Revised Eburnean geodynamic evolution of the gold-rich southern Ashanti Belt, Ghana, with new field and geophysical evidence of pre-Tarkwaian deformations

Abstract Integration of regional geophysical datasets and detailed field observations provide new insights into the paleoproterozoic structural evolution of southwestern Ghana. The study area is dominated by three metavolcanic and metasedimentary packages known as the Sefwi Group, the Kumasi Group (Birimian) and the Tarkwa Group (Tarkwaian) that were intruded by abundant TTG granitoids during the Eoeburnean and Eburnean phases of an event termed the “Eburnean Orogeny”. This study identifies an Eoeburnean (pre-Tarkwaian) deformation event (D1) that produced significant deformation in the Sefwi Group metavolcanics. D1 is associated with N-S shortening manifested as regional scale folding in the southern Ashanti Belt. D1 synorogenic granitoids were intruded between 2187 Ma and 2158 Ma under greenschist metamorphic condition. Syn-D1 gold mineralisation associated with quartz veining could be the original source of Tarkwaian paleo-placers and/or remobilised gold concentrations along major shear zones. D2 represents an extensional phase associated with the Kumasi Group sedimentation (2154–2125 Ma) which could be related to activation of major structures such as the Ashanti Fault as low angle detachments that controlled the deposition of the Kumasi Group and the opening of the Kumasi and Akyem Basin. The Tarkwa Group (2107–2097 Ma) unconformably overlies the Birimian Supergroups and was deposited in response to D3 shortening. D3 resulted in the inversion of syn-D2 detachments faults within the Ashanti Belt. NW-SE D3 shortening produced regional scale folding within the Birimian and the Tarkwaian metasediments. D4 deformation corresponds with sinistral reactivation of D3 thrust faults, and is locally associated with macro-scale folding at Obuasi and Wassa gold mines. By the end of D4, the regional scale architecture was built and was only slightly modified by the two last events. D5 postdates the Eburnean metamorphic peak and corresponds to open recumbent folds associated with a subhorizontal crenulation cleavage. D6 is present as a subvertical crenulation cleavage and reverse faults associated with NE-SW shortening.

[1]  I. Lahti,et al.  Tilt derivative multiscale edges of magnetic data , 2010 .

[2]  Keith Jones,et al.  3-D analytic signal in the interpretation of total magnetic field data at low magnetic latitudes , 1993 .

[3]  M. Fleet,et al.  Evolution of hydrothermal fluids in the Ashanti gold belt, Ghana; stable isotope geochemistry of carbonates, graphite, and quartz , 1996 .

[4]  M. Evans,et al.  Geochemistry of an ultramafic-rodingite rock association in the Paleoproterozoic Dixcove greenstone belt, southwestern Ghana , 2006 .

[5]  P. Ledru,et al.  Markers of the last stages of the Palaeoproterozoic collision: evidence for a 2 Ga continent involving circum-South Atlantic provinces , 1994 .

[6]  T. Oberthür.  Age constraints on gold mineralization and Paleoproterozoic crustal evolution in the Ashanti belt of southern Ghana , 1998 .

[7]  E. Klein,et al.  Paleoproterozoic Crustal Evolution of the São Luís Craton, Brazil: Evidence from Zircon Geochronology and Sm-Nd Isotopes , 2005 .

[8]  B. N. Eisenlohr.  Conflicting evidence on the timing of mesothermal and paleoplacer gold mineralisation in early Proterozoic rocks from Southwest Ghana, West Africa , 1992 .

[9]  S. Osae,et al.  Geochemistry of Paleoproterozoic metavolcanic rocks from the southern Ashanti volcanic belt, Ghana: Petrogenetic and tectonic setting implications , 2008 .

[10]  Mark Jessell,et al.  A geophysically constrained litho-structural analysis of the Eburnean greenstone belts and associated granitoid domains, Burkina Faso, West Africa , 2011 .

[11]  Y. Ntiamoah-Agyakwa.  Relationship between gold and manganese mineralizations in the Birimian of Ghana, West Africa , 1979, Geological Magazine.

[12]  C. Stanley,et al.  Telluride mineralization at Ashanti gold mine, Ghana , 1990 .

[13]  K. Hein.  Succession of structural events in the Goren greenstone belt (Burkina Faso): Implications for West African tectonics , 2010 .

[14]  M. Jessell.  Three-dimensional geological modelling of potential-field data , 2001 .

[15]  M. Fleet,et al.  Gold mineralization in As-rich mesothermal gold ores of the Bogosu-Prestea mining district of the Ashanti Gold Belt, Ghana: remobilization of “invisible” gold , 1994 .

[16]  M. Etheridge,et al.  Timing and Structural Controls on Gold Mineralization at the Bogoso Gold Mine, Ghana, West Africa , 2002 .

[17]  Donald W. Davis,et al.  UPb age constraints on deposition and provenance of Birimian and gold-bearing Tarkwaian sediments in Ghana, West Africa , 1994 .

[18]  P. Affaton,et al.  Constraints on provenance, stratigraphic correlation and structural context of the Volta basin, Ghana, from detrital zircon geochronology: An Amazonian connection? , 2008 .

[19]  A. E. Kitson.  Provisional geological map of the Gold Coast and Western Togoland : with brief descriptive notes thereon , 1928 .

