关键词: 花岗岩;铀成矿作用;部分熔融;分配系数;活化迁移;成矿机理;模拟实验

Abstract:

Abstract:  Based on the theory of “uranium preconcentration system” and the theory of precipitation, the author has conducted the “partial fusion experiment” of uranium productive granite and its mother rock. The result shows that  the mother rocks for forming uranium productive  granite are originated from the sedimentary rocks of Cambrian and the Lower Palaeozoic, etc. The test indicated that the uranium distribution coefficient (Kfm) between the uranium productive granite fluid (f) and the coexisting fused mass (m) at magma temperature is remarkably smaller than 1, showing that the uranium is intensively concentrated in the fused mass, and the continuous remelting can make the uranium content increase in granite. During the period of magma crystallization, the distribution coefficient (Kfc) between fluid (f) and crystalline fused mass (c) increases with the advance of crystallization, indicating it is favourable for forming the hydrothermal uranium deposit. By analyzing the uranium distribution coefficients of different crystals, we found that the uranium distribution coefficient is the largest, when ferruginous material and uranium mineral crystals are coexisting. The experiment results are concordant with the fact that uranium content is higher when the uranium productive granite contains more uraninite and pyrite, which is consistent with the fact that biotite captures uranium during the crystallization. The experiment of uranium mobilization in the period of preore alteration before mineralization shows that about 3％30％ uranium is released when the biotite is converted into muscovite (muscovitization). During the granite muscovitization, about 30％60％ uranium will be released from the total rock and 14％21％ uranium will be released from zircon; the uraninite is disintegrated and parts of them are dissolved. The experiment indicates that the total uranium which migrated into the solution is (104130)×10-6. Hydrothermal experiments of waterrock reaction exhibit that in the solution of a sealed system, the dissolution of uranium increases (up to 23 orders) with pressure decreasing. This conclusion smashed the traditional view point that the uranium will precipitate when pressure is decreased. New conclusions have been drawn from the experiments of hydrothermal uranium mineralization: (1) Moderate decarbonation is favourable for uranium precipitation and also favourable for “uraniumsilicon separation”  from the “uraniumsiliconcarbonate” system. (2) The key factor for uranium precipitation is the remarkable decrease in the pH of the mineralization solution. The experiments have confirmed and developed the theory of the preconcentration system of strata and granite masses, and have a great significance for uranium prospecting.

Key words:

Key words: granite; uranium mineralization; partial fusion; distribution coefficient; mobilization migration; mineralization mechanism; simulation test