James Kenneth Mortensen

James Kenneth Mortensen
University of British Columbia - Vancouver | UBC · Department of Earth, Ocean and Atmospheric Sciences

PhD, University of California, Santa Barbara

About

264
Publications
69,259
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8,554
Citations
Additional affiliations
September 1992 - June 2016
University of British Columbia - Vancouver
Position
  • Professor
Description
  • Currently an Emeritus Professor at UBC

Publications

Publications (264)
Article
Full-text available
The Bigorne deposit is classified as an orogenic gold system that comprises gold-bearing veins cutting through the syn-orogenic Variscan granites in the northern Iberia. The mineralized structures are subparallel of the regional Penacova-Régua-Verín strike-slip fault system. The mineralized bodies include quartz-sulfide veins, disseminated sulfides...
Article
Existing published models for orogenic gold deposits (OGDs) do not adequately describe or explain most deposits of Phanerozoic age, and there are numerous reasons why Phanerozoic OGDs might differ significantly from older deposits. We subdivide Phanerozoic OGDs into four main subtypes, based on a number of descriptive criteria, including tectonic s...
Article
Mineral inclusions within native gold are features of lode gold occurrences that are preserved in detrital particles. Inclusion assemblages in populations of gold particles in placers from specific localities are revealed through inspection of polished sections, and assimilation of robust data sets permits reconstruction of the lode source mineralo...
Article
The Late Devonian Corner Bay pluton is a part of the Sitkoh alkaline plutonic complex on the Chichagof Island, southeastern Alaska, which is located in the Alexander terrane of the North American Cordillera. The intrusion, about 12 km long and 4 km wide, is composed predominantly of amphibole-biotite-bearing syenitic/ monzonitic rocks with minor al...
Article
The tectonic significance and age of carbonatite intrusions in the central Foreland Belt of the Canadian Cordillera are poorly constrained. Recent work has demonstrated that one of these carbonatite intrusions, the Aley carbonatite, was emplaced as a syn-kinematic sill, coeval with a major nappe-forming tectonic event. Determining the age of the Al...
Conference Paper
Full-text available
Orogenic gold deposits (OGDs) produced most of the gold that was mined during Roman times in the Variscan Belt in NW Iberia, and continue to be the focus of active exploration activity. OGDs in this region appear to post-date most collisional tectonism and oroclinal bending that affected the area, but pre-date the emplacement of scattered post-tect...
Conference Paper
Full-text available
Most published orogenic gold deposit (OGD) models are based heavily on world-class Precambrian deposits, many of which are interpreted to have a spatial and genetic association with crustal-scale, commonly terrane-bounding, transpressive fault zones. Numerous examples of multi-million ounce Phanerozoic OGDs exist, however, and results of recent stu...
Presentation
Full-text available
SGA 2019 Meeting Presentation - Low resolution image version - Society for Geology Applied to Ore Deposits 27-30 August 2019. Orogenic gold deposits in the Variscan belt in northwestern Iberia MacKenzie, D. and Mortensen, J.K.; Camino Geoscience Inc., Canada Abstract. Orogenic gold deposits (OGDs) produced most of the gold that was mined during...
Presentation
Full-text available
SGA 2019 Meeting Presentation - High resolution image version - Society for Geology Applied to Ore Deposits 27-30 August 2019. Orogenic gold deposits in the Variscan belt in northwestern Iberia MacKenzie, D. Mortensen, J.K. Camino Geoscience Inc., Canada Abstract. Orogenic gold deposits (OGDs) produced most of the gold that was mined during Roma...
Article
Zircon grains from a granitic pegmatite clast from conglomerate at the base of the Ross Island Formation on Grand Manan Island indicate an igneous crystallization age of 664.1 ± 4.6 Ma. The clast also contains abundant older inherited grains back to the Archean. Muscovite in the same clast and an additional similar clast yielded cooling ages of 607...
Article
Felsic schist units in the Lone Star Ridge area of the northern Klondike Gold District, Yukon, Canada, host both locally gold-bearing orogenic quartz veins and much more extensive zones of disseminated gold mineralization that is stratabound within specific schist units and is interpreted to be syngenetic in origin. Scarcity of outcrop and the diff...
Technical Report
New data tables, figures and imagery from northern Yukon and adjacent Arctic Alaska document the field relationships, lithologies, petrography, geochronology and geochemistry of a suite of Late Devonian granites and syenite, as well as an Eocene syenite. These data sets support an interpretation and synthesis of the tectonic implications of these m...
