Chile said yesterday it would send anti-depressants down a tiny shaft to 33 miners trapped half a mile underground for 20 days, as it told them it will take at least three more months to dig them out.

Health minister Jaime Manalich said the miners had reacted calmly, AFP news agency said. “We were able to tell them… they would not be rescued before the Fiestas Patrias (Chile’s Independence Day on 18 September), and that we hoped to get them out before Christmas,” AFP quoted Mr Manalich as saying.

Although they took the news calmly, he said, “a period of depression, anguish and severe malaise” was possible.

Rescuers are now sending fresh clothes, medicine and games down a 2,300 feet bore hole the diameter of a grapefruit to help keep the men physically and mentally fit for the gruelling wait ahead.

The government has asked NASA and Chile’s submarine fleet for tips on survival in extreme, confined conditions, and are looking to send them space mission-like rations.

Manalich said rescue workers had managed to finish a second narrow bore hole which will be dedicated to channelling drinking water to the miners and keeping communications flowing.

They are also preparing to drill a vertical shaft around 2 feet in diameter to evacuate the miners one by one via a pulley.

“We expect that after the initial euphoria of being found, we will likely see a period of depression and anguish,” the minister said. “We are preparing medication for them. It would be naive to think they can keep their spirits up like this.”

The miners and their relatives are exchanging letters via the shaft, a crucial part of maintaining their mental health.

“You have no idea how much my soul ached to have been underground and unable to tell you I was alive,” trapped miner Edison Pena said in a letter to his family. “The hardest thing is not being able to see you.”

Fellow miner Esteban Rojas promised his wife he would finally buy her a wedding dress as soon as he gets out, and hold a church marriage ceremony, 25 years after they wed in a registry office.

Officials are vetting letters sent by relatives, to avoid any shocks. Some disagree with the method.

“It’s very important for the miners’ mental health that they communicate openly with their families, and without filters, either by letter or by phone,” said Claudio Barrales, a psychologist at the Universidad Central in Santiago.

Trapped miners’ relatives, who have been living in plastic tents at the mine head in a makeshift settlement dubbed Camp Hope, are gradually returning to their normal lives, but some are drawing up rosters to take turns being at the mine.

The miners have lost around 22 pounds each after having survived on half a glass of milk and two mouthfuls of canned tuna every 48 hours until supplies ran out.

The men sent samples of water from underground tanks that have helped them to survive to the surface for testing, and rescuers are sending down fortified mineral water.

The miners are in remarkable health, and have stripped off their shirts to cope with the heat.

Officials are looking for ways to help ease psychological pressure and plan to set up special lighting in the tunnel to mimic night and day, with dull red lights to help the miners sleep. They are also going to send down games like cards.

Until now, the miners have used vehicle batteries to power lights and charge their helmet lamps.

Two small tremors shook northern Chile early on Wednesday, but witnesses at the mine head said they did not feel them at ground level. It was unclear if the miners, who are 4.5 miles inside the winding mine, were jolted.

The nation is still recovering from a devastating quake on 27 February – one of the biggest ever recorded – and ensuing tsunamis, which killed more than 500 people and ravaged cities, roads and industries in south central Chile.

The accident in the small gold and copper mine has turned a spotlight on mine safety in Chile, the world’s No. 1 copper producer, although accidents are rare at major mines. The incident is not seen having a significant impact on output.

President Sebastian Pinera has fired officials of Chile’s mining regulator and vowed to overhaul the agency.

Analysts say the feel-good factor of finding the miners alive, coupled with the government’s hands-on approach, could help Pinera as he tries to push through changes to mining royalties that the centre-left opposition had shot down.