Reply to the Comment by David W. Morrow on 'Self-accelerating dolomite-for-calcite replacement: Self-organized dynamics of burial dolomitization and associated mineralization'

We welcome David W. Morrow's Comment to our article Merino and Canals (2011) (MC-2011 hereafter), in which we presented a new model of burial dolomitization. Morrow raises several questions and sees conflicts of some of the model's parts with published experiments

Genesis of self-organized zebra textures in burial dolomites: Displacive veins, induced stress, and dolomitization

The dolomite veins making up rhythmites common in burial dolomites are not cement infillings of supposed cavities, as in the prevailing view, but are instead displacive veins, veins that pushed aside the host dolostone as they grew. Evidence that the veins are displacive includes a) small transform-fault-like displacements that could not have taken place if the veins were passive cements, and b) stylolites in host rock that formed as the veins grew in order to compensate for the volume added by the veins. Each zebra vein consists of crystals that grow inward from both sides, and displaces its walls via the local induced stress generated by the crystal growth itself. The petrographic criterion used in recent literature to interpret zebra veins in dolomites as cements - namely, that euhedral crystals can grow only in a prior void - disregards evidence to the contrary. The idea that flat voids did form in dolostones is incompatible with the observed optical continuity between the saddle dolomite euhedra of a vein and the replacive dolomite crystals of the host. The induced stress is also the key to the self-organization of zebra veins: In a set of many incipient, randomly-spaced, parallel veins just starting to grow in a host dolostone, each vein¿s induced stress prevents too-close neighbor veins from nucleating, or redissolves them by pressure-solution. The veins that survive this triage are those just outside their neighbors¿s induced stress haloes, now forming a set of equidistant veins, as observed

La composición isotópica del azufre y del plomo en las mineralizaciones de Zn-Pb del Valle de Arán (Pirineo central) y su significado metalogenético

La composición isotópica del azufre en sulfuros (δ34S) de las mineralizaciones tipo sedimentario-exhalativo del Ordovícico superior del valle de Arán (Pirineos Centrales) varía entre +3,5 y +15,1 ‰ en los encajados en carbonatos y entre -2,7 y +5,5 ‰ en los encajados en materiales detríticos. Estos valores sugieren que dichos depósitos se formaron a partir de dos fuentes de azufre distintas: una originada por reducción de sulfato de origen marino y otra por lixiviación de materiales detríticos y/o volcánicos de edad cambro-ordovícica. El metamorfismo Hercínico no ha afectado significativamente las composiciones isotópicas originales de los sulfuros y las variaciones de la δ34S de los mismos en cada una de las dos litologías encajantes, podrían explicarse por pequeños cambios en la fO2, temperatura o pH durante la formación de los depósitos. La composición isotópica del plomo de 6 galenas analizadas presenta las relaciones siguientes: 18,02≤ 206Pb/204Pb≤ 18,08; 15,66≤ 207Pb204Pb≤ 15,70 y 38,16 ≤ 208Pb/ 204Pb≤ 38,29, similares a los reportados por Marcoux (1987) en los depósitos de Pierrefitte (Pirineo Central, Francia). A diferencia de los datos de isótopos de azufre, estos valores son muy homogéneos y apuntan hacia un reservorio de plomo situado en la corteza superior. Las edades calculadas a partir del modelo de evolución del plomo de Cumming y Richards (1975), varían entre 422 y 452 m.a. (Ordovícico superior), edad de los materiales encajantes. Este dato confirma la hipótesis del origen sedimentario-exhalativo de las mineralizaciones.The sulfur isotopic composition of sulfides from sedex-type deposits enclosed within Upper Ordovician rocks in the valle de Arán (Central Pyrenees) ranges from +3.5 to +15.1 %0 in mineralizations enclosed in carbonates and from -2.7 %0 to +5.5 in mineralizations enclosed in detritic rocks. These values suggest two different sources of sulfur: a heavy source of crustal origin, probably related to the reduction of seawater sulfate, and a lighter one, resulting from leaching of underlying detritic and/or volcanic rocks of cambro-ordovician age. Hercynian metamorphism has not significantly altered the original sulfur isotopic composition of sulfides and their variation at the deposit scale can be explained by changes in T, pH or f02 during sulfide deposition. Lead isotope composition of 6 galena samples have the following ratios: 18.02::; 206Pbp04Pb ::; 18.08; 15.66 ::; 207PbP04Pb::; 15.70 and 38.16 s 208PbP04Pb ::; 38.29, similar to those reported by Marcoux (1987) in the Pierrefitte deposits (Central Pyrenees, France). These values are very homogeneous and suggest alead source situated within the upper crust. Calculated ages based on Cumming and Richards (1975) lead evolution model range from 422 to 452 m.a. (Upper Ordovician), which is the age of the enclosing rocks. These data confirm the hypothesis of a sedimentary-exhalative origin of the deposits

