Mineralogical zonation of wall rock alterations in Mesozoic granitoids is summarized from 18 gold deposits in Jiaodong gold province on the Asian mobile continental margin of the west circum Pacific rim. This paper ...Mineralogical zonation of wall rock alterations in Mesozoic granitoids is summarized from 18 gold deposits in Jiaodong gold province on the Asian mobile continental margin of the west circum Pacific rim. This paper deals with wall rock alterations developed around gold mineralizations of the quartz vein type in granitoids and the wall rock alteration type in granitoid basement contacts along Mesozoic fault zones trending mostly NNE SSW and NE SW. Five alteration zones are distinguished from host rock to ore zone, namely the chloritization and sericitization zone, the hematitization rutilization and microclinization zone, the quartz sericitization zone, the pyrite quartz sericitization zone and the pyrite silicification zone. The former two are outer zones marked by incomplete alteration of first mafic and then felsic minerals of the granitoids, while the later three are inner zones marked by complete alteration of both mafic and felsic minerals of the granitoids leading to retrogressive sericitization and progressive silicification with participation of ore elements. The whole process proceeds under dynamometamorphism with high fugacity of volatiles. Wall rock alteration is the intermediate link between unaltered host rock and ore mineralization both in time and space. Development of the alteration zonation and its mineral composition controls genetic type of mineralization, size and grade of the deposit and location of the ore zones.展开更多
The Baoban gold field, located in the area of Hainan Island, South China, bears three gold de-posits: Tuwaishan, Baoban, and Erjia, which belong to the wall-rock alteration type. In terms of the petrography data, four...The Baoban gold field, located in the area of Hainan Island, South China, bears three gold de-posits: Tuwaishan, Baoban, and Erjia, which belong to the wall-rock alteration type. In terms of the petrography data, four alteration zones can be recognized from the ore-vein outwards: (1) the silicification zone; (2) the sericitization zone, (3) the chloritization zone; and (4) the calcitization zone. The geochemical kinetic simulation was carried out on sericitization and chloritization . Results of the study showed that the formation of the alteration zones is connected with the properties of hydrothermal fluids: the initial concentration of Al (O H)3, the diffusion coefficient and the velocity of fluid flow. The alteration zones in this field are the result of multiple interaction between hydrothermal fluids and wall rocks.展开更多
Abstract The Shibangou gold deposit in western Henan is associated with irregular quartz veinlets occurring in altered shear zones dissecting a dioritic intrusion. The altered shear zones are characterized by silicifi...Abstract The Shibangou gold deposit in western Henan is associated with irregular quartz veinlets occurring in altered shear zones dissecting a dioritic intrusion. The altered shear zones are characterized by silicification, pyritization, sericilization, chloritization and K-feldspar alteration. Zoning of altered rocks adjacent to the Au-bearing quartz veins is obviously exhibited. Fine-grained sulphides and quartz veinlets of different ages and small-scale fissures are widely distributed in the central part of the altered zones. Major mineralization types in this gold deposit are Au-bearing quartz veinlets and altered rocks in the shear zones. Samples were collected from drilling cores according to the alteration zoning and mineralization type and all samples were analyzed for major and trace elements. Mass balance, volume change (fv=97.3–71.9%) and major element variation sequences are studied in terms of major elements. The changes of mobile components (SiO2, K2O, Fe2O3) and CaO) and immobile component (Al2O3) in the wall-rock alteration are discussed. The gold mineralization is associated with the enrichment of As, Ag, Hg and Pb and depletion of Cu and Zn. The study of compositional variation of altered rocks proves to be a very efficient method for defining the extent of wall-rock alteration, fluid activity and mineralization and enrichment.展开更多
Reported for the first the in this paper are the results of simulating experimnts on theγ-irradiation-induced oxidation of Fe2+ under the physicochemical conditions tr= 200℃,P= 50 MPa,Eh= -0.1V, PH=7.2) similar to t...Reported for the first the in this paper are the results of simulating experimnts on theγ-irradiation-induced oxidation of Fe2+ under the physicochemical conditions tr= 200℃,P= 50 MPa,Eh= -0.1V, PH=7.2) similar to tfor under which moderate-low temperature hydrothermal uraniumdeposits are formed . Evdence shows that the effect of groundwater radiolysis m to be the majormechanism of wall-rock alteration (hematitizaton ) of hydrothermal uranium deposits.Moreover, adiscussion was made of possible dets of radiolyss of the waterrock system on wall-rock alterationsincluding argillization and decoloration of uranium ore deposits on the basis of the experimentalresults.展开更多
