Unraveling the link between worldwide adakite-like rocks and porphyry Cu deposits

Abstract

Adakite-like rocks, as an important recorder of magmatic evolution in mantle and crust, are closely associated with major porphyry Cu deposits. However, the underlying mechanism connecting these associations remains insufficiently elucidated. This study compiles ca. 7000 whole-rock geochemical data from Phanerozoic adakite-like rock samples and from ore-forming porphyries in porphyry Cu deposits. Machine learning investigations are performed to characterize the geochemical variations of adakite-like rocks from various orogenic or cratonic systems and investigate any geochemical similarities with rocks associated with porphyry ore systems. Principal component analysis (PCA), along with t-distributed Stochastic Neighbor Embedding (t-SNE), highlights elemental distinctions between adakite-like rocks formed in mature and juvenile crust and the similarities of rocks from porphyry CuMo deposits with the former and rocks from porphyry CuAu deposits with the latter. Extreme Gradient Boosting (XGBoost) and Support Vector Machine (SVM) analyses are applied to the original dataset and the PCA data derived from the dataset to discriminate adakite-like rocks from various geodynamic settings from each other and from rocks associated with porphyry ore deposits. Our models show that XGBoost and SVM can identify the tectonic regions of adakite-like rocks and rocks from porphyry copper systems with high efficiency and confidence e.g., accuracy = 0.88–0.94 and area under curve (AUC) = 0.69–0.86. The application of SHapley Additive exPlanations (SHAP) values is employed to elucidate the parameters that discriminate the different environments, providing insight into the underlying petrogenetic processes, including diverse levels of formation depth and extent of mantle interaction. Additionally, when examining ore-forming porphyries and adakite-like rocks, the incorporation of heatmaps into taxonomic classification (HTC) provides significant distinguishing factors with substantial geological implications. These findings suggest potential geological processes (e.g., remelting of Cu-sulfide-bearing cumulates or flotation of Cu-sulfide phases attached to vapor bubbles) that may enrich the source magma of ore-forming porphyries beyond the conventional geological processes responsible for adakite-like rock formation, which could serve as an exploration indicator.