Lonmin is getting closer to securing its purchase of Southern Platinum, with both companies having jointly mailed off offering documents.

The documents, accompanied by a Southern Platinum directors' circular supporting the offer, have now been filed with all relevant securities regulators.

According to the companies, the offer will be open for acceptance until 17:00 EST on May 20th, unless Lonmin withdraws or extends its offer.

The deal is worth $190 million and will bring a host of benefits to Southern Platinum shareholders.

Management and directors at Southern Platinum have agreed to support the offer and have all agreed that it is fair to holders of common shares and is in the company's best interests.

Under the acquisition, Lonmin would acquire Southern Platinum's Messina platinum mine in South Africa, where production is expected to rise to 75,000 ounces a year.