The alteration types of the large-scale Tsagaan Suvarga Cu-Mo porphyry deposit mostly comprise stockwork silicification, argillization, quartz-sericite alteration, K-silicate alteration, and propylitization. The miner...The alteration types of the large-scale Tsagaan Suvarga Cu-Mo porphyry deposit mostly comprise stockwork silicification, argillization, quartz-sericite alteration, K-silicate alteration, and propylitization. The mineralized and altered zones from hydrothermal metallogenic center to the outside successively are Cu-bearing stockwork silicification zone, Cu-beating argillized zone, Cu-Mo-bearing quartz-sericite alteration zone, Cu-Mo-bearing K-silicate alteration zone, and pro- pylitization zone. The K-silicate alteration occurred in the early phase, quartz-sericite alteration in the medium phase, and argillization and carbonatization （calcite） in the later phase. Ore-bearing-altered rocks are significantly controlled by the structure and fissure zones of different scales, and NE- and NW-trending fissure zones could probably be the migration pathways of the porphyry hydrothermal system. Results in this study indicated that the less the concentrations of REE, LREE, and HREE and the more the extensive fractionation between LREE and HREE, the closer it is to the center circulatory hydrothermal ore-forming and the more extensive silicification. The exponential relationship between the fractionation of LREE and HREE and the intensity of silicification and K-silicate alteration was found in the Cu-Mo deposit studied. The negative Eu anomaly, normal Eu, positive Eu anomaly and obviously positive Eu anomaly are coincident with the enhancement of Na2O and K2O concentrations gradually, which indicated that Eu anomaly would be significantly controlled by the alkaline metasomatism of the circulatory hydrothermal ore-forming system. Therefore, such characteristics as the positive Eu anomaly, the obvious fractionation between LREE and HREE and their related special alteration lithofacies are suggested to be metallogenic prognostic and exploration indications for Tsagaan Suvarga-style porphyry Cu-Mo deposits in Mongolia and China.展开更多
The study of changes in rocks due to interaction with hydrothermal fluids at active volcanoes provides insights into wall rock alteration associated with ore deposits formed in the geological past. Therefore, the natu...The study of changes in rocks due to interaction with hydrothermal fluids at active volcanoes provides insights into wall rock alteration associated with ore deposits formed in the geological past. Therefore, the nature of mineral alteration and chemical changes experienced by wall rocks can be investigated at eruptive sites on active volcanoes and the results used to better constrain ore-forming processes. In this study, we investigated the alteration at eruptive sites at Mount Cameroon volcano. These eruptive vents lie along NE-SW-trending fissures that define the Mount Cameroon rift. The vents are surrounded by cones composed largely of pyroclastic materials and to a lesser extent lava. Fumaroles (volcanic gases) rising through the vents during and after the 1999 eruption have resulted in the alteration of the pyroclastic robble along the fissures and the inner walls of the cones. Consequently, altered basaltic materials are covered with thin films of reddish, yellowish to whitish secondary minerals. These coatings result from an interaction between the surfaces of the basaltic glass with volcanically-derived acidic fluids. Petrographic investigations and XRD analysis of the basalts have identified primary mineral phases, such as olivine, pyroxene (mainly augite) and feldspars. Alteration products revealed include ubiquitous silica as well as gypsum, magnetite, feldspar, alunite and jarosite. Jarosite occurrence indicates that SO2 is the primary volcanically-derived acid source involved in coating formation. High contents of sulfur identified in the basalts indicate that melts at Mount Cameroon can be sulfur saturated as backed by previous melt inclusion data. Whole rock geochemical analysis shows a gain in silica in the altered samples and this ties with the mass balance calculations although minor gains of Al2O3, , MgO, MnO, CaO and K2O are shown by some samples.展开更多
