Eocene age for Ag–Pb–Zn–Au vein and replacement deposits of the Kokanee Range, southeastern British Columbia

1992 ◽  
Vol 29 (1) ◽  
pp. 3-14 ◽  
Author(s):  
G. Beaudoin ◽  
J. C. Roddick ◽  
D. F. Sangster
Keyword(s):  
British Columbia ◽  
Middle Jurassic ◽  
Middle Eocene ◽  
Hanging Wall ◽  
Spatial Association ◽  
High Heat ◽  
Time Interval ◽  
Genetic Link ◽  
Metasedimentary Rocks ◽  
Magmatic Event

The Ag–Pb–Zn–Au vein and replacement deposits of the Kokanee Range, southeastern British Columbia, are hosted by the Middle Jurassic Nelson batholith and surrounding Cambrian to Triassic metasedimentary rocks in the hanging wall of the transcrustal Slocan Lake Fault, Field relations indicate that mineralization is younger than the Nelson batholith and a Middle Jurassic foliation in the Ainsworth area but coeval or older than Eocene unroofing of the Valhalla metamorphic core complex in the footwall of the Slocan Lake Fault. Lamprophyre and gabbro dykes are broadly coeval with mineralization and have biotite and hornblende K–Ar ages defining a short-lived Middle Eocene alkaline magmatic event between 52 and 40 Ma. An older, Early Cretaceous alkaline magmatic event (141 – 129 Ma) is possible but incompletely documented.K–Ar and step-heating 40Ar/39Ar analyses on hydrothermal vein and alteration muscovite indicate that hydrothermal fluids were precipitating vein and replacement deposits 58–59 Ma ago. Crosscutting relationships with lamprophyre dykes indicate the Kokanee Range hydrothermal system lasted for more than 15 Ma. Eocene crustal extension resulted in a high heat flow and structures which were probably responsible for hydrothermal fluid movement and flow paths.A 100 Ma time interval is documented between batholith emplacement and spatially associated mineralization, ruling out any genetic link between the two. Similar large age differences between granite intrusion and peripheral mineralization have recently been documented for two world-sea le Ag–Pb–Zn vein districts, which suggest that spatial association between granite and Ag–Pb–Zn mineralization is not sufficient to infer a genetic link.

Deformation of the western margin of the Omineca Belt near Crooked Lake, east-central British Columbia

1990 ◽  
Vol 27 (3) ◽  
pp. 414-425
Author(s):  
Jeffrey A. Fillipone ◽  
John V. Ross
Keyword(s):  
British Columbia ◽  
North America ◽  
Middle Jurassic ◽  
Phase 1 ◽  
Late Devonian ◽  
East Central ◽  
Western Margin ◽  
Metasedimentary Rocks ◽  
Narrow Zone ◽  
Minimum Age

The western margin of the Omineca Belt near Crooked Lake, British Columbia, consists of metasedimentary rocks (Snowshoe Group) and orthogneisses of the Barkerville terrane, structurally overlain by a mafic volcanic – sedimentary package of rocks belonging to the allochthonous Slide Mountain (Crooked Amphibolite) and Quesnel terranes (Triassic phyllite and Nicola Group). At least two episodes of regional deformational (phases 2 and 3) affected this composite package. Deformation and metamorphism (phase 1) in the Snowshow Group predate the formation of this package and are nowhere evident within the allochthonous terranes.Middle Jurassic metamorphism ranging from chlorite zone through sillimanite zone affected all units. Isograds are folded, together with the junction between the terranes, indicating that the metamorphic assemblages developed prior to folding of this boundary. Granitic orthogneiss (Boss Mountain, Quesnel Lake, and Perseus gneisses), having a minimum age of Late Devonian to Early Pennsylvanian, was intruded into and deformed with the Snowshoe Group during the earliest recognizable phase of deformation in the Barkerville terrane (phase 1). Slide Mountain terrane rocks occupy a narrow zone where large eastward displacement occurred during overthrusting of the Intermontane superterrane upon the western margin of North America in Middle Jurassic time.

