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Daniel Moncada - One of the best experts on this subject based on the ideXlab platform.
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mineralogical petrographic and fluid inclusion evidence for the link between Boiling and epithermal ag au mineralization in the la luz area guanajuato mining district mexico
Ore Geology Reviews, 2017Co-Authors: Daniel Moncada, Darcy Baker, Robert J BodnarAbstract:Abstract Theoretical, experimental and observation data provide strong evidence that Boiling is the dominant depositional mechanism in many low to intermediate sulfidation epithermal precious metals deposits. Textural and petrographic features that are evidence for Boiling in the epithermal environment include the presence of coexisting liquid-rich and vapor-rich fluid inclusions, assemblages consisting of only vapor-rich fluid inclusions, colloform quartz, adularia and bladed calcite. We have examined 213 samples collected from surface outcrops, underground workings and drill cores from the central part of the La Luz vein system in the Guanajuato mining district, Mexico. In each sample, the various features that are evidence of Boiling have been recorded. These observations have been quantified using a Boiling Confidence Factor that provides a means of scoring and rating each sample or area relative to the likelihood that Boiling occurred. Homogenization temperatures of liquid-rich fluid inclusions within assemblages of coexisting liquid-rich and vapor-rich fluid inclusions have been measured to estimate the depth of trapping of the inclusions, and these data have been used to estimate the depth to the 300 °C isotherm along the La Luz vein system. Fluid inclusions and mineral textural features show strong evidence of Boiling in the deepest levels sampled in the La Luz system. This observation suggests that the bottom of the Boiling Zone is at some depth beneath the deepest levels explored and opens the potential for additional resources at depth.
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mineral textures and fluid inclusion petrography of the epithermal ag au deposits at guanajuato mexico application to exploration
Journal of Geochemical Exploration, 2012Co-Authors: Daniel Moncada, S Mutchle, Antonio Nieto, T J Reynolds, J D Rimstid, Robe J OdnaAbstract:article Fluid inclusion petrography and vein mineral textures indicative of Boiling have been characterized in 855 samples from epithermal precious metals deposits along the Veta Madre at Guanajuato, Mexico. Mineral tex- tures and fluid inclusions characteristic of fluid immiscibility or Boiling, including colloform quartz, plumose/ feathery/flamboyant quartz, lattice-bladed calcite and lattice-bladed calcite replaced by quartz, as well as coexisting liquid-rich and vapor-rich fluid inclusions and assemblages of vapor-rich only inclusions, have been identified in mineralized samples from the Veta Madre. Most samples studied were assayed for Au, Ag, Cu, Pb, Zn, As and Sb, and were divided into ore grade and sub-economic samples based on the gold and silver concentrations. For silver, samples containing >100 ppm were classified as ore grade, and ore grade gold samples contained >1 ppm Au. The feature that is most closely associated with ore grades of both gold and silver is colloform quartz that was originally precipitated as amorphous silica, and this feature also shows the largest difference in average grade between samples that show colloform texture (178.8 ppm Ag and 1.1 ppm Au) and those that do not exhibit this texture (17.2 ppm Ag and 0.2 ppm Au). Statistical anal- ysis of the data confirmed the petrographic observations that indicated that colloform quartz is the feature that has the greatest predictive power for distinguishing between ore grade and sub-economic samples. For both Ag and Au, there is no significant difference in average grade of samples containing coexisting liquid-rich and vapor-rich fluid inclusions or assemblages of vapor-only inclusions and those that do not, sug- gesting that fluid inclusion evidence for Boiling is not correlative with ore grades. This result is consistent with the fact that most forms of silica that are precipitated during Boiling do not trap useful fluid inclusions. The results of this study suggest that mineral textures and fluid inclusions provide complementary informa- tion that should both be used in exploration for epithermal precious metal deposits. Metal grades and Boiling intensity of samples collected along a traverse perpendicular to the Veta Madre and above known economic mineralization are both low at relatively short distances away from the vein and in- crease as the vein is approached. This suggests that mineralogical and fluid inclusion evidence for Boiling are restricted to the immediate vicinity of, and increase in the direction of, mineralized veins and may be used in exploration to establish vectors towards vein systems that may host precious metal mineralization. Previous studies of epithermal systems show that the Ag and Au mineralization Zone is most often located at or above the bottom of the Boiling Zone. In this regard, the presence of abundant evidence for Boiling that is observed in the deepest levels of the Veta Madre that have been sampled suggests that additional precious metal min- eralization may be present beneath the deepest levels that have been explored.
Christian Marignac - One of the best experts on this subject based on the ideXlab platform.
