Four samples of plagioclase and biotite from the Shaxi porphyry in the lower part of the Yangtze metallogenic belt were analyzed for age determination with the ^40 Ar/^39Ar method. The results yield reproducible ages ...Four samples of plagioclase and biotite from the Shaxi porphyry in the lower part of the Yangtze metallogenic belt were analyzed for age determination with the ^40 Ar/^39Ar method. The results yield reproducible ages of 126 Ma to 135 Ma with a high level of confidence according to the agreement between isochron and plateau ages. The four Ar-Ar ages are relatively consistent within the analytical error. These ages are also consistent with, but more precise than, previous K-Ar and Rb-Sr ages and thus provide better constraints on the time of porphyry formation and associated Cu-Au mineralization along the middle to lower part of the Yangtze metallogenic belt. The ages of 126 to 135 Ma are interpreted to represent the intrusive time of the Shaxi porphyry, so that the Cu-Au mineralization should have occurred later due to the post-magmatic hydrothermal event.展开更多
Ali Javad porphyry Cu-Au deposit is located 20 Km north of Ahar city in Arasbaran metallogenic zone which is considered as a part of Alp-Himalayan mineralization belt. Magmatism in this area began in Late Cretaceous, ...Ali Javad porphyry Cu-Au deposit is located 20 Km north of Ahar city in Arasbaran metallogenic zone which is considered as a part of Alp-Himalayan mineralization belt. Magmatism in this area began in Late Cretaceous, followed by extensive magmatism in Cenozoic and Quaternary periods. Porphyry type mineralization developed in Ali Javad quartz monzonitic porphyry stock and Eocene pyroclastic and volcanic country rocks. Ali Javad porphyry intrusion has shoshonitic nature and shows characteristics of volcanic arc granitoids that it is have been emplaced in a post-collision tectonic setting. Alteration zones at the deposit demonstrated zoning which is comparable with Lowel-Guilbert model proposed for quartz-monzonite type porphyry copper deposits. Phyllic, argillic, silicic and propylitic alteration zones were observed at the surface while potassic alteration zone could be observed at depth in drill core samples. Mineralization was recognized both as supergene and hypogene, the latter was as veins, veinlets and disseminations. Dominant hypogene minerals were chalcopyrite, bornite, molybdenite, pyrite and magnetite while chalcocite, covellite and limonite were dominant supergene minerals. Four mineralization zones were observed in the deposit as leached, transitional, supergene and hypogene zones. Average grades were 0.75% for copper and 1.86 ppm for gold with 81.5 Mt proved reserve for copper and 37.8 Mt for gold.展开更多
Shaxi porphyry Cu-Au deposit was one of the important discoveries of the exploration in the middle-lower reaches of Yangtze River in China in 1970s. Gold occurrence in the Shaxi porphyry copper-gold deposit (central (...Shaxi porphyry Cu-Au deposit was one of the important discoveries of the exploration in the middle-lower reaches of Yangtze River in China in 1970s. Gold occurrence in the Shaxi porphyry copper-gold deposit (central (Anhui) province, eastern China) was investigated by means of microscope analyses, EPMA and PIXE. Combined with geological and mineralogical methods, the characteristics of occurrence of gold in the large scale sulfide mineralization in this region were fully investigated. The results show that gold distributes in both chalcopyrite and pyrite as submicroscopic inclusions (less than 1 μm) . Au is positively correlated with As, Fe, S, Cu, Zn and Ti. The condition of gold transformation in thermal fluid system controlling deposition of Au in the region is probably the oxidation potential of the red sedimentary rocks of shale and fine grain sandstone which may be crucial as a geochemical barrier to the reducing fluid. This study lays foundation for the further research and exploration of the porphyry copper-gold deposit both theoretically and practically in the lower reaches of Yangtze region.展开更多
Lithocaps are composed of silicic and advanced argillic altered rocks,and represent an important target for porphyry-epithermal Cu-Au exploration.Previous studies showed that integrating alunite spectral and compositi...Lithocaps are composed of silicic and advanced argillic altered rocks,and represent an important target for porphyry-epithermal Cu-Au exploration.Previous studies showed that integrating alunite spectral and composition with lithocap whole-rock geochemistry can effectively aid exploration for concealed Cu-Au mineralization.The Zijinshan Cu-Au and Dafanshan alunite deposits are located in the Coastal Volcanic Belt in SE China,where alunite is an indicator of hypogene mineralization and alteration.Detailed mineralogical studies of alunite from these two deposits were performed with short-wavelength infrared spectroscopy(SWIR),whole-rock geochemistry and laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS).For Zijinshan,wavelength variation of the SWIR alunite absorption peak at 1480 nm is proportional to the whole-rock Na/(Na+K)molar ratio of alunitebearing samples.Different percentage of alunite and mineral assemblages in the lithocap samples would both affect the wavelength of the SWIR alunite absorption peak at1480 nm.We suggest that the alunite Ba-Bi contents and the whole-rock Nb/La value(of alunite-bearing rocks)are reliable vectoring tools for detecting magmatic-hydrothermal mineralization center in the district.Comparing the alunite SWIR spectral and mineral geochemical features and whole-rock geochemistry of alunite-bearing rocks between the Zijinshan and Dafanshan deposits,Au–Ag mineralization may be concealed at depth in northwestern Dafanshan.展开更多
基金This study is supported by funds from the Ministry of Science and Technology of China （2006CB403500） ； National Natural Science Foundation of China （40473021）.
