document: Cleveland Potash, which runs the site near Saltburn, said the development would secure the plant for 40 years.
  Plans include extending the mine to the east and upgrading facilities to increase production capacity.
  Some groups have raised concerns the development could have an intrusive effect on the local area.
  The company hopes to extend its planning permission with the North York Moors National Park Authority to 2063.
  Cleveland Potash's parent company Israel Chemicals Ltd (ICL) is set to invest Â£300m in the area over the next five years.
  As well as funding the development of the Boulby site, the investment will go towards upgrading the company's Teesport operation near Middlesbrough, which exports potash mined at Boulby.
  One of the first steps will be the Â£16m replacement of the tower at the top of the Boulby site's rock shaft, which lifts the mineral up from the mine.
  The renewal will raise the amount of ore lifted to around 5.3 million tonnes a year, a one million tonne increase on the current maximum.
  The mine's underground equipment, which Cleveland Potash general manager Phil Baines described as "aged", will also be modernised.
  Mr Baines said: "Our present combination of potash resources and reserves totals around 70 million to 80 million tonnes, but following a major exploration programme we expect this figure will increase significantly over the new few years.
  "Our plan is to extend operations out to the east in parallel to the area worked over the past 40 years, effectively providing a new mine for the next 40 years."
summary: Plans to extend a potash mine at Boulby in East Cleveland are expected to create more than 270 jobs by the end of 2015, the owners said.