By Shivani Singh and Judy Hua

BEIJING (Reuters) - The rare earths arm of state-owned China Minmetals Corp on Sunday bought metal and rare earth inventories formerly held by the defunct Fanya Metal Exchange as the sole bidder in online auctions, paying 780.4 million yuan (89.6 million pounds).

China Minmetals Rare Earth Co bought three lots of antimony, terbium oxide and dysprosium oxide for starting prices set by the Kunming Intermediate People's Court, according to the e-commerce site that hosted the auction. The prices paid are below current market value.

The Fanya exchange was launched in 2011 in Kunming, in southwest China's Yunnan province, with the aim of raising the prices of minor metals like bismuth by building up stockpiles using money borrowed from thousands of individual investors.

But the exchange froze transactions and members' accounts in 2015 after experiencing "liquidity" problems and was later taken over by government investigators.

The auctions on Taobao, a platform owned by e-commerce giant Alibaba, are being closely watched by creditors of the bourse owed nearly 40 billion yuan following its collapse in 2015, as well as by minor metals and rare earth traders given the significant volumes coming on to the market.

A 24-hour auction of about 18,661 tonnes of antimony, the entire stock of the metal used in fire retardants that Fanya held when it folded, ended at 1000 Beijing time (0200 GMT) on Sunday, with a China Minmetals Rare Earth Co bid of 546.1 million yuan securing the lot.

That price works out at around 29,264 yuan a tonne, or 18.7% discount to the current spot price. Chinese spot antimony prices, as assessed by industry data provider Asian Metal, have fallen by almost 28% so far this year, to 36,000 yuan a tonne, amid the Fanya stock overhang.

Global antimony production in 2018 was 140,000 tonnes, according to the U.S. Geological Survey, with China accounting for more than 70% of supply. The Fanya volume auctioned is equivalent to more than 13% of last year's global output.

The Kunming Intermediate People's Court, which previously sold some of the bourse's indium ingots on Taobao, had put its market value 25% higher at 682.6 million yuan.

The other two simultaneous auctions that concluded on Sunday were of 4.05 tonnes of terbium oxide - a type of rare earth used in fluorescent lamps and colour television tubes - and 148.75 tonnes of dysprosium oxide, used in ceramics and lasers.

The volumes, also representing the entire inventory of those compounds that Fanya held, were won with China Minmetals Rare Earth Co bids of 12.8 million yuan and 221.5 million yuan, respectively, according to the auction pages.

(Reporting by Judy Hua, Shivani Singh and Tom Daly; Editing by Kenneth Maxwell)