Migration Modeling Of Geochemical Elements Based On Catchment Basin

As a common method of geological prospecting,geochemical prospecting is to explore geochemical anomalies in different scales and explain their characteristics by sampling river sediments,rock cuttings and soil.The geochemical anomalies obtained by river sediment sampling are usually applied to large area geological scanning,and there are relatively obvious advantages and disadvantages in this method.It can reflect the obvious geochemical anomalies more efficiently in large scale areas,while it cannot effectively determine the migration sources and directions of the primary anomalies.At present,the research goal of geologists is to combine the geochemical data of different scales to determine the process of geochemical elements,and to make more sophisticated arrangements for geochemical anomalies.Catchment basin is the basis of mineral resource prediction,investigation and evaluation.Atmospheric natural precipitation is the main driving force and carrier for the weathering and migration of heavy minerals on the surface,and it will eventually converge to the outlet point of the catchment basin.Therefore,catchment basin is very suitable for studying the migration process of geochemical elements.It can be used as the research basis for the element migration law by exploring the relationship between the sampled data at the outlet of the catchment basin and the lithological units at its upstream.In this paper,the Milashan integrated exploration area in Tibet is taken as the research area.According to the DEM data,the surface catchment basin is generated,and the catchment basin is taken as the unit to draw the geochemical element anomaly map in combination with the actual geochemical data.The results show that compared with the element anomaly map drawn by the traditional interpolation method,its concentration of element anomaly is more accurate in spatial position.Taking Jiama mining area in the study area as an example,the geochemical element anomaly map of different level catchment basins with river classification as the standard can further clarify the source of geochemical anomaly.In the study of the migration mechanism of elements in the catchment basin,the SCBA method and the sediment tracing technique are used to estimate the contribution value of each lithologic unit in the catchment basin,so as to calculate 13 kinds of lithologic units concentration of geochemical elements at the outlet of catchment basin.A three-step successive process is designated to identify the proper tracers,and the BFGS method is used to find the optimal solution of the contribution rate of each sediment source.After calculation,the contribution value(C_ij)of each lithologic unit estimated by the mixed model based on the sediment tracing technique is greatly related to its area size(X_ij).It shows that the area of lithologic unit can be used as an alternative index for its contribution to the element content at the outlet of catchment basin under certain conditions.Compared with the SCBA method,except for Au and Hg,the geochemical element concentration value estimated by the sediment tracing method at the outlet of most catchment basins is closer to the observe value.