BHP Billiton (LON:BLT) is to divest a 75% stake in its Indonesian coal unit IndoMet Coal to PT Alam Tri Abadi for $120 million.

The deal comes at a time when mining companies have started to slow spinning off units considered to be non-core.

A slowdown in China exposed the years of rash spending by mining companies in the boom years leading to major overcapacity when demand from China began to weaken.

BHP Billiton’s recent sale follows the divestment of assets into South 32 last year.

News of the sale came as the port authority in Port Headland, Australia, released data showing exports of iron-ore leaving the port increased 4.5% mom in May.

BHP Billiton along with Fortescue are the largest iron-ore miners in Pilbara region of north-west region of Australia, with much of their ore destined for China, Japan and Korea.