Abstract
The Oleninskoe intrusion-related gold–silver deposit is the first deposit in the Precambrian of the Fennoscandian Shield, where mustard gold has been identified. The mustard gold replaces küstelite with impurities of Sb and, probably, gold-bearing dyscrasite and aurostibite. The mosaic structure of the mustard gold grains is due to different orientations and sizes of pores in the matrix of noble metals. Zonation in the mustard gold grains is connected with mobilization and partial removal of silver from küstelite, corresponding enrichment of the residual matter in gold, and also with the change in the composition of the substance filling the pores. Micropores in the mustard gold are filled with iron, antimony or thallium oxides, silver chlorides, bromides, and sulfides. The formation of mustard gold with chlorides and bromides shows that halogens played an important role in the remobilization of noble metals at the stage of hypergene transformation of the Oleninskoe deposit.
Highlights
Mustard gold is a relatively rare mineral aggregate, formed in the zone of hypergenesis as a result of oxidation and decomposition of gold tellurides and antimonides
The mosaic structure of this mustard gold can be seen even with an optical microscope (Figure 2A), and with an scanning electron microscope (SEM) we see that the blocks differ in size of pores, which varies from the nanoscale to 8 μm, and in the direction of the gold filaments (Figure 2C–E)
Findings of mustard gold are numerous in the zones of hypergenesis of epithermal low-depth Au–Ag–Te and Au–Ag–Sb deposits in the Mesozoic and Cenozoic volcanic belts [2,3,4,5,6,7,8,9,10,11,12,13,14], which got to the surface and are actively denudated at present
Summary
For Au/Ag = 1/1 and “küstelite" for Au/Ag = 1/3 are used when the composition of Au–Ag alloy is important) is a relatively rare mineral aggregate, formed in the zone of hypergenesis as a result of oxidation and decomposition of gold tellurides and antimonides. It represents a lacy network, or sponge of native gold with very fine (often less than a micrometer) pores either filled with Fe, Te, Pb, Cu, Au, Ag, Sb, Hg oxides or unfilled. A more extensive study of mustard gold refers to the end of the XX and the beginning of the XXI century—to the time of fast development of local methods of mineral analysis
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