + Ti + Mg + Mn = Al + Ca + Fe). The allanite U-Pb-Th- weighted mean age of 265 ± 15 Ma (MSWD = 0.57) is roughly similar to the age of emplacement of the lamprophyres in the upper crust in the mid-late Permian, and coincides with the period following the main tectonometamorphic and magmatic events of the post-collisional evolution in the Catalan Coastal Range. Th/U and La/Sm ratios suggest a metamorphic origin for most allanite grains, but a combination of metamorphic processes prior to partial melting, early-late magmatic crystallization, and/or post-magmatic hydrothermal processes is the most plausible explanation to account for the diversity of allanite grains in Les Guilleries lamprophyres

The enriched Variscan lithosphere of NE Iberia: data from postcollisional Permian calc-alkaline lamprophyre dykes of Les Guilleries

Post-collisional mafic dykes crosscut the Paleozoic metamorphic basement and late-Variscan plutons in Les Guilleries massif (Catalan Coastal Ranges, NE Iberia). The predominance of mafic phenocrysts, porphyritic texture, abundant amphibole, high MgO and volatile content, together with crustal-like trace-element patterns indicate that the dykes correspond to calc-alkaline lamprophyres, mainly spessartites. Their enrichment in LILE, HFSE and REE and initial Sr-Nd isotopic compositions (87Sr/86Sri between 0.70851 and 0.71127, ε Ndi between -5.23 and -4.63) are consistent with an enriched subcontinental lithospheric mantle source. U-Pb ages of matrix titanite crystals yield concordia ages of 262±7Ma, congruent with crosscutting relationships. Post-magmatic processes are evidenced by intense chloritization and albitization of the lamprophyres, together with systematic variations of Na2O vs SiO2, K2O, CaO, Ba, Rb, Cs, Pb, Sr, Tl, and Zn, and possibly the removal of F. The geochemical and geochronological data support an orogenic geochemical affinity, in accordance with the transitional tectonic regime between Variscan compression/transpression and post-collisional transtension/extension, related to the fragmentation of Pangea and thinning of the lithosphere. The lamprophyre dykes studied could represent the youngest pulse of Variscan orogenic magmatism and, therefore, mark its end in NE Iberia before the onset of the generalized Triassic extension. Calc-alkaline lamprophyre. Post-collisional dykes. Sr-Nd isotopes. Les Guilleries Massif. Catalan Coastal Ranges. Variscan Orogeny.KEYWORDSABSTRACTCitation: Mellado, E., Corbella, M., Navarro-Ciurana, D., Kylander-Clark, A., 2021. The enriched Variscan lithosphere of NE Iberia: data from post-collisional Permian calc-alkaline lamprophyre dykes of Les Guilleries

MINESCOPE : projecte d'innovació docent amb suport del DDD

Minescope és una aplicació per mòbils que simula l'observació de minerals en un microscopi petrogràfic. Aquest microscopi és un aparell òptic molt utilitzat pels geòlegs per tal d'observar els detalls dels minerals de sediments, roques o falles

An open source Python library for environmental isotopic modelling

Altres ajuts: from the Balearic Island Government through the Margalida Comas postdoctoral fellowship programme (PD/036/2020).Isotopic composition modelling is a key aspect in many environmental studies. This work presents Isocompy, an open source Python library that estimates isotopic compositions through machine learning algorithms with user-defined variables. Isocompy includes dataset preprocessing, outlier detection, statistical analysis, feature selection, model validation and calibration and postprocessing. This tool has the flexibility to operate with discontinuous inputs in time and space. The automatic decision-making procedures are knitted in different stages of the algorithm, although it is possible to manually complete each step. The extensive output reports, figures and maps generated by Isocompy facilitate the comprehension of stable water isotope studies. The functionality of Isocompy is demonstrated with an application example involving the meteorological features and isotopic composition of precipitation in N Chile, which are compared with the results produced in previous studies. In essence, Isocompy offers an open source foundation for isotopic studies that ensures reproducible research in environmental fields

Petrography and geochemistry of fault-controlled hydrothermal dolomites in the Riópar area (Prebetic Zone, SE Spain)

