Geologic understanding of the richly mineralized Dawson Range gold belt (DRGB) in the central Yukon, Canada is hindered by: (1) limited outcrop exposure due to thick soil cover; and (2) low resolution age-constraints despite a long history of porphyry Cu–Au–Mo deposit (PCD) exploration. Here, the well-preserved Klaza Au–Ag–Pb–Zn porphyry–epithermal deposit is used as a type-example of Late Cretaceous magmatic–hydrothermal mineralization to address the complex metallogeny of the DRGB. U–Pb zircon dating defines four magmatic pulses of Late Triassic to Late Cretaceous ages with the latter consisting of the Casino (80–72 Ma) and Prospector Mt. (72–65 Ma) suites. The Casino suite has five phases of intermediate-to-felsic calc-alkaline composition, correspond with older (77 Ma) porphyry mineralization, and displays evidence of magma mingling. The intermediate-to-mafic, slightly alkalic Prospector Mt. suite shows evidence of mingling with the youngest Casino suite phases, correlates with younger (71 Ma), intermediate-sulfidation epithermal and porphyry-type mineralization, and shoshonitic basalts of the Carmacks Group. Zircon trace element data suggest a common melt source for these suites; however, the younger suite records features (e.g., high La/Yb) that indicate a higher pressure melt source. The results from this study highlight the Prospector Mt. suite as a historically overlooked causative magma event linked to Au-rich PCDs in the DRGB and extends the temporal window of PCD prospectivity in this area. The transition from mid-Cretaceous Whitehorse suite magmas to Late Cretaceous Casino-Prospector Mt. suite magmas is proposed to reflect a transition from subduction to localized extension, which is becoming more recognized as a common characteristic of productive porphyry belts globally.

The invisible-gold deposits known as Carlin-type are becoming more important as easier to find deposits are progressively depleted. The combination of the invisible nature of the Au in these deposits, as well as the limited surface indicators of these deposits, makes exploration to find new Carlin-type deposits extremely difficult. Comprehensive mineralization models are essential to find new Carlin-type deposits in similar geologic settings. The Nadaleen Trend of Yukon, Canada, is one such district where an improved understanding of this deposit type has led to new discoveries. Previous studies compared and contrasted the tectonic setting, host rock depositional setting, structural preparation, and mineralization style of the Nadaleen Trend with those in Carlin-type localities, Nevada. However, the comparisons at an atomic scale, between Carlin-type Au deposits in the Nadaleen Trend and those in Nevada, has yet to be investigated. This study fills this knowledge gap by combining high resolution microanalytical techniques with atom probe tomography to examine the distribution of Au and other trace elements in the Nadaleen Trend, compare them to a representative Carlin-type deposit in Nevada (Turquoise Ridge), and determine how widespread the mineralization model is. Our findings show that in the Nadaleen Trend, as in Nevada, Au is generally directly linked with As at the macro to atomic scale, and is incorporated into As/Au rich overgrowths on sedimentary/diagenetic pyrite. Gold-rich pyrite rims in the Nadaleen Trend are generally smaller than those found in Nevada (0.5–2 µm vs > 10 µm), although the ore grades appear comparable. We find that the Au in the pyrite of the Nadaleen Trend is homogenously distributed (i.e. lattice bound) at the atomic scale, but that there is a notable enrichment of As surrounding individual Au atoms. These findings are in agreement with those from previous work on a representative deposit in Nevada, and support the assertation that As is the key ingredient in facilitating the incorporation of Au into the pyrite lattice. Arsenic as an essential component in the trapping mechanisms of Au in CTG deposits, is something that has been as to yet underappreciated in the current models of CTG deposit formation.

