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Evidence for magmatic-hydrothermal fluids and ore-forming processes in epithermal and porphyry deposits of the Baguio district, Philippines / David R. Cooke in Economic geology, Vol. 106 N° 8 (Décembre 2011) 

Public ISBD [article]  in Economic geology > Vol. 106 N° 8 (Décembre 2011) . - pp. 1399-1424 Titre : Evidence for magmatic-hydrothermal fluids and ore-forming processes in epithermal and porphyry deposits of the Baguio district, Philippines Type de document : texte imprimé Auteurs : David R. Cooke, Auteur ; Cari L. Deyell, Auteur ; Patrick J. Waters, Auteur Année de publication : 2011 Article en page(s) : pp. 1399-1424 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Magmatic-hydrothermal  fluids  Mineral  deposits  Epithermal  deposits  Porphyry  deposits  Philippines Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Baguio district contains a diverse array of epithermal, porphyry and skarn deposits, together with a large, broadly strata bound, advanced argillic lithocap. Magmatism, mineralization, and alteration occurred in response to subduction of the South China Sea plate and the Scarborough Ridge beneath northern Luzon over the past 3 m.y. Rapid uplift and exhumation resulted in epithermal veins overprinting several porphyry Cu-Au deposits. Most of the epithermal Au-Ag deposits of the Baguio district (including Antamok and Acupan, the two largest Au deposits) are intermediate sulfidation state quartz-carbonate-adularia-illite-base metal sulfide veins that contain electrum and minor Au-Ag tellurides. In contrast, high sulfidation mineralization at Kelly includes enargite, tennantite, electrum, and precious metal tellurides and is associated with advanced argillic alteration. Although the mineralizing fluids that formed the porphyry and epithermal deposits had distinct temperatures and salinities, stable and radiogenic data provide evidence for direct magmatic contributions into each deposit type. The epithermal mineralizing fluids were dilute (generally, <2 wt % NaCl equiv) and had moderate temperatures (<300°C). Porphyry-style mineralization was associated with high temperature (300° to >600°C) hypersaline brines (30 to >70 wt % NaCl equiv) and low-density vapor. Sulfur isotope compositions of sulfides in the porphyry, skarn and intermediate sulfidation epithermal veins of the southern and central Baguio district are mostly between +1 and +6 per mil, consistent with a predominance of H2S in the mineralizing fluids (i.e., reducing conditions). In contrast, sulfides from the high sulfidation, porphyry, and intermediate sulfidation deposits located adjacent to the Baguio lithocap mostly have negative sulfur isotope values (−6.9 to +0.8‰), consistent with oxidizing (SO42−-predominant) mineralizing fluids. Intermediate sulfidation epithermal veins at Acupan have crosscut a well-mineralized porphyry Cu-Au stock-work at Ampucao. The two deposits cannot be distinguished on the basis of radiometric age determinations (Ampucao: 0.51 ± 0.26 Ma; Acupan: 0.65 ± 0.07 Ma), and are interpreted to be cogenetic, with telescoping of the two environments caused by the rapid uplift and exhumation associated with ridge subduction. Measured δ34Ssulfide (+1.1 to +6.6‰), δ34Ssulfate (+10.4 to +31.8‰) values and initial strontium ratios of anhydrite (0.70378–0.70385) are consistent with identical and predominantly magmatic sources of these components for the Ampucao porphyry and Acupan epithermal veins. Helium isotopes provide further evidence of mantle-derived components in the epithermal veins (R/Ra values of 6.0 and 6.7). Oxygen, deuterium, and carbon isotopes provide evidence for predominantly magmatic water at Ampucao and for hybrid magmatic-meteoric waters at Acupan that precipitated precious metals due to boiling. The proportion of magmatic water relative to meteoric water and precious metal grades both decreased with time during epithermal vein formation at Acupan. The common observation of cross-cutting relationships between porphyry and epithermal veins observed throughout the Baguio district imply that the evolution of porphyry-style to intermediate sulfidation-style mineralization was a common phenomenon in this region, and contributed significantly to its rich metal endowment. