Hydrothermal Fluids

The~1.5 Moz Yaouré gold deposit, which is located within the Birimian greenstone belts of central Côte d'Ivoire (West Africa), is associated with two stages of economic gold mineralization. Both ore-forming stages occurred during protracted E-W-directed shortening associated with the Eburnean orogeny. The first mineralization stage is hosted by fault-fill veins along conjugate ENE-striking (dextral) and WNW-striking (sinistral) strike-slip fault arrays. This ore stage is associated with a polymetallic assemblage including Mo, Bi, Pb, W, Te, Ag, and Au and cryptic alteration in wall rocks. The second and main gold mineralization stage is associated with a low-displacement fault-fracture-vein mesh formed during a reverse faulting episode. This second gold phase is associated with a polymetallic assemblage including W and Au ± Pb and is characterized by pronounced albite-ankerite-pyrite hydrothermal alteration in wall rocks. Shear veins associated with this second mineralization episode formed during episodic fluid pressure variations under low differential stress within pre-existing low-angle reverse fault planes. Permeability destruction by albite-ankerite-pyrite hydrothermal sealing of these low-angle reverse faults resulted in fluid pressure build-up and ultimately in the development of extension veins under low differential stress in the late stages of the structural evolution of the deposit. This study presents the structural evolution of a polyphase orogenic gold deposit and highlights that the interplay between fault zone activity, hydrothermal alteration, and fluid pressure fluctuations at low differential and deviatoric stresses were key in controlling fluid flow and the formation of ore within optimally-oriented faults.

Malaysian oil palm industry produces a significant amount of oil palm residue as solid wastes. These solid wastes are comprised of oil palm residue which contains the stem, fronds from the farms, empty fruit bunch (EFB), mesocarp fibre (MF), and palm kernel shell (PKS) from the oil palm–processing factories. These residues are not successfully reused for other purposes, and the current dumping methods can possibly trigger unfavourable effects to the environment. As oil palm residues are a readily available waste biomass, it has a high potential to be converted into valuable energy-derived products. Hydrothermal carbonization (HTC), which is a thermochemical process, is a method used to treat biomass to produce hydrochar under hot-compressed water. Oil palm residues (palm leaves, palm fronds, and palm shell) were used as the feedstock for producing carbonaceous hydrochar. The key objective of this study is to examine the effect of the reaction temperature, residence time, and acid catalysts on the HTC process. HTC of oil palm residues was optimized at different operating temperatures from 140 to 300 °C and different reaction times between 30 and 240 minutes with a biomass-to-water ratio of 1:10 wt%. Acid catalysts such as citric acid and ascorbic acid were used for the HTC process. The hydrochar produced is further characterized using heating value and elemental and Fourier transform infrared (FTIR) analysis. The yield of hydrochar reduces with the rise of temperature and time but it increases in the presence of acid catalysts. The carbon content of hydrochar is observed to be between 44.36 and 49.50%. The FTIR analysis showed that a high intensity at 1423 cm−1 indicates a high content of lignin and cellulose in the hydrochar. A considerable decrease in the H/C and O/C atomic ratio shows that the dehydration and decarboxylation take place during the HTC process.

Penelitian mengenai Area Geothermal Kamojang telah banyak dilakukan, namun dari sekian penelitian
tersebut hanya berfokus pada metode gravity. Pada penelitian ini metode yang digunakan untuk monitoring
Area Geothermal Kamojang adalah metode MEQ (Micro-Earthquake) dengan tujuan memperoleh sebaran
hiposenter menggunakan metode penentuan hiposenter SED (Single Event Determination). Gempa mikro
pada suatu area geothermal disebabkan oleh adanya zona lemah yang terbuka akibat injeksi air, zona
tersebut akan semakin terbuka seiring pertambahan volume, laju, dan tekanan air reinjeksi, adanya kontak
antara air dingin dengan batuan reservoir yang panas maupun heat-source, serta berkurangnya pori batuan
akibat hilangnya fluida pengisi peori tersebut sebagai dampak aktivitas produksi. Karakteristik gempa mikro
yaitu memiliki magnitudo 􀂔 3 SR (Skala Richter) serta durasi gempanya yang tidak akan lebih dari satu menit.
Metode penentuan hiposenter gempa yang dikembangkan oleh Geiger (1910) yaitu metode SED merupakan
sebuah proses iterasi dengan optimasi Gauss-Newton untuk menentukan lokasi sumber gempa bumi.
Metode tersebut merupakan pemodelan ke depan dengan tujuan meminimalkan nilai travel time residual
antara arrival time yang teramati dengan arrival time yang diprediksi atau hasil pemodelan. Dari pengolahan
data rekaman gempa selama bulan April – Mei 2014, diperoleh 56 events/kejadian gempa mikro dengan
rincian terdapat 39 events yang memiliki magnitudo gempa 0,1 SR, 14 events dengan magnitudo 0,2 SR, 2
events 0,3 SR, serta 1 events magnitudo 0,4 SR. Mayoritas hiposenter gempa yang diperoleh dari
pengolahan data ternyata berada di luar Area Geothermal Kamojang.