文摘Four samples of plagioclase and biotite from the Shaxi porphyry in the lower part of the Yangtze metallogenic belt were analyzed for age determination with the ^40 Ar/^39Ar method. The results yield reproducible ages of 126 Ma to 135 Ma with a high level of confidence according to the agreement between isochron and plateau ages. The four Ar-Ar ages are relatively consistent within the analytical error. These ages are also consistent with, but more precise than, previous K-Ar and Rb-Sr ages and thus provide better constraints on the time of porphyry formation and associated Cu-Au mineralization along the middle to lower part of the Yangtze metallogenic belt. The ages of 126 to 135 Ma are interpreted to represent the intrusive time of the Shaxi porphyry, so that the Cu-Au mineralization should have occurred later due to the post-magmatic hydrothermal event.
文摘Ali Javad porphyry Cu-Au deposit is located 20 Km north of Ahar city in Arasbaran metallogenic zone which is considered as a part of Alp-Himalayan mineralization belt. Magmatism in this area began in Late Cretaceous, followed by extensive magmatism in Cenozoic and Quaternary periods. Porphyry type mineralization developed in Ali Javad quartz monzonitic porphyry stock and Eocene pyroclastic and volcanic country rocks. Ali Javad porphyry intrusion has shoshonitic nature and shows characteristics of volcanic arc granitoids that it is have been emplaced in a post-collision tectonic setting. Alteration zones at the deposit demonstrated zoning which is comparable with Lowel-Guilbert model proposed for quartz-monzonite type porphyry copper deposits. Phyllic, argillic, silicic and propylitic alteration zones were observed at the surface while potassic alteration zone could be observed at depth in drill core samples. Mineralization was recognized both as supergene and hypogene, the latter was as veins, veinlets and disseminations. Dominant hypogene minerals were chalcopyrite, bornite, molybdenite, pyrite and magnetite while chalcocite, covellite and limonite were dominant supergene minerals. Four mineralization zones were observed in the deposit as leached, transitional, supergene and hypogene zones. Average grades were 0.75% for copper and 1.86 ppm for gold with 81.5 Mt proved reserve for copper and 37.8 Mt for gold.
文摘Shaxi porphyry Cu-Au deposit was one of the important discoveries of the exploration in the middle-lower reaches of Yangtze River in China in 1970s. Gold occurrence in the Shaxi porphyry copper-gold deposit (central (Anhui) province, eastern China) was investigated by means of microscope analyses, EPMA and PIXE. Combined with geological and mineralogical methods, the characteristics of occurrence of gold in the large scale sulfide mineralization in this region were fully investigated. The results show that gold distributes in both chalcopyrite and pyrite as submicroscopic inclusions (less than 1 μm) . Au is positively correlated with As, Fe, S, Cu, Zn and Ti. The condition of gold transformation in thermal fluid system controlling deposition of Au in the region is probably the oxidation potential of the red sedimentary rocks of shale and fine grain sandstone which may be crucial as a geochemical barrier to the reducing fluid. This study lays foundation for the further research and exploration of the porphyry copper-gold deposit both theoretically and practically in the lower reaches of Yangtze region.
基金financially supported by the National Natural Science Foundation of China(Grant No.41925011)the National Key Research and Development Program of China(Grant No.2022YFC2903601)。
文摘Lithocaps are composed of silicic and advanced argillic altered rocks,and represent an important target for porphyry-epithermal Cu-Au exploration.Previous studies showed that integrating alunite spectral and composition with lithocap whole-rock geochemistry can effectively aid exploration for concealed Cu-Au mineralization.The Zijinshan Cu-Au and Dafanshan alunite deposits are located in the Coastal Volcanic Belt in SE China,where alunite is an indicator of hypogene mineralization and alteration.Detailed mineralogical studies of alunite from these two deposits were performed with short-wavelength infrared spectroscopy(SWIR),whole-rock geochemistry and laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS).For Zijinshan,wavelength variation of the SWIR alunite absorption peak at 1480 nm is proportional to the whole-rock Na/(Na+K)molar ratio of alunitebearing samples.Different percentage of alunite and mineral assemblages in the lithocap samples would both affect the wavelength of the SWIR alunite absorption peak at1480 nm.We suggest that the alunite Ba-Bi contents and the whole-rock Nb/La value(of alunite-bearing rocks)are reliable vectoring tools for detecting magmatic-hydrothermal mineralization center in the district.Comparing the alunite SWIR spectral and mineral geochemical features and whole-rock geochemistry of alunite-bearing rocks between the Zijinshan and Dafanshan deposits,Au–Ag mineralization may be concealed at depth in northwestern Dafanshan.
