Precipitation and alteration of coffinite (USiO4·nH 2O) in the presence of apatite
Precipitation and alteration of coffinite (USiO4·nH 2O) in the presence of apatite
复制标题
磷灰石存在下咖啡石(USSiO4·nH 2O)的沉淀和蚀变
DOI：
10.1127/0935-1221/2010/0022-1990
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发表时间：
2010
影响因子：
2.1
通讯作者：
R. Ewing
中科院分区：
文献类型：
--
作者：
A. Deditius;A. Deditius;S. Utsunomiya;V. Pointeau;R. Ewing
研究了新墨西哥州格兰茨铀区Woodrow矿的咖啡石USiO4-TiH2O(n=0-2)、碳酸盐-氟磷灰石(CFAP)和(Ca，Sr)-(偏)奥陶石(Maut)的矿物组合，以了解富集型微地球化学环境对咖啡石沉淀及其在氧化条件下的后续变化的影响。在还原条件下沉淀的细粒棺材(<；10μm)取代了CFAP、黄铁矿和铝硅酸盐。电子探针分析(EMPA)表明，在CFAP置换过程中，P2O5和CaO分别为2.7和3.0wt%有限地掺入到棺材结构中。咖啡石的化学式为(U0.95±0.09Ca0.15±0.02)Σ1.10±0.1(Si0.84±0.08P0.06±0.02)<；0.90±0.08。随后，富(Na，Ba，Sr)氧化流体渗入裂缝，导致富锶的M-Aut(高达4wt%的SRO)析出，损害了辉石和CFAP。高分辨透射电子显微镜显示，富钠流体导致了由于α衰变事件辐射损伤而形成的无定形微区的扭曲和非晶区的稳定。随后，富钠无定形区优先改变，次生孔洞形成于∼-1骨灰盒的尺度。在CFAP向M-AUT转变过程中也形成了孔洞，这有利于氧化流体在∼150μm的距离内向CFAP迁移，M-AUT的沉淀证明了这一点。我们首次报道了在富磷的氧化条件下，以磷灰石为代价的棺材的沉淀和随后的棺材的蚀变。这些结果表明，磷灰石的微尺度溶解可以为U(IV)和U(VT)矿物的析出创造条件，导致还原和氧化条件下U物种的流动性降低。
A mineral assemblage of coffinite, USiO4-TiH2O, n= 0-2, carbonate-fluorapatite (CFAp) and (Ca, Sr)-(meta)autunite (MAut) from the Woodrow Mine, Grants uranium region, New Mexico, has been investigated in order to understand the influence of a Prich micro-geochemical environment on precipitation of coffinite and its subsequent alteration under oxidizing conditions. Finegrained coffinite (< 10 μm) precipitated under reducing conditions replacing CFAp, pyrite and aluminosilicates. Electron-microprobe analyses (EMPA) of coffinite indicate limited incorporation of P 2O5 and CaO, <2.7 and <3.0 wt%, respectively, into the coffinite structure during replacement of CFAp. The chemical formula of coffinite is (U0.95±0.09Ca 0.15±0.02)Σ1.10± 0.1(Si0.84±0.08P 0.06±0.02)<0.90 ± 0.08- Analysis by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) revealed that coffinite initially formed as crystals as large as 100 nm at the edges of altered CFAp. Subsequently, infiltration of (Na, Ba, Sr)-rich oxidizing fluids into fractures resulted in precipitation of Sr-rich M-Aut (up to 4 wt% of SrO) at the expense of coffinite and CFAp. Highresolution TEM reveals that Na-rich fluids caused a distortion of the ideal coffinite structure and stabilized amorphous domains that formed due to alpha-decay event radiation damage. Subsequently, the Na-enriched amorphous areas of coffinite were preferentially altered, and secondary porosity formed at the scale of ∼1 urn. Porosity also was formed during alteration of CFAp to M-Aut, which facilitated the migration of oxidizing fluids over distances of ∼ 150 μm; in to CFAp, as evidenced by precipitation of M-Aut. We report, for the first time, the precipitation of coffinite at the expense of apatite and the subsequent alteration of coffinite under P-rich, oxidizing conditions. These results show that micro-scale dissolution of apatite can create conditions conducive to the precipitation of U(IV)- and U(VT)-minerals, leading to the reduced mobility of U-species under both reducing and oxidizing conditions.
影响因子：
3.7
作者：
Whissell PD;Tohyama S;Martin LJ
通讯作者：
Martin LJ
溶解磷灰石浸出层中铀矿物的形成：磷灰石掺入铀的机制
DOI：
--
发表时间：
2004
期刊：
Chemical Geology 211
影响因子：
--
作者：
Ohnuki;T.
通讯作者：
T.