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Mineralogy of gold in the Elshitsa massive sulphide deposit, Sredna Gora zone, Bulgaria

Bogdanov, Kamen
Tsonev, Dimitar
Published in Mineralium Deposita. 1997, vol. 32, p. 219-229
Abstract The Elshitsa volcanic hosted massive sulphide deposit occurs in the central part of the Srena Gora metallogenic zone in Bulgaria. The gold-bearing massive sulphide mineralization is considered to be the product of an island arc volcano-plutonic process and hydrothermal activity that took place during the Late Cretaceous. In addition to the major gold-hosted opaque minerals such as pyrite, chalcopyrite, sphalerite and galena there are minor phases of tennantite, gold®eldite, Se-bearing aikinite, native silver and bornite in the massive sulphide lenses and stringer zones. Most of the sulphide minerals are Se-bearing. All of the six mineral assemblages that were deposited during the pyrite and copper-pyrite stages of mineralization are gold-bearing. The gold tenor as a rule is less than 1 g/t. Native gold and electrum occur as blebs or intergranular particles in the sulphide minerals. Gold in the early massive pyrite is of submicroscopic type (< 0,1 lm) and of colloidal ori-gin. Pyrite deformation and recrystallization in the temperature range 250°±160 °C has led to Au and Ag migration to cracks and grain boundaries of the sulphide minerals. As a result of these process the native gold and electrum grain size increases from submicroscopic (< 0,1 lm) in the early colloform pyrite to microscopic (0,1±100 lm) and macroscopic (> 100 lm) in the late gold-sulphide assemblages. The electrum ®neness in 41 individually studied grains varies between 780 and 992&with a mean of 895&. Native silver was found in association with bornite. Cu, Te, Sb and Bi are the most common traceelements in gold and electrum. The Cu-Zn-Pb association is most important as a Au-Ag-carrier. A model for gold behaviour during sulphide deformation is proposed involving coarsening of gold grain size from the earlier to the later sulphide mineral assemblages.
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Research group Mineral Resources and Geofluids
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BOGDANOV, Kamen, TSONEV, Dimitar, KOUZMANOV, Kalin. Mineralogy of gold in the Elshitsa massive sulphide deposit, Sredna Gora zone, Bulgaria. In: Mineralium Deposita, 1997, vol. 32, p. 219-229.

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