* AMCU leader to address strikers
* Lonmin had been aiming for a "mass return"
* 16-week strike has hit 40 pct of global output (Adds AMCU leader's address)
By Zandi Shabalala
MARIKANA, South Africa, May 14 (Reuters) - About 1,000 stick-wielding strikers gathered outside Lonmin's Marikana platinum mine in South Africa on Wednesday, preventing workers from breaking the longest and costliest bout of industrial action in the sector's history.
Some of the strikers, clad in the green shirts of the Association of Mineworkers and Construction Union (AMCU), told Reuters they planned to block anyone from reaching the shafts in a dramatic show of force.
London-listed Lonmin had been aiming for a "mass return" of workers, many of whom have signalled a willingness to end a crippling 16-week strike over pay that has also hit rivals Anglo American Platinum and Impala Platinum.
The strike has halted 40 percent of normal global output and dented already sluggish growth in Africa's most advanced economy.
AMCU's charismatic president Joseph Mathunjwa was to address the Lonmin strikers at around 0800 GMT at a rally, with mass meetings also scheduled later in the day at Implats' and Amplats' operations.
Buses were bringing AMCU members to a stadium in Marikana near the site where police shot dead 34 striking Lonmin miners in August 2012 during a violent, wildcat strike.
The current AMCU strike is legal but has become increasingly violent as an end game looms.
The rival National Union of Mineworkers (NUM) said its members were unable to return to work because of AMCU intimidation. Four people have been murdered around the platinum mines in the last four days, with no arrests.
"The miners cannot get to work because the intimidation is very high," Sydwell Dokolwana, NUM's regional secretary on the platinum belt, told Reuters.
A police spokesman told the eNCA television channel that officers were out in force and were on hand to escort those who wished to return to the mine gates.
"Buses and vehicles taking them to work will receive a police escort to make sure they are protected," police spokesman Thulani Ngubane said.
The companies have been taking their latest wage offer directly to AMCU's members after wage talks with the union collapsed three weeks ago.
Platinum's spot price, which has been largely unmoved by the strike, was up 1.2 percent to $1,465 an ounce, its highest level in four weeks, according to Reuters' data. (Additional reporting and writing and Ed Stoddard; Editing by Ed Cropley and Mark Potter)