The source bed usually refers to an original stratigraphic horizon from whichsecondary ore minerals were derived. It is mainly represented by a (metamor-phosed) sedimentary fromation with or without syngenetic volcanics. Throughlater actions of geological agents and subsursface hydrothermal fluids, theore substances are believed to be released from the bed and migrate to afavourable site to form relevant deposits. Therefore, the source bed has its limi-tation, i. e. it refers to one (or some) particular kind(s) of ore and has a definitevertical and lateral extent. The gold source bed is a branch of it. The primaryore substance abundace of a rock formation is utterly different from that meas-ured currently in the samples. The former comprises the readily reactive part andthe less reactive part. The readily reactive part tends to be first remobilized andreleaced out of the bed resulting in to a component part of ore through latermineralization. The content of ore substances of the current samples collected inor rear ore district are most probably the product undergone the same geologicaprocesses as the existing ore deposit. In most cases, the figure of major contentrepresents the less reactive part of ore substances. Thus, it is not advisable tomerely discuss the existence of the source bed and its relevant problems bymeans of the existing ore substance content. It is rather practicable for prospectingto integrate the content of ore substane of a bed with the whole special (volcanic)sedimentary formation as the regional background value.