公家坪金矿是北秦岭新近勘查的一处中型金矿床,矿体以石英脉型为主,产于中—晚三叠世花岗(斑)岩的NW-NWW向脆韧性断层中。矿石以富Au-Ag-Te-(Bi)矿物为特征,然而关于其矿物共生组合、成矿物理化学条件及金的富集机理尚不清楚。显微矿相...公家坪金矿是北秦岭新近勘查的一处中型金矿床,矿体以石英脉型为主,产于中—晚三叠世花岗(斑)岩的NW-NWW向脆韧性断层中。矿石以富Au-Ag-Te-(Bi)矿物为特征,然而关于其矿物共生组合、成矿物理化学条件及金的富集机理尚不清楚。显微矿相学观察和电子探针分析表明:公家坪金矿床的碲化物有碲金银矿、碲银矿、六方碲银矿、碲铅矿、碲铋矿、辉碲铋矿和硫碲铋矿B;金矿物以含金碲化物和自然金为主,且自然金成色为835~889,平均值为855。矿物共生关系、流体包裹体及热力学相图研究结果显示:主成矿阶段石英中的原生流体包裹体主要有3种类型,即H_(2)O-NaCl包裹体(W型)、CO_(2)-H_(2)O-NaCl包裹体(C型)和纯CO_(2)包裹体(PC型);成矿流体总体属于中温(180~320℃)、低盐度(0.7%~8.7%)、中酸性、低氧逸度、高碲逸度及相对低硫逸度的偏还原CO_(2)-H_(2)O-NaCl±CH_(4)体系。其中,热液成矿期Ⅱ阶段以富铋(硫)碲化物(碲铋矿+辉碲铋矿+硫碲铋矿B)为特征,含矿热液的pH=4.1~6.2、log f O_(2)=-42.0~-36.5、log f Te_(2)=-13.2~-10.5和log f S_(2)=-14.4~-11.1;Ⅲ阶段发育大量Au-Ag-(Pb)-Te矿物(自然金+碲金银矿+碲银矿+六方碲银矿+碲铅矿),成矿流体的pH=4.1~5.7、log f O_(2)=-42.0~-36.5、log f Te_(2)=-10.5~-9.5和log f S_(2)=-14.4~-11.9。富Au-Ag-Te熔体对热液中金的抽提,可能是导致金发生富集沉淀的关键机制。展开更多
Diamonds were formed in the mantle lithosphere,mostly at depths of 150~200km in the centres of Precambrian cratons,the buoyant ancient cores of continents.From there they were normally transported into the upper crust...Diamonds were formed in the mantle lithosphere,mostly at depths of 150~200km in the centres of Precambrian cratons,the buoyant ancient cores of continents.From there they were normally transported into the upper crust in kimberlite pipes whose diamonds are largely colourless and light yellow related to trace element N(Ia type),although brown,green,and more rarely blue-coloured diamonds are related to lattice defect and trace amounts of H,more rarely B and Ni.Pink diamonds are extremely rare in the approximately 90 diamondiferous pipes mined globally.Although small quantities have been discovered elsewhere,about 90%have been mined from the ca.1.3Ga Argyle diamond pipe in Western Australia,with the Arkhangelskaya diamond pipe in Russia the only other significant source.The pink colour at both Argyle and Arkhangelskaya is unrelated to trace elements and instead results from absorption of light from nanoscale(550nm)defects related to shear stress and plastic deformation.Macroscopically,defects are shown by glide planes,lamellae,and grain lines imposed on the originally colourless diamonds derived from their mantle source.The key question is why these defects were uniquely acquired in diamonds in the Argyle and Arkhangelskaya pipes.Unlike most diamondiferous pipes,Argyle is a rare diamondiferous volatile-rich lamproite pipe that was emplaced into the multiply deformed and rifted NNE-trending Halls Creek Orogen on the margin of the Kimberley Craton.Similarly,Arkhangelskaya in the Devonian Lomonosov kimberlite cluster is a volatile-rich low-Ti type kimberlite,a close relative to lamproite,that was emplaced into the multiply deformed Lapland-Kola Orogen on the rifted margin of the Kola Craton.These craton margins are underlain by subduction-induced volatile-enriched metasomatized mantle lithosphere in contrast to the more primeval mantle under craton centres.It is thus likely that shear stresses were exacerbated at Argyle and Arkangelskaya by rapid vertical emplacement of the anomalous volatile-enriched magmas at supercritical pressures and temperatures,that induced catastrophic phase separation of these volatiles and'mini seismic events'during rapid pressure drops during ascent from 200km depth to the surface.Such a mechanism is consistent with the presence of strongly resorbed and plastically deformed small brown industrial diamonds in the Argyle pipe.From a China perspective,it is potentially important that at 1.3Ga the alkaline Argyle pipe in northern Australia is placed adjacent to the North China Craton(NCC),with numerous world-class mineral deposits including the giant ca.1.4~1.2Ga alkaline Bayan Obo REE system on its margin.However,it is the southeastern margin of the Yangtze Craton and the Jiangnan Orogen with their lamproite pipes derived from metasomatized mantle lithosphere that present the most prospective regions for pink diamond occurrences.展开更多
