During January–May in 2007,the Chinese research cruise DY115-19 discovered an active hydrothermal field at 49°39′E/37°47′S on the ultraslow spreading Southwest Indian Ridge (SWIR).This was also the first ...During January–May in 2007,the Chinese research cruise DY115-19 discovered an active hydrothermal field at 49°39′E/37°47′S on the ultraslow spreading Southwest Indian Ridge (SWIR).This was also the first active hydrothermal field found along an ultraslow-spreading ridge.We analyzed mineralogical,textural and geochemical compositions of the sulfide chimneys obtained from the 49°39′E field.Chimney samples show a concentric mineral zone around the fluid channel.The mineral assemblages of the interiors consist mainly of chalcopyrite,with pyrite and sphalerite as minor constitunets.In the intermediate portion,pyrite becomes the dominant mineral,with chalcopyrite and sphalerite as minor constitunets.For the outer wall,the majority of minerals are pyrite and sphalerite,with few chalcopyrite.Towards the outer margin of the chimney wall,the mineral grains become small and irregular in shape gradually,while minerals within interstices are abundant.These features are similar to those chimney edifices found on the East Pacific Rise and Mid-Atlantic Ridge.The average contents of Cu,Fe and Zn in our chimney samples were 2.83 wt%,45.6 wt% and 3.28 wt%,respectively.The average Au and Ag contents were up to 2.0 ppm and 70.2 ppm respectively,higher than the massive sulfides from most hydrothermal fields along mid-ocean ridge.The rare earth elements geochemistry of the sulfide chimneys show a pattern distinctive from the sulfides recovered from typical hydrothermal fields along sedimentstarved mid-ocean ridge,with the enrichment of light rare earth elements but the weak,mostly negative,Eu anomaly.This is attributed to the distinct mineralization environment or fluid compositions in this area.展开更多
Massive sulfide precipitates found in the Southwest Indian Ridge （SWIR） 49.6°E hydrothermal field are enriched in gold. Here, the mineralogy and mineral chemistry of these massive sulfides to constrain the proc...Massive sulfide precipitates found in the Southwest Indian Ridge （SWIR） 49.6°E hydrothermal field are enriched in gold. Here, the mineralogy and mineral chemistry of these massive sulfides to constrain the process of gold precipitation were studied. Sulfide samples in this field include lower- temperature Zn-rich sulfides and relative higher-temperature Fe-rich sulfides. Zn-rich sulfides are dominated by sphalerite-pyrite-chalcopyrite assemblages, with concentrations of gold ranging from 9.08 to 17.0 μg/g. Fe-rich sulfides consist mainly of pyrite-marcasite-isocubanite assemblages, with gold concentrations from 2.17 to 3.79 μg/g. The significant enrichment in gold within the lower- temperature Zn-rich sulfides and the effective separation of Zn and Fe in hydrothermal precipitates at the surface of this field are here interpreted to reflect the strong temperature dependence of gold transportation and deposition within the sulfides. In Zn-rich samples, large amounts of isolated native gold grains were identified. They were found mainly as inclusions up to 8 μm in diameter, occupying porous cavities in sphalerite or in the elevated iron content rim of sphalerite. The fineness of the gold ranged from 810 to 830. Unlike previously published results on other hydrothermal fields, these data show a low gold fineness values in SWIR 49.6°E. The FeS content of sphalerite associated with gold grains ranged from 3.2 mole % to 18.9 mole %. This was higher than in other fields, indicating that the sulfur activity is relatively low during the gold precipitation process and that sulfur activity may be one of the main factors affecting gold fineness in the SWIR 49.6°E hydrothermal field. Evidence regarding gold fineness and sulfur activity suggests that gold was quite likely transported as AuHS° rather than as a Au（HS）2- complex.展开更多
