Phumelele Gura survived a barrage of police bullets and more than two weeks in prison, where he lay awake listening to the sound of workmates allegedly being tortured. His grandfather and his father backed the ANC. He no longer will.

"I won't vote for the ANC next time because they failed the people," he said. "My family always voted ANC but we don't trust it any more."

Gura, 49, is not alone in thinking the events of 16 August 2012 marked a tectonic shift in South Africa. That was the day when police, enforcing the will of the country's black-majority government, opened fire on striking miners, killing 34 and injuring 78.

The massacre represented "probably the lowest moment in the short history of a democratic South Africa", wrote Cyril Ramaphosa, a senior figure in the African National Congress and a former mining union leader.

Comparisons were made with the bloodiest days of apartheid: Sharpeville, Soweto, now Marikana.

Three weeks on, the strike persists and the dust has not settled. But it is increasingly apparent that this tragedy has shaken faith in the ANC and its union allies as never before; that it has focused scrutiny on the exploitative 140-year relationship between foreign capital and black labour and led some to speculate that the tinderbox of South African inequality is just a spark away from conflagration.

Mining has powered the South African economy, and warped its society, since the arrival of the empire builder Cecil Rhodes. Like many of the millions who burrowed underground to extract diamonds, gold and other minerals, Gura came a long way from home in search of a working wage. He found it as a rock driller at the Marikana platinum mine, owned by the British-based company Lonmin.

"It's hard work and sometimes you drill the rock and a rock falls down on you," he reflected. "That's what we're afraid of.

"We spend eight hours underground. It's very hot and you can't see daylight. There is no air sometimes and you have to get air from the pipes down there."

Gura said he lived in a tin shack with a pit toilet and intermittent electricity and water. He earned about 5,000 rand (£380) a month and, like many workers here, sent a portion home to his family in Eastern Cape province. He ran for his life when the shooting began on 16 August, but was arrested and jailed. "From my cell I could hear the police beating my brothers, telling them to speak what they want."

Betrayed

His partner, Primrose Magwangqana, 45, was afraid she would never see him again. "I thought he was dead," she recalled. "They said to some people, 'your husband is in prison', but later they found out he was in the mortuary."

She too feels betrayed by the party she supported all her life. "I am an ANC member but I won't vote for them next time because they failed us. Only [the expelled youth leader] Julius Malema helped us."

Striking mineworkers interviewed by the Guardian in Marikana this week echoed the sentiment. The ANC, the party of Nelson Mandela, which liberated black South Africans and is celebrating its centenary year, can no longer take their support for granted.

Samkele Mpampani, 36, a ringleader who marched on another Lonmin mineshaft this week, said: "I won't vote ANC. They have killed our workers. I don't recognise the ANC any more. Jacob Zuma must step down. It's over now. It's over."

The ANC was already bleeding electoral support before Marikana and sinking into factionalism. The party is accused of enriching a tiny black elite while failing to bring decent education, healthcare and jobs to the poor.

Once a courageous anti-apartheid warrior, Ramaphosa now sits on the board of Lonmin and, it was recently reported, can afford to bid up to R19.5m (£1,480,000) for a prize buffalo.

Protests over poor service delivery have been swelling for years, sometimes fatally, but the scale of Marikana looks like a watershed.

Allister Sparks, a veteran journalist and analyst, said: "It is a cataclysm. Black people saw the police of the black ANC government shooting their own workers. It's shattered the deep-seated trust of the ANC as 'our party', the party you're born into, the party your fathers belonged to.

"The ANC was in the black mind, the black soul, it took on an almost mystical quality. But now they've lost faith in it. The bond is shattered and it happened on television."

The unwritten, almost Faustian, pact made by the ANC at the end of apartheid is creaking under the weight of curdled promises. It set up the ANC's union allies to deliver modestly higher wages for workers while also ensuring labour stability for big business. It saw Thabo Mbeki, the former president, assuring business owners that they should donate to the ANC because "people trust us, we fought for them … they will be patient".

The patience now appears exhausted. Critics say white capital was essentially left untouched and that the purportedly socialist ANC was co-opted by the establishment.

Malema has been calling for a revolution that will make the mines ungovernable until they are nationalised. He has lashed out at British firms such as Lonmin for scooping mineral resources from under the soil upon which workers live in squalid conditions.

Lonmin is easily portrayed as a ruthless capitalist vulture presiding over Orwellian conditions, but the details are bitterly disputed. Mineworkers continue to insist they are paid R4,000 a month and want R12,500. Lonmin asserts that most workers get about 10,500, if bonuses are included.