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/106/8/1399.abstract [article] Evidence for magmatic-hydrothermal fluids and ore-forming processes in epithermal and porphyry deposits of the Baguio district, Philippines [texte imprimé] / David R. Cooke, Auteur ; Cari L. Deyell, Auteur ; Patrick J. Waters, Auteur . - 2011 . - pp. 1399-1424. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 106 N° 8 (Décembre 2011) . - pp. 1399-1424 Mots-clés : Magmatic-hydrothermal  fluids  Mineral  deposits  Epithermal  deposits  Porphyry  deposits  Philippines Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Baguio district contains a diverse array of epithermal, porphyry and skarn deposits, together with a large, broadly strata bound, advanced argillic lithocap. Magmatism, mineralization, and alteration occurred in response to subduction of the South China Sea plate and the Scarborough Ridge beneath northern Luzon over the past 3 m.y. Rapid uplift and exhumation resulted in epithermal veins overprinting several porphyry Cu-Au deposits. Most of the epithermal Au-Ag deposits of the Baguio district (including Antamok and Acupan, the two largest Au deposits) are intermediate sulfidation state quartz-carbonate-adularia-illite-base metal sulfide veins that contain electrum and minor Au-Ag tellurides. In contrast, high sulfidation mineralization at Kelly includes enargite, tennantite, electrum, and precious metal tellurides and is associated with advanced argillic alteration. Although the mineralizing fluids that formed the porphyry and epithermal deposits had distinct temperatures and salinities, stable and radiogenic data provide evidence for direct magmatic contributions into each deposit type. The epithermal mineralizing fluids were dilute (generally, <2 wt % NaCl equiv) and had moderate temperatures (<300°C). Porphyry-style mineralization was associated with high temperature (300° to >600°C) hypersaline brines (30 to >70 wt % NaCl equiv) and low-density vapor. Sulfur isotope compositions of sulfides in the porphyry, skarn and intermediate sulfidation epithermal veins of the southern and central Baguio district are mostly between +1 and +6 per mil, consistent with a predominance of H2S in the mineralizing fluids (i.e., reducing conditions). In contrast, sulfides from the high sulfidation, porphyry, and intermediate sulfidation deposits located adjacent to the Baguio lithocap mostly have negative sulfur isotope values (−6.9 to +0.8‰), consistent with oxidizing (SO42−-predominant) mineralizing fluids. Intermediate sulfidation epithermal veins at Acupan have crosscut a well-mineralized porphyry Cu-Au stock-work at Ampucao. The two deposits cannot be distinguished on the basis of radiometric age determinations (Ampucao: 0.51 ± 0.26 Ma; Acupan: 0.65 ± 0.07 Ma), and are interpreted to be cogenetic, with telescoping of the two environments caused by the rapid uplift and exhumation associated with ridge subduction. Measured δ34Ssulfide (+1.1 to +6.6‰), δ34Ssulfate (+10.4 to +31.8‰) values and initial strontium ratios of anhydrite (0.70378–0.70385) are consistent with identical and predominantly magmatic sources of these components for the Ampucao porphyry and Acupan epithermal veins. Helium isotopes provide further evidence of mantle-derived components in the epithermal veins (R/Ra values of 6.0 and 6.7). Oxygen, deuterium, and carbon isotopes provide evidence for predominantly magmatic water at Ampucao and for hybrid magmatic-meteoric waters at Acupan that precipitated precious metals due to boiling. The proportion of magmatic water relative to meteoric water and precious metal grades both decreased with time during epithermal vein formation at Acupan. The common observation of cross-cutting relationships between porphyry and epithermal veins observed throughout the Baguio district imply that the evolution of porphyry-style to intermediate sulfidation-style mineralization was a common phenomenon in this region, and contributed significantly to its rich metal endowment. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/106/8/1399.abstract

Geochemistry of tertiary igneous rocks of northern Luzon, Philippines / Pete Hollings in Economic geology, Vol. 106 N° 8 (Décembre 2011) 

