More than a trace of oxygen: Ichnological constraints on the formation of the giant Zn-Pb-Ag ± Ba deposits, Red Dog district, Alaska

Reynolds, Merilie A.; Gingras, Murray K.; Gleeson, Sarah A.; Stemler, James U.

doi:10.1130/g36954.1

Cited by 15 publications

(7 citation statements)

References 27 publications

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“…Ore genesis models for clastic-dominated Pb-Zn mineralisation in the basins of northern Australia and western North America often assume contemporaneity of mineral deposits with extensional faulting or thermal sag in a rift or passive margin setting (Betts et al, 2003;Goodfellow, 2007;Huston et al, 2006;Leach et al, 2010;Leach et al, 2005;Reynolds et al, 2015;Slack et al, 2015). As argued here, the case for such models is open to question and a majority of deposits in the Calvert and Isa superbasins more likely formed subsequent to crustal extension during times of basin inversion (Fig.…”

Section: Pb-zn Mineralisation and Its Tectonic Drivers In Northern Aumentioning

confidence: 99%

“…Mt Isa-type deposits are thought to form later in the supercontinent cycle when plate convergence has largely ceased and continental assembly has given way to rifting followed by continental breakup and thermal subsidence (Cawood and Hawkesworth, 2013). However, while a backarc basin or passive margin setting is commonly inferred for this type of mineral deposit (Betts et al, 2003;Gibson et al, 2012;Goodfellow, 2007;Goodfellow et al, 1993;Huston et al, 2006;Large et al, 2005;Leach et al, 2005;Reynolds et al, 2015), most are hosted by sedimentary rocks or basins that have since been deformed so that the evidence in support of a syn-extensional as opposed to later origin for mineralisation is not always immediately obvious or conclusive. Moreover, even where Pb isotopic data are available to better constrain the age of mineralisation as is the case with many of the Mount Isa deposits (Carr et al, 2004), doubts persist as to its timing and relationship to basin formation, particularly in younger parts of the succession where the evidence for mineralisation during active rifting is least convincing.…”

Section: Introductionmentioning

confidence: 99%

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Basin inversion and supercontinent assembly as drivers of sediment-hosted Pb–Zn mineralization in the Mount Isa region, northern Australia

Gibson

Hutton

Holzschuh

2017

JGS

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Deep seismic reflection imaging combined with geochronological, paleomagnetic and stratigraphic data indicate that the world class sediment-hosted Pb-Zn deposits of northern Australia are preferentially concentrated in the post-extensional syn-inversion fraction of the Calvert and Isa superbasins. These fractions were deposited from 1654-1640 Ma and 1615-1575 Ma respectively, and overlap the age of known orogenic events in both Australia and western Laurentia, pointing to a common origin linked to crustal shortening and supercontinent assembly. Crustal shortening resulted in thrust faulting and reactivation of earlier-formed extensional faults leading to upward expulsion of mineralising fluids at or close to the seafloor while basin inversion and sedimentation were still in progress. This is contrary to most existing models for Pb-Zn ore genesis in northern Australia where fluid flow and mineralisation have been attributed to syn-extensional processes accompanying continental breakup or thermal sag. Instead, mineralisation postdates passive margin formation and more likely occurred in a foreland basin or convergent plate tectonic setting involving one or more collisional events. The terminal continent-continent collision between Australia and Laurentia resulted in the 1600 Ma Isan and Racklan orogenies and assembly or reassembly of the Nuna supercontinent.

