Numerous Tertiary, hydrocarbon bearing basins occur around the periphery of Borneo (Hutchison, 1989). A large portion of East Kalimantan is covered by the Kutei Basin. The Kutei Basin is the largest (160000 square kilometres) and deepest (12000 to 14000 metres) Tertiary basin in Indonesia.
Formations of the Kutei Basin are essentially a succession of eastward prograding deltas. The stratigraphic succession around the tenement area is summarised in below Tables. Formations developed within the tenement area are highlighted in yellow.
|  Stratigraphy of the Samarinda Quadrangle|
|  Age||  Formation||Lithology||Thickness|
|Upper Middle Miocene||Balikpapan Formation (Tmbp)||Alternating quartz sandstone, silty claystone and shale with intercalations of marl, limestone and coal. Deposited in a littoral to shallow marine environment. Conformably overlies the Paulua Balang Formation.||800 m|
|Middle Miocene||Paulau Balang Formation (Tmpb)||Alternating quartz sandstone, sandstone and claystone with intercalations of coal seams. Deposited in a shallow sublittoral environment. Conformably overlies the Bebuluh Formation.||900 m|
|Early Miocene||Bebulu Formation (Tmbl)||Limestone with intercalations of claystone and marl. Shallow marine environment.|
|Late Oligocene to Middle Miocene||Pamaluan Formation (Tomp)||Claystone and shale intercalated with marl, sandstone and limestone. Deposited in deep sea environment.||1500 - 2500 m|
|Early Eocene||Kuaro Formation (Tek)||Sandstone and conglomerate. Intercalations of coal, shale, marl and limestone. Shallow marine environment.||700 m|
|Late Cretaceous||Haruyan Group (Kvh)||Lava,breccia and tuff. Lava basaltic.|
|Early Cretaceous||Pintap Formation (Ksp)||Flysch deposits. Alternating sandstone, claystone, siltstone, shale, limestone and basaltic lavas. Deposited in arc trench gap area.||<1500 m|
|Jurrasic||Ultramafic Complex (Ju)||Serpentinites and harzburgites|
Within the region the Tanjung, Kuaro, Pamaluan, Paulua Balang, Warukin and Balikpapan Formations are coal bearing. Based on calorific value and sulphur content, the best quality coal is found in the older Tanjung and Kuaro Formation.
|  Stratigraphy of the Sampanahan Quadrangle in vicinty of PT BSS tenement|
|  Age||  Formation||Lithology||Thickness|
|Middle Miocene||Warukin Formation (Tmw)||Interbedded sandstone and claystone. Intercalations of coal and shale.||1500 m|
|Middle Miocene||Paulau Balang Formation (Tmpb)||Alternating quartz sandstone, sandstone and claystone with intercalations of coal seams. Deposited in a shallow sublittoral environment.||700 m|
|Late Oligocene to Middle Miocene||Pamaluan Formation (Tomp)||Claystone and shale intercalated with marl, sandstone and limestone. Deposited in deep sea environment.||2500 m|
|Early Oligocene to Early Miocene||Berai Formation (Tomb)||Limestone with intercalations of marl and claystone. Shallow marine environment.||1250 m|
|Late Eocene||Tanjung Formation (Tet)||Alternating sanstone, claystone, siltstone, limestone and conglomerate. Deposited in fluviatile to shallow marine environment||400 m|
|Late Cretaceous||Haruyan Group (Kvh)||Mainly basaltic lava flows. Interfingers with Pintap Formation.|
|Early Cretaceous||Pintap Formation (Ksp)||Flysch deposits. Alternating sandstone, claystone, siltstone, shale, limestone and basaltic lavas. Deposited in arc trench gap area.||>2000 m|
|Jurrasic||Ultramafic Complex (Mub)||Serpentinites and harzburgites|
Structurally the Kutei Basin is characterised by a series of NNE – SSW trending folds that parallel the coast line. Dips range between 10 and 40 degrees. Folds are typically asymmetrical with steeper dips occurring on the western limb of folds.
Coal bearing units of the Kuaro, Tanjung and Pamaluan Formations are exposed in the PT BSS tenement. All of these formations hold the potential of containing economic coal deposits. Additional work will be needed to assess the full potential of this very large tenement area.
In the north eastern portion of the tenement units of the Kuaro Formation and the Pamaluan Formation are developed. These units form the western limb of a broad anticline trending in a NNW direction. Coal bearing units are developed for the entire length of this north eastern portion of the tenement.
In the south western portion of the tenement, coal bearing units of the Tanjung and Pamaluan Formations are confined to the northern portion of this area.
PTBSS holds exploration rights over a tenement totalling 683.6 km2 . The company also holds coal mining rights by way of a PKP2B licence over an area of 8.9 km2 within the larger concessions.
APAC’s exploration was concentrated within the 8.9km2 mining licence, an area known as the Bekorok (Bekoso-Lempesu) Block. The exploration program included 32 diamond drill holes (totaling 2,465m) at a spacing of between 200m and 500m apart.
Drilling culminated in a JORC-compliant resource estimate for the Bekorok Block.
|Mineral Resource Statement APAC Coal Project|
|M e a s u r e d|
|I n d i c a t e d     A     S e a m|
|I n d i c a t e d     B     S e a m|
|I n f e r r e d     1     S e a m|
The resource could be increased and the confidence improved by additional drilling. This could result in an upgrading of a portion or the entire Indicated Resource within the 8.9 km2 lease to a Measured Resource status.
Furthermore, there is potential for defining significant additional coal resources both inside and outside of the 8.9 km2 area.