Tectonic Setting of the Pebble and Other Copper-Gold-Molybdenum Porphyry Deposits within the Evolving Middle Cretaceous Continental Margin of Northwestern North America

Goldfarb, Richard J.; Anderson, Eric D.; Hart, Craig J.R.

doi:10.2113/econgeo.108.3.405

Cited by 32 publications

(8 citation statements)

References 81 publications

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“…Slip initiated on the previously unknown Susitna Glacier thrust fault and then propagated west to east along the Denali fault and then onto the Totschunda fault (Eberhart-Phillips et al, 2003). Several possible inception ages and activity periods for the Totschunda fault have been proposed: early Cenozoic and possibly earlier (Goldfarb et al, 2013), middle Miocene (Trop et al, 2012), and middle Pleistocene (Richter and Matson, 1971;Plafker et al, 1977). A recent study by Brueseke et al (2019) added to the debate.…”

Section: ■ Totschunda Fault Zonementioning

confidence: 99%

“…Given that lithospheric strength contrasts in suture zones are often reactivated as long-lived structures (Fitzgerald et al, 2014), constraining the long-term history of lithospheric-scale faults can provide additional constraints on the suturing process. Various possible inception ages for the Totschunda fault have been previously proposed: early Cenozoic and possibly earlier (Goldfarb et al, 2013), Oligocene (Brueseke et al, 2019), middle Miocene (Trop et al, 2012), and middle Pleistocene (Richter and Matson, 1971;Plafker et al, 1977). The fault may have an even longer history of deformation, given that seismic velocities differ substantially across the fault (Allam et al, 2017), and it may provide insight in the deformation history of the Insular terrane during accretion.…”

Section: ■ Introductionmentioning

confidence: 99%

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Stitch in the ditch: Nutzotin Mountains (Alaska) fluvial strata and a dike record ca. 117–114 Ma accretion of Wrangellia with western North America and initiation of the Totschunda fault

et al. 2019

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The Nutzotin basin of eastern Alaska consists of Upper Jurassic through Lower Cretaceous siliciclastic sedimentary and volcanic rocks that depositionally overlie the inboard margin of Wrangellia, an accreted oceanic plateau. We present igneous geochronologic data from volcanic rocks and detrital geochronologic and paleontological data from nonmarine sedimentary strata that provide constraints on the timing of deposition and sediment provenance. We also report geochronologic data from a dike injected into the Totschunda fault zone, which provides constraints on the timing of intra–suture zone basinal deformation. The Beaver Lake formation is an important sedimentary succession in the northwestern Cordillera because it provides an exceptionally rare stratigraphic record of the transition from marine to nonmarine depositional conditions along the inboard margin of the Insular terranes during mid-Cretaceous time. Conglomerate, volcanic-lithic sandstone, and carbonaceous mudstone/shale accumulated in fluvial channel-bar complexes and vegetated overbank areas, as evidenced by lithofacies data, the terrestrial nature of recovered kerogen and palynomorph assemblages, and terrestrial macrofossil remains of ferns and conifers. Sediment was eroded mainly from proximal sources of upper Jurassic to lower Cretaceous igneous rocks, given the dominance of detrital zircon and amphibole grains of that age, plus conglomerate with chiefly volcanic and plutonic clasts. Deposition was occurring by ca. 117 Ma and ceased by ca. 98 Ma, judging from palynomorphs, the youngest detrital ages, and ages of crosscutting intrusions and underlying lavas of the Chisana Formation. Following deposition, the basin fill was deformed, partly eroded, and displaced laterally by dextral displacement along the Totschunda fault, which bisects the Nutzotin basin. The Totschunda fault initiated by ca. 114 Ma, as constrained by the injection of an alkali feldspar syenite dike into the Totschunda fault zone. These results support previous interpretations that upper Jurassic to lower Cretaceous strata in the Nutzotin basin accumulated along the inboard margin of Wrangellia in a marine basin that was deformed during mid-Cretaceous time. The shift to terrestrial sedimentation overlapped with crustal-scale intrabasinal deformation of Wrangellia, based on previous studies along the Lost Creek fault and our new data from the Totschunda fault. Together, the geologic evidence for shortening and terrestrial deposition is interpreted to reflect accretion/suturing of the Insular terranes against inboard terranes. Our results also constrain the age of previously reported dinosaur footprints to ca. 117 Ma to ca. 98 Ma, which represent the only dinosaur fossils reported from eastern Alaska.

