ALBERT

Description: Cerro Quema (Azuero Peninsula, southwest 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 estimates (indicated + inferred) are 30.86 Mt at 0.73 g/t Au, containing 728,000 oz Au (including 76.900 oz Au equiv 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 disseminations 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 occurs in the Cretaceous-Paleogene fore arc. This consideration should be taken into account when exploring for this deposit type in similar geologic terranes.

Description: 〈span〉〈div〉Abstract〈/div〉Vein and stratabound Zn-Pb sulfides are hosted within siliciclastic rocks and marine carbonates of Cretaceous age and within caprock carbonates at the margins of the Murguía and Orduña saline diapirs in the Basque-Cantabrian basin. Organic matter is ubiquitous, and textures indicate a genetic link to sulfide precipitation. Sulfides (pyrite, sphalerite, and galena) precipitated from brines with halogen ratios compatible with halite dissolution. Thermal indicators (fluid inclusion, organic matter, and sulfur isotope data), point to formation temperatures between 150° and 200°C.The 〈span〉δ〈/span〉〈sup〉34〈/sup〉S values of sphalerite and galena (4.1–15.1‰) suggest a sulfur source related to the reduction of evaporite sulfate (thermochemical sulfate reduction) of Triassic age (15.3–17.4‰). The interaction of carbon-poor, metal- and sulfate-bearing hot brines with host rocks activated the cracking of organic matter, triggering sulfide precipitation at a rate controlled by the H〈sub〉2〈/sub〉S production.Textural relationships suggest that ore precipitation was related to dolomitization of host rocks (siliciclastic rocks, marine carbonates, and caprock). The 〈span〉δ〈/span〉〈sup〉13〈/sup〉C and d〈sup〉18〈/sup〉O of carbonates range from 3.5 to –20.5‰ and from 16.1 to 28.7‰, respectively, indicative of different carbon sources and host-rock types. Carbonates associated with sulfide mineralization depict 〈span〉δ〈/span〉〈sup〉13〈/sup〉C/〈span〉δ〈/span〉〈sup〉18〈/sup〉O assemblages and 〈sup〉87〈/sup〉Sr/〈sup〉86〈/sup〉Sr ratios (0.70801–0.71202) resulting from the interaction of a basinal brine with the different host rocks. Galena Pb isotope ratios—〈sup〉206〈/sup〉Pb/〈sup〉204〈/sup〉Pb from 18.643 to 18.696, 〈sup〉207〈/sup〉Pb/〈sup〉204〈/sup〉Pb from 15.650 to 15.676, and 〈sup〉208〈/sup〉Pb/〈sup〉204〈/sup〉Pb from 38.720 to 38.780—point to metal source rocks similar to other Mississippi Valley-type (MVT) deposits of the Basque-Cantabrian basin.Sulfide concentrations around the Murguía and Orduña diapirs are not concomitant with caprock formation but with dolomitization, as in MVT deposits. This is in contrast with the diapir-related deposits of the Gulf Coast and shares characteristics with the diapir-related mineralization in North Africa.〈/span〉

Description: 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.

Description: Partially dolomitized carbonate rocks of the Middle East and North America host large hydrocarbon reserves. The origin of some of these dolomites has been attributed to a hydrothermal mechanism. The Benicàssim area (Maestrat Basin, eastern Spain) constitutes an excellent field analogue for fault-controlled stratabound hydrothermal dolomitization: dolostone geobodies are well exposed and extend over several kilometres away from seismic-scale faults. This work investigates the main controls on the formation of stratabound versus massive dolomitization in carbonate sequences by means of two-dimensional (2D) reactive transport models applied to the Benicàssim case study. Simulation results suggest that the dolomitization capacity of Mg-rich fluids reaches a maximum at temperatures around 100 °C and a minimum at 25 °C (studied temperature range: 25–150 °C). It takes of the order of hundreds of thousands to millions of years to completely dolomitize kilometre-long limestone sections, with solutions flowing laterally through strata at velocities of metres per year (m/a). Permeability differences of two orders of magnitude between layers are required to form stratabound dolomitization. The kilometre-long stratabound dolostone geobodies of Benicàssim must have formed under a regime of lateral flux greater than metres per year over about a million years. As long-term dolomitization tends to produce massive dolostone bodies not seen at Benicàssim, the dolomitizing process there must have been limited by the availability of fluid volume or the flow-driving mechanism. Reactive transport simulations have proven a useful tool to quantify aspects of the Benicàssim genetic model of hydrothermal dolomitization.