Eleven Quaternary fissure ridge travertines from Mammoth Hot Springs (Wyoming) and seventeen ones from Bridgeport (California) were mapped and studied with a morphotectonic approach to understand possible relationships between travertines and active versus passive tectonics. Results are compared with other known geothermal fissure ridges on the Earth. The studied fissure ridges are all located in the hangingwall of normal faults, but the fissure ridges appear as non-dislocated by faults, rather by axial fissures. Both in the two principal study areas and elsewhere, azimuthal analyses of faults and fissure ridges show that the distribution of fissure ridge long axis is rather dispersed around the strike of the local normal faults. No correlation occurs between the fissure ridge length and the angle between the strike of the normal fault and the strike of fissure ridges. The studied fissure ridges are 2 to 360 m long (mean length: 72.1 m), 1 to 15 m wide (mean width: 6.7 m), and 0.5 to 8 m high (mean height: 3.9 m). Fissure ridge aspect ratios show a moderate correlation between the length and both the width and the height of fissure ridges, whereas the correlation between width and height is less marked. The growth in height and width of ridges appears as much more inhibited than in length. A model is proposed in which fissure ridge travertines grow with enhanced elongation along one sub-horizontal direction, which seems moderately controlled by the associated normal fault and the regional extension. Other factors, such as the inherited fracture network and the geothermal and artesian pressure of fluids (fluid discharge) may be important in the development of the studied fissure ridges. Results from this study may contribute to the knowledge of factors that control the long-term geothermal circulation and also the long-term hermetic durability of CO2 subsurface repositories.

This study focused on the geochemical and isotopic features of thermal fluids discharged from five zones located in the high altitude Puna plateau (Jujuy Province between S 22°20′-23°20′ and W 66°-67°), i.e. Granada, Vilama, Pairique, Coranzulí and Olaroz. Partially mature waters with a Na +-Cl − composition were recognized in all the investigated zones, suggesting that a deep hydrothermal reservoir hosted within the Paleozoic crystalline basement represents the main hydrothermal fluid source. The hydrothermal reservoirs are mainly recharged by meteoric water, although based on the δ 18 O-H 2 O and δD-H 2 O values, some contribution of andesitic water cannot be completely ruled out. Regional S-oriented faulting systems, which generated a horst and graben tectonics, and NE-, NW-and WE-oriented transverse structures, likely act as preferentially uprising pathways for the deep-originated fluids, as also supported by the Rc/Ra values (up to 1.39) indicating the occurrence of significant amounts of mantle He (up to 16%). Carbon dioxide, the most abundant compound in the gas phase associated with the thermal waters, mostly originated from a crustal source, although the occurrence of CO 2 from a mantle source, contaminated by organic-rich material due to the subduction process, is also possible. Relatively small and cold Na +-HCO 3 −-type aquifers were produced by the interaction between meteoric water and Cretaceous, Palaeogene to Miocene sediments. Dissolution of evaporitic surficial deposits strongly affected the chemistry of the thermal springs in the peripheral zones of the study area. Geothermometry in the Na-K-Ca-Mg system suggested equilibrium temperatures up to 200°C for the deep aquifer, whereas lower temperatures (from 105 to 155°C) were inferred by applying the H 2 geothermometer, likely due to re-equilibrium processes during the thermal fluid uprising within relatively shallow Na-HCO 3 aquifers. The great depth of the geothermal resource (possibly N 5000 m b.g.l.) is likely preventing further studies aimed to evaluate possible exploitation, although the occurrence of Liand Ba-rich deposits associated may attract financial investments, giving a pulse for the development of this remote region.