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Section: ■ Totschunda Fault Zonementioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Stitch in the ditch: Nutzotin Mountains (Alaska) fluvial strata and a dike record ca. 117–114 Ma accretion of Wrangellia with western North America and initiation of the Totschunda fault

et al. 2019

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“…The Kahiltna Basin is believed to have formed during the late Jurassic due to the collision of the Talkeetna island arc system with the North American backstop (Wallace et al, 1989;Plafker and Berg, 1994;Kalbas et al, 2007;Goldfarb et al, 2013). The basin now separates arc volcanic and plutonic rocks of the Alaska-Aleutian range and various accreted terranes to the southeast from the Mesozoic North American terranes to the northwest.…”

Section: Geologic Settingmentioning

confidence: 99%

“…Numerous plutonic rocks of Jurassic to Cretaceous age reflect a major pulse from 101 to 96 Ma and additional activity from 91 to 89 Ma, with intrusion types ranging from granodiorite, diorite, and monzonite to gabbro and pyroxenite. Tertiary igneous activity included the widespread extrusion of volcanic rocks as well as emplacement of plutons with distinct pulses from 70 to 60 Ma and 44 to 42 Ma (Detterman and Reed, 1980;Amato et al, 2007;Goldfarb et al, 2013). Quaternary glacial deposits cover much of the region.…”

Section: Geologic Settingmentioning

confidence: 99%

Integrated geophysical imaging of a concealed mineral deposit: A case study of the world-class Pebble porphyry deposit in southwestern Alaska

et al. 2013

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We combined aeromagnetic, induced polarization, magnetotelluric, and gravity surveys as well as drillhole geologic, alteration, magnetic susceptibility, and density data for exploration and characterization of the Cu-Au-Mo Pebble porphyry deposit. This undeveloped deposit is almost completely concealed by postmineralization sedimentary and volcanic rocks, presenting an exploration challenge. Individual geophysical methods primarily assist regional characterization. Positive chargeability and conductivity anomalies are observed over a broad region surrounding the deposit, likely representing sulfide minerals that accumulated during multiple stages of hydrothermal alteration. The mineralized area occupies only a small part of the chargeability anomaly because sulfide precipitation was not unique to the deposit, and mafic rocks also exhibit strong chargeability. Conductivity anomalies similarly reflect widespread sulfides as well as water-saturated glacial sediments. Mineralogical and magnetic susceptibility data indicate magnetite destruction primarily within the Cu-Au-Mo mineralized area. The magnetic field does not show a corresponding anomaly low but the analytic signal does in areas where the deposit is not covered by postmineralization igneous rocks. The analytic signal shows similar lows over sedimentary rocks outside of the mineralized area, however, and cannot uniquely distinguish the deposit. We find that the intersection of positive chargeability anomalies with analytic signal lows, indicating elevated sulfide concentrations but low magnetite at shallow depths, roughly delineates the deposit where it is covered only by glacial sediments. Neither chargeability highs nor analytic signal lows are present where the deposit is covered by several hundred meters of sedimentary and volcanic rocks, but a 3D resistivity model derived from magnetotelluric data shows a corresponding zone of higher conductivity. Gravity data highlight geologic features within the deposit, including shallow diorite sills that locally contain higher-grade mineralization. The results thus show ways in which an integrated survey approach might be used to distinguish zones of potentially economic mineralization.

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“…Recent studies of porphyry Cu (Mo/Au) deposits have made significant contributions to the understanding of their environment of formation (Richards, 2003(Richards, , 2009Hou et al, 2003;Goldfarb et al, 2013;Lu et al, 2013;Richard et al, 2013). These studies have demonstrated that large-scale porphyry Cu (Mo/Au) deposits can form not only in island arc environments but also within orogenic belts.…”

Section: Introductionmentioning

confidence: 99%

Formation of Au-polymetallic ore deposits in alkaline porphyries at Beiya, Yunnan, Southwest China

Wang

et al. 2016

Ore Geology Reviews

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Tectonic Setting of the Pebble and Other Copper-Gold-Molybdenum Porphyry Deposits within the Evolving Middle Cretaceous Continental Margin of Northwestern North America

Cited by 32 publications

References 81 publications

Stitch in the ditch: Nutzotin Mountains (Alaska) fluvial strata and a dike record ca. 117–114 Ma accretion of Wrangellia with western North America and initiation of the Totschunda fault

Stitch in the ditch: Nutzotin Mountains (Alaska) fluvial strata and a dike record ca. 117–114 Ma accretion of Wrangellia with western North America and initiation of the Totschunda fault

Integrated geophysical imaging of a concealed mineral deposit: A case study of the world-class Pebble porphyry deposit in southwestern Alaska

Formation of Au-polymetallic ore deposits in alkaline porphyries at Beiya, Yunnan, Southwest China

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