铌(Nb)、钽(Ta)广泛应用于全球高新科技领域,是不可替代的稀有金属资源,在中国,铌钽属于紧缺战略性矿产。铌钽成矿主要与内生作用有关,国内外目前发现的铌钽矿床几乎都产于过铝质花岗岩、花岗伟晶岩、碱性花岗岩、碳酸岩等侵入体中。国...铌(Nb)、钽(Ta)广泛应用于全球高新科技领域,是不可替代的稀有金属资源,在中国,铌钽属于紧缺战略性矿产。铌钽成矿主要与内生作用有关,国内外目前发现的铌钽矿床几乎都产于过铝质花岗岩、花岗伟晶岩、碱性花岗岩、碳酸岩等侵入体中。国外大型—超大型铌钽矿床主要分布于古老克拉通内部,形成于各类前寒武纪侵入体中,尤其是早前寒武纪花岗伟晶岩中,例如西澳地区2.8 Ga的Wodgina矿床和加拿大2.6 Ga的Tanco矿床(Melcher et al.,2017)。中国目前可供工业利用的铌钽矿床主要分布在华南等地区的过铝质花岗岩和花岗伟晶岩中,主要形成于燕山期,成矿与中国东部显生宙强烈的构造岩浆活动有关。展开更多
The uncommon Mg-rich and Ti-poor Zhaoanzhuang serpentine-magnetite ores within Taihua Group of the North China Craton （NCC） remain unclear whether the protolith was sourced from ultramafic rocks or chemical sediment...The uncommon Mg-rich and Ti-poor Zhaoanzhuang serpentine-magnetite ores within Taihua Group of the North China Craton （NCC） remain unclear whether the protolith was sourced from ultramafic rocks or chemical sedimentary sequences. Here we present integrated petrographic and geochemical studies to characterize the protoliths and to gain insights on the ore-forming processes. Iron ores mainly contain low-Ti magnetite （TiO2 -0.1wt%） and serpentine （Mg#=92.42-96.55）, as well as residual olivine （Fo=89-90）, orthopyroxene （En=89-90） and hornblende. Magnetite in the iron ores shows lower AI, Sc, Ti, Cr, Zn relative to that from ultramafic Fe-Ti-V iron ores, but similar to that from metamorphic chemical sedimentary iron deposit. In addition, interstitial minerals of dolomite, calcite, apatite and anhydrite are intergrown with magnetite and serpentine, revealing they were metamorphic, but not magmatic or late hydrothermal minerals. Wall rocks principally contain magnesian silicates of olivine （Fo=83-87）, orthopyroxene （En=82-86）, humite （Mg#=82-84） and hornblende [XMg=0.87--0.96]. Dolomite, apatite and anhydrite together with minor magnetite, thorianite （Th-rich oxide） and monazite （LREE-rich phosphate） are often seen as relicts or inclusions within magnesian silicates in the wall rocks, revealing that they were primary or earlier metamorphic minerals than magnesian silicates. And olivine exists as subhedral interstitial texture between hornblende, which shows later formation of olivine than hornblende and does not conform with sequence of magmatic crystallization. All these mineralogical features thus bias towards their metamorphic, rather than magmatic origin. The dominant chemical components of the iron ores are SiO2 （4.77-25.23wt%）, Fe203T （32.9-80.39wt%） and MgO （5.72- 27.17wt%） and uniformly, those of the wall rocks are also SiO2 （16.34-48.72wt%）, MgO （16.71- 33.97wt%） and Fe203T （6.98-30.92wt%）. The striking high Fe-Mg-Si contents reveal that protolith of the Zhaoanzhuang iron deposit was more likely to be chemical sedimentary rocks. The distinct high-Mg feature and presence of abundant anhydrite possibly indicate it primarily precipitated in a confined seawater basin under an evaporitic environment. Besides, higher contents of AI, Ti, P, Th, U, Pb, REE relative to other Precambrian iron-rich chemical precipitates （BIF） suggest some clastic terrestrial materials were probably input. As a result, we think the Zhaoanzhuang iron deposit had experienced the initial Fe-Mg-Si marine precipitation, followed by further Mg enrichment through marine evaporated process, subsequent high-grade metamorphism and late-stage hydrothermal fluid modification.展开更多
