Fluid inclusion studies in the polymetallic ores of Gyöngyösoroszi (north Hungary) — Spatial and temporal evolution of ore-forming fluids

Abstract

The PbZnCu-bearing vein-like poly-ascendent occurrence of Gyöngyösoroszi is related to Neogene volcanic formations. The characteristic curved veins occur in the so-called “middle varying andesite” sequence accompanied by typical rock alterations (potash metasomatism, silicification, clay mineralization). Fluid inclusion studies were carried out on quartz, barite, sphalerite and calcite. The identified inclusion types are as follows: (1) vapor (low-density vapor); (2) monophase liquid (high-density liquid); (3) two-phase (l + v) hydrous inclusions; (4) three-phase (l + v + s) inclusions; (5) hydrocarbon-bearing (often oil-rich) inclusions. Based on the homogenization measurement data the occurrence was formed under epi-mesothermal conditions, concordant with the mineral paragenesis and textural-structural features of the locality. Based on the aqueous leaching data and the cryoscopic measurements two types of fluid can be identified: 1. (a) the alkali-bicarbonate type in the veinlets with druses of the wall-rock in the early phase of mineralization; 2. (b) NaCaCl type in the main (vein forming) phase of mineralization. Fluids are often accompanied by CO 2 in minor quantities being of heterogeneous distribution and occasionally by hydrocarbon derivates. The salt concentration, density and vapor pressure data of the ore-forming fluids are characteristic of the young volcanic and subvolcanic vein-like mineralizations. By means of the dynamic interpretation of the physico-chemical data the spatial and temporal evolution of fluids can be followed. The spatial evolution is reflected by isotherm maps constructed from the fluid data and by gradient determinations, the temporal evolution can be followed by the fluid control of the mineral paragenesis.