|
Abstract
|
Skarn formation is a metasomatic process that can affect both wall rocks and igneous rocks, forming exoskarn and endoskarn, respectively. Accurate classification of endoskarn and exoskarn has important implications for exploration and mining. Systematic mapping of the rock types and mineralogical zoning patterns in a skarn system can improve the accuracy of a deposit model and reveal vectors to ore. Additionally, the endoskarn-exoskarn contact can mark a change in ore grade, metal distribution, and rock hardness. Therefore, distinguishing these skarn types can inform mining and milling processes to improve metal recovery. Field-based classification of skarns relies heavily on inherited precursor textures; as such, skarns with relict textures are the easiest to classify as either endoskarn or exoskarn. Banded textures in exoskarn provide a clear link to a layered metasedimentary precursor, while weakly altered endoskarns commonly display patches of residual igneous rock (e.g., at the Ghale Rutale skarn Fe (Cu-Au) deposit, NW Iran). Compared to endoskarn, exoskarn are less likely to retain primary textures, because carbonate-rich wall rocks are more reactive than igneous rocks in the presence of acidic magmatic-hydrothermal fluids. At Ghale Rutale, mottle-textured skarns are common, and although the precursor connection is not clearly linked, they are typically classified as endoskarn because of a subtle resemblance to porphyritic igneous rocks. In this study, we compare the bulk-rock geochemical signatures of skarns to unaltered precursors from Ghale Rutale with the aim of developing a method to distinguish endoskarn from exoskarn. We demonstrate that the geochemical classification of skarns is more reliable than textural classification because mottle-textured skarns can be either endoskarn or exoskarn. Furthermore, we quantify the compositional changes that take place during skarn formation in order to gain insight on the influence of immobile elements on our classi
|