Patrick A Carr
email: patrick.carr@univ-lorraine.fr

Emeline Moreira

Leonid Neymark

Marc D Norman

Julien Mercadier

A LA-ICP-MS Comparison of Reference Materials Used in Cassiterite U-Pb Geochronology

Keywords: Cassiterite, U-Pb geochronology, LA-ICP-MS

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Introduction

The U-Pb isotopic composition of cassiterite (SnO2) has been used to constrain the absolute age and duration of magmatic-hydrothermal Sn(-W) systems (e.g. [START_REF] Gulson | Genesis of the Gaosong Sn-Cu deposit, Gejiu district, SW China: Constraints from in situ LA-ICP-MS cassiterite U-Pb dating and trace element fingerprinting[END_REF]Blevin and Norman, 2010;[START_REF] Yuan | In situ LA-MC-ICP-MS and ID-TIMS U-Pb geochronology of cassiterite in the giant Furong tin deposit[END_REF]Zhang et al., 2017a;[START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF][START_REF] Cheng | Controls on cassiterite (SnO 2 ) crystallization: Evidence from cathodoluminescence, trace-element chemistry, and geochronology at the Gejiu Tin District[END_REF][START_REF] Rizvanova | A New Approach to ID-TIMS U-Pb Dating of Cassiterite by the Example of the Pitkäranta Tin Deposit[END_REF][START_REF] Carr | A new method for U-Pb geochronology of cassiterite by ID-TIMS applied to the Mole Granite polymetallic system[END_REF][START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF][START_REF] Denholm | The Geochronology of Tasmanian Tin Deposits Using LA-ICP-MS U-Pb Cassiterite Dating[END_REF][START_REF] Gemmrich | Trace element composition and U-Pb ages of cassiterite from the Bolivian tin belt[END_REF][START_REF] Marcoux | Âge et genèse de la coupole granitique à métaux rares (Sn, Li[END_REF] and raremetal pegmatite systems [START_REF] Kendall-Langley | U-Pb and reconnaissance Lu-Hf isotope analysis of cassiterite and columbite group minerals from Archean Li-Cs-Ta type pegmatites of Western Australia[END_REF]Liu et al., 2020a;[START_REF] Nambaje | SHRIMP U-Pb dating of cassiterite: Insights into the timing of Rwandan tin mineralisation and associated tectonic processes[END_REF]. The advantages of using cassiterite instead of other geochronometers within these deposits is that cassiterite directly dates the Sn mineralising event rather than relying on minerals assumed to be cogenetic with the alteration (e.g., Rb-Sr dating of micas). Additionally, cassiterite is resistant to chemical and physical abrasion such that it can preserve its primary U-Pb isotopic composition through pervasive hydrothermal alteration (e.g., [START_REF] Carr | A new method for U-Pb geochronology of cassiterite by ID-TIMS applied to the Mole Granite polymetallic system[END_REF], passage through the sedimentary cycle (e.g., [START_REF] Oberthür | Mineralogy and mineral chemistry of detrital heavy minerals from the Rhine River in Germany as evidence to their provenance, sedimentary and depositional history: focus on platinum-group minerals and remarks on cassiterite, columbite-group minerals and ur[END_REF] and even magmatic recycling as evidenced from age inheritance identified within cassiterite grains (Neymark et al., 2021a). 206 Pb diagram) provides a matrix-matched session correction factor. This method benefits from the fact that Pb-Pb ages of Precambrian cassiterite are more easily obtained by LA-ICP-MS compared to the U-Pb age because IMF effects on Pb isotopes are often considered insignificant relative to the total uncertainty of LA-ICP-MS analyses, and Pb isotope ratios can be normalised to non-matrix matched references materials such as the NIST synthetic glasses (e.g., [START_REF] Pietruszka | Evaluation of laser ablation double-focusing SC-ICPMS for "common" lead isotopic measurements in silicate glasses and minerals[END_REF].

A few studies have proposed the use of matrix-mismatched reference materials for normalisation of U-Pb ratios in cassiterite including the NIST612 glass [START_REF] Cheng | Controls on cassiterite (SnO 2 ) crystallization: Evidence from cathodoluminescence, trace-element chemistry, and geochronology at the Gejiu Tin District[END_REF][START_REF] Kendall-Langley | U-Pb and reconnaissance Lu-Hf isotope analysis of cassiterite and columbite group minerals from Archean Li-Cs-Ta type pegmatites of Western Australia[END_REF], zircon [START_REF] Yuan | In situ LA-MC-ICP-MS and ID-TIMS U-Pb geochronology of cassiterite in the giant Furong tin deposit[END_REF][START_REF] Oberthür | Mineralogy and mineral chemistry of detrital heavy minerals from the Rhine River in Germany as evidence to their provenance, sedimentary and depositional history: focus on platinum-group minerals and remarks on cassiterite, columbite-group minerals and ur[END_REF], baddeleyite [START_REF] Marcoux | Âge et genèse de la coupole granitique à métaux rares (Sn, Li[END_REF] and rutile [START_REF] Gemmrich | Trace element composition and U-Pb ages of cassiterite from the Bolivian tin belt[END_REF].

These studies and others have noted significant bias in U-Pb cassiterite ages determined by LA-ICP-MS systems when using a NIST612 (up to 15%) (Blevin and Norman, 2010a;[START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF], zircon (ca 7%) [START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF], and rutile (ca 8%) as the primary reference material and have suggested that this approach is inaccurate and not reproducible. Note that the relative offset of U-Pb ages from these matrix-mismatched studies is dependent on the laser spot properties used.

The uncertainty of U-Pb ages determined by LA-ICP-MS must encompass the intra-(instrument drift) and inter-session (i.e., excess variance; ε') reproducibility which typically is quantified by repeated analyses of primary and secondary reference materials, respectively. In the zircon U-Pb geochronology literature, the excess variance for LA-ICP-MS is estimated at ca 1.5% [START_REF] Horstwood | Community-Derived Standards for LA-ICP-MS U-(Th-)Pb Geochronology -Uncertainty Propagation[END_REF], and this represents a minimum age uncertainty obtainable by this method. Currently, very few reference cassiterites with well-defined U-Pb ages and common Pb composition exist to quantify intra-and inter-session reproducibility. This is largely due to the time-consuming process of obtaining high precision ID-TIMS data. For this reason, many studies report only the repeatability (i.e., 'in-run') precision of better than 1.5% for individual analytical sessions which is likely unrealistically small . Therefore, the use of multiple cassiterite reference materials in an analytical session for normalisation and validation of U-Pb data [START_REF] Liu | Cassiterite U-Pb dating of the lower Cretaceous Yanbei tin porphyry district in the Mikengshan volcanic basin[END_REF] will yield more robust ages and realistic uncertainties of U-Pb cassiterite ages, as currently applied for in situ zircon geochronology (e.g., [START_REF] Horstwood | Community-Derived Standards for LA-ICP-MS U-(Th-)Pb Geochronology -Uncertainty Propagation[END_REF].

For this study, we analysed four cassiterites previously analysed by ID-TIMS and that have been used as U-Pb reference materials for LA-ICP-MS analyses (SPG, Yankee, AY-4, and Jian-1).

Additionally, we include the 91500 zircon, NIST612 and NIST614 matrix-mismatched materials to assess their suitability for use as reference materials of U-Pb and Pb-Pb cassiterite ages determined by LA-ICP-MS. Using these materials, we quantify reasonable uncertainties for U-Pb and Pb-Pb ages and compare the traditional data reduction methods (e.g., [START_REF] Paton | Iolite: Freeware for the visualisation and processing of mass spectrometric data[END_REF][START_REF] Chew | U-Pb LA-ICPMS dating using accessory mineral standards with variable common Pb[END_REF] using both matrix-matched and -mismatched materials with the novel approach described in [START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF]. Finally, we summarise the important characteristics of each of the studied cassiterite, including its availability to laboratories, internal chemical and petrographic features.

Materials

The first ID-TIMS study of cassiterite yielded variable results probably due to the incomplete digestion of cassiterite in HCl prior to analysis [START_REF] Gulson | Genesis of the Gaosong Sn-Cu deposit, Gejiu district, SW China: Constraints from in situ LA-ICP-MS cassiterite U-Pb dating and trace element fingerprinting[END_REF] and subsequently no cassiterites from that study have been used as reference materials. The vast majority of published LA-ICP-MS studies have used the AY-4 cassiterite from the Furong deposit in the Nanling Range, Hunan Province, P.R. China, following the initial publication of ID-TIMS data by [START_REF] Yuan | In situ LA-MC-ICP-MS and ID-TIMS U-Pb geochronology of cassiterite in the giant Furong tin deposit[END_REF] and subsequently by [START_REF] Carr | A new method for U-Pb geochronology of cassiterite by ID-TIMS applied to the Mole Granite polymetallic system[END_REF] and [START_REF] Yang | U-Pb isotopic dating of cassiterite: Development of reference materials and in situ applications by LA-SF-ICP-MS[END_REF].