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Section: Pb-zn Mineralisation and Its Tectonic Drivers In Northern Aumentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Basin inversion and supercontinent assembly as drivers of sediment-hosted Pb–Zn mineralization in the Mount Isa region, northern Australia

Gibson

Hutton

Holzschuh

2017

JGS

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“…Rocks of the Ikalukrok unit are characterized by high concentrations of organic carbon, silicon, and phosphate, with abundant radiolarians (Dumoulin et al, 2004(Dumoulin et al, , 2014. Upwelling of nutrient-rich waters played an important role in the regional depositional regime (Dumoulin et al, 2014) and may have given rise to a fluctuating oxygen minimum zone that resulted in variable redox conditions (Reynolds et al, 2015). Carbonate layers in the Ikalukrok can be up to 40 m thick and up to 80 m in cumulative thickness and are generally thought to originate from the erosion of adjacent carbonate platforms (Dumoulin et al, 2004).…”

Section: Regional Geologymentioning

confidence: 99%

Diagenetic Controls on the Formation of the Anarraaq Clastic-Dominated Zn-Pb-Ag Deposit, Red Dog District, Alaska

et al. 2021

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The Anarraaq clastic-dominated (CD) Zn-Pb-Ag deposit (Red Dog district, Alaska, USA) has an inferred mineral resource of 19.4 Mt at 14.4% Zn, 4.2% Pb, and 73 g/t Ag and is spatially associated with a separate ~1 Gt barite body. This study presents new cross sections and petrographic evidence from the Anarraaq area. The barite body, previously shown to have formed in a shallow subsurface environment akin to a methane cold seep, contains multiple generations of barite with locally abundant calcite masses, which are discordant to sedimentary laminae, and is underlain by an interval of massive pyrite containing abundant framboids and radiolarians. Calcite and pyrite are interpreted to have formed by methane-driven diagenetic alteration of host sediment at the sulfate-methane transition (SMT). The sulfide deposit contains two zones of Zn-Pb mineralization bounded by faults of unknown displacement. The dominant hydrothermal minerals are marcasite, pyrite, sphalerite, quartz, and galena. The presence of hydrothermal pseudomorphs after barite, early pyrite resembling diagenetic pyrite associated with the barite body, and hydrothermal quartz and sphalerite filling voids formed by dissolution of carbonate all suggest that host sediment composition and origin was similar to that of the barite body prior to hydrothermal mineralization. Rhenium-osmium isochron ages of Ikalukrok mudstone (339.1 ± 8.3 Ma), diagenetic pyrite (333.0 ± 7.4 Ma), and hydrothermal pyrite (334.4 ± 5.3 Ma) at Anarraaq are all within uncertainty of one another and of an existing isochron age (~338 Ma) for the Main deposit in the Red Dog district. This indicates that the Anarraaq deposit formed soon after sedimentation and that hydrothermal activity was approximately synchronous in the district. The initial Os composition of the Anarraaq isochrons (0.375 ± 0.019–0.432 ± 0.025) is consistent with contemporaneous seawater, indicating that a mantle source was not involved in the hydrothermal system. This study highlights the underappreciated but important role of early, methane-driven diagenetic processes in the paragenesis of some CD deposits and has important implications for mineral exploration.

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“…These results suggest that the REY systematics are strongly influenced by apatite abundance and carbonate content of the samples. Gleeson et al, 2013;Reynolds et al, 2015), reduced sulfur at the site of deposition and euxinic conditions are important in the generation of some VMS deposits in sediment-rich environments, resulting in more efficient complexing of metals from hydrothermal vents (Goodfellow et al, 2003b). Identification of these conditions is best achieved using a multiproxy approach (Tribovillard et al, 2006;Lyons et al, 2009;Piper and Calvert, 2009;Little et al, 2015), and in the Wolverine deposit the combination of low Mn contents (<1,000 ppm); V-Cr-Ni systematics (i.e., high V/Cr and V/(V + Ni) ratios); U-Mo enrichment (i.e., UEF and MoEF >10); and high S/ Corganic ratios (>0.32) and REY (Ce/Ce* ~1) systematics of unmineralized and relatively unaltered samples provide the best indicators of basin redox conditions.…”

