MODE OF OCCURRENCE AND BITUMEN GRADES

OF ASPHALT ROCKS

• Exposed asphaltic rocks occurs in groups of gradually to sharply separated bitumen impregnated bodies that made up a so-called asphalt field.

• In South Buton, the asphalt fields occur along down block-faulted zones of 5 to 7 km wide that developed on the east side of a NNE – SSW trending somewhat sigmoidal wrench fault extending about 75 km from bays of Sampolawa to Lawele.

• Percentage of bitumen in the impregnated bodies varies both vertically and laterally, even within the same host rock.

• The bitumen impregnated bodies may occur in the form of layers, irregular forms, plates, lenses, elongated and scarcely rounded.

• Discovered larger bitumen impregnated bodies of higher grades occurs mostly in South Buton, and at least 1 (one) in North Buton.

• The most economic and workable asphalt deposits are the asphaltic limestone and asphaltic marl of Sampolaka Formation.

• Based on preliminary investigation including by applying geo-electric sounding, the asphalt deposit in Epe area of north Buton  is estimated 120,000,000 tons grading 10-30% impregnated bitumen by assuming specific gravity of 0.8. Locally, as heavy viscous asphalt of about 60% bitumen. The bitumen is impregnated in globigerina bearing limestone and marl.

• The areas surrounding West Kulisusu and Bubu (both are parts of north Buton) are really underlain by beds of Sampolakosa and Tondo Formations which are susceptible for asphalt impregnation especially along the zone of their boundary. If the beds of Sampolakosa Formation are slightly folded trending previously NE – SW but later trending towards another direction due to the rotation, only then those areas become promising prospect areas. Therefore, careful examination should be carried out to identify the existence of the folding.