Quantitative description of geochemical backgrounds of gold due to rock weathering in Jiaodong peninsula, China

Geochemical backgrounds of trace elements can be described quantitatively on the bulk chemistry of the sample. Three weathering profiles developed over granite, granodiorite, and basalt respectively in Jiaodong peninsula, China are selected far from any ore-deposit areas to investigate the quantitative changes in gold distribution during weathering of barren parent rocks. Samples are collected from the topsoil downward to its parent rock in each in situ weathering profile. Contents of 12 major oxides, LoI (loss on ignition), and Au in each sample are analyzed. From parent rocks to their top soils in the in situ weathering profiles, three features are illustrated clearly. The first is that contents of Au increase gradually which indicates the enrichment behavior of Au due to rock weathering, the second is that values of WIG decrease gradually which reflects the increasing weathering degree, and the third is that ratios of Al2O3/Ti and K2O/SiO2 show no clear variations in each profile but are remarkable different among profiles developed over different parent rocks. According to the documented equation form between contents of trace elements and their weathering indices (WIG, Al2O3/Ti, and K2O/SiO2), an empirical equation is regressed on 50 samples from the weathering profiles:lgAu=1.79∗1.2−WIG/100+0.37∗lgAl2O3/Ti−0.922∗lgK2O/SiO2−1.25where the content unit of Au is ng/g, the content unit of Al2O3, K2O, SiO2 is weight %, and the unit of Ti is μg/g. WIG ranges from ca. 44 to 101, Al2O3/Ti varies from ca. 0.001 to 0.035, and K2O/SiO2 varies from ca. 0.02 to 0.09 in the regression data. The empirical equation can be used to describe gold geochemical backgrounds and will have an important potential application on geochemical exploration.