Article
A suite of six Devonian granites and one syenite were emplaced into the upper crust of northern Yukon between 364.8 ± 2.7 and 371.2 ± 1.4 Ma. The Bear Mountain syenite and related rhyolite porphyry in adjacent Alaska intruded at 52.3 ± 0.4 and 53.5 ± 0.2 Ma, respectively. A felsic volcaniclastic unit and quartz-phyric sill are newly documented adja...
Article
The Ushuaia pluton (UP) and the Ushuaia Peninsula Andesites (UPA) are intrusive units of a Late Cretaceous rear-arc in the Southernmost Andes. We report new LA-ICP-MS zircon ages from ∼71 to 75 Ma for the UP, and of ∼84 Ma for the UPA, which allow to differentiate these two magmatic events; consistent with their distinct petrography and geochemistr...
Conference Paper
Full-text available
The Otago Schist belt is well known for metamorphogenic enrichment of Au and W and there has been a long history of gold mining interspersed with some scheelite mining. However, the roles of processes of accumulation and metamorphism of the schist belt in redistributing strategic metals such as Cu and Co and Mo are less well understood. We present...
Article
Full-text available
Porphyry-epithermal and orogenic gold are two of the most important styles of gold-bearing mineralization within orogenic belts. Populations of detrital gold resulting from bulk erosion of such regions may exhibit a compositional continuum wherein Ag, Cu, and Hg in the gold alloy may vary across the full range exhibited by natural gold. This paper...
Presentation
Full-text available
Most published orogenic gold deposits (OGD) models are based heavily on world-class Precambrian deposits, many of which are interpreted to have a spatial and genetic association with crustal-scale, commonly terrane-bounding, transpressive fault zones. Numerous examples of multi-million ounce Phanerozoic OGDs exist, however, and results of recent st...
Article
Full-text available
Several gold deposits hosted mainly by Variscan granites and Precambrian to Palaeozoic metasediments occur in the northwestern part of Portugal. Most of these deposits were mined by the Romans (in the period I BC to II AD) as open pits and surface galleries. The Castromil-Serra da Quinta gold deposit is an important example of such a mined site; it...
Conference Paper
Full-text available
Most published orogenic gold deposits (OGD) models are based heavily on world-class Precambrian deposits, many of which are interpreted to have a spatial and genetic association with crustal-scale, commonly terrane-bounding, transpressive fault zones. Numerous examples of multi-million ounce Phanerozoic OGDs exist, however, and results of recent st...
Conference Paper
Full-text available
There is a spectrum of mineralisation styles in orogenic gold deposits from quartz vein systems, through vein systems with associated wall rock alteration, to pervasively altered rocks with only rare quartz veins. Historic exploration and mining has focussed on quartz vein systems, but the mining industry is currently in transition towards the perv...
Article
Metamorphosed felsic volcanic rocks occur interlayered with metasedimentary schist in close association with a 7 km long metabasaltic (greenschist) horizon in the Otago Schist belt of Central Otago. The felsic metavolcanic rocks are weakly foliated and locally segregated and consist principally of quartz and albite. Geochemical analyses suggest pho...
Article
We report eight new U-Pb detrital zircon ages for quartzose metasedimentary rocks from four lithotectonic units of parautochthonous North America in east-central Alaska: the Healy schist, Keevy Peak Formation, and Sheep Creek Member of the Totatlanika Schist in the northern Alaska Range, and the Butte assemblage in the northwestern Yukon-Tanana Upl...
Article
The Willow Creek mining district was the third-largest lode gold district in Alaska in the 20th century, having produced 19 metric tons (t) of gold from vein deposits and another 2 t of gold from associated placer deposits. The district is located in the southern Talkeetna Mountains, north of the Castle Mountain strike-slip fault system. Most gold...
Article
Full-text available
Gem-quality corundum (sapphire) occurs in scapolite-rich calc-silicate rock hosted in marble of the Lake Harbour Group near Kimmirut, southern Baffin Island. A deposit of blue and colorless gem corundum (Beluga occurrence) is compared to a similar calc-silicate pod generally lacking corundum but containing nepheline (Bowhead occurrence) and located...
Article
Full-text available
In southwest Yukon, the boundary between the Alexander terrane and Wrangellia corresponds with the Duke River fault. In this paper, we report on observations of the Duke River fault from four localities in southwest Yukon, and provide new constraints on (1) Permian regional metamorphism within the Alexander terrane, (2) Cretaceous ductile deformati...
Article
This study comprises the first systematic classification of native gold geochemistry within alkalic porphyry Cu-Au systems and the placer expression of such systems. The geochemistry and mineral associations of gold from four alkalic porphyry deposits in British Columbia, Canada (Afton, Mount Milligan, Mount Polley and Copper Mountain) have been co...