文摘公家坪金矿是北秦岭新近勘查的一处中型金矿床,矿体以石英脉型为主,产于中—晚三叠世花岗(斑)岩的NW-NWW向脆韧性断层中。矿石以富Au-Ag-Te-(Bi)矿物为特征,然而关于其矿物共生组合、成矿物理化学条件及金的富集机理尚不清楚。显微矿相学观察和电子探针分析表明:公家坪金矿床的碲化物有碲金银矿、碲银矿、六方碲银矿、碲铅矿、碲铋矿、辉碲铋矿和硫碲铋矿B;金矿物以含金碲化物和自然金为主,且自然金成色为835~889,平均值为855。矿物共生关系、流体包裹体及热力学相图研究结果显示:主成矿阶段石英中的原生流体包裹体主要有3种类型,即H_(2)O-NaCl包裹体(W型)、CO_(2)-H_(2)O-NaCl包裹体(C型)和纯CO_(2)包裹体(PC型);成矿流体总体属于中温(180~320℃)、低盐度(0.7%~8.7%)、中酸性、低氧逸度、高碲逸度及相对低硫逸度的偏还原CO_(2)-H_(2)O-NaCl±CH_(4)体系。其中,热液成矿期Ⅱ阶段以富铋(硫)碲化物(碲铋矿+辉碲铋矿+硫碲铋矿B)为特征,含矿热液的pH=4.1~6.2、log f O_(2)=-42.0~-36.5、log f Te_(2)=-13.2~-10.5和log f S_(2)=-14.4~-11.1;Ⅲ阶段发育大量Au-Ag-(Pb)-Te矿物(自然金+碲金银矿+碲银矿+六方碲银矿+碲铅矿),成矿流体的pH=4.1~5.7、log f O_(2)=-42.0~-36.5、log f Te_(2)=-10.5~-9.5和log f S_(2)=-14.4~-11.9。富Au-Ag-Te熔体对热液中金的抽提,可能是导致金发生富集沉淀的关键机制。
文摘Diamonds were formed in the mantle lithosphere,mostly at depths of 150~200km in the centres of Precambrian cratons,the buoyant ancient cores of continents.From there they were normally transported into the upper crust in kimberlite pipes whose diamonds are largely colourless and light yellow related to trace element N(Ia type),although brown,green,and more rarely blue-coloured diamonds are related to lattice defect and trace amounts of H,more rarely B and Ni.Pink diamonds are extremely rare in the approximately 90 diamondiferous pipes mined globally.Although small quantities have been discovered elsewhere,about 90%have been mined from the ca.1.3Ga Argyle diamond pipe in Western Australia,with the Arkhangelskaya diamond pipe in Russia the only other significant source.The pink colour at both Argyle and Arkhangelskaya is unrelated to trace elements and instead results from absorption of light from nanoscale(550nm)defects related to shear stress and plastic deformation.Macroscopically,defects are shown by glide planes,lamellae,and grain lines imposed on the originally colourless diamonds derived from their mantle source.The key question is why these defects were uniquely acquired in diamonds in the Argyle and Arkhangelskaya pipes.Unlike most diamondiferous pipes,Argyle is a rare diamondiferous volatile-rich lamproite pipe that was emplaced into the multiply deformed and rifted NNE-trending Halls Creek Orogen on the margin of the Kimberley Craton.Similarly,Arkhangelskaya in the Devonian Lomonosov kimberlite cluster is a volatile-rich low-Ti type kimberlite,a close relative to lamproite,that was emplaced into the multiply deformed Lapland-Kola Orogen on the rifted margin of the Kola Craton.These craton margins are underlain by subduction-induced volatile-enriched metasomatized mantle lithosphere in contrast to the more primeval mantle under craton centres.It is thus likely that shear stresses were exacerbated at Argyle and Arkangelskaya by rapid vertical emplacement of the anomalous volatile-enriched magmas at supercritical pressures and temperatures,that induced catastrophic phase separation of these volatiles and'mini seismic events'during rapid pressure drops during ascent from 200km depth to the surface.Such a mechanism is consistent with the presence of strongly resorbed and plastically deformed small brown industrial diamonds in the Argyle pipe.From a China perspective,it is potentially important that at 1.3Ga the alkaline Argyle pipe in northern Australia is placed adjacent to the North China Craton(NCC),with numerous world-class mineral deposits including the giant ca.1.4~1.2Ga alkaline Bayan Obo REE system on its margin.However,it is the southeastern margin of the Yangtze Craton and the Jiangnan Orogen with their lamproite pipes derived from metasomatized mantle lithosphere that present the most prospective regions for pink diamond occurrences.