[20]  S. Moorbath,et al.  Early Proterozoic crustal evolution in the birimian of Ghana: constraints from geochronology and isotope geochemistry , 1992 .

[21]  J. Kuma,et al.  Constrained gravity models and structural evolution of the Ashanti Belt, southwest Ghana , 1998 .

[22]  M. Landisman,et al.  Rapid gravity computations for two‐dimensional bodies with application to the Mendocino submarine fracture zone , 1959 .

[23]  R. Powell,et al.  The effect of Mn on mineral stability in metapelites , 1997 .

[24]  M. Fleet,et al.  Evolution of gold mineralization in the Ashanti Gold Belt, Ghana: Evidence from carbonate compositions and parageneses , 1995 .

[25]  Peter Bär,et al.  Les microflores des séries paléozoïques du Ghana (Afrique occidentale) et leurs relations paléofloristiques , 1974 .

[26]  L. Robb,et al.  Gold mineralization in Palaeoproterozoic granitoids at Obuasi, Ashanti region, Ghana: Ore geology, geochemistry and fluid characteristics , 2000 .

[27]  D. Davis,et al.  First UPb zircon age of extrusive volcanism in the Birimian Supergroup of Ghana/West Africa , 1998 .

[28]  W. Hirdes,et al.  The structural development of the early Proterozoic Birimian and tarkwaian rocks of southwest Ghana, West Africa , 1992 .

[29]  C. Guerrot,et al.  The paleoproterozoic Ghanaian province: Geodynamic model and ore controls, including regional stress modeling , 2006 .

[30]  R. Klemd,et al.  The metamorphic evolution of the Paleoproterozoic (Birimian) volcanic Ashanti belt (Ghana, West Africa) , 1999 .

[31]  M. Schwartz,et al.  Fluid inclusion re-equilibration and P-T-X constraints on fluid evolution in the Ashanti gold deposit, Ghana , 1992 .

[32]  F. Nyame,et al.  Spessartine Garnets in a Manganiferous Carbonate Formation from Nsuta, Ghana , 1998 .

[33]  P. Murphy,et al.  Fluid Characteristics of Granitoid-Hosted Gold Deposits in the Birimian Terrane of Ghana: A Fluid Inclusion Microthermometric and Raman Spectroscopic Study , 2001 .

[34]  Pei-Jung Chung,et al.  Estimation of seismic-wave parameters and signal detection using maximum-likelihood methods , 2001 .

[35]  T. Oberthür,et al.  Mineralogical siting and distribution of gold in quartz veins and sulfide ores of the Ashanti mine and other deposits in the Ashanti belt of Ghana: genetic implications , 1997 .

[36]  R. Klemd,et al.  Fluid inclusion studies of the Abawso gold prospect, near the Ashanti Belt, Ghana , 2004 .

[37]  G. Kesse,et al.  The mineral and rock resources of Ghana , 1985 .

[38]  D. Groves,et al.  Age constraints on Tarkwaian palaeoplacer and lode-gold formation in the Tarkwa-Damang district, SW Ghana , 2003 .

[39]  T. Oberthür,et al.  Fluid inclusions in quartz-pebbles of the gold-bearing Tarkwaian conglomerates of Ghana as guides to their provenance area , 1993 .

[40]  P. Fralick,et al.  Sedimentology of archean greenstone belts: Signatures of tectonic evolution , 1994 .

[41]  D. Davis,et al.  Reassessment of Proterozoic granitoid ages in Ghana on the basis of U/Pb zircon and monazite dating , 1992 .

[42]  P. Ledru,et al.  Early proterozoic ore deposits and tectonics of the Birimian orogenic belt, West Africa , 1992 .

[43]  R. Armstrong,et al.  Geochemistry and zircon geochronology of paleoproterozoic granitoids: Further evidence on the magmatic and crustal evolution of the São Luís cratonic fragment, Brazil , 2008 .

[44]  D. Selley,et al.  Vein mineralization at the Damang Gold Mine, Ghana: controls on mineralization , 2004 .

[45]  Bruno Verduzco,et al.  The meter readerNew insights into magnetic derivatives for structural mapping , 2004 .

[46]  David A. Hastings,et al.  On the tectonics and metallogenesis of West Africa: A model incorporating new geophysical data☆ , 1982 .

[47]  P. Ledru,et al.  The metallogenic relationship between Birimian and Tarkwaian gold deposits in Ghana , 1991 .

[48]  A. Leube,et al.  The early Proterozoic Birimian Supergroup of Ghana and some aspects of its associated gold mineralization , 1990 .

[49]  M. Jessell,et al.  Juvenile Paleoproterozoic crust evolution during the Eburnean orogeny (~2.2-2.0Ga), western Burkina Faso , 2011 .

[50]  T. Oberthür,et al.  High CO2 content of fluid inclusions in gold mineralisations in the Ashanti Belt, Ghana: a new category of ore forming fluids? , 1997 .

[51]  K. Hein,et al.  The Markoye Shear Zone in NE Burkina Faso , 2009 .

[52]  Richard Armstrong,et al.  Geochronology of the Birim Supergroup of the West African craton in the Wa-Bolé region of west-central Ghana: Implications for the stratigraphic framework , 2011 .