The Katanga region of Congo has been a major source of the world's ore, principally copper, for over 1,000 years. Copper is still an important part of the economy and vital worldwide, mainly for electrical wiring and equipment – from tiny printed circuit boards to huge power generators. In Central Africa it has been traditionally used for cooking utensils, roofing, plumbing, etc., and for making the Katanga Cross.
At that time, there were a chosen few who belonged to a rather mysterious guild that gave them sole rights to extract, smelt and cast copper. They were called the 'copper eaters' and sacred rituals were associated with their craft.
One ceremonial was to make ingots by channelling the hot, near-liquid metal, from a clay furnace into an X-shaped mould solemnly traced by the master's finger in the sand. This custom continued until 1903, when the Union Minière du Haut Katanga took over most of the region's copper production. Even today, however, there are still a few people who extract and process copper in the traditional way.
For hundreds of years, Katanga Crosses served as a form of currency and traded across several African countries by Arab merchants. Congolese with sufficient means could easily retain the ingots as a reserve commodity and as a status symbol of wealth and power. In the 18th and 19th centuries, the crosses were used for paying taxes to the Lunda Empire, dowries, etc.
In 1960 Congo declared independence and following a coup d'état, Katanga took the opportunity to taste its own autonomy, aided and abetted by European mercenaries, sponsored by Belgian businessmen who were understandably anxious about losing control of Katanga's resources.
The Katanga Cross became an emblem on the breakaway state's flag, appeared on postage stamps and also on coins issued by the National Bank of Katanga.
This may have been an attempt to show the world that their desire for independence was based on indigenous nationalism. The UN forcefully disagreed and the independence ended in early 1963, returning Katanga to the control of the central Congolese government.
The Katanga Cross no doubt has religious symbolism, but we don't associate it with the Christian St Andrew's Cross. Several Katanga Crosses have been found in 13th century tombs, laid on the chest of the deceased, just as other cultures bury valuables with the departed for their journey to the next life.
This predates the arrival of Christianity, brought by Portuguese explorers in 1491. Therefore it seems the cross shape, if influenced by anything at all, was chosen by the 'copper eaters' to replicate an existing sacred symbol, as explained in the page about the Sun Cross.
Many problems in Congo today are blamed on the actions of Europeans in the past, and all nations in the present. See the excellent BBC commentary and also how our vanity perpetuates the suffering of so many Congolese.
Union Minière du Haut Katanga later became Gécamines, the Générale des Carrières et des Mines
The Lunda Empire spanned the present-day Katanga, northern Zambia and eastern Angola
Flag of Congo-Léopoldville 1960-3
Flag of Belgian Congo until 1960
There's a natural sympathy for people wanting to retain their indigenous identity, and there's a possibility that the crosses were added to the flag to subliminally suggest the region was 'Christian', in contrast to the Communist-leaning Republic of Congo-Léopoldville, whose flag included a 5-pointed star similar to the Soviet's.