1:50000-SCALE GEOCHEMICAL EXPLORATION IN THE LOW MOUNTAIN-HILL REGION AS VIEWED IN THE LIGHT OF THE EXPERIMENTAL RESULTS OF GEOCHEMICAL EXPLORATION IN THE YIPIAO AREA

Stream sediment surveys may be applied in the 1:50000-scale geochemical exploration in the low mountain-hill region of the middle and lower reaches of the Changjiang（Yangtze） River.The general arrangement is as follows:1:200000 stream sediment survey→1:50000 stream sediment survey in an area with a high background value→check of anomalies.During the check of anomalies, if the soil survey is applied,either the rectilinear method or the geologic traverse method may be used for the lay-out of the profiles.The selection of a proper method depends on topography and accessibility. To carry out 1:50000-seale stream sediment surveys in an area with a high background value delineated during the 1:20000-scale stream sediment surveys allows us to reject rapidly large tracts of land without ore prespects,speed up the pace of mineral exploration and raise economic effectiveness.So doing,in terms of 1:50000-scale geochemical exploration,about 1/3 of work amount may be reduced.Take for example the Yipiao area which has an area of 1300 km~2 where samples can be taken,about 400 km~2 of work amount may be reduced and about 20000 yuan（about 5000 dollars）for the costs of sampling,preparation and analysis may be saved.