The Tongling ore district is one of the most economically important ore areas in the Middle–Lower Yangtze River Metallogenic Belt, eastern China. It contains hundreds of polymetallic copper–gold deposits and occurre...The Tongling ore district is one of the most economically important ore areas in the Middle–Lower Yangtze River Metallogenic Belt, eastern China. It contains hundreds of polymetallic copper–gold deposits and occurrences. Those deposits are mainly clustered(from west to east) within the Tongguanshan, Shizishan, Xinqiao, Fenghuangshan, and Shatanjiao orefields. Until recently, the majority of these deposits were thought to be skarn-or porphyry–skarn-type deposits; however there have been recent discoveries of numerous vein-type Au, Ag, and Pb-Zn deposits that do not fall into either of these categories. This indicates that there is some uncertainty over this classification. Here, we present the results of several systematic geological studies of representative deposits in the Tongling ore district. From investigation of the ore-controlling structures, lithology of the host rock, mineral assemblages, and the characteristics of the mineralization and alteration within these deposits, three genetic types of deposits(skarn-, porphyry-, and vein-type deposits) have been identified. The spatial and temporal relationships between the orebodies and Yanshanian intrusions combined with the sources of the ore-forming fluids and metals, as well as the geodynamic setting of this ore district, indicate that all three deposit types are genetically related each other and constitute a magmatic–hydrothermal system. This study outlines a model that relates the polymetallic copper–gold porphyry-, skarn-, and vein-type deposits within the Tongling ore district. This model provides a theoretical basis to guide exploration for deep-seated and concealed porphyry-type Cu(–Mo, –Au) deposits as well as shallow vein-type Au, Ag, and Pb–Zn deposits in this area and elsewhere.展开更多
The Nyasirori gold deposit,located in the middle-western end of the Musoma-Mara Archean greenstone belt in Tanzania,is a tectonic altered rock type gold deposit controlled by shear tectonic zone.This work conducted hi...The Nyasirori gold deposit,located in the middle-western end of the Musoma-Mara Archean greenstone belt in Tanzania,is a tectonic altered rock type gold deposit controlled by shear tectonic zone.This work conducted high-precision ground magnetic measurements to delineate fault structures and favorable prospecting targets,utilized induced polarization(IP)intermediate gradient to roughly determine the distribution and extension of the tectonic altered zone and gold ore(mineralized)bodies,and further carried out IP sounding and magnetotelluric sounding to locate the tectonic altered zone and gold ore(mineralized)bodies.The anomalous gradient belt of the combination of positive and negative micromagnetic measurements reflects the detail of shallow surface tectonic alteration zone and gold mineralization body.Micromagnetic profile anomalies indicate the spatial location and occurrence of concealed tectonic alteration zone and gold(mineralized)ore bodies.Soil geochemical measurements indicate that the ore-forming element Au correlates well with As and Sb,and As and Sb anomalies have a good indication to gold orebodies.Based on the multi-source geological-geophysical-geochemical information of the Nyasirori gold deposit,this work established an integrated prospecting model and proposed a set of geophysical and geochemical methods for optimizing prospecting targets.展开更多
The Gacun Kuroko-type deposit, Southwestern China, is hosted in rhyolitic rocks associated with the underlying mafic rocks occurred in the - 1000 m deep fault - bounded basin within the intra -arc rifting zone which f...The Gacun Kuroko-type deposit, Southwestern China, is hosted in rhyolitic rocks associated with the underlying mafic rocks occurred in the - 1000 m deep fault - bounded basin within the intra -arc rifting zone which formed on the Triassic Yidun island - arc. Two vertically separated alteration systems are recognized: one is conformable or semiconformable alteration zone developed in - 150 m thick mafic unit 1-1.5 km below the massive sulfide ore body; the other is discordant alteration pipe directly surrounded around stockwork ore within rhyolitic unit. The lower conformable alteration zone extending for several kilometers along strike is characterized by silicification and epidotization which result in the development of quartz vein and quartz-epidote vein systems in mafic lava flows and replacement of primary minerals and groundmass in spilitized mafic volcanics and dikes by quartz, epidote - group minerals and sodic plagioclase. Sulfides often occur in the vein system and altered mafic volcanics. Quartz solubility relation indicates that silicification is a consequence of interaction of Si- saturated fluids with mafic rocks in a higher temperature system (T>340℃), intensifying by intrusion of mafic dike or high-level acidic magma