Re-Os dating of pyrite confirms an early diagenetic onset and extended duration of mineralization in the Irish Zn-Pb ore field

0000-0002-7706-6003The Irish Midlands region contains one of the world’s largest hydrothermal Zn-Pb ore districts, but uncertainty exists in the timing of mineralization relative to host rock ages. Consequently, genetic models for ore formation are poorly constrained and remain controversial. Here we use Re-Os geochronology to show that ore-stage pyrite from the Lisheen deposit formed at 346.6 ± 3.0 Ma, shortly after host rock deposition. Pyrite from the Silvermines deposit returns an age of 334.0 ± 6.1 Ma, indicating that at least some mineralization occurred during later burial. These age determinations show that the much younger paleomagnetic ages reported for the Irish Zn-Pb deposits reflect remagnetization during the Variscan orogeny, a process that we suggest affects paleomagnetic dating more widely. The Re-Os ages overlap with the ages of lower Carboniferous volcanic rocks in the Midlands, which are the product of magmatism that has been invoked as the driving force for hydrothermal activity. The relatively low initial Os ratios for both Lisheen (0.253 ± 0.045) and Silvermines (0.453 ± 0.006) are compatible with derivation of Os from these magmas, or from the Caledonian basement that underlies the ore deposits.This journal is published under the terms of Green Open Access. Authors may post a copy of the accepted (i.e., post-peer review) version of their paper (https://doi.org/10.1130/G36296.1) in a repository of their choice or to their personal website after the relevant embargo period has passed. The embargo period will be 12 months from formal online publication

A More Reduced Mantle Source for Enriched Shergottites; Insights from the Olivine-Phyric Shergottite Lar 06319

A detailed petrographic study of melt inclusions and Cr-Fe-Ti oxides of LAR 06319 leads to two main conclusions: 1) this enriched oxidized olivine- phyric shergottite represents nearly continuous crystallization of a basaltic shergottite melt, 2) the melt became more oxidized during differentiation. The first crystallized mineral assemblages record the oxygen fugacity which is closest to that of the melt s mantle source, and which is lower than generally attributed to the enriched shergottite group

Data for: Understanding the microscale spatial distribution and mineralogical residency of Re in pyrite: Examples from carbonate-hosted Zn-Pb ores and implications for pyrite Re-Os geochronology

Tables 2-4 - Provide the raw Re-Os ratio's used for geochronology.Table A1 - Provide the raw ICP-MS data used in the manuscript (e.g. Figure A2)Tables A2-A4 - Raw sulfur isotope dataTables A5-A12 - LA-ICP-MS data used to create the compositional maps seen in the manuscript. Contains Mg, Al, Si, S, K, Ca, Ti, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Ag, Sb, Te, Tm, Re, Pb)

Data for: Understanding the microscale spatial distribution and mineralogical residency of Re in pyrite: Examples from carbonate-hosted Zn-Pb ores and implications for pyrite Re-Os geochronology

Tables 2-4 - Provide the raw Re-Os ratio's used for geochronology.Table A1 - Provide the raw ICP-MS data used in the manuscript (e.g. Figure A2)Tables A2-A4 - Raw sulfur isotope dataTables A5-A12 - LA-ICP-MS data used to create the compositional maps seen in the manuscript. Contains Mg, Al, Si, S, K, Ca, Ti, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Ag, Sb, Te, Tm, Re, Pb).THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

Re-Os systematics of löllingite and arsenopyrite in granulite-facies garnet rocks: Insights into the metamorphic history and thermal evolution of the Broken Hill Block during the Early Mesoproterozoic (New South Wales, Australia)

Löllingite and arsenopyrite aggregates occur in spessartine-almandine garnet rocks (garnetite) metamorphosed to granulite facies, which are spatially associated with Pb-Zn-Ag mineralization in the giant Broken Hill deposit, southern Curnamona Province, New South Wales, Australia. Sulfarsenide and sulfide minerals comprise löllingite and coexisting arsenopyrite ± galena ± tetrahedrite that occur interstitial to garnet crystals. Löllingite formed first while gold-bearing löllingite, which occurs as rare relicts in arsenopyrite, was destroyed to produce arsenopyrite ± detectable micro-inclusions of invisible gold. Standard mineral separation procedures produced pure separates of löllingite, arsenopyrite, and mixtures of arsenopyrite ± löllingite and löllingite ± arsenopyrite. In a plot of 187Re/188Os versus187Os/188Os, samples of löllingite and löllingite ± arsenopyrite have 187Re/188Os ratios between 6.87 and 7.40 and 187Os/188Os ratios between 0.8506 and 0.8651, whereas arsenopyrite and arsenopyrite ± löllingite samples have higher 187Re/188Os ratios (7.14 to 11.32) and more radiogenic 187Os/188Os ratios (0.8828 to 0.9654). Thirteen analyses of arsenopyrite and arsenopyrite ± löllingite define a Model 1 isochron with an age of 1574 ± 38 Ma (2σ; MSWD = 1.4, initial 187Os/188Os ratio of 0.666 ± 0.006), whereas the five löllingite and löllingite ± arsenopyrite samples define a Model 1 isochron with an age of 1707 ± 290 Ma (2σ; MSWD = 0.32, initial 187Os/188Os ratio of 0.652 ± 0.036) that is indistinguishable from the arsenopyrite age. Rhenium and Os contents are extremely high for löllingite and arsenopyrite (Re = 120–475 ppb; Os = 65–345 ppb), likely as a result of concentration of Re and Os in these minerals during granulite-facies metamorphism from the inferred exhalite protolith. Petrographic observations combined with the Model 1 Re-Os ages and literature SHRIMP U-Pb ages of monazite in garnetite suggest that arsenopyrite formed on the retrograde path at the expense of löllingite. Cooling from peak Olarian P-T conditions (∼800 °C at 1602 Ma) to at least 550 °C (first temperature of stability of arsenopyrite) at ca. 1574 Ma occurred at a rate of ∼9 °C/Myr, which is similar to the rate of cooling determined for previously published SHRIMP U-Pb ages from successive monazite generations (McFarlane & Frost 2009). These results are consistent with the late phase of retrograde metamorphism that began between ca. 1590 and 1575 Ma

