Geology

The Adaro Coal Concession is located on the eastern margin of the Barito Sub-basin, close to the Meratus Ridge. The Barito Sub-basin is the southern part of the Kutai Basin, a broad sedimentary basin that occupied south and east Kalimantan during Tertiary time. The Kutai Basin is one of transition between fluvial and marine deposition.

The basin commenced formation during the Eocene Period, where subsidence resulted in a marine transgression. During the Period, the Tanjung Formation coals were formed in the brackish coastal plains. The overlying Berai Formation consists of marine muds and limestones, typical of shallow to deep marine environments.

At the end of the Lower Miocene Period, the basin was uplifted and formed a relative wide flat plain over East and South Kalimantan. The stable condition of the basin was ideal for the accumulation of thick organic material in huge peat swamps or bog forests. As the peat accumulated in a fresh water terrestrial environment with dense vegetation that made the swamps impenetrable to all but the largest of flood events, the coal formed is low in ash content and extremely low in sulphur and other pollutants.

At Adaro, a number of thick coal seams were lain down during the Miocene Period (Warukin Formation). Compressive forces from the east caused tilting and folding of the sediments. The major stress release in the Adaro Concession area was a fault plane, which allowed the sedimentary layers to be thrust upwards forming a low ridge in the Tutupan area.

The Tutupan coal deposit comprises basically 3 coal seams, each ranging in thickness between 5 and 50 meters. The coal generally strikes in a northeast – southwest orientation, and dips to the east at between 20 and 55o. To the south east of Tutupan lies the Paringin deposit, which is basically a single coal seam with a thickness of coal up to 60m. The Wara 1 and 2 Coal Deposits lie to the west of Tutupan.

To date, 2.8 billion tonnes of coal have been identified in the Adaro Coal Concession area. Quality variation in the coal seams is minimal, and all coal in the concession exhibit the same low ash and sulphur characteristics.