The Yangla copper deposit, located in western Yunnan Province, China, is a typical giant, newly started mining copper deposit with an estimated Cu reserves of about 1,200,000 tons. The deposit is spatially and tempora...The Yangla copper deposit, located in western Yunnan Province, China, is a typical giant, newly started mining copper deposit with an estimated Cu reserves of about 1,200,000 tons. The deposit is spatially and temporally associated with the Linong granodiorite, which is rich in SiO2 （SIO2=58.25 wt%-69.84 wt%） and alkalis （Na20＋K20=5.98 wt%-8.34 wt%）, indicating an association with shoshonitic series to high-K calc-alkaline series granites, and shows low contents of TiO2 （0.35 wt%- 0.48 wt%）, MgO （1.51 wt%-1.72 wt%）, and A1203 （13.38 wt%-19.75 wt%）. The 34S values of sulfides of the main ore stage from copper ores vary range from -4.2%o to -0.9%o, indicating a much greater contribution from the mantle to the ore-forming fluids. The 34S values of the late ore stage is -9.8%0, indicating enrichment of biogenic sulfur which may derive from the crustal hydrothermal fluid. The 208pb/204pb, 207pb/204pb and 206pb/204pb of sulfides of the main ore stage from copper ores range within 38.66-38.73, 15.71-15.74 and 18.35-19.04, respectively, implying that the Pb was derived from the mantle, with the crustal component, probably representing mixtures of mantle lead and crustal lead. Sulfide of the late ore stage in their Pb isotopic composition, 208pb/204pb= 38.69, 207pb/204pb=15.70, 206Pb/204pb=18.35, implying that the Pb was derived from the crust. The Linong granodiorite is syn- collisional, produced by partial melting of thickened lower crust, which was triggered by the westward subduction of the Jinshajiang Oceanic plate. During a transition in geodynamic setting from collision- related compression to extension, gently dipping ductile shear zones （related to subduction） were transformed to brittle shear zones, consisting of a series of thrust faults in the Jinshajiang tectonic belt. The tensional thrust faults would have been a favorable environment for ore-forming fluids. The ascending magma provided a channel for the ore-forming fluid from the mantle wedge. After the magma arrived at the base of the early-stage Linong granodiorite, the platy granodiorite at the base of the body would have shielded the late-stage magma from the fluid. The magma would have cooled slowly, and some of the ore-forming fluid in the magma would have entered the gently dipping thrust faults near the Linong granodiorite, resulting in mineralization.展开更多
The Tongchanghe native copper-chalcocite deposit at Ninglang occurs in low-Ti basalts of western Yunnan, and the mode of fault-filling & metasomatism metallogenesis indicates that this deposit is of late-stage hyd...The Tongchanghe native copper-chalcocite deposit at Ninglang occurs in low-Ti basalts of western Yunnan, and the mode of fault-filling & metasomatism metallogenesis indicates that this deposit is of late-stage hydrothermal origin. This makes it more complicated to define the source of ore-forming materials. This paper introduces the Pb isotope data of Himalayan alkali-rich porphyries, regional Early-Middle Proterozoic metamorphic rock basement and various types of rocks of the mining district in western Yunnan with an attempt to constrain the origin of the Tongchanghe native copper-chalcocite deposit at Ninglang. The results showed that the ores are relatively homogeneous in Pb isotopic composition, implying a simple ore-forming material source. The three sets of Pb isotopic ratios in the Himalayan alkali-rich porphyries are all higher than those of the ores; the regional basement metamorphic rocks show a wide range of variations in Pb isotopic ratio, quite different from the isotopic composition of ore lead; the Pb isotopic composition of the Triassic sedimentary rocks and mudstone and siltstone interbeds in the Late Permian Heinishao Formation (corresponding to the forth cycle of basaltic eruption) in the mining district has the characteristics of radiogenic lead and is significantly different from the isotopic composition of ore lead; like the ores, the Emeishan basalts in the mining district and those regionally distributed possess the same Pb isotopic composition, showing a complete overlap with respect to their distribution range. From the above, the possibilities can be ruled out that the ore-forming materials of the Tongchanghe deposit were derived from the basement, a variety of Himalayan magmatic activities, etc. It is thereby defined that the ore-forming materials were derived largely from the Emeishan basalts. From the data available it is deduced that the native cupper-chalcocite-type metallogenesis that occurred in the Emeishan basalt-distributed area has the same metal source as the Tongchanghe deposit.展开更多