This study utilizes the trace and rare earth element geochemistry of bulk ores and in situ LA-ICP-MS analyses of mineral grains to clarify the controversy in the origin of the Bahariya sedimentary iron ores, Egypt. Different types of iron ores were identified in the Bahariya Oasis including high grade, high-Mn, high-Ba, oolitic, and ochreous iron ores. Hematite and goethite are the main constituents of the studied ores with some manganese oxide and hydroxide minerals (pyrolusite, bixbyite, cryptomelane, aurorite, romanechite, manjiroite, and pyrochroite). Barite is common in the high-Ba ore, while some quartz, calcite, and halite are detected in the oolitic iron ore. High-Mn iron ores are characterized by higher contents of SiO 2 , Al 2 O 3 , MgO, CaO, Na 2 O, and K 2 O, while high-Ba iron ore has higher TiO 2 contents. Analyses of bulk ores and in situ mineral grains are characterized by substantially high contents of Ba (average of 9497 ppm); also Zn and Sr occur in considerably high concentrations (averages of 4263 and 429 ppm, respectively). Mn-rich ores and Mn-bearing minerals show relative enrichments of trace metals compared to the Mn-poor ores probably due to the ability of Mn-bearing minerals to fix such trace metals by adsorption, absorption, and/or replacement. The ΣREE ranges between 2.6 and 80 ppm with an average of 23 ppm. High-Mn ores show higher ΣREE (average of 61 ppm) compared with the low Mn ore (average of 13 ppm). The oolitic iron ore shows very low ΣREE content (7 ppm). Red and yellow ochers from El Gedida mine have similar ΣREE values (38 and 39 ppm, respectively), while red ocher from the Ghorabi area has relatively higher ΣREE (57 ppm). Chondrite-normalized REE patterns of all types of iron ores, whether in the form of bulk ores or Fe-and Mn-bearing grains, have LREE enrichment relative to HREE as shown by (La/Yb) N ratios that vary from 1.7 to 29.4. Majority of the bulk samples and mineral grains have negative Eu anomalies with Eu N /Eu* ranges from 0.68 to 0.8. However, bulk samples of one high grade and high-Ba ores as well as some of the Mn-bearing grains from El Gedida ores show positive Eu anomalies with Eu/Eu* ranges from 1.1 to 17.7. With few exceptions , all bulk ores and mineral grains show negative Ce anomalies with Ce/Ce* range from 0.28 to 0.96. A seawater precipitation (hydrogenous to hydrothermal exhalite) is proposed for the Bahariya iron ores. The hy-drogenous origin is suggested based on the occurrence of high-Mn iron ores in the base of the iron ore succession, oolitic texture of some of these ores, Si–Al plot, low La/Ce ratios, high Y/Ho ratios, and LREE-enriched patterns with negative Eu anomalies of most of the bulk ores and mineral grains. The hydrothermal contribution to the source of these iron ores can be evident from the high contents of some trace elements such as Ba, Zn, and Mo, and plots the analyzed samples in the hydrothermal fields of the Fe–M–(Ni + Co + Cu) * 10 ternary diagram, (Co + Ni)–(As + Cu + Mo + Pb + V + Zn) and (Co + Ni + Cu–Co/Zn) binary plot, low ΣREE concentrations and positive Eu anomalies and high La/Ce ratios in some of the analyzed samples. The hydrothermal contribution looks for local effect and is restricted to El Gedida area.

In the Bardo Syncline (Holy Cross Mountains, Poland), two beds of tuffite (named the Niewachlów tuffites) have been discovered within greywackes of Ludlow (Silurian) age. K-Ar dating of the lower bed yielded an age of 292.8 ±4.0 Ma, while the upper bed provided an age of 341.9 ±4.3 Ma. The dates pertain to metamorphic alteration of the tuffite, related to reactivation of the Daleszyce Fault Zone. In this zone, biotite crystals present in the foliation zones were recrystallized and their K-Ar isotopic system was rejuvenated in a temperature range of ~270-300°C. The dates that were obtained define the ages of two tectono-metamorphic episodes and reflect the timing of displacements along the fault which, in turn, reflect two deformation phases during the Variscan Orogeny (Mississippian and Early Permian). More over the dates may be correlated with Late Variscan magmatic activity in the Holy Cross Mountains and adjacent areas. The deformation of the Daleszyce Fault Zone may be regarded as resulting from displacements of lithospheric blocks within the Trans European Suture Zone during the Late Variscan reconstruction of the Baltica palaeocontinent margin.

