It is common practice for geological studies based on interpretation of 3D seismic data to utilize two-way time datasets for convenience. Even depth-imaged or depth-converted 3D datasets have limitations if palaeogeometries are important in understanding the geological process under investigation. In this study I introduce the production of a back-stripped 3D seismic cube to allow examination of restored geometries and depths, which requires time-to-depth conversion and 3D back-stripping. For both processes, either standard functions or more complex models can be utilized as merited. To illustrate the method, I have produced a back-stripped 3D seismic cube across a saucer-shaped igneous intrusion. The sill's restored original geometry fits recent observational and experimental intrusion models, with some modification. Magma supply appears to have been to a deep off-centre point within the inner sill, 3000 m below palaeosurface, with a possible contribution to a more peripheral feeder system below the inclined sheet, and magma propagation to the outer sill being outwards and upwards. The value of a back-stripped 3D seismic cube is not limited to studies of igneous intrusions, but may have application in many areas of subsurface sedimentary basin studies, such as fluid migration path modelling and evolution of hydrocarbon trap geometries.