Clay Mineralogy and Geochemistry of Fossil and Active Hydrothermal Alteration in the Hisaralan Geothermal Field (Sındırgı‐Balıkesir), western Turkey

Year 2016, Volume: 16 Issue: 1, 132 - 154, 30.04.2015

Cumhur Kocabaş Murat Tokçaer Mümtaz Çolak

https://doi.org/10.5578/fmbd.10852

Cited By: 1

Abstract

Hisaralan geothermal field is located at the intersection between Simav Graben and
İzmir–Balıkesir Transfer Zone (IBTZ). The area is hosted by Early Miocene dacitic and
rhyolitic volcanics. Clay mineralogy was investigated for the purpose of identifying the
present and fossil hydrothermalsystems. HS–2 drillhole and surface clay mineralogy were
examined by XRD, SEM and optical microscopy. R2 I–S and smectite are dominant clay
mineral close to the surface while discerete illite and R3 I‐S are the dominant clay
minerals at the deeper parts of the geothermal field. The fossil hydrothermal system
developed at two stages. Initially, Fe–rich chlorite, calcite and pyrite indicative of
propylitic alteration occurred. Subsequently, discrete illite and I‐S postdated the
propylitic alteration. Rb/Sr isotope data from illitic minerals (illite and/or I–S) shows they
are coeval and cogenetic with Early Miocene volcanism. On the other hand, active
hydrothermal system is supposed to precipitate dioctahedral smectite. Activity of
elements indicates the thermal waters are in equilibrium with smectite at temperatures
below 100 °C. Halloysite found in the cracks and coating on the surfaces of former
alteration products indicates a late phase precipitation. O and H isotopes of clay minerals
indicate that low temperature geothermal systems precipitate clay minerals as smectite,
and intersection of fault zones are characteristic for present day geothermal fluids
Hisaralan and ıts surroundings.

Keywords

Volcanics, Geothermal, Hydrothermal Alteration, Mixed Layer Illite–Smectite, Smectite