A biogeochemical orientation study in Mo skarn deposits, Jecheon district in Korea

Abstract

A biogeochemical orientation survey was conducted in the vicinity of Mo skarn deposits in the Jecheon district in Korea. The main litholigies of the study area are Ordovician dolostone, limestone and calc-silicate rocks intruded by ‘Jurassic Jecheon biotite granite’. The skarn zones occur at the contacts of granite and limestone. Molybdenum mineralization occurs in fracture zones in skarns within the screen and in disseminated form. The skarn ore minerals are mainly molybdenite, scheelite, galena and chalcopyrite. The control area is Gwanak mountain where the Seoul National University is located and the geology consists of Jurassic granite with no Mo mineralization. Samples of soils and two plant species (Daimyo oak leaves/branches — Quercus dentata, and Sargent cherry leaves — Prunus sargentii) were collected from the target area and control area in May and June 2011, and analyzed for Mo and 59 other elements by ICP-MS. Each of three sampling lines was designed to cross over each orebody at 30m spacings in the study area and 10 sampling points were chosen randomly in the control area. The soil samples (n=36/10, target/control) collected from the target area show higher values of Mo (<0.1–38.7, median: 1.5ppm) than those from the control area (<0.1–3.2, median: 0.9ppm Mo). The concentration of Mo in plants (n=108/30, target/control) from the target area (0.51ppm in Q. dentata leaves, 0.19ppm in Q. dentata branches and 0.31ppm in P. sargentii leaves) is 1.5–5 times higher than that from the control area (0.16ppm in Q. dentata leaves, 0.04ppm in Q. dentata branches and 0.21ppm in P. sargentii leaves). The biological absorption coefficient (BAC) of Mo is generally high (Q. dentata leaves=1.4, Q. dentata branches=0.4 and P. sargentii leaves=1.2) and Mo content in soils and plants is strongly correlated. The geochemical variation patterns of Mo in plants are similar to those in soils, which suggest a corresponding Mo anomaly and enhanced contrast near the Mo orebodies. The three plant organs (Q. dentata leaves, branches and P. sargentii leaves) may be used as indicators for the biogeochemical prospecting of Mo.