Cusack's early research at the Broken Hill mineral procession operations, highlighted by his innovative AVCRA flotation cell and process automation and control work, led him into a career in management of major operations at Broken Hill, Woodlawn, Dampier, and Hamersly. In each role his tenure was associated with technological innovation leading to increased profitability and efficiency. Significant technological innovation marked his leadership of the large and complex HIsmelt pilot plant, one of Australia's largest R&D ventures of recent years. He plays a leading role in national and international business, education and management bodies in the profession. He is also a Fellow of AusIMM.