Motsepe made the announcement at a high-profile event in Sandton, northern Johannesburg, yesterday.

But he stressed that he would not be donating "a lump sum", or liquidating his assets and selling his shares in his company, African Rainbow Minerals .

He will, instead, channel some of the revenue from his family's huge holdings to a foundation that he and his wife, Precious, established in 1999.

Motsepe is considered South Africa's wealthiest man. In October, the Sunday Times Rich List estimated his wealth at about R20-billion.

Though details are still sketchy, Motsepe said he would "contribute at least half of the funds generated by our family assets to the Motsepe Foundation".

He did not give a figure but it would be "about R300-million to R400-million" a year.

Motsepe said the foundation would distribute the money to improve the "lifestyles and living conditions of the poor, disabled, the unemployed, women, youth, workers and marginalised South Africans".

An advisory council of traditional and religious leaders would meet foundation representatives each year to decide on the projects to benefit.

According to his wife, "a technical team will ensure that the money goes to the right places".

Zulu king Goodwill Zwelithini, Education Minister Angie Motshekga and a number of traditional and religious leaders were among the guests at yesterday's Sandton function.

Gates, founder of software giant Microsoft , sent a pre-recorded personal message, via big-screen TV, to the Motsepes.

He said he was "thrilled" by their plans.

The Motsepes last year met Gates and his wife, Melinda, in Cape Town, and got "encouragement" from the US couple.

According to the Motsepes, they are the first couple outside the US to commit themselves to the Giving Pledge established by Gates and Buffett.

In the pledge "the wealthiest individuals and families in America commit to giving the majority of their wealth to philanthropic causes and charitable organisations of their choice, either during their lifetime or after their death".

Motsepe said the money would assist in creating an environment in which recipients were able to stand on their own feet and "have control over [their] own future".

"We don't want Africa to be forever a continent of charity," he said - but donations would be needed for years to come.

He stressed that, though he would not limit his philanthropy to South Africa, the "overwhelming majority" of the funds would be earmarked for this country.

He acknowledged that South African businesses and other tycoons had been involved in philanthropy and had made "very significant" contributions.

His aim was not to challenge other wealthy South Africans.

His message to the poor was: "We are not going to allow you to suffer on your own."

According to Forbes magazine, Motsepe was, as of November, the fourth-richest person in South Africa, the eighth on the continent and 442nd in the world.

Gates said more than 90 rich people had already committed themselves to the Giving Pledge.

THEY GAVE AT THE OFFICE

IN 2006, Bill and Melinda Gates upped the ante on their previous philanthrophic endeavours by partnering with Warren Buffett.

The Bill and Melinda Gates Foundation has, according to its website, since paid out more than $25-billion to charitable causes. It has an asset trust endowment of $36.2-billion.

Buffett gave the foundation a large chunk of his Berkshire Hathaway shares in 2006.

Since then more than 90 wealthy individuals and families have pledged to give most of their wealth to charitable causes.

Among them are South African-born inventor and entrepreneur Elon Musk, Microsoft co-founder Paul Allen, Star Wars creator George Lucas and CNN founder Ted Turner.

Facebook's Mark Zuckerberg has also pledged money.

BUFFETT ONE OF THE FIRST

THE Oracle of Omaha, billionaire US investor Warren Buffett, announced in 2006 that he would give most of his wealth to philanthropic foundations.

His shares in his investment company Berkshire Hathaway comprise most of his wealth and Buffett committed to give all of his stock to charitable causes over time.

At the time, he was usually in a close - a few hundred million dollars - race with Bill Gates to be the richest man in the world.

In 2010, Buffett and Gates openly started encouraging other billionaires to pledge most of their wealth to charitable causes.

Buffett reiterated his pledge: "More than 99% of my wealth will go to philanthropy during my lifetime or at death."