Understanding the microscale spatial distribution and mineralogical residency of Re in pyrite: Examples from carbonate-hosted Zn-Pb ores and implications for pyrite Re-Os geochronology

Accurate and precise geochronology using the Re-Os isotopic system in pyrite is an invaluable tool for developing and confirming genetic models of ore systems. However, as a bulk method, the results produced by pyrite Re-Os geochronology are commonly complex, and many imprecise isochrons exist in the literature. Using LA-ICPMS methods it is now possible to map and quantify Re distribution at the ppb level, allowing an unprecedented look into the Re-Os systematics of pyrite-bearing ore. Two samples from the Lisheen Zn-Pb ore deposit in Ireland showing disparate Re-Os isotopic behavior were investigated. In-situ sulfur isotope measurements using SIMS, an analytical technique not previously attempted on the Irish deposits, was used to supplement the Re-Os dataset. A massive pyrite sample from the Main Zone produced a precise, low-scatter isochron (346.6 ± 3.0 Ma, MSWD = 1.6). The Re distribution in this sample is relatively homogeneous, with the Re budget dominated by pyrite containing 1–5 ppb Re, but the δ34S varies significantly from −45.2‰ to 8.2‰. A second, more paragenetically complex, sample from the Derryville Zone produced a younger age with high scatter (322 ± 11 Ma, MSWD = 206) and this also displays a large variation in δ34S (−53‰ to +4‰). The cores of grains of main-stage iron sulfide are depleted in trace elements and show low Re abundances (<10 ppb) but have been altered in an irregular fashion leading to Re-enriched domains that exceed 100 ppb. Additionally, micron-scale molybdenite crystals, found in close association with altered sulfides, contain Re at levels that locally exceed 10 ppm. The highly scattered (MSWD = 206) and younger age (322 Ma), produced by the Derryville Zone sample are interpreted to result from mixing of different generations of sulfide, potentially involving fluids associated with Variscan deformation (<310 Ma). Therefore, the Re-Os data produced from the Derryville Zone sample does not reflect the timing of iron sulfide mineralization, even though a relatively precise age was obtained. A second Re-Os dataset from Zn-Pb mineralization at Hawker Creek, Nunavut, Canada was produced from massive pyrite that displays low Re concentrations (<1 ppb). However, on grain boundaries and in fractures, silicate-rich material contains Re at levels that can locally exceed 500 ppb. Analyses of fracture-free pyrite produced by bulk separation using magnetic separation yielded the oldest model age (1083 Ma), whereas mineral separates containing the highest fracture density produced the youngest age (413 Ma). In general, therefore, the complexities of pyrite Re-Os geochronology can result from impurities in mineral separates. Attempts to eliminate impurities through different mineral separation techniques (e.g. crushing, heavy liquid separation, magnetic separation, acid leaching) are frequently only partially successful and therefore full characterization of any resulting mineral separates is extremely important. We conclude that LA-ICPMS mapping of Re and Mo distributions is essential for the identification of such impurities. Although other trace element LA-ICPMS maps, in-situ sulfur isotope measurements, and petrographic evidence were of limited use in assessing the Re budget of a sample, they are invaluable in linking the documented Re distribution obtained through LA-ICPMS to Re-Os geochronological results.© 2019 Elsevier B.V. All rights reserved. The attached document is the author(’s’) final accepted/submitted version of the journal article. You are advised to consult the publisher’s version if you wish to cite from it

Application of the 187Re-187Os geochronometer to crustal materials: Systematics, methodology, data reporting, and interpretation

The rhenium-osmium (187Re-187Os) system is a highly versatile chronometer that is regularly applied to a wide range of geological and extraterrestrial materials. In addition to providing geo- or cosmo-chronological information, the Re-Os system can also be used as a tracer of processes across a range of temporal (millennial to gigayear) and spatial scales (lower mantle to cryosphere). An increasing number of sulfide minerals are now routinely dated, which further expands the ability of this system to refine mineral exploration models as society moves toward a new, green economy with related technological needs. An expanding range of natural materials amenable to Re-Os geochronology brings additional complexities in data interpretation and the resultant translation of measured isotopic ratios to a properly contextualized age. Herein, we provide an overview of the 187Re-187Os system as applied to sedimentary rocks, sulfides, and other crustal materials and highlight further innovations on the horizon. Additionally, we outline next steps and best practices required to improve the precision of the chronometer and establish community-wide data reduction procedures, such as the decay constant, regression technique, and software packages to use. These best practices will expand the utility and viability of published results and essential metadata to ensure that such data conform to evolving standards of being findable, accessible, interoperable, and reusable (FAIR)