安徽贵池地区含锰岩系地质地球化学特征

The Geological and Geochemical Characteristics of Manganese-bearing Sequences of Guichi , Anhui Province, East China

安徽贵池地区沉积锰矿床赋存于二叠纪孤峰组,包括沉积作用形成的碳酸锰矿和经后期氧化作用形成的氧化锰矿。二叠纪含锰岩系一般为钙、泥、硅质岩石组合,主要处于二叠纪孤峰组下部,自东向西钙质增加、厚度变大。常量元素特征为Ca、Si低,Mn、Fe、P相对富集。微量元素总体特征显示本区锰矿层及含锰岩系的物质来源具有多源性,Sr异常和Sr/Ba值以及Co/Ni值反映出当时含锰岩系处在高盐度的海相沉积环境。稀土元素属LREE富集型。球粒陨石标准化的稀土元素配分模式图显示重稀土亏损特点,均为右倾斜、中等Eu、Ce负异常,利用海水的标准化值进行标准化的模式曲线,则出现明显的Ce正异常特征,反映区内沉积物具有相似的物质来源。氧、碳同位素具有比较大的变化范围,δ13CV-PDB=-4.1‰~5‰,δ18OV-PDB=-3.4‰^-9.9‰,表明碳的来源主要为早二叠纪海水的重碳酸盐。6个含锰灰岩样品δ18OSMOW值稳定在22‰~24‰,这些均一的氧同位素组成可能反映出它们有一个相似的海相源区。古海水温度比正常沉积要高,约49~71℃。综合地球化学各参数特征分析表明本区孤峰组含锰岩系的沉积是热水活动间歇式、多次活动的结果。含锰岩系和锰的物源既有热水成因的也有非热水成因的物质。结合沉积特征及地史演化分析,自栖霞期发生的海侵在茅口早期达最大,本区处于深水陆棚相—盆地相沉积环境,发生含锰地层的沉积。

The sedimentary manganese deposit located in Gufeng Formation of Permian in Guichi area, Anhui Province, including carbonate-manganese ores formed by sedimentation and oxidant-mangnaese ores formed by later oxidation. The manganese-bearing sequence of Permian is commonly calcareous, argillaceous, siliceousrock assemblages, mostly located in the lower part of the Permian Gufeng Formation, increased about calcareous from east to west, lessened in thickness from west to east. The major element contents of bearingmanganese sequence varies greatly, its characteristics is low concentration of Ca, Si, and relatively enrichment in Mn, Fe, P. The trace element＇s characteristics of manganese-bearing sequence make clear that the manganese-bearing sequence and ore body＇s materials are multi-sourced. Sr anomaly, Sr/Ba and Co/Ni values suggest that the manganese-bearing sequence was deposited from high-salinity environment of marine. The characteristics of rare earth elements of the manganese-bearing sequence is LREE enrichment. Seawaternormalized REE patterns of the manganese-bearing sequence have distinct positive Ce anomalies, indicating similar source of sediment in the area. The analyses of stable isotope indicate that there exist a wider range of δ^13CV.PDB and δ^18Ov.PDB in ore-bearing formation, with the values of ~δ^13CV.PDB=-4.1‰～5‰,δ^18OV.PDB=-3.4‰～-9.9‰. The carbon isotopic data of the Mn carbonate ore and Mn-bearing limestones show that sources of carbon primarily come from seawater bicarbonate. Six Mn-bearing limestone samples yielded δ^18OSMOW values ranging from 22‰ to 24‰, the homogeneous oxygen isotope pattern for Mn-bearing limestones seems to indicate a similar marine source. The palaeotemperature has usually higher than normal, about 49-71℃. The analyses of synthesizing geochemical parameter characteristics indicate that deposition of the manganese-bearing sequences was the consequence of episodic, multi-cycle activities of hydrothermal solution. The material sources of Mn-bearing sequence and manganese have been both hydrothermal genesis and nonhydrothermal genesis. Analysis of sedimentary features and geohistoric evolvement reveals the maximum transgression of Qixia Period, ore district was then in deep shelf-basin sedimentary setting and the Mn-bearing sequence was deposited.