Mineralogy and Trace Element Chemistry of Ferberite/Reinite from Tungsten Deposits in Central Rwanda

Tungsten mineralization in hydrothermal quartz veins from the Nyakabingo, Gifurwe and Bugarama deposits in central Rwanda occurs as the iron-rich endmember of the wolframite solid solution series (ferberite) and in the particular form of reinite, which represents a pseudomorph of ferberite after scheelite. Primary ferberite, reinite and late secondary ferberite are characterized by their trace element chemistry and rare earth element patterns. The replacement of scheelite by ferberite is also documented in the trace element composition. Primary ferberite shows high Mg, Zn, Sc, V, Nb, In and Sn concentrations, but very low Ca, Pb, Sr and Ba contents. Reinite and late secondary ferberite display an uncommon trace element composition containing high concentrations of Ca, Pb, Sr, Ba, As and Ga, but very low levels in Sn, Zr, Hf, In, Ti, Sc, Nb, Ta, Mg and Zn. Late secondary ferberite replacing primary ferberite is characterized by additional enrichments in Bi, Pb, As and Sb. The rare earth element patterns of reinite and secondary ferberite are also similar to hydrothermal scheelite. The formation of the tungsten deposits in central Rwanda is interpreted to be epigenetic in origin, and the hydrothermal mineralizing fluids are related to the intrusion of the G4-granites.