More recently, three ID-TIMS studies based on HBr digestion have presented U-Pb compositions of the Yankee cassiterite from eastern Australia [START_REF] Carr | A new method for U-Pb geochronology of cassiterite by ID-TIMS applied to the Mole Granite polymetallic system[END_REF], the SPG from the Russian Karelia [START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF],

Jian-1 from the Nanling Range [START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF], and cassiterite from Cligga Head of the Cornubian Batholith, SW England [START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF]. Note that the U-Pb isotopic compositions of SPG and Jian-1

were originally characterised by LA-ICP-MS in [START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF]. In Figure 1 we present a summary of published U-Pb ages of the cassiterite used in this study. In addition, we use three matrix-mismatched materials including the 91500 zircon [START_REF] Wiedenbeck | Three natural zircon standards for U-Th-Pb, Lu-Hf, trace element and REE analyses[END_REF] and the NIST612 and NIST614 synthetic glasses (U-Pb data found in [START_REF] Baker | Pb isotopic analysis of standards and samples using a 207Pb-204Pb double spike and thallium to correct for mass bias with a double-focusing MC-ICP-MS[END_REF] to test their suitability for U-Pb cassiterite geochronology.

Pitkäranta ore district, Russian Karelia (SPG)

Cassiterite of the Pitkäranta ore district in the Russian Karelia (Larin et al., 1991 and references therein) occurs in skarn deposits. Skarn mineralisation is associated with late intrusions within the 1.55-1.53 Ga Salmi anorthosite rapakivi granite batholith [START_REF] Amelin | Salmi batholith and Pitkäranta ore field in Soviet Karelia[END_REF][START_REF] Amelin | Chronology of multiphase emplacement of the Salmi rapakivi graniteanorthosite complex, Baltic Shield: Implications for magmatic evolution[END_REF][START_REF] Larin | Relation of the mineralization in the Pitkäranta ore district to the Salmi batholith[END_REF][START_REF] Neymark | Pb-Nd-Sr isotopic and geochemical constraints on the origin of the 1.54-1.56 Ga Salmi rapakivi granite-Anorthosite batholith (Karelia, Russia)[END_REF] and U-Pb ages of zircons from this batholith range from 1547 Ma to 1530 Ma [START_REF] Amelin | Chronology of multiphase emplacement of the Salmi rapakivi graniteanorthosite complex, Baltic Shield: Implications for magmatic evolution[END_REF]. Multi-mineral and whole rock Sm-Nd isochron ages of the skarn and an associated greisen deposit are 1546 ± 20 Ma and1491 ± 42 Ma, respectively (Amelin et al., 1991). In situ LA-ICP-MS U-Pb and Pb-Pb ages for six cassiterite samples from the skarns range from 1536 ± 25 Ma to 1551 ± 28 Ma (Neymark et al., 2021b).

Samples SPG-II and SPG-IV (aliquots of sample SPG) were collected from a pyroxene-garnet skarn. As both the SPG-II and -IV aliquots have similar U-Pb ages, we refer only to the sample name SPG for simplicity. [START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF] present U-Pb isotopic compositions of the SPG determined by ID-TIMS. The three aliquots were slightly discordant due to common Pb, and the authors present two lower intercept ages of 1535.9 ± 5.5 Ma when the regression is unconstrained and 1536.6 ± 1.0 Ma when initial 207 Pb/ 206 Pbi is anchored to 1.0104 ± 0.0062 (determined on galena from the same deposit; [START_REF] Larin | Relation of the mineralization in the Pitkäranta ore district to the Salmi batholith[END_REF]

Yankee deposit, Australia

The Yankee Sn deposit is one of over 1200 polymetallic deposits occurring within and adjacent to the highly fractionated Mole Granite of eastern Australia [START_REF] Brown | Metallogenic Map SH/56-5[END_REF]. The deposit includes quartz-cassiterite veins that are 10 to 40 cm thick. Initially, cassiterite was obtained from the state collection of the Geological Survey of NSW and contained cassiterite grains of 0.4-1 mm in diameter occurring in large vugs within ore veins (Blevin and Norman, 2010a;[START_REF] Carr | Assessment of crystallographic orientation effects on secondary ion mass spectrometry (SIMS) analysis of cassiterite[END_REF][START_REF] Carr | A new method for U-Pb geochronology of cassiterite by ID-TIMS applied to the Mole Granite polymetallic system[END_REF]. A detailed description of the Yankee deposit is available in [START_REF] Brown | Metallogenic Map SH/56-5[END_REF]pg. 55).

The Yankee cassiterite has an ID- The AY-4 cassiterite is from the Bailashui-Anyuan ore belt within Furong deposit of the Hunan Province, China. Mineralisation is within skarn at the contact between Permian carbonate rocks and granite [START_REF] Yuan | In situ LA-MC-ICP-MS and ID-TIMS U-Pb geochronology of cassiterite in the giant Furong tin deposit[END_REF]. The granite is associated with the Qitanling granite batholith, which has zircon U-Pb ages that indicate three stages of emplacement between 163-160 Ma, 157-153 Ma and 150-146 Ma (Jingwen et al., 2010). Multiple 39 Ar-40 Ar ages from muscovite, hornblende, and phlogopite associated with greisenisation within the Furong deposit fall between 160 and 150 Ma [START_REF] Peng | 40Ar/39Ar isotopic dating of tin mineralization in Furong deposit of Hunan Province and its geological significance[END_REF][START_REF] Jingwen | Geological Characteristics of the Furong Tin Orefield, Hunan, 40Ar-39Ar Dating of Tin Ores and Related Granite and Its Geodynamic Significance for Rock and Ore Formation[END_REF].

The first U-Pb isotopic study of the AY-4 cassiterite reported a U-Pb ID-TIMS age of 158.2 ± 0.4 Ma based on 3 aliquots of the cassiterite digested in HCl [START_REF] Yuan | In situ LA-MC-ICP-MS and ID-TIMS U-Pb geochronology of cassiterite in the giant Furong tin deposit[END_REF]. Subsequently, two younger ID-TIMS U-Pb ages of 151.9 ± 2.2 Ma (n=3; Carr etal. 2020) and 154.3 ± 0.7 Ma (n= 6;[START_REF] Yang | U-Pb isotopic dating of cassiterite: Development of reference materials and in situ applications by LA-SF-ICP-MS[END_REF] were reported after HBr dissolution. Since the initial publication, many studies have used the AY-4 as the primary matrix-matched reference material for in situ LA-ICP-MS cassiterite U-Pb geochronology and assumed its age of 158.2 ± 0.4 Ma (e.g., [START_REF] Li | Dating cassiterite using laser ablation ICP-MS[END_REF][START_REF] Cao | U-Pb dating of zircon and cassiterite from the Early Cretaceous Jiaojiguan iron-tin polymetallic deposit, implications for magmatism and metallogeny of the Tengchong area, western Yunnan[END_REF]Zhang et al., 2017a[START_REF] Zhang | Neoproterozoic tin mineralization in South China: geology and cassiterite U-Pb age of the Baotan tin deposit in northern Guangxi[END_REF][START_REF] Gulson | Genesis of the Gaosong Sn-Cu deposit, Gejiu district, SW China: Constraints from in situ LA-ICP-MS cassiterite U-Pb dating and trace element fingerprinting[END_REF][START_REF] Deng | Cassiterite U-Pb geochronology of the Kekekaerde W-Sn deposit in the Baiganhu ore field, East Kunlun Orogen, NW China: Timing and tectonic setting of mineralization[END_REF][START_REF] Yang | Granite-Related Tin Metallogenic Events and Key Controlling Factors in Peninsular Malaysia, Southeast Asia: New Insights from Cassiterite U-Pb Dating and Zircon Geochemistry[END_REF][START_REF] Fei | Petrogenesis of the Lijiagou spodumene pegmatites in Songpan-Garze Fold Belt, West Sichuan, China: Evidence from geochemistry, zircon, cassiterite and coltan U-Pb geochronology and Hf isotopic compositions[END_REF].

Jian-1

Cassiterite Jian-1 was purchased at a mineral show in Denver, USA, in 2017 and was said to originate from Chongyi, Jiangxi, China. No other location information is available for this sample. The Jiangxi W-Sn district has a multistage magmatic emplacement history between 170 and 150 Ma [START_REF] Chengyou | Chronology of the Tungsten Deposits in Southern Jiangxi Province, and Episodes and Zonation of the Regional W-Sn Mineralization -Evidence from High-precision Zircon U-Pb, Molybdenite Re-Os and Muscovite Ar-Ar Ages[END_REF]. Cassiterite mineralisation in this region occurs in quartz veins, greisen and skarn deposits associated with granitic rocks [START_REF] Chengyou | Chronology of the Tungsten Deposits in Southern Jiangxi Province, and Episodes and Zonation of the Regional W-Sn Mineralization -Evidence from High-precision Zircon U-Pb, Molybdenite Re-Os and Muscovite Ar-Ar Ages[END_REF]. A LA-ICP-MS age of 156.6 ± 0.4 Ma (only session reproducibility reported) was determined after normalisation to the SPG cassiterite [START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF]. Subsequently this age has been superseded by a lower intercept age of 154.97 ± 0.08 Ma based on ID-TIMS data obtained on four aliquots [START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF].

