SOME GEOCHEMICAL PECULIARITIES OF THE SKARN FORMATION PROCESS OF A CERTAIN DISTRICT,KIANGSU

A horizontal zonality has been established for the skarn (Table 1,Fig.2).Themain skarn minerals are diopside and garnet,with subordinate actinolite,epidote,plagio-clase,chlorite,calcite,quartz and sulphides,etc.There are multiple stages of constituentminerals and mineralization.The ore-minerals sulphides and scheelite are generally pre-sent as replacing the earlier formed skarn minerals. Analyses have been made both of the host rocks and the secondary silicate rocksresulting from it in order to see what changes accompanied the skarn formation process.On the basis of studying the distribution and behaviour of major and trace elements inthe skarn process,the following conclusions have been made. Under the metasomatism calcium,iron,aluminium,manganese and magnesium werecarried in and alkalis,silicon,titanium and phosphorus were simultaneously carried outand partly redeposited (Table 2,3,Fig.3).Germanium,indium,nickel and rare earthelements were carried in during the process of skarn formation,the other trace elementsenter into the skarns from the surrounding rocks (chiefly granodiorite) (Table 7).Thetrace elements follow the major elements for which they can substitute in favourablecrystal lattices (Table 9). The skarn genesis is nicely coordinated with the theory of metasomatic contact-reaction processes between a granitoid and a carbonate environment with the participationof post-magnetic solutions.The variety of metasomatic rocks and the zonal structure ofthe skarn body are the results of a reactive interaction of solutions with host rocks in theprocess of an infiltration metasomatis with a subordinate significance of bimetasomatis.All the mineralogical compositions of the rocks in the skarn zones may be comprehendedby the relative activity of Ca,Al and Si. The order of formation of the skarn body has been approximately determined asthe following:altered granodiorites → diopside-plagioclase skarns → diopside-garnetskarns → garnet skarns in the inner zone;simultaneously marmorized limestones diop-side skarns → diopside-garnet skarns and banded skarns in the outer zone.