Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> The ability to constrain the age of calcite formation is of great utility to the Earth science community, due to the ubiquity of calcite across a wide spectrum of geological systems. Here, we present the first in situ laser ablation inductively coupled tandem quadrupole mass spectrometry (LA-ICP-MS/MS) Lu–Hf ages for calcite, demonstrating geologically meaningful ages for iron oxide copper gold (IOCG) and skarn mineralisation, carbonatite intrusion, and low-grade metamorphism. The analysed samples range in age between ca. 0.9 and ca. 2 Ga with uncertainties between 1.7 % and 0.6 % obtained from calcite with Lu concentrations as low as ca. 0.5 ppm. The Lu–Hf system in calcite appears to be able to preserve primary precipitation ages over a significant amount of geological time, although further research is required to constrain the closure temperature. The in situ approach allows calcite to be rapidly dated while maintaining its petrogenetic context with mineralisation and other associated mineral processes. Therefore, LA-ICP-MS/MS Lu–Hf dating of calcite can be used to resolve the timing of complex mineral paragenetic sequences that are a feature of many ancient rock systems.

Highlights

  • IntroductionSuspendisse Calcite (CaCO3) is the main mineral phase of most carbonate sedimentary rocks and their metamorphic equivalents, and is a major component of carbonatites

  • Accurate in-situ U–Pb geochronology of calcite has been applied to a variety of geological systems (e.g; Li et al, 2014; Ring and Gerdes, 2016; Roberts and Walker, 2016)

  • This result demonstrates that calcite Lu–Hf geochronology is a viable technique to directly date carbonatite magmatism and associated mineralisation, even in the case of old calcite samples with only ~0.5 ppm Lu

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Summary

Introduction

Suspendisse Calcite (CaCO3) is the main mineral phase of most carbonate sedimentary rocks and their metamorphic equivalents, and is a major component of carbonatites. Calcite is a common product of hydrothermal alteration and constituent of mineralising systems where it may precipitate from fluids during pre-ore, ore-stage, and post-ore forming processes (Debruyne et al, 2016). The ability to directly date calcite unlocks the possibility to constrain the timing of a vast array of geological processes that can be difficult to date using conventional methods. Mineral Exploration Cooperative Research Centre (Minex CRC), The University of Adelaide, Adelaide SA-5005, Australia. Accurate in-situ U–Pb geochronology of calcite has been applied to a variety of geological systems (e.g; Li et al, 2014; Ring and Gerdes, 2016; Roberts and Walker, 2016). Calcite often incorporates significant quantities of Pb during crystallisation (i.e. ‘initial’ or ‘common’ Pb), which can limit the utility of U–Pb geochronology (Rasbury and Cole, 2009).

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