Thallium enrichment mechanism and geological significance of the Xiangquan thallium deposit in Anhui Province, China

The discovery of the independent thallium (Tl) deposit in Xiangquan, Anhui Province, provides an example for the study of the enrichment and mineralization of the highly dispersed rare metal element Tl. In this paper, a range of methods are used to characterize the enrichment, depletion, migration and occurrence state of Tl in different types of rocks and ores: lithogeochemistry; electron microprobe and principal component analysis; and exploring the significance of geochemical anomalies on the geological indication of Tl deposit formation. The results show that Tl is mainly distributed in silicified rocks of the Ordovician Lunshan Formation, and its average content is 307.08 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>μ</mml:mi> </mml:math> g g –1 . The contents of As, Sb, S, Fe 2 O 3 and Tl in wall rocks, altered rocks and ores are significantly correlated, indicating a close relationship with Tl accumulation. The geochemical characteristics confirm that pyrite in the study area originates from submarine hot-water deposition. The main carrier of Tl is pyrite of hydrothermal sedimentary origin, in which Tl occurs as isomorphs in fine grains of pyrite. Tl mineralization may be accompanied by silicification, and the metallogenic environment is in a relative oxidation state. The mineralization process results in the geochemical differentiation of elements. Under the influence of tectonic and low-temperature hydrothermal activities, ore-forming elements migrate to structurally favourable conditions for mineralization to occur. This study provides a basis for further understanding the mechanisms of co-enrichment and separation of Tl and guidance for Tl mineral exploration.