Geology of Taman Bukit Tawau, Semporna Peninsula, Sabah

Abstract

The volcanic mountains crowned by the peaks Magdalena (1,320 m), Lucia (1,210 m), and Maria (1,090 m) consist of Quaternary pyroclastics and lava flows of dacitic, and character. Some of these products have become silicified, probably through hydrothermal action. High silica content is also evident in the basaltic and andesitic volcanic rocks that we analysed. On the other hand, nephelinite was determined among the rock of Bukit Tiger. Evidence of the most recent volcanicity consists of a 24 ka old carbonised tree trunk embedded in a lava flow. In spite of its geologic youth, the complex, including the extensive lava surfaces, is transacted by numerous long lineaments that occur either as single strands or as zones several kilometres wide. Common lineament directions are 340°, approximately north, 10-15°, 75°, and east. Several of the volcanic peaks are also aligned along three of the mentioned directions, spanning distances between 4 km and 22 km. Along a few northerly trending lineaments, normal faulting downthrowing to the west, is suggested by triangular facets (more than a hundred metres high) and scarps facing west. A major fault zone, 3 km across and traceable over almost 30 km is indicated by strongly developed lineaments trending approximately 10° across Mount Magdalena. This interpreted fault zone is transacted by many east-striking lineaments that reach lengths of 5 km. Indications of widespread hydrothermal processes affecting the volcanic rocks of the Taman Bukit Tawau area suggest the occurrence of mineralisation and geothermal sources. The lineament map of the Lucia-Marla-Magdalena complex may prove useful for delineating mineralisation targets and geothermal centres.