Fe-kaolinite in granite saprolite beneath sedimentary kaolin deposits: A mode of Fe substitution for Al in kaolinite
Fe-kaolinite in granite saprolite beneath sedimentary kaolin deposits: A mode of Fe substitution for Al in kaolinite
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DOI：
10.2138/am-2018-6478
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发表时间：
2018-07-01
影响因子：
3.1
通讯作者：
Tsukimura, Katsuhiro
中科院分区：
文献类型：
--
作者：
Jige, Mayumi;Takagi, Tetsuichi;Tsukimura, Katsuhiro
在日本中部濑户地区沉积高岭土矿床下的花岗岩腐岩中发现了铁高岭石。花岗岩腐殖岩是在河流和湖泊环境中形成的沉积高岭土矿床之下发现的，经历了高岭土化作用。花岗岩腐殖岩的粘土组分主要由高岭石和次要的云母粘土、石英和长石组成。电子探针微区分析（EPMA）结果表明，粘土矿物中高岭石平均含有3.30- 3.72wt%的Fe_2O_3，为铁高岭石。铁-高岭石中的Fe+Si与Al成反比，表明Fe+Si与Al之间存在耦合取代。铁-高岭石中K2 O含量随着Fe 2 O3的增加而增加，最高可达0.77wt%，而K与其他元素无关，表明K不含在高岭石的结构中，而是存在于其层间。X射线吸收近边结构（XANES）光谱表明粘土组分中约60 - 70%的Fe是三价铁，扩展X射线吸收精细结构（EXAFS）光谱表明Fe位于八面体位置取代Al。Fe-高岭石可能是通过具有较高Fe和碱含量的酸性地下水渗入花岗岩腐岩中而沉淀的，伴随着沉积高岭土矿床的强烈高岭土化。
Fe-kaolinite has been detected in granite saprolite beneath sedimentary kaolin deposits in the Seto district of central Japan. Granite saprolite, which was found underneath sedimentary kaolin deposits formed in fluvial and lacustrine environments, had been subjected to kaolinization. The clay fractions of granite saprolite consist mostly of kaolinite with subordinate micaceous clay, quartz, and feldspars. Electron probe microanalysis (EPMA) showed that the kaolinite in clay fractions contained an average 3.30-3.72 wt% of Fe2O3, indicative of Fe-kaolinite. Fe+Si was inversely proportional to Al in Fe-kaolinite, indicating coupled substitution between Fe+Si and Al. The K2O contents of Fe-kaolinite increased with increasing Fe2O3 up to 0.77 wt%, whereas K did not correlate with other elements, suggesting that K was not contained with the structure of kaolinite but was present in its interlayers. X-ray absorption near-edge structure (XANES) spectroscopy showed that about 60 to 70% of Fe in the clay fractions is ferric iron, and extended X-ray absorption fine structure (EXAFS) spectroscopy indicated that Fe is situated in octahedral sites replacing Al. Fe-kaolinite was likely precipitated by the infiltration of acidic groundwater with higher Fe and alkali contents into granite saprolite, accompanied by the intense kaolinization of sedimentary kaolin deposits.