U–Pb geochronology of Jurassic to early Tertiary granitic intrusives from the Nelson–Castlegar area, southeastern British Columbia, Canada

1995 ◽  
Vol 32 (10) ◽  
pp. 1668-1680 ◽  
Author(s):  
Dipak K. Ghosh
Keyword(s):  
British Columbia ◽  
Middle Jurassic ◽  
Middle Eocene ◽  
Biotite Granite ◽  
Published Data ◽  
Crustal Material ◽  
Granitoid Magmatism ◽  
Continental Arc ◽  
Two Samples ◽  
Deformation Event

Eleven U–Pb zircon dates from seven intrusives in the Nelson–Castlegar area provide new age constraints on the granitoid magmatism in southeastern British Columbia. Four samples from the Nelson Batholith date three distinct intrusive phases spanning ca. 10 Ma. One sample from the eastern porphyritic phase (Coffee Creek) yields the oldest age at 172.5 ± 5.0 Ma. Two samples from the central K-feldspar megacrystic phase (Crescent Bay) give precise ages at 162.0 ± 1.0 and 161.5 ± 1.5 Ma, and possibly date the youngest phase of the batholith. An intermediate age of emplacement at 166.0 ± 3.0 Ma is suggested for the southern tail of the batholith. The new and published data suggest that the Nelson Batholith was emplaced in roughly concentric zones. In contrast, the southern quartz diorite phase and the northwestern granodiorite phase of the Bonnington Pluton were emplaced coevally during the Middle Jurassic at 167.4 ± 2.0 and 165.0 ± 3.0 Ma, respectively. Middle Jurassic ages were also obtained for a sample of hornblende orthogneiss (166.0 ± 7.5 Ma) that intrudes the Trail Gneiss, and for a leucocratic gneiss sample (156.6 ± 6.0 Ma), a remnant from the Kinnaird Gneiss. A biotite granite sheet that intrudes the Kinnaird Gneiss yields a Middle Eocene age (40.5 ± 6.0 Ma), and possibly dates the youngest deformation event in the region. The Early Eocene ages (55.1 ± 3.7 and 50.6 ± 0.5 Ma) obtained from the Ladybird Granite and Coryell Syenite agree with previous estimates. Early Proterozoic ages of inherited zircon components in most of the samples agree with Nd–Sr isotopic evidence for incorporation of old crustal material in the intrusives empiaced in continental-arc settings.

Paleomagnetism of Eocene rocks of the Kelowna and Castlegar areas, British Columbia: studies in determining paleohorizontal

1989 ◽  
Vol 26 (4) ◽  
pp. 829-844 ◽  
Author(s):  
M. Bardoux ◽  
E. Irving
Keyword(s):  
British Columbia ◽  
North America ◽  
Middle Eocene ◽  
Hanging Wall ◽  
Bedding Plane ◽  
Normal Extension ◽  
South Central ◽  
Normal Polarity ◽  
Coast Plutonic Complex ◽  
Partial Unfolding

The middle Eocene Marron volcanics (mean age 52 ± 2 Ma) of the Kelowna outlier form the upper part of the hanging wall of the westerly dipping Okanagan Valley fault (OVF) in south-central British Columbia. They overlie Quesnellia. The OVF is currently interpreted as the westernmost member of a network of low-angle extension faults in the southern Omenica belt. The OVF was active in the middle Eocene at much the same time that the Marron volcanics were cooling. Relative to present horizontal, the magnetizations are widely scattered (Fisher's precision parameter k = 8) and after correction for bedding attitudes, there is no significant improvement (k = 9). Evidently, some magnetizations were acquired before (referred to as category 1) and others after (category 2) tilting; that is, the horizontal plane at the time of magnetization sometimes did and sometimes did not coincide with the bedding plane. Partial unfolding experiments, carried out on the two categories separately, yield a precision comparable to that expected for paleosecular variation, and a mean direction (D, I) of 352°, 70° (24 sites spanning 2000 m, 275 specimens, k = 23, α95 = 6°, paleopole 86°N, 230°E, A95 = 10°). The Marron is predominantly normally magnetized. Rock units slightly older and others slightly younger are reversely magnetized. The transition from reversed to normal polarity occurs in basal beds of the Marron Formation. The overall mean direction of the Marron and stratigraphically adjacent units is 352°, 69 °(28 sites, 300 specimens, spaning 4000 m, k = 21, α95 = 6°), yielding a paleopole at 85°N, 197°E (A95 = 10°), which is in excellent agreement with that for middle Eocene rocks of cratonic North America. Hence this part of Quesnellia had reached its present position relative to North America by middle Eocene time, and there has been no significant rotation of it. In contrast, the mean direction (020°, 72°, k = 9, α95 = 11°) after correction for bedding (calculated assuming the magnetization to be entirely pretilting) implies a clockwise rotation of 28°. We believe that this is incorrect; the apparent rotation, we argue, is caused by wrongly assuming that the bedding plane always coincides with the paleohorizontal at the time magnetism is acquired.Further tests have been carried out on intrusive and metamorphic core-complex rocks in the region of Eocene crustal extension 100 km to the east of Kelowna. These rocks are coeval with the Marron, and are located in both the hanging walls and footwalls of the Slocan Lake normal extension fault, which dips 30° eastward. Paleodirections are very different from those at Kelowna (four bodies, mean direction (D, I) 60°, 52°, k = 66, α95 = 6°), and we argue that this divergence is caused by tilting 37 ± 10° to the west antithetical to the Slocan Lake fault. We suggest that paleomagnetism provides a means by which tilts in such plutonic and metamorphic terrains can be determined. We suggest further that such tilts may have been responsible for some of the aberrant magnetizations observed in plutonic rocks of the Coast Plutonic Complex being much more widespread in the cordillera than previously envisioned.