Based on analysing the wall rock alterations and related rocks which were used as a hint for mineral deposits and as a basis of mechanism research of fluid rock interaction, according to the results of petrographic an...Based on analysing the wall rock alterations and related rocks which were used as a hint for mineral deposits and as a basis of mechanism research of fluid rock interaction, according to the results of petrographic analysis, the authors of this paper consider that the hydrothermally altered conglomerates have the following features. First, the conglomerates studied can be divided into two groups: Group A consists mainly of the gravels of granite and basalt; Group B is mainly composed of the gravels of basalt, limestone, mudstone and granite. Second, three distinct hydrothermal alterations or diagenesis were distinguished in Group A, that is, pre depositional hydrothermal alteration of the volcanic gravels (saussuritzation chloritization, epidotization chloritization, albitization and sericitization), mechanical diagenesis and post diagenetic hydrothermal alteration (epidote chlorite and prehnite calcite association). Third, the Group B is subjected mainly to pre depositional hydrothermal alteration; the alteration types are the same as of Type A. Last, the origin of the post diagenetic hydrothermal alteration of Group A is presumed to be related to the ascending of thermal water along the Naer Creek fault.展开更多
文摘Mineralogical zonation of wall rock alterations in Mesozoic granitoids is summarized from 18 gold deposits in Jiaodong gold province on the Asian mobile continental margin of the west circum Pacific rim. This paper deals with wall rock alterations developed around gold mineralizations of the quartz vein type in granitoids and the wall rock alteration type in granitoid basement contacts along Mesozoic fault zones trending mostly NNE SSW and NE SW. Five alteration zones are distinguished from host rock to ore zone, namely the chloritization and sericitization zone, the hematitization rutilization and microclinization zone, the quartz sericitization zone, the pyrite quartz sericitization zone and the pyrite silicification zone. The former two are outer zones marked by incomplete alteration of first mafic and then felsic minerals of the granitoids, while the later three are inner zones marked by complete alteration of both mafic and felsic minerals of the granitoids leading to retrogressive sericitization and progressive silicification with participation of ore elements. The whole process proceeds under dynamometamorphism with high fugacity of volatiles. Wall rock alteration is the intermediate link between unaltered host rock and ore mineralization both in time and space. Development of the alteration zonation and its mineral composition controls genetic type of mineralization, size and grade of the deposit and location of the ore zones.
文摘The Baoban gold field, located in the area of Hainan Island, South China, bears three gold de-posits: Tuwaishan, Baoban, and Erjia, which belong to the wall-rock alteration type. In terms of the petrography data, four alteration zones can be recognized from the ore-vein outwards: (1) the silicification zone; (2) the sericitization zone, (3) the chloritization zone; and (4) the calcitization zone. The geochemical kinetic simulation was carried out on sericitization and chloritization . Results of the study showed that the formation of the alteration zones is connected with the properties of hydrothermal fluids: the initial concentration of Al (O H)3, the diffusion coefficient and the velocity of fluid flow. The alteration zones in this field are the result of multiple interaction between hydrothermal fluids and wall rocks.
文摘Abstract The Shibangou gold deposit in western Henan is associated with irregular quartz veinlets occurring in altered shear zones dissecting a dioritic intrusion. The altered shear zones are characterized by silicification, pyritization, sericilization, chloritization and K-feldspar alteration. Zoning of altered rocks adjacent to the Au-bearing quartz veins is obviously exhibited. Fine-grained sulphides and quartz veinlets of different ages and small-scale fissures are widely distributed in the central part of the altered zones. Major mineralization types in this gold deposit are Au-bearing quartz veinlets and altered rocks in the shear zones. Samples were collected from drilling cores according to the alteration zoning and mineralization type and all samples were analyzed for major and trace elements. Mass balance, volume change (fv=97.3–71.9%) and major element variation sequences are studied in terms of major elements. The changes of mobile components (SiO2, K2O, Fe2O3) and CaO) and immobile component (Al2O3) in the wall-rock alteration are discussed. The gold mineralization is associated with the enrichment of As, Ag, Hg and Pb and depletion of Cu and Zn. The study of compositional variation of altered rocks proves to be a very efficient method for defining the extent of wall-rock alteration, fluid activity and mineralization and enrichment.
文摘Reported for the first the in this paper are the results of simulating experimnts on theγ-irradiation-induced oxidation of Fe2+ under the physicochemical conditions tr= 200℃,P= 50 MPa,Eh= -0.1V, PH=7.2) similar to tfor under which moderate-low temperature hydrothermal uraniumdeposits are formed . Evdence shows that the effect of groundwater radiolysis m to be the majormechanism of wall-rock alteration (hematitizaton ) of hydrothermal uranium deposits.Moreover, adiscussion was made of possible dets of radiolyss of the waterrock system on wall-rock alterationsincluding argillization and decoloration of uranium ore deposits on the basis of the experimentalresults.
