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Hydrothermal dolomite (HTD) bodies are known as high-quality hydrocarbon reservoirs; however few studies focus on the geometry and distribution of reservoir characteristics. Across the platform-to-basin transition of the Ramales Platform, fault-controlled HTD bodies are present. Three kinds of bodies can be distinguished based on their morphology, that is, elongated HTD corridors, a massive HTD body (Pozalagua body) and an HTD-cemented breccia body. The differences in size and shape of the HTD bodies can be attributed to differences in local structural setting. For the Pozalagua body, an additional sedimentological control is invoked to explain the difference in HTD geometry. A (geo)-statistical investigation of the reservoir characteristics in the Pozalagua body revealed that the HTD types (defined based on their texture) show spatial clustering controlled by the orientation of faults, joints and the platform edge. Porosity and permeability values are distributed in clusters of high and low values; however, they are not significantly different for the three HTD types. Two dolomitization phases (i.e. ferroan and non-ferroan) can be observed in all HTD bodies. In general, the HTDs resulting from the second non-ferroan dolomitization phase have lower porosity values. No difference in permeability is found for the ferroan and non-ferroan dolomites. © The Geological Society of London 2012.

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A NNW-oriented thrust is exposed in the western part of the Dikulushi mine, marked by ductile deformed shale that was transported upward and is in faulted contact with an overlying dolomite-sandstone sequence. The brecciated layers in the west and non-brecciated sandstone layers in the central part of the mine are crosscut by several E-W and NE-oriented faults. The complex set of faults produced a damage zone that was a favorable site for the migration of mineralising fluids. The faults and brecciated layers contain Cu-Pb-Zn-Fe mineralisation consisting of chalcopyrite, bornite and chalcocite, with minor pyrite, arsenopyrite, sphalerite, and galena, with dolomite, calcite, and quartz as gangue minerals. The fault zones were sites of remobilisation and enrichment of the previously deposited Cu-Pb-Zn-Fe mineralisation. The remobilised sulphides consist of Ag-rich chalcocite, with barite, calcite and quartz as gangue minerals. The deposit is structurally controlled by a crosscutting set of E-W and NE-oriented faults. Similar structural settings in the mine and in the Dikulushi region represent important future exploration targets., A NNW-oriented thrust is exposed in the western part of the Dikulushi mine, marked by ductile deformed shale that was transported upward and is in faulted contact with an overlying dolomite-sandstone sequence. The brecciated layers in the west and non-brecciated sandstone layers in the central part of the mine are crosscut by several E-W and NE-oriented faults. The complex set of faults produced a damage zone that was a favorable site for the migration of mineralising fluids. The faults and brecciated layers contain Cu-Pb-Zn-Fe mineralisation consisting of chalcopyrite, bornite and chalcocite, with minor pyrite, arsenopyrite, sphalerite, and galena, with dolomite, calcite, and quartz as gangue minerals. The fault zones were sites of remobilisation and enrichment of the previously deposited Cu-Pb-Zn-Fe mineralisation. The remobilised sulphides consist of Ag-rich chalcocite, with barite, calcite and quartz as gangue minerals. The deposit is structurally controlled by a crosscutting set of E-W and NE-oriented faults. Similar structural settings in the mine and in the Dikulushi region represent important future exploration targets.

Gold-bearing quartz veins along Variscan faults at the southern border of the Stavelot Massif contain sulphides. A petrographic and microthermometric study of these veins indicates that the conditions of the fluids which migrated along the faults changed from a H2O-CO2-NaCl fluid with minimum temperatures and pressures of 300-450 degrees C and 130-500 MPa to a H2O-NaCl fluid with a lower minimum temperature (225-290 degrees C) and possibly pressure range (130-270 MPa). The main sulphide and gold mineralisation probably occurred after peak temperature and pressure conditions., Gold-bearing quartz veins along Variscan faults at the southern border of the Stavelot Massif contain sulphides. A petrographic and microthermometric study of these veins indicates that the conditions of the fluids which migrated along the faults changed from a H2O-CO2-NaCl fluid with minimum temperatures and pressures of 300-450 degrees C and 130-500 MPa to a H2O-NaCl fluid with a lower minimum temperature (225-290 degrees C) and possibly pressure range (130-270 MPa). The main sulphide and gold mineralisation probably occurred after peak temperature and pressure conditions.

Six generations of syntectonic and post-Variscan veins have been identified in Palaeozoic rocks in the southern part of the Moravian Karst, Czech Republic. The significant syntectonic veins precipitated from medium to highly saline fluids at a minimum temperature of 82-136 degrees C. Small amounts of quartz, pyrite and galena are associated with post-Variscan calcite veins. The mineralising fluid had a relatively low temperature (50-88 degrees C) and high salinity. This type of fluid is similar to the fluids from which Mississippi Valley-type Pb-Zn deposits formed in other parts of the Rhenohercynian zone., Six generations of syntectonic and post-Variscan veins have been identified in Palaeozoic rocks in the southern part of the Moravian Karst, Czech Republic. The significant syntectonic veins precipitated from medium to highly saline fluids at a minimum temperature of 82-136 degrees C. Small amounts of quartz, pyrite and galena are associated with post-Variscan calcite veins. The mineralising fluid had a relatively low temperature (50-88 degrees C) and high salinity. This type of fluid is similar to the fluids from which Mississippi Valley-type Pb-Zn deposits formed in other parts of the Rhenohercynian zone.

The Portovelo epithermal vein-system in southwestern Ecuador has produced more than 120 tons of gold and about 250 tons of silver. The veins result from hydrothermal processes close to a Miocene volcano which produced an andesitic to dacitic sequence followed by collapse and post-collapse rhyolitic activity which generated most of the alteration and mineralization. Three main structural segments are defined by NW-trending strike-slip faults, which show later stages of vertical movement. These faults are responsible for development of an extensive N-S dilatational jog within andesitic rocks, which acted as the main host to ore-deposition. A large-scale propylitic aureole surrounds a quartz-chlorite-sericite-adularia core, centered on the rhyolites, within a system of collapse-related ring-structures. A quartz-chlorite-sericite-adularia-calcite assemblage is the most common wall-rock alteration close to the veins. The size (4 x 15 km) and vertical range (1400 m) of the vein-system is exceptional. Alteration, textures and mineral assemblage, including a quartz-calcite gangue, sulfides, abundant sulfosalts and free gold (electrum), are quite typical of an adularia-sericite epithermal deposit. Spatially, the mineralization is arranged in three zones. In addition, three successive stages can be distinguished. The bulk of economic mineralization was deposited during the second stage, in association with a clear quartz and calcite gangue. Tm-ice and Tm-clath data of fluid inclusions in the clear quartz indicate a high salinity (similar to 10.5 eq. wt% NaCl). The homogenization temperatures of fluid inclusions in the gangue minerals and in the altered host-rocks vary between 180 degrees and 310 degrees C. Quartz delta(18) O-values from hydrothermally altered wall-rocks reflect the original isotopic values of the latter. These values show a narrower range in vein quartz (delta O-18 between +7.7 parts per thousand, and +11.5 parts per thousand, SMOW). In addition, the delta O

vol. spécial in memoriam R. Conil, info:eu-repo/semantics/published