Pegmatites outcrop in a zone several km wide around granitic intrusive as at Entata, located in the triangle formed between the Namirroe and Metuisse rivers. Granitic pegmatites occur in central and N-central Zambésia Province and SW portion of Moçambique Province.
The gem bearing pegmatites of Northern Mozambique have been known since the late 1920’s and the mines around the mining center of Alto Ligonha have yielded a wonderful variety of gemstones such as emerald, morganite, aquamarine, deep blue beryl, green tourmalines, rubelite and many others.
In 1974 the communist revolution in Portugal resulted in Mozambique gaining its independence from Portugal in the same year. Friction developed between rival ethnic groups wanting political power and the end result was a civil war that devastated the country, its infrastructure and the people. The war finally subsided in the early 90’s, and today the country is amongst the poorest in Africa.
During the 20 year civil war most mining activity stopped because the small mines were out in the bush and prime targets for attacks by warring factions. In many cases the tropical bush has grown over the small shafts, addits and open cast holes and the whereabouts of the mines are lost-probably forever.
The Muiane body was mined by Empressa Mines of Alto Ligonha in a quarry where the dike-like body is 40 m. wide.
The granitic pegmatites intrude Precambrian gneisses and metasediments. The bodies strike radially from the granite masses.
The enclosing rock of the Muiane body are gneisses or amphibolite schists. It is well zoned and contains large masses of lepidolite in its upper portion, also large crystal quartz, several feldspars, muscovite, spodumene, garnet, tourmaline, topaz, zircon, phosphate and sulfides.
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