Few studies have focused on the application of the Tl isotopic system for geochemical exploration. We report 205Tl values of rock samples from the TL Deposit, British Columbia, Canada - a sediment-hosted massive sulfide (SHMS) deposit with characteristics of a Broken Hill-type deposit - and investigate relationships with major and trace element geochemistry. Maps generated using Tl isotope and trace element data indicate that 205Tl values can potentially be used to fingerprint ore mineralization at the TL Deposit. The sources of Tl and other metals (Ag, Pb, Zn) are assessed using Tl isotope data. Measured 205Tl values exhibit positive correlations with Pb, sedimentary exhalative (SEDEX) metal index (Zn+100*Pb+100*Tl), and the redox proxy, U/Th, and negative correlations with Be, Cd, Ce, La, Ni, and Th. Individual lithologies have distinct Tl isotopic compositions. Metal-rich heavily altered samples have relatively high 205Tl values (-5.0 to -2.5 -units) reflecting the euxinic conditions of the global Paleoproterozoic ocean and hydrothermal influence. Samples with lower 205Tl values (-15 to -7.6 -units) reflect a combination of their mineralogy (phyllosilicate minerals such as biotite and clinochlore), Tl from sediments reflecting the Tl isotopic composition of modern seawater, and possible low-temperature alteration processes. Samples with high Pb and Ag contents have high 205Tl values, indicating a hydrothermal origin of these metals, whereas Zn is highest in samples with low 205Tl values, indicating a low-temperature or sedimentary origin. Thallium isotopes, paired with conventional geochemical data, show promise as a useful tool for exploration of SHMS deposits with Broken Hill-type characteristics.
Thematic collection: This article is part of the Geochemical processes related to mined, milled, or natural metal deposits collection available at: https://www.lyellcollection.org/topic/collections/geochemical-processes-related-to-mined-milled-or-natural-metal-deposits