Trace element geochemistry of some mesozoic yanshanian copper-gold deposits on anhui middle-lower Yangtze metallogenic valley, central-east china

Yangtze valley is one of the most important metallogenic regions in the Jurassic-Cretaceous period in East Asian continent, where more than 200 polymetallic Cu-Fe-Au and Mo, Zn, Pb, Ag deposits are documented. Cu-Au deposits in Anhui Province (Lower part of Yangtze) are the most important among these deposits. Data of chemical compositions of trace elements were collected from literature for Yanshanian (Mesozoic) igneous rocks which have close relationship with the Cu-Au mineralization. The Cu-Au nuneralization in middle to lower Yangtze valley can be divided into three types: mainly skarn type, porphyry type and volcanic type. In this paper, the details of trace and rare earth elements from Shaxi, Anqing, Chuxian, Tongling and Luzong Cu-Au bearing deposits are dealt with in detail. Rocks in the localities of Shaxi, Chuxian and Anqing intrusives have almost similar REE distribution patterns which show little assimilation with the wall rocks during the formation of Cu-Au deposits. However, the REE distribution patterns in Tongling skarn deposit are different altogether when compared to the other Cu-Au related rocks adjacent to areas of Mesozoic intrusives. This might have resulted due mainly to the volatile transport or assimilation of some elements producing complex patterns of trace element distributions superimposed on effects caused by crystal/melt equilibria. The trace element distribution shows that the mantle compatible elements such as Sc, Cr, Co and Ni and some transitional compatible elements such as Ti, V, Mn, Fe and Cu have strongly fractionated compared to the average contents of trace elements of crustal rocks, especially those of Cu, with very largely positive anomaly. This could be interpreted as an important crustal-mantle interaction during the Yanshania (Mesozoic) period when the multiple Cu-Au mineralization formed in the Yangtze metallogenic belt in China. The lithophile elements such as K, Rb, Th, Sr, Ba, Li and La are also enriched compared to the average contents of the crustal rocks, reflecting the regional geochemical anomalies of these elements and may be interpreted as an important reason of Cu-Au mineralization in this region.