The Abra deposit,a large lead-silver-copper–gold polymetallic deposit in Western Australia,is located at the eastern of the metallogenic belt of the Jillawarra basin in the Bangemall basin.The 4 th to the 6 th rock s...The Abra deposit,a large lead-silver-copper–gold polymetallic deposit in Western Australia,is located at the eastern of the metallogenic belt of the Jillawarra basin in the Bangemall basin.The 4 th to the 6 th rock section of the Irrigully Group of Edmund Series are the principal ore-host strata,composed mainly of sandstone and fine sandstone.The orebody in Abra can be classified into two types as upper layer-like lead-silver and lower veins or netvein copper–gold.The metal minerals are mainly galena,chalcopyrite,and pyrite,while the gangue minerals are mainly quartz,dolomite,and barite.Both ReOs isotopic age of the pyrite(1329.5±98 Ma)with the initial(187Os/188Os)=5.0±3.8 and Pb isotopic compositions(206 Pb/204 Pb=15.914–15.967,207Pb/204Pb=15.425–15.454,208Pb/204Pb=35.584–35.667)suggests that the metal minerals were sourced from the wall-rocks.d DV-SMOWvalues of quartz range from-35%to-17%whereas d18 OV-SMOWvalue range from 12%to 16%which indicates that the ore-forming fluids of Abra were mediumlow temperature and medium–low salinity,and were mainly metamorphic water and secondary atmospheric precipitation.When the medium–low temperature oreforming fluids are mixed with oxidizing reducing fluids carrying a large number of metal substances,a large number of ore-forming substances will be precipitated when the physical and chemical conditions change,thus it can be considered that the Abra deposit is a medium–low temperature hydrothermal polymetallic deposit.展开更多
The Phapon gold deposit, located in northern Laos, is a unique large-scale gold deposit in Luang Prabang-Loei metallogenic belt. It is hosted in the Lower Permian limestone and controlled by a NE-trending ductile-brit...The Phapon gold deposit, located in northern Laos, is a unique large-scale gold deposit in Luang Prabang-Loei metallogenic belt. It is hosted in the Lower Permian limestone and controlled by a NE-trending ductile-brittle fault system. There are three types of primary ore including auriferous calcite vein type, disseminated type, and breccia type, and the first two are important in the Phapon gold deposit. Based on fluid inclusion petrography and microthermometry, three types of primary fluid inclusions including type 1 liquid-rich aqueous, type 2 vapor-rich aqueous and type 3 daughter mineralbearing aqueous were identified in hydrothermal calcite grains. The ore-forming fluids are normally homogeneous, as indicated by the widespread type 1 inclusions with identical composition. The coexistence of type 1 and type 2 inclusions, showing similar final homogenization temperature but different compositions, indicate that fluid immiscibility did locally take place in both two types of ores. The results of microthermometry and H-O isotopes geochemistry indicate that there are little differences on ore-fluid geochemistry between the auriferous calcite vein-type and disseminated type ores. The oreforming fluids are characterized by medium-low temperatures(157–268 oC) and low salinity(1.6 wt.%–9.9 wt.% NaCl eq.). It is likely to have a metamorphic-dominant mixed source, which could be associated with dehydration and decarbonisation of Lower Permian limestone and Middle–Upper Triassic sandstones during the dynamic metamorphism. The fluid-wallrock interaction played a major role, and the locally occurred fluid-immiscible processes played a subordinate role in gold precipitation. Combined with the regional and ore deposit geology, and ore-fluid geochemistry, we suggest that the Phapon gold deposit is best considered to be a member of the epizonal orogenic deposit class.展开更多
基金funded by the Joint Fund Projects(U1812402)the National Natural Science Foundation of China(41103024)the“Financial Subsidy for Overseas Mineral Resource Risk Exploration in 2010”project。
文摘The Abra deposit,a large lead-silver-copper–gold polymetallic deposit in Western Australia,is located at the eastern of the metallogenic belt of the Jillawarra basin in the Bangemall basin.The 4 th to the 6 th rock section of the Irrigully Group of Edmund Series are the principal ore-host strata,composed mainly of sandstone and fine sandstone.The orebody in Abra can be classified into two types as upper layer-like lead-silver and lower veins or netvein copper–gold.The metal minerals are mainly galena,chalcopyrite,and pyrite,while the gangue minerals are mainly quartz,dolomite,and barite.Both ReOs isotopic age of the pyrite(1329.5±98 Ma)with the initial(187Os/188Os)=5.0±3.8 and Pb isotopic compositions(206 Pb/204 Pb=15.914–15.967,207Pb/204Pb=15.425–15.454,208Pb/204Pb=35.584–35.667)suggests that the metal minerals were sourced from the wall-rocks.d DV-SMOWvalues of quartz range from-35%to-17%whereas d18 OV-SMOWvalue range from 12%to 16%which indicates that the ore-forming fluids of Abra were mediumlow temperature and medium–low salinity,and were mainly metamorphic water and secondary atmospheric precipitation.When the medium–low temperature oreforming fluids are mixed with oxidizing reducing fluids carrying a large number of metal substances,a large number of ore-forming substances will be precipitated when the physical and chemical conditions change,thus it can be considered that the Abra deposit is a medium–low temperature hydrothermal polymetallic deposit.
基金financially supported by the China Geological Survey Project (No. 121201010000150013)
文摘The Phapon gold deposit, located in northern Laos, is a unique large-scale gold deposit in Luang Prabang-Loei metallogenic belt. It is hosted in the Lower Permian limestone and controlled by a NE-trending ductile-brittle fault system. There are three types of primary ore including auriferous calcite vein type, disseminated type, and breccia type, and the first two are important in the Phapon gold deposit. Based on fluid inclusion petrography and microthermometry, three types of primary fluid inclusions including type 1 liquid-rich aqueous, type 2 vapor-rich aqueous and type 3 daughter mineralbearing aqueous were identified in hydrothermal calcite grains. The ore-forming fluids are normally homogeneous, as indicated by the widespread type 1 inclusions with identical composition. The coexistence of type 1 and type 2 inclusions, showing similar final homogenization temperature but different compositions, indicate that fluid immiscibility did locally take place in both two types of ores. The results of microthermometry and H-O isotopes geochemistry indicate that there are little differences on ore-fluid geochemistry between the auriferous calcite vein-type and disseminated type ores. The oreforming fluids are characterized by medium-low temperatures(157–268 oC) and low salinity(1.6 wt.%–9.9 wt.% NaCl eq.). It is likely to have a metamorphic-dominant mixed source, which could be associated with dehydration and decarbonisation of Lower Permian limestone and Middle–Upper Triassic sandstones during the dynamic metamorphism. The fluid-wallrock interaction played a major role, and the locally occurred fluid-immiscible processes played a subordinate role in gold precipitation. Combined with the regional and ore deposit geology, and ore-fluid geochemistry, we suggest that the Phapon gold deposit is best considered to be a member of the epizonal orogenic deposit class.
