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 (Na2O+K2O=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 Al2O3 (13.38 wt%-19.75 wt%). The δ34S values of sulfides of the main ore stage from copper ores vary range from ?4.2‰ to ?0.9‰, indicating a much greater contribution from the mantle to the ore-forming fluids. The δ34S values of the late ore stage is 9.8‰, 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
Four layers of cherts were found for the first time in the Yanglacopper deposit, western Yunnan Province. The cherts possessed the following geochemical characteristics: ① Low TiO2 and Al2O3 contents, but high ore-fo...Four layers of cherts were found for the first time in the Yanglacopper deposit, western Yunnan Province. The cherts possessed the following geochemical characteristics: ① Low TiO2 and Al2O3 contents, but high ore-forming element (e.g. Cu, Au, Ag) contents; ② low total REE contents and clear negative Eu anomalies when normalized to chondrite similar to the REE contents and distribution patterns of associated massive sulfide ores; ③ silicon isotopic compositions of cherts in the Yangla deposit being the same as cherts and geyserite of hot-water sedimentary origin; ④ lead and sulfur isotopic compositions of cherts in the Yangla deposit being similar to those of the massive sulfide ores in the Yangla deposit; ⑤ Rb-Sr isochron age of cherts from the Yangla deposit being identical with that of host strata. Hence, we conclude that the cherts in the Yangla deposit are of hot-water sedimentary origin, which have a close relationship with the massive sulfide ores. The discovery of hydrothermal cherts from the Yangla copper deposit provides further evidence for the hydrothermal exhalative origin of the massive sulfide deposits.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 (Na2O+K2O=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 Al2O3 (13.38 wt%-19.75 wt%). The δ34S values of sulfides of the main ore stage from copper ores vary range from ?4.2‰ to ?0.9‰, indicating a much greater contribution from the mantle to the ore-forming fluids. The δ34S values of the late ore stage is 9.8‰, 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 work was jointly supported by key project of Chinese Academy of Sciences (KZ952-S1-407) state Key Project of China (G1999043208 and 1999043210) China Postdoctoral Science Foundation.
文摘Four layers of cherts were found for the first time in the Yanglacopper deposit, western Yunnan Province. The cherts possessed the following geochemical characteristics: ① Low TiO2 and Al2O3 contents, but high ore-forming element (e.g. Cu, Au, Ag) contents; ② low total REE contents and clear negative Eu anomalies when normalized to chondrite similar to the REE contents and distribution patterns of associated massive sulfide ores; ③ silicon isotopic compositions of cherts in the Yangla deposit being the same as cherts and geyserite of hot-water sedimentary origin; ④ lead and sulfur isotopic compositions of cherts in the Yangla deposit being similar to those of the massive sulfide ores in the Yangla deposit; ⑤ Rb-Sr isochron age of cherts from the Yangla deposit being identical with that of host strata. Hence, we conclude that the cherts in the Yangla deposit are of hot-water sedimentary origin, which have a close relationship with the massive sulfide ores. The discovery of hydrothermal cherts from the Yangla copper deposit provides further evidence for the hydrothermal exhalative origin of the massive sulfide deposits.
