For deeper deposits in mining, the most suitable mode of entry is a shaft. Shafts are vertical or near-vertical tunnels that provide direct access to deep underground deposits, allowing for efficient transport of materials, personnel, and equipment. Horizons and adits are typically used for shallower deposits, as they involve horizontal or near-horizontal access. Inclines, while useful for moderately deep deposits, are less efficient than shafts for very deep mining operations due to their angled approach.
Thus, the correct answer is Shaft.