Fault-controlled hydrothermal dolomitization of the Late Aptian to Early Albian Benassal Fm shallow water carbonates resulted in the seismic-scale stratabound dolostone geobodies that characterize the Benicàssim case study (Maestrat Basin, E Spain). Petrological and geochemical data indicate that dolomite cement (DC1) filling intergranular porosity in grain-dominated facies constituted the initial stage of dolomitization. The bulk of the dolostone is formed by a replacive nonplanar-a to planar-s dolomite (RD1) crystal mosaic with very low porosity and characteristic retentive fabric. Neomorphic recrystallization of RD1 to form replacive dolomite RD2 occurred by successive dolomitizing fluid flow. The replacement sequence DC1-RD1-RD2 is characterized by a depletion in the oxygen isotopic composition (mean δ 18 O (V-PDB) values from -6.92, to -8.55, to -9.86‰), which is interpreted to result from progressively higher temperature fluids. Clear dolomite overgrowths (overdolomitization) precipitated during the last stage of the replacement. Strontium isotopic composition suggests that the most likely origin of magnesium was Cretaceous seawater-derived brines that were heated and enriched in radiogenic strontium and iron while circulating through the Paleozoic basement and/or Permo-Triassic red beds. Burial curves and analytical data indicate that the replacement took place at burial depths between 500 and 750 m, which correspond to the Late Cretaceous post-rift stage or early Tertiary extension of the Maestrat Basin, and by hydrothermal fluids likely exceeding temperatures of 80ºC. Following the partial dolomitization of the host rock, porosity considerably increased in dolostones by burial corrosion related to the circulation of acidic fluids likely derived from the emplacement of the Mississippi Valley-Type deposits. Acidic fluids, probably overpressured, circulated along faults, fractures and stylolites. Saddle dolomite and ore-M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 4 stage calcite cement filled most of the newly created vuggy porosity. Subsequent to MVT mineralization, precipitation of calcite cements resulted from the migration of meteoric-derived fluids during uplift and subaerial exposure. This late calcite cement destroyed most of the dolostone porosity and constitutes the main cause for the present day poor reservoir quality of the Benassal Fm dolostones.

i ExxonMobil (FC) 2 Alliance_Fundamental Controls on Flow in Carbonates, USA Syn-rift shallow-marine carbonates of Late Aptian to Early Albian age in the southern Maestrat Basin (E Spain) register the thickest Aptian sedimentary record of the basin, and one of the most complete carbonate successions of this age reported in the northern Tethyan margin. The host limestones (Benassal Formation) are partially replaced by dolostones providing a new case study of fault-controlled hydrothermal dolomitization. The syn-rift sediments filled a graben controlled by normal basement faults. The Benassal Fm was deposited in a carbonate ramp with scarce siliciclastic input. The lithofacies are mainly characterized by the presence of orbitolinid foraminifera, corals and rudist bivalves fauna. The succession is stacked in three transgressiveeregressive sequences (TeR) bounded by surfaces with sequence stratigraphic significance. The third sequence, which is reported for the first time in the basin, is formed by fully marine lithofacies of Albian age and represents the marine equivalent to the continental deposits of the Escucha Fm in the rest of the basin. The dolomitization of the host rock is spatially associated with the basement faults, and thus is faultcontrolled. The dolostone forms seismic-scale stratabound tabular geobodies that extend several kilometres away from the fault zones, mostly in the hanging wall blocks, and host Mississippi Valley Type (MVT) deposits. The dolostones preferentially replaced middle to inner ramp grain-dominated facies from the third TeR sequences consisting of bioclastic packestones and peloidal grainstones. Field and petrology data indicate that the replacement took place after early calcite cementation and compaction, most likely during the Late Cretaceous post-rift stage of the basin. The dolostone registers the typical hydrothermal paragenesis constituted by the host limestone replacement, dolomite cementation and sulfide MVT mineralization. The Aptian succession studied provides a stratigraphic framework that can be used for oil exploration in age-equivalent rocks, especially in the València Trough, offshore Spain. Moreover, this new case study constitutes a world class outcrop analogue for similar partially stratabound, dolomitized limestone reservoirs worldwide.

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The mechanisms responsible for the formation of huge volumes of dolomitized rocks associated with faults are not well understood. We present a case study for high-temperature dolomitization of an Early Cretaceous (Aptian-Albian) ramp in Benicàssim (Maestrat basin, E Spain). In this area, seismic-scale fault-controlled stratabound dolostone bodies extend over several kilometres away from large-scale faults. This work aims at evaluating different Mg sources for dolomitization, estimating the reactivity of dolomitizing fluids at variable temperature and quantifying the required versus available fluid volumes to account for the Benicàssim dolostones. Field relationships, stable 13 C and 18 O isotopes, as well as radiogenic 87 Sr/ 86 Sr isotopes, indicate that dolomitization at Benicàssim was produced by a high temperature fluid (> 80ºC). 13 C and 18 O isotopic compositions for dolomite vary from +0.5 and +2.9 ‰ V-PDB and from +21.1 and +24.3 V-SMOW, respectively. A Mg source analysis reveals that the most likely dolomitizing fluid was seawater-derived brine that interacted with underlying Triassic red beds and Paleozoic basement. Geochemical models suggest that evolved seawater can be considerably more reactive than high-salinity brines, and that the maximum reactivity occurs at about 100ºC. Mass-balance calculations indicate that interstitial fluids with high pressure and/or high temperature relative to the normal geothermal gradient cannot account for the volume of dolomite at Benicàssim. Instead a pervasive fluid circulation mechanism, like thermal convection, is required to provide a sufficient volume of dolomitizing fluid, which most likely occurred during the Late Cretaceous post-rift stage of the Maestrat Basin. This study illustrates the importance of fluid budget quantification to critically evaluate genetic models for dolomitization and other diagenetic processes.

