Abstract
Regional geochemical anomalies in stream sediments often have close spatial relationships with metallogenic provinces or ore districts, but the relationships between them have not been examined in depth. In this study, stream sediments were collected around the Zijinshan Copper-Gold Orefield, Fujian Province, China. Element geochemistry, U–Pb geochronology and Hf isotope compositions of detrital zircons, and electron microprobe and LA-ICP-MS analyses of iron oxides were conducted. The aims of this study were to investigate the relationship between the provenance of the stream sediments and ore-bearing magmatic rocks in the Zijinshan Copper-Gold Orefield, and to explore the enrichment mechanism of the ore-forming elements in stream sediments. The results show that the ore-forming elements and their associated elements are most significantly enriched in stream sediments near the orefield. U–Pb ages and Hf isotopic compositions of detrital zircons in the sediments closest to the orefield carry information on the ore- bearing magmatic rocks in the orefield. However, as the stream sediments are relatively far from the orefield, the degree of enrichment of ore-forming elements and the detrital zircon U–Pb age signals of the ore-bearing magmatic rocks in the orefield rapidly weaken. This weakening of the geochemical signals may have been affected by many factors, such as lithological resistance to weathering, vegetation coverage, micro-topographic conditions, etc. In-situ elements analysis of iron oxides and elemental correlation analysis of stream sediments indicate iron oxides and clay minerals are the main carrier minerals for the migration of ore-forming elements.
Highlights
Geochemical surveying and mapping of stream sediments play major roles in ore prospecting
Geochemical blocks are presumed to have provided some amount of metallogenic materials for the formation of ore districts [9], but the relationships between them have not been explored in depth
In stream sediments around the Zijinshan copper-gold deposit, the SiO2 content varies from 70.92% to 87.43%; the Al2O3 content ranges between 5.32% and 12.97%; the TFe2O3 content falls in the 0.93%–4.23% range; the MgO and CaO contents are within the 0.19%–0.52% and 0.12%–2.13% ranges, respectively; the total alkali (Na2O + K2O) content is in the 1.88%–2.83% range
Summary
Geochemical surveying and mapping of stream sediments play major roles in ore prospecting. Regional geochemical anomalies in stream sediments often have close spatial relationships with metallogenic provinces or ore districts [1,2,3,4]. The spatial distribution of Cu geochemical blocks with Cu content greater than 30 ppm in stream sediments of South China is very consistent with that of famous metallogenic belts in China, such as the Middle and Lower Yangtze Metallogenic belt [3]. Based on geochemical data of stream sediments of the Fujian Province (1:500,000) and the Zijinshan Copper-Gold Orefield (1:200,000) in China, Wang et al [6,7] delineated eight gold geochemical blocks and five copper geochemical blocks using 2.5 ppb and 15 ppm, respectively, as the lower limits of anomalies. Geochemical blocks are presumed to have provided some amount of metallogenic materials for the formation of ore districts [9], but the relationships between them have not been explored in depth
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