Földtani Közlöny, 2000 (130. évfolyam, 1-4. szám)
2000 / 1. szám
Földtani Közlöny 130/1,1-23 (2000) Budapest Adulár-szericit típusú hidrotermás indikáció ásványtani és genetikai vizsgálata a sárszentmiklósi Szarvas-hegyen Mineralogical and genetical study of an adularia-sericite type hydrothermal deposit at the Szarvas Hill, Sárszentmiklós Szentpéteri Krisztián1 - Molnár Ferenc1 (7 ábra, 2 táblázat, 4 fényképtábla) Tárgyszavak: hidrotermás elváltozás, adulár, breccsásodás, folyadékzárvány, alunit-kaolinit ásványparagenezis, epitermás ércesedés Keywords: hydrothermal alteration, adularia, brecciation, fluid inclusions, boiling, alunite-kaolinite overprint, epithermal system Abstract The hydrothermally altered Lower Miocene rhyolite tuff of Szarvas Hill contains a hydrothermal structure which can be separated into a central breccia zone and a clay- and silica mineral bearing marginal stockwork zone. Optical, x-ray powder diffraction, quantitative optical emission spectra and fluid inclusion analytical methods have been carried out on systematically collected samples. On the basis of the analytical data the evolution of the hydrothermal activity started with intensive fracturing, characterised by the development of pm-cm thin quartz-adularia veinlets and dissemination of pyrite in the host rock. This was associated with pervasive silicification and the replacement of plagioclase with hydrothermal K-feldspar and the occasional sericitic alteration. The paragenesis indicates slightly acidic-neutral-slightly alkalic pH and reductive chemistry of the fluids. The hydrothermal fluids underwent boiling at about 220°C temperature, indicating 270-300 m minimum palaeodepth of processes. These early fluids had minor amount of carbon dioxide indicated by the occurrence of C02-hydrate during the freezing of fluid inclusions. The boiling of the hydrothermal fluids introduced the next, explosive stage of the system, characterised by intensive hydrothermal brecciation in the central zones. The breccia is cemented by a variously textured siliceous matrix. The still open spaces of the hydrothermal breccia were filled with kaolinite-smectite as well as quartz-opal kaolinite-alunite haematite parageneses in the varying stages of the hydrothermal activity. The temperature of the acidic-oxidative fluids was around 160-190°C. Arsenic shows the most pronounced anomalies in these late hydrothermal products. According to the textural, paragenetical and geochemical features the hydrothermal system of the Szarvas Hill at Sárszentmiklós represents a shallow zone of an adularia-sericite (low sulphidation) type epithermal system. This evidence can be considered as an indicator of a precious metal-bearing ephitermal ore deposit, analogous to other deposits of the Tertiary volcanic areas of the Carpathian region. Manuscript received: 01 20 1999 1 Eötvös Loránd Tudományegyetem, Ásványtani Tanszék, 1088 Budapest, Múzeum krt. 4/a