SOME CHARACTERISTICS OF THE FENGHUANGSHAN INTRUSION AND ITS AFFINITY TO MINERALIZATION
安徽铜陵凤凰山岩体若干特征及成矿关系

The Fenghuangshan intrusion is situated in Tongling county, Anhui province, China. It occurs as a stocklike body with an area of about 9 km2 emplaced mainly in Middle Trias Biandanshan limestones. According to its bulk mineralogical ccmposition, the rock of the intrusion belongs togranodiorite. Accessory minerals are magnetite, sphene, apatite etc. The copper deposits of contact-metasomatic type are located at the contact zone, mainly at the western part, and to the less extent, at the northestern and southeastern parts of the intrusion. In addition to copper ores, associated ore minerals are magnetite, sphalerite, galena, etc. Both the emplacement of tie intrusion and the mineralization took place in the Late Yanshanian period. Systematic study of the intrusion has been made by the authors.The above studies of the Fenghuangshan intrusion result in the following main points.1) In the intrusion, the general trend of processes of magmatic differentiation and evolution appears to develop from border to core. From petrologic features an evident contaminated periphery probably formed by assimilation of country rocks has been separated from the inner part. As a result of trend surface analysis, the inner part, in turn, shows two, instead of one, centres of differentiation,and evolution, i. e., the normal centre located near the core of the intrusion while the abnormal one at the southeastern part.2) It is shown by trend surface analysis that the present pattern can only be implied as a result from rotational motion in the course of fluidal magmatic differential evolution and crystallization till consolidation, and such rotational motion is, mostly beleaved to be caused by vortex movement developed successively by ascending magma. Thus, the vortex movement is a rather general movement in the whole course of magmatism.3) Basic forms of probability distribution of major chemical components and relevant physical parameters in the intrusion are essentially normal distribution, although skewed moderately due to contamination and assimilation during its emplacement. Basic forms of probability distribution of minor elements are lognormal distribution, which is a single population in rock-forming minerals and a complex population in rocks.4) From tre trend surface analysis,it is also shown that a remarkable increasing trend of content of ore-foming elements--copper and molybdenum--in magnetite toward area of mineralization. This probably reveals where was increase in supplement of ore-forming substances. On the contrary, the magnetite content and magnetic susceptibility of the rock show a decreasing trend toward the area of mineralization. This implies that deuteric release existed.The above trends of such a type of intrusion near area of mineralization give significant evidence for the affinity between the intrusion and the mineralization.The geometric mean of copper in the rock of the intrusions under study in the Tongling region is 31 ppm and that of magneti