On his return to Belgrade, he noticed that one of the biggest problems for his father’s brewery  was a dependence on expensive coal which the brewery  used in large quantities. He started to search around Serbia, which is rich in coal sediments, for a place profitable for exploitation. After just one year, in 1873, he was given a  concession to a coal mine in Kostolac, in Eastern Serbia  on the river Danube. This was a great success: the mine was rich and he was able to transport the coal in barges up the Danube. This 'beginner's luck’ stirred  in him a passion for mining, that remained with  him throughout his life, and mining became his main occupation.

In the following years he opened up numerous mines^[10]  in Serbia , but they largely proved to be financial disasters. By 1895, most of his business partners and investors had left him, and he had accumulated debts  that neither his mine in Kostolac nor his father’s brewery could cover.

In 1895, he started to dig around Bor^[11], and after initial disappointments  his mining engineers struck lucky.  This location proved to have the richest sediment of copper in Europe. In just  a couple of years  the small village of Bor became a large mining town and George Weifert, now the richest man in Serbia, was called ‘the father of the mining industry’.

The financial success enabled him to enlarge his beer brewing company. He opened up breweries in Sremska Mitrovica and Nis, and ‘Weifert’s beer’ became the most popular in Serbia.

In 1867, Serbia  gained independence from Turkey. The new state was in need of commercial and financial institutions   to support the industrialization of this impoverished country. George Weifert, who became a Serbian citizen in 1873, played a part in this endeavor. In 1880, he was one of  the founders of the Serbian Chamber of Commerce and its first president. In 1884, against the wishes of King Milan Obrenovich’s government, which favored foreign capital, George Weifert and a group of Serbian investors met the requirements for establishing the National Bank  of Serbia, and was elected   its first Governor. He was to hold this position till 1926. His efforts were instrumental in transforming the National Bank of Serbia into a National Bank of Serbs, Croats and Slovenians after unification in 1919, and in stabilizing the dinar as a currency in Europe.