GEOCHEMICAL PATTERNS FROM LOCAL TO GLOBAL

The historical development of geochemical exploration is, in a sense, a process of progressive enlargement of areal coverage by exploration projects and progressive widening of sampling space. Along with this p rocess, a hierarchy of geochemical patterns from small to large is gra dually discovered and understood. In this paper, we try to summarize s ystematically the whole hierarchy of geochemical patterns from local, regional, provincial, megaprovincial to global, using examples obtaine d in China. Local anomalies (various types of dispersion halos, trains and fans) within areas not exceeding a few km2, can be delineated whe n sampling is done with very close intervals in limited areas. Regiona l anomalies within areas of tens to hundreds km2 and threshold values lower than local anomalies can be identified only when large areas of more than thousands of km2 are mapped with wider space sampling. Geoch emical provinces with areas of thousands or tens of thousands of km2 c an be discovered if even larger areas, of more than tens or hundreds o f thousands of km2, are covered with very low density sampling. More t han millions of km2 should be covered in order to discover geochemical megaprovinces somewhere in the world. Such megaprovinces are often as sociated with extraordinarily large mineral resources. If ultra-low de nsity geochemical mapping can be carried out across national boundarie s on a continental or global scale, we could find even broader geochem ical patterns which will reflect the global tectonic features. The cla ssification of geochemical patterns according to their sizes is necess ary because it will be extremely useful in planning sampling layout in order to hit targets of certain size ranges. This in turn is arranged in different geochemical projects for achieving specific aims.