Methods

Sample preparation and cathodoluminescence (CL) imaging of cassiterite

Handpicked cassiterite grains were placed onto double-sided tape under a binocular microscope, mounted in epoxy, ground to expose the grain interior using 1500-grit sandpaper, and polished sequentially using 6 µm and 1 µm diamond suspension pastes. Prior to in situ analysis, all samples were imaged in transmitted and/or reflected light on a petrographic microscope, and examined for compositional zoning and the presence of inclusions using back-scattered electron (BSE) and CL images from the scanning electron microscopes JEOL 5800LV™ and FEI Quanta 450 FEG™ operated at 10 keV, beam intensity of 18 nA and 20-mm working distance with a photomultiplier tube at the United States Geological Survey (USGS) Microbeam Laboratory in Denver, Colorado, USA and a TESCAN VEGA3 LM conventional scanning electron microscope (SEM) equipped with a Gatan

ChromaCL2UV CL detector at GeoRessources, Université de Lorraine and an operating voltage of 25 keV, beam intensity of 18 nA and working distance of 15 mm.

U-Pb isotopes by LA-SF-ICP-MS

U-Pb isotopic compositions of all materials were measured in two laboratories at GeoRessources, Université de Lorraine, France, and at USGS, Denver, USA. Key technical parameters used in each laboratory are summarised below and included in Table 1. Each sample consisted of multiple grains that were analysed during at least three analytical sessions. Three analytical sessions were carried out in a 'round-robin' style comparison of the four cassiterite studied here.

During these sessions and under the same analytical conditions, we also analysed the 91500 zircon [START_REF] Wiedenbeck | Three natural zircon standards for U-Th-Pb, Lu-Hf, trace element and REE analyses[END_REF] and NIST614 [START_REF] Baker | Pb isotopic analysis of standards and samples using a 207Pb-204Pb double spike and thallium to correct for mass bias with a double-focusing MC-ICP-MS[END_REF] to test their applicability to cassiterite U-Pb geochronology.

Additional sessions were carried out during 2021 and 2022 using only the Yankee and Jian-1 cassiterite. Prior to each analysis the targeted region was ablated with 5 pulses of a larger and lower-energy dense (2 J/cm 2 ) laser spot to remove surficial Pb. The analytical approaches to calibration and correction for LIEF and IMF are described in section 3.2.3.

USGS, Denver, USA

U-Pb isotopic compositions of all materials were analysed at USGS following procedures described previously [START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF]. All data were collected during multiple sessions between 2017 and 2019 with laser spot diameters of 85-135 µm, a laser repetition rate of 5 Hz and laser energy density of between 4.0 and 5.0 J/cm 2 . The U-Pb data for SPG-and Jian-1 were presented initially in [START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF] and are also discussed here. Data from 5 new analytical sessions including the Jian-1, SPG samples have been added to Appendix A. The U-Pb data from the Yankee and AY-4 are presented here for the first time. [START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF], the AY-4 with 238 U/ 206 Pb* =41.28 ± 0.17 corresponding to an age of 154.3 ± 0.8 Ma [START_REF] Yang | U-Pb isotopic dating of cassiterite: Development of reference materials and in situ applications by LA-SF-ICP-MS[END_REF], and the Jian-1 cassiterite assuming an ideal composition of 238 U/ 206 Pb* = 41.10 ± 0.02 corresponding to an age of 154.94 ± 0.08 Ma [START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF]. In the DRS used, the 238 U/ 206 Pb of the primary cassiterite reference materials is corrected initially for common Pb prior to normalisation by assuming an initial 207 Pb/ 206 Pb of 0.74 ± 0.10 for the Yankee cassiterite [START_REF] Carr | A new method for U-Pb geochronology of cassiterite by ID-TIMS applied to the Mole Granite polymetallic system[END_REF], 1.0104 ± 0.0062 for the SPG [START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF] and 0.85 ± 0.01 for the AY-4 and Jian-1 cassiterites [START_REF] Stacey | Approximation of terrestrial lead isotope evolution by a two-stage model[END_REF]. Isochron ages were calculated using the online IsoplotR program [START_REF] Vermeesch | IsoplotR: A free and open toolbox for geochronology[END_REF].

The measured U-Pb and Pb-Pb ratios of USGS were initially corrected using the U_Pb_Geochronology3 DRS of Iolite™ [START_REF] Paton | Iolite: Freeware for the visualisation and processing of mass spectrometric data[END_REF] using the NIST612 glass as the primary reference material. The assumed 207 Pb/ 206 Pb and 208 Pb/ 206 Pb compositions of NIST612 were 0.90745 ± 0.0004 and 2.1651 ± 0.0001, respectively [START_REF] Baker | Pb isotopic analysis of standards and samples using a 207Pb-204Pb double spike and thallium to correct for mass bias with a double-focusing MC-ICP-MS[END_REF]. The assumed 238 U/ 206 Pb of NIST612 was 3.456 ± 0.019 that was calculated from the published concentration data [START_REF] Jochum | Determination of Reference Values for NIST SRM 610-617 Glasses Following ISO Guidelines: Geostandards and Geoanalytical Research[END_REF] to sequentially place isotope peaks into a single ion-counting detector and in this mode have a limited mass range (~40%) so an internal standard element (i.e., Sn) could not be included in the mass sweep. Due to the significantly different matrices between cassiterite and the NIST glasses we assume an uncertainty of 20% on element mass fractions [START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF].

Results

Crystallographic features of cassiterite

Cathodoluminescence images of cassiterite are shown in Figures 2 (SPG and Yankee) and 3 (AY-4 and Jian-1). The grain size (75-200 µm) and rare secondary alteration of the SPG cassiterite allows for laser spot diameters of frequently >90 µm. This cassiterite is generally featureless in CL images (Figure 2A), however, concentric zoning is evident in some grains.

The Yankee deposit cassiterite can vary from 'gem-quality' euhedral crystals with resinous lustre, and no apparent alteration, to subhedral crystals with visible alteration and intergrown quartz. Gem-quality Yankee cassiterite is dominated by primary growth features such as concentric and sector zoning that are defined in the CL images (Figure 2B). Internal zones within the cassiterite that display a quenched afterglow (i.e., dark CL response) are notably more enriched in U and are therefore favourable for U-Pb analyses [START_REF] Carr | Assessment of crystallographic orientation effects on secondary ion mass spectrometry (SIMS) analysis of cassiterite[END_REF]. Other, less pristine crystals have secondary features such as the resorption of primary textures (Figure 2B) and internal cracks with alteration selvage.

AY-4 grains used in this study measure between 100 and 500 µm. Cathodoluminescence imaging shows common oscillatory zoning within grains that define both diffuse and abrupt terminations prior to the adjacent lamination (Figure 3A). Resorption of primary textures can occur (e.g., Figure 3A). Mineral inclusions are common, and during this study unstable signals on all measured isotopes were observed due to ablation of these inclusions that were hidden at the surface. Only the portions of the signal that were not clearly contaminated by these inclusions were selected.

Jian-1 crystal fragments that have been analysed are >500 µm, permitting large laser spot diameters if necessary. Oscillatory zoning, shown in CL images of Figure 3B, is the dominant textural characteristic of the Jian-1 cassiterite. Alteration features and mineral inclusions are rare although an internal network of cracks with a bright CL response is present.

Pb, Th and U mass fraction

Box and whisker plots of the U mass fraction (in µg/g) and the proportion of common/or initial 206 Pb ( 206 Pbc)

relative to total Pb ( 206 Pbt) and expressed as f206c are shown in Figures 4A and4B, respectively.

f206c is calculated according to the following equation [START_REF] Williams | U-Th-Pb Geochronology by Ion Microprobe[END_REF]:

f206c=(7Rm-7R*)/(7Rc-7R*)
where 7Rm is the measured 207 Pb/ 206 Pb, 7R* is the radiogenic 207 Pb/ 206 Pb (determined iteratively), and 7Rc is the non-radiogenic 207 Pb/ 206 Pb. We estimate the 7Rc using the values described in section 3.2.3.

