【作者】 申金超；

【导师】 郭坤一；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2013， 硕士

【摘要】 宁芜地区分布有大量硅质岩,多数与层状铁矿床有关,主要分为两类,第一类是静龙山-龙旗山等地区硅质岩,出露范围较广,同层状赤铁矿矿床密切相关,前人研究程度高,对其成因主要有火山沉积成因及水成沉积成因等观点；另一类是和尚砚地区硅质岩,出露范围不大,顶部形成厚度不大的铁矿层,主要为磁铁矿、褐铁矿,达不到可成矿的规模,前人对其儿乎没有研究。本次研究主要目的是揭示宁芜地区不同类型硅质岩在成因环境上的差异及同铁成矿的关系。本文主要利用主、微量及稀土元素及氧同位素等地球化学分析研究方法,阐明宁芜地区不同类型硅质岩的成因类型、物质来源,及同铁成矿的关系。通过本次研究,并结合前人研究成果,可得出如下结论：1、从龙旗山-静龙山地区样品主量、微量元素地球化学特征可以看出,硅质岩的地球化学特征很大程度上符合热水沉积的特点；和尚砚地区硅质岩在Fe/Ti-Al/(Al+Fe+Mn)图解中显示为泥质硅岩,在沉积物U-Th成因判别图及Cr-Zr成因判别图中显示宁芜和尚砚地区硅铁沉积物为正常水成成因。2、原始地幔标准化后微量元素蛛网图及稀土元素配分模式图中可以看出,宁芜静龙山-龙旗山地区样品同区域火山岩、上地壳相差较大,示踪元素比值较上地壳值及区域火山岩值低,在Th-Th/U图解中样品落在上地壳以下的位置,高的U含量也反映出硅质岩形成过程中有深部物质的加入,正的Eu异常也说明宁芜静龙山-龙旗山地区样品的物质来源为深部,同区域火山岩无成因上联系。和尚砚地区样品在SiO2-Al2O3等主量元素图解中发现该地区硅质岩的形成与火山作用密切相关,原始地幔标准化后微量元素蛛网图及稀土元素配分模式图中可以看出和尚砚地区硅质岩同区域火山岩近乎相同,示踪元素比值同区域火山岩值相近,表明其物源为区域火山岩。因此和尚砚地区沉积物的形成与区域火山作用密切相关。3、静龙山-龙旗山地区硅质岩的氧同位值组成显示了对硅质岩成岩有贡献的深部岩浆源区可能是分异出后期玢岩体的母岩浆源,深部热水在上升过程中溶解携带了壳源硅质成分。和尚砚地区硅质岩全岩的氧同位素值同其上方铁矿层的磁铁矿氧同位素值很相近,表明和尚砚地区硅铁沉积物的硅质和铁质应为同一来源,均源于区域火山岩,其形成与区域火山物质短时间快速水下沉积密切相关。4、宁芜静龙山-龙旗山地区硅质岩同闪长玢岩体没有空间上的直接联系,并且其形成要早于闪长玢岩体。微量、稀土元素地球化学特征也显示硅质岩的主要成岩成矿物质应来源于深部,可能为下地壳,并非闪长玢岩体,其分布范围广泛,具有较大的找矿潜力。和尚砚地区硅质岩规模很小,没有太大的找矿潜力。更多还原

【Abstract】 The cherts has a very wide distribution in Ningwu area,most associated with the Stratified Iron Deposits,and mainly divided into two types.The first type is the cherts of Jinglong-Longqi mountain area.Its have a extensive range of exposing area,closely associated with the Stratified hematite ores,and have a high degree of research.The views of its origin have volcanic-sedimentary origin and water-deposited origin.Another type is the cherts of Heshangyan area.Its exposing area is small,and have a thin iron ore layer at the top.The iron ore layer consists of magnetite and limonite,and did not reach the metallogenic scale,and have a low degree of research.The main purpose of this study is to reveal the differences of genetic environment and the relations of iron mineralization of the different types of cherts in Ningwu area.This paper expounded original types,material source and relations of iron mineralization of the different types of cherts in Ningwu area,using the analysis method of major elements, trace elements,REE and oxygen isotope.By this study and the results of previous studies,the following conclusions can be drawn:1.According to the geochemical characteristics of the major and trace elements of the samples in Jinglong-Longqi mountain area, it indicated a hydrothermal sedimentary origin.In Fe/Ti-Al/(A1+Fe+Mn) diagram,the samples in Heshangyan area shows that the samples are argillaceous siliceous rocks.The samples in Heshangyan area indicated a water-deposited origin in U-Th and Cr-Zr origin diagram.2.According to the primitive mantle normalized trace element patterns and REE disturbution patterns diagram,We can find that the samples in Jinglong-Longqi mountain area are very difference from regional volcano rock and upper crust.Indicator element ratios are lower than regional volcano rock and upper crust.In Th-Th/U diagram,the samples in Jinglong-Longqi mountain area all fall in the below the upper crust.High U and positive δEu in samples indicates that deep materials took part in the cherts,and have no relate with regional volcano rock in origin.We can find that the formation of the cherts in Heshangyan area is closely related to volcanism from some major elements diagram.The primitive mantle normalized trace element patterns and REE disturbution patterns diagram show that the samples in Heshangyan area are the same as regional volcano rock.The indicator element ratios of the samples in Heshangyan area and regional volcano rock are close.Its shows that material source of the cherts in Heshangyan area cameTrom regional volcano rock.Therefore,the formation of the cherts in Heshangyan area is closely related to regional volcano rock.3.The oxygen isotope compositions of the cherts in Jinglong-Longqi mountain area show that the deep magma source region which contributed to diagenesis of cherts may be original magma of late stage porphyrite.The rising deep hydrothermal fluid can dissolve and carry material of silica.The oxygen isotope compositions of the samples in Heshangyan area and iron ore layer above cherts are close.It can show that material of silica and mafic all came from regional volcano rock.The formation of material of silica and mafic is closely related to the rapid water-deposited of regional volcano rock.4.This study found no time-space relationship between the cherts in Jinglong-Longqi mountain area and porphyrite.The geochemical characteristics of the major and trace elements show that the material of cherts originate from deep source,may be from lower crust,not porphy rite. Its have a extensive range of exposing area and great potential for prospecting.But the cherts in Heshangyan area have a small range of exposing area and no potential for prospecting.更多还原