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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

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