Voltýřov gold deposit: Case history from the Bohemian Massif, Czechoslovakia

Abstract

The Voltýřov gold deposit in Central Bohemia is situated in the contact zone of granitic rocks of Variscan age and the Upper Proterozoic and Lower Paleozoic metasediments of the Krasna Hora Metamorphic Islet — the relict of an original sedimentary cover. Goldbearing quartz mineralization of vein and stockwork types is developed in rocks of both geological units, its form depending upon lithology. While ore shoots in metasediments and orthogneiss form generally regular bodies several tens of meters thick, those developed in granodiorite are rather irregular, without any indication of the tectonic control of the mineralization. The mineralized zone peters out extremely rapidly downwards, with a marked decrease both in extent and in gold contents. The gold-bearing mineralization is formed by two generations of gold, both of high fineness (over 900) and very fine-grained (5–20 μm). The gold is accompanied by accessory arsenopyrite, maldonite and other Bi-Te minerals, scheelite, and exceptionally chalcopyrite, pyrite, and sulphosalts. Gold contents are 2–3 g/t on average. In addition, late quartz-carbonate mineralization, with U and Se minerals and remobilized gold, is also present. Detailed soil prospecting (25 × 50 m grid) of the deposit detected a large and constrasting gold halo with gold contents exceeding 2 ppm (−200 mesh fraction), accompanied by higher concentrations of characteristic pathfinders — above all As and Bi. The halo extent exceeds the area of the ore outcrop by several times. The origin of gold mineralization in the deposit is explained by remobilization of gold from orthogneiss by the intrusion of the Central Bohemian Pluton.