(1. 中南大學(xué) 有色金屬成礦預(yù)測教育部重點(diǎn)實(shí)驗(yàn)室，長沙 410083；
2. 中南大學(xué) 地球科學(xué)與信息物理學(xué)院，長沙 410083)
摘 要: 扶綏鋁土礦是近年來在桂西南地區(qū)探獲的一個典型喀斯特型鋁土礦床。在野外地質(zhì)工作的基礎(chǔ)上，通過顯微鏡觀察、X射線衍射、氫氧同位素測試等手段，對礦床中礦物組合及一水硬鋁石、高嶺石的氫氧同位素進(jìn)行分析，探討成礦環(huán)境的變化及硬水鋁石的成因。結(jié)果表明:硬水鋁石、高嶺石是鋁土礦石中的主要礦物，其次為勃姆石、赤鐵礦、銳鈦礦，沉積期礦石中還含有綠泥石和黃鐵礦等，沉積期后礦石中含葉臘石、伊利石等，堆積礦石中均不含勃姆石。氫氧同位素測試表明:一水硬鋁石的δ18O值為0.95%~1.98%，δD值為-6.5%~-7.94%；高嶺石δ18O值為1.3%~1.89%，δD值為-7.04%~-8.97%。礦物組合指示，鋁土礦沉積于缺氧環(huán)境中，沉積期后轉(zhuǎn)變?yōu)楦谎醐h(huán)境，且經(jīng)歷了干濕交替的氣候變化。一水硬鋁石氫氧同位素組成與鈣紅土三水鋁石有較好的協(xié)調(diào)性，且兼具“風(fēng)化殼”及“紅土”的特征，反映其由鈣紅土風(fēng)化殼演化而來。高嶺石氫氧同位素組成推算沉積階段溫度為33 ℃，沉積期后為18 ℃，與二疊紀(jì)末期—中三疊世海水溫度相似。扶綏沉積鋁土礦的形成是對二疊—三疊紀(jì)全球氣候變化的響應(yīng)，且沉積階段三水鋁石或勃姆石向硬水鋁石的轉(zhuǎn)換與古特提洋俯沖作用有關(guān)的火山活動有密切關(guān)系；堆積鋁土礦的形成則與印支運(yùn)動及后來的表生喀斯特化作用密切相關(guān)。
關(guān)鍵字: 硬水鋁石；氫氧同位素；喀斯特型鋁土礦；沉積
（1. Key Laboratory of Metallogenic Prediction of Nonferrous Metals, Ministry of Education,
Central South University, Changsha 410083, China;
2. School of Geoscience and Info-Physics, Central South University, Changsha 410083, China）
Abstract:Fusui bauxite deposit is a typical Karst bauxite deposit, which is found in southwest of Guangxi Province. Based on the field survey, by the means of microscope, X-ray diffraction, hydrogen and oxygen isotope testing, the mineral intergrowth and H, O sotopes date were analyzed, and the changes of metallogenic environment and the genesis of diaspore were discussed. XRD and microscope observations show that the diaspore and kaolinite are the main minerals, and boehmite, hematite and anatase are the subordinate minerals. Chlorite and pyrite form during deposition stage. Pyrophyllite and illite form during post sedimentary stage. Boehmite is not obtained in accumulative bauxite. H, O isotopes data show that δ18O of diaspore is at range of 0.95%-1.98%, and δD is between -6.5% and -7.94%; kaolinite δ18O is 1.3%-1.89%, and δD is -7.04%- -8.97%. Mineral association indicates that the bauxite is deposited in anoxic environment, which experiences the oxidizing environment and alternation of arid and wet climates during post sedimentary stage. H-O isotopes composition of diaspore is coordinated with terra rossa, and have the characteristics of weathering crust and laterite, which indicates Fusui bauxite is transformed by terra rossa. H-O isotopes composition of kaolinite shows the temperatures of 33 ℃ in deposition and 18 ℃ in post deposition, which approximate sea water from the Late Permian to middle triassic. In conclusion, the transformation of gibbsite and boehmite to diaspore is related to the volcanic activity caused by subduction of the Tethys sea. The formation of the primary sedimentary bauxite is a response to global climate change in the Permian-Triassic. The formation of diaspore in accumulation ores are related to the indosinian movement and karstification.
Key words: diaspore; H-O isotopes; Karst bauxite; deposit