chamber. The alteration pipe of diameter about 2 km shows a similar mineralogical zoning to Kuroko deposits of Japan. The sequence is quartz + hyalophane; sericite + chlorite + quartz and zeolite-like zones from core to margins of the pipe. The chlorite core only occurs in the root part of the alteration pipe and downwards transfers into epidote - chlorite and epidote - quartz vein swarm extending 500 m downwards. The felsic rocks away from the orebody and alteration pipe took place district-scale alteration, which has typical low-temperature mineral association: illite + albite + quartz + calcite. Whole -rock and quartz δ18O values indicate that district - scale alteration is a result of interaction of seawater with rocks at lower temperature (T<200℃)under water-dominated condition. However, the altered rocks from the pipe show remarkably δ18O enrichment, and bulk -rock δ18O values decreased gradually toward stockwork orebody from 15.1‰-l5. 75‰ in zeolite-like zone and 12. 05‰-14. 2‰ in sericite - quartz zone to 11.3 ‰ - 14. 4‰ in quartz - hyalophane zone. The filled temperatures of fluid inclusions in quartz and sphalerite lie in the ranges of 280 -320 ℃ for quartz - hyalophane zone and 250 ℃ to 297 ℃ for sericite-quartz zone. The estimated δ18O values of hydrothermal fluids are 7. 98‰ and3.2‰, respectively, based on quartz δ18O data in the deposit. The lower conformable alteration is considered to be approximately coeval with the alteration pipe, based on the SiO2 concentration in the fluids, which restrict the main fluid - rock reaction zone to be located in mafic horizon by quartz barometer, and metal element flux calculation and sulfide - epidote vein system developed both in alteration systems. High - salinity fluid inclusions in gangue quartz (>8% eq. NaCl) from stockwork ore and in quartz phenocryst (>40% eq. NaCl) in footwall rhyolite strongly suggest the existence of hot-saline brine to react with mafic complex and leach metal components, which probably originates mainly from magmatic fluid derived from high-level acidic magma chamber. The brine layer located in mafic unit possibly heats and drives the overlying single -pass convective seawater reacting with felsic rocks. The 'density window' may be expected to occur on the interface between seawater and brine layer, when the brine becomes to be gravitationally instability by the turbulent entrainment of seawater during magmatic and/or tectonic activities. The sulfide mineralization and alteration pipe is inter preted as an effect of the 'density window' through which the mixed fluids of brine with seawater adiabatically discharges upwards.展开更多
Metallogenic models of gold deposits of quartz vein type and altered rock type will be dis-cussed in this note. They are considered to be closely related to granite spatially andgenetically.
基金funded by the National Natural Science Foundation of China(NSFC)(grant numbers 41472066,40972063 and 41672038)the Program of the Deep Exploration in China(SinoProb-03-05)+1 种基金the National KeyR&S Program of China(2016 YFC0600209)the Land and Resources Science and Techonolgy Foundation of Anhui Province(2016-K-03 and No.2014-K-03)
文摘The Tongling ore district is one of the most economically important ore areas in the Middle–Lower Yangtze River Metallogenic Belt, eastern China. It contains hundreds of polymetallic copper–gold deposits and occurrences. Those deposits are mainly clustered(from west to east) within the Tongguanshan, Shizishan, Xinqiao, Fenghuangshan, and Shatanjiao orefields. Until recently, the majority of these deposits were thought to be skarn-or porphyry–skarn-type deposits; however there have been recent discoveries of numerous vein-type Au, Ag, and Pb-Zn deposits that do not fall into either of these categories. This indicates that there is some uncertainty over this classification. Here, we present the results of several systematic geological studies of representative deposits in the Tongling ore district. From investigation of the ore-controlling structures, lithology of the host rock, mineral assemblages, and the characteristics of the mineralization and alteration within these deposits, three genetic types of deposits(skarn-, porphyry-, and vein-type deposits) have been identified. The spatial and temporal relationships between the orebodies and Yanshanian intrusions combined with the sources of the ore-forming fluids and metals, as well as the geodynamic setting of this ore district, indicate that all three deposit types are genetically related each other and constitute a magmatic–hydrothermal system. This study outlines a model that relates the polymetallic copper–gold porphyry-, skarn-, and vein-type deposits within the Tongling ore district. This model provides a theoretical basis to guide exploration for deep-seated and concealed porphyry-type Cu(–Mo, –Au) deposits as well as shallow vein-type Au, Ag, and Pb–Zn deposits in this area and elsewhere.
基金This work is financially supported by the Special Fund for Foreign Mineral Resources Risk Exploration(201210B01600234).
