In the early 1960s cross shaped copper ingots were used as currency in which break-away state in Central Africa?

The state was Katanga, which broke away from the newly independent Republic of Congo (now the Democratic Republic of Congo) in 1960. Led by Moïse Tshombe, Katanga declared its independence shortly after Congo's independence from Belgium.

During this period Katanag even issued its own currency. Cross-shaped copper bars, known as "Katanga crosses", were historically used as a form of currency in the region, symbolising wealth and trade. The use of these copper bars during Katanga's secession was a nod to the region's traditional currency, although they were quickly replaced by more conventional forms of currency during the conflict that followed Katanga's secession. After military intervention and diplomatic efforts, Katanga rejoined the Congo in 1963.

https://en.wikipedia.org/wiki/Katanga_Cross

https://en.wikipedia.org/wiki/State_of_Katanga