The present paper reports the first detailed petrographical and geochemical studies of hydrothermal dolomites related to MVT Zn-(Fe-Pb) deposits in the Riópar area (Mesozoic Prebetic Basin, SE Spain), constraining the nature, origin and evolution of dolomitizing and ore-forming fluids. Mapping and stratigraphic studies revealed two stratabound dolostone geobodies connected by other patchy bodies, which replace carbonate units of Upper Jurassic to Lower Cretaceous ages. These dolostones are associated to the W-E trending San Jorge fault, indicating a main tectonic control for fluid flow. Seven different dolomite types were identified: i) matrix-replacive planar-s (ReD-I); ii) matrix-replacive planar-e (ReD-II); iii) planar-e sucrosic cement (SuD); iv) non-planar grey saddle dolomite cement (SaD-I) pre-dating Zn-(Fe-Pb) sulfides; v) non-planar milky to pinkish saddle dolomite cement (SaD-II) post-dating Zn-(Fe-Pb) ores; vi) ore-replacive planar-e porphyrotopic (PoD); and vii) planar-s cloudy cement (CeD). Meteoric calcite types were also recognized. The different dolomite types are isotopically characterized by: i) depleted δ18O (from +25.1 to +27.6¿ V-SMOW) and δ13C (from -2.3 to +0.9¿ V-PDB) values compared to Upper Jurassic to Lower Cretaceous limestone signature (δ18O: +27.6 to +30.9¿ V-SMOW; δ13C: +0.5 to +3.2¿ V-PDB); and ii) 87Sr/86Sr ratios for the main dolomitization phases (ReD and SuD: 0.70736-0.70773) close to the Jurassic and Cretaceous carbonate values (0.70723-0.70731) whereas more radiogenic values (0.70741-0.70830) for saddle dolomites (SaD) related to the Zn-(Fe-Pb) sulfide mineralization prevailed after fluid interaction with Rb-bearing minerals. Microthermometrical studies on two-phase liquid and vapor fluid inclusion populations in planar and non-planar dolomites and sphalerite show homogenization temperatures between 150 and 250ºC. These data indicate that both planar and non-planar dolomite textures formed at high-temperatures under hydrothermal conditions in deep-burial diagenetic environments. The main dolomitizing phase (ReD-I/ReD-II and SaD-I) shows low to moderate fluid inclusions salinity (5 to 14 wt.% eq. NaCl), whereas the dolomitization related to ore precipitation (sphalerite and SaD-II) spreads to higher salinity values (5 to 25 wt.% eq. NaCl). These data may respond to a mixing between a low salinity fluid (fluid A, less than 5 wt.% eq. NaCl) and a more saline brine (fluid B, more than 25 wt.% eq. NaCl) at different fluid proportions

Sulfur and lead isotope systematics: Implications for the genesis of the Riópar Zn-(Fe-Pb) carbonate-hosted deposit (Prebetic Zone, SE Spain)

The Zn-(Fe-Pb) deposits of the Riópar area (Prebetic Zone, SE Spain) are hosted by dolostones that replace Berriasian to Valanginian (Upper Jurassic-Lower Cretaceous) limestones. Mineralization consists of hypogene sphalerite, marcasite and galena, and supergene calamine zones. The hypogene ores are associated with a saddle dolomite gangue. The ore bodies occur as discordant and stratiform lenses, ore-cemented breccias, cm- to mm-wide veins and veinlets, disseminations and stylolite porosity filling within the host dolomites. The main ore controls include stratigraphy and/or lithology, tectonics (faults, fractures and breccias) and availability of metals and sulfur. The morphologies and epigenetic character of the hypogene ore bodies are consistent with the classification of this mineralization as a Mississippi Valley-type (MVT) deposit. The Ga/Ge geothermometer in sphalerite yielded a temperature range of 194-252ºC, which represents the temperature of the source region of the ore solution. This value is comparable to the temperature obtained in the ore deposition site, 159±15ºC from the Δ34S geothermometer in sphalerite galena pairs. This similitude points to a hydrothermal fluid that did not cool down significantly during flow from the fluid reservoir area to the precipitation site. δ34S values of base-metal sulfides (-7.5 to +3.5 ¿) are consistent with thermochemical reduction of Triassic sulfate (seawater and/or derived from dissolution of evaporites) by interaction with organic compounds (e.g., hydrocarbons, methane), which reduced sulfate to sulfide in the deposition site. The lead isotope ratios (206Pb/204Pb = 18.736-18.762; 207Pb/204Pb = 15.629-15.660; 208Pb/204Pb = 38.496-38.595) of galena suggest that Pb, and probably other metals as Zn, is derived from continental crustal rocks. On the other hand, these relations points to an unique metal source probably derived from the Paleozoic basement rocks. The relationship between bedding-parallel stylolites, dolomitization, sulfide precipitation and Alpine tectonic affecting the MVT ore, suggests a relative timing range for the mineralization in the Riópar area of 95 to 20 Ma (Upper Cretaceous-Tertiary). The sulfide mineralization and the associated dolomitization are thus explained by the contribution of two fluids that mixed in different proportions during dolomitization and mineralization: i) a fluid probably derived from Cretaceous seawater saturating Mesozoic sediments (Fluid A), characterized by being dilute and initially low temperature, which should have contained organic rich compounds in the ore deposition site (e.g., hydrocarbons and CH4 dissolved gas); and ii) a high salinity hydrothermal brine (Fluid B) rich in both metals and sulfate, circulated through the Paleozoic basement. During the pre-ore dolomitizing stage the fluid phase was dominated by the diluted fluid (Fluid A > Fluid B), whereas in a later fluid pulse, the proportion of the high salinity fluid increased (Fluid A < Fluid B) which allowed sulfide precipitation. MVT exploration in the Prebetic Zone should focus towards the SW of the Riópar mines, in the vicinity of the Alto Guadalquivir-San Jorge fault

Origin and timing of stratabound dolomitization in the Cretaceous carbonate ramp of Benicàssim

Hydrothermal dolomitization is one of the most important processes that may enhance or degrade carbonate porosity and permeability. Burial, high emperature or hydrothermal dolomite forms due to the interaction of one or more solutions, mainly seawater-derived or deep brines, with limestone. The Early Cretaceous Benicassim ramp (Maestrat Basin, E Spain) is an excellent outcrop analog for partially dolomitized petroleum reservoirs. In this area seismic-scale sub-stratiform dolomitized bodies extend for several kilometers, away from large-scale faults, in Aptian limestones (Fig. 1). In the present work the Benicassim ramp is used as a case study to characterize dolomite events and to evaluate controls on dolomitization via reactive transport simulations