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"It is not a question of leadership locking themselves in a room... we go through a painstaking process," he told reporters in Johannesburg.
"The conference was the culmination of a massive exercise in participatory democracy involving ANC members in thousands of branches throughout the country over a number of months."
Mantashe was briefing the media after the African National Congress's national executive committee's two-day lekgotla and its list conference which were held in Pretoria at the weekend.
Mantashe held up two books which he said had the names of the party's candidates. However these lists were not distributed to the media.
However, he did confirm that President Jacob Zuma was number one on the list followed by party deputy president Cyril Ramaphosa.
Mantashe said the list had been sent to the national list committee to check it.
"The national list committee doesn't just rubber-stamp what's brought to it," he said.
He said the ANC would release the list after it had registered it with the Independent Electoral Commission.