Sedimentary Geochemistry and Regional Distribution of Gold in Middle Triassic Banna Formation in Northwest Guangxi

This paper deal with trace elements' sedimentary geochemistry and distribution of gold of Banna Formation, Middle Triassic in Northwest Guangxi. The formation is deep sea turbidite, with four petrological parts and 150-5000m thick, main petrologic types are sand stone, silt stone, mud stone and marl. Based on statistics of gold concentration of 240 samples collected from 11 field sections, the distribution of gold in the formation is classified into 6 types original, slightly uneven lean, seriously lean, slightly uneven enriched,0 middle-degree unevenly lean and middle-degree unevenly enriched type. Regional distribution of gold is classified into original, lean and enriched rigion. Nandan geological section which is located in the gold enriched region has different characteristics of petrological chemical composition, REE and trace elements from other sections, which indicate that the sedimentary source of Nandan section(and other sections in gold en- riched region) is different from that of others. Siderofile elements(Fe,Mg,Ti,Co,Cr,Ni,V) in the stratum are lower and lithofile elements(Li,Be,Th) are higher than the mean value in crust, gold concentration correlated with that of Li and Cd in the strata and in the ore of Karlin-type gold ore deposite hosted in the strata. Trace elements in marl mainly concentrated in mud and have the same compositional character as that of detrital rocks, that illustrate that mud in marl had the same source as detrital rocks. Mn,P,Cu,Pb,Sr,Cd are compairly enriched in marl, concentrations of S,As are lower and Sb is near compair with the mean value of the same rocks in the world, but S,As,Sb have much higher variation coefficient than other elements, which show that those elements are mobile and easy to migrate, forming ore deposits or being host elements in Karlin-type gold ore deposits.