Use Of Trench Geochemical Results To Delineate Surface Gold Mineralization At The Apapam Concession Of The Kibi Gold Belt

Abstract

Twenty five (25) grass root exploration trenches in the Apapam concession in the Kibi Winneba Gold Belt Ghana were used for this thesis. The trenches were sampled and geological features controlling gold mineralization were mapped in detail to better delineate gold –in- soil anomalies delineated during the initial soil sampling exercise carried out. It was also to determine the major features that may control surface gold mineralization in the Apapam concession and to eliminate possible forms of false anomaly associated with surface gold delineation. The Apapam concession was divided into five main zones for the follow up trenching exercise namely: the Big Bend zone, East Dyke zone, South Ridge zone, Mushroom zone of the western ends of the Atewa range and the Cobra Creek zone of the eastern end. Five trenches with varying lengths were excavated in each zone on a 200m interval north west – south east grid. A total of four thousand, seven hundred and sixty nine (4769) trench samples were collected and submitted to the laboratory for gold (Au_ppm) analysis. Major lithologies of the four zones of the western end of the concession were metasediments, mafic volcanics and quartz diorite in contact with the volcaniclastic sediments of the eastern ends of the concession. Lithologically, trenches showed high correlation of gold anomalies in the (granitoids) quartz diorite in the western part of the concession as compare to the metasediments and the mafic volcanics while gold mineralization in the eastern end was strictly confined to the gold bearing volcaniclastic sediments shear. A careful structural analysis and interpretation was undertaking on each of the five gold zones to help understand and delineate the major structure controls on the concession. The study showed that the high grade gold mineralization in the Big Bend zone were concentrated in the limbs and nose of the folded quartz diorite respectively while that of the East Dyke zone was found in the Jogs and the pinching sections of the Pinch and Swell diorite . The low grade South Ridge deposit corresponded to a sill which was concordant to the mafic volcanic ridge. The Mushroom zone which showed significant mineralization during the soil geochemistry survey recorded very low grades far below the trench cut -off grade. This shows that, those areas were depositional environments. The soil sampling done in the Mush Room zone were not representative fraction of these zones but rather these soils were transported from areas of good mineralization to these area. The source of mineralization in the Mush Room zone was not in-situ but was as a result of sediment transportation and was termed a false anomalous zone. Alternatively, the super high deposit of the Cobra creek zone was strictly confined to the gold bearing shear with exceptional high value within the intense carbonate alteration zone. The dissertation concludes that surface gold mineralization in the Apapam concession is influence by lithology, structural intensity, wall rock alteration other than specific rock types. It also emphasizes that exploration trenching is an effective economic follow up tool in delineating surface gold anomalies in the Kibi Winneba Gold Belt.