The morphotectonic features and their evolution of the central Southwest Indian Ridge （SWIR） are dis- cussed on the base of the high-resolution flfll-coverage bathyraetric data on the ridge between 49°-51°...The morphotectonic features and their evolution of the central Southwest Indian Ridge （SWIR） are dis- cussed on the base of the high-resolution flfll-coverage bathyraetric data on the ridge between 49°-51°E. A comparative analysis of the topographic features of the axial and flank area indicates that the axial topogra- phy is alternated by the ridge and trough with en echelon pattern and evolved under a spatial-temporal mi- gration especially in 49°-50.17°E. It is probably due to the undulation at the top of the mantle asthenosphere, which is propagating with the mantle flow. From 50.17° to 50.7°E, is a topographical high terrain with a crust much thicker than the global average of the oceanic crust thickness. Its origin should be independent of the spreading mechanism of ultra-slow spreading ridges. The large numbers of volcanoes in this area indicate robust magmatic activity and may be related to the Crozet hot spot according to RMBA （residual mantle Bouguer anomaly）. The different geomorphological feature between the north and south flanks of the ridge indicates an asymmetric spreading, and leading to the development of the OCC （oceanic core complex）. The tectonic activity of the south frank is stronger than the north and is favorable to develop the OCC. The first found active hydrothermal vent in the SWIR at 37°47＇S, 49°39＇E is thought to be associated with the detach- ment fault related to the OCC.展开更多
The REE compositions of hydrothermal deposits and basalt samples from the Southwest Indian Ridge （SWIR） were determined with ICP-MS. The results show that there are significant differences between different types of...The REE compositions of hydrothermal deposits and basalt samples from the Southwest Indian Ridge （SWIR） were determined with ICP-MS. The results show that there are significant differences between different types of samples although all samples show relative LREE enrichment. The contents of REE in hydrothermal sulfides and alterated rocks samples are lower （from 7.036× 10^-6 to 23.660×10^-6）, while those in the white chimney deposits are relatively higher （ranging from 84.496 × 10^-6 to 103.511 × 10^- 6）. Both of them are lower than basalts. Chondrite-normalized REE distribution patterns show that sulfides and alterated rocks samples are characterized by significant positive Eu anomalies. On the contrary, white chimney deposits have obvious negative Eu anomalies, which may be caused by abundant calcite existing in the white chimney samples. Both the content and distribution pattern of REE in sulfides suggest that REE most possibly is originally derived from hydrothermal fluids, but influenced by the submarine reducing ore-forming environment, seawater convection, mineral compositions as well as the constraint of mineral crystallizations.展开更多
The ultraslow-spreading Southwest Indian Ridge （SWIR） to the east of the Melville fracture zone is characterized by very low melt supply and intensive tectonic activity. Due to its weak thermal budget and extremely ...The ultraslow-spreading Southwest Indian Ridge （SWIR） to the east of the Melville fracture zone is characterized by very low melt supply and intensive tectonic activity. Due to its weak thermal budget and extremely slow spreading rate, the easternmost SWIR was considered to be devoid of hydrothermal activity until the discovery of the inactive Mt. lourdanne hydrothermal field （27°51＇S, 63°56＇E） in 1998. During the COMRA DYl15-20 cruise in 2009, two additional hydrothermal fields （i.e., the Tiancheng （27°51＇S, 63°55＇E） and Tianzuo （27°57＇S, 63°32＇E） fields） were discovered. Further detailed investigations of these two hydrothermal sites were conducted by Chinese manned submersible liaolong in 2014-2015. The Tiancheng filed can he characterized as a low- temperature （up to 13.2℃） diffuse flow hydrothermal field, and is hosted by fractured basalts with hydrothermal fauna widespread on the seafloor. The Tianzuo hydrothermal field is an inactive sulfide field, which is hosted by ultramafic rocks and controlled by detachment fault. The discovery of the three hydrothermal fields around Segment #11 which receives more melt than the regional average, provided evidence for local enhanced magmatism providing heat source to drive hydrothermal circulation. We further imply that hydrothermal activity and sulfide deposits may be rather promising along the easternmost SWIR.展开更多