Despite extensive study, Carlin-type gold (CTG) mineralization is still poorly understood. These deposits predominantly along major regional faults and are characterized by invisible gold thought to be hosted in sulfide minerals (Cline et al., 2005). CTG was until recently only thought to occur in central-Nevada, but discoveries in the Yukon Territory, China, and Kyrgyzstan have made us re-evaluate this. Additionally, a significant invisible gold component in other deposit types (epithermal, orogenic, porphyry, etc.) is drastically increasing the importance of these deposits. We investigated four invisible gold occurrences (Yukon, Nevada, Guizhou, and Austria) and reveal that gold is hosted in these deposits (in part) as lattice bound gold. Our study combines high-resolution electron probe microanalysis and nano-secondary ion mass spectrometry with atom probe tomography to better understand the commonalities / differences in how gold is hosted in these geographically distant deposits and why sulfide minerals make such great hosts for gold and other critical metals. Furthermore, our atomic scale characterization suggests that the presence of arsenic is integral to the mechanisms by which gold is accommodated into the pyrite lattice, and is a commonality shared by all deposits we investigated.

Sediment-hosted gold deposits in central Yukon have most of the diagnostic characteristics of Carlin-type gold deposits in Nevada. This study combines organic matter geothermometry with fluid inclusion microthermometry, clumped isotope data (Δ 47 ) for late ore-stage hydrothermal calcite, and apatite fission-track analyses to constrain the thermal evolution of Carlin-type gold zones in central Yukon. The Tmax parameter derived from pyrolysis analyses indicates that organic matter is overmature and records regional temperatures of > 150 °C. Calcite and fluorite associated with the waning stage of mineralization at ca. 74 Ma have mean fluid inclusion homogenization temperatures of 123–173 °C, with an average salinity of 4.8 wt.% NaCl equiv. These temperatures overlap values of 91–162 °C determined from calcite clumped isotope measurements and are similar to data from Carlin-type deposits in Nevada. Fluid mixing is suggested by a variation of the isotopic composition of the fluid in equilibrium with calcite, with the higher temperature end-member having higher δ 18 O H2O values. In thermal models based on Tmax, fluid inclusion microthermometry, clumped isotope measurements, and apatite fission-track data, a higher temperature event at approximately 220 °C is consistent with pyrobitumen reflectance measurements. This event is either related to maximum tectonic burial prior to mineralization or to the flow of acidic hydrothermal fluids early in the main ore-stage. Each analytical technique used in this study is independent of the others and records part of the thermal and chemical evolution of the Yukon Carlin-type gold deposits and their host rocks.

In northern Canada and eastern Alaska, Late Cretaceous to Eocene mineral deposits formed at upper crustal levels, after the accretion of allochthonous terranes against North America. To analyse their preservation potential, an orogen-scale study of multiple low temperature thermochronometers has been initiated. This study will enable a large-scale investigation into spatio-temporal variations in exhumation, and thus delineate areas favourable for preservation of mineral deposits formed at shallow depths.

End‐on arc collision and onset of the northern Cordilleran orogen is recorded in Late Triassic to Jurassic plutons in the Intermontane terranes of Yukon, and in development of the synorogenic Whitehorse trough (WT). A synthesis of the extensive data set for these plutons supports interpretation of the magmatic and tectonic evolution of the northern Intermontane terranes. Late Triassic juvenile plutons that locally intrude the Yukon‐Tanana terrane represent the northern extension of arc magmatism within Stikinia. Early Jurassic plutons that intrude Stikinia and Yukon‐Tanana terranes were emplaced during crustal thickening (200–195 Ma) and subsequent exhumation (190–178 Ma). The syn‐collisional magmatism migrated to the south and shows increasing crustal contributions with time. This style of magmatism in Yukon contrasts with coeval, juvenile arc magmatism in British Columbia (Hazelton Group), that records southward arc migration in the Early Jurassic. Exhumation and subsidence of the WT in the north were probably linked to the retreating Hazelton arc by a sinistral transform. East of WT, Early Jurassic plutons intruded into Yukon‐Tanana record continued arc magmatism in Quesnellia. Middle Jurassic plutons were intruded after final enclosure of the Cache Creek terrane and imbrication of the Intermontane terranes. The post‐collisional plutons have juvenile isotopic compositions that, together with stratigraphic evidence of surface uplift, are interpreted to record asthenospheric upwelling and lithospheric delamination. A revised tectonic model proposes that entrapment of the Cache Creek terrane was the result of Hazelton slab rollback and development of a sinistral transform fault system linked to the collision zone to the north.