Ampelia area is a newly discovered area with geothermal interest and no surface manifestations (hidden resource). It is located in Farsala basin and belongs to the Enipeas graben. The geothermal anomaly is related with the E-W trending faults, which mainly control the basin development and the NNW-SSE trending faults of the area. The temperature values from the deep water boreholes (>200m depth) range from 20 to 41 o C. The chemical composition of the studied groundwater samples varies in all chemical parameters. Most of the samples have affected by shallow cold aquifers (high E.C. and NO3-values). The most representative samples (T > 30 o C) are from the deepest boreholes (hydrochemical type Na-HCO3), which cut the fractured crystalline basement, i.e. limestones, flysch and ophiolitic rocks. They present the highest pH values (pH > 8) and the lowest E.C. compared with the rest of the samples. Their Ni and Cr concentrations are very low, indicating that the groundwater is not in contact with the ultramafic rocks from the ophiolite sequence. According to silica chemical geothermometers for the most representative samples, the expected temperature values of a potential geothermal reservoir range from ~ 60 to 100 o C. Περίληψη Η περιοχή της Αμπελίας είναι μια νέο-ανακαλυφθείσα περιοχή, η οποία παρουσιάζει γεωθερμικό ενδιαφέρον, χωρίς να παρουσιάσει επιφανειακές γεωθερμικές εκδηλώσεις. Εντοπίζεται στη λεκάνη των Φαρσάλων και ανήκει στο τεκτονικό βύθισμα του Ενιπέα. Η γεωθερμική ανωμαλία συνδέεται με τα ρήματα διεύθυνσης Α-Δ, που ελέγχουν την δημιουργία της κοιλάδας και τα διασταυρούμενα σε αυτά ρήγματα διεύθυνσης ΒΒΔ-ΝΝΑ. Οι θερμοκρασίες από τις βαθιές γεωτρήσεις (> 200 μ) κυμαίνονται από 20 έως 41 o C. Η χημική σύσταση των δειγμάτων παρουσιάζει έντονες διαφοροποιήσεις. Τα περισσότερα δείγματα έχουν επηρεαστεί από κρύους επιφανειακούς υδροφόρους (υψηλές τιμές E.C. και NO3-). Τα πιο αντιπροσωπευτικά δείγματα με T > 30 o C προέρχονται από βαθιές γεωτρήσεις που αναπτύσσονται και μέσα στο τεκτονισμένο κρυσταλλικό υπόβαθρο (ασβεστόλιθοι, φλύσχης, οφιολιθικά πετρώματα). Τα δείγματα αυτά παρουσιάζουν τις υψηλότερες τιμές pH (pH > 8) και τις χαμηλότερες τιμές E.C. Επίσης, παρουσιάζουν πολύ χαμηλές συγκεντρώσεις Ni και Cr, ενδεικτικό ότι δεν είναι σε επαφή με τα υπερβασικά πετρώματα των οφιολιθικών σχηματισμών. Βασιζόμενοι σε πυριτικά χημικά γεωθερμόμετρα και εστιάζοντας κυρίως στις τιμές των πιο αντιπροσωπευτικών δειγμάτων εκτιμάται ότι η θερμοκρασία ενός πιθανού γεωθερμικού ταμιευτήρα στην περιοχή πρέπει να κυμαίνεται από ~ 60 έως 100 o C. Λέξεις κλειδιά: γεωθερμική ενέργεια, γεωχημεία θερμών υπόγειων νερών, συγκεντρώ-σεις ιχνοστοιχείων και ιόντων, Ανατολική Θεσσαλία, Ελλάδα.

