ARTICLE Sven E. Wille Æ Reiner Klemd Fluid inclusion studies of the Abawso gold prospect, near the Ashanti Belt, Ghana Received: 9 January 2002 / Accepted: 15 May 2003 / Published online: 29 October 2003 Ó Springer-Verlag 2003 Abstract The major Ghanaian lode gold deposits are preferentially aligned along the western and eastern contacts of the Kumasi Basin with the Ashanti and Se- fwi Belts, respectively. The investigated area of the Abawso small-scale concession, covering the workings of the old Ettadom mine, is situated 3 km west of the lithological contact of the Birimian metavolcanic rocks of the Akropong Belt in the east with the Birimian me- tasedimentary rocks of the Kumasi Basin in the west. The rocks of the Abawso concession represent a steeply NW-dipping limb of a SE-verging anticline with an axis plunging to the SW. Quartz veining occurs predomi- nantly in the form of en e´chelon dilatational veins along NNE–SSW-striking shear zones of a few metres width and shows evidence of brittle and ductile deformation. Also stockwork-style quartz veining occurs in the vicinity of the main shaft of the old Ettadom mine. Hydrothermal alteration includes sericitisation, sulphi- dation and locally carbonatisation. The auriferous quartz veins mainly follow the trend of brittle to ductile deformed quartz veins; however, some occur in stock- work. Fluid inclusion studies reveal a large number of H 2 O inclusions along intragranular trails in auriferous quartz vein samples, as well as an overall dominance of H 2 O and H 2 O-CO 2 inclusions over CO 2 inclusions. Textural observations and physico-chemical fluid inclu- sion properties indicate post-entrapment modifications for all quartz vein samples due to grain boundary migration recrystallisation. This process is interpreted to be responsible for the generation of the CO 2 inclusions from a H 2 O-CO 2 parent fluid. In comparison with mineralisation at the Ashanti and Prestea deposits, which are characterised by CO 2 ±N 2 inclusions, the observed inclusion assemblage may be due to a shal- lower crustal level of mineralisation, or different degrees and styles of recrystallisation, or a less pronounced development of laminated quartz veins due to compa- rably restricted pressure fluctuations. Furthermore, the microthermometric observations allow the reconstruc- tion of a possible retrograde P-T path, depicting near- isothermal decompression in the P-T range of the brittle/ ductile transition. Keywords Fluid inclusions Æ Gold Æ Quartz veins Æ Re-equilibration Æ Shear zone Æ Stockwork Æ Ashanti Belt Æ Kumasi Basin Æ Birimian Æ Ghana Introduction Ghana is the second most important gold-producing country in Africa (e.g. Kesse 1985; Phelps 2002) after South Africa. Major gold mines are concentrated in and along the NE–SW-striking Ashanti Belt (Fig. 1), pref- erentially along its western contact with the Kumasi Basin, which is marked by major shear zones at Obe- nemase, Konongo, Obuasi, Bogosu and Prestea. The noble metal is mainly extracted from mesothermal quartz veins/lodes, paleo-placer and placer deposits. Furthermore, disseminated and stockwork occurrences in Birimian granitoid bodies have been described (Obe- rthu¨ r et al. 1998; Yao and Robb 2000). In deposits of the quartz-vein/lode type, mineralisation is epigenetic and structurally controlled by shear zones (Junner 1935; Kesse 1985; Leube et al. 1990; Mile´ si et al. 1991; Eisenlohr 1992). The investigated Abawso small-scale concession covers the workings of the former Ettadom mine. Dur- ing 1910–1914, a shaft was sunk to the third level at a depth of 122 m and a second shaft was completed about 100 m NNE of the main shaft. From 1933–1934 the main shaft was reclaimed down to the second level and two adits were developed. There are no data on the production during these two periods of mining. In the course of recent exploration activities, a total ore reserve Mineralium Deposita (2004) 39: 31–45 DOI 10.1007/s00126-003-0380-1 Editorial handling: E. Frimmel S. E. Wille (&) Æ R. Klemd Mineralogisches Institut, Universita¨t Wu¨rzburg, Am Hubland, 97074 Wu¨rzburg, Germany E-mail: sven.wille@mail.uni-wuerzburg.de