Title: Tracing geochemical signatures associated with carbonate-hosted Zn-Pb mineraliz
Researchers: Dr Thomas Riegler, Dr Sean McClenaghan
Deposit models for hydrothermal systems have evolved tremendously over the past 30 years with new discoveries, the advancement of analytical methods, and the development of new micro-analytical techniques. This has led to a greater understanding of ore systems and physiochemical constraints on their formation. From an exploration perspective, it is important to fully understand processes responsible for the formation of a deposit, which limit the size, distribution, and grade of deposits. Constraints may include the composition of a source region (basement), structural controls on fluid transport, physiochemical state of hydrothermal fluids, and the nature of host strata at the site of ore deposition. Hydrothermal fingerprinting of ore systems through bulk geochemical analyses and detailed mineral chemistry can reveal much about a hydrothermal system’s protracted history of deposition. Such data could be used to model hydrothermal vectors for Zn-Pb-(Ba-Ag) deposits of the Irish Midlands aiding significantly in unexplored regions. In addition to the mapping of fault structures and sulfide distribution, differentiating regional dolomitization from hydrothermal varieties of dolomite can be an important exploration criterion, where the two occur in close proximity to Zn-Pb-(Ba-Ag) ore systems. Geochemical analyses of hydrothermally altered lithotypes proximal to ore zones should reveal a geochemical fingerprint of the ore forming event. However, regionally dolomitized limestone (Waulsortian Formation) in the surrounding strata may also exhibit cryptic alteration that indicates a hydrothermal vector towards mineralization. Metasomatism of carbonate-bearing strata by ore-related hydrothermal fluids has likely imparted a unique trace-element signature on carbonate mineral assemblages. Trace element signatures, including the rare earth elements (REE) have been used in altered volcanic sequences to vector towards hydrothermal centers, and could also be applicable to carbonate sequences hosting Irish-type Zn-Pb-(Ba-Ag) deposits. With inferred hydrothermal fluid temperatures approaching 250°C, REE signatures in such a fluid would exhibit anomalous LREE and Eu behaviour, ideal for vectoring within hydrothermal systems. Trace-element signatures of carbonate minerals may systematically vary with proximity to the ore mineralizing system and provide a hydrothermal fingerprint in host carbonate strata. Alteration of carbonate-bearing strata along fault structures has imparted a distinctive trace-element fingerprint on carbonate mineral assemblages that systematically varies with proximity to an ore mineralizing system. The elucidation of cryptic hydrothermal halos in regionally altered dolostones could be identified and used as an exploration vector.