Geology of Tawau hills Park, Sabah

anglais. The volcanic mountains crownedby thepeaks Magdalena (1320m), Lu- cia (121 Om) and Maria (1090m) consist of Quaternary pyroclastics and lava flows of dacitic, andesitic and basaltic 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 de- termined among the basaltic rock of Bukit Tiger. Evidence of the most recent volcanicity consists of a 24ka old carbonized tree trunk embed- ded in a lavaflow. 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 degrees,approximately north, 10-15 degrees, 75 degrees, andeast. Several of the volcanic peaks are also aligned along three of the mentioned directions, spanning dis- tances between 4km and 22km. A long a few northerly trending line- aments, normal faulting down-throwing to the west, is suggested by triangularfacets (more than a hundred metres high) andscarpsfacing west. A majorfault zone, 3km across andtraceable over almost 30km, is indicated by a strongly developed lineament trending approximately 10 degrees across Mount Magdalena. This interpretedfault zone is trans- acted by many east-striking lineaments that reach lengths of 5km. Indi- cations of widespread hydrothermal processes affecting the volcanic rocks of the Tawau Hills Park area suggest the occurrence of minerali- zation andgeothermal sources. The lineament map ofthe Lucia-Maria- Magdalena complex may prove useful for delineating mineralization targets andgeothermal centres.

inconnu. Pergunungan volkanoyang berkemuncakkan Magdalena (1320m), Lu- cia(121 Om) dan Maria (1090m) terdiri daripada piroklas serta aliran lava dasit, andesit dan basalt yang berumur Kuaterner. Sebahagian daripada batuan tersebut telah menjadi kaya dengan silika, mungkin kerana tindakan hidrotermal. Contoh batuan yang kononnya bersifat basalt dan andesit didapati berkadar silika melebihi 60 peratus. Se- baliknya, di antara basalt Bukit Tiger telah dikenal batuan nefelinit. Petunjuk aktiviti volkano yangpaling muda ialah batangpokok terkar- bonkan dan berumur 24 ka di antara aliran lava. Walaupun batuan di Taman Bukit-Bukit Tawau begitu muda, namun seluruh kawasan, ter- masuk permukaan lava yang luas, direntasi banyak lineamen panjang yang wujud sebagai utas tunggal atau sebagai zon berkelebaran be- berapa kilometer. A rah lineame yang umum adalah 340 darjah, hampir utara, J 0-15 darjah, 75 darjah dan timur. Sejumlah kemuncak volkano juga menunjukkan kedudukan sepanjang tiga arah lineamen yang tersebut dan mencapaijarak antara 4 km dan 22 km. Beberapa sesar normal dengan bongkah sesar sebelah barat yang menurun, didapati berjurus mengutara dan ditandai faset segitiga menghadap ke barat danjuga oleh tubir. Sebatang zon sesar utama berke/ebaran 3 km dan yang boleh dikesan sejauh hampir 30 km dita dai lneamenjelas berju- rus sekitar JO darjah memotong tubuh Gunung Magdalena. Zon sesar inipula dipotong oleh banyak lineamen menjurus ke timur, setiap satu zon boleh berkepanjangan hingga 5 km. Petunjuk mengenai tindakan hidrotermalyang meluas di Taman Bukit-Bukit Tawau mencadangkan kemungkinan wujudnya permineralan dan punca geotermal di sana. Peta lineamen daripada kompleks Lucia-Maria-Magdalena akan ber- guna bagi menentukan sasaran permineralan dan pusat geotermal.