Middle Eocene sedimentary and volcanic infilling of an evolving supradetachment basin: White Lake Basin, south-central British Columbia

2005 ◽  
Vol 42 (1) ◽  
pp. 49-66 ◽  
Author(s):  
Jason D McClaughry ◽  
David R Gaylord
Keyword(s):  
British Columbia ◽  
Middle Eocene ◽  
Hanging Wall ◽  
Metamorphic Core Complex ◽  
Lake Basin ◽  
Alluvial Fans ◽  
Core Complex ◽  
South Central ◽  
Metamorphic Core ◽  
Okanagan Valley

The middle Eocene White Lake and Skaha formations in the White Lake Basin, British Columbia record the sedimentary and volcanic infilling of a supradetachment basin that developed during the latter stages of Shuswap metamorphic core complex exhumation. The 1.1-km-thick White Lake Formation is characterized by volcanogenic sediment gravity flow, fluvial, and sheetflood facies interbedded with volcanic deposits. Facies relations suggest White Lake strata accumulated on coalesced, west-sloping alluvial fans that drained an active volcanic center. The overlying 0.3-km-thick Skaha Formation records increased tectonism and mass-wasting. Pervasively shattered Skaha avalanche, slide, and sheetflood deposits accumulated on alluvial fans, shed from hanging-wall and footwall sources exposed along the Okanagan Valley fault. Clast compositions of the White Lake and Skaha formations record alluvial and tectonic stripping that locally eliminated hanging-wall blocks. Mylonite clasts in upper Skaha beds imply significant Okanagan Valley fault footwall uplift during the middle Eocene and syntectonic erosion of the Shuswap metamorphic core complex. The syntectonic sedimentary record preserved within the White Lake Basin elucidates the relations and timing between core complex exhumation and extensional tectonism in this region. The White Lake and Skaha formations are the apparent age equivalent of the Klondike Mountain Formation of northern Washington (USA.). White Lake Basin strata, however, are more complexly interstratified, post-depositionally disrupted, and contain a more complete record of core complex unroofing. Variations in the spatial distributions and textural and compositional character of middle Eocene strata in this area underscore the need to exercise care when developing regional-scale sedimentary–tectonic–volcanic models.

Isotopic evidence for complex Pb sources in the Ag–Pb–Zn–Au veins of the Kokanee Range, southeastern British Columbia

1992 ◽  
Vol 29 (3) ◽  
pp. 418-431 ◽  
Author(s):  
Georges Beaudoin ◽  
D. F. Sangster ◽  
C. I. Godwin
Keyword(s):  
British Columbia ◽  
Geographic Distribution ◽  
Upper Mantle ◽  
Hanging Wall ◽  
Normal Fault ◽  
Isotopic Signature ◽  
Fracture Permeability ◽  
Metasedimentary Rocks ◽  
Pb Isotopic Composition ◽  
Lower Crustal

