Mineralogy and chemical distribution study of placer cassiterite and some associated new recorded minerals, east Rosetta, Egypt

摘要

Highly purified picked minerals of cassiterite and associated new recorded minerals were chemically and mineralogically investigated. Most of the investigated cassiterite exhibits homogeneous grains without obvious zoning. The analyzed cassiterites have more than 98 wt.% SnO2, which reveal clearly their considerable purity. Minor gold with traces of ferrotapiolite, cinnabar, native lead, chromite, and chevkinite are well detectable within the obtained cassiterite concentrate. The origin of the present cassiterite and the associated minerals is also discussed. The variation in color and grain size of cassiterite may be attributed to the various lithology and/or areas drained by the River Nile. The color of cassiterite is appeared to be intensified with increased Nb and Fe contents. Three categories of cassiterites are identified, (a) Ta_2O_5-rich (0.46-2.65 wt.%); (b) TiO_2-rich (0.42-1.41 wt.%), and (c) Ta_2O_5-Nb_2O_5-Fe_2O_3 rich one (Ta_2O_5:0.42-3.58 wt.%, Nb_2O_5: 0.7-1.98 wt.% and Fe_2O_3: 0.56-1.02 wt.%). Sn is usually substituted by Ta, Nb, and Fe. Minor gold with traces of new recorded ferrotapiolite, cinnabar, native lead, chromite, and chevkinite are well detectable within the obtained cassiterite concentrate. Ferrotapiolite is composed mainly of Ta, Fe, and Nb with minor Ti, Sn, and Mn, which similar to that derived from pegmatites and quartz veins. Chevkinite is generally enriched in Ti, Fe, and LREEs and depleted in P, Th, and U which analogous to that crystallized from felsic igneous rock suites.