Late and post-Hercynian low temperature veins in the Catalonian Coastal Ranges

Many of the veins enclosed within the Paleozoic basement of the Catalonian Coastal Ranges show several common characteristics: low temperature of formation (between 75 and 200°C), the presence of complex polisaline fluids and a certain relationship to the pretriassic paleosurface. Mineralogical composition and age are variable, ranging from Pb-Zn veins with carbonate gangue of late Hercynian age through metal poor fluorite rich veins to barite rich veins of Triasssic age. Mineralizing fluids are not related to late Hercynianmagmatism and deposition took place in active fractures developed either in extensional as in compressive regimes.La mayoria de mineralizaciones filonianas encajadas en el zócalo Paleozoica de la Cadenas Costeras Catalanas, presentan una serie de características comunes: baja temperatura de formación (entre 75 a 200°C); presencia de fluídos polisalinos complejos y una cierta relación con la paleosuperficie pretriásica. La composición mineralógica y la edad son variables, comprendiendo desde filones de edad tardiHercínica con Pb-Zn y ganga carbonatada, filones de fluorita, pobres en metales, hasta filones con baritina dominante de edad Triásica. Los fluidos mineralizantes no tienen relación con el magmatismo tardi-Hercinico, y la deposición tuvo lugar en fracturas activas, tanto en regímenes compresivos como distensivos

Zn-Pb Mineralization Associated with Salt Diapirs in the Basque-Cantabrian Basin, Northern Spain: Geology, Geochemistry, and Genetic Model

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 δ34S 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 H2S production. Textural relationships suggest that ore precipitation was related to dolomitization of host rocks (siliciclastic rocks, marine carbonates, and caprock). The δ13C and d18O 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 δ13C/δ18O assemblages and 87Sr/86Sr ratios (0.70801-0.71202) resulting from the interaction of a basinal brine with the different host rocks. Galena Pb isotope ratios¿206Pb/204Pb from 18.643 to 18.696, 207Pb/204Pb from 15.650 to 15.676, and 208Pb/204Pb 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

The Roses giant quartz vein (Cap de Creus, Eastern Pyrenees): Geology and fluid inclusion data.

The Pyrenean Axial Zone is characterized by thick series of metasedimentary and orthogneissic materials derived from pre-Variscan rocks. These sequences were intruded by large bodies of Variscan granitoids, some exposed after the Alpine orogeny. In the Eastern Pyrenees, a number of quartz veins of kilometric length and metric to decametric width, are present. Although these veins are mostly hosted by Variscan and pre-Variscan rocks, in the utheastern limit of the Roc de Frausa Massif, large fault related quartz bodies rossc utting Mesozoic sedimentary rocks, have also been recognized Liesa, 1988). The Roses giant quartz vein constitutes a remarkable example of the seregional scale quartz veins. It is located at the south ernportion of the Cap de Creus Massif, extending for 2700 mand reaching widths up to 25m. Apparently, the vein continues towards the NW depicting a much longer structure