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Boiling and fluid mixing in the chlorite Zone of the larderello geothermal system
Chemical Geology, 1999Co-Authors: Giovanni Ruggieri, Michel Cathelineau, Christian Marignac, Mariechristine BoironAbstract:Abstract The geochemical features of the geothermal fluids produced within the Boiling Zone in the relatively shallow parts of the Larderello geothermal system (Italy) have been documented as a result of deep drilling which provided samples from 1480 to 2500 m depth. Four wells (Monteverdi 1, Monteverdi 2A, Sasso 22 and Capannoli 2B) have been sampled in the intermediate parts of the Larderello aquifer located in a metamorphic basement underlying the Tertiary nappe complex which constitutes the shallow aquifer at Larderello. Fluid inclusions from recrystallized quartz lenses and quartz veins in samples displaying a predominant quartz–chlorite–(epidote–adularia) paragenesis have been studied by microthermometry and Raman spectroscopy. The inclusions are primary and pseudo-secondary in origin when formed in authigenic quartz, or of secondary origin, when located in fluid inclusion planes related to microfracturing of metamorphic quartz lenses. Several generations of fluids are present and include: H 2 O–(CO 2 )-dominated vapours and liquids, and a series of aqueous liquids, for the most part of relatively low salinity. The T m -ice of both early and late inclusions are mostly between 0.0 and −4.5°C, indicating that the salinities of the hydrothermal fluid were very low to moderate. However, rare fluid inclusions with lower T m -ice (from −4.9 to −25.0°C) were also observed. These inclusions may record the occasional input of saline fluids, which may be derived from the interaction of the hydrothermal waters with the evaporites present in the shallow part of the Larderello field. At Capannoli 2B, earliest H 2 O–(CO 2 ) liquids were trapped under minimal pressures of 610–645 bars, which bracket the estimated present-day lithostatic pressure (640 bars). In all other samples, the main stage of quartz–chlorite crystallization occurs under Boiling conditions attested by the presence of liquid and vapour-rich inclusions, that, in some instances, can be texturally interpreted to be coeval. Their trapping conditions (350–375°C, 160–215 bars) are higher than the present day temperatures at the same depth. Later fluid inclusions attest to a significant cooling of the fluids down to temperatures similar to the present-day temperatures. During this time, pressures were close to hydrostatic conditions. Most fluid inclusions were trapped within the liquid field, this indicating that a significant pressure drop has since affected the main aquifers or fractured Zones which are, at present, under vaporstatic conditions.
Robe J Odna - One of the best experts on this subject based on the ideXlab platform.
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mineral textures and fluid inclusion petrography of the epithermal ag au deposits at guanajuato mexico application to exploration
Journal of Geochemical Exploration, 2012Co-Authors: Daniel Moncada, S Mutchle, Antonio Nieto, T J Reynolds, J D Rimstid, Robe J OdnaAbstract:article Fluid inclusion petrography and vein mineral textures indicative of Boiling have been characterized in 855 samples from epithermal precious metals deposits along the Veta Madre at Guanajuato, Mexico. Mineral tex- tures and fluid inclusions characteristic of fluid immiscibility or Boiling, including colloform quartz, plumose/ feathery/flamboyant quartz, lattice-bladed calcite and lattice-bladed calcite replaced by quartz, as well as coexisting liquid-rich and vapor-rich fluid inclusions and assemblages of vapor-rich only inclusions, have been identified in mineralized samples from the Veta Madre. Most samples studied were assayed for Au, Ag, Cu, Pb, Zn, As and Sb, and were divided into ore grade and sub-economic samples based on the gold and silver concentrations. For silver, samples containing >100 ppm were classified as ore grade, and ore grade gold samples contained >1 ppm Au. The feature that is most closely associated with ore grades of both gold and silver is colloform quartz that was originally precipitated as amorphous silica, and this feature also shows the largest difference in average grade between samples that show colloform texture (178.8 ppm Ag and 1.1 ppm Au) and those that do not exhibit this texture (17.2 ppm Ag and 0.2 ppm Au). Statistical anal- ysis of the data confirmed the petrographic observations that indicated that colloform quartz is the feature that has the greatest predictive power for distinguishing between ore grade and sub-economic samples. For both Ag and Au, there is no significant difference in average grade of samples containing coexisting liquid-rich and vapor-rich fluid inclusions or assemblages of vapor-only inclusions and those that do not, sug- gesting that fluid inclusion evidence for Boiling is not correlative with ore grades. This result is consistent with the fact that most forms of silica that are precipitated during Boiling do not trap useful fluid inclusions. The results of this study suggest that mineral textures and fluid inclusions provide complementary informa- tion that should both be used in exploration for epithermal precious metal deposits. Metal grades and Boiling intensity of samples collected along a traverse perpendicular to the Veta Madre and above known economic mineralization are both low at relatively short distances away from the vein and in- crease as the vein is approached. This suggests that mineralogical and fluid inclusion evidence for Boiling are restricted to the immediate vicinity of, and increase in the direction of, mineralized veins and may be used in exploration to establish vectors towards vein systems that may host precious metal mineralization. Previous studies of epithermal systems show that the Ag and Au mineralization Zone is most often located at or above the bottom of the Boiling Zone. In this regard, the presence of abundant evidence for Boiling that is observed in the deepest levels of the Veta Madre that have been sampled suggests that additional precious metal min- eralization may be present beneath the deepest levels that have been explored.
