The controversial Mineral and Petroleum Resources Development Amendment Bill was sent back because it did not pass constitutional muster, President Jacob Zuma's office said on Monday.

Zuma was therefore required by the Constitution to refer it back to the National Assembly for reconsideration, spokesman Mac Maharaj said.

The president found a number of faults.

As the bill stood, it gave Mineral Resources Minister Ngoako Ramatlhodi the power to amend or repeal certain instruments when the need arose, by-passing constitutionally-mandated procedures for legislative changes.

Zuma felt the public participation process around the bill had been flawed.

The consultation period was highly compressed and provincial legislatures did not appear to have given sufficient notice of public hearings.

Maharaj said Zuma believed the bill should have been referred to the National House of Traditional Leaders for comments as it affected the customs of traditional communities.

It allowed people to set foot on land for an investigation after notifying and consulting the owner, ignoring the consent principle in customary law.

Lastly, the bill elevated certain codes and charters -- the codes of good practice for the South African minerals industry, the housing and living conditions standards for the minerals industry, and the amended broad-based socio-economic empowerment charter for the South African mining and minerals industry -- to the status of national legislation.

The bill was passed by Parliament in March and sent to Zuma for assent.

Among other things, the bill aims "to provide for the regulation of associated minerals, partitioning of rights and enhanced provisions relating to the regulation of the mining industry through beneficiation of minerals or mineral products".

Economists have warned it could scare off investors and create difficulties for the sector.