Brief Geology

The Republic Democratic of Timor-Leste (RDTL), also known as Timor-Leste is an island country with mountainous landmass and has potential for mineral resources to be explored. Geographically, Timor-Leste is located between Australia and Indonesia, and form part of the Timor Island (Figure 1). The territory of Timor-Leste consists of eastern half of the Timor Island with approximately total area of 14,874 km2, Atauro Island with total area of 140 km2, Jaco island (a total area of 10 km2), and an enclave, Special Administrative Region of Oe-cusse Ambeno (RAEOA) which located in the western part of the Timor Island with a total area of 814 km2.

Figure 1: Geographical location map of Timor-Leste (dark green) within the Indonesian region (light green) showing present tectonic boundaries and volcanoes. Red arrows show convergence vectors for the Australian Plate relative to Pacific Plate (AUS-PAC), and the Indian and the Philippine Sea plates relative to Eurasia, IND-EUR and PSP-EUR, respectively (adapted and modified from Hall 2008).

Timor-Leste is part of the Timor Island, which form part of the Banda Arc. It is located at a convergence of three major tectonic plates, the Pacific, Eurasian, and Indo-Australian Plates. The Banda Arc consists of an outer non-volcanic arc and an inner volcanic-arc (Hinschberger et al. 2005; Hall 2008). The territory of Timor-Leste encompassing the two, with the mainland and an enclave within the Nusa Tenggara Timur Province, located as part of the Timor Island is part of an outer non-volcanic arc, and the Atauro Island which located 25 km north of the capital Dili, is part of an inner volcanic arc. The Timor Island was formed as a result of collision between the NW Australian continental margin and the Banda Arc system, resulting in incorporation of various lithological units associated with the different plate fragments on the island (Hamilton 1979; Von der Borch 1979; Harris 2011; Audley-Charles 2004, 2011; Duffy et al. 2013; Dinis et al. 2013). The collision between the Banda Arc and the Australian crust strongly dictated the geology of the island resulting in extensive faulting incorporating various rock types into numerous small fault-bounded blocks which form the most prominent structures on the island (Berry 1981, Falloon et al. 2006).

The geological process of formation of the Timor Island is critical in the formation of both metallic and non-metallic minerals potential in Timor-Leste. It is widely known that zones of arc-continent collision are one of the producers of much of the world’s mineral deposit (Brown & Ryan 2011) because it can preserve any mineral deposits that had formed in the oceanic arc rocks or micro-continental blocks that become accreted or obducted (Herrington & Brown 2011).

The exploration of the mineral sectors within the country is very limited in the past, only few literatures is available on the mineral potential. Previous studies conducted within the country and indicated that there is potential for various mineralisation style and commodity from metallic such as copper, manganese, gold, silver, and zinc to non-metallic such as kaolinite, gypsum, and many other rocks such as marble, limestone and amphibolite which can served as process material and/or ornamental stone (Allied Mining Corporation (AMC) 1937; UN-ESCAP 2003; IPG 2016; Lay et al. 2017; PEM 2020; KARVAK 2022; ANPM 2022a, b). It is noted in the report that the likely mineralisation styles to host copper and its associated gold and silver is Cyprus-type volcanogenic massive sulfides (VMS) related to ophiolites for some of the indicated copper mineralization. Whilst potential gold and silver indicated to occur in Atauro, the island located within the inner volcanic arc, is suggested hosted within epithermal style mineralization (UN-ESCAP 2003).