SPG has on average the highest U contents of the cassiterites studied here with a mass fraction that varies between 2.2 and 250 µg/g (Figure 4A). Analyses of the SPG generally contain little common Pb and 194 of 227

analyses have a f206c <0.05. The U mass fraction within the Yankee cassiterite is relatively restricted between 4.2-52 µg/g, and generally contains little common Pb (129 of 162 analyses with f206c <0.05). Gem quality crystals have lower U µg/g and f206c compared to altered crystals. The AY-4 cassiterite is highly variable in U (8.6-317 µg/g) which is a much greater range than apparent in the ID-TIMS data (Figure 4). f206c is highly variable with 77 of 139 analyses <0.05, however, this is generally lower than the range observed in ID-TIMS data. The U mass fraction in Jian-1 is variable between 0.86 and 52 µg/g. Analyses of Jian-1 generally have little common Pb with 257 of 281 having f206c <0.05.

Excess variance of Pb-Pb and U-Pb cassiterite ages

Repeated analyses of reference materials using different laboratories, analytical set-ups and data treatment methods allows for the determination of excess variation of Pb-Pb and U-Pb cassiterite ages. For 208 Pb/ 206 Pb-207 Pb-206 Pb isochron ages, only the SPG has been analysed enough times at both laboratories to determine an excess variance ±0.33% (Figure 5A). For U-Pb ages, only the Jian-1 has been analysed enough times at both laboratories to determine an excess variance ±1.9% (Figure 5B). Excess variance of U-Pb ages of all cassiterite and normalisation methods relative to the accepted values is ±1.8% (Figure 5C).

Pb-Pb and U-Pb ages of cassiterite

Pb-Pb and U-Pb isotopic compositions and ages using matrix-matched and mismatched reference materials are listed in Appendices A-D. Average U-Pb ages of cassiterite obtained using matrix-matched reference materials are within uncertainty of the accepted ages for those samples (Figure 5C). It is noteworthy that for numerous sessions, the determined ages without consideration of excess variance are biased from the accepted ages. The within-session uncertainty of ages varied between 0.24 and 3.5%, whereas the inter-session 2SD reproducibility of ages varied between 0.5 and 3.4%.

U-Pb ages of cassiterite using matrix mis-matched reference materials were highly variable between sessions and material used (Figure 7). In general, ages normalised to the NIST614 underestimated the assumed age for each sample by up to 8.5%. Ages normalised to the 91500 zircon are within -2.5% of the assumed age for the first two analytical sessions at GeoRessources but overestimate the age by up to 9.4 % for the third analytical session.

Discussion

Geochronology of 'old' cassiterite

)
and here is 1540.9 ± 12.0 (13.1) Ma (2SD; n=43), within uncertainty of the ID-TIMS U-Pb ages of 1536 ± 1.0 Ma [START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF] and 1539.53 ± 0.90 Ма [START_REF] Rizvanova | A New Approach to ID-TIMS U-Pb Dating of Cassiterite by the Example of the Pitkäranta Tin Deposit[END_REF]. We note that the original age of the SPG published in [START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF] 2018) and without high precision ID-TIMS age data [START_REF] Kendall-Langley | U-Pb and reconnaissance Lu-Hf isotope analysis of cassiterite and columbite group minerals from Archean Li-Cs-Ta type pegmatites of Western Australia[END_REF][START_REF] Denholm | In addition, Precambrian cassiterite from tin deposits in Brazil (Rondônia and Pitinga tin provinces) and South Africa (related to Archean Bushveld complex)[END_REF] therefore require multiple analytical sessions to determine the 2SD uncertainty in the age of the reference material in addition to the propagation of excess variance uncertainty.

Pb-Pb normalisation of cassiterite

The individual session 208 Pb ∕ 206 Pb-207 Pb ∕ 206 Pb isochron ages reported here agree with the published ID-TIMS ages of the SPG (Appendix D). Despite these apparently accurate ages, a difference of between 0.5 and 0.8% is observed in ages between 91500 zircon and NIST614 normalised Pb-Pb ratios using the same dataset and indicates that some matrix-mismatched reference materials can introduce bias. A minor systematic bias towards heavier isotopes is clearly observed in all analysed materials in the measured data, and the magnitude of this bias is different between materials. For example, within a single session the measured 207 Pb/ 206 Pb and 208 Pb/ 206 Pb are 0.4% and 1% higher, respectively, in the NIST614 than the accepted values, and 0.8% and 3.2% higher, respectively, for the 91500 zircon (Figure 8). Note that in the two sessions in which the NIST612 was also measured, a similar bias in measured Pb isotope ratios to the NIST614 was observed.

sensitivity of laser parameters and instrument tuning to the matrix-bias between the NIST glasses and zircon for U-Pb cassiterite geochronology. In Figure 7, the analytical sessions 7025 and 7465 used a laser spot size of 95 µm, 5Hz repetition rate and 5J/cm 2 energy density, whilst session 7490 used a 95µm spot size, 8 Hz repetition rate and 3J/cm 2 energy density. Therefore, the difference observed between ages from session 7025 and 7465 compared to 7490 may be due to downhole fractionation. between the NIST614, 91500 zircon and cassiterite means that these matrix-mismatched reference materials will produce variably inaccurate U-Pb cassiterite ages depending on the aspect ratios of the ablation pits. For the largest aspect ratio shown in Figure 9A (Laser parameters: 70 µm spot size, 5 Hz laser repetition rate and 5 J/cm² laser density), the downhole corrected mean 206 Pb/ 238 U of the Yankee cassiterite is 5.9% higher (or age is 5.9% older) than the true value when normalised to the NIST614 model, and 5.6% lower (or younger) than the true value when normalised to the 91500 zircon model. For the smallest aspect ratio in Figure 9A (Laser parameters: 35 µm spot size, 8 Hz and 5 J/cm²), the downhole corrected mean 206 Pb/ 238 U of the Yankee cassiterite is 3.5% higher (or 3.5% older) than the true value when normalised to the NIST614 model, and 11% lower (or younger) when using the 91500 zircon model. Differential 206 Pb/ 238 U downhole fractionation models of 206 Pb/ 238 U between the 91500 zircon and cassiterite and NIST614 and cassiterite can explain younger and older cassiterite ages, respectively, shown in [START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF], but not in GeoRessources dataset which shows a more varied relationship.

Downhole fractionation of U and

Therefore, some process in addition to LIEF of U-Pb seems necessary to explain the matrix biases noted in these data when U-Pb ratios of cassiterite are normalised to synthetic glasses or zircon. A possibility is variable mass load on the plasma related to the widely different ablation efficiencies and densities of the cassiterite (ca 7 g/cm 3 ), zircon (ca 4.6 g/cm 3 ) and glass (ca 2.5 g/cm 3 ) matrices (e.g., Kroslakova and Günther, 2007b). Mass load effects can produce variable intensity ratios for volatile/refractory elements, possibly through incomplete vaporization of ablated particles (e.g., [START_REF] Guillong | Application of a particle separation device to reduce inductively coupled plasma-enhanced elemental fractionation in laser ablation-inductively coupled plasma-mass spectrometry[END_REF][START_REF] Yu | Major and Trace Element Analysis of Silicate Rocks by XRF and Laser Ablation ICP-MS Using Lithium Borate Fused Glasses: Matrix Effects[END_REF] or element-dependent ionization structures within the plasma (Kroslakova and Günther, 2007b;[START_REF] Fietzke | Experimental evaluation of elemental behavior during LA-ICP-MS: influences of plasma conditions and limits of plasma robustness[END_REF]. Fietszke and Fritch (2016) predict strong matrix effects related to mass load on the plasma when the sample represents more than 1% of the total aerosol (i.e., the remaining 99% of the aerosol is Ar and He gas) and this limit can be surpassed with the ablation parameters (spot size, repetition rate) commonly used in LA-ICP-MS geochronology of cassiterite.

Mass load effects are problematic when using different laser spot sizes or repetition rates on a similar matrix, but they are potentially even more significant when normalising to matrix-mismatched reference materials with significantly different densities and ablation characteristics. For example, Si-rich synthetic glasses such as NIST612 ablate at twice the rate of cassiterite due to their different material densities and laser absorptivities [START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF] and this large difference will result in very different quantities of material arriving at the plasma source. The relative ablation rates of a zircon and cassiterite are unavailable; here we considered them to be similar because the NIST610 glass ablates approximately 1.5 times faster compared to the 91500 zircon (Kuhn et al., 2010b), and the NIST612 glass ablates approximately 2 times faster than cassiterite [START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF].

