• Chlorite chemistry reveals distinct signatures across ore deposit types. • Principal Component Analysis classifies chlorite by deposit type. • Host-rock normalization improves chlorite-based classification accuracy. • Tennant Creek chlorite confirms IOCG affinity. Minerals belonging to the chlorite mineral group commonly form as alteration products of primary ferromagnesian minerals in and around hydrothermal ore deposits, where the chemistry of chlorite species can be used as a powerful tool for mineralization vectoring. In this study, we present a compilation and evaluation of chlorite-group major and trace element data from ninety-six localities, including samples from porphyry Cu, epithermal Au, IOCG, orogenic Au, and VHMS deposits, to assess the potential of chlorite chemistry for classifying ore deposit types. Our results show that a variety of elements, including Al, Co, Cr, Fe, Ga, Li, Mg, Mn, Ni, Pb, Sr, Th, Ti, U, V, Zn, and REE, are controlled primarily by hydrothermal fluid chemistry and metal enrichment rather than whole-rock chemistry, which allows for discrimination of the different hydrothermal ore-forming environments in our sample suite. Host rock composition and precursor minerals play an important role in controlling the Cr, Co, Ni, V, and Pb (and to a lesser extent, Fe, Mg, and Ga) contents in chlorite. These elements can mask the hydrothermal signal related to the ore deposit type, and we propose a normalization method to account for the influence of the host rock composition. Fluid temperature exerts a major control on Si, Al, Li, and Ti contents in chlorite, but the impact of temperature on deposit classification is relatively limited. Principal Component Analysis (PCA) shows that the assemblage of Mg, Fe, Sr, U, and Zn in chlorite is sufficient to classify samples into specific deposit types. Comparison of Tennant Creek chlorite to a global database indicates that major and some trace element contents (e.g., Zn, Sn, Cu) from the Hermitage and Mauretania deposits are similar to IOCG deposits globally. However, Tennant Creek chlorites exhibit higher Co, Bi, REE, and U concentrations than chlorite from other IOCG systems, reflecting unique metal composition of the hydrothermal fluids that formed these deposits. PCA places Tennant Creek clearly within the IOCG field, providing new insights into deposit classification. Overall, this study highlights the potential of chlorite chemistry as a tool for ore deposit classification and exploration targeting.
Braize et al. (2026) studied this question.