浙江省衢州市上方镇大理岩矿床矿物学、地球化学特征及其地质意义

衢州市上方镇位于钦杭结合带东段,是中国著名的重钙用大理岩产区,区内大理岩矿床均赋存于石炭系黄龙组碳酸盐岩地层.在野外地质调查的基础上,对上方镇大理岩矿床的碳酸盐岩进行了详细的岩相学、矿物学和地球化学研究.研究结果表明,上方大理岩矿床矿石主要为大理岩和大理岩化灰岩,具粒状变晶结构,大理岩方解石结晶较好,颗粒较大且规则,含杂质较少,大理岩化灰岩则含较多杂质,其方解石结晶较差,颗粒不规则且有溶蚀交代现象.地球化学特征显示两类碳酸盐岩化学组成相似,大离子亲石元素(Sr、Ba等)和高场强元素(Nb、Zr、U、Hf、Th等)明显富集,而Ti明显亏损.K2O/Na2O、100×MgO/Al2O3、Ga、Ba、Sr和U/Th等指标暗示碳酸盐岩原岩为沉积型碳酸盐岩,且沉积环境为受陆源碎屑物质影响较少的浅海海相沉积,显示为较强的贫氧-缺氧的还原环境特征.

Mineralogy and Geochemistry Characteristics of Shangfang marble deposit, Quzhou, Zhejiang Province and Their Geological Significances

Shangfang town of Quzhou City is located in the eastern Qinhang belt, and is well endowed with heavy calcium carbonate. Marble deposits in Shangfang town are all hosted in the Huanglong Formation of Carboniferous. Based on detailed field investigation, petrographic, mineralogical and geochemical characteristics of the carbonatite samples were studied. The results show that the ores of the marble deposits could be divide into marble and marbleized limestone with granoblastic texture. Compare with the marbleized limestone, the marble has higher transparency and less impurities, and calcite grains are better crystalized with larger and more regular grains. For the elemental compositions, the marble and marbleized limestone have similar elements compositions. The two types of carbonate are enriched in large ion lithophile elements (Sr and Ba) and high field strength elements (Nb, Zr, U, Hf and Th), but are depleted in Ti. K2O/Na2O, 100×MgO/Al2O3, Ga, Ba, Sr and U/Th index indicate that protoliths of the marble and marbleized limestone are sedimentary-type carbonate rocks, likely formed under marine sedimentary environment with little of the influence of terrigenous materials, and display the characteristics of oxygen deficit-deficient reducing environment.