Roger Dixon

Illicit trade in gold, mainly sourced from South America and Africa, is used to fund criminal activities such as the drug trade. Laundering money through the purchase of illicit gold, then having it refined and being paid for in clean funds is a major problem, and drives further growth in illicit mining. In order to restrict the influx of illicit gold into the legal domain, it is necessary to be able to identify the traded item as being of a licit or illicit nature. The only way that this can be done with any certainty is by determining, from its chemical composition, the source of the gold and the means by which it has been processed and upgraded. The example dealt with here shows how the use of compositional, processing and geological knowledge is able to discriminate gold from different origins. Data derived from a physical sample is far better able to constrain the source than a paper trail of certification, which can be manipulated.

Rosa Maria Di Maggio, Laurance J. Donnelly, Khudooma Saeed Al Naimi, Pier Matteo Barone, Fabio Augusto Da Silva Salvador, Lorna Dawson, Roger Dixon, Rob Fitzpatrick, Olga Gradusova, Ekaterina Nesterina, Marina Peleneva, Olga Ushacova, Carlos Martin Molina Gallego, Duncan Pirrie, Alastair Ruffell, Jennifer McKinley, Gullermo Sagripanti, Diego Villalba, Bill Schneck, Ritsuko Sugita, Grant Wach, Ricardo Silva, and Shari Forbes. Episodes 2017;40:120-31. https://doi.org/10.18814/epiiugs/2017/v40i2/017014

We observed, in a dense succulent thicket, a glossy blue-plumaged bird which we at first thought was a Cape Glossy Starling. We saw that this blue bird was accompanied by a sunbird with dark brown dorsal plumage and a white belly. The blue bird was then seen to be a sunbird as well. No matter which way it turned, clambering through the dense scrub, no green was observed, only a deep, royal blue. The blue bird was identified as a male Malachite Sunbird Nectarinia famosa, with aberrant plumage, and the second bird as a female of the same species. Why was typical metallic green plumage of this species blue? This paper makes suggestions. Birders need to be alert to this colour variation.

The identification of gold‐bearing material is essential for combating the theft of gold in South Africa. Material seized in police operations is generally a mixture of gold from different mines, and as such cannot be traced back to a single location. ICP‐OES analysis of material dissolved by acid dissolution provided a database of gold compositions comprising gold from South African mines, illegal gold stolen from the mines, and commercial gold alloys and jewelery. Discrimination between legal and illegal gold was possible due to the presence of Pb, As, Sb, Sn, Se, and Te in the stolen material, elements which are not present in legally produced gold. The presence of these elements is a quick and simple way to distinguish between gold alloys based on refined gold, such as in commercially manufactured jewelery, and gold alloys containing a proportion of unrefined and therefore illegally obtained gold.

The new minerals manganvesuviante and tweddillite, both formed by hydrothermal alteration of primary manganese ores, are described from the Kalahari manganese fields (Republic of South Africa). In addition, single-crystal X-ray structure refinements of both new minerals are presented.Manganvesuvianite is a tetragonal vesuvianite mineral with the simplified formula Ca₁₉Mn³⁺(Al,Mn³⁺,Fe³⁺)₁₀(Mg,Mn²⁺)₂Si₁₈O₆₉(OH)₉, characterized by Mn³⁺ occupying the five-coordinated position (square pyramid). The crystals simple prismatic forms: {100}, {110} terminated by {101} and exhibit deep maroon red colour. With polarized light the crystals are strongly pleochroic, yellowish parallel to E and dark red to lilac parallel to O.Tweddillite is an epidote-group mineral (space group P2₁/m, a = 8.932(5), b = 5.698(4), c = 10.310(5) Å, β = 114.56(4), V = 477.3(8) ų) with the simplified formula CaSr(Mn³⁺,Fe³⁺)₂Al[Si₃O₁₂](OH), closely related to strontiopiemontite. The difference between strontiopiemontite and tweddillite is the concentration of octahedral Mn³⁺. Strontiopiemontite has Mn³⁺ mainly on the M3 site whereas tweddillite has Mn³⁺ with minor Fe³⁺ on M3 and M1. Tweddillite forms aggregates of very thin dark red {001} blades characterized by striking pleochroism. The crystals appear dark red parallel to b and orange-yellow parallel to a. Perpendicular to (001) the blades appear magenta to red.