The linear beaches of Mining Area 1 (MA1) on Namibia’s south-western coastline host the onshore portion of the world’s largest diamond placer deposit. These beaches have been actively mined for over 80 years but land-based mining methods are close to reaching their practical limit on this vigorous wave-dominated coast. Seismic data and sparse sampling data confirm that the linear beach deposits continue offshore onto the inner shelf, which is characterised by a number of erosional nick-points and wave-cut platforms developed over the bedrock topography. This environment constitutes a techno-economic challenge and a target ranking methodology is required for economic development of the offshore extension of the deposit. Detailed analysis of the historical onshore mining dataset (including footwall elevation survey data, diamond grade information and detailed geological mapping and modelling), was integrated with newly acquired geophysical data that spans the onshore and offshore sectors of the deposit. This shows that relative diamond grade is controlled by the gradient of the bedrock and the wave-cut platform width. An inherited structural control on bedrock gradient is also shown. The direct gradient-grade and indirect platform width-grade relationships can be extended to the offshore realm and used as target ranking criteria. These results greatly aid risk mitigation of decision making against the backdrop of techno-economic challenges associated with developing and mining the nearshore extension of the placer. Keywords: Marine diamond placer exploration, Inner shelf, Inherited geological framework control, Integrated onshore-offshore modelling, Transgressive deposits.