Determination of Anomalous Gold Targets by Use of Geochemical Exploration and Multivariate Statistics Methods in Chirano Gold Mining Area of the Western Region, Ghana

ABSTRACT 

The main aim of this dissertation was to identify pathfinder elements for gold and generate new gold targets for further exploration at Chirano Gold Mining Area. A geochemical data was generated from 521 soil samples which were analysed for 51 elements and evaluated using multivariate statistical methods. Principal Components and Factor Analyses were used to reduce the data into two groups and Cluster Analysis conducted to find element associations hence pathfinders for gold. Anomalous trends were determined on Ranked Variable Maps and Gridded Maps and used in selection of targets. Soil samples taken from the study area were analysed by ICP-AES (inductively coupled atomic emission spectrometry) for trace elements/base metals and ICP-MS (inductively coupled mass spectrometry) for gold. In order to guide in the determination of anomalies and identification of pathfinders for gold, descriptive statistics, correlation matrices, probability plots, ranked variable maps and gridded maps were made. Ranked variable maps and gridded maps created in IoGAS showed that elements such as La, Mg, Mn, Ba, Th and Ti have strong anomalies whiles Ca, Cd, In, Sn, S, Sc, Sr, V, Zr and Y have weak to moderate anomalies that correlate with the Chirano Shear Zone. Gold mineralization along the Bibiani shear zone, on the other hand, was clearly marked by strong anomalies of As, Cs, Sb and W and also weak to moderate anomalies of Na, Cd, S, Sc, Sr, V and Zr.  Others such as Bi, Li, Re, Se, Ta, Te, Sc, U, B and Li were not anomalous in the project area.  B and Li were depleted whiles Ta had high but localized values. Principal Components, Factor and Cluster Analyses were conducted in Minitab software. The first six Principal Components extracted 55.8 % of the explained variance in the variables. The first principal component extracted 21.3% of variability with large positive loadings from Ag, Al, Fe, Sc, Th, U, V, Zr, In and Sn which were linked to the underlying felsic intrusive rocks such as tonalite, granodiorite and quartzfeldspar porphyry. The second principal component also extracted 10.2% of variance and had large negative loadings from Cu, Ni, Zn, Ba, Co, La, Mg, Mn, Sr, Ca and Cd which were linked to the underlying mafic rocks such as basalts, dolerites and diorites. Cluster Analysis also reduced the whole data to six clusters. The first cluster or the gold group consisted of Au, Mo, W, Re, B, Ta, Ce, Tl, Y and Be. Pathfinders for gold in the area under investigation were identified as Mo, W, Re, B, Ta, Ce, Tl, Y and Be. Twenty gold targets were identified including thirteen from Chirano North Gold project and seven from the Chirano Mining Lease. These targets must be ranked according to priority for further exploration work, preferably RC drilling.