Public ISBD [article]  in Economic geology > Vol. 106 N° 8 (Décembre 2011) . - pp. 1257-1277 Titre : Geochemistry of tertiary igneous rocks of northern Luzon, Philippines : evidence for a back-arc setting for alkalic porphyry copper-gold deposits and a case for slab roll-back? Type de document : texte imprimé Auteurs : Pete Hollings, Auteur ; Rohan Wolfe, Auteur ; David R. Cooke, Auteur Année de publication : 2011 Article en page(s) : pp. 1257-1277 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Tertiary  igneous  rocks  Alcalic  prophyry  Copper  deposits  Gold  deposits Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Oligocene to early Miocene volcanic rocks are preserved in the Central Cordillera range and Cagayan Valley of northern Luzon, Philippines. Basaltic and andesitic rocks of the Pugo Formation in the Baguio district of the Central Cordillera were intruded by the ~27 to 20 Ma calc-alkaline Central Cordillera Diorite Complex. In the southern Cagayan Valley the subalkaline to alkaline late Oligocene Mamparang Formation overlies the Cretaceous Caraballo Formation and has been intruded by the Didipio Igneous Complex, the Cordon Syenite Complex, and the Palali batholith. The Didipio complex comprises an early suite of diorites, which were intruded by the strongly mineralized stocks of the Dinkidi Cu-Au porphyry deposit. Whole-rock geochemical data for intrusive and extrusive rocks of the Baguio district range from low K calc-alkaline to shoshonitic basalts to dacites with rare earth element (REE) and high field strength element (HFSE) characteristics of suprasubduction zone magmas and are all interpreted to have been sourced from the same parent melt. Samples from Didipio display higher alkali contents but similar trace element characteristics. New age dates for the Didipio area range from 25.7 to 24.8 Ma. The potassic magmas of the Cagayan Valley are interpreted to have formed in a back-arc coeval to the main-arc sequence that is preserved in the Baguio Miocene rocks. This contradicts earlier models, which invoke an early Miocene arc reversal in the northern Luzon archipelago with the switch from early westward subduction to later eastward subduction attributed to a variety of causes. The lack of a single compelling trigger for arc reversal combined with the coeval emplacement of arc magmas in the west and back-arc magmas in the east in northern Luzon is best interpreted as the result of eastward subduction since the late Oligocene. The presence of ~20 Ma adakitic magmas in the Baguio district may indicate that flattening of the downgoing slab resulted in a hiatus in magmatism and termination of back-arc rifting. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/106/8/1257.abstract [article] Geochemistry of tertiary igneous rocks of northern Luzon, Philippines : evidence for a back-arc setting for alkalic porphyry copper-gold deposits and a case for slab roll-back? [texte imprimé] / Pete Hollings, Auteur ; Rohan Wolfe, Auteur ; David R. Cooke, Auteur . - 2011 . - pp. 1257-1277. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 106 N° 8 (Décembre 2011) . - pp. 1257-1277 Mots-clés : Tertiary  igneous  rocks  Alcalic  prophyry  Copper  deposits  Gold  deposits Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : Oligocene to early Miocene volcanic rocks are preserved in the Central Cordillera range and Cagayan Valley of northern Luzon, Philippines. Basaltic and andesitic rocks of the Pugo Formation in the Baguio district of the Central Cordillera were intruded by the ~27 to 20 Ma calc-alkaline Central Cordillera Diorite Complex. In the southern Cagayan Valley the subalkaline to alkaline late Oligocene Mamparang Formation overlies the Cretaceous Caraballo Formation and has been intruded by the Didipio Igneous Complex, the Cordon Syenite Complex, and the Palali batholith. The Didipio complex comprises an early suite of diorites, which were intruded by the strongly mineralized stocks of the Dinkidi Cu-Au porphyry deposit. Whole-rock geochemical data for intrusive and extrusive rocks of the Baguio district range from low K calc-alkaline to shoshonitic basalts to dacites with rare earth element (REE) and high field strength element (HFSE) characteristics of suprasubduction zone magmas and are all interpreted to have been sourced from the same parent melt. Samples from Didipio display higher alkali contents but similar trace element characteristics. New age dates for the Didipio area range from 25.7 to 24.8 Ma. The potassic magmas of the Cagayan Valley are interpreted to have formed in a back-arc coeval to the