Geochemical patterns of Cu, Au, Pb and Zn in stream sediments from Tongling of East China: Compositional and geostatistical insights

摘要

Geochemical patterns of elements in surficial sediments are of significance in deciphering processes and locating mineral resources. Stream sediment geochemical data of four ore-forming elements (Cu, Au, Pb and Zn) and fourteen associated elements (Ag, As, Bi, Cd, La, Mn, Mo, Nb, Sb, Th, U, W, Y and Zr) from the Tongling Ore Cluster District (TOCD), East China were analyzed by compositional multivariate and geostatistical approaches. It is shown that the median values of the four ore-forming and main associated elements including Ag, As, Bi, Cd and Sb are at least two times larger than those in stream sediments of China, indicating that there was a noteworthy addition of such ore minerals as (gold-rich) chalcopyrite and pyrite, galena and sphalerite into the sediments. The first three factors that explain 71.4% of the total variance could represent the dominant geology in the TOCD including the felsic intrusive rocks by F-1 (-) (Zr-Th-Nb-Y-La) and F-2 (-) (U-Y-Th-Nb-La), Pb and Zn-bearing strata and related mineralization by F-1 (+) (Pb-Cd-Ag-Mn-Sb-Zn), skarn Cu mineralization by F-2 (+) (Bi-Cu-Au-As) and porphyry Cu mineralization by F-3 (-) (MoeW). Simultaneously, regression analysis exhibited a closer relationship of Cu in the stream sediments with the skarn-type Cu mineralization than the porphyry counterpart. The geostatistical semivariogram modeling reflected that the greatest continuity of Cu, Au, Pb and Zn is at NE4 degrees, SE95 degrees, NE50 degrees and NE42 degrees, respectively. Moreover, the factor score and balance maps from factor analysis and sequential binary partition (SBP) illustrated the geochemical patterns of the elements. According to the modeling and spatial patterns, not only the possible sources (geogenic vs. anthropogenic), but also the controlling factors have determined. High levels of Cu, Bi, Mo and W are dominated by the felsic intrusives and related mineralization. That of Au, however, is governed by combined effect of the basement fault system and felsic intrusives. In contrast, high concentrations of Pb and Zn and such associated elements as Cd and Sb are controlled by the Permian and Triassic strata and associated Pb-Zn mineralization. Exploration suggestions and targets were proposed accordingly. It demonstrates that compositional and geostatistical analyses are effective to characterize geochemical patterns of elements.