This paper presents the development of a downhole assay tool specifically engineered for mining environments, with a strong focus on iron ore resource evaluation. Moving beyond the constraints of repurposed oilfield technologies and design philosophies, this tool leverages the relatively benign conditions encountered in mining boreholes to optimise measurement accuracy, precision, and operational efficiency. A key design innovation is the use of non-metallic housings to eliminate interference from iron-bearing tool components, ensuring reliable detection and quantification of iron and associated gangue elements critical to ore characterisation. The tool employs pulsed fast and thermal neutron activation–gamma ray spectrometry to temporally separate gamma rays generated by distinct neutron interactions—fast neutron interactions and thermal neutron interactions—and from radioactive decay of unstable nuclides created from such interactions. This approach enhances element identification and quantification through cross validation of elemental responses across interaction types. Monte Carlo nuclear modelling guided key design decisions, including detector configuration, shielding geometry, and material selection to minimise tool background. The resulting tool is compact and lightweight, while maintaining robustness and reliability for high-volume mining operations. The tool design enables efficient measurement acquisition across all stages of mining. It is engineered to handle the deeper boreholes encountered during early exploration and resource development, while also optimised for the rapid cycle time between holes critical in production environments. To meet the demands of blasthole logging, the tool incorporates a standby capability that facilitates streamlined movement between holes, supporting high productivity while maintaining safe operating practices. By integrating advanced nuclear measurement principles with mining-specific design priorities, this technology delivers accurate, reproducible, and timely compositional data suitable for modern resource evaluation, with potential applications in near-real-time decision support during drilling, grade-informed blast design, load and haul optimisation, grade control, and geometallurgical modelling.