main-arc sequence that is preserved in the Baguio Miocene rocks. This contradicts earlier models, which invoke an early Miocene arc reversal in the northern Luzon archipelago with the switch from early westward subduction to later eastward subduction attributed to a variety of causes. The lack of a single compelling trigger for arc reversal combined with the coeval emplacement of arc magmas in the west and back-arc magmas in the east in northern Luzon is best interpreted as the result of eastward subduction since the late Oligocene. The presence of ~20 Ma adakitic magmas in the Baguio district may indicate that flattening of the downgoing slab resulted in a hiatus in magmatism and termination of back-arc rifting. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/106/8/1257.abstract

Geology of the Didipio region and genesis of the dinkidi alkalic porphyry Cu-Au deposit and related pegmatites, northern Luzon, Philippines / Rohan C. Wolfe in Economic geology, Vol. 106 N° 8 (Décembre 2011) 

Public ISBD [article]  in Economic geology > Vol. 106 N° 8 (Décembre 2011) . - pp. 1279-1315 Titre : Geology of the Didipio region and genesis of the dinkidi alkalic porphyry Cu-Au deposit and related pegmatites, northern Luzon, Philippines Type de document : texte imprimé Auteurs : Rohan C. Wolfe, Auteur ; David R. Cooke, Auteur Année de publication : 2011 Article en page(s) : pp. 1279-1315 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Alcalic  prophyry  Pegmatite  Philippine Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Dinkidi Cu-Au porphyry deposit, northern Luzon, Philippines, formed at the tip of the southward-propagating Cagayan Valley basin in a late Oligocene to early Miocene back-arc setting. The 110 Mt ore deposit is characterized by elevated hypogene grades (avg 1.2 g/t Au and 0.5% Cu) and is one of only a few alkalic porphyry deposits to have been discovered outside of British Columbia and eastern Australia. Dinkidi is hosted by the Didipio intrusive complex, which intruded calc-alkalic to shoshonitic volcanic rocks of the Mamparang and Upper Mamparang formations in the late Oligocene. An early, composite diorite-monzodiorite pluton was intruded by the Surong monzonite and the Dinkidi stock. The initial phases of the Cu-Au mineralized Dinkidi stock were the equigranular biotite-amphibole–bearing Tunja monzonite and the Balut dike—a thin, variably textured and strongly mineralized clinopyroxene syenite pegmatite dike. The youngest phases of the Dinkidi stock are a plagioclase-phyric monzonite-syenite (Quan porphyry) and the Bufu syenite, a crystal-crowded leucocratic quartz syenite. Postmineralization andesite dikes cut the intrusive complex. Emplacement of the Tunja monzonite was temporally and spatially associated with pervasive stage 1 biotite-magnetite-K silicate alteration, which primarily affected the diorite-monzodiorite pluton. Emplacement of the diopside-phyric Balut dike produced the stage 2 calc-potassic diopside-actinolite-K feldspar-bornite vein stockwork and a calc-potassic alteration assemblage typical of silica-undersaturated alkalic porphyry deposits. Stage 2 lacks quartz, contains high gold grades (2–8 g/t Au) and its sulfides have δ34S values of −3.5 to −0.7 per mil. The stage 2 calc-potassic assemblage is inferred to have formed at temperatures in excess of 600°C from an oxidized (sulfate-predominant) Na-K-Ca-Fe–rich brine. Intrusion of the quartz-saturated Quan porphyry and Bufu syenite led to the formation of the stage 3 quartz-illite-calcite-chalcopyrite stockwork vein and alteration assemblage. The quartz stockwork hosts most of the lower-grade (1–2 g/t Au) mineralization at Dinkidi and is typical of silica-saturated alkalic porphyry systems. A coarse-grained assemblage of quartz-actinolite-perthite (the Bugoy pegmatite) formed as an apophysis on the Bufu syenite and was subsequently brecciated by faulting late in stage 3. The stage 3 quartz stockwork was emplaced at high temperatures (mostly >600°C) from a quartz-saturated, oxidized (sulfate-predominant) Na-K-Fe brine (>68 wt % NaCl equiv) that contained up to 0.6 wt percent Cu and 4 wt percent Fe. Cooling to ~430°C and sulfate reduction by wall-rock interaction led to the precipitation of stage 3 sulfides with δ34S values of −4.2 to −0.2 per mil in the quartz stockwork. The quartz-bearing assemblage formed at paleodepths