In 2008-2009, hydrothermal barnacle and sediment samples were collected from the Southwest Indian Ridge during a survey of the China Ocean Mineral Resources R＆D Association （COMRA）. Samples were ana- lyzed by gas c...In 2008-2009, hydrothermal barnacle and sediment samples were collected from the Southwest Indian Ridge during a survey of the China Ocean Mineral Resources R＆D Association （COMRA）. Samples were ana- lyzed by gas chromatography-mass spectrometer （GC-MS）, revealing the main organic constituents of hy- drothermal barnacle and sediment to be fatty acids and alkylbenzenes. N-alkanes which possessed obvious even carbon advantage were also detected in hydrothermal sediment. The high concentrations of aromatic compounds might be the result of macromolecular thermal alteration. Microorganism in the submarine hydrothermal ecosystem, especially those related to sulfur metabolism, might be the source of the high con- centrations of fatty acids detected in these samples. In high temperature and high pressure hydrothermal environments, n-alkanes which possessed obvious even carbon advantage might originate from thermal alteration of carboxylic acids and other lipid compounds.展开更多
Suspended particle samples collected in the water column at 7 stations in the hydrothermal vent area in the Southwest Indian Ridge were studied by electronic scanning microscope(SEM)and energy dispersive X-ray spectro...Suspended particle samples collected in the water column at 7 stations in the hydrothermal vent area in the Southwest Indian Ridge were studied by electronic scanning microscope(SEM)and energy dispersive X-ray spectrometry(EDX).A method of zinc sulfide(ZnS)mineral phase identification by SEM and EDX data was proposed,and related adequacy and limitation of the method were presented.29 ZnS particles with various morphologies were found.27 sphalerite particles and two wurtzite particles were distinguished by joint consideration of their morphology and chemical element composition.Two types of sphalerite particles with different dissolving intensities were differentiated,which may be depended on the duration of the particles existence in the water column.More than half of the total sphalerite particles include 12high Fe-containing particles(Fe[10 wt%)were found at the Station 21VII-CTD7,suggesting a close link to the adjacent active hydrothermal vent.Sphalerite particles at Station 2VI-CTD3 contained only one Fe-containing particle and their amount ranked second among that at all the survey stations,suggesting a good correspondence to the adjacent inactive hydrothermal vent.Only six non-iron ZnS particles were found at the rest eastern 5 stations,suggesting a weak influence of hydrothermal activities in the eastern area.展开更多
基金supported by the China Ocean Min-eral Resources Research and Development Association Program (DY115- 02-1-01)the State Oceanic Administration Youth Science Fund (2010318)
文摘During January–May in 2007,the Chinese research cruise DY115-19 discovered an active hydrothermal field at 49°39′E/37°47′S on the ultraslow spreading Southwest Indian Ridge (SWIR).This was also the first active hydrothermal field found along an ultraslow-spreading ridge.We analyzed mineralogical,textural and geochemical compositions of the sulfide chimneys obtained from the 49°39′E field.Chimney samples show a concentric mineral zone around the fluid channel.The mineral assemblages of the interiors consist mainly of chalcopyrite,with pyrite and sphalerite as minor constitunets.In the intermediate portion,pyrite becomes the dominant mineral,with chalcopyrite and sphalerite as minor constitunets.For the outer wall,the majority of minerals are pyrite and sphalerite,with few chalcopyrite.Towards the outer margin of the chimney wall,the mineral grains become small and irregular in shape gradually,while minerals within interstices are abundant.These features are similar to those chimney edifices found on the East Pacific Rise and Mid-Atlantic Ridge.The average contents of Cu,Fe and Zn in our chimney samples were 2.83 wt%,45.6 wt% and 3.28 wt%,respectively.The average Au and Ag contents were up to 2.0 ppm and 70.2 ppm respectively,higher than the massive sulfides from most hydrothermal fields along mid-ocean ridge.The rare earth elements geochemistry of the sulfide chimneys show a pattern distinctive from the sulfides recovered from typical hydrothermal fields along sedimentstarved mid-ocean ridge,with the enrichment of light rare earth elements but the weak,mostly negative,Eu anomaly.This is attributed to the distinct mineralization environment or fluid compositions in this area.
