Geology and ore genesis of the Ma On Shan iron deposit, Hong Kong

Abstract

Ma On Shan Iron Mine was a only few economic deposit in Hong Kong for which have been closed for more than decades. There is lack of modern geological study of the mine. In order to understand the origin of the iron mine formation, microscopic and macroscopic study of underground were used in terms of field observation, thin section, Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS). In this study, ore formation is due to granitic magma contact with dolomitic marble which formed the Ma On Shan magnetite Skarn. Moreover, the mineral forming sequence is proposed. Magnetite and magnesium humite subgroup form in the early stage. Then the retrograde minerals are dominated by actinolite, tremolite fluorite and magnesium humite subgroup. In the late stage, some metallic minerals and rare earth mineral are disseminated within late stage vein, they are pyrite, cassiterite, scheelite and thorium/yttrium compound. Sellaite, cassiterite, scheelite, thorium/yttrium compound are newly discovered in Ma On Shan Iron Mine thanks to the modern technology. However, some common minerals have been mentioned by pervious authors are not found, e.g. garnet, this may due to the zonation and spatial distribution of mineral formation.