Fluid Evolution in a Subvolcanic Granodiorite Pluton Related to Fe and Pb-Zn Mineralization, Banska Stiavnica Ore District, Slovakia

摘要

The central zone of the Miocene Stiavnica stratovolcano (Western Carpathians) hosts an extensive sub-volcanic intrusive complex dominated by a granodiorite pluton (14,5-15.5 Ma). The granodiorite intrusion has a bell-jar form and was emplaced mainly into basement rocks, although its central part extends to the base of a subvolcanic and volcanic andesitic complex, 1.5 to 3 km below the paleosurface. In the more uplifted western part of the complex, the margin of the granodiorite includes numerous apophyses with associated magnetite skarns, whereas in the central, apical part it contains an irregular network of fractures hosting base metal stock-work mineralization that extends to a depth of 250 m. The granodiorite intrusion, especially in the marginal fades, is altered. High-temperature subsolidus deuteric (K-feldspar, secondary biotite, and amphibole) and en-doskaro (pyroxene) alteration, intimately related to magnetite skarns, resulted in depletion in Fe_(total) and increase in CaO and MgO in the intrusion. Low-temperature, hydrothermal alteration (epidote, chlorite, K-feldspar, sericite), closely related to the stockwork mineralization, is characterized by enrichment in K_2O, Pb, Zn, Cu, and MnO, and depletion in Na_2O. The overlying andesite are affected by acid leaching.