基金The International Seabed Area 11th Five Year Plan Program of China Ocean Mineral Resources R&D Association under contract No. DYXM-115-01-2-1the International cooperation program of the Ministry of Science and Technology under contract No.2006DFB21620+1 种基金the program of the National Natural Science Foundation of China under contract No. 40776034Grant from the scientific research fund of the First Institute of Oceanography,SOA under contract No.GY02-2012G10
文摘Massive sulfide precipitates found in the Southwest Indian Ridge （SWIR） 49.6°E hydrothermal field are enriched in gold. Here, the mineralogy and mineral chemistry of these massive sulfides to constrain the process of gold precipitation were studied. Sulfide samples in this field include lower- temperature Zn-rich sulfides and relative higher-temperature Fe-rich sulfides. Zn-rich sulfides are dominated by sphalerite-pyrite-chalcopyrite assemblages, with concentrations of gold ranging from 9.08 to 17.0 μg/g. Fe-rich sulfides consist mainly of pyrite-marcasite-isocubanite assemblages, with gold concentrations from 2.17 to 3.79 μg/g. The significant enrichment in gold within the lower- temperature Zn-rich sulfides and the effective separation of Zn and Fe in hydrothermal precipitates at the surface of this field are here interpreted to reflect the strong temperature dependence of gold transportation and deposition within the sulfides. In Zn-rich samples, large amounts of isolated native gold grains were identified. They were found mainly as inclusions up to 8 μm in diameter, occupying porous cavities in sphalerite or in the elevated iron content rim of sphalerite. The fineness of the gold ranged from 810 to 830. Unlike previously published results on other hydrothermal fields, these data show a low gold fineness values in SWIR 49.6°E. The FeS content of sphalerite associated with gold grains ranged from 3.2 mole % to 18.9 mole %. This was higher than in other fields, indicating that the sulfur activity is relatively low during the gold precipitation process and that sulfur activity may be one of the main factors affecting gold fineness in the SWIR 49.6°E hydrothermal field. Evidence regarding gold fineness and sulfur activity suggests that gold was quite likely transported as AuHS° rather than as a Au（HS）2- complex.
基金The National Natural Science Foundation of China under contract No.91028006the Dayang 115 under contract No.DYXM115-02-3-01
文摘The morphotectonic features and their evolution of the central Southwest Indian Ridge （SWIR） are dis- cussed on the base of the high-resolution flfll-coverage bathyraetric data on the ridge between 49°-51°E. A comparative analysis of the topographic features of the axial and flank area indicates that the axial topogra- phy is alternated by the ridge and trough with en echelon pattern and evolved under a spatial-temporal mi- gration especially in 49°-50.17°E. It is probably due to the undulation at the top of the mantle asthenosphere, which is propagating with the mantle flow. From 50.17° to 50.7°E, is a topographical high terrain with a crust much thicker than the global average of the oceanic crust thickness. Its origin should be independent of the spreading mechanism of ultra-slow spreading ridges. The large numbers of volcanoes in this area indicate robust magmatic activity and may be related to the Crozet hot spot according to RMBA （residual mantle Bouguer anomaly）. The different geomorphological feature between the north and south flanks of the ridge indicates an asymmetric spreading, and leading to the development of the OCC （oceanic core complex）. The tectonic activity of the south frank is stronger than the north and is favorable to develop the OCC. The first found active hydrothermal vent in the SWIR at 37°47＇S, 49°39＇E is thought to be associated with the detach- ment fault related to the OCC.
基金The National Natural Science Foundation of China under contract No.40872063
文摘The REE compositions of hydrothermal deposits and basalt samples from the Southwest Indian Ridge （SWIR） were determined with ICP-MS. The results show that there are significant differences between different types of samples although all samples show relative LREE enrichment. The contents of REE in hydrothermal sulfides and alterated rocks samples are lower （from 7.036× 10^-6 to 23.660×10^-6）, while those in the white chimney deposits are relatively higher （ranging from 84.496 × 10^-6 to 103.511 × 10^- 6）. Both of them are lower than basalts. Chondrite-normalized REE distribution patterns show that sulfides and alterated rocks samples are characterized by significant positive Eu anomalies. On the contrary, white chimney deposits have obvious negative Eu anomalies, which may be caused by abundant calcite existing in the white chimney samples. Both the content and distribution pattern of REE in sulfides suggest that REE most possibly is originally derived from hydrothermal fluids, but influenced by the submarine reducing ore-forming environment, seawater convection, mineral compositions as well as the constraint of mineral crystallizations.
