Abstract

• Iron ore deposits are located around Baw village (N Latitude 21° 53'96'' and E Longitude 96° 32'08''), Mandalay region, Myanmar. It lies in the western margin of the Shan Plateau within SibumasuTerrane. Rock units exposed in the area are Paleozoic rocks including Nyaungbaw Formation (Silurian age), Zebingyi Formation (early to middle Devonian age) and Maymyo Formation (middle Devonian to Permian age). Iron ores are mainly limonite and hematite with minor amounts of pyrite and magnetite. The deposit mainly forms in Maymyo Formation. Ore deposit entirely overlies on dolomite and sandstone of Maymyo Formation. Large ore boulders may reach about 15 cubic meters in size. Small nodular, concretionary iron ore and float ore also occur. In some places, these iron ores are embedded in reddish brown ferruginous sandy soil and sandy loam layers. Based on the result of borehole data, ore boulders decrease in size from south to north. This is because the fault that separates the two blocks, impounds oxidizing water and enriches iron in the hanging wall block (south), causing more concentration and thickening of the iron deposits. The occurrences of micro fossils (forams?) and ooids which are entirely or partially replaced by interlayered hematite indicate that the iron deposit is primarily of sedimentary origin probably formed at the end of Paleozoic time (Tin AungMyint, 2002). The porous and soluble nature of Maymyo Formation is the favorable place for the formation of iron deposits on Shan Plateau. Besides, chemical weathering processes leached dolomite and calcite minerals from earlier formed iron deposit, causing the increasing of iron grade in the ore as well as removing of gangue minerals from the ore in order to form the ferric iron oxides as secondary residues that are found sporadically around Baw village. Jordan et al., (2017) dated the zircon U-Pb ages of 399 Ma, for a limestone near Pyinoolwin which suggests that the age is consistent with fossil ages of the Middle Devonian Maymyo Formation. The relativity plots of the zircons suggest that the provenance has a Gondwana affinity, as the peaks of the zircons confirm the affinity with the Sibumasu Terrane.