Such matrix effects can be mitigated somewhat by optimizing experimental conditions such as sampling depth of the plasma (e.g., [START_REF] Yu | Major and Trace Element Analysis of Silicate Rocks by XRF and Laser Ablation ICP-MS Using Lithium Borate Fused Glasses: Matrix Effects[END_REF], removing large particles [START_REF] Guillong | Application of a particle separation device to reduce inductively coupled plasma-enhanced elemental fractionation in laser ablation-inductively coupled plasma-mass spectrometry[END_REF], or diluting the ablation stream before it enters the plasma (Kroslakova and Günther, 2007b). Unfortunately, it is difficult to generalise laser and ICP-MS parameters that prevent mass load effects, as these will vary between instrument systems and mineral matrices. Cassiterite U-Pb geochronology often requires substantially larger spot sizes in order to increase 207 Pb signal intensity, which will increase the likelihood of mass load effects when using the NIST glasses for IMF corrections. However, it may be difficult to explain the contrasting behaviour of U-Pb between different labs noted here (e.g., older vs. younger apparent ages in the USGS vs. GeoRessources data) by any single process and further work is required to better understand possible matrix effects in LA-ICPMS geochronology.

Matrix-mismatched reference materials appear to produce accurate U-Pb ages under certain analytical conditions, although these conditions are not applicable for all studies or samples. In U-Pb geochronology, mass load effects may be more influential when using larger spot sizes and synthetic glasses for 238 U/ 206 Pb normalisation, whilst down-hole fractionation will be more important when using smaller spot sizes and a zircon for 238 U/ 206 Pb normalisation. Therefore, we suggest that in the absence of matrix-matched reference materials, that a NIST glass is more appropriate for smaller spot sizes (i.e.. <50 µm) and zircon for larger spot sizes (>50 µm) and common laser repetition rates (5 Hz) and fluence (5 J/cm 2 ). However, there are large uncertainties in the reproducibility of both methods as demonstrated here, and preference should be given to matrix-matched reference materials when available. Older cassiterite U-Pb ages can be verified using the Pb-Pb ages of the same samples, however, younger cassiterite requires other independent geochronological constraints to verify U-Pb ages determined using matrix-mismatched materials. Note that operating conditions of the ICP-MS (e.g., the distance between sampler cone and the load coil and/or carrier gas flow rate) can also influence the transmission of elements (e.g., [START_REF] Yu | Major and Trace Element Analysis of Silicate Rocks by XRF and Laser Ablation ICP-MS Using Lithium Borate Fused Glasses: Matrix Effects[END_REF], but these conditions were not investigated here.

Matrix matched reference materials

Normalisation of U-Pb ratios using matrix-matched reference materials is currently the most accurate method for LA-ICP-MS geochronology of cassiterite younger than ca 1.5 Ga. U-Pb ages determined here using the SPG, Yankee, AY-4 and Jian-1 cassiterite for normalisation of 238 U/ 206 Pb each yield ages that are mostly comparable to each other and relative to the independently determined ages of those cassiterites (Figure 5; Appendix B). The U-Pb age of the AY-4 after normalisation to the SPG, Yankee and Jian-1 suggests a crystallisation age of ca 154 Ma (Table 3) that is similar to a recent ID-TIMS age 154.3 ± 0.7 Ma [START_REF] Yang | U-Pb isotopic dating of cassiterite: Development of reference materials and in situ applications by LA-SF-ICP-MS[END_REF] but not with two previous ID-TIMS ages of 151.9 ± 1.5 Ma [START_REF] Carr | A new method for U-Pb geochronology of cassiterite by ID-TIMS applied to the Mole Granite polymetallic system[END_REF] and 158.2 ± 0.4 Ma [START_REF] Yuan | In situ LA-MC-ICP-MS and ID-TIMS U-Pb geochronology of cassiterite in the giant Furong tin deposit[END_REF]. The reason for the discrepancy between the ID-TIMS ages of these two earlier studies is unclear but could be related to analytical bias within the ID-TIMS data or the use of inappropriate common Pb compositions as suggested by [START_REF] Yang | U-Pb isotopic dating of cassiterite: Development of reference materials and in situ applications by LA-SF-ICP-MS[END_REF], or real age variability within the splits used for these analyses.

In this study, the novel method for normalisation without high precision ID-TIMS data of cassiterite presented by [START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF] yields similar U-Pb ages to conventional methods. The minor bias in LA-ICP-MS 208 Pb/ 206 Pb-207 Pb-206 Pb isochron ages observed when using the 91500 zircon for normalisation of Pb-Pb isotopes (as discussed previously) should be considered. Although this bias is small, it highlights the necessity of appropriate age uncertainty propagation in LA-ICP-MS U-Pb geochronology to account for analysis induced bias.

A note on common Pb corrections

Common Pb corrections or anchored Discordia can introduce bias in U-Pb cassiterite ages by incorrectly assuming the common Pb composition (by terrestrial earth Pb evolution models such as [START_REF] Stacey | Approximation of terrestrial lead isotope evolution by a two-stage model[END_REF] or within associated low U minerals) as discussed in Tapster and Bright [START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF] and documented in [START_REF] Carr | A new method for U-Pb geochronology of cassiterite by ID-TIMS applied to the Mole Granite polymetallic system[END_REF], Neymark et al. (2021b) and [START_REF] Yang | U-Pb isotopic dating of cassiterite: Development of reference materials and in situ applications by LA-SF-ICP-MS[END_REF]. This bias is most important for high precision ID-TIMS studies; however, it can potentially introduce inaccuracies within LA-ICP-MS data that are outside the total uncertainty if the assumed common Pb composition is significantly different from the true composition. For example, [START_REF] Carr | A new method for U-Pb geochronology of cassiterite by ID-TIMS applied to the Mole Granite polymetallic system[END_REF] determined a 207 Pb/ 206 Pbi of 0.74 ± 0.10 from the upper intercept of a 'Total Pb' isochron of ID-TIMS data that was later reproduced by [START_REF] Yang | U-Pb isotopic dating of cassiterite: Development of reference materials and in situ applications by LA-SF-ICP-MS[END_REF] with a value of 0.722 ± 0.075 from the upper intercept of a 207 Pb/ 206 Pb vs. 238 U/ 206 Pb Discordia of LA-ICP-MS data. The value predicted including other Mesozoic deposits of South China, and the Malaysia and Indonesia that make up 60-65% of the worlds historical production (Lehmann, 2020).

We note that other well-defined reference materials are those reported in [START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF] and [START_REF] Yang | U-Pb isotopic dating of cassiterite: Development of reference materials and in situ applications by LA-SF-ICP-MS[END_REF].

Conclusions

We have compared key compositional parameters of four cassiterites that have been used as reference materials in previous U-Pb geochronology studies (SPG, Yankee, AY-4, and Jian-1) and determined the relative accuracy of each cassiterite for normalisation of 238 U/ 206 Pb ratios during in situ LA-ICP-MS U-Pb age determinations. We also tested the suitability of the matrix-mismatched reference materials of the NIST614 and NIST612 synthetic glasses and the 91500 zircon for their applicability as normalising reference materials for cassiterite geochronology. [START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF]. Symbols represent the method used for age determination: circle = ID-TIMS, square = LA-ICP-MS, triangle = LA-MC-ICP-MS. Tables Table 1. Accessory N2 gas: ca 3.0 mL min -1 5.5-6.0 mL min -1

Ni sampler cone: "Dry" plasma type, 0.9 mm orifice Ni skimmer cone: "Dry" plasma type, 0.7 mm orifice Total U sensitivity Session 1: ~8.7× 10 4 cps µg/g -1

Session 2: ~1.1 × 10 5 cps µg/g -1 Session 3: ~5.4 × 10 4 cps µg/g -1 (NIST614, 95 μm spot)

All sessions: ~2.8× 10 4 cps µg/g -1 (NIST612, 85 μm spot)

  3.2.1. GeoRessources, Université de Lorraine, France U-Pb compositions of all materials were analysed at GeoRessources on a Nu Instruments AttoM TM ES sector field inductively-coupled mass spectrometer (SF-ICP-MS) coupled to an ESI 193 nm, ArF excimer laser ablation system with a two-volume 'TwoVol2' sample cell. Gas flow rates and ion lens parameters were optimised on the NIST 612 glass in line scan mode to provide the highest sensitivity of the measured isotopes whilst maintaining low oxide levels (ThO/Th < 0.05%) and to minimize the fractionation of Th/U, which was typically from 0.93 to 0.97 for NIST612 (accepted value = 1.01;[START_REF] Jochum | Determination of Reference Values for NIST SRM 610-617 Glasses Following ISO Guidelines: Geostandards and Geoanalytical Research[END_REF]. Maximum gas blank signal intensities were 180 counts per second (cps) for 206 Pb, 140 cps for 207 Pb, 330 cps for 208 Pb, 2 cps for 232 Th, and 100 cps for 238 U. The measurement of U ( 238 U and 235 U), Th ( 232 Th), and Pb ( 204 Pb, 206 Pb, 207 Pb and 208 Pb) isotopes was conducted using fast-scanning ion deflectors to place a series of flat-topped isotope peaks into a single ion-counting detector. Deflection of the ion beam is performed at a fixed accelerating voltage (~6000 V) and magnetic field strength.

