大厂锡多金属矿床热液喷气沉积的证据——含矿建造及热液沉积岩

EVIDENCE FOR EXHALATIVE ORIGIN FOR ROCKS AND ORES OF THE DACHANG TIN POLYMETALLIC FIELD: THE ORE-BEARING FORMATION AND HYDROTHERMAL EXHALATIVE SEDIMENARYT ROCKS

通过对大厂锡多金属矿床含矿建造特征及容矿岩石的岩石学、地球化学研究,探讨了矿床形成的地质环境,证明了主要容矿岩石是从海底热卤水系统中以化学沉淀方式形成的热液沉积岩。

The Dechang tin-polymetallic ore district is located in a midlate Paleozoic rift that flanks the southwestern border of the Jiangnan Massif. The Devonian sequence contains the main ore-hosting stratigraphic units, and main ore bodies are strictly confined within certain host strata. The host rocks consist mainly of massive and bedded siliceous rocks, with lesser but important proportions of alternating thin beds of carbonates, feldspar-rich rocks and tourmaline-bearing rocks, or tourmalinites. Some of these rocks exhibit soft sedimentary deformation structures and textures. Petrologic and petrochemical studies indicate that the siliceous rocks contain virtually no siliceous tests of biogenic origin, but are enriched in A1_2O_3, TiO_2, MgO, K_2O, and Na_2O, suggesting that these siliceous rocks are different from biogenic ones. The tourmalinites alternating with carbonaceous beds are enriched in MgO, and composition of the tourmaline is similar to that in bedded tourmalinites from massive base metal sulfide deposits. The feldspar-rich beds often contain important amounts of cassiterite. They generally also contain a high content of barium, and BaO content of individual feldspar grains reaches 4.51%. These data suggests that these siliceous and other unusual bedded rocks are of submarine hydrothermal exhalative origin.