of 2.9 to 3.5 km. Periods of quartz growth from overpressured brines were interrupted episodically by brittle failure events that caused the system to depressurize to near-hydrostatic conditions, triggering vapor generation via boiling. Mineralization was followed by intermediate argillic and high-level advanced argillic alteration (stage 4), and by late-stage, fault-related zeolite-calcite alteration and veins (stage 5). The hydrothermal mineral assemblages at Dinkidi reflect the composition and degree of fractionation of the associated intrusions. Extensive fractionation in a silica-undersaturated dioritic magma chamber is interpreted to have ultimately caused quartz saturation and the development of the late-stage syenite intrusions and related quartz stockwork mineralization. The calcic, silica-undersaturated pegmatitic Balut dike, which is associated with the calc-potassic stockwork, does not fit this fractionation trend and is interpreted to have formed by interaction between the late-stage syenitic melt and a comagmatic mafic melt that underplated the siliceous magma chamber prior to formation of the Balut dike. A reversion to fractionation-dominated magmatic processes in the silicic magma chamber then led to the intrusion of the quartz-saturated Quan porphyry and Bufu syenite. Ultimately, the residual mafic melt was emplaced as a series of late-stage andesite dikes. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/106/8/1279.abstract [article] Geology of the Didipio region and genesis of the dinkidi alkalic porphyry Cu-Au deposit and related pegmatites, northern Luzon, Philippines [texte imprimé] / Rohan C. Wolfe, Auteur ; David R. Cooke, Auteur . - 2011 . - pp. 1279-1315. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 106 N° 8 (Décembre 2011) . - pp. 1279-1315 Mots-clés : Alcalic  prophyry  Pegmatite  Philippine Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Dinkidi Cu-Au porphyry deposit, northern Luzon, Philippines, formed at the tip of the southward-propagating Cagayan Valley basin in a late Oligocene to early Miocene back-arc setting. The 110 Mt ore deposit is characterized by elevated hypogene grades (avg 1.2 g/t Au and 0.5% Cu) and is one of only a few alkalic porphyry deposits to have been discovered outside of British Columbia and eastern Australia. Dinkidi is hosted by the Didipio intrusive complex, which intruded calc-alkalic to shoshonitic volcanic rocks of the Mamparang and Upper Mamparang formations in the late Oligocene. An early, composite diorite-monzodiorite pluton was intruded by the Surong monzonite and the Dinkidi stock. The initial phases of the Cu-Au mineralized Dinkidi stock were the equigranular biotite-amphibole–bearing Tunja monzonite and the Balut dike—a thin, variably textured and strongly mineralized clinopyroxene syenite pegmatite dike. The youngest phases of the Dinkidi stock are a plagioclase-phyric monzonite-syenite (Quan porphyry) and the Bufu syenite, a crystal-crowded leucocratic quartz syenite. Postmineralization andesite dikes cut the intrusive complex. Emplacement of the Tunja monzonite was temporally and spatially associated with pervasive stage 1 biotite-magnetite-K silicate alteration, which primarily affected the diorite-monzodiorite pluton. Emplacement of the diopside-phyric Balut dike produced the stage 2 calc-potassic diopside-actinolite-K feldspar-bornite vein stockwork and a calc-potassic alteration assemblage typical of silica-undersaturated alkalic porphyry deposits. Stage 2 lacks quartz, contains high gold grades (2–8 g/t Au) and its sulfides have δ34S values of −3.5 to −0.7 per mil. The stage 2 calc-potassic assemblage is inferred to have formed at temperatures in excess of 600°C from an oxidized (sulfate-predominant) Na-K-Ca-Fe–rich brine. Intrusion of the quartz-saturated Quan porphyry and Bufu syenite led to the formation of the stage 3 quartz-illite-calcite-chalcopyrite stockwork vein and alteration assemblage. The quartz stockwork hosts most of the lower-grade (1–2 g/t Au) mineralization at Dinkidi and is typical of silica-saturated alkalic porphyry systems. A coarse-grained assemblage of quartz-actinolite-perthite (the Bugoy pegmatite) formed as an apophysis on the Bufu syenite and was subsequently brecciated by faulting late in stage 3. The stage 3 quartz stockwork was emplaced at high temperatures (mostly >600°C) from a