Primary oxide minerals in the system WO3 . Nb2O5 . TiO2 . Fe2O3 . FeO and their breakdown products from the pegmatite No. 3 at Dolní Bory . Hatě, Czech Republic
Primary oxide minerals in the system WO3 . Nb2O5 . TiO2 . Fe2O3 . FeO and their breakdown products from the pegmatite No. 3 at Dolní Bory . Hatě, Czech Republic
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DOI：
10.1127/0935-1221/2008/0020-1834
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发表时间：
2008-07
影响因子：
2.1
通讯作者：
M. Novak;Z. Johan;R. Škoda;P. Černý;V. Šrein;F. Veselovský
中科院分区：
文献类型：
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作者：
M. Novak;Z. Johan;R. Škoda;P. Černý;V. Šrein;F. Veselovský
捷克共和国 Dolni Bory-Hatě 对称分区的 3 号贫瘠伟晶岩堤切割了麻粒岩。它含有少量到副的黑云母、黑云母、白云母、钾长石、红柱石、水硬铝石、磷灰石和几种稀有的副矿物。黑色、板状的铁长石晶体——“钨丝硅石”几乎完全出现在红柱石-水铝石聚集体中，并依次堆积有晚期叶腊石、高岭石和白云母。铁锰矿单个晶体的复杂分带——“钨铁锰矿”显示出主要的粗振荡分带，由铁锰矿 (5.01-6.00 apfu W) 和占主导地位的铌铁锰矿 I (5.00-3.01 apfu W) 的狭窄区域组成，直至“钨铁锰铁矿”（钨-钛铁铌铁矿 >> 铌铁矿和铌铁矿） 钨金红石>ScPO4相>白钨矿。主相和副相的特征是 W/(W+Nb+Ta) 和计算出的 Fe2+/(Fe2++Fe3+) 变化较大，但 Mn/(Mn+Fetot) 和 Ta/(Ta+Nb) 较低且几乎恒定。 P、U、Ti、Zr、Si、Sc、Al 和 Ca 的含量从铁碱体中可忽略不计到 次要成分为“钨丝硅石”及其富U品种：UO2 2.71（富U品种19.82）、P2O5 0.30、TiO2 4.81、ZrO2 2.84、SiO2 0.93、Sc2O3 4.36、Al2O3 0.87、CaO 1.02（均以重量%计）。组合交换向量： (R3+)8(R4+)6(R5+)16(R2+)−13(R6+)−17，其中 R2+ = Fe2+ > Mn、Ca； R3+ = Fe3+ > Sc、Al； R4+=Ti>Zr、Si、U； R5+=Nb>Ta、P； R6+ = W，似乎是从铁锰矿到实际替代机制的最佳表达 “钨丝硅石”，理论最终组成为(R2+1.1R3+3.4R4+1.9R5+5.6)Σ12O24。由交换载体 Fe2+Mn−1、TaNb−1 和 ScFe3+−1 表示的同价取代是相当可以忽略不计的。原生W、Nb、Fe氧化物矿物的形成与组合密切相关 红柱石+水铝石，在 T < ~ 400 °C（P = 2 kbar）时形成。分解过程可能在稍低的温度（约 350-300 °C）下进行。分解产物的结构关系以 BSE 图像中完全不存在任何耗尽的初生相为特征，表明二次组合并非源自外溶型过程。初级的完全再结晶和重构 矿物质似乎是其起源的原因。产自 Dolni Bory-Hatě 的原生铌长铁矿至“钨丝铁锰矿”的化学成分与迄今描述的所有其他富钨铌、钽氧化物矿物不同，除了莫桑比克努阿帕拉花岗伟晶岩中的铌铌锰矿之外。
Symmetrically zoned barren pegmatite dike No. 3 cuts granulite at Dolni Bory-Hatě in the Czech Republic. It contains minor to accessory biotite, schorl, muscovite, sekaninaite, andalusite, diaspore, apatite and several rare accessory minerals. Black, tabular crystals of ferberite-"wolframoixiolite" occur almost exclusively in an andalusite-diaspore aggregate with sequential accumulations of late pyrophyllite, kaolinite, and muscoviteillite. Complex zoning of the individual crystals of ferberite-"wolframoixiolite" shows primary, coarse oscillatory zoning consisting of narrow zones of ferberite (5.01-6.00 apfu W) and dominant niobian ferberite I (5.00-3.01 apfu W) to "wolframoixiolite" ( tungstenian-titanian ferrocolumbite >> niobian and tungstenian rutile > ScPO4 phase > scheelite. Primary and secondary phases are characterized by large variation in W/(W+Nb+Ta) and calculated Fe2+/(Fe2++Fe3+) but low and almost constant Mn/(Mn+Fetot) and Ta/(Ta+Nb). The contents of P, U, Ti, Zr, Si, Sc, Al and Ca vary from negligible in ferberite to minor in "wolframoixiolite" and its U-rich variety: UO2 2.71 (19.82 U-rich variety), P2O5 0.30, TiO2 4.81, ZrO2 2.84, SiO2 0.93, Sc2O3 4.36, Al2O3 0.87, CaO 1.02 (all in wt.%). The combined exchange vector: (R3+)8(R4+)6(R5+)16(R2+)−13(R6+)−17, where R2+ = Fe2+ > Mn, Ca; R3+ = Fe3+ > Sc, Al; R4+ = Ti > Zr, Si, U; R5+ = Nb > Ta, P; R6+ = W, seems to be the best expression of the actual substitution mechanism from ferberite to "wolframoixiolite" with the theoretical end composition (R2+1.1R3+3.4R4+1.9R5+5.6)∑12O24. The homovalent substitutions expressed by the exchange vectors: Fe2+Mn−1, TaNb−1 and ScFe3+−1 are rather negligible. Formation of primary W, Nb, Fe-oxide minerals is closely related to the assemblage andalusite+diaspore, formed at T < ~ 400 °C for P = 2 kbar. The breakdown process probably proceeded at slightly lower temperatures of about 350-300 °C. Textural relations of the breakdown products characterized by the total absence of any depleted primary phase in the BSE images indicate that the secondary assemblage did not originated from an exsolution-type process. Complete recrystallization and reconstitution of the primary minerals seems to be responsible for its origin. The chemical composition of the primary niobian ferberite to "wolframoixiolite" from Dolni Bory-Hatě is distinct from all other W-rich Nb,Ta-oxide minerals described to date except niobian wolframite from the granitic pegmatite at Nuaparra, Mozambique.