Section: Shale Geochemistry As An Exploration Vectormentioning

confidence: 99%

Ambient Redox and Hydrothermal Environment of the Wolverine Volcanogenic Massive Sulfide Deposit, Yukon: Insights from Lithofacies and Lithogeochemistry of Mississippian Host Shales

et al. 2016

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The Wolverine volcanogenic massive sulfide (VMS) deposit is a polymetallic, felsic-siliciclastic deposit hosted by ~352 to 347 Ma volcanic and sedimentary rocks of the Yukon-Tanana terrane, Yukon, Canada. Shales are located at various stratigraphic levels and in various mineralized zones within the Wolverine deposit area (e.g., Fisher, Puck, and Sable zones). Shales present along the mineralized horizon near the immediate hanging wall and footwall were deposited under anoxic conditions (e.g., low Mn, anoxic VCr -Mo-U systematics), whereas in the stratigraphically deeper footwall and uppermost hanging wall, the redox signatures imply deposition under suboxic to oxic conditions. The Mo-U systematics of the shales suggest that during the time of sulfide mineralization, the ambient basin was periodically euxinic with aqueous H2S present in the water column that this H2S contributed to the sulfur budget of the deposit. Furthermore, the Mo-U and Corg-Ni systematics favor deposition in a restricted basin (i.e., nutrient trap) where restriction of the water column led to H2S formation via sulfate reduction associated with excess organic carbon preservation. There is also evidence of a progressive shift upward in the stratigraphy to more oxygenated conditions in the uppermost hanging wall. The shift from euxinic to oxic-suboxic conditions is consistent with regional tectonic models that indicate a change from rifting during Wolverine deposit formation, where the basin was partially restricted with minimal circulation (i.e., restricted depocenter), to an incipient back-arc basin accompanied by extension and likely ingress of oxygenated seawater. The rare earth element and Y (REY) systematics in Wolverine shales illustrate that proximal to the mineralized horizon, shales have higher Y/Ho (>27), and Ce/Ce*<<1 and negative Ce anomalies indicative of oxygenated seawater. The Ce/Ce* values in the Wolverine shales have an inverse correlation with P2O5 content and suggest partial control by detrital apatite. It is envisioned that apatite formed in the upper, oxygenated portion of the water column, inherited the REE signature of oxygenated seawater (i.e., Ce/Ce*<<1), and was subsequently deposited into deeper waters as detrital grains. The Ce/Ce* and Y/Ho also correlate with CO2 and carbonate content of the shales. Moreover, the shales that have the strongest REY signature of oxygenated seawater also coincide with the strongest euxinic signatures. This paradox can be reconciled by enhanced deposition of apatite coincident with deposit formation, coupled with a late hydrothermal overprint on the shales from low-temperature, CO2-rich (oxygenated?) hydrothermal fluids (i.e., high Y/Ho and Ce/Ce*<<1) in a ventproximal environment. This model is consistent with the geology, stratigraphy, and hydrothermal alteration in the immediate footwall and hanging wall of the deposit. Prospective shales in the Wolverine basin, and similar sediment-rich hydrothermal basins globally, should exhibit evidence for deposition under anoxic conditions (i....

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More than a trace of oxygen: Ichnological constraints on the formation of the giant Zn-Pb-Ag ± Ba deposits, Red Dog district, Alaska

Cited by 15 publications

References 27 publications

Basin inversion and supercontinent assembly as drivers of sediment-hosted Pb–Zn mineralization in the Mount Isa region, northern Australia

Basin inversion and supercontinent assembly as drivers of sediment-hosted Pb–Zn mineralization in the Mount Isa region, northern Australia

Diagenetic Controls on the Formation of the Anarraaq Clastic-Dominated Zn-Pb-Ag Deposit, Red Dog District, Alaska

Ambient Redox and Hydrothermal Environment of the Wolverine Volcanogenic Massive Sulfide Deposit, Yukon: Insights from Lithofacies and Lithogeochemistry of Mississippian Host Shales

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