青藏高原水系沉积物地球化学衰减模式与区域地球化学勘查对策

THE DISCUSS OF THE GEOCHEMICAL ATTENUATION PATTERN AND REGIONAL EXPLORATION COUNTERMEASURE IN STREAM SEDIMENTS ON QINGHAI—TIBET PLATEAU

文章主要涉及青藏高原干旱荒漠、半干旱草原、高寒草甸等三个景观区。风力搬运的影响遍及整个干旱荒漠和半干旱草原景观区,使其疏松覆盖层中的本域地球化学模式受到不同程度的干扰和变型。干旱荒漠区中水系沉积物的地球化学性质受到风成沙和黄土的双重稀释。高寒草甸区,化学风化作用加强,基本上无外域物质干扰。 考虑技术可能和经济合理两个因素,提出现有交通状况下的区域地球化学勘查对策。

This paper deals mainly with three parts of the five landscape zones in Qinghai--Tibet Plateau. They are dry desert, semiarid prairie and high cold pratum. Based on the brief discussion of the supergene geochemical characteristics in the land-scape zones, the geochemical attenuation pattern and countermeasure in regional geochemicalexploration is stressed. The influence of the wind transport spread whole landscape area of the dry desert andsemiarid prairie. The aboriginal geochemical pattern in tectorium can be disturbed and de-formed variant in varying degrees. The geochemical properties of stream sediments in dry desert areas is effected by the di-lution both from windblown sand and loess. Under the dilution, the original dispersionlength of geochemical anomaly in stream sediments is shorter, and the attenuation patternexpresses that concentration ridge of anomaly appears 'r' shape. The main fraction of anoma-lies carrier deviates to coarse grain. This is a coarse grain retaining attenuation pattern underthe dilutions from windblown sand (superior size0. 125--0. 5mm) and windblown loess (<0.125mm). In high cold pratum area, because the chemical weathering is strengthened, and trans-portation of ancient glacier and modern stream is more powerful, geochemical anomalies ofthe stream sediments dispersion length is longer. As increasing of transporting distance, themain fraction of anomalies carrier deviate to fine grain and concentration ridge of anomaly ap-pears 'L' shape, basically belong to nature attenuation pattern without disturbance from for-eign matter. At semiarid prairie area, the weather character and weathering agency are betweenabove two landscape areas, main disturbance from foreign windblown matters is dilution ac-tion of the windblown loess. The parts of an area was disturbed clearly by windblown sand,on the shape of concentration ridge of anomaly, the anomalous attenuation pattern in astream sediments is also between above two landscape areas. Balancing consider two factors between technical possible and economical reasonable,making the following main points about the regional geochemical exploration given the pre-sent the traffic conditions. 1 The basic method of work of regional geochemical scanning. A. Individually project deal with the area should be above several ten thousand square kilometer that is the conjunction several 1: 200000map sheet, therefore it not only reducethe work cost per unit area but also have a wind field of vision about mineral informationstudying. B. Making use of stream sediments survey seeking the discovery anomalous of largescale and middle scale deposit, At semi--humid high cold pratum area, anomaly samplingdensity can be chosen a sample per 16 square kilometers. It is a suitable that samples prima-ry processing take the interception grade on 40# or 60# sieve under size as prepared analy-ses samples at dry desert area and semiarid prairie area at first sampling abundance compositesample of per a sample in 16 square kilometers as a first round of the prepare analyses, onlythe single sample on anomalous area take a second round of analyzing. So it can be saved lotsof analyzing cost. The method is recommended of sample primary processing: Taking inter-ception grain--size 0. 5--5mm as a prepared analyses sample in the district frequently--oc-curring strong wind of the dry desert landscape area and prairie landscape area and taking in-terception grain--size 0. 25--2mm as a prepared analyses sample in another area of preparedlandscape area. C. Preferred the method of affirming and sieving regional anomalies, improve the de-pendence of selecting exploration target. 2 Preferred the method and technique of seeking and examining anomalies, improve thepercentage of hits of looking for mineral deposits.