Burnt rocks usually exhibit magnetic enhancement, which can be used to detect the spontaneous combustion zone of a coal fire or locate the resources in burnt rocks. To elucidate the mechanisms underlying magnetic enhancement, sandstone is heated to high temperatures between 100 and 1200°C. The mass susceptibility of the sandstone is measured after cooling, and the magnetic characteristics are explained based on the changes in colour and porosity, thermogravimetric and differential thermal analysis experiments and the observation of thin sections of rocks and scanning electron microscopy images. The findings are as follows: (1) the magnetic susceptibility of sandstone increases rapidly by two orders of magnitude as the temperature rises above 800°C. (2) The oxidation of iron ions and the formation of magnetite enhance the magnetic susceptibility of sandstone. The formation of magnetite at 800°C significantly enhances the magnetic susceptibility. (3) The highest temperature experienced by a burnt rock can be evaluated by analysing the different responses of the susceptibility of sandstone to temperature. Furthermore, it is possible to use the magnetic anomaly of the burnt rock to locate it and develop and utilise the beneficial resources in the burnt rock.

中文翻译：

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高温加热后砂岩质量磁化率的变化

烧过的岩石通常表现出磁性增强，可用于探测煤火的自燃带或定位烧过的岩石中的资源。为了阐明磁增强的潜在机制，将砂岩加热到 100 到 1200°C 之间的高温。冷却后测量砂岩的质量磁化率，并根据颜色和孔隙率的变化，热重和差热分析实验以及岩石薄片和扫描电子显微镜图像的观察来解释磁性特征。研究结果如下：（1）随着温度升高到800℃以上，砂岩的磁化率迅速增加两个数量级。(2)铁离子的氧化和磁铁矿的形成增强了砂岩的磁化率。在 800°C 时磁铁矿的形成显着提高了磁化率。(3) 通过分析砂岩的敏感性对温度的不同反应，可以评价岩石烧成所经历的最高温度。此外，还可以利用烧成岩的磁异常对其进行定位，开发利用烧成岩中的有益资源。