  Figure 9A, and the relative change in 206 Pb/ 238 U with time in Figure 9B. Cassiterite and the NIST614 show a linear evolution of 206 Pb/ 238 U with time, with cassiterite yielding a slightly positive trend in samples without significant common Pb compared to the negative trend of the NIST614. Time resolved Pb/U of the 91500 zircon is defined by logarithmic functions for all laser parameters. The differential trend in downhole fractionation of 206 Pb/ 238 U

208

  Pb/ 206 Pb-207 Pb-206 Pb isochron ages are advantageous for dating > 1.5 Ga low-Thcassiterite such as the SPG by LA-ICP-MS due to the minor matrix effect on instrumental mass fractionation of Pb isotopes. We note a 0.6% bias introduced in these ages of the SPG when using the NIST614 and NIST612 (1539.7 ± 6.1 (8.0) Ma) vs. 91500 zircon (1531.1 ± 7.1 (8.68) Ma) matrix-mismatched reference materials for normalisation of Pb-isotope ratios. We conclude that ideally reference materials with similar Pb concentration and composition should be used for normalisation of Pb-Pb ratios.U-Pb ratios derived from normalisation to matrix-mismatched reference materials such as the NIST glasses or 91500 zircon show varied results in this study and within the literature. Certain analytical conditions may permit the use of matrix mismatched reference materials; however, those conditions are poorly defined and may vary between LA-ICP-MS systems. Ideally, U-Pb ratios are best normalised to matrix-matched reference materials such as the Yankee, SPG, Jian-1 or AY-4 cassiterite. The U-Pb ages of ca 1535 for the SPG, ca 245 Ma for the Yankee, and ca 155 Ma for the Jian-1 and AY-4 cassiterite are equally obtained when any of those cassiterites are used for normalisation of 238 U/ 206 Pb indicating internal consistency in their assumed ages. The use of these well characterized matrix-matched reference materials such as those presented in this study can now permit LA-ICP-MS U-Pb cassiterite ages that approach the long-term reproducibility achieved in in situ zircon geochronology (ca 1.9 % in cassiterite; this study, and ca1.5 % in zircon; e.g., Hortswood et al., 2016) and permit greater confidence in accuracy of the presented ages and more realistic uncertainties

Figures and captions Figure 1 .

 captions1 Figures and captions

Figure 2 :

 2 Figure 2: Cathodoluminescent images of cassiterite from (A) the SPG, Pitkäranta ore district, Russian Karelia showing very little CL response and (B) the best quality crystals with minor alteration of primary textures of Yankee lode, eastern Australia (B).

Figure 4 .Figure 5 .

 45 Figure 4. Box and whisker plot showing key parameters for the cassiterite used in this study including A) Umass fraction (in µg/g), B) proportion of common Pb (f206c; see equation 1 in text). The "X" marks the median value. The range in U mass fraction and f206c[START_REF] Carr | A new method for U-Pb geochronology of cassiterite by ID-TIMS applied to the Mole Granite polymetallic system[END_REF][START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF] of ID-TIMS data for the same samples are shown in A and B. ID-TIMS data of AY-4 originates only from Carr et al.[START_REF] Carr | A new method for U-Pb geochronology of cassiterite by ID-TIMS applied to the Mole Granite polymetallic system[END_REF] as these are not reported in Yuan et al.[START_REF] Yuan | In situ LA-MC-ICP-MS and ID-TIMS U-Pb geochronology of cassiterite in the giant Furong tin deposit[END_REF]

Figure 6 :

 6 Figure 6: 208 Pb ∕ 206 Pb-207 Pb ∕ 206 Pb isochron ages of SPG cassiterite normalised to the NIST614 glass (teal) and 91500 zircon (dark red) in a single session. C) Enlarged panel from A showing isochron ages.

Figure 7 :

 7 Figure 7: Measured/Accepted U-Pb lower intercept ages for all cassiterite and normalised to the 91500 (maroon infill), NIST614 (teal infill) and cassiterite (black infill). Cassiterite data are normalised to the Yankee cassiterite, except the Yankee cassiterite itself that is normalised to the SPG. The average and 2SD for each analytical session are marked for each session and normalisation material. Data are from three analytical sessions from GeoRessources (Sessions 7025,7465 and 7490). Laser parameters for each session as follows: 7025 and 7465; 95 µm spot diameter, 5 Hz repetition rate, 5 J/cm 2 ; 7490; 95 µm, 8Hz and 3 J/cm 2 .

Figure 8 :

 8 Figure 8: Measured/Accepted Pb/Pb values for the NIST614 (A) and 91500 zircon (B) for a single analytical session (Session 7025). 208 Pb/ 206 Pb are shown in red, and 207 Pb/ 206 Pb in blue. The average value and 2SD uncertainty are presented by the dashed line and shaded area for each ratio.

Figure 8 :

 8 Figure 8: A) Time-resolved 206 Pb/ 238 U and downhole fractionation models of cassiterite (SPG, Yankee, Jian-1 and AY-4), zircon (91500) and synthetic glass (NIST614) matrices for three different laser ablation parameters: 1) 70 µm, 5Hz, and 5Jcm², 2) 50 µm, 8 Hz, and 5Jcm², and 3) 35 µm, 8 Hz and 5Jcm². B) Relative change in 206 Pb/ 238 U during ablation for all materials shown in A and based on linear (for NIST614 and Yankee cassiterite) logarithmic functions (91500 zircon).

  Analytical setup and parameters for U-Pb LA-ICP-

  and a 204 Pb/ 206 Pb vs. 207 Pb/ 206 Pb isochron age of 1540.9 ± 3.6 Ma. A different ID-TIMS study found a U-Pb Concordia intercept age of 1539.53 ± 0.90 Ma from two aliquots of the SPG (Rizvanova and Kuznetsov, 2020). The weighted mean 207 Pb/ 206 Pb age of these two aliquots is 1539.55 ± 0.46 Ma. Neymark et al. (2018) report a LA-ICP-MS 207 Pb/ 206 Pb age of 1542.7 ± 1.5 Ma (2SE, 2 standard error) after normalisation of Pb isotopic ratios to the NIST612 glass.

  Typical gas blank signal intensities were 90-120 cps for 206 Pb, 80-110 cps for 207 Pb, 200-250 cps for 208 Pb, 1-2 cps for 232 Th, and 70-100 cps for 238 U. U/ 206 Pb ratios were normalised to four cassiterite reference materials: the Yankee cassiterite assuming

	238 U/ 206 Pb*=25.66 ± 0.05 corresponding to an age of 246.48 ± 0.51 Ma (Carr et al., 2020), the SPG with 238 U/ 206 Pb*
	=3.717 ± 0.002 corresponding to an age of 1536.6 ± 1.0 Ma

3.2.3. Normalisation of Pb-Pb and U-Pb ratios

Measured U-Pb and Pb-Pb isotope ratios were corrected for LIEF and IMF by two different methods employed by GeoRessources and USGS, separately. All isotope ratio uncertainties are reported at the 2SE (2 × standard error where SE=SD/√𝑛, where SD is the sample standard deviation and n is the number of values) level and ages at the 95% confidence level with overdispersion (= 95% conf. int. × √MSWD; Mean Square of Weighted Deviates).

At GeoRessources, measured U-Pb isotopic compositions were reduced in Iolite™ 4 using the UComPbine data reduction scheme (DRS;

[START_REF] Paton | Iolite: Freeware for the visualisation and processing of mass spectrometric data[END_REF]

. We normalise 207 Pb/ 206 Pb and 208 Pb/ 206 Pb compositions to two reference materials for comparison: the NIST614 glass with accepted values of 207 Pb/ 206 Pb = 0.87101 ± 0.00042 and 208 Pb/ 206 Pb = 2.1017 ± 0.0007

[START_REF] Baker | Pb isotopic analysis of standards and samples using a 207Pb-204Pb double spike and thallium to correct for mass bias with a double-focusing MC-ICP-MS[END_REF]

and the 91500 zircon with accepted values of 207 Pb/ 206 Pb = 0.07488 ± 0.00001 and 208 Pb/ 206 Pb = 0.10690 ± 0.00051

[START_REF] Wiedenbeck | Three natural zircon standards for U-Th-Pb, Lu-Hf, trace element and REE analyses[END_REF]

. When counts per second on 238 U exceeds 2.0 × 10 6 the 238 U/ 206 Pb ratios are calculated from 235 U and assuming a 238 U/ 235 U of 137.818

(Heiss et al. 2012)

. This ensures that U isotopes are measured in non-attenuated mode and avoids additional errors associated with uncertainties in attenuation factors. This correction is applied point-by-point in the UComPbine data reduction scheme (DRS;

[START_REF] Paton | Iolite: Freeware for the visualisation and processing of mass spectrometric data[END_REF]

. Note, however, that this assumes negligible IMF between the U isotopes.

