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ENVIRONMENTAL STATISTICAL ANALYSIS OF THE BASINS OF THE MINING DISTRICT OF PONCE ENRIQUEZ (ECUADOR)
Abstract
Camilo Ponce Enriquez is in the southwest coastal zone of Ecuador, and it is surrounded by 4 river basins (Gala, Tenguel, Siete and Pagua) with an area of 1,780 km2. Mining has been the main economic activity since 1980 and is classified as Artisanal and Small-Scale Mining Activity. However, since 2000s there is evidence of contamination by heavy metals in water and sediments due to irregular mining practices and inefficiency environmental-s regulations. Despite the evidence, there are not enough scientific studies, and few reports are published about chemistry and contamination. The study goal is to analyze 333 river sediments samples taken from the four river basins, using geostatistical and geochemical methods, to determinate possible correlations and associations between contaminant elements. Samples were analyzed for 35 elements (Ag, Al, As, Au, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, Hg, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, Pb, Sb, Sc, Sr, Te, Ti, Tl, V, W, Y, Zn, Zr). The elements results were studied using univariate statistical methods, Spearman's Ordinal Correlation, factor analysis using PCA, and cluster analysis using Ward-s method. The results evidence nine elements (Co, Cr, Cu, Fe, Mg, Ni, Sc, Ti and V) with significant correlations (r ? 0.5). The strongest correlation is V-Fe (0.91), followed by V-Ti, Ni-Co and Ni-Cr and Sc-Co (r ? 0.8). The correlation in the V, Fe, Ni, Cr elements are related with orthomagmatic deposits. Also, V and Ti are related to titanium and iron oxides mainly in mafic deposits, which could be associated with the Pallatanga Fm. The factor analysis identified five groups of elements that are comparable to the Goldschmidt classification, where the groups are related with arsenopyrite, oxy-hydroxides, mafic and porphyry deposits. The cluster analysis revealed four groups, where the spatial distribution matched with the contamination level areas in the Siete, Tenguel and Gala River basins. The results provide an environmental baseline against which the impacts of anthropogenic activities (including mining) may be assessed. A basis for the formulation of sediment quality criteria and for the identification of natural geochemical hazards is also provided.
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References12
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