Relationship Of Geochemical Anomalies And Ore Deposits

Hebei Province is geologically located in the northern margin of North China Platform, which hosts three metallogenic megaprovinces:the Precambrian, the Paleoasian and the Circum Pacific. Iron, nonferrous and precious metals deposits are rich in the province formed in six main metallogenic periods of Archean, paleoproterozoic, mesoprozerozoic, early paleozoic, late paleozoic and mesozoic. In recent years, most of surface outcropping ore deposits have been explored and evaluated in Hebei, therefore it is more and more difficult to find large or giant ore deposits. The activities in past exploration and assessment process are concentrated on local geochemical anomalies to find single ore deposit. How to use a amount of geochemical data to delineate regional and provincial anomalies for potential large-size ore deposits is a chanllenge. The author tries to reveal the relationship of large-scale geochemical anomalies with large ore deposits or ore districts in order to predict new large ore deposits by using geochemical anomalies..Based on the 1:200000 stream sediments geochemical data in Hebei province, combined with regional rock survey and mineral data, the following results are achieved (1) Good correlation between geochemical provinces and the ore districts:3 gold,7 lead and 4 zinc geochemical provinces, each of them covering an area more than 1000km2, are delineated in whole territory of Hebei province. Two large gold districts and one lead-zinc districts are located within the geochemical provinces. Geochemical provinces are indicates to potential large ore districts. (2) Close relationship of regional anomalies with large deposits:all large gold, lead and zinc deposits are hosted within regional gold, lead and zinc geochemical anomalies (each regional anomalous area more than 20 km2) respectively. (3) Genesis of large-scale geochemical anomalies. Three sources for large-scale geochemical anomalies (regional and provincial):deposits, mineralization beds and high background rocks. High background rocks can provide high background of elements without significant concentration centers; mineralization beds can supply initial concentration of elements; weathering of deposits as point sources can further can be despersed to form superimposed contents, which have obvious concentration centers. Therefore, a multi-nested geochemical anomalies can be formed and delineated that a geochemical province contains regional anomalies, and further regional anomalies contains local anomalies around a mineral district or a large ore deposit. (4) Statistics for distribution of rare earth elements are used to identify the mineralization source of gold in Malanyu and Jinchangyu area. The fact of REE distribution model closer to that of metamorphic rocks show that Qianxi and Zunhua rock group possibly is the main mineralization source of gold. The results of surface transportation of gold in Jinchangyu deposit show that gold contents decrease gradually from ore bodies to wall rocks near mine to wall rocks far from mine to background rocks. The gold contents in stream sediments continue to reduce from ore deposit area to lower reaches of streams. (5) Quantitative resource predictions are conducted for 3 gold geochemical provinces and 21 regional anomalies within gold geochemical provinces. Areal productivity and available metals methods are used for mineral resource predictions. Geochemical province or regional anomalies containing the known gold deposits with explored reserves are chosen as reference areas. Prediction results show that Xinglong-Zunhua-Kuancheng-Qinglong gold geochemical province is potential for large gold deposits in the eastern Hebei. In regional anomalies located at Douziyu in Xinglong County, Malanyu in Zunhua County, Anziling in Qinglong County within Xinglong-Zunhua-Kuancheng-Qinglong gold geochemical province have large potential resources, particularly, Malanyu is a main prediction area of large gold deposits.