Zircon U--Pb geochronology is a vital tool for dating geological events, yet interpreting discordant zircon ages---often the result of Pb loss due to fluid-rock interactions---remains challenging. Although frequently disregarded, discordant data can yield valuable geological insights. Here, we introduce a Python application that models the timing of Pb loss in zircon, enabling efficient analysis of discordant U--Pb data. Our application uses the concordant-discordant comparison test in Tera-Wasserburg concordia space to classify zircon analyses based on a customisable discordance threshold. Featuring a user-friendly interface, the application models possible Pb loss events and calculates optimal Pb loss ages by minimising the dissimilarity between concordant and reconstructed age distributions. When applied to the Mount Isa Inlier in northeastern Australia, the tool identifies a major Pb loss event around 481 Ma, corresponding to Palaeozoic tectonic activity along Gondwana's active margin, including the Delamerian Orogeny. Older Pb loss ages cluster along major NE-SW fault systems, suggesting that long-lived, reactivated structures facilitated fluid migration and subsequent Pb mobilisation in zircon. Sensitivity analyses confirm the consistency of Pb loss age estimates across various model parameters. This study provides new insights into fluid-rock interactions in the Mount Isa Inlier and offers a methodological framework for exploring Pb loss in zircon U--Pb datasets. The application is broadly applicable for future research in regions with complex tectonic histories.