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb dating of hydrothermal calcite associated with the waning stage of mineralization is used to constrain the age of Neoproterozoic-hosted Carlin-type gold deposits in central Yukon, Canada. Samples exhibiting minor textural complexity show low dispersion of individual spot analyses and define Tera-Wasserburg lower intercept ages between 75.1 ± 2.5 and 71.2 ± 4.3 Ma. Samples with U-rich microfractures and/or a second generation of calcite associated with vein reopening record the primary stage of calcite growth related to hydrothermal activity at ca. 74 Ma and a younger ca. 48 Ma event related to fluid-assisted U mobility. The minimum age for mineralization at ca. 74 Ma overlaps with a maximum age based on a zircon U-Pb date of 74.1 ± 1.0 Ma for a gabbro dike that is locally altered and mineralized. These time constraints indicate that mineralization is ca. 74 Ma and penecontemporaneous with dike emplacement. Furthermore, mineralization is contemporaneous with a regional gold-bearing, intrusion-related, metallogenic event in eastern Alaska and central Yukon. This temporal link between Carlin-type mineralization and other mineralization types bears similarities with world-class sedimentary rock-hosted gold deposits of Nevada. This study demonstrates the potential of using LA-ICP-MS U-Pb dating on calcite to constrain the age of mineral deposits lacking synmineralization minerals amenable to classic dating techniques.

In central Yukon, the Neoproterozoic to Carboniferous complexly deformed Rackla belt is along the northern boundary of the Selwyn basin. Toward the eastern end of the Rackla belt, a series of gold deposits in the Nadaleen trend exhibit similarities with Carlin-type deposits of the southwestern United States and may represent some of the best examples of this type of mineralization outside Nevada. These replacement-style gold deposits are hosted in two Neoproterozoic carbonate-dominated intervals and in a Paleozoic siltstone/mudstone unit at the contact with less permeable strata. In Neoproterozoic-hosted deposits, mineralized zones are grossly concordant with bedding. Favorable host rocks (including sedimentary units formed through debris flows) form complexly shaped faulted anticlines that constituted mixed stratigraphic/structural traps for mineralizing fluids. This and the association of gold with arsenic-rich pyrite, the common occurrence of realgar/orpiment, alteration styles dominated by decarbonatization of impure carbonate rocks, late Au-stage calcite characterized by a depleted δ18O signature, the very low base metal content and Ag/Au ratio, and enrichment in a series of diagnostic pathfinder elements (Hg, Tl ± Sb, As) are among the key features that are consistent with classification of the eastern Rackla belt as a Carlin-type district. Mineralization style varies significantly at the centimeter to 10-m scale, indicating that mineralizing fluids exploited permeable pathways, regardless of their sedimentary and/or tectonic origin. Alternating finely laminated limestone, siltstone, and floatstone intervals are the dominant host rocks to mineralization in the Conrad, Sunrise, and Osiris deposits. Premineralization fractures acted as feeders for selective bed replacement, and premineralization calcite vein networks, preferentially dissolved by early acidic fluids, acted as conduits to later gold-bearing fluids. Limited evidence suggests that synmineralization deformation was relatively minor and possibly dominated by oblique strike-slip faulting.

In central Yukon, the Neoproterozoic to Carboniferous complexly deformed Rackla belt is along the northern boundary of the Selwyn basin. Toward the eastern end of the Rackla belt, a series of gold deposits in the Nadaleen trend exhibit similarities with Carlin-type deposits of the southwestern United States and may represent some of the best examples of this type of mineralization outside Nevada. These replacement-style gold deposits are hosted in two Neoproterozoic carbonate-dominated intervals and in a Paleozoic siltstone/mudstone unit at the contact with less permeable strata. In Neoproterozoic-hosted deposits, mineralized zones are grossly concordant with bedding. Favorable host rocks (including sedimentary units formed through debris flows) form complexly shaped faulted anticlines that constituted mixed stratigraphic/structural traps for mineralizing fluids. This and the association of gold with arsenic-rich pyrite, the common occurrence of realgar/orpiment, alteration styles dominated by decarbonatization of impure carbonate rocks, late Au-stage calcite characterized by a depleted delta O-18 signature, the very low base metal content and Ag/Au ratio, and enrichment in a series of diagnostic pathfinder elements (Hg, Tl +/- Sb, As) are among the key features that are consistent with classification of the eastern Rackla belt as a Carlin-type district. Mineralization style varies significantly at the centimeter to 10-m scale, indicating that mineralizing fluids exploited permeable pathways, regardless of their sedimentary and/or tectonic origin. Alternating finely laminated limestone, siltstone, and floatstone intervals are the dominant host rocks to mineralization in the Conrad, Sunrise, and Osiris deposits. Premineralization fractures acted as feeders for selective bed replacement, and premineralization calcite vein networks, preferentially dissolved by early acidic fluids, acted as conduits to later gold-bearing fluids. Limited evidence suggests that synmineralization deformation was relatively minor and possibly dominated by oblique strike-slip faulting.

