Quantitative Description Of Geochemical Backgrounds Of Gold Due To Rock Weathering

The behaviors of trace elements are commonly described by mass balance calculation and geochemical background value based on chemical weathering indices.The fromer isn't used for regional geochemical exploration and multi-target geochemical survey in China because of the restriction of the parent rocks.The quantitative description of geochemical background value of gold is studied in this paper.Three weathering,developed in background area of gold in Jiaodong,profiles are researched,and it is found that the gold content in soil is orders of magnitude higher than those of their parent rocks and the features of parent rocks can be distinguished by the weathering index Al2O3/Ti.The enrichment of Au due to rock weathering can be described quantitatively aslg?Au?=1.79×?1.2-WIG/100?+0.37×lg?Al₂O₃/Ti?-0.922lg×?K₂O/SiO₂?-1.25where the content unit of Au is ng/g,the content unit of Al2O3,K2O,SiO2 is weight%,the unit of Ti is?g/g,WIG varies from ca.44 to 101.5,10000×Al₂O₃/Ti varies from ca.10.9 to348.5,and K₂O/SiO₂ varies from ca.0.022 to 0.088,SiO₂ varies from ca.45 to 77,CaO varies from ca.0.45 to 9.23,and Al₂O₃ varies from ca.13.4 to 18.0 about the 50 sets of data.Much data is collected on a national scale and 194 samples are obtained,including 87sapmples of 7 weathering profiles,51 samples of 7 sets of soil and stream sediment,28samples with different grain size,28 samples of undissolved substances from dilute salt solution and dilute hydrochloric acid.The enrichment of Au due to rock weathering can be described quantitatively aslg?Au?=-0.0221x-0.543y-1.255z-0.679yz+0.00338xyzwhere x is WIG,y is lg?Al2O3/Ti?,z is lg?K2O/SiO2?,the content unit of Au is ng/g,the content unit of Al₂O₃,K₂O,SiO₂ is weight%,the unit of Ti is?g/g,WIG varies from ca.1.8 to 118,10000×Al₂O₃/Ti varies from ca.7.1 to 348.5,and K₂O/SiO₂ varies from ca.0.0059 to 0.0986,SiO₂ varies from ca.45 to 83,CaO varies from ca.0.09 to 9.23,and Al2O3 varies from ca.8.3 to 22.3.The quation can describe rocks and weathering materials with different lithology,soil and stream sediment with different grain size all over the country,which describe quantitatively the geochemical background value of gold in the weathering process of rock?soil?stream sediment?undissolved substances from dilute salt and dilute hydrochloric acid.Baed on 1:200,000 data from the Regional Geochemistry-National Reconnaissance?RGNR?and the Seven-levels Anomaly Classification Project,the geochemical anomalies are delineated in Qibaoshan gold deposit,Hetai gold deposit,and Axi gold deposit with900 km² single research area.The results suggested that above regression equation has a good effect to describe quantitatively the geochemical background values in differtent climate zone in China.