The contract is for structural mechanical piping electrical and installation of the kiln feed hood and waste gas treatment circuit at the circa $500 million facility, which will treat rare earth concentrate from Lynas' Mt Weld mine.
The project the largest in terms of value to be awarded in Alltype's 37 years of operations.
The contract award follows Alltype's successful execution of the rotary kiln contract at Lynas' facility.
Works have started and will be completed in 2023.
This contract award brings Weststar's 2023 financial year consolidated group contracted revenue to about $120 million.
Alltype managing director Kelvin Andrijich said the project contributed to the company's continued presence at the Kalgoorlie site, and further strengthened the working relationship with Lynas.
"Our project team has done a fantastic job on the rotary kiln project to date, and we appreciate Lynas' recognition of this performance and the positive collaboration between our companies, who are both focused on safe and efficient construction of this critical process plant infrastructure," he said.
WestStar's other subsidiary is diversified services company SIMPEC, which currently has a $145 million construction contract for Fortescue Metals Group and Formosa Steel's Iron Bridge magnetite project.
WestStar shares last traded at 18c, giving it a market capitalisation of just under $20 million.