Copper is classified as a strategic or critical metal in many countries. Its importance extends beyond complementing critical metals, as copper is indispensable for electrification technologies, including power generation, transmission, energy storage, and electric mobility. Ensuring secure and efficient copper production is therefore a prerequisite for enabling large-scale electrification goals worldwide. For decades, the Australian copper industry has benefited from high-quality concentrates, enabling the widespread adoption of streamlined processing technologies. A prime example is the BHP Olympic Dam operation, which utilises the Direct-to-Blister (DB) smelting process. Although DB smelting is renowned for its efficiency and high throughput, it is inherently inflexible and requires high-grade feed to maintain stable operation. With declining ore grades, Olympic Dam is forced to adapt to the more accessible concentrates with lower copper grades and higher impurity levels. To maintain metallurgical recovery and product quality under these conditions, a shift toward two stage continuous processing comprising flash smelting followed by flash continuous converting is becoming increasingly important. This double-flash configuration offers greater flexibility for treating complex feeds and is already being implemented in rapidly growing processing hubs, such as the Manyar smelter in Indonesia. For Olympic Dam, this technology provides a potential pathway to maintain high throughput while reducing environmental impact. The transition to two stage processing introduces additional complexity, particularly in slag chemistry, slag refractory interactions, and impurity removal mechanisms. Flash converting furnaces employ calcium ferrite slags, which differ fundamentally in chemistry from the more commonly studied fayalite slags and for which fundamental thermodynamic data remain limited. This study addresses that gap through an experimental investigation of the CuO0.5-FeO1.5-CaO-MgO-SiO2 AsO2.5 system equilibrated with metallic copper, using high temperature equilibration combined with electron probe microanalysis (EPMA WDS) to determine phase relationships and trace element partitioning. The resulting experimental data were used to refine the FactSage thermodynamic database for calcium ferrite slags, improving the accuracy of predicted phase boundaries and liquidus relationships within this system. A key finding demonstrates that the behaviour of arsenic bearing solid phases in the calcium ferrite slag system provides insight into how arsenic partitions between coexisting phases, with implications for impurity control and emission regulation compliance during converting. By generating new data for this less studied slag system, the study supports the development of resilient continuous copper processing technologies.