The Changkeng gold-silver deposits consist of a sediment-hosted, disseminated gold deposit and a replacement-type silver deposit. The mineralizations of gold and silver are zoned and closely related to the silicificat...The Changkeng gold-silver deposits consist of a sediment-hosted, disseminated gold deposit and a replacement-type silver deposit. The mineralizations of gold and silver are zoned and closely related to the silicification of carbonate and clastic rocks, so that siliceous ores dominate in the deposit. The mineralizing temperature ranges mainly from 300 to 170℃, and K+, Na+, Ca2+, Mg2+, and Cl- are the major ions in the ore-forming fluid. Calculations of distribution of metal complexes show that gold is mainly transported by hydrosulphide complexes, but chloride complexes of silver, iron, lead, and zinc, which are transformed into hydroxyl and hydrosulphide complexes under neutral to weak-alkaline circumstances in the late stage, predominate in the ore-forming solutions. Water-rock interaction is confirmed to be the effective mechanism for the formation of silver ores by computer modelling of reaction of hydrothermal solution with carbonate rocks. The solubility analyses demonstrate that the展开更多
Gold-silver deposits in the Atalla area occur as hydrothermal quartz veins in NE–SW pre-existing fractures within the Atalla granitic pluton.The orientation of such quartz veins has been attributed to extensional beh...Gold-silver deposits in the Atalla area occur as hydrothermal quartz veins in NE–SW pre-existing fractures within the Atalla granitic pluton.The orientation of such quartz veins has been attributed to extensional behavior related to the Atalla Shear Zone(ASZ).The Atalla area is covered by a variety of lithologies that are(from oldest to youngest):metasedimentary rocks,metavolcanic rocks,ophiolite assemblage(serpentinites/talc-carbonates),Atalla granite and Dokhan volcanic rocks.Microscopically,Atalla granite ranges in composition from granodiorite to monzogranite.Wholerock geochemistry constrains the calc-alkaine affinity of the Atalla granite that was intruded within an orogenic(syncollision)tectonic regime.The ore minerals are represented by gold/silver(electrum),pyrite(Py1&Py2),arsenopyrite,pyrrhotite,sphalerite,chalcopyrite,galena,covellite and goethite.The temperature of ore formation ranges from 240 to 285℃and the estimated fluid pressure is in the range of 20–100 MPa.Based on the geological setting,ore textures and fluid characteristics;the Atalla Au-Ag deposits are considered to be orogenic in nature,formed from a continental collision(~653-590 Ma),synchronous with the emplacement of calc-alkaline magmatism during the evolutionary history of the Arabian Nubian Shield(ANS).The initial ore-forming fluid was primarily derived from a metamorphic source related to ophiolitic-serpentinite rocks under deep regional conditions of greenschist-amphibolite facies,where the Atalla granitic eruption provided the required temperature conditions for the metamorphic process to take place.Under such conditions,the transportation of ore metals as bisulfide complexes is favoured.The deposition of ore minerals was triggered by fluidwallrock interaction through fracture pathways in conjunction with a temperature-pressure drop that is likely to have been related to uplift into the crustal levels.展开更多
基金This project was financially supported by Research Funds of Gold Resources and Doctoral Training Funds sponsored by Chinese Academy of Sciences
文摘The Changkeng gold-silver deposits consist of a sediment-hosted, disseminated gold deposit and a replacement-type silver deposit. The mineralizations of gold and silver are zoned and closely related to the silicification of carbonate and clastic rocks, so that siliceous ores dominate in the deposit. The mineralizing temperature ranges mainly from 300 to 170℃, and K+, Na+, Ca2+, Mg2+, and Cl- are the major ions in the ore-forming fluid. Calculations of distribution of metal complexes show that gold is mainly transported by hydrosulphide complexes, but chloride complexes of silver, iron, lead, and zinc, which are transformed into hydroxyl and hydrosulphide complexes under neutral to weak-alkaline circumstances in the late stage, predominate in the ore-forming solutions. Water-rock interaction is confirmed to be the effective mechanism for the formation of silver ores by computer modelling of reaction of hydrothermal solution with carbonate rocks. The solubility analyses demonstrate that the
文摘Gold-silver deposits in the Atalla area occur as hydrothermal quartz veins in NE–SW pre-existing fractures within the Atalla granitic pluton.The orientation of such quartz veins has been attributed to extensional behavior related to the Atalla Shear Zone(ASZ).The Atalla area is covered by a variety of lithologies that are(from oldest to youngest):metasedimentary rocks,metavolcanic rocks,ophiolite assemblage(serpentinites/talc-carbonates),Atalla granite and Dokhan volcanic rocks.Microscopically,Atalla granite ranges in composition from granodiorite to monzogranite.Wholerock geochemistry constrains the calc-alkaine affinity of the Atalla granite that was intruded within an orogenic(syncollision)tectonic regime.The ore minerals are represented by gold/silver(electrum),pyrite(Py1&Py2),arsenopyrite,pyrrhotite,sphalerite,chalcopyrite,galena,covellite and goethite.The temperature of ore formation ranges from 240 to 285℃and the estimated fluid pressure is in the range of 20–100 MPa.Based on the geological setting,ore textures and fluid characteristics;the Atalla Au-Ag deposits are considered to be orogenic in nature,formed from a continental collision(~653-590 Ma),synchronous with the emplacement of calc-alkaline magmatism during the evolutionary history of the Arabian Nubian Shield(ANS).The initial ore-forming fluid was primarily derived from a metamorphic source related to ophiolitic-serpentinite rocks under deep regional conditions of greenschist-amphibolite facies,where the Atalla granitic eruption provided the required temperature conditions for the metamorphic process to take place.Under such conditions,the transportation of ore metals as bisulfide complexes is favoured.The deposition of ore minerals was triggered by fluidwallrock interaction through fracture pathways in conjunction with a temperature-pressure drop that is likely to have been related to uplift into the crustal levels.