To discover or delineate mineral deposits and other geological features such as faults and lithological boundaries in their host rocks, seismic methods are preferred for imaging the targets at great depth. One major goal for seismic methods is to produce a reliable image of the reflectors underground given the typical discontinuous geology in crystalline environments with low signal-to-noise ratios. In this study, we investigate the usefulness of the reverse time migration (RTM) imaging algorithm in hardrock environments by applying it to a 2D dataset, which was acquired in the Ludvika mining area of central Sweden. We provide a how-to solution for applications of RTM in future and similar datasets. When using the RTM imaging technique properly, it is possible to obtain high-fidelity seismic images of the subsurface. Due to good amplitude preservation in the RTM image, the imaged reflectors provide indications to infer their geological origin. In order to obtain a reliable RTM image, we performed a detailed data pre-processing flow to deal with random noise, near-surface effects, and irregular receiver and source spacing, which can downgrade the final image if ignored. Exemplified with the Ludvika data, the resultant RTM image not only delineates the iron oxide deposits down to 1200 m depth as shown from previous studies, but also provides a better inferred ending of sheet-like mineralization. Additionally, the RTM image provides much-improved reflection of the dike and crosscutting features relative to the mineralized sheets when compared to the images produced by Kirchhoff migration in the previous studies. Two of the imaged crosscutting features are considered to be crucial when interpreting large-scale geological structures at the site and the likely disappearance of mineralization at depth. Using a field dataset acquired in hardrock environment, we demonstrate the usefulness of RTM imaging workflows for deep targeting mineral deposits.

中文翻译：

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瑞典 Ludvika 矿区氧化铁矿床的逆时偏移 (RTM) 成像

为了发现或描绘矿床和其他地质特征，如母岩中的断层和岩性边界，地震方法是对目标进行深部成像的首选方法。地震方法的一个主要目标是在低信噪比的结晶环境中，鉴于典型的不连续地质情况，生成地下反射层的可靠图像。在本研究中，我们通过将逆时偏移 (RTM) 成像算法应用于在瑞典中部 Ludvika 矿区获得的二维数据集来研究硬岩环境中的逆时偏移 (RTM) 成像算法的有用性。我们为 RTM 在未来和类似数据集中的应用提供了一个操作方法解决方案。当正确使用RTM成像技术时，可以获得地下的高保真地震图像。由于在 RTM 图像中保留了良好的振幅，成像的反射体提供了推断其地质起源的迹象。为了获得可靠的 RTM 图像，我们执行了详细的数据预处理流程来处理随机噪声、近地表效应以及不规则的接收器和源间距，如果忽略这些会降低最终图像的质量。以 Ludvika 数据为例，所得 RTM 图像不仅描绘了先前研究中显示的深达 1200 m 的氧化铁沉积物，而且还提供了更好的片状矿化结束推断。此外，与之前研究中基尔霍夫迁移产生的图像相比，RTM 图像提供了大大改善的堤坝和横切特征相对于矿化片的反射。在解释现场的大型地质结构和深度矿化可能消失时，两个成像的横切特征被认为是至关重要的。使用在硬岩环境中获得的现场数据集，我们展示了 RTM 成像工作流程对深层定位矿床的有用性。