基金supported by the National Basic Research Program of China (2009CB421003,2009CB421005)by the 111 Project (Grant No. B07011)
文摘The Yangla copper deposit, located in western Yunnan Province, China, is a typical giant, newly started mining copper deposit with an estimated Cu reserves of about 1,200,000 tons. The deposit is spatially and temporally associated with the Linong granodiorite, which is rich in SiO2 （SIO2=58.25 wt%-69.84 wt%） and alkalis （Na20＋K20=5.98 wt%-8.34 wt%）, indicating an association with shoshonitic series to high-K calc-alkaline series granites, and shows low contents of TiO2 （0.35 wt%- 0.48 wt%）, MgO （1.51 wt%-1.72 wt%）, and A1203 （13.38 wt%-19.75 wt%）. The 34S values of sulfides of the main ore stage from copper ores vary range from -4.2%o to -0.9%o, indicating a much greater contribution from the mantle to the ore-forming fluids. The 34S values of the late ore stage is -9.8%0, indicating enrichment of biogenic sulfur which may derive from the crustal hydrothermal fluid. The 208pb/204pb, 207pb/204pb and 206pb/204pb of sulfides of the main ore stage from copper ores range within 38.66-38.73, 15.71-15.74 and 18.35-19.04, respectively, implying that the Pb was derived from the mantle, with the crustal component, probably representing mixtures of mantle lead and crustal lead. Sulfide of the late ore stage in their Pb isotopic composition, 208pb/204pb= 38.69, 207pb/204pb=15.70, 206Pb/204pb=18.35, implying that the Pb was derived from the crust. The Linong granodiorite is syn- collisional, produced by partial melting of thickened lower crust, which was triggered by the westward subduction of the Jinshajiang Oceanic plate. During a transition in geodynamic setting from collision- related compression to extension, gently dipping ductile shear zones （related to subduction） were transformed to brittle shear zones, consisting of a series of thrust faults in the Jinshajiang tectonic belt. The tensional thrust faults would have been a favorable environment for ore-forming fluids. The ascending magma provided a channel for the ore-forming fluid from the mantle wedge. After the magma arrived at the base of the early-stage Linong granodiorite, the platy granodiorite at the base of the body would have shielded the late-stage magma from the fluid. The magma would have cooled slowly, and some of the ore-forming fluid in the magma would have entered the gently dipping thrust faults near the Linong granodiorite, resulting in mineralization.
基金This study was financially supported by the Key Research OrientationProject of Chinese Academy of Sciences (KZCX3-SW-125).
文摘The Tongchanghe native copper-chalcocite deposit at Ninglang occurs in low-Ti basalts of western Yunnan, and the mode of fault-filling & metasomatism metallogenesis indicates that this deposit is of late-stage hydrothermal origin. This makes it more complicated to define the source of ore-forming materials. This paper introduces the Pb isotope data of Himalayan alkali-rich porphyries, regional Early-Middle Proterozoic metamorphic rock basement and various types of rocks of the mining district in western Yunnan with an attempt to constrain the origin of the Tongchanghe native copper-chalcocite deposit at Ninglang. The results showed that the ores are relatively homogeneous in Pb isotopic composition, implying a simple ore-forming material source. The three sets of Pb isotopic ratios in the Himalayan alkali-rich porphyries are all higher than those of the ores; the regional basement metamorphic rocks show a wide range of variations in Pb isotopic ratio, quite different from the isotopic composition of ore lead; the Pb isotopic composition of the Triassic sedimentary rocks and mudstone and siltstone interbeds in the Late Permian Heinishao Formation (corresponding to the forth cycle of basaltic eruption) in the mining district has the characteristics of radiogenic lead and is significantly different from the isotopic composition of ore lead; like the ores, the Emeishan basalts in the mining district and those regionally distributed possess the same Pb isotopic composition, showing a complete overlap with respect to their distribution range. From the above, the possibilities can be ruled out that the ore-forming materials of the Tongchanghe deposit were derived from the basement, a variety of Himalayan magmatic activities, etc. It is thereby defined that the ore-forming materials were derived largely from the Emeishan basalts. From the data available it is deduced that the native cupper-chalcocite-type metallogenesis that occurred in the Emeishan basalt-distributed area has the same metal source as the Tongchanghe deposit.
