Age constraints of the Wassa and Benso mesothermal gold deposits, Ashanti Belt, Ghana, West Africa Luis A. Parra-Avila a,b,⇑ , Yan Bourassa c , John Miller a,b , Stéphane Perrouty d , Marco L. Fiorentini a,b , T. Campbell McCuaig a,b a Centre for Exploration Targeting, ARC Centre of Excellence for Core to Crust Fluid Systems, School of Earth and Environment, The University of Western Australia, Perth, Australia b ARC Centre of Excellence for Core to Crust Fluid Systems, Department of Earth and Planetary Sciences Macquarie University, NSW 2109, Australia c Golden Star Resources Ltd, 150 King Street West, Sun Life Financial Tower, Suite 1200, Toronto, ON M5H 1J9, Canada d Western University, Earth Sciences, 1151 Richmond Street, London, ON N6A 5B7, Canada article info Article history: Received 17 February 2015 Received in revised form 19 May 2015 Accepted 20 May 2015 Available online xxxx Keywords: Ashanti Wassa Benso Gold U–Pb SHRIMP abstract The Ashanti Belt in Ghana hosts numerous multi-million ounce gold deposits and is one of the most richly gold endowed Paleoproterozoic belts of the West African Craton. This work shows that the Wassa min- eralized intrusion is part of the Sefwi Group. This unit at Wassa is strongly magnetic and show a distinctly high response in regional magnetic data sets compared to other units of equivalent age within the belt. The unit is inferred to be a lateral extension of an exposed fragment of what defines the substrate to the Tarkwa Basin sediments. The Wassa deposit, located in the eastern limb of the belt, is hosted within mafic to intermediate vol- canic flows that are interbedded with minor horizons of volcaniclastics, clastic sediments. The clastic sed- iments include wackes and magnetite rich sedimentary layers, presumably derived from banded iron formations. The previously described sequence is intruded by syn-volcanic mafic intrusives and felsic porphyries rocks that are all part of the Birimian stratigraphy. Two new key SHRIMP II U–Pb ages were determined as part of this study: a new age of 2191 ± 6 Ma was determined on magmatic zircon grains of the Wassa porphyry host rock, which now represents the oldest known felsic intrusion hosting gold mineralization in the Ashanti Belt region. The Benso gold deposit system, which is located in the eastern limb of the Ashanti Belt approximately 38 km southwest of Wassa is hosted within a series of volcanic units intruded by mafic to intermediate units. A SHRIMP II U–Pb age of 2157 ± 5 Ma was determined from magmatic zircons obtained from a gra- nodiorite of the G-Zone of the Benso deposit. This granodiorite is the main host rock for gold mineraliza- tion and thus the age provides an upper constraint for mineral emplacement. The newly determined ages provide an upper constraint for the gold mineralization within this region of the Ashanti Belt. They also support recent structural studies that have interpreted that the Wassa min- eralization is related to the Eoeburnean period, defined to have occurred between 2191 and 2158 Ma (D1 event) prior to the main phase of gold mineralization. This new U–Pb age on the host rock provides an upper age limit to the Wassa mineralization of ca. 2191 Ma and is compatible with the proposed Eoeburnean early mineralization model for the Wassa deposit. The age of the intrusion along with the location of the deposit in the Sefwi Group give a unique characteristic that distinguishes Wassa from the other gold deposits along the Ashanti belt which are believed to have been the result of a mineralizing event between ca. 2090 and 2070 Ma. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction The southwest Ghana region is one of the richest gold endowed terranes in the West African Craton (Feybesse et al., 2006). Of par- ticular relevance are the giant Obuasi (>60 MOz) and other multi- million ounce deposits e.g. Pampe, Bogoso, Prestea, Damang and Tarkwa (Allibone et al., 2002a,b)(Fig. 1). The most common http://dx.doi.org/10.1016/j.jafrearsci.2015.05.017 1464-343X/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Centre for Exploration Targeting, School of Earth and Environment, The University of Western Australia, M006 35 Stirling Highway, Crawley, WA 6009, Australia. Tel.: +61 8 6488 1809. E-mail addresses: luis.parraavila@uwa.edu.au (L.A. Parra-Avila), ybourassa@gsr. com (Y. Bourassa), john.miller@uwa.edu.au (J. Miller), sperrout@uwo.ca (S. Perrouty), marco.fiorentini@uwa.edu.au (M.L. Fiorentini), campbell.mccuaig@uwa. edu.au (T. Campbell McCuaig). Journal of African Earth Sciences xxx (2015) xxx–xxx Contents lists available at ScienceDirect Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci Please cite this article in press as: Parra-Avila, L.A., et al. Age constraints of the Wassa and Benso mesothermal gold deposits, Ashanti Belt, Ghana, West Africa. J. Afr. Earth Sci. (2015), http://dx.doi.org/10.1016/j.jafrearsci.2015.05.017