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Abstract Carbonates are ubiquitous gangue phases in many hydrothermal ore deposits, often forming throughout the lifetime of individual systems. Clumped C-O isotope analysis represents a novel technique for the acquisition of accurate carbonate precipitation temperatures, allowing calculation of fluid δ18O values. This may be particularly useful when suitable fluid inclusions are not available. We have applied this technique to the Irish Zn-Pb ore field to test the applicability of clumped isotope analysis on a hydrothermal system. We demonstrate a close match between clumped isotope temperatures (TΔ47) and fluid inclusion homogenization temperatures (Th), particularly in dolomite from Lisheen, and late calcite veins that contain remobilized sphalerite above the South West Extension orebody at Navan. At the Lisheen deposit, our new data confirm that hydrothermal dolomitization at ~150° to 210°C led to the recrystallization and isotopic resetting of earlier, fine-grained diagenetic dolomite. Subsequent carbonate phases were precipitated from hydrothermal fluids in isotopic equilibrium with these early, widespread dolomite phases, as ascending, hot (170°–220°C), mildly acidic fluids produced dissolution (pseudo)breccias and extensive replacement in the Waulsortian limestone. In the hanging wall of the Lisheen deposit, white hydrothermal dolomites formed at ~100° to 170°C, cementing subsidence breccias formed above the orebodies. Calcite in basement veins from Navan yields TΔ47 values ~30° to 40°C lower than measured Th. This likely reflects either solid-state bond reordering due to burial or skewed Th distributions due to the failure of bubbles to nucleate in fluid inclusions trapped at low temperatures. Clumped isotope analysis has the potential to revolutionize our understanding of a range of ore systems, particularly when combined with traditional methodologies (e.g., fluid δD, crush-leach) and in situ techniques such as laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis of minerals and fluid inclusions and U-Pb carbonate geochronology. However, care must be taken with regard to sample characterization, sulfide contamination, and the subsequent burial history of samples.
Hollis et al. (Sun,) studied this question.