THE SKARN ORE DEPOSIT SYSTEM ALONG THE MIDDLE AND LOWER YANGTZE RIVER VALLEY, CHINA

摘要

The middle and lower Yangtze River valley is one of the main regions in China where skarn and skarn type ore deposits are concentratedly distributed. The study in the post decade has revealed that skarns may be classified into the following genetic types: (1) interlay-ering reaction-replacement skarn related to high-grade thermal metamorphism caused by emplacement of intrusive rocks into impure limestone and / or thin-bedded pelitic arenaceous limestone and calcareous shale: (2) contact (diffusion-infiltration) replacement skarn associated mainly with postmagmatic skarn-forming pneumatolytic - hydrothermal metasomatism, which include those formed by replacement (thermal metamorphic) of sedimentary calcareous layer under conditions of emplacement of intermediate to shallow seated igneous rocks and those formed by replacement of volcanic rocks during terristial volcanic and subvolcanic activities; (3) magmatic skarns resulting from crystallization and cryptoexplosive crystallization of calcareous skarnic melts (fluids) or magma injected along structural fissures; (4) composite skarns formed by superimposition of any two of the above-mentioned processes (Fig. 1).