Contribución al conocimiento de la geología del depósito de Au-Cu de La Pava (Península de Azuero, Panamá)

The «La Pava» Au-Cu deposit is hosted by a vulcanosedimentary sequence, named Ocú Formation,developed in an island arc environment that resulted from the subduction of the Nazca Plate beneath the Caribbean Plate during the Cretaceous times. The deposit consists of disseminations and stockworks of pyrite and chalcopyrite accompanied by barite, quartz and carbonates. Three hydrothermal alteration zones have been recognized: silicic, argillic and propilityc, typical of gold-related high sulfidation systems. A supergenic alteration overprints the hydrothermal alterations developing a cap rich in silica and Feoxides. The detailed study of the Ocú Fm. indicates that the sulfides and the accompanying gold was formed in a submarine environment. Therefore we suggest that «La Pava» represents an Au-Cu hybrid deposit between high sulphidation epithermal and VMS types, which are found in volcanogenic massive sulphide environments

Interpretando la Mina Rica (Pulpí, Almeria): estructura, mineralogía y geoquímica.

En este trabajo se presenta la estructura, mineralogía y geoquímica de la Mina Rica, un excelente ejemplo de la metalogenia del SE peninsular. Para ello se ha realizado la cartografía geológica detallada de las galerías, el estudio etrográfico de las zonas mineralizadas y no mineralizadas y el análisis isotópico de los sulfatos y sufuros

Tourmaline records the hydrothermal events related to Zn-Pb mineralization around the Murguía diapir (Basque Cantabrian Basin, N Spain)

The chemical composition of tourmaline has been used as a host environment register as well as a potential exploration tool for mineral deposits. In this study, the textural and chemical composition of tourmalines associated with Zn-Pb mineralizations around the Murguía diapir (Basque Cantabrian Basin, N Spain) are examined to verify if they record the mineralizing events in the area. Petrographically, tourmalines have been differentiated between inherited and authigenic. Colorless authigenic tourmalines are present as halos partially around green and pleochroic detrital grains or as individual crystals. Inherited and authigenic tourmalines are also chemically distinct. Authigenic tourmalines show different X-site occupancies, a Mg/(Mg+Fe) ratio above 0.77, and are aluminum rich and plot to the right of the povondraite-oxidravite join, above the schorl-dravite join. Inherited tourmalines plot within the alkaline (Na+K) group field, and have a Mg/(Mg+Fe) ratio below 0.77. These data suggest that authigenic tourmalines grew under reducing conditions, compatible with the hydrothermal event responsible for the ore deposition and caprock formation during the diapir ascent

The origin of large gypsum crystals in the Geode of Pulpí (Almería, Spain)

The Geode of Pulpí (Almería, Spain) is an ∼11 m3 ovoid cavity, the walls of which are covered with meter-sized idiomorphic and highly transparent gypsum (CaSO4●2H2O) crystals. We performed a thorough study based on field work, and petrographic and geochemical data collection, which aimed to reconstruct the geological history leading to the formation of this geode. The geode is hosted in mineralized Triassic carbonate rocks with a discontinuous mineral sequence from iron-carbonates and barite to celestine and finally gypsum (microcrystalline and selenite). Data from fluid inclusions show that barite precipitated above 100 °C, celestine at ∼70 °C, and gypsum below 25 °C. All δ34S sulfate phases fall between Triassic and Tertiary evaporite values. Barite and gypsum, either microcrystalline or large selenite crystals, show variable δ34S and δ18O compositions, whereas celestine and centimetric selenite gypsum have homogeneous values. We propose that the growth of the large selenite crystals in the Geode of Pulpí was the result of a self-feeding mechanism consisting of isovolumetric anhydrite replacement by gypsum at a temperature of 20 ± 5 °C, episodically contributed by a ripening process enhanced by temperature oscillations due to climatic change