Behavior Of Elements During Weathering And Its Implication To Geochemical Anomaly Recognition

Major trace element contents of regolith materials are often orders of magnitudehigher than those of their parent rocks. This weathering enrichment is often confusedwith mineralization. In order to quantitatively describe trace element behaviors due toweathering, we selected a regolith profile developed over the Xiong’er group andesitein the western Henan Province. The weathering behaviors of12trace elements arequantitatively described using an exponential relationship between element contentsand WIG values in the studied regolith profile. Trace element contents calculatedaccording to this exponential relation can be viewed as background values resultingonly from differences of weathering degree of the same parent rock.The optimal sampling granularity of stream sediments remains variable indifferent supergene environments． In this paper，element behavior of differentgranularity soils and stream sediments in weathering processes is investigated takingthe Niutougou gold deposit in western Henan Province as an example． The resultsshow that the weathering degree of gneiss soils and stream sediments increase withthe decreasing soil granularities．But the weathering degree of andesite soils isirregular since the particle size is smaller. Sample granularity can not reflect theweathering degree. As a whole, sample granularity cannot reflect degree ofweathering. Element content shows a stable trend in soils or stream sediments whenthe sample granularity decreases from4to100mesh，but the element content changessharply when granularity is less than100mesh. This sharp change may be resultedfrom the transfer of weathering mechanisms. Hydrothermal ore-forming elements areconcentrated in the60～100mesh granularity in soils and80～100mesh in streamsediments，respectively. The sample granularity of60～100mesh is optimal for themeasurement of stream sediments in the Niutougou gold deposit．The geochemical survey at a scale of1∶50000was carried out in the Niutougougold deposit choosing the sample granularity of60～100mesh，and using thebackground values calculated according to the exponential relation to determine thelower limit of element geochemical anomaly. For the case study in the Niutougougold deposit region, compared with the traditional statistical methods, the resultsindicate that element anomaly zoning and concentration trend is obviously. Theanomaly centers of elements coincide with the ore blocks in the district. This resultvalidates the feasibility of sampling granularity and provides guidance forgeochemical surveys in the Xiong’ershan gold mine.