Geochemical anomalies from a survey of stream sediments in the Maquelab area (Oecusse, Timor-Leste) and their bearing on the identification of mafic-ultramafic chromite rich complex

Abstract

Timor-Leste and Oecusse in particular have very little geological data coverage due to the many conflicts generated mainly by Portuguese colonization and Indonesian occupation. The main work that has been done was aimed at oil prospecting on the south coast. A regional stream sediment campaign was started from the Maquelab area in the Oecusse enclave, west of Timor-Leste, where no mineralization had been reported before. The geochemical characteristics of stream sediments in Maquelab area drainage basins, located in NW of Oecusse enclave, Timor-Leste, were investigated in order to establish the geochemical baseline conditions prior to any type of new mineral occurrences. Stream sediments demonstrated a different chemical composition with elevated values mainly for Cr (49–12,520 mg kg−1), Ni (11.6–863 mg kg−1) and Co (19.8–77.1 mg kg−1) which was not expected going by the present geological cartography of the area where the existence of ultramafic rocks is not supported. Principal component analysis (PCA) was used after centered log-ratio (CLR) transformation of data that allowed for the observance of different compositional groupings and the identification of the drainage basins they represented. Aided by the stream sediments geochemical results, a geological recognition of the area was then made, which allowed for the discovery of a new ultramafic complex, consisting of dunites, peridotites and serpentinites, containing metamorphic rocks, predominantly calc-silicate, basalts and gabbros. This complex is named the Maquelab Complex due to its proximity to this village. Inside the peridotitic rocks, small boulders of massive chromite with about 56% Cr2O3 were also found.