Fissure ridge travertines grown from geothermal springs of Denizli Basin, southwestern Turkey, are investigated through stratigraphic, structural, geochemical, and geochronological methods, with the aim of understanding the growth of these elongate mound-shaped structures. Two main types of travertine deposits are recognized: (1) bedded travertines, which grew as flowstone on sloping surfaces and form the bulk of fissure ridges, and (2) banded travertines, which grew as veins within the bedded travertine chiefly along its central feeding conduit. Stratigraphic and structural observations shed light on the bedded-banded travertine relationships, where the banded features grew through successive accretion phases, crosscutting the bedded travertine or forming sill-like structures. The bedded and banded travertines alternated their growth, as demonstrated by complicated crosscutting relationships and by the upward suture, in places, of banded travertine by bedded travertine that was, in turn, crosscut by younger banded travertine. The bedded travertine is often tilted away from the central axis of the fissure ridge, thus leaving more room for the central banded travertine to form. U-series ages confirm the bedded-banded travertine temporal relationships and show that the growth of the studied fissure ridges lasted up to several tens of thousands of years during Quaternary time. The banded travertine was deposited mainly during cold events, possibly in coincidence with seismic events that might have triggered the outflow of deep geothermal fluids. C and O stable isotope and rare earth element data indicate a shallow feeding circuit for the studied structures with a fluid component deriving from a deeper geothermal circuit. A crack-and-seal mechanism of fissure ridge growth is proposed, modulated by the interplay of local and regional influencing factors and mechanisms such as geothermal fluid discharge, paleoclimate, tectonics, and the progressive tilting of bedded travertine limbs over a soft substratum creating the necessary space for the central veins to grow.

An integrated geochemical and microbiological investigation of soils from the Solfatara Crater (Campi Flegrei, southern Italy) demonstrated that interstitial soil gases dominated by CO2 and other typical hydrothermal gaseous species (e.g. H2S, CH4, ethane, benzene, alkenes and S-bearing organic compounds) influenced the composition of microbial communities. The relatively high concentrations of hydrothermal fluids permeating the soil produced acidic conditions and whitish deposits that characterize the Solfatara Crater floor. Archaea and Bacteria showed almost equal cell abundance (up to 3.2 x 107 and 4.2 x 107 cell/g, respectively) with relatively low levels of biodiversity and equitability in sites characterized by elevated temperatures (up to 70°C), very low pH values (up to 2.2) and reducing conditions. In these sites, high-throughput sequencing showed the marked selection of microorganisms, mainly affiliated with the genera Thermoplasma, Ferroplasma and Acidithiobacillus. A rel...

An exact solution of three-dimensional theory of elasticity in an infinite elastic rock medium around magma reservoirs of various aspect ratios and the criteria of rock fracturing provide an important tool for the interpretation of the origin and nature of distribution of many ore-bearing fracture systems around magmatic bodies in the world. Theoretical analyses suggest the conditions and regions of formation of (1) dominant radial fractures, (2) dominant concentric fractures or combination of radial and concentric fractures, and (3) central subsidence (or graben) in domal uplift related to intrusions of magma bodies of various shapes and sizes. The relations of these fracture systems to the deposition of ore-bearing fluids are discussed in the light of excess magma and hydrothermal fluid pressures. Caldera subsidence and dominant concentric fractures, such as in the San Juan Mountains mining district in Colorado, are, according to our analyses and interpretations, related to intrusion(s) of vertically elongated magma cupolas and high magma and hydrothermal fluid pressures. This differs from Anderson's original contention (1936) that caldera subsidence and outward-dipping ring fractures are due to lower relative magma pressure than lithostatic pressure. Wedging action of magma immediately above a vertically elongated prolate magma body is suggested as a cause of central graben bounded by funnel-shaped normal faults over wide domal uplift. Displacement along normal faults causes underground subsidence above magma cupolas. Extension of such faults close to the surface and displacement along them can produce surface caldera subsidence. Vein-type deposits commonly associated with funnel-shaped felsic (rhyolitic) bodies may be related to near-surface caldera subsidence. The origin of arcuate zones of breccia pipes such as in Silverton cauldron, Colorado, appears to be related to axial symmetric stress condition(s) due to vertically elongated magma body at depth. Estimation of stress distribution around spheroidal and prolate magma bodies suggests development of possible zonal distribution of fractures from the periphery of the magma outward in the order of (1) continuous tension fracture zone, (2) brittle fault zone, (3) ductile fault zone followed by no fault zone. Brittle fault and continuous tension fracture zones provide excellent sites for ore mineral localization. The zonal distribution of fractures also suggests. in a general way, mode of origin and possible extent of distribution of various fracture types, hydrothermal zoning, and their alterations.

