相山铀矿田同位素地质学特征

ISOTOPE GEOLOGY OF THE XIANGSHAN URANIUM OREFIELD

文章总结了近10年来相山矿田同位素研究成果,探讨了相山矿田岩石成因、成岩成矿年龄、矿液和矿质来源几个方面的问题。同位素年代学研究表明:火山岩的形成时代为140×10~6a,其特征表明岩源为下部地壳。成矿溶液是岩浆水和火气降水的混合,但其成分是不断演化的,成矿前岩浆水占有一定的比例,到了成矿期则主要为大气降水。成矿物质可能主要来自于火山岩。

The Xiangshan uranium orefield is a typical volcanogene hydrothermal orefield, in which there are two main types of uranium mineralization, i. e., soda metasomatic type and fluorite-hydromica type. In the past decade, a series of isotopic research work has been devoted to this orefield. In the light of isotope geology, the present paper makes a preliminary discussion on such problems of the Xiangshan orefield as origin of rocks, ages of diagenesis and mineralization, and sources of ore fluids and ore materials. The whole rock is 140×10~6a , indicating Late Jurassic. (^(87)Sr/^(86)Sr)_0>0.706, and ε_(Nd) values are in the range of-5.4～9.1, suggesting that the volcanic rock was formed mainly through the remelting of the lower crust materials. The U-Pb age determination of pitchblende and the Rb-Sr age determination of the altered rock show that the mineralization age of soda m.etasomatic type and that of f luorite-hydromica type are 120×Τ10~6a± and 100×l0~a± respectively. Hydrogen and oxygen isotope studies of minerals and inclusions show that oxygen isotopic compotition varies remarkably (7.2‰～-9.14‰), whereas hydrogen isotopic composition is relatively stable. Oxygen isotope studies of the protolith and the altered rocks reveal an obvious decrease of oxygen isotopic composition from 10‰±to 4‰ ±in the process of alteration, and this suggests convincingly that the ore-forming solution was mainly meteoric water. Lead isotope characteristics show that ore-forming materials might have been extracted from the volcanic rock through leaching.