Trace elements in corundum, chrysoberyl, and zircon: application to mineral exploration and provenance study of the western Mamfe gem clastic deposits (SW Cameroon, Central Africa)

Trace element abundances in three indicator minerals (corundum, chrysoberyl, and zircon grains) from the western Mamfe gem placers, as determined by LA-ICP-MS analytical techniques, are shown to be sensitive to their crystallization conditions and source rock types.

Corundum is dominantly composed of Al (standardized at 529,300 ppm), Fe (2496–12,899 ppm), and Ti (46–7070 ppm). Among element ratios, Fe/Mg (73–1107), Fe/Ti (0.5–245.0), Ti/Mg (1–175), and Ga/Mg (4–90) are generally higher whereas, Cr/Ga (<0.072) is low. The Fe (≤12,899), Ga (≤398), Mg (2–62), Cr (1.1–33.0), and V (3.0–93.0) contents (in ppm) mostly typify corundum grains formed in magmatic rocks, although some are metamorphic affiliated. A very higher Ti and significantly low Ga, Ta and Nb contents in some blue grains, suggest interesting concentrations of those high-tech metals in their source rocks.

Chrysoberyl is dominantly composed of Al (standardized at 425,000 ppm) and Be (62701–64371 ppm). Iron (7605–9225 ppm), Sn (502–3394 ppm), and Ti (33–2251 ppm) contents are high, whereas Ga (333–608 ppm), Ta (<456.0 ppm), and Nb (<3.0 ppm) are significantly low. The high (Be and Sn) and significantly low Ga–Rb abundances, and Ta > Nb in the western Mamfe chrysoberyls show that they were crystallized in granitic pegmatites, with some of those source rocks being enriched in Ta and Sn.

Zirconium oxide (ZrO₂: standardized at 66.1 wt.%)) is the only major oxide in analysed coarse-grained zircons. Within the minor elementary suites: Hf (4576–12,565 ppm) and Y (48–2805 ppm) contents are significantly high. The trace element suites include: Th (7–1565 ppm), U (13–687 ppm), and ∑REE (50–2161 ppm), whose values are significantly low. The (Yb/Sm)_N, Ce/Ce*, and Eu/Eu* anomalies range from 1.0 to 227.0, 0 to 308, and 0.08 to 1.7 respectively. They are Hf-Y-HREE enriched and depleted zircons mainly crystallized in magmatic oxidized environments. They were mainly sorted from granitoids, syenites and kimberlites.