BEIJING, June 18 (Xinhua) -- The China Coast Guard (CCG) has busted a large criminal ring involved in illegal mining of sea sand and arrested 90 suspects.

An initial probe revealed that the case involves more than 50 million tonnes of sea placers worth 2 billion yuan (over 280 million U.S. dollars), the CCG said in a statement Thursday.

The investigation was a concerted effort of coast guard personnel and local police spanning over two months, and all the primary suspects have been arrested, the statement said.

Further investigation is underway.

Sea sand is an important marine resource, the loss of which will harm the country's coastal zones and its marine geology.

The market price of sea sand remains high due to the rising demands for construction materials in recent years. However, often unpurified sea sand containing excessive chloride ion reduces the durability of buildings and endangers the life of residents.