quartz-saturated, oxidized (sulfate-predominant) Na-K-Fe brine (>68 wt % NaCl equiv) that contained up to 0.6 wt percent Cu and 4 wt percent Fe. Cooling to ~430°C and sulfate reduction by wall-rock interaction led to the precipitation of stage 3 sulfides with δ34S values of −4.2 to −0.2 per mil in the quartz stockwork. The quartz-bearing assemblage formed at paleodepths of 2.9 to 3.5 km. Periods of quartz growth from overpressured brines were interrupted episodically by brittle failure events that caused the system to depressurize to near-hydrostatic conditions, triggering vapor generation via boiling. Mineralization was followed by intermediate argillic and high-level advanced argillic alteration (stage 4), and by late-stage, fault-related zeolite-calcite alteration and veins (stage 5). The hydrothermal mineral assemblages at Dinkidi reflect the composition and degree of fractionation of the associated intrusions. Extensive fractionation in a silica-undersaturated dioritic magma chamber is interpreted to have ultimately caused quartz saturation and the development of the late-stage syenite intrusions and related quartz stockwork mineralization. The calcic, silica-undersaturated pegmatitic Balut dike, which is associated with the calc-potassic stockwork, does not fit this fractionation trend and is interpreted to have formed by interaction between the late-stage syenitic melt and a comagmatic mafic melt that underplated the siliceous magma chamber prior to formation of the Balut dike. A reversion to fractionation-dominated magmatic processes in the silicic magma chamber then led to the intrusion of the quartz-saturated Quan porphyry and Bufu syenite. Ultimately, the residual mafic melt was emplaced as a series of late-stage andesite dikes. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/106/8/1279.abstract

Igneous geochemistry of mineralized rocks of the Baguio district, Philippines / Pete Hollings in Economic geology, Vol. 106 N° 8 (Décembre 2011) 

Public ISBD [article]  in Economic geology > Vol. 106 N° 8 (Décembre 2011) . - pp. 1317-1333 Titre : Igneous geochemistry of mineralized rocks of the Baguio district, Philippines : implications for tectonic evolution and the genesis of porphyry-style mineralization Type de document : texte imprimé Auteurs : Pete Hollings, Auteur ; David R. Cooke, Auteur ; Patrick J. Waters, Auteur Année de publication : 2011 Article en page(s) : pp. 1317-1333 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Tectonic  evolution  Mineralized  rocks  Porphyry-style  mineralization  Philippine Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Baguio district of the Philippines is one of the world’s premier mineral provinces, containing >35 million ounces (Moz) of gold and 2.7 million metric tons (Mt) of copper in epithermal, porphyry, and skarn deposits that formed in the last 3.5 m.y. Pliocene and Pleistocene magmatic rocks of the Baguio district that are spatially and temporally associated with mineralization can be broadly subdivided into an intermediate to felsic suite of mineralized low to medium K intrusions, some of which have adakitic affinities and a suite of mafic to intermediate, medium K to shoshonitic hornblende-phyric dikes. The geochemical and isotopic characteristics of the dikes are consistent with primitive mantle-derived melts that underwent minimal crustal contamination as they ascended through the arc crust. In contrast, the intermediate to felsic suite has been contaminated by young arc crust, suggesting ponding and fractionation within shallow-crustal magma chambers. The Philippine arc has formed in a complex tectonic environment and is currently sandwiched between two active subduction zones. Eastward-directed subduction of the Scarborough Ridge along the Manila trench is currently associated with flattening of the downgoing slab. The formation of the Mafic dike complex is broadly coeval with the onset of subduction of the Scarborough Ridge and slab flattening. The extinct Scarborough Ridge would have been younger than the downgoing plate and consequently more susceptible to melting. These melts can account for the isotopic recharge of the Pliocene subarc mantle as well as the generation of the primitive melts and adakitic rocks found within the Baguio district. The interaction between primitive mafic melts and the more felsic calc-alkaline rocks has generated fertile melts that were highly productive for porphyry copper and epithermal gold mineralization. