Welcome in the mines of ZIMBABWE
This deposit is located near Sandawana, about 120 km. SW of Masvingo (formerly Fort Victoria).
Once the importance of the find became obvious, the Sandaawana Emeralds, S. A. (a Geneva corporation) was formed to exploit the deposit and market the stones. By 1959 it became Zeus claims, which passed to Rio Tinto (Rhodesia) Ltd., who formed Sandawana Mines (Pvt)Ltd.
The Mweza Range contains a core of metasediments with inclusion of banded ironstones, phyllites, sericite-quaartz schist and quarzites, all tightly folded. Narrow peridodites sills, altered to serpentinites and allied rocks, intrude in older rocks. Range rocks are flanked by basalts and dolerites metamorphosed into greenstones and epidorites. Granites and associated pegmatites intrude the range rocks with emeralds occurring in tremolite schists adjacent to the granitic pegmatites. Many of these pegmatites contain: beryl, lepidolite, petalite, spodumene and Ta-Nb species. Local metamorphism is believed responsible for the formation of emeralds.
For each mine we calculated the medium value of lattice parameter. For each mine we calculated the medium value of chemical analyses (analysed 20 point ) by EMPA (Cameca CX 827). Mn, Se, F, Rb are under detection limits except in few cases. Li and Be are not determined. Chemical analyses have been normalized at 85%. H2O was deetermined by EA 1108 Carlo Erba ( gas cromatographer).
Reflectance FTIR (Fourier Transform Infrared Spectra) of gemstones have been acquired using a microscope IRscopeII (Bruker) accumulating 200 scans with a resolution of a cm-1 or better, in the range 7000-600 cm-1. Here are given only the skeletal bands which lie in the interval 1500-600 cm-1.
When the samples were suitably cut in direction parallel or normal to the c axis, polarized spectra were also obtained on the pinacoid or on the basis respectively or both.
According to the group theory 6A2u + 16 E1u infrared modes are predicted: the E1u modes are observed in the spectrum when the electric field is perpendicular to the c-axis (ordinary ray) and the A2u modes are observed for the extraordinary ray (E|| c). Therefore, non degenerate bands (A2u) are observed on pinacoids and show intensity changes in polarization, while degenerate bands (E1u) are detected on basis spectra and show only a lowering in intensity in polarized light.
1. Sinkankas J. 1981 "Emeralds and Other Beryls" Pensylvania, Chilton Book Co. p. 542-548