Research on the alkali metasomatic veins in skarn of the Shizhuyuan W-Sn polymetallic deposit

Abstract：The Shizhuyuan W-Sn polymetallic deposit in the middlel of Nanling region is a superlarge W-Sn-Mo-Bi polymetallic deposit rarely seen in the world, characterized by multi-mineral resources,large size and rich associated components. It has numerous veins of different types, composed mainly of acid magmatic dikes, greisen veins and alkali metasomatic veins in the skarns, with the alkali metasomatic veins comprising the largest and most widely distributed ore bodies. Based on detailed field investigation, microscopic petrographic analysis and EPA analysis, the authors found that the main minerals in the veins are potassium feldspar, plagioclase, quartz and fluorite, the muscovite content is small (<3%), and topaz, tourmaline content is rare. They hence do not belong to the “greisen veins” or “greisen stockwork”. The vein body has extensively developed some skarn minerals, and the vein body and its both sides contain more tungsten and magnetite. On the whole, the alkali composition in the alkali metasomatic vein is relatively high, and has experienced strong alkali metasomatism. The vein bodies can be divided into two types, i.e., the early alkali metasomatic vein and the late alkali metasomatic vein. The early alkali metasomatic vein contains more plagioclase and wolframite, which is the main ore-forming period of the wolframite in accord with the evolution of the skarn. The late alkali metasomatic vein contains more potassium feldspar, tungsten and magnetite, which is the main ore-forming period of the scheelite in accord with degradation metamorphic stage. The authors thus hold that the alkali metasomatic veins in skarn of the Shizhuyuan ore district restricted and affected the formation of skarns and the ore-forming process, and their evolution passed through the skarn stage and the degradation metamorphic stage. The alkali metasomatic veins belong to the skarn type ore bodies.