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Trace element compositions of zircon can be used to estimate the chemistry of their host magmas; as such they provide a useful tool in zircon provenance, and in the assessment of changing magma chemistries in time and space. Granites derived from the melting of sedimentary protoliths (S-types) have previously been discriminated by their P contents and P vs. REE+Y correlations, largely based on data from the Lachlan Fold Belt. Using a range of magmatic suites from different locations, we show that this discrimination commonly fails to discriminate S-type granite from others. We propose an alternative discrimination tool, based on a plot of Ce/U vs. Th/U, which makes use of low LREE/U and Th/U in metapelite-derived melts. Through coupled thermodynamic and accessory mineral saturation modelling, we demonstrate that these low ratios can be explained by monazite co-crystallisation. We demonstrate that Himalayan S-types, which are inferred to have formed from partial melting of metapelite, and thus can be classified as pure S-types, exhibit the lowest Ce/U and Th/U ratios, and overlap those of metapelitic zircon. Granites formed in oceanic arcs (I-types) and mantle-derived suites both have the highest Ce/U and Th/U ratios. Other S-types, such as those known to have mixed sedimentary and igneous protoliths, which we term Hybrid S-types, form a field overlapping pure I- and S-types. We use Ce/U versus Th/U to demonstrate the dominant I-type origin to early Earth (>3.6 Ga) zircon, and using a large detrital zircon database we assess the proportion of S-type zircon through Earth history. In contrast to previous findings, we find that the supercontinent Rodinia had a normal abundance of S-type zircon, as with other supercontinents, and that instead the period 1.7–1.2 Ga exhibits a marked low in S-type zircon, corresponding to fewer continental collisions.

In both nature and synthetic experiments, the common iron oxide haematite (α‐Fe2O3) can incorporate significant amounts of U into its crystal structure and retain radiogenic Pb over geological time. Haematite is a ubiquitous component of many ore deposit types and, therefore, represents a valuable hydrothermal mineral geochronometer, allowing direct constraints to be placed on the timing of ore formation and upgrading. However, to date, no suitable natural haematite reference material has been identified. Here, a synthetic haematite U‐Pb reference material (MR‐HFO) is characterised using LA‐ICP‐MS and ID‐TIMS. Centimetre‐scale ‘chips’ of synthesised α‐Fe2O3 were randomly microsampled via laser ablation‐extraction and analysed using ID‐TIMS. Reproducible U/Pb and Pb/Pb measurements were obtained across four separate chips (n = 13). Subsequently, an evaluation of the suitability MR‐HFO in constraining U‐Pb data via LA‐ICP‐MS is presented using a selection of natural samples ranging from Cenozoic to Proterozoic in age. The MR‐HFO normalised U‐Pb ratios are more concordant and ages more accurate versus the same LA‐ICP‐MS spot analyses normalised to zircon reference material, when compared with independently acquired ID‐TIMS data from the same natural haematite grains. Results establish MR‐HFO as a suitable reference material for LA‐ICP‐MS haematite U‐Pb geochronology.

Establishing timescales for iron oxide copper-gold (IOCG) deposit formation and the temporal relationships between ores and the magmatic rocks from which hydrothermal, metal-rich fluids are sourced is often dependent on low-precision data, particularly for deposits that formed during the Proterozoic. Unlike accessory minerals routinely used to track hydrothermal mineralization, iron oxides are dominant components of IOCG systems and are therefore pivotal to understanding deposit evolution. The presence of ubiquitous, magmatic-hydrothermal U-(Pb)-W-Sn-Mo–bearing zoned hematite resolves a range of geochronological issues concerning formation of the ~1.6 Ga Olympic Dam IOCG deposit, South Australia, at up to ~0.05% precision (207Pb/206Pb weighted mean; 2σ) using isotope dilution-thermal ionization mass spectrometry (ID-TIMS). Coupled with chemical abrasion-ID-TIMS zircon dates from host granite and volcanic rocks within and enclosing the ore-body, a confident magmatic-hydrothermal chronology is defined. The youngest zircon date from the granite intrusion hosting Olympic Dam indicates magmatism was occurring up until 1593.28 ± 0.26 Ma. The orebody was principally formed during a major mineralizing event following granite uplift and during cupola collapse, whereby the hematite with the oldest age is recorded in the outer shell of the deposit at 1591.27 ± 0.89 Ma, ~2 m.y. later than the youngest documented magmatic zircon. Hematite dates captured throughout major lithologies, different ore zones, and the ~2-km vertical extent of the deposit support ~2 m.y. of hydrothermal activity. New age constraints on the spatial-temporal evolution of the formation of Olympic Dam are considered with respect to a mantle to crustal continuum model. Cyclical tapping of magma reservoirs to maintain crystal mushes for extended time periods and incremental building of batholiths on the million-year scale prior to main mineralization pulses can explain the ~2-m.y. temporal window temporal win