基金The National Key Research and Development Program of China under contract Nos 2017YFC0306603,2018YFC0309901,2016YFC0304905,2017YFC0306803 and 2018YFC0309902the China Ocean Mineral Resources Research and Development Association Major Project under contract Nos DY135-S1-1-01 and DY135-S1-1-02
文摘The ultraslow-spreading Southwest Indian Ridge （SWIR） to the east of the Melville fracture zone is characterized by very low melt supply and intensive tectonic activity. Due to its weak thermal budget and extremely slow spreading rate, the easternmost SWIR was considered to be devoid of hydrothermal activity until the discovery of the inactive Mt. lourdanne hydrothermal field （27°51＇S, 63°56＇E） in 1998. During the COMRA DYl15-20 cruise in 2009, two additional hydrothermal fields （i.e., the Tiancheng （27°51＇S, 63°55＇E） and Tianzuo （27°57＇S, 63°32＇E） fields） were discovered. Further detailed investigations of these two hydrothermal sites were conducted by Chinese manned submersible liaolong in 2014-2015. The Tiancheng filed can he characterized as a low- temperature （up to 13.2℃） diffuse flow hydrothermal field, and is hosted by fractured basalts with hydrothermal fauna widespread on the seafloor. The Tianzuo hydrothermal field is an inactive sulfide field, which is hosted by ultramafic rocks and controlled by detachment fault. The discovery of the three hydrothermal fields around Segment #11 which receives more melt than the regional average, provided evidence for local enhanced magmatism providing heat source to drive hydrothermal circulation. We further imply that hydrothermal activity and sulfide deposits may be rather promising along the easternmost SWIR.
基金The National Key Basic Research Program of China under contract No.2013CB429700National Special Fund for the 12th Five Year Plan of COMRA under contract Nos DY125-12-R-02 and DY125-11-R-05+1 种基金Shandong Province Natural Science Foundation of China for Distinguished Young Scholars under contract No.JQ200913the National Natural Science Foundation of China under contract Nos 40830849,40976027and 40906029
文摘In 2008-2009, hydrothermal barnacle and sediment samples were collected from the Southwest Indian Ridge during a survey of the China Ocean Mineral Resources R＆D Association （COMRA）. Samples were ana- lyzed by gas chromatography-mass spectrometer （GC-MS）, revealing the main organic constituents of hy- drothermal barnacle and sediment to be fatty acids and alkylbenzenes. N-alkanes which possessed obvious even carbon advantage were also detected in hydrothermal sediment. The high concentrations of aromatic compounds might be the result of macromolecular thermal alteration. Microorganism in the submarine hydrothermal ecosystem, especially those related to sulfur metabolism, might be the source of the high con- centrations of fatty acids detected in these samples. In high temperature and high pressure hydrothermal environments, n-alkanes which possessed obvious even carbon advantage might originate from thermal alteration of carboxylic acids and other lipid compounds.
基金supported by the Projects of China Ocean Mineral Resources Research and Development(DYXM-11502-1-13 and DY125-11-R-01-04)
文摘Suspended particle samples collected in the water column at 7 stations in the hydrothermal vent area in the Southwest Indian Ridge were studied by electronic scanning microscope(SEM)and energy dispersive X-ray spectrometry(EDX).A method of zinc sulfide(ZnS)mineral phase identification by SEM and EDX data was proposed,and related adequacy and limitation of the method were presented.29 ZnS particles with various morphologies were found.27 sphalerite particles and two wurtzite particles were distinguished by joint consideration of their morphology and chemical element composition.Two types of sphalerite particles with different dissolving intensities were differentiated,which may be depended on the duration of the particles existence in the water column.More than half of the total sphalerite particles include 12high Fe-containing particles(Fe[10 wt%)were found at the Station 21VII-CTD7,suggesting a close link to the adjacent active hydrothermal vent.Sphalerite particles at Station 2VI-CTD3 contained only one Fe-containing particle and their amount ranked second among that at all the survey stations,suggesting a good correspondence to the adjacent inactive hydrothermal vent.Only six non-iron ZnS particles were found at the rest eastern 5 stations,suggesting a weak influence of hydrothermal activities in the eastern area.
