Exploration and Sources of Bauxite Deposit in the Boloven Plateau, Southern Laos

The Boloven bauxite deposit occurs either in the weathered basalt(alkali basalt and tholeiite), or in the Cretaceous sandstone. It is generally agreed that the bauxite deposits/laterites overlying the alkali basalt and tholeiite were derived from weathering of underlying basalt, however, the origin of bauxite deposit overlying the sandstone remains controversial. Chondrite-normalized REE patterns show that the bauxite ores/laterites overlying the sandstone exhibit quite similar chondrite-normalized REE patterns to those overlying the alkali basalt. Diagram of Al-Ti-Zr shows that the bauxite ores/laterites overlying the sandstone, tholeiite and alkali basalt are close to each other and to the calc-alkaline suite, however, significantly different from the sandstone and shales. Binary diagram of log Nb/Y vs log Zr/Ti further indicates that the parent rocks of bauxite ores/laterites overlying the sandstone belong to the suit of ultra-alkali to alkali basalt. Multivariate statistical analysis of geochemical data exhibit that the geochemical characteristics of HREE, Y, LREE and Al_2O_3 for bauxite ores/laterites overlying the sandstone are similar to those overlying the alkali basalt(15.7 Ma), obviously different from those overlying the tholeiite(1.2 to 0.5 Ma). Consequently, it can be inferred that the bauxite deposits/laterites overlying the sandstone were derived from the alkali basalt.

老挝Boloven高原玄武岩风化壳中稀土元素富集与主量元素关系

老挝南部Champasak省东北部Boloven高原玄武岩喷发于晚中生代-新生代,在长期热带季风型气候和热带季雨林植被条件下,高原玄武岩上已经发育砖红壤型风化壳。在一条风化壳剖面上采集了11件样品并在室内细碎到200目,使用X射线荧光光谱仪分析了11个样品中的主量元素含量,使用ICP-MS分析了11件样品REE含量。结果表明,玄武岩风化壳中主量元素Na2O和MgO淋失量最大,K2O和CaO淋失量次之,并在淋失一定程度后淋失速度减慢;样品LR157和LR158中TiO2,P2O5分别为6.07%,1.45%和8.43%,0.82%,为整个剖面中的最高值;CaO的含量是松散风化产物中的最高值。风化玄武岩(LR140,LR141)的∑REE较低,为57.8×10-6和87.9×10-6;随着玄武岩风化程度和成壤作用的加强,∑REE逐渐富集,并在风化壳表土下(LR157,LR158)达到最高值1003×10-6和775×10-6。风化壳中LREE/HREE值为3.59～14.9,稀土元素分布型式属轻稀土富集型。随着风化程度加深,Ce由弱负异常逐渐变为强正异常,而Eu由弱正异常逐渐变小并呈现出强负异常,整个剖面中Ce正负异常和Eu正负异常的变化幅度较大。REE在剖面中的分布与含TiO2,P2O5的矿物有明显的相关关系,并且在TiO2,P2O5含量最高的样品LR157和LR158中最为富集。REE富集和Ce正异常出现在pH值为5.23～6.12的酸性和Fe2+/Fe3+为0.007～0.13的氧化环境下,证明在酸性氧化环境也能出现REE富集。

老挝波罗芬高原铝土矿地质特征与成矿规律

老挝南部占巴赛省波罗芬高原分布大面积玄武岩,红土化作用强烈。通过野外地质调查、浅井施工,结合样品化学分析、X射线衍射、X射线荧光、等离子质谱等分析方法,对老挝波罗芬高原的铝土矿地质特征与成矿规律进行研究。研究结果表明:老挝波罗芬高原存在丰富的铝土矿,该铝土矿是由玄武岩风化而成,分布于整个波罗芬高原及周边地区,Al2O3含量为30%～50%,Fe2O3含量为25%～40%,铝硅比为5～20,具有中铝、高铁、低硅与高铝硅比,分布范围广,资源量巨大,覆盖浅,地势平缓等特点,适合于大型机械化露天开采,是一个红土型风化壳型三水铝土矿巨型矿带。

老挝波罗芬高原红土型铝土矿地质特征与成矿规律

老挝南部占巴塞省的波罗芬高原分布大面积的玄武岩。该区气候属热带季风型,炎热多雨、干湿交替。在这种湿热气候和地貌间隙性抬升、基地裂隙发育排水通畅的地质背景下,形成了丰富的红土型铝土矿资源。

老挝南部波罗芬高原玄武岩砖红壤风化壳微量元素地球化学特征

老挝南部波罗芬高原分布大面积新生代玄武岩,并一直在缓慢抬升,由于老挝地属热带季风气候,炎热和高降雨量作用,形成了砖红壤风化壳,厚度在25m以上。论述了风化壳中20种微量元素分散富集规律,大部分微量元素在表生环境下的化学活动性符合元素在氧化环境和酸性环境中的元素活动规律。