238

  ). NIST-normalised Pb-isotope ratios calculated by Iolite™ were then used for further data reduction and age calculations. Using the Pb-Pb age of the SPG cassiterite, we calculate an ideal 238 U/ 206 Pb of the cassiterite that would correspond the Pb-Pb age, with the quotient of the NIST612-corrected 238 U/ 206 Pb and the 238 U/ 206 Pb calculated from the Pb-Pb age providing a correction factor for the analytical session. Excess uncertainty of 207 Pb/ 206 Pb-208 Pb/ 206 Pb isochrons ages and 207 Pb/ 206 Pb vs 238 U/ 206 Pb lower interceptages are estimated in section 4.4. Ages and their uncertainties are reported in the format a ± b (c) Ma where a is the age in millions of years before the present, b is the within-session reproducibility and c is the total uncertainty that includes b, decay constant uncertainty and the excess variation added in quadrature. To account for the difference in Pb isotopic composition between NIST glasses and cassiterite, the measured intensities for 206 Pb, 207 Pb and 208 Pb were summed to give a 'total Pb' intensity. The two AttoM ES ICP-MS instruments used fast-scanning ion deflectors

	3.2.4. Pb, Th and U	mass fraction
	Total Pb, Th and U mass fractions in the cassiterite were estimated by normalising the raw measured count
	rates in cps of each isotope to that measured in the NIST614 glass (accepted values: Pb = 2.32 µg/g, Th = 0.748

Note that new ID-TIMS data of SPG

[START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF]

yield a younger age than the Pb-Pb age determined by LA-ICP-MS, however, we use the latter in order to test the accuracy of this method without the insight of ID-TIMS data.

Ages were calculated using Isoplot v. 4.15

[START_REF] Ludwig | Isoplot version 4.15: a geochronological toolkit for microsoft Excel: Berkeley Geochronology Center[END_REF]

.

We determine

207

Pb/ 206 Pb-208 Pb/ 206 Pb isochrons ages that are analogous to inverse 207 Pb/ 206 Pb-204 Pb/ 206 Pb isochrons (Ludwig, 2008) commonly applied to chondritic meteorites. The generally low Th contents of cassiterite indicate negligible in situ produced radiogenic 208 Pb (Neymark et al., 2018) and a good estimation of common Pb. In the isochron diagrams the age is determined from the y-intercept of the isochron that yields the radiogenic 207 Pb*/ 206 Pb* of the sample. µg/g and U = 0.823 µg/g; Jochum et al., 2011) at GeoRessources and NIST612 glass (accepted values: Pb = 38.57 µg/g, Th = 37.79 µg/g and U = 37.38 µg/g; Jochum et al., 2011) at USGS.

  4.4.1 208 Pb/ 206 Pb-207 Pb-206 Pb isochron ages 208 Pb/ 206 Pb-207Pb-206 Pb isochron ages of SPG vary between ca 1535.7 ± 9.9 (11.1)Ma and 1542.6 ± 17.3 We note very minor difference in lower intercept ages on 207 Pb/ 206 Pb vs.

	(18.1) Ma	when normalised to the NIST614 or the NIST612, with a mean age of 1539.7 ± 6.1 (8.0) Ma for all
	analytical sessions (n=8). In contrast, 208 Pb/ 206 Pb-207 Pb-206 Pb isochron ages of between 1527.1 ± 6.9 (8.6) Ma and
	1533.8 ± 5.8 (7.6) Ma were obtained when normalised to the 91500 zircon with a mean age of 1531.1 ± 7.1 (8.68)
	Ma for the three analytical sessions where the zircon was included. A comparison of 208 Pb/ 206 Pb-207 Pb-206 Pb
	isochron ages from a single session but normalised to the NIST614 and 91500 zircon is shown in Figure 6. Both
	methods yield ages within uncertainty of the ID-TIMS determined age of 1536.6 ± 1.0 Ma. 208 Pb/ 206 Pb-207 Pb/ 206 Pb
	isochron ages for the Yankee, AY-4, and Jian-1 cassiterites have high uncertainty for individual sessions (> ca
	10%) and inter-session variability (30%) that suggest this method is not appropriate for samples of this geologically
	young age.
	4.4.2 U-Pb ages

238

U/ 206 Pb diagrams using Pb-Pb data normalised to either the NIST614 or 91500 zircon, therefore in the following sections we discuss only lower intercept ages determined from NIST614 or NIST612 normalised Pb-Pb data.

  Ga because measured207 Pb ∕ 206 Pb ratios require only minor corrections for IMF compared to LIEF-corrected 238 U/ 206 Pb, and the older minerals have sufficient radiogenic 207 Pb to yield well-defined 207 Pb/ 206 Pb ages. Cassiterite often contains some common Pb so 207 Pb/ 206 Pb ages must be determined using a 208 Pb ∕ 206 Pb-207 Pb ∕ 206 Pb isochron as the208 Pb can be considered entirely non-radiogenic in low-Th cassiterite[START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF]. Excess variance of 208 Pb ∕ 206 Pb-207 Pb ∕ 206 Pb isochron ages for LA-ICP-MS systems is estimated here at ca 0.33% and the total uncertainty of 208 Pb ∕ 206 Pb-207 Pb ∕ 206 Pb isochron ages is dominantly controlled by the measurement uncertainty and natural heterogeneity (session age uncertainties are typically in the range of 0.36 and 1.2%).The mean 208 Pb ∕ 206 Pb-207 Pb ∕ 206 Pb isochron age of the SPG for all data presented in[START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF]

Spencer et al. (2016)

showed that 207 Pb/ 206 Pb ages measured by LA-ICP-MS are generally more precise than U-Pb ages for zircon older than ca 1.5

  of 1542.7 ± 1.5 (2SE) Ma was older than the subsequent U-Pb ID-TIMS U-Pb age (this did not include excess variance) and emphasise that 2SD is a better estimate of the true uncertainty than the 2SE.208 Pb ∕ 206 Pb-207 Pb ∕ 206 Pb isochron ages determined in cassiterite using methods similar toNeymark et al. (

  208 Pb ∕ 206 Pb-207 Pb ∕ 206 Pb isochron ages determined from data normalised to the 91500 zircon slightly underestimate the age of the SPG (or lower corrected207 Pb*/ 206 Pb*), whilst those ages normalised to the NIST614 are slightly overestimated, although within uncertainty of its accepted age (or higher corrected 207 Pb*/ 206 Pb*).

  204 Pb/ 206 Pb vs.207 Pb/ 206 Pb isochron age)[START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF], 1542.7 ± 1.5 (0.10%) Ma (mean weighted 208 Pb/ 206 Pb vs. 207 Pb/ 206 Pb isochron age)[START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF] and 1539.5 ± 0.9 (0.06%) (Concordia intercept

	age) (Rizvanova and Kuznetsov, 2020), B) the Yankee lode, Eastern Australia: 246.48 ± 0.51 (0.20%) Ma (Carr
	et al., 2020) ('Total Pb' isochron age), and C) the Nanling Range, South China including the AY-4: 158.2 ± 0.4
	(0.25%) Ma (mean weighted 206 Pb*/

Ma (Tera-Wasserburg lower intercept age or T-W age), 1540.9 ± 3.6 (0.2%) Ma ( 238 U age)

[START_REF] Yuan | In situ LA-MC-ICP-MS and ID-TIMS U-Pb geochronology of cassiterite in the giant Furong tin deposit[END_REF]

, 151.9 ± 2.2 (1.44%) Ma ('Total Pb' isochron age)

[START_REF] Carr | A new method for U-Pb geochronology of cassiterite by ID-TIMS applied to the Mole Granite polymetallic system[END_REF]

and 159.9 ± 1.9 (1.20%) Ma ( 206 Pb/ 207 Pb vs. 238 U/ 207 Pb isochron age)

[START_REF] Yuan | In situ LA-MC-ICP-MS and ID-TIMS U-Pb geochronology of cassiterite in the giant Furong tin deposit[END_REF]

and the Jian-1: 154.969±0.082 (0.05%) Ma (T-W age)

[START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF]

and 156.55 ± 0.36 Ma (0.23%) (T-W age)

It is difficult to determine the bias of Pb isotope ratios observed in cassiterite due to the potential presence of common Pb. We estimate the bias to be between -0.9-+3.3% for 207 Pb/ 206 Pb in the Yankee cassiterite and between -0.4%-+2.5% in the SPG cassiterite using the most concordant data (calculated from the 2SD of the mean 207 Pb/ 206 Pb of analyses with f206c < 0.02). Note the bias of 208 Pb/ 206 Pb cannot be determined because a purely radiogenic cassiterite without Th should not have 208 Pb.