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/106/8/1317.abstract [article] Igneous geochemistry of mineralized rocks of the Baguio district, Philippines : implications for tectonic evolution and the genesis of porphyry-style mineralization [texte imprimé] / Pete Hollings, Auteur ; David R. Cooke, Auteur ; Patrick J. Waters, Auteur . - 2011 . - pp. 1317-1333. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 106 N° 8 (Décembre 2011) . - pp. 1317-1333 Mots-clés : Tectonic  evolution  Mineralized  rocks  Porphyry-style  mineralization  Philippine Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais Résumé : The Baguio district of the Philippines is one of the world’s premier mineral provinces, containing >35 million ounces (Moz) of gold and 2.7 million metric tons (Mt) of copper in epithermal, porphyry, and skarn deposits that formed in the last 3.5 m.y. Pliocene and Pleistocene magmatic rocks of the Baguio district that are spatially and temporally associated with mineralization can be broadly subdivided into an intermediate to felsic suite of mineralized low to medium K intrusions, some of which have adakitic affinities and a suite of mafic to intermediate, medium K to shoshonitic hornblende-phyric dikes. The geochemical and isotopic characteristics of the dikes are consistent with primitive mantle-derived melts that underwent minimal crustal contamination as they ascended through the arc crust. In contrast, the intermediate to felsic suite has been contaminated by young arc crust, suggesting ponding and fractionation within shallow-crustal magma chambers. The Philippine arc has formed in a complex tectonic environment and is currently sandwiched between two active subduction zones. Eastward-directed subduction of the Scarborough Ridge along the Manila trench is currently associated with flattening of the downgoing slab. The formation of the Mafic dike complex is broadly coeval with the onset of subduction of the Scarborough Ridge and slab flattening. The extinct Scarborough Ridge would have been younger than the downgoing plate and consequently more susceptible to melting. These melts can account for the isotopic recharge of the Pliocene subarc mantle as well as the generation of the primitive melts and adakitic rocks found within the Baguio district. The interaction between primitive mafic melts and the more felsic calc-alkaline rocks has generated fertile melts that were highly productive for porphyry copper and epithermal gold mineralization. DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/106/8/1317.abstract

Philippine porphyry and epithermal deposits / David R. Cooke in Economic geology, Vol. 106 N° 8 (Décembre 2011) 

Public ISBD [article]  in Economic geology > Vol. 106 N° 8 (Décembre 2011) . - pp. 1253-1256 Titre : Philippine porphyry and epithermal deposits : an introduction Type de document : texte imprimé Auteurs : David R. Cooke, Auteur ; Pete Hollings, Auteur ; Zhaoshan Chang, Auteur Année de publication : 2011 Article en page(s) : pp. 1253-1256 Note générale : Economic geology Langues : Anglais (eng) Mots-clés : Gold  mining  Silver  mining  Philippine  Epithermal  deposits Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/106/8/1253.extract [article] Philippine porphyry and epithermal deposits : an introduction [texte imprimé] / David R. Cooke, Auteur ; Pete Hollings, Auteur ; Zhaoshan Chang, Auteur . - 2011 . - pp. 1253-1256. Economic geology Langues : Anglais (eng) in Economic geology > Vol. 106 N° 8 (Décembre 2011) . - pp. 1253-1256 Mots-clés : Gold  mining  Silver  mining  Philippine  Epithermal  deposits Index. décimale : 553 Géologie économique. Minérographie. Minéraux. Formation et gisements de minerais DEWEY : 553 ISSN : 0361-0128 En ligne : http://econgeol.geoscienceworld.org/content/106/8/1253.extract

Porphyry and epithermal deposits and 40Ar/39Ar geochronology of the Baguio district, Philippines / Patrick J. Waters in Economic geology, Vol. 106 N° 8 (Décembre 2011) 

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The trace metal chemistry of deep geothermal water, palinpinon geothermal field, negros island, Philippines / Andrew J. Rae in Economic geology, Vol. 106 N° 8 (Décembre 2011) 

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