Mega volcanic eruptions associated with the formation of Large Igneous Provinces (LIPS) pump vast amounts of carbon dioxide and sulfur-rich gases into the atmosphere and stratosphere with the potential to totally change the chemistry of the global ocean. Here we investigate the sedimentary pyrite sulfur isotope record of black shales through time and demonstrate two coherent populations termed P1 and P2. Population P1 dominates the Archean pyrites, has a mean of delta S-34 = +3.7 parts per thousand, standard deviation of 5.3 parts per thousand, and is considered to represent S of mantle origin. Population P2 appears toward the start of the Proterozoic, dominates the Phanerozoic, has a mean around +25 parts per thousand and standard deviation of 13.5 parts per thousand, and is considered to represent S of seawater sulfate origin. Population P1 can be identified in sedimentary pyrite at certain times in the Proterozoic and Phanerozoic, which correspond, within error, with the timing of 25 major LIP events. Our data suggest that at regular times through the Proterozoic, coinciding with major LIP events, the oceans contained a mixture of seawater sulfate and dissolved mantle sulfide derived from the LIPs. LA-ICP-MS analyses of the sedimentary pyrite indicate that metals, particularly gold, nickel, cobalt, and PGE were also enriched in the oceans at these times. The long periods between major LIP eruptions enabled the oceans to return to a seawater sulfate background equilibrium with a decrease in the mantle-derived metals.

Dublin Gulch reduced intrusion-related gold system (RIRGS), located in the Selwyn Basin area of western Canada, represents one of the best examples of RIRGS mineralization globally and hence can be studied to unravel genesis and evolution of these types of deposits. Based on textural relationships, mineralogy, and trace element mineral chemistry, three auriferous vein stages were identified. The paragenetic sequence for the auriferous vein stages are: 1) Eagle Style (ES), quartz-albite, low sulfide and sulfosalt content ( < 5% vol.), As-Fe-Mo-W-Pb-Bi-Au-Ag veins; 2) Potato Hills Style-1 (PHS-1), quartz, high sulfide and sulfosalt content ( > 30% vol.), As-Fe-W-Pb-Bi-Au-Ag veins; and, 3) Potato Hills Style-2 (PHS-2), high sulfide and sulfosalt content ( > 30% vol.), Fe-Pb-Sb-Zn-Cu-Au-Ag veins. In the ES and PHS-1 veins, Au is present both as native gold (Au, Ag) and as invisible gold in arsenopyrite, whilst in the PHS-2 veins, Au is present as invisible gold in pyrite. Native gold micrograins (individual grains, 1-100's mu m in size) are observed associated with Pb minerals (in anhedral-toglobular cosalite (Pb2Bi2S5) in ES veins, or galena (PbS) in the PHS-1 veins]. Native gold is also observed as micrograins along arsenopyrite margins and in quartz fractures. We suggest a variation on the hydrothermal Bi melt collector model to explain the Au-Pb +/- Bi association. The Au, Ag, Pb, and Bi are interpreted to have been locally remobilized from arsenopyrite, which shows textures and trace element distribution patterns consistent with fluid-and-deformation assisted recrystallization. We suggest Pb and Bi were mobilized either as immiscible nanodroplets that coalesced to form larger Pb +/- Bi liquid accumulations or into the hydrothermal fluid and subsequently exsolved to form immiscible Pb +/- Bi liquids. We propose that remobilized Au and Ag were collected by these Pb +/-Bi immiscible liquids. Subsequent retrograde alteration (sulfidation) is interpreted to have converted the Au-Ag-Pb +/- Bi alloys to native gold and cosalite (ES), and native gold and galena mineral assemblages (PHS-1). The similarity of the Au/Ag ratios in native gold and arsenopyrite supports a local source for the native gold micrograins. Temperatures required to attain liquid Pb-0.Bi-5(0).(5) ( > 145.2 degrees C) and Pb (> 327.5 degrees C), are consistent with arsenopyrite geothermometry (ES 345-405 degrees C; PHS-1 approximate to 380 degrees C). These suggested new variations (Pb-Bi and Pb) on the hydrothermal melt (Bi) collector model are important, given the common association of native gold with Pb +/- Bi sulfosalts in many gold deposits, and the relatively low temperatures required to maintain these liquids and collect Au from the hydrothermal fluid.

