利用TM数据快速提取含矿蚀变带方法研究

热液蚀变岩类是在含矿热液作用下引起原岩化学成分和物理性质发生变化的结果，因此蚀变岩类往往与内生产矿产伴生，有时其本身就是含矿体。不同蚀变矿特级组合具有独特的光谱响应，但是光谱的反射和吸收产特征较弱称为遥感找矿弱信息标志。     

Varicolored and vesiculated tuffs from La Fossa volcano,Vulcano Island (Aeolian Archipelago,Italy): evidence of syndepositional alteration processes

Chemical and mineralogical data for samples collected from a surge sequence from La Fossa cone (Vulcano Island, Italy) show a wide variety of alteration states between adjoining beds, the macroscopic features of which are expressed by various degrees of reddening. The effects of the alteration processes on pyroclastic rocks are as follows: hydration and oxidation of each component of the pyroclastic rocks to varying degrees; formation of authigenic smectite; precipitation of a large variety of soluble salts; and corrosion on the surface of glass fragments (pitting). Dry surge beds, emplaced from a two-phase, dry steam + solid, suspension do not show significant alteration. By contrast, wet surge deposits, suggesting an emplacement from free water-bearing turbulent flows, show an increasing degree of alteration, passing from grey to red coloured beds. The strict relationship between the present alteration state and the depositional unit rules out any post-depositional processes. The occurrence of alteration in wet surge beds and the lack of alteration in dry beds shows that the main controlling agent was water condensed from the eruptive cloud and suggests a syn-depositional character to the alteration itself. These observed differences can be ascribed to the different chemical reactivities of the water, probably related to the amounts of acidic species carried by the eruptive cloud and/or by the efficiency of their capture during the condensation of the water vapour.