Article
Full-text available
The Mount Nansen volcanic complex (MNVC), which is best preserved on Mount Nansen in the southeastern Dawson Range of west-central Yukon, is a 51 km2 erosional remnant of what was originally a continuous, Early to mid-Cretaceous (115-104 Ma) continental magmatic arc. The MNVC consists of fragmental and massive andesitic flows and minor rhyolite flo...
Chapter
Full-text available
This paper provides a regional-scale background for understanding gold-mineralising processes in the Otago Schist during the Cretaceous. At this time the Schist belt was in the latter stages of formation as an accretionary exhumed accretionary wedge of structurally stacked clastic metasedimentary rocks with minor metabasic rocks. metasedimentary ro...
Article
New isotopic ages have been obtained from euhedral, first-cycle zircon grains recovered from Rhaetian strata preserved at the Black Bear Ridge section in northeastern British Columbia. Two statistically significant populations are present: an older population ca. 224 Ma, and a dominant younger population ca. 205 Ma. The younger population includes...
Article
There is a strong association between regions containing orogenic gold mineralization and exploitation of placer gold, although in many cases the nature of the source mineralization for these placer deposits remains unclear. This study describes a novel approach to evaluating the economic potential of in situ orogenic gold mineralization through ch...
Article
Full-text available
Triassic rocks of the Western Canada Sedimentary Basin (WCSB) have previously been interpreted as being deposited on the passive margin of North America. Recent detrital zircon provenance studies on equivalent Triassic rocks in the Yukon have suggested that these rocks were in part derived from the pericratonic Yukon–Tanana terrane and were deposit...
Article
Full-text available
The Mesozoic magmatic history of the North American margin records the evolution from a more segmented assemblage of parautochthonous and allochthonous terranes to the more cohesive northern Cordilleran orogenic belt. We characterize the setting of magmatism, tectonism, and epigenetic mineralization in the western Fortymile mining district, east-ce...
Article
Full-text available
The Yukon-Tanana Terrane (YTT) of western Yukon Territory in NW Canada and Otago Schist belt (OSB) of South Island, New Zealand share similar geological evolutionary histories as convergent orogenic belts. Both belts host orogenic gold deposits of mainly Jurassic to Early Cretaceous age. Jurassic mineralization in the YTT occurred during convergent...
Article
The Middle Cambrian Mount Read Volcanics of western Tasmania, Australia, host several world-class volcanic-hosted massive sulfide (VHMS) deposits, representing a wide range of deposit styles. Although the deposits and their host sequences are variably deformed and locally preserve spectacular examples of primary textures and structures, rapid later...
Article
Mineral de Talca is a rare occurrence of Mesozoic, gold-bearing quartz vein mineralisation situated within the Coastal Range of northern Chile. Quartz veins controlled by NNW–SSE-trending faults are hosted by Devonian-Carboniferous metasediments of greenschist facies and younger, undeformed granitoid and gabbro intrusions. The principal structural...
Article
Full-text available
Aeromagnetic lineaments interpreted from reduced-to-pole (RTP) magnetic grids were compared with gravity, topography, and field-based geologic maps to infer regional structural controls on hydrothermal mineral occurrences in a poorly exposed portion of the North American Cordillera in western Yukon and eastern Alaska. High-frequency and variable-in...
Conference Paper
Full-text available
Northwestern Iberia was the most important single source of gold for the Roman Empire in the 1st and 2nd centuries, with several very large placer and paleoplacer (e.g., Las Médulas) and lode mines (e.g., Salave, Três Minas) in production, along with several thousand smaller operations. Both intrusion-related (IRG) and orogenic gold (OG) deposits a...
Article
The Xietongmen district is located 260 km west-southwest of Lhasa in the Tibet Autonomous Region, China. The district occurs within the Gangdese belt, which forms the eastern part of the Trans-Himalayan magmatic belt and is the product of complex magmatic activity that began during the Late Triassic or Early Jurassic and ended in the Eocene. The Xi...
Article
Full-text available
Porphyry and epithermal mineralization of early Late Cretaceous Age (ca. 76-74Ma) at Casino, Revenue/Nucleus and Sonora Gulch areas in the central and eastern Dawson Range in west-central Yukon is spatially related to numerous placer gold mining areas. Placer- lode relationships have been established through study of gold alloy compositions and ass...
Article
Full-text available
Rasmussen, K.L., Mortensen, J.K. and Falck, H., 2007. Morphological and compositional analysis of placer gold in the South Nahanni River drainage, Northwest Territories. In: Yukon Exploration and Geology 2006, D.S. Emond, L.L. Lewis and L.H. Weston (eds.), Yukon Geological Survey, p. 237-250. ABSTRACT Placer gold has been reported in small amounts...
