Abstract:Gibbsite in weathering crust is generally considered to have formed under laterization conditions related mainly to iron-rich intermediate and basic or alkaline igneous rocks, so the existence of relationship between this sort of mineral with acid igneous rocks is seldom known. In the weathering crust of niobium and tantalum-bearing albitized granite of 414 mining district, however, gibbsite has been found concentrated exclusively within the weathering crust of the intensely albitized granite alteration zone. The distribution features of this mineral suggest that its formation had nothing to do with laterization environments but was closely related to the high content of fluorine (2.41%) in the intensely albitized granite alteration zone. During the weathering of granite, large amounts of fluorine were leached out to form I-LF solution, which in turn vigorously dissolved the products of earlier weathering (kaolinite), giving rise to gibbsite, The reactions might be summarized thus. The gibbsite gel may become crystalline after a long period of oscillation and accumulation. The weathering crust of the intensely albitized alteration zone contains s-24% gibbsite and its Al2O3/SiO2 is 0.31-0.59. The gibbsite content of samples may be raised up to over 60% and Al2O3/SiO2 to 2.09 if coarse-grained quartz and feldspar are rejected beforehand. It is clear, therefore, that gibbsite in weathering crust of intensely albitized granite is of some economic value.
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郑秀中, 葛金荣.1983.江西41 4含钽、铌钠长石化花岗岩风化壳中三水铝石的发现及其成因研究[J].矿床地质,2(1):87~92.1983.The discovery and genesis studies of gibbsite from the weathering crust of niobium and tantalum-bearing albitized granite in 414 mining district, Jiangxi Province[J].Mineral Deposits2(1):87~92
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