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在圣弗朗西斯科克拉通Lagoa Real地区的蚀变基底里,角闪石一变粒岩相长英片麻岩产有重要的铀矿床。配重计算表明,在绿帘石一角闪岩相条件下,退化蚀变表现为钠的增加,氧化作用,二氧化硅的带出以及铀的富集。氧同位素数据表明,铀是在近500℃温度时从轻同位素流体中沉淀出来的。流体包裹体数据表明在不同的盐度下温度相近。据认为,地球化学观测同基底推覆到元古代沉积物之上的模式一致,其过程是受逆向地温梯度控制的。
In the alluvial basement of the Lagoa Real area of the San Francisco craton, amphibole-granodioritic amphibolite gneiss have important uranium deposits. The weight calculation shows that the degraded alteration shows the increase of sodium, the oxidation, the outtake of silica and the enrichment of uranium under the amphibolite facies. Oxygen isotope data show that uranium precipitates from light isotope fluids at temperatures near 500 ° C. Fluid inclusion data show similar temperatures at different salinities. It is believed that the geochemical observations are consistent with the model of basal uplifting over Proterozoic sediments, the process of which is controlled by the inverse geothermal gradient.