Article
The Cerro Bayo low sulfidation epithermal district is located in the Aysén region, Chilean Patagonia, at the western tip of the Deseado Massif epithermal silver-gold province. Mineralization is hosted in the mainly rhyolitic fragmental successions of the Jurassic Ibáñez Formation. New biotite 40Ar/39Ar and zircon U-Pb ages together with published a...
Article
Full-text available
Onset and termination of Eocene felsic volcanism in the Chilcotin Plateau of central British Columbia is constrained between 54.6 and 46.6 Ma by 33 new U–Pb and 40Ar/39Ar isotopic age determinations. Dates were obtained from representative felsic coherent and fragmental volcanic rocks that comprise the Ootsa Lake Group. The resulting chronostratigr...
Article
A detailed study of apatite and biotite compositions in multiple intrusive phases from five composite plutons in the northern Canadian Cordillera was undertaken with the aim of determining the composition of magmatic fluids relative to F:Cl:OH for several plutons―both barren and mineralizing―and for specific intrusive phases from each pluton that m...
Article
Full-text available
Geochemical, isotopic and U-Pb dating studies of volcanic rocks of the Tlansanlin Formation in central Aishihik Lake map area (115H) show that these are Late Cretaceous (75.8 ± 0.4 Ma to 77.3 ± 1.3 Ma), relatively primitive magmas that were emplaced in a continental arc setting. Intrusive rocks in the immediate area, associated with the Hopper porp...
Article
The Archean Blake River Group of the Abitibi greenstone belt represents a megacaldera complex which evolved over 8–11 M.y. from approximately 2704 to 2696 Ma. The early Misema Caldera developed from a series of amalgamated shield volcano complexes identified by the remnants of mafic dyke and sill systems. These remnants are found in the Jevis-Cleri...
Article
The Archean Hope Bay greenstone belt is located in the Bathurst Block of the northeastern part of the Slave Structural Province, a predominantly Archean, granite-greenstone-metasedimentary terrane. The greenstone belt is dominated by mafic volcanic rocks with less common felsic volcanic and volcaniclastic products and subordinate ultramafic bodies...
Article
Full-text available
Geochemistry and Sm–Nd and U–Pb (magmatic zircon) isotope data from a postcollisional batholith that crosscuts the allochthonous South Portuguese Zone (SPZ) of southern Iberia suggest that the basement is compositionally more juvenile than the exposed upper crust. The SPZ is an allochthonous terrane of the late Paleozoic Variscan orogen. The oldest...
Article
Full-text available
Between 1978 and 2009, approximately 430,000oz of placer gold were obtained from the Indian River and Black Hills Creek, which equates to roughly 20% of the production for the entire Yukon Territory during that period. The area is unglaciated, exposure is poor, and there are few known lode gold occurrences present. The technique of microchemical ch...
Article
Cashes Ledge igneous suite in the central Gulf of Maine is represented by 10 granitic and two felsic tuff samples collected from bedrock outcrops using the submersible Alvin in 1971-1972 and archived at the Woods Hole Oceanographic Institute. Laser ablation ICP-MS analyses of zircon grains yielded crystallization ages of 414.9 ± 1.1 Ma and 399.7 ±...
Article
Full-text available
The northern Canadian Cordillera exhibits coeval accreted arc, subduction zone, ocean basin, and continental margin assemblages that make the region an exceptional place to understand tectonic processes involved in arc-continent collision. In this study, we use U-Pb zircon and monazite geochronology to define the timing and provenance record of Lat...
Article
Full-text available
The >5 Moz (1 oz (troy) = 31.103 g) gold veins of the Liese Zone and nearby prospects in the Goodpaster Mining District of east central Alaska are spatially and temporally associated with late-Early to Late Cretaceous reduced granitoids that are divided into a granite suite, tonalite suite, and diorite suite in decreasing age. Synkinematic to postk...
Article
Full-text available
We report the first detailed study of the paleomagnetism, U–Pb geochronology and major element geochemistry of Paleoproterozoic north-trending Marathon dykes north of Lake Superior. The paleomagnetic and geochemical results demonstrate that Marathon dykes can be divided into two subsets, one of normal magnetic polarity, the other of reverse polarit...
Article
Orogenic gold camps are commonly associated with placer deposits although in many cases the relationship between placer and lode source may be unclear. Placer gold deposits in Bonanza and Eldorado Creeks in the northern Klondike district goldfield, Yukon, Canada, probably yielded more than 2 million ounces (Moz) from a small geographic area, but kn...
Article
Alloy compositions and associated suites of opaque mineral inclusions have been used to define the microchemical signature of 3,050 placer gold grains from 34 localities and 561 gold grains from six lode localities from the northeastern, central, and southern Klondike gold district, Yukon, Canada. These data augment those from a detailed parallel s...