South African platinum producer Lonmin PLC (LMI.LN) has increased its stake in Canada-based joint venture exploration partner Wallbridge Mining Co. Ltd. (WM.T) via a private placement of common shares and warrants, the two companies said Tuesday.

Lonmin, the world's third largest primary platinum producer, agreed to subscribe to 13,157,895 units of Wallbridge, an exploration mining company which specializes in nickel, copper, platinum and palladium projects in North America, at a price of C$0.19 per unit.

Each unit comprises a common share in Wallbridge's capital and half of one common share purchase warrant with each Warrant purchased via the private placement, entitling Lonmin to purchase a whole common share in Wallbridge at an exercise price of C$0.40 between now and Dec. 31.

The private placement will increase Lonmin's equity stake in Wallbridge, which has a strong focus in Sudbury, Ontario, Canada, by 12.8% so that Lonmin will directly or indirectly control about 19.8% of the Wallbridge's capital via shares and warrants.

"This recent investment shows Lonmin's continued confidence and support for our exploration work in Sudbury," said Alar Soever, CEO of Wallbridge, in a statement.

"The Sudbury Basin is the most attractive target area in the world for the discovery of high grade copper, nickel and platinum deposits," he added.

Albert Jamieson, chief commercial officer of Lonmin said "We've been exploring for [platinum group of metals] with our joint venture partners in Sudbury Basin for nearly 10 years and are now beginning to see the fruits of that hard work. We look forward to progressing the projects in the coming year."

Toronto-listed Wallbridge has 48 mineral projects ranging from grassroots exploration to pre-feasibility stage projects. These include 12 joint ventures with partners Impala Platinum Holdings Ltd, Lonmin, Xstrata Nickel, a unit of Xstrata PLC (XTA.LN) and a number of junior mining companies.

Wallbridge said 60% of the proceeds from the private placement will be used to advance exploration in the Sudbury area. Meanwhile Lonmin said it acquired the units for investment purposes and not for the purpose of influencing management or acquiring control of Wallbridge. It however said it may from time to time increase or decrease its holdings in Wallbridge.

-By Alex MacDonald, Dow Jones Newswires; +44 (0)20 7842 9328; alex.macdonald@dowjones.com