More than 400 construction jobs may be created when a mineral processing plant is built at Wilton, a planning document reveals.

The Gazette told in December how Australian firm Peak Resources wants to base its £70m UK plant on the Wilton International site .

It would process and refine “rare earth” minerals - mainly mined in Tanzania - for use in a range of products, including mobile phones, wind turbines and for the automotive sector.

Peak Resources, which chose Wilton as its preferred site after a search of more than 25 countries, originally estimated up to 100 jobs would be created.

But in an environmental impact assessment submitted to Redcar and Cleveland Council, it is predicting up to 140 full-time jobs might be needed when the plant is operating - and hundreds more during the construction phase.

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The document reads: “It is anticipated that during construction of the facility there would be a need for an average of 280 contractors employed, with a maximum of 420 during peak phases of construction.

“Once the facility is operational, it is anticipated that approximately 140 staff would be required on a permanent basis.”

Peak Resources, which has described the case for choosing Wilton as “compelling”, cited access to global shipping, cheap and reliable bulk reagent supplies, a skilled labour force and readily available power and water as some of the reasons for its decision.

Invista Site Wlton, showing planned refinery in black outline

The firm is mining and processing neodymium and praseodymium – two soft metals, found in the Ngualla mine in Tanzania. Both are used in the “permanent magnet” market, which is expected to grow due to increasing demand for electric cars and bikes, and wind power generation.

If the Wilton proposal gets the go-ahead, production is expected to start towards the end of 2019. The proposed site has been empty since 2012.

The EIA says: “It is anticipated that it would take around two years to construct the facility, with construction commencing early 2018.”

If Peak Resources does set up at Wilton, it will be the site’s second mineral processing plant, with Sirius UK planning to process and ship the minerals it mines beneath the North York Moors in a proposed £237m development.

And there could be a ready supply of energy on tap, with Sembcorp Utilities UK considering a new gas-fired power plant on the site of the former Teesside Power Station - right next door to the proposed Peak Minerals site. As revealed yesterday, Sembcorp hopes to build the Teesside Combined Cycle Power Plant on the site of the old Enron power station, creating hundreds of jobs and producing 1.7MW of electricity - enough for up to 1.5m homes.