In the Maritime Alps (north-west Italy – south-east France), the Middle Triassic–lowermost Cretaceous platform carbonates of the Provençal Domain locally show an intense dolomitization. Dolomitized bodies, irregularly shaped and variable in size from some metres to hundreds of metres, are associated with tabular bodies of dolomite-cemented breccias, cutting the bedding at a high angle, and networks of dolomite veins. Field and petrographic observations indicate that dolomitization was a polyphase process, in which episodes of hydrofracturing and host-rock dissolution, related to episodic expulsion of overpressured fluids through faults and fracture systems, were associated with phases of host-rock dolomitization and void cementation. Fluid inclusion analysis indicates that dolomitizing fluids were relatively hot (170 to 260°C). The case study represents an outstanding example of a fossil hydrothermal system, which significantly contributes to the knowledge of such dolomitization sys...

In the summer 2013, mercury concentrations in soils and air from Nisyros (Greece), an active volcanic island located in the Aegean Sea, were determined. Up to 102 samples of soil were collected in the Lakki plain caldera and analyzed for mercury by using a cold vapour atomic absorption analyzer, following 7473 US EPA method. Concentrations of mercury in air were also investigated in the same sites with a portable spectrophotometer (Lumex RA-915M). Soil mercury concentrations were in the range from 0.023 to 13.7 µg/g. The mercury concentrations in air showed high background values in the Lakki plain caldera, ranging from 21 to 36 ng/m3 and maximum values up to 493 ng/m3 in the proximity of the fumarolic areas, in contrast with the relatively low values (from 2 to 5 ng/m3 ) measured in the distal sites outside of the caldera. The positive correlation between mercury and CO2 and H2S in the atmosphere highlights the important role of fumarolic gases as carrier for gaseous mercury (Hg0 )...

In the Maritime Alps (NW Italy-SE France), the Middle Triassic-lowermost Cretaceous platform carbonates of the Provençal Domain locally show an intense dolomitization. Dolomitized bodies, irregularly shaped and variable in size from some metres to hundreds of metres, are associated with tabular bodies of dolomite-cemented breccias, cutting the bedding at a high angle, and networks of dolomite veins. Field and petrographic observations indicate that dolomitization was a polyphase process, in which episodes of hydrofracturing and host-rock dissolution, related to episodic expulsion of overpressured fluids through faults and fracture systems, were associated with phases of host-rock dolomitization and void cementation. Fluid inclusion analysis indicates that dolomitizing fluids were relatively hot (170-260 °C). The case study represents an outstanding example of a fossil hydrothermal system, which significantly contributes to the knowledge of such dolomitization systems in continental margin settings. The unusually favourable stratigraphic framework allows precise constraint of the timing of dolomitization (earliest Cretaceous), and, consequently, direct evaluation of the burial setting of dolomitization, which, for the upper part of the dolomitized succession, was very shallow or even close to the surface. The described large-scale hydrothermal system was probably related to deep-rooted

Shallow marine carbonate sedimentation dominated during the Albian in the western part of the Basque Cantabrian Basin in Northern Spain, forming the large Ramales Platform. This platform originated on a less subsiding tectonic block facing deeper and more subsiding areas to the south and east, which were created by tectonic activity in the Basin. Fracture-related hydrothermal dolomites hosted in these Albian carbonates are well exposed in the Asó n valley area. Mapping in the studied area revealed several dolomite bodies related to main faults that cut the stratification almost at right angles. The bodies show a vertical development along fault-strike up to 900 m thick from which kilometre-scale branches expand following the stratification. Dolomitization is pervasive and independent of the limestone facies. Main dolomite facies are fine replacive, sucrosic and saddle. Petrography, C, O and Sr isotopes and fluid-inclusion analysis support a polyphase hydrothermal dolomitization at fluid temperatures between 75 C and 240 C and highly variable salinity of up to 22 wt.% NaCl. Fine dolomite replaced limestone first and then, sucrosic and saddle dolomites replaced part of the first dolomite and cemented newly created fracture porosity together with different calcite cements. Zebra dolomites and hydroclastic breccias are products of this later stage. Burial analysis of the host rock supports maximum burial temperatures of 80 C and intense tectonic activity from the Albian to Turonian with a latest Albian peak subsidence. Albian stretching of the crust and subsequent ascent of the isotherms in the area is suggested to have produced sufficient heat to the dolomitizing fluids. The structural analysis indicates a strong transtensional tectonic activity in the studied area during Albian to Turonian time with the creation of an overstep between WE trending and N-S trending faults. Fluids moved from subsiding areas to fractured uplifted parts of the Ramales Platform, enhanced by diapiric activity.