Robert J Bodnar - One of the best experts on this subject based on the ideXlab platform.
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mineralogical petrographic and fluid inclusion evidence for the link between Boiling and epithermal ag au mineralization in the la luz area guanajuato mining district mexico
Ore Geology Reviews, 2017Co-Authors: Daniel Moncada, Darcy Baker, Robert J BodnarAbstract:Abstract Theoretical, experimental and observation data provide strong evidence that Boiling is the dominant depositional mechanism in many low to intermediate sulfidation epithermal precious metals deposits. Textural and petrographic features that are evidence for Boiling in the epithermal environment include the presence of coexisting liquid-rich and vapor-rich fluid inclusions, assemblages consisting of only vapor-rich fluid inclusions, colloform quartz, adularia and bladed calcite. We have examined 213 samples collected from surface outcrops, underground workings and drill cores from the central part of the La Luz vein system in the Guanajuato mining district, Mexico. In each sample, the various features that are evidence of Boiling have been recorded. These observations have been quantified using a Boiling Confidence Factor that provides a means of scoring and rating each sample or area relative to the likelihood that Boiling occurred. Homogenization temperatures of liquid-rich fluid inclusions within assemblages of coexisting liquid-rich and vapor-rich fluid inclusions have been measured to estimate the depth of trapping of the inclusions, and these data have been used to estimate the depth to the 300 °C isotherm along the La Luz vein system. Fluid inclusions and mineral textural features show strong evidence of Boiling in the deepest levels sampled in the La Luz system. This observation suggests that the bottom of the Boiling Zone is at some depth beneath the deepest levels explored and opens the potential for additional resources at depth.
S Mutchle - One of the best experts on this subject based on the ideXlab platform.
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mineral textures and fluid inclusion petrography of the epithermal ag au deposits at guanajuato mexico application to exploration
Journal of Geochemical Exploration, 2012Co-Authors: Daniel Moncada, S Mutchle, Antonio Nieto, T J Reynolds, J D Rimstid, Robe J OdnaAbstract:article Fluid inclusion petrography and vein mineral textures indicative of Boiling have been characterized in 855 samples from epithermal precious metals deposits along the Veta Madre at Guanajuato, Mexico. Mineral tex- tures and fluid inclusions characteristic of fluid immiscibility or Boiling, including colloform quartz, plumose/ feathery/flamboyant quartz, lattice-bladed calcite and lattice-bladed calcite replaced by quartz, as well as coexisting liquid-rich and vapor-rich fluid inclusions and assemblages of vapor-rich only inclusions, have been identified in mineralized samples from the Veta Madre. Most samples studied were assayed for Au, Ag, Cu, Pb, Zn, As and Sb, and were divided into ore grade and sub-economic samples based on the gold and silver concentrations. For silver, samples containing >100 ppm were classified as ore grade, and ore grade gold samples contained >1 ppm Au. The feature that is most closely associated with ore grades of both gold and silver is colloform quartz that was originally precipitated as amorphous silica, and this feature also shows the largest difference in average grade between samples that show colloform texture (178.8 ppm Ag and 1.1 ppm Au) and those that do not exhibit this texture (17.2 ppm Ag and 0.2 ppm Au). Statistical anal- ysis of the data confirmed the petrographic observations that indicated that colloform quartz is the feature that has the greatest predictive power for distinguishing between ore grade and sub-economic samples. For both Ag and Au, there is no significant difference in average grade of samples containing coexisting liquid-rich and vapor-rich fluid inclusions or assemblages of vapor-only inclusions and those that do not, sug- gesting that fluid inclusion evidence for Boiling is not correlative with ore grades. This result is consistent with the fact that most forms of silica that are precipitated during Boiling do not trap useful fluid inclusions. The results of this study suggest that mineral textures and fluid inclusions provide complementary informa- tion that should both be used in exploration for epithermal precious metal deposits. Metal grades and Boiling intensity of samples collected along a traverse perpendicular to the Veta Madre and above known economic mineralization are both low at relatively short distances away from the vein and in- crease as the vein is approached. This suggests that mineralogical and fluid inclusion evidence for Boiling are restricted to the immediate vicinity of, and increase in the direction of, mineralized veins and may be used in exploration to establish vectors towards vein systems that may host precious metal mineralization. Previous studies of epithermal systems show that the Ag and Au mineralization Zone is most often located at or above the bottom of the Boiling Zone. In this regard, the presence of abundant evidence for Boiling that is observed in the deepest levels of the Veta Madre that have been sampled suggests that additional precious metal min- eralization may be present beneath the deepest levels that have been explored.