文摘The Nyasirori gold deposit,located in the middle-western end of the Musoma-Mara Archean greenstone belt in Tanzania,is a tectonic altered rock type gold deposit controlled by shear tectonic zone.This work conducted high-precision ground magnetic measurements to delineate fault structures and favorable prospecting targets,utilized induced polarization(IP)intermediate gradient to roughly determine the distribution and extension of the tectonic altered zone and gold ore(mineralized)bodies,and further carried out IP sounding and magnetotelluric sounding to locate the tectonic altered zone and gold ore(mineralized)bodies.The anomalous gradient belt of the combination of positive and negative micromagnetic measurements reflects the detail of shallow surface tectonic alteration zone and gold mineralization body.Micromagnetic profile anomalies indicate the spatial location and occurrence of concealed tectonic alteration zone and gold(mineralized)ore bodies.Soil geochemical measurements indicate that the ore-forming element Au correlates well with As and Sb,and As and Sb anomalies have a good indication to gold orebodies.Based on the multi-source geological-geophysical-geochemical information of the Nyasirori gold deposit,this work established an integrated prospecting model and proposed a set of geophysical and geochemical methods for optimizing prospecting targets.
基金The study is supported by Agence of International Science and Technology, Japan
文摘The Gacun Kuroko-type deposit, Southwestern China, is hosted in rhyolitic rocks associated with the underlying mafic rocks occurred in the - 1000 m deep fault - bounded basin within the intra -arc rifting zone which formed on the Triassic Yidun island - arc. Two vertically separated alteration systems are recognized: one is conformable or semiconformable alteration zone developed in - 150 m thick mafic unit 1-1.5 km below the massive sulfide ore body; the other is discordant alteration pipe directly surrounded around stockwork ore within rhyolitic unit. The lower conformable alteration zone extending for several kilometers along strike is characterized by silicification and epidotization which result in the development of quartz vein and quartz-epidote vein systems in mafic lava flows and replacement of primary minerals and groundmass in spilitized mafic volcanics and dikes by quartz, epidote - group minerals and sodic plagioclase. Sulfides often occur in the vein system and altered mafic volcanics. Quartz solubility relation indicates that silicification is a consequence of interaction of Si- saturated fluids with mafic rocks in a higher temperature system (T>340℃), intensifying by intrusion of mafic dike or high-level acidic magma chamber. The alteration pipe of diameter about 2 km shows a similar mineralogical zoning to Kuroko deposits of Japan. The sequence is quartz + hyalophane; sericite + chlorite + quartz and zeolite-like zones from core to margins of the pipe. The chlorite core only occurs in the root part of the alteration pipe and downwards transfers into epidote - chlorite and epidote - quartz vein swarm extending 500 m downwards. The felsic rocks away from the orebody and alteration pipe took place district-scale alteration, which has typical low-temperature mineral association: illite + albite + quartz + calcite. Whole -rock and quartz δ18O values indicate that district - scale alteration is a result of interaction of seawater with rocks at lower temperature (T<200℃)under water-dominated condition. However, the altered rocks from the pipe show remarkably δ18O enrichment, and bulk -rock δ18O values decreased gradually toward stockwork orebody from 15.1‰-l5. 75‰ in zeolite-like zone and 12. 05‰-14. 2‰ in sericite - quartz zone to 11.3 ‰ - 14. 4‰ in quartz - hyalophane zone. The filled temperatures of fluid inclusions in quartz and sphalerite lie in the ranges of 280 -320 ℃ for quartz - hyalophane zone and 250 ℃ to 297 ℃ for sericite-quartz zone. The estimated δ18O values of hydrothermal fluids are 7. 98‰ and3.2‰, respectively, based on quartz δ18O data in the deposit. The lower conformable alteration is considered to be approximately coeval with the alteration pipe, based on the SiO2 concentration in the fluids, which restrict the main fluid - rock reaction zone to be located in mafic horizon by quartz barometer, and metal element flux calculation and sulfide - epidote vein system developed both in alteration systems. High - salinity fluid inclusions in gangue quartz (>8% eq. NaCl) from stockwork ore and in quartz phenocryst (>40% eq. NaCl) in footwall rhyolite strongly suggest the existence of hot-saline brine to react with mafic complex and leach metal components, which probably originates mainly from magmatic fluid derived from high-level acidic magma chamber. The brine layer located in mafic unit possibly heats and drives the overlying single -pass convective seawater reacting with felsic rocks. The 'density window' may be expected to occur on the interface between seawater and brine layer, when the brine becomes to be gravitationally instability by the turbulent entrainment of seawater during magmatic and/or tectonic activities. The sulfide mineralization and alteration pipe is inter preted as an effect of the 'density window' through which the mixed fluids of brine with seawater adiabatically discharges upwards.
基金Project supported by Doctorate Foundation of the State Education Commission of China.
文摘Metallogenic models of gold deposits of quartz vein type and altered rock type will be dis-cussed in this note. They are considered to be closely related to granite spatially andgenetically.
