BEIJING, Sept. 26 (Xinhua) -- Chinese President Xi Jinping on Thursday sent a congratulatory letter to honor the 60th anniversary of the discovery of the Daqing Oilfield, China's largest oil production base in northeastern Heilongjiang Province. Xi, also general secretary of the Communist Party of China (CPC) Central Committee and chairman of the Central Military Commission, extended sincere greetings to staff of the oil field, those retired and their families on behalf of the CPC Central Committee. China's oil workers and geologists found the oil field after great hardships 60 years ago, opening a new chapter of historic significance in the country's oil exploration and development history, Xi said in the letter. Xi said that the outstanding contributions of the Daqing Oilfield have been engraved on the historical monument of the great motherland, with the spirit of Daqing and "Iron Man" being important parts of the great national spirit of Chinese nation.