Gold mineralization within contact-metamorphic and shear zones in the "Złoty Jar" quarry the Złoty Stok As-Au deposit area (Sudetes)

Stanisław Z. Mikulski

Abstract


Mineral paragenesis of gold mineralization in the "Złoty Jar" quarry has been formed during three separated stages. The stage I of skarn-like mineralization was due to metasomatic processes developed in the exocontact zone of the Variscan Kłodzko - Złoty Stok granodiorite massif. Preliminary results of primary fluid inclusion studies demonstrate that the earliest stage with pyroxene, garnet and scheelite have low salinity fluids (4.9-5.2 wt. % NaCI equiv.) at temperatures between 464-480°C and pressure below 1.4 kbar. During later phases of this stage widespread gold-bearing ore mineralizations (loellingite, arsenopyrite) were formed. Definitely most gold occurs as fine-dispersed submicroscopic particles within ore minerals in calc-silicate and black serpentinite rocks (up to 10 and 29 g/t, respectively). Younger gold-bearing stages (II and III) revealed a succession of cycles of brittle deformation and hydrothermal infill of mineralizing fluids connected with development of shear zones. Th of primary inclusions of quartz veins containing ores with native gold were determined at 220-280°C and salinity 4-10 wt. % NaCl equiv. "Visible" gold was found as inclusions from 5 to 50 mm in size among Ni-Pe-Co sulphoarsenides, sulphides and as individual micro-grains in quartz ± calcite veinlets. In the youngest described gold-bearing stage (III), inclusions of electrum and gold-bismuth myrmekites in sulphoarsenides were commonly observed. Processes of redistribution of primary gold on a local scale from loellingite-arsenopyrite mineralization, and on regional scale from metavolcanic rocks, were widely developed. Precipitation of ''visible'' gold within sulphoarsenides and sulphides was carried out by sulphur-bearing solutions at 350-250°C and near neutral- to alkaline environments, with dominant role of hydrosulphide complex Au(HS)2-. Main sources of metals were probably the metal preconcentrations in volcano-sedimentary rocks with mantle contribution (Pt, Pd) (?) which later underwent mobilization due to formation of granitoid intrusions and development of shear zones.


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