文摘铌(Nb)、钽(Ta)广泛应用于全球高新科技领域,是不可替代的稀有金属资源,在中国,铌钽属于紧缺战略性矿产。铌钽成矿主要与内生作用有关,国内外目前发现的铌钽矿床几乎都产于过铝质花岗岩、花岗伟晶岩、碱性花岗岩、碳酸岩等侵入体中。国外大型—超大型铌钽矿床主要分布于古老克拉通内部,形成于各类前寒武纪侵入体中,尤其是早前寒武纪花岗伟晶岩中,例如西澳地区2.8 Ga的Wodgina矿床和加拿大2.6 Ga的Tanco矿床(Melcher et al.,2017)。中国目前可供工业利用的铌钽矿床主要分布在华南等地区的过铝质花岗岩和花岗伟晶岩中,主要形成于燕山期,成矿与中国东部显生宙强烈的构造岩浆活动有关。
基金funded by the National Natural Science Foundation of China (Grant No. 41672078)
文摘The uncommon Mg-rich and Ti-poor Zhaoanzhuang serpentine-magnetite ores within Taihua Group of the North China Craton （NCC） remain unclear whether the protolith was sourced from ultramafic rocks or chemical sedimentary sequences. Here we present integrated petrographic and geochemical studies to characterize the protoliths and to gain insights on the ore-forming processes. Iron ores mainly contain low-Ti magnetite （TiO2 -0.1wt%） and serpentine （Mg#=92.42-96.55）, as well as residual olivine （Fo=89-90）, orthopyroxene （En=89-90） and hornblende. Magnetite in the iron ores shows lower AI, Sc, Ti, Cr, Zn relative to that from ultramafic Fe-Ti-V iron ores, but similar to that from metamorphic chemical sedimentary iron deposit. In addition, interstitial minerals of dolomite, calcite, apatite and anhydrite are intergrown with magnetite and serpentine, revealing they were metamorphic, but not magmatic or late hydrothermal minerals. Wall rocks principally contain magnesian silicates of olivine （Fo=83-87）, orthopyroxene （En=82-86）, humite （Mg#=82-84） and hornblende [XMg=0.87--0.96]. Dolomite, apatite and anhydrite together with minor magnetite, thorianite （Th-rich oxide） and monazite （LREE-rich phosphate） are often seen as relicts or inclusions within magnesian silicates in the wall rocks, revealing that they were primary or earlier metamorphic minerals than magnesian silicates. And olivine exists as subhedral interstitial texture between hornblende, which shows later formation of olivine than hornblende and does not conform with sequence of magmatic crystallization. All these mineralogical features thus bias towards their metamorphic, rather than magmatic origin. The dominant chemical components of the iron ores are SiO2 （4.77-25.23wt%）, Fe203T （32.9-80.39wt%） and MgO （5.72- 27.17wt%） and uniformly, those of the wall rocks are also SiO2 （16.34-48.72wt%）, MgO （16.71- 33.97wt%） and Fe203T （6.98-30.92wt%）. The striking high Fe-Mg-Si contents reveal that protolith of the Zhaoanzhuang iron deposit was more likely to be chemical sedimentary rocks. The distinct high-Mg feature and presence of abundant anhydrite possibly indicate it primarily precipitated in a confined seawater basin under an evaporitic environment. Besides, higher contents of AI, Ti, P, Th, U, Pb, REE relative to other Precambrian iron-rich chemical precipitates （BIF） suggest some clastic terrestrial materials were probably input. As a result, we think the Zhaoanzhuang iron deposit had experienced the initial Fe-Mg-Si marine precipitation, followed by further Mg enrichment through marine evaporated process, subsequent high-grade metamorphism and late-stage hydrothermal fluid modification.