基金Project supported by Chinese State Key Project on Fundamental Research Planning (2007CB411304) Open Project of StateKey Laboratory of Deposit Geochemistry of Institute of Geochemistry, Chinese Academy of Sciences
文摘The alteration types of the large-scale Tsagaan Suvarga Cu-Mo porphyry deposit mostly comprise stockwork silicification, argillization, quartz-sericite alteration, K-silicate alteration, and propylitization. The mineralized and altered zones from hydrothermal metallogenic center to the outside successively are Cu-bearing stockwork silicification zone, Cu-beating argillized zone, Cu-Mo-bearing quartz-sericite alteration zone, Cu-Mo-bearing K-silicate alteration zone, and pro- pylitization zone. The K-silicate alteration occurred in the early phase, quartz-sericite alteration in the medium phase, and argillization and carbonatization （calcite） in the later phase. Ore-bearing-altered rocks are significantly controlled by the structure and fissure zones of different scales, and NE- and NW-trending fissure zones could probably be the migration pathways of the porphyry hydrothermal system. Results in this study indicated that the less the concentrations of REE, LREE, and HREE and the more the extensive fractionation between LREE and HREE, the closer it is to the center circulatory hydrothermal ore-forming and the more extensive silicification. The exponential relationship between the fractionation of LREE and HREE and the intensity of silicification and K-silicate alteration was found in the Cu-Mo deposit studied. The negative Eu anomaly, normal Eu, positive Eu anomaly and obviously positive Eu anomaly are coincident with the enhancement of Na2O and K2O concentrations gradually, which indicated that Eu anomaly would be significantly controlled by the alkaline metasomatism of the circulatory hydrothermal ore-forming system. Therefore, such characteristics as the positive Eu anomaly, the obvious fractionation between LREE and HREE and their related special alteration lithofacies are suggested to be metallogenic prognostic and exploration indications for Tsagaan Suvarga-style porphyry Cu-Mo deposits in Mongolia and China.
文摘The study of changes in rocks due to interaction with hydrothermal fluids at active volcanoes provides insights into wall rock alteration associated with ore deposits formed in the geological past. Therefore, the nature of mineral alteration and chemical changes experienced by wall rocks can be investigated at eruptive sites on active volcanoes and the results used to better constrain ore-forming processes. In this study, we investigated the alteration at eruptive sites at Mount Cameroon volcano. These eruptive vents lie along NE-SW-trending fissures that define the Mount Cameroon rift. The vents are surrounded by cones composed largely of pyroclastic materials and to a lesser extent lava. Fumaroles (volcanic gases) rising through the vents during and after the 1999 eruption have resulted in the alteration of the pyroclastic robble along the fissures and the inner walls of the cones. Consequently, altered basaltic materials are covered with thin films of reddish, yellowish to whitish secondary minerals. These coatings result from an interaction between the surfaces of the basaltic glass with volcanically-derived acidic fluids. Petrographic investigations and XRD analysis of the basalts have identified primary mineral phases, such as olivine, pyroxene (mainly augite) and feldspars. Alteration products revealed include ubiquitous silica as well as gypsum, magnetite, feldspar, alunite and jarosite. Jarosite occurrence indicates that SO2 is the primary volcanically-derived acid source involved in coating formation. High contents of sulfur identified in the basalts indicate that melts at Mount Cameroon can be sulfur saturated as backed by previous melt inclusion data. Whole rock geochemical analysis shows a gain in silica in the altered samples and this ties with the mass balance calculations although minor gains of Al2O3, , MgO, MnO, CaO and K2O are shown by some samples.
文摘Based on analysing the wall rock alterations and related rocks which were used as a hint for mineral deposits and as a basis of mechanism research of fluid rock interaction, according to the results of petrographic analysis, the authors of this paper consider that the hydrothermally altered conglomerates have the following features. First, the conglomerates studied can be divided into two groups: Group A consists mainly of the gravels of granite and basalt; Group B is mainly composed of the gravels of basalt, limestone, mudstone and granite. Second, three distinct hydrothermal alterations or diagenesis were distinguished in Group A, that is, pre depositional hydrothermal alteration of the volcanic gravels (saussuritzation chloritization, epidotization chloritization, albitization and sericitization), mechanical diagenesis and post diagenetic hydrothermal alteration (epidote chlorite and prehnite calcite association). Third, the Group B is subjected mainly to pre depositional hydrothermal alteration; the alteration types are the same as of Type A. Last, the origin of the post diagenetic hydrothermal alteration of Group A is presumed to be related to the ascending of thermal water along the Naer Creek fault.