Late Cretaceous Carlin-type mineralization at the Conrad prospect in central Yukon (Canada) is mainly hosted in Neoproterozoic limestone (and in a lesser amount in calcareous siltstone) in the core of a doubly-plunging anticline. The limestone unit is in fault-contact to the north and in stratigraphic contact to the south with non-calcareous siliciclastic units with low porosity and permeability. The upper part of the limestone unit that consists of lime mudstone, packstone, floatstone (deposited as debris flows) and calcareous siltstone and shale played an important role in channeling fluid flow. In more massive lithologies, fractured and brecciated intervals also focused fluid flow via the selective replacement of irregular and often complex pre-mineralization vein sets that were preferentially dissolved by acidic fluids early in the mineralizing process. Multiple feedback effects between sedimentologic, hydrothermal and tectonic parameters resulted in complex ore shapes and variable mineralization styles.

Selwyn basin area strata contain sedimentary pyrite with Au above background levels when analyzed by laser ablation-inductively coupled mass spectrometry. Hyland Group rocks contain framboidal pyrite contents of 670ppb Au, 1223ppm As, and 5.3ppm Te; the mean of all types of sedimentary pyrite in the Hyland Group is 391ppb Au, 1489ppm As, and 3.8ppm Te. These levels are similar to sedimentary pyrite in host lithologies from major orogenic gold districts in New Zealand and Australia. Comparison of whole rock and pyrite data show that rocks deposited in continental slope settings with significant terrigenous input contain pyrite that is consistently enriched in Au, As, Te, Co, and Cu. Although data are limited, whole rock samples of stratigraphic units containing Au-rich pyrite also contain high Au, indicating that most of the Au is within sedimentary pyrite. Based on geologic characteristics and comparison of pyrite chemistry data with whole rock chemistry, Selwyn basin area strata have the necessary ingredients to form orogenic gold deposits: Au-enriched source rocks, metamorphic conditions permissive of forming a metamorphic ore fluid, and abundant structural preparation for channeling fluids and depositing ore.

Precious, semi-, and base metals have been shown to be mobilised from metasedimentary rocks during prograde metamorphism. These form an important source of metals for orogenic gold systems. Similar metal enrichments are observed in reduced intrusion-related gold systems (RIRGS) hosted in the Selwyn basin area. However, no assessment has previously been attempted to determine whether prograde metamorphism of the surrounding metasediments could represent an important metals source for RIRGS. In this study, we focus on the availability and mobilisation of semi- and base metals through mineral reactions occurring in the contact aureole around the Dublin Gulch RIRGS. Pyrite and chlorite are observed in the regionally metamorphosed rocks dominating the semi- and base metals budget. During contact metamorphism, these recrystallise to pyrrhotite and chalcopyrite, and biotite, respectively. These mineral phases contain significantly lower concentrations of metals, compared to their precursor minerals (except Cu and Zn in chalcopyrite). Whole rock geochemistry shows that relative to the contact metamorphosed rocks, the regionally metamorphosed rocks are enriched in As, Sb, Te, Bi, Pb, Zn, and H2O. This suggests, mobilisation of these elements has occurred, possibly as a metal-rich fluid that could provide an alternative or additional metal source for RIRGS.