Hematite (α-Fe2O3) is a common iron-oxide mineral known to incorporate U into its crystal lattice at up to wt% concentrations and has been previously used to date ore formation within iron-oxide copper gold and banded iron formation deposits. However, there has been no detailed evaluation of the potential challenges this novel mineral geochronometer may present for accurate temporal interpretation. We report a multi-technique UPb geochronological study comprising laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), sensitive high-resolution ion microprobe (SHRIMP) and the first isotope dilution-thermal ionization mass spectrometry (ID-TIMS) procedure and analyses using an in-situ grain micro-sampling technique. We assess intra- and inter-sample data reproducibility, and examine the compatibility of spatial and analytical resolutions to texturally and compositionally diverse samples. Five samples of hydrothermal, primary, oscillatory-zoned hematite were analysed from distinct lithologies throughout the ~1.59 Ga Olympic Dam Cu-U-Au-Ag deposit, with typical U concentrations ranging between ~20 and 1000 ppm. LA-ICP-MS mapping of isotope distributions across mm-sized grains allows pinpointing of U-rich and relatively U/Pb isotopically ‘homogeneous’ domains. Micro-domains were extracted via laser-cut square shaped trenches (100 × 100 μm). UPb datum range in complexity, with concordant age domains measured by ID-TIMS indicating that hematite can retain a near-closed UPb system over ~1.6 Ga, while also demonstrating that younger Pb-loss events may be recorded. Significant reverse discordance is common in the data, likely to be a real feature due to both internal decoupling and mobility of Pb within a single grain and UPb fractionation during microbeam analysis. These effects will obscure the interpretation of real ages for Proterozoic samples where non-zero age Pb-loss events occur, and restricts the evaluation of common Pb mixing components. As a result

Here, we document a detailed characterisation of two zircon gemstones, GZ7 and GZ8. Both stones had the same mass at 19.2 carats (3.84 g) each; both came from placer deposits in the Ratnapura district, Sri Lanka. The U‐Pb data are in both cases concordant within the uncertainties of decay constants and yield weighted mean 206Pb/238U ages (95% confidence uncertainty) of 530.26 Ma ± 0.05 Ma (GZ7) and 543.92 Ma ± 0.06 Ma (GZ8). Neither GZ7 nor GZ8 have been subjected to any gem enhancement by heating. Structure‐related parameters correspond well with the calculated alpha doses of 1.48 × 1018 g−1 (GZ7) and 2.53 × 1018 g−1 (GZ8), respectively, and the (U‐Th)/He ages of 438 Ma ± 3 Ma (2s) for GZ7 and 426 Ma ± 9 Ma (2s) for GZ8 are typical of unheated zircon from Sri Lanka. The mean U mass fractions are 680 μg g−1 (GZ7) and 1305 μg g−1 (GZ8). The two zircon samples are proposed as reference materials for SIMS (secondary ion mass spectrometry) U‐Pb geochronology. In addition, GZ7 (Ti mass fractions 25.08 μg g−1 ± 0.18 μg g−1; 95% confidence uncertainty) may prove useful as reference material for Ti‐in‐zircon temperature estimates.