Article HistoryKeywords Conglomerate Sandstone Greywacke Indurated Immature Tarkwaian.This study geologically compares conglomerate and sandstone units in the Chagupana area of the Upper West Region and the Kawere conglomerate and Kawere-Huni-Banket sandstone units in the Tarkwa area of the Western Region in Ghana. Some work in the area has over time proposed that rocks from the two areas as similar based on only field relations, hence the need for more detailed work for re-classification. Macro and microscopic studies of the composition, mineralogy and texture of the rock types reveal that the conglomerates in both areas are metamorphic-clast units, greenish-grey, polymictic, foliated and texturally immature. Compositionally and mineralogically, Chagupana conglomerate is matrix-supported and immature, while Kawere conglomerate is clast-supported and mature; these constraint similarities between the conglomerates to only composition. The sandstones from both areas have similar mineralogical compositions, but with decreasing feldspar in the order of Chagupana>Huni>Kawere>Banket. Texturally, all the sandstones are sub-mature, well-indurated and angular-rounded; except the Huni sandstone, which is fine to medium-grained, while the other sandstones are medium-coarse-grained. Based on the feldspar contents, the Chagupana, Huni, Banket and Kawere sandstones classify as greywacke, feldspathic arenite, sub-litharenite and sub-feldspathic-feldspathic arenite, respectively. The greywacke and sandstones have the same cementing materials as quartz, sericite and chlorite. Concluding, the Chagupana rocks are not entirely the same as those from the Tarkwaian Group, probably due to differences in provenance.
This study investigates basin-type granitoid samples from the north-eastern margin of the Kumasi Basin in Ghana to establish their source and geodynamic setting. Petrographic analysis, TAS and A/NK-A/CNK plots classify the granitoids as metaluminous quartz diorite, metaluminous granodiorite, and peraluminous monzogranite; and exhibiting I-type signatures. These rocks are formed by magma differentiation and/or partial melting at various stages. Distribution patterns of incompatible elements and the positive Eu/Eu* anomalies of 1.15 and 1.47 exhibited by quartz diorite and granodiorite, respectively, the values suggest the rocks crystallized from melts formed in a water-saturated environment. The negative Eu/Eu* anomaly exhibited by monzogranite indicate fractionation of plagioclase in the final stages of the magma evolution. The water-rich environment is probably due to dewatering of the basin’s foreland volcaniclastic sediments during regional subsidence, burial and metamorphism. K2O enrichments and wide variations suggest that the granodiorite and monzogranite are formed from fractional crystallization and/or crustal assimilation of the continental crust by under-plating dioritic magma. The higher Al2O3/TiO2 enrichment and the shift from metaluminous to peraluminous in the monzogranite suggest a longer residence time within the continental crust, during which fractional crystallization and the assimilation of pre-existing crustal components into the dioritic magma that resulted in the formation of the monzogranite. The study requires replication at other areas within the basin to generate enough data to enhance metallogenic studies in the terrain.
The study described in this paper involves the application of a conventional resource estimation method, inverse distance weighting (IDW), and univariate geostatistical technique, ordinary kriging (OK) to the gold grades data from the modified palaeoplacer Teberebie gold deposit, in Ghana. The deposit consists of 4 layered well-defined orebodies referred to as A reef, CDE reef, F24 reef and G reef at the mine environment. Simple, reliable, and adequately accurate resource/reserve estimation are essential to mining operations. Data used for the research were collected by diamond and reverse circulation (RC) drilling. A total of 19353 one-meter composite samples, consisting of 18962 RC chip samples from 695 RC drill holes, and 391 diamond drill core samples from 11 DD holes. Samples were analysed by atomic absorption spectrometry (AAS) for gold (Au). Descriptive statistical treatment was conducted on grade values for the reefs. To analyse for spatial structure of Au mineralisation, experimental downhole, and several horizontal directional semi-variograms were computed, and models fitted. Ore reserves were estimated by OK and IDW methods, and results of the various reefs compared. Regression analysis of estimated results indicate that, the inverse distance square (ID2) model produced estimates that compared well with the OK model in all the ore zones. It is therefore, appropriate to use ID2 as an alternative estimation method to the OK method for purposes of mine planning and grade control.
This paper seeks to assess the potential of Alkali-Silica Reaction on some granitic rocks in Kumasi in Ghana. Alkali-Silica reactions occur over time between alkaline cement paste and silica contained in rock aggregates as a result of the swelling due to the reaction of certain constituents in the rock aggregates with alkali hydroxides. Alkali-Silica reactions become potentially harmful when they cause significant expansion. Aggregates used for this research were sought from three different quarries, namely, Consar Stone Quarry in Barekese, Nnagot Quarry in Kona and Modern Granite Quarry in Buoho. To achieve the objectives of this project, two test methods were employed such as Accelerated Mortar Bar test (ASTM C1260) and Petrographic analysis. Presence of strained quartz is an indicator for the occurrence of Alkali-Silica Reaction. Samples from Kona contained quite an appreciable amount of strained quartz and exhibited an expansion above the ASTM C 1260 specification, implying that it is potentially reactive and thus not useful for construction works, whilst samples from Barekese, and Buoho were innocuous and may be used for construction works. Supplementary cementing materials such as pozzolans (which are readily available) can be added to concrete mixtures with aggregates from Kona to reduce the harsh effects of ASR.
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