A systematic bias towards higher 207 Pb/ 206 Pb and 208 Pb/ 206 Pb for the 91500 zircon relative to cassiterite could explain the slightly younger ages determined for cassiterite by overcorrection of Pb isotope ratios (leading to lower corrected 207 Pb/ 206 Pb and 208 Pb/ 206 Pb) when normalised to the zircon (Figure 6). The origin of a bias that is more pronounced in the 91500 zircon, and 208 Pb/ 206 Pb relative to 207 Pb/ 206 Pb, in our LA-ICP-MS data is unclear. The bias per atomic mass unit is not equal between 207 Pb/ 206 Pb and 208 Pb/ 206 Pb and suggests that it is not related to IMF, but rather some matrix effect such as an unknown mass interference on 208 Pb that is more significant for zircon compared to the NIST glasses, or potentially an underestimation of the true 208 Pb*/ 206 Pb* value for the 91500 zircon. Note that a mass bias towards higher 207 Pb/ 206 Pb in zircon was also observed in SIMS U-Pb data on zircon (Stern et al. 2009). In that study, the mass bias was variable between sessions with an average offset of +0.07 ± 0.052 % ( 208 Pb/ 206 Pb was not measured). Note that we do not consider the low abundance sensitivity of the systems used in this study (~80 ppm determined for mass 237 during analysis of natural U at the USGS) or inaccurate deadtime corrections for high signals, because both mechanisms will more strongly affect 207 Pb ∕ 206 Pb relative to 208 Pb ∕ 206 Pb which is contrary to the observations made here.

The 91500 zircon and NIST614 have very different Pb isotopic compositions, and the dominantly radiogenic compositions of the 91500 zircon (and cassiterite) with lower 207 Pb/ 206 Pb and 208 Pb/ 206 Pb compared to the NIST614 glass will make isotopic ratios more sensitive to analytical artifacts that overestimate 207 Pb or 208 Pb, or underestimate 206 Pb. Although the differences in mass bias shown are more significant for 208 Pb∕ 206 Pb relative to 207 Pb∕ 206 Pb it is, in fact, the 207 Pb∕ 206 Pb that exerts the most control on the isochron age as analyses with lower 208 Pb∕ 206 Pb (i.e., lower common Pb) are more strongly weighted in the isochron age (Figure 6). Caution is warranted when producing Pb-Pb isochron ages for cassiterite using matrix-mismatched materials as slight inaccuracies can be introduced as discussed here. Although both the NIST614 and 91500 zircon produced ages within an acceptable age range for the SPG cassiterite, we prefer the NIST614 (and NIST612) as it displays less mass bias in Pb-Pb ratios and yields ages that are more like the 204 Pb/ 206 Pb vs. 207 Pb/ 206 Pb ID-TIMS isochron age of 1540.9 ± 3.6 Ma of that sample [START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF]. However, we encourage the use of multiple reference materials with variable Pb concentrations and compositions so that the most appropriate calibration for the unknown cassiterite sample can be used.

Geochronology of 'young' cassiterite: U-Pb normalisation of cassiterite

Although U-Pb ages are generally more precise compared to 207 Pb/ 206 Pb ages for samples younger than 1.5 Ga (Spencer et al. 2016), the measured 206 Pb/ 238 U ratios require large corrections for LIEF and IMF (up to 40 % and largely dependent on analytical conditions such as laser spot diameter and repetition rate) and significant intersession reproducibility (i.e., excess variance). Since the publication of high precision ID-TIMS ages for the cassiterites used in this study, the largest source of uncertainty in U-Pb LA-ICP-MS ages comes from the excess variance of 206 Pb*/ 238 U of the primary reference material; estimated to be ±1.9%.

.2.1. Matrix-mismatched reference materials Matrix-mismatched reference materials have been employed in U-Pb cassiterite geochronology due to the inaccessibility of quality matrix-matched reference materials (Blevin and Norman, 2010b;[START_REF] Yuan | In situ LA-MC-ICP-MS and ID-TIMS U-Pb geochronology of cassiterite in the giant Furong tin deposit[END_REF][START_REF] Oberthür | Mineralogy and mineral chemistry of detrital heavy minerals from the Rhine River in Germany as evidence to their provenance, sedimentary and depositional history: focus on platinum-group minerals and remarks on cassiterite, columbite-group minerals and ur[END_REF][START_REF] Cheng | Controls on cassiterite (SnO 2 ) crystallization: Evidence from cathodoluminescence, trace-element chemistry, and geochronology at the Gejiu Tin District[END_REF][START_REF] Kendall-Langley | U-Pb and reconnaissance Lu-Hf isotope analysis of cassiterite and columbite group minerals from Archean Li-Cs-Ta type pegmatites of Western Australia[END_REF][START_REF] Gemmrich | Trace element composition and U-Pb ages of cassiterite from the Bolivian tin belt[END_REF][START_REF] Marcoux | Âge et genèse de la coupole granitique à métaux rares (Sn, Li[END_REF]. [START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF] document a matrix bias yielding U-Pb ages ca 12 and 15% older in cassiterite when 238 U/ 206 Pb is normalised to the NIST612 using a laser spot size between 85 and 135 µm and a repetition rate of 5 Hz and energy density of 5 J/cm 2 . In that study, the larger laser spot size (135 µm) also produced older apparent ages (higher corrected Pb/U). [START_REF] Cheng | Controls on cassiterite (SnO 2 ) crystallization: Evidence from cathodoluminescence, trace-element chemistry, and geochronology at the Gejiu Tin District[END_REF] use the NIST610 glass for U-Pb normalisation of cassiterite and using spot sizes of 44-58 µm, laser fluence of 4 J/cm 2 , a laser repetition rate of 10 Hz, and tuning of the LA-ICP-MS system such that the 206 Pb/ 238 U ratio obtained at the start of ablation was similar to the reference value for the NIST610 glass. In this study, we show that when used as a reference material, the NIST614 yields U-Pb ages that are systematically too young for all cassiterites (Figure 7). The 2SD uncertainty of U-Pb ages for 3 analytical sessions at GeoRessources where NIST614 was used for normalisation of Pb/U was equal to or greater than when when using cassiterite reference materials. Two studies have normalised 238 U/ 206 Pb in cassiterite to the 91500 zircon as a matrix mismatched reference material [START_REF] Yuan | In situ LA-MC-ICP-MS and ID-TIMS U-Pb geochronology of cassiterite in the giant Furong tin deposit[END_REF][START_REF] Oberthür | Mineralogy and mineral chemistry of detrital heavy minerals from the Rhine River in Germany as evidence to their provenance, sedimentary and depositional history: focus on platinum-group minerals and remarks on cassiterite, columbite-group minerals and ur[END_REF], whilst [START_REF] Neymark | In situ LA-ICPMS U-Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF] suggest this method introduces ca 7% bias towards older U-Pb ages. In this study, two analytical sessions yield U-Pb ages 0.4 and 2% younger than the accepted values of the cassiterite samples (Figure 7), whilst the third session yield an age 8% older. The variable older and younger bias noted in here and in other studies when using either the NIST612 (or NIST614) or zircon matrix-mismatched reference materials, indicates a high degree of by [START_REF] Stacey | Approximation of terrestrial lead isotope evolution by a two-stage model[END_REF] terrestrial Pb evolution model for the Earth of 0.852 ± 0.017 is significantly higher than the original ID-TIMS estimate. However, in this study the 207 Pb/ 206 Pbi values range between 0.69 ± 0.03 and 0.95 ± 0.03 and suggest heterogeneity in common Pb composition of the Yankee cassiterite. Fortunately, the large number of concordant and near concordant analyses that are typical to the Yankee cassiterite restrict the influence of this variable common Pb on the lower intercept age. However, caution is warranted particular for samples with only moderate to high common Pb (e.g., f206c > 0.1) and poor dispersion along the Discordia. Despite these drawbacks, common-Pb corrected ages and mean weighted 206 Pb*/ 238 U ages can be reported for cassiterite geochronology (e.g., [START_REF] Zhang | Cassiterite U-Pb geochronology constrains magmatichydrothermal evolution in complex evolved granite systems: The classic Erzgebirge tin province[END_REF]. Common-Pb corrections can be applied to raw data prior to processing (e.g., Zack et al., 2011) or data already treated for the effects of LIEF and IMF (e.g., [START_REF] Chew | U-Pb LA-ICPMS dating using accessory mineral standards with variable common Pb[END_REF]. An example of the effect of different common Pb corrections on ages is shown in Appendix E for the Jian- [START_REF] Tapster | High-precision ID-TIMS cassiterite U-Pb systematics using a low-contamination hydrothermal decomposition: implications for LA-ICP-MS and ore deposit geochronology: Geochronology[END_REF]. If data populations do not contain concordant analyses to 'fix' the lower intercept age, then age bias is more susceptible to the common Pb composition selected.

Characteristics of cassiterite reference materials

Supplementary Materials:

Appendix A1: U-Pb isotopic data of cassiterite and normalisation to the Yankee, SPG and Jian-1 cassiterite for U-Pb and the 91500 zircon, NIST612 and NIST614 glasses for Pb-Pb.