Economists claim this amount would put them in the top 25% of formal-sector earners in South Africa. "There are a hell of a lot of people in the country worse off than those miners," said one.

Yet it is hard to gloss over the bleak landscape in Marikana, where mine headgear spins, chimneys belch smoke, and giant corrugated steel and concrete silos loom over scrubland dotted with shacks, rubbish and dung.

The Bench Marks Foundation, an organisation monitoring corporate social responsibility, has described a "yawning gap" between Lonmin's promises and the experience of local communities. "They don't engage, they don't communicate properly with the community," it said.

Defenders of Lonmin argue that housing is also a local government responsibility and that many mine workers use part of their wage to maintain homes in distant provinces.

Lonmin claimed: "There are factual inaccuracies within the Bench Marks report and the company doesn't agree with all the findings. However, it does acknowledge that there are certain areas in which it could be doing better. This is a challenge faced by the entire mining community and requires the co-operation and involvement of many parties."

Writing in South Africa's Sunday Times, Ramaphosa admitted: "There are few innocents in this tragic saga … For wherever we find ourselves, we cannot escape the sense that, through our action or inaction, we bear some responsibility for the circumstances that made such a tragedy possible.

"As we mourn, so too must we introspect … What we do now as a people will determine what we become as a nation."

The government has expressed frustration at the mining sector's slow pace of transformation. The sector failed to meet last year's target of 15% black ownership, transferring only 9% of wealth into black hands. It looks unlikely to achieve the required 26% by 2014.

The horror of Marikana and the daily grinding poverty of mines like it can be traced to boardrooms in London and elsewhere.

Robust

Moeletsi Mbeki, an economist and brother of the former president, said: "It's a 140-year-old problem. The mining industry in South Africa effectively started in 1870. Marikana is telling us that the change in 1994 was to incorporate the black elite into the socioeconomic system that the white elite had been running for 140 years. It is a formula loaded with conflict in which violence keeps repeating itself."

Mbeki does not expect a national "catastrophe" to follow but warned: "There is a lot of popular discontent; you can't say popular discontent is not endemic. The reason why the government reacted the way it did is that they have got to show the poor they can react like the previous regime and crack down on discontent.

"We have seen it before with service delivery protests around the country. The difference this time is a lot of people died in one place on the property of a foreign company."

Just how far could the rage spill in this, one of the world's most unequal and violent industrial societies?

Zwelinzima Vavi, general secretary of the Congress of South African Trade Unions, has cast Marikana as a warning, "a bomb waiting to explode".

Justice Malala, a political analyst, wrote of the disenfranchised: "It might make many of us quiver with fear, but here is the cold, hard, truth: they will opt out of the current social, economic and political arrangements and they will choose anarchy."

Paul Verryn, a Methodist minister visiting Marikana this week where he helped broker talks between striking workers and mine management, said the prospect of more violence "nestles in the consciousness of all of us".

He said: "We've got to look very carefully at history. It teaches us that this kind of disparity between rich and poor doesn't go to bed at night. If we don't shift we are preparing ourselves for a revolution."

But while the scars of apartheid unquestionably run deep, other voices warn against nihilism. They argue that racial disparities are narrowing due to the growth of a black middle-class and a gradual but discernible increase in black ownership of companies, homes and land.

Unlike regimes toppled by the Arab spring, South Africa is a country with robust democratic institutions, courts and civil society.

Asked if South Africa was hurtling towards disaster, Sparks said: "I've read that in foreign newspapers for the last 18 years. This is a substantial country, not just a pile of bricks. This is not a country in imminent crisis but it is a country being badly governed, and the constituency that always supported it is losing faith in it."

Meanwhile, amid allegations that police in Marikana shot some miners in cold blood or ran over them in armoured vehicles, the strike continues to boil.

On Wednesday more than 3,000 workers took to the streets. At the head of the march one man carried a handwritten cardboard sign that read: "Lonmin, who gave you power to kill us on our own land? Protect us Juju [Malema].

One demonstrator said: "We work very hard to earn peanuts. Whenever you enter the [lift] cage you risk your life. If they don't give us 12,500, we'll go back to where we're from and break the bank. We will do whatever we have to do to get money. Even if we have to kill to get money, we'll do it."

Asked if he believed whether violence could ever be the answer, the miner replied: "Sometimes violence is the answer."