桂中铝土矿成矿时代及意义研究

The unique bauxite ores known as Ca-laterite type located at the central Guangxi Zhuang autonomous region are distinctly discriminated from those of the sedimentary type dominated in China and those of the laterite type dominated in other regions globally. There is increasing evidence indicating that bauxites are not only the most important resource of global aluminum, but their associated "three rare elements" (rare, rare earth and rare dispersed elements) may have even higher economic value. This is more significant for the ores in central Guangxi due to their low grade thus to be hardly utilized economically as Al and/or Fe resources. These bauxite ores are hosted by Cenozoic weathering profiles developing based on the late Paleozoic carbonate strata. However, position of bauxitic layers in the profile, lithology of the bed rocks beneath the profile and textures of the ore bodies are markedly different from those of the typical laterite deposits. It has been revealed that geochemical behaviors of the “three rare elements” during the mineralization of diverse types of bauxites are obviously different, thus both to metallogeny theory and regional resource exploration, it is critical to understand the genesis of the bauxite deposits in the central Guangxi. This proposal aims at the timing of the bauxite mineralization in the central Guangxi. Given that the ore-hosting authigenic minerals are relatively small in grain size, dating methods of Th-U-Pbtotal chemical age and U-Th-Pb isotope system are to be applied using the minerals of Ce-monazite (cerianite) and xenotime. By understanding the main metallogenic timing of these deposits, it is expected to provide new findings as a solid foundation for exploring the genesis of the deposits and the redistributive behavior of the associated three-rare elements.

位于广西中部的钙红土型铝土矿矿床类型明显区别于在我国占主导的晚古生代沉积型和在全球占主导的中-新生代红土型。越来越多的研究表明，铝土矿不仅是全球铝金属的主要资源，且伴生的“三稀元素”可能具有更高经济价值，这对品位低、经济效益上难以作为Al-Fe元素利用的桂中铝土矿意义更加突出。桂中铝土矿寄主于晚古生代碳酸盐岩之上的新生代风化剖面，但成矿层的剖面位置、基岩岩性、矿石结构等均与典型红土型铝土矿明显不同，由于不同成因铝土矿的“三稀元素”分配行为差异明显，故了解桂中铝土矿的成因在矿床学理论和区域矿产勘查上均具重要意义。本申请项目拟以查明区内铝土矿矿床主要成矿时代为研究目标，根据其自生矿物粒度较小的特征，应用Th-U-Pbtotal化学法和U-Th-Pb同位素比值法，对矿石中自生Ce-独居石(方铈矿)和磷钇矿进行定年，通过了解矿床主要成矿时代，为认识矿床成因和伴生元素再分配行为提供依据。

位于广西中部的钙红土型铝土矿矿床类型明显区别于在我国占主导的晚古生代沉积型和在全球占主导的中-新生代红土型。越来越多的研究表明，铝土矿不仅是全球铝金属的主要资源，且伴生的“三稀元素”可能具有更高经济价值，这对品位、经济效益上难以作为Al-Fe元素利用的桂中铝土矿意义更加突出。桂中铝土矿寄主于晚古生代碳酸岩之上的新生代风化剖面，但成矿层的剖面位置、基岩岩性、矿石结构等均与典型红土型铝土矿明显不同，由于不同成因铝土矿的“三稀元素”分配行为差异明显，故了解桂中铝土矿的成因在矿床学理论和区域矿产勘查上均具有重要意义。独居石、磷钇矿封闭温度较锆石低，可更为详细地记录热液过程、变质过程发生时间，据此本项目选择了独居石、磷钇矿等磷酸盐矿物作为定年矿物，结合锆石U-Pb定年的结果，对矿产的主要成矿时代进行了详细厘定，为矿床成因和伴生元素再分配行为研究提供了依据。