Nanomineralogy And Geochemistry Of Limonite Of Xinqiao Ore-field In Tongling, Anhui Province

Xinqiao ore-field of Tonling is a huge representative and typical Fe-S-Au ore-field in the MiddleLower Yangtze metallgenic belt, and limonite are widely distribute in this field. The stratiform-like limonite existed in the upside of polymetallic sulfide ore body and top of siderite in Qixia Formation. Based on analysis of the ore-forming geological setting, geology characteristics and geochemical characteristics of gossan-type gold deposit. About 90 samples, from the Xinqiao ore-field were investigated using X-Ray Powder Diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and atomic absorption spectroscopy (AAS), etc. By studying the morphological characteristics, microstructures and mineralogical of limonite, it's can divided into two categories:Limonite (I) was mainly sourced from the weathering of pyrite ore; Limonite (II) was derived from the weathering of siderite ore.The major minerals of Limonite (I) identified were represented by goethite with a minor hematite and quartz, a little pyrite and magnetite. The particle size range of goethite is 500nm-2?m with a higher ratio of length/diameter. The content of total iron is high, and its containing a small amount of SiO2, most of the quartz are nonapowders. And Limonite (I) is located more closer to pyrite in chemical composition.Goethite was also the major mineral of Limonite (II), and the secondary minerals were quartz, pyrolusite, hematite, illite and a few siderite. The length of goethite is 20-60nm, with a lower ratio of length/width. The size of quartz is 3-10?m and it has a higher psephicity. the pyrolusite in Limonite (II) ias platy; and it has nonapowders hematite, more like siderite in chemical composition.By discussing the relation between two kinds of limonite, it's thought that the Limonite(II) could become a new nanometer materials, but Limonite (I) have a few poisonouseness. We can distinguish this two type of limonites by it's chemical composition. The information on the mineralogy and microstructure of limonite not only can infer the type of primary mineral, but also was a proxy of gold deposit in gossans.