The lamprophyres are late dykes that cut the formations hosting the gold mineralization in the Nassara deposit. They are geographically and spatially related to most orogenic gold deposits. It is with the aim of chara...The lamprophyres are late dykes that cut the formations hosting the gold mineralization in the Nassara deposit. They are geographically and spatially related to most orogenic gold deposits. It is with the aim of characterizing them and seeing their implications for exploration that this work is carried out. To achieve our objective, petrographic studies and chemical analyses of minerals (pyroxenes, amphiboles, feldspars, chromite) and geochemical analyses of total rock were carried out. These studies have enabled us to classify the Nassara lamprophyres as calc-alkaline lamprophyres of the spessartite type. The Cr, Co, Ni and Mg enrichment of these rocks would indicate a depleted mantle source, with LILE enrichment by fluids probably related to metasomatic activity. The various diagrams show that they are depleted in HREE and enriched in LREE. The high Nb/Ta ratios in our data indicate metasomatic activity probably linked to amphibole and rutile in the mantle prior to melting. The geodynamic context of spessartite-type lamprophyres indicates a signature linked to late-orogenic to post-collisional subduction. They are late-orogenic to post-collisional lamprophyres enriched in compatible elements (Cr, Ni, Co) and display a negative Ta-Nb-Ti (TNT) anomaly. The frequent association of these lamprophyre dykes with the deposits does not indicate the source of the gold for these deposits, but rather zones of crustal permeability capable of draining hydrothermal fluids at the time of emplacement. Good mapping of lamprophyre dykes, especially in shear zones, could therefore guide prospecting and identify potential zones of hydrothermal fluid circulation.展开更多
Paleoproterozoic subduction strongly occurred in the western margin of Yangtze plate. The basalticandesite volcanics of Ailaoshan Group and Dibadu Formation had been formed during paleo QinghaiTibet oceanic plate s...Paleoproterozoic subduction strongly occurred in the western margin of Yangtze plate. The basalticandesite volcanics of Ailaoshan Group and Dibadu Formation had been formed during paleo QinghaiTibet oceanic plate subduction under the paleoYangtze plate. Their trace element geochemistry suggests that their forming environments are continentalmarginarc and back arcbasin respectively. Consequently, the Paleoproterozoic subduction system in the western margin of Yangtze plate was established. Ailaoshan Group and Dibadu Formation came from an enriched mantle source that was contaminated by crustal sediments carried by subducted slab, and formed the Paleoroterozoic metamorphic basement of western margin of Yangtze plate. Ailaoshan Group is actually western boundary of Yangtze plate.展开更多
Basalt discriminant diagrams have been used to identify the tectonic setting of basaltic magmatism since the 1970s and have played an important role in reconstructing paleotectonic environments.However,the significant...Basalt discriminant diagrams have been used to identify the tectonic setting of basaltic magmatism since the 1970s and have played an important role in reconstructing paleotectonic environments.However,the significant increase in the availability of geochemical data has led to a reassessment of these diagrams,suggesting that some of the tectonic settings indicated by these diagrams are not accurate.Here,we use a database of global ocean island basalt(OIB),mid-ocean ridge basalt(MORB),and island arc basalt(IAB)geochemistry to propose a series of new tectonic discriminant diagrams based on the ratios of large-ion lithophile elements(LILEs)to high field strength elements(HFSEs).These new diagrams indicate that the LILE can be used to differentiate OIB,MORB,and IAB samples,meaning that LILE/HFSE ratios can discriminate between these basalts that form in different tectonic settings.Our new diagrams can correctly assign samples to OIB,MORB,and IAB categories more than 85%of the time,with the discrimination between OIB and MORB having an accuracy of slightly less than 85%.展开更多
文摘The lamprophyres are late dykes that cut the formations hosting the gold mineralization in the Nassara deposit. They are geographically and spatially related to most orogenic gold deposits. It is with the aim of characterizing them and seeing their implications for exploration that this work is carried out. To achieve our objective, petrographic studies and chemical analyses of minerals (pyroxenes, amphiboles, feldspars, chromite) and geochemical analyses of total rock were carried out. These studies have enabled us to classify the Nassara lamprophyres as calc-alkaline lamprophyres of the spessartite type. The Cr, Co, Ni and Mg enrichment of these rocks would indicate a depleted mantle source, with LILE enrichment by fluids probably related to metasomatic activity. The various diagrams show that they are depleted in HREE and enriched in LREE. The high Nb/Ta ratios in our data indicate metasomatic activity probably linked to amphibole and rutile in the mantle prior to melting. The geodynamic context of spessartite-type lamprophyres indicates a signature linked to late-orogenic to post-collisional subduction. They are late-orogenic to post-collisional lamprophyres enriched in compatible elements (Cr, Ni, Co) and display a negative Ta-Nb-Ti (TNT) anomaly. The frequent association of these lamprophyre dykes with the deposits does not indicate the source of the gold for these deposits, but rather zones of crustal permeability capable of draining hydrothermal fluids at the time of emplacement. Good mapping of lamprophyre dykes, especially in shear zones, could therefore guide prospecting and identify potential zones of hydrothermal fluid circulation.
文摘Paleoproterozoic subduction strongly occurred in the western margin of Yangtze plate. The basalticandesite volcanics of Ailaoshan Group and Dibadu Formation had been formed during paleo QinghaiTibet oceanic plate subduction under the paleoYangtze plate. Their trace element geochemistry suggests that their forming environments are continentalmarginarc and back arcbasin respectively. Consequently, the Paleoproterozoic subduction system in the western margin of Yangtze plate was established. Ailaoshan Group and Dibadu Formation came from an enriched mantle source that was contaminated by crustal sediments carried by subducted slab, and formed the Paleoroterozoic metamorphic basement of western margin of Yangtze plate. Ailaoshan Group is actually western boundary of Yangtze plate.
基金Technological Leading Talents Program of Yunnan Province[grant number 2013HA001]the National Natural Science Foundation of China[grant number 41502076]+1 种基金the State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences program[grant number 81300001]the China Geological Survey[grant number 12120114013701].
文摘Basalt discriminant diagrams have been used to identify the tectonic setting of basaltic magmatism since the 1970s and have played an important role in reconstructing paleotectonic environments.However,the significant increase in the availability of geochemical data has led to a reassessment of these diagrams,suggesting that some of the tectonic settings indicated by these diagrams are not accurate.Here,we use a database of global ocean island basalt(OIB),mid-ocean ridge basalt(MORB),and island arc basalt(IAB)geochemistry to propose a series of new tectonic discriminant diagrams based on the ratios of large-ion lithophile elements(LILEs)to high field strength elements(HFSEs).These new diagrams indicate that the LILE can be used to differentiate OIB,MORB,and IAB samples,meaning that LILE/HFSE ratios can discriminate between these basalts that form in different tectonic settings.Our new diagrams can correctly assign samples to OIB,MORB,and IAB categories more than 85%of the time,with the discrimination between OIB and MORB having an accuracy of slightly less than 85%.
