西澳Darling Range地区铝土矿特征及成矿控制因素

Geological Characteristics and Ore-Controlling Factors of the Bauxite Deposits in Darling Range,Western Australia

我国铝土矿资源相对匮乏,但需求量大。澳大利亚铝土矿资源丰富,是我国铝土矿进口主要国家之一。Darling Range地区为澳大利亚铝土矿主产地之一,了解该区的铝土矿成矿特征将有助于我国企业走出去在该地区或相似地区找矿提供依据。Darling Range位于西澳大利亚的伊尔岗克拉通,该区铝土矿以红土型为主,铝土矿的显著特点是品位较低,铁、硅含量高,但对铝土矿冶炼有害的可溶性硅含量低,资源潜力巨大。铝土矿产于红土层中,厚度受后期剥蚀作用控制。红土剖面从上到下依次分为覆盖层、硬壳、碎屑层和底部粘土层。覆盖层以砂砾为主,具有经济意义的铝土矿主要集中在碎屑层和硬壳中,底部粘土层则阻止铝土矿继续向下运移。铝土矿中的矿石矿物主要是三水铝石,也有少量一水软铝石,主要由花岗岩或基性岩(如辉绿岩、绿岩)中的长石经过风化淋滤形成。Darling Range地区铝土矿根据基岩的种类可分为花岗岩类铝土矿和镁铁质类铝土矿,分别以Jarrahdale铝土矿矿床和Mount Saddleback铝土矿矿床为代表。铝土矿的成矿主要受气候、母岩、地貌、排水和植被等因素控制。气候主要通过控制气温和降水影响红土化作用的进行;母岩通过自身的物理化学性质和矿物组成控制铝土矿的形成;地貌和排水影响铝土矿的风化速度;植被的作用既保证了土壤风化淋滤所需的渗透性,又降低了外部因素对土壤的侵蚀速率。在各种成矿因素的综合作用下,经过漫长的时间演化最终形成了红土型铝土矿。

China resources, and is one is short of bauxite resources, but demands more. Australia, however, is rich in bauxite of the major countries of China＇ s imports of bauxite. The Darling Range is one of the main bauxite concentration areas in Australia, and understanding the characteristics of bauxite in this area will help our Chinese mining companies to do the mineral exploration in this or other similar regions. Located in the Yilgarn Craton, western Australia, Darling Range is famous for lateritic bauxite deposit characterized by low ore grade, high content of iron and silica, low content of soluble silica harmful to smelting bauxite, and huge resources potential. The thickness of bauxite hosting in laterite is controlled by late erosion. Laterite profile is composed of overburden, duricrust, friable fragmental unit and basal clay from top to bottom. Overburden is mainly gravel, while the economic bauxite mainly occurs in friable fragmental unit and duricrnst. The basal clay at the bottom stops bauxite downward migration. The ore minerals in bauxite are predominantly composed of gibbsite, with minor boehmite, and are derived from weathering and leaching of the feldspar in granite or basic rock （ such as diabase or greenstone）. According to the type of bedrock, Darling Range bauxite can be divided into granite bauxite and magnesium iron bauxite, exemplified by Jan＇ahdale bauxite deposit and Mount Saddleback bauxite deposit, respectively. The ore-forming process of the bauxite in Darling Range was mainly controlled by climate, parent rocks, drainage, topography, and vegetation. Climate affects mainly through the temperature and precipitation. The physicochemical property and mineralogy of the parent rocks control the bauxite formation, while the temperature and precipitation affects the laterization, and the topography and drainage influences the bauxite weathering speed. The effect of vegetation can not only ensure the soil permeability required for weathering and leaching, but also reduce the rate of external factors on soil erosion. Under the comprehensive effect of various factors, the laterite bauxite deposit was formed through the long time evolution.