Lithium producer Orocobre will join the S&P/ASX 100 index on December 20.

The company recently completed a merger with Galaxy Resources and will be known as Allkem from today.

Its shares have doubled since the start of the year and the company now has a market capitalisation of A$5.85 billion.

Fellow lithium player Liontown Resources will continue its stratospheric rise by joining the ASX 200.

Fresh from a definitive feasibility study and $450 million capital raising, Liontown shares are up 376% since the start of the year, giving the company a market value of $3 billion.

Also joining the ASX 200 is uranium developer Paladin Energy, up 243% since the start of the year and valued at $2.25 billion.

Contractor Monadelphous is among the companies to be removed from the ASX 200.