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The fluorite deposits of Asturias (northern Iberian Peninsula) are hosted by rocks of Permo-Triassic and Palaeozoic age. Fluid inclusions in ore and gangue minerals show homogenization temperatures from 80 to 170°C and the presence of two types of fluids: an H20-NaCI low-salinity fluid «8 eq. wt% NaCI) and an H20-NaCI-CaCI2 fluid (7-13 wt% NaCI and 11-14 wt% CaCI2). The low salinity and the Cl/Br and NalBr ratios (CI/Brmolar 100-700and NalBr molar 20-700) are consistent with an evaporated sea water origin of this fluid. The other end-member of the mixture was highly saline brine with high Cl/Br and NalBr ratios (CI/Brmolar 700-13 000 and NalBrmolar 700-11 000) generated after dissolution of Triassic age evaporites.

Cerro Quema (Azuero Peninsula, SW Panama) is a high sulfidation epithermal Au-Cu deposit hosted by a dacite dome complex of the Río Quema Formation (Late Campanian to Maastrichtian), a fore-arc basin sequence. Mineral resource estimate (Indicated + Inferred) are 30.86 Mt @ 0.73 g/t Au, containing 728,000 Oz Au (including 76.900 Oz AuEq of Cu ore). Hydrothermal alteration and mineralization are controlled by an E trending regional fault system. Hydrothermal alteration consists of an inner zone of vuggy quartz with locally developed advanced argillic alteration, enclosed by a well-developed zone of argillic alteration, grading to an external halo of propylitic alteration. Mineralization produced dissemination and microveinlets of pyrite and minor chalcopyrite, enargite and tennantite, with traces of sphalerite, crosscut by late stage base metal veins. New 40 Ar/ 39 Ar data of igneous rocks combined with biostratigraphic ages of the volcanic sequence indicate a maximum age of Lower Eocene (~55-49 Ma) for the Cerro Quema deposit. It was probably triggered by the emplacement of an underlying porphyry-like intrusion associated with the Valle Rico batholith. The geologic model suggests that in the Azuero Peninsula high sulfidation epithermal mineralization occur in the Cretaceous-Paleogene fore-arc. This consideration should be taken into account when exploring for this deposit type in similar geologic terranes.

The Azuero Peninsula, located in SW Panama, is a region characterized by a long-lived intra-oceanic subduction zone. Volcanism began in Late Cretaceous time, as the result of subduction of the Farallon plate beneath the Caribbean plate. Usually, ancient volcanic arcs related to intra-oceanic subduction zones are not preserved, because they are in areas with difficult access or covered by modern volcanic arc material. However, on the Azuero peninsula, a complete section of the volcanic arc together with arc basement rocks provides the opportunity to study the sedimentation and volcanism in the initial stages of volcanic arc development. The lithostratigraphic unit which records fore-arc evolution is the “Río Quema” Formation (RQF), a volcanic apron composed of volcanic and volcaniclastic sedimentary rocks interbedded with hemipelagic limestones, submarine dacite lava domes, and intruded by basaltic-andesitic dikes. The “Río Quema” Formation, interpreted as a fore-arc basin infilling sequence, lies discordantly on top of arc basement rocks. The exceptionally well exposed arc basement, fore-arc basin, volcanic arc rocks and arc-related intrusive rocks provide an unusual opportunity to study the relationship between volcanism, sedimentation and magmatism during the arc development, with the objective to reconstruct its evolution. The “Río Quema” Formation can be divided into three groups: 1) proximal apron, a sequence dominated by lava flows, interbedded with breccias, mass flows and channel fill, all intruded by basaltic dikes. The rocks represent the nearest materials to the volcanic source, reflecting a coarse sediment supply. This depositional environment is similar to gravel-rich fan deltas and submarine ramps; 2) medial apron, characterized by a volcanosedimentary succession dominated by andesitic lava flows, polymictic volcanic conglomerates and crystal-rich sandstones with minor pelagic sediments and turbidites. These rocks were deposited from high-density turbidity currents and debris flows, directly derived from erupted material and gravitational collapse of an unstable volcanic edifice or volcaniclastic apron; 3) distal apron, a thick succession of sandy to muddy volcaniclastic rocks, interbedded with pelagic limestones and minor andesitic lavas, intruded by dacite domes and by basaltic to andesitic dikes. Bedforms and fossils suggest a quiet, relatively deep-water environment characterized by settling of clay and silt (claystone, siltstone) and by dilute turbidity currents of reworked volcaniclastic detritus. The timing of the initial stages of the volcanic arc has been constrained through a biostratigraphic study, using planktonic foraminifera and radiolarian species. The fossil assemblage indicates that the age of the “Río Quema” Formation ranges from Late Campanian to Maastrichtian, providing a good constraint for the development of the volcanic arc and volcaniclastic apron, during the initial stages of an intra-oceanic subduction zone.