New evidence discovered in northwest China's Gansu Province showed Japan had finished secret investigation into China's mineral resources in the early 1990s as part of its preparations for its aggression against China.

An individual collector, Du Zhiyong, recently made public two books on investigation of mineral resources in China, which were written by two Japanese and left in Gansu Province after the victory of the Chinese people in their war of resistance against Japanese aggression during World War II.

The two books, written in Japanese, were issued in 1911 and 1942 respectively. They recorded the location, topography, layers and quality of coal resources, coal mining, transportation, sales, ground structures of coal mines and miners in various parts of China including Fushun in northeast China and Pingxiang in the east.

The investigations, which was carried out between 1908 and 1915, also covered coal resources in Bangkok, India, Singapore, the Philippines, New Zealand and Australia.

In one book, the Japanese writer made a thorough investigation into the geological conditions, salt and placer resources in China 's Sichuan, Shaanxi and Shanxi provinces in 1915. It bore the words of "military secret" on the upper left corner on the title page.