Foreign mining firms have locked down operations in Guinea and pulled out some international staff, executives said, as the death toll from suspected cases of Ebola there hit 83.
Five new suspected infections were reported in the last 24 hours, the UN's World Health Organisation (WHO) said, bringing the total to 127.
Medical charity Medecins Sans Frontieres (MSF) has warned of an unprecedented epidemic that is testing weak health systems across West Africa.
Suspected cases of one of the world's most lethal infectious diseases have also been reported in neighbouring Liberia and Sierra Leone.
The epicentre of Guinea's two-month-old outbreak has been in the southeast, close to its main iron ore reserves. The country is also the world's top exporter of bauxite, the raw material used in aluminium production, and has rich deposits gold.
"Everyone is practising precautionary strict hygiene but there has been no real impact on production so far," a senior executive at a mining company told Reuters news agency.
The executive said he had been placed on extended leave, while other companies were preventing people from entering or leaving their mines.
Firms were more concerned by what was happening in the densely populated capital Conakry than in remote mining sites in the interior, where controls were easier to put in place, he added.
'Health workers infected'
The WHO has reported 12 suspected cases and four deaths in the ocean-front city of two million people.
Gregory Hartl, the organisation's spokesman, said all the cases in Conakry were linked to one man who came from the central Guinean town of Dobala, about 300km away.
"Unfortunately, this one person infected both family members and health care workers when he went to Conakry for medical attention and died," Hartl told Reuters in Geneva.
Brazilian iron ore miner Vale said its VBG joint venture with BSG Resources (BSGR) - the mining arm of Israeli billionaire Beny Steinmetz's business conglomerate - had pulled its six international staff out of Guinea.
"The expatriates have been transferred temporarily to their home countries," Vale said in an emailed statement in Brazil.
"The local employees ... have been given leave from work until there is more accurate information about the risks of the disease."
There has not been any official statement from the chamber of mines but the executive said mining firms had been calling each other to discuss the best response. "People are locking down camps and keeping movements to a minimum," the executive added.
Neighbouring Senegal has closed its land borders with Guinea, and countries across the region have taken precautionary measures, including banning the sale and consumption of bats, a regional delicacy but an animal believed to be a vector for the virus.
The British Foreign Office said on its website on Wednesday there were reports of suspected cases in Gambia.
But Gambia's director of health, promotion and education, Momadou Njai, denied there were any such infections, saying one elderly man had been tested and cleared.