Highly metalliferous black shales (HMBS) are enriched in organic carbon and a suite of metals, including Ni, Se, Mo, Ag, Au, Zn, Cu, Pb, V, As, Sb, Se, P, Cr, and U ± PGE, compared to common black shales, and are distributed at particular times through Earth history. They constitute an important future source of metals. HMBS are relatively thin units within thicker packages of regionally extensive, continental margin or intra-continental marine shales that are rich in organic matter and bio-essential trace elements. Accumulation and preservation of black shales, and the metals contained within them, usually require low-oxygen or euxinic bottom waters. However, whole-rock redox proxies, particularly Mo, suggest that HMBS may have formed during periods of elevated atmosphere pO2. This interpretation is supported by high levels of nutrient trace elements within these rocks and secular patterns of Se and Se/Co ratios in sedimentary pyrite through Earth history, with peaks occurring in the middle Paleoproterozoic, Early Cambrian to Early Ordovician, Middle Devonian, Middle to late Carboniferous, Middle Permian, and Middle to Late Cretaceous, all corresponding with time periods of HMBS deposition. This counter-intuitive relationship of strongly anoxic to euxinic, localized seafloor conditions forming under an atmosphere of peak oxygen concentrations is proposed as key to the genesis of HMBS. The secular peaks and shoulders of enriched Se in sedimentary pyrite through time correlate with periods of tectonic plate collision, which resulted in high nutrient supply to the oceans and consequently maximum productivity accompanying severe drawdown into seafloor muds of C, S, P, and nutrient trace metals. The focused burial of C and S over extensive areas of the seafloor, during these anoxic to euxinic periods, likely resulted in an O2 increase in the atmosphere, causing short-lived peaks in pO2 that coincide with the deposition of HMBS. As metals become scarce, particularly Mo, Ni, Se, Ag, and U, the geological times of these narrow HMBS horizons will become a future focus for exploration.

This paper presents results of a laser ablation – inductively coupled plasma – quadrapole mass spectrometer (LA–ICP–QMS) U–Pb dating study of small in situ zircon grains from samples collected in the vicinity of the Greens Creek massive sulphide deposit, on northern Admiralty Island, southeast Alaska. The Greens Creek mine is a volcanogenic massive sulphide deposit in the central portion of the Alexander Triassic metallogenic belt (ATMB) and is one of the top global silver producers despite having a dominantly mafic metavolcanic stratigraphic footwall. The stratigraphic footwall is a Mississippian mafic metavolcanic sequence with a protolith age of approximately 340–330 Ma. The first U–Pb zircon constrained chronostratigraphy for the area places the deposit near, or at, the base of the host Late Triassic stratigraphy just above an approximately 100 million year old unconformity and probably 10–15 million years older than mineralization at the Palmer and Windy Craggy deposits in the northern portion of the ATMB. The stratigraphic location of the Greens Creek deposit is atypical for a syngenetic massive sulphide deposit, and this may, at least partly, explain its unusual metal endowment. Pre-mineralization Permian U–Pb zircon metamorphic ages are consistent with published 273–260 Ma white mica ages related to the collision of the Admiralty and Craig subterranes, the basement to the ATMB. The much older age of the footwall rocks and their Permian pre-mineralization metamorphism demonstrates that though the mafic volcanic rocks are not genetically linked to the deposit, they likely influenced the style of alteration and mineralization.

Availability of nutrients in the ocean can be a major factor affecting bioproductivity, burial of carbon and release of oxygen. However, the nutrient trace element (TE) composition of the palaeo-ocean cannot be measured directly. Here we present a comprehensive global dataset on the TE content of marine sedimentary pyrite in black shales, dating back 700 million years, and demonstrate a systematic cyclic evolution of pyrite TE composition with time. The nutrient TE, molybdenum, selenium, cadmium and thallium measured in pyrite, and phosphorus measured on whole rock, rise sharply at 560 to 550Ma followed by several cycles of TE variation through the Palaeozoic and into the Mesozoic. A number of factors could explain the trends. We suggest that variations in continental uplift, erosion and nutrient flux rates were possible drivers of the oceanic nutrient cycles. The cyclic patterns through the Phanerozoic suggest periods of nutrient-rich oceans that fostered key evolutionary events, followed by nutrient-poor oceans that encompass several major mass extinction events.