Geology and Geochemistry of Huanggangliang Stratabound Skarn Deposit in Inner Mongolia, China

Over the recent three decades, exploration of a large-size Sn-Fe polymetallic ore deposit at the Huanggangliang, the Da Hinggan Mountains, Inner Mongolia, China, has been largely focused on the premise that the mineralization represents epigenetic magmatic hydrothermal ore deposit in genetic connection with the Mesozoic magmatism. The Huanggangliang Sn-Fe polymetallic ore deposits occurred in Permian strata, with siltstone/marble of the Zhesi Formation and spilite/andesite/tuff of the Dashizhai Formation. The characteristics of geological and geochemical data demonstrated that sedimentary hydrothermal mineralization occurred during the basin evolution at the Permian, rather than representing epigenetic magmatic hydrothermal genesis with the following evidences. The ore-bearing skarns are stratiform with underlying metasedimentary rocks and overlying volcanic sedimentary rocks. Sedimentary hydrothermal textures and structures are observed in the stratabound ore-hearing skarn such as bedded-laminated skarn and magnetite ores with small-size folding or soft deformation, synsedimentary breccia of skarn and magnetite ores and concentric shell structure of magnetite ores. So the stratabound ore-bearing skarns associated with magnetite ore and micro-disseminated tin, are peculiar examples of exhalite. The REE contents of the stratabound ore-bearing skarns display, ΣLREE-rich (36.91×10^(-6)) but ΣHREE-depletion (6.42×10^(-6)), with positive Eu anomaly (Eu/Eu(superscript *) 1.28) and negative Ce anomaly (Ce/Ce(superscript *) 0.88), which is totally different from REE pattern of the Huanggang magmatic rocks (with ΣREE 277.73×10^(-6), ΣLREE 220.24×10^(-6), ΣHREE 57.49×10^(-6), Eu/Eu(superscript *) 0.06, Ce/Ce(superscript *) 1.52), which is comparable with modern sea-floor hydrothermal fluid, sedimentary hydrothermal ore deposit and associated hydrothermal sedimentary rocks. Calcite samples with δ^13C(subscript PDB) from -5.400‰ to -4.397‰ and δ^18 O(subscript SMOW) from 9.095‰ to 9.364‰ in the stratabound ore-bearing skarns show sedimentary hydrothermal genesis of the Huanggangliang deposit. This proposition is useful not only for interpretation of the genesis of the Huanggangliang large Sn-Fe polymetallic ore deposit hut also significant for mineral exploration in the area especially for finding large deposits caused by sedimentary exhalative mineralization processes.