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The performance of iron-rich calcium sulfoaluminate (IR-CSA) cement is greatly affected by mineral composition and mineral activity in the clinker. This study aims to identify the effect of CaO sources, either CaCO₃ or CaSO₄, on the phase formation and mineral composition of the IR-CSA clinker. Targeted samples were prepared with different proportions of CaCO₃ and CaSO₄ as CaO sources at 1300 °C for 45 min. Multiple methods were used to identify the mineralogical conditions. The results indicate that the mineral composition and performance of the IR-CSA clinker could be optimized by adjusting the CaO source. Both Al₂O₃ and Fe₂O₃ tend to incorporate into C₄A_3−<i>x</i>F<i>_x</i><inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover><mi mathvariant="normal">S</mi><mo>¯</mo></mover></mrow></semantics></math></inline-formula> with an increase in CaSO₄ as a CaO source, which leads to an increased content of C₄A_3−<i>x</i>F<i>_x</i><inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover><mi mathvariant="normal">S</mi><mo>¯</mo></mover></mrow></semantics></math></inline-formula> but a decreased ferrite phase. In addition, clinkers prepared with CaSO₄ as a CaO source showed much higher <i>x</i> value in C₄A_3−<i>x</i>F<i>_x</i><inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover><mi mathvariant="normal">S</mi><mo>¯</mo></mover></mrow></semantics></math></inline-formula> and higher compressive strength than clinker prepared with CaCO₃ as the sole CaO source. The crystal types of both C₄A_3−<i>x</i>F<i>_x</i><inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mover><mi mathvariant="normal">S</mi><mo>¯</mo></mover></mrow></semantics></math></inline-formula> and C₂S were also affected, but showed different trends with the transition of the CaO source. The findings provide a possible method to produce IR-CSA cement at a low cost through cooperative utilization of waste gypsum and iron-bearing industrial solid wastes.