In the Kokanee Range, more than 370 Ag–Pb–Zn–Au vein and replacement deposits are hosted by the Middle Jurassic Nelson batholith and surrounding Cambrian to Triassic metasedimentary rocks. The Kokanee Range forms the hanging wall of the Slocan Lake Fault, an Eocene, east-dipping, low-angle normal fault. The Pb isotopic compositions of galenas permit the deposits to be divided into four groups that form linear arrays in tridimensional Pb isotopic space, each group having a distinct geographic distribution that crosses geological boundaries. The Kokanee group Pb is derived from a mixture of local upper crustal country rocks. Ainsworth group Pb and Sandon group Pb plot along a mixing line between a lower crustal Pb reservoir and the upper crustal Pb reservoir. The Ainsworth group Pb isotopic signature is markedly lower crustal, whereas the Sandon group Pb is slightly lower crustal. The Bluebell group Pb plots along a mixing line between a depleted upper mantle Pb reservoir and the lower crustal Pb reservoir.The geographic distribution and the Pb isotopic composition of each group probably reflect deep structures that permitted mixing of lower crustal, upper crustal, and mantle Pb by hydrothermal fluids. Segments of, or fluids derived from, the lower crust and the upper mantle were leached by, or mixed with, evolved meteoric water convecting in the upper crust. Fracture permeability, hydrothermal fluid flow, and mineralization resulted from Eocene crustal extension in southeastern British Columbia.

Fossil Mosses from the Bisaccate Zone of the Mid-Eocene Allenby Formation, British Columbia

1974 ◽  
Vol 11 (3) ◽  
pp. 409-421 ◽  
Author(s):  
Marian Kuc
Keyword(s):  
British Columbia ◽  
Middle Eocene ◽  
Plant Tissues ◽  
Plant Remains ◽  
Lake Bottom ◽  
White Colour

New fossil taxa (Ditrichites fylesi, Muscites maycocki, M. ritchiei, Palaeohypnum jovet-asti and P. steerei); unnamed moss and moss-like fossils, detrital fragments of various plant tissues, and paleobotanical evidence of the bisaccate zone are described from the Middle Eocene Allenby Formation near Princeton, British Columbia. These remains occur in laminated, tuffaceous, silty and pyroclastic shale, deposited under lacustrine conditions.Detailed examination of the various laminae indicates that beds of white colour and composed of coarser silt grains are poor in fossils and could be related to periods of decreasing bioproduction; less silty and darker coloured beds are rich in macro- and microfossils and could be related to periods of extensive bioproduction. The rock features, lamination, and distribution of macrofossils indicate the slow and undisturbed accumulation of plant remains on a lake bottom.

Detachment-parallel recharge explains high discharge fluxes at the TAG hydrothermal field

2021 ◽  
Author(s):  
Lars Rüpke ◽  
Zhikui Guo ◽  
Sven Petersen ◽  
Christopher German ◽  
Benoit Ildefonse ◽  
...  
Keyword(s):  
High Temperature ◽  
Hanging Wall ◽  
Massive Sulfide ◽  
Hydrothermal Activity ◽  
High Heat ◽  
Heat Fluxes ◽  
Long Distance ◽  
High Discharge ◽  
Circulation Mode ◽  
Spreading Ridges

Abstract Submarine massive sulfide deposits on slow-spreading ridges are larger and longer-lived than deposits at fast-spreading ridges1,2, likely due to more pronounced tectonic faulting creating stable preferential fluid pathways3,4. The TAG hydrothermal mound at 26°N on the Mid-Atlantic Ridge (MAR) is a typical example located on the hanging wall of a detachment fault5-7. It has formed through distinct phases of high-temperature fluid discharge lasting 10s to 100s of years throughout at least the last 50,000 years8 and is one of the largest sulfide accumulations on the MAR. Yet, the mechanisms that control the episodic behavior, keep the fluid pathways intact, and sustain the observed high heat fluxes of up to 1800 MW9 remain poorly understood. Previous concepts involved long-distance channelized high-temperature fluid upflow along the detachment5,10 but that circulation mode is thermodynamically unfavorable11 and incompatible with TAG's high discharge fluxes. Here, based on the joint interpretation of hydrothermal flow observations and 3-D flow modeling, we show that the TAG system can be explained by episodic magmatic intrusions into the footwall of a highly permeable detachment surface. These intrusions drive episodes of hydrothermal activity with sub-vertical discharge and recharge along the detachment. This revised flow regime reconciles problematic aspects of previously inferred circulation patterns and can be used as guidance to one critical combination of parameters that can generate substantive mineral systems.

Telluride Mineralogy of the Deer Horn Au-Ag-Te-(Bi-Pb-W) Deposit, British Columbia: Implications for the Generation of Tellurides

2021 ◽  
Author(s):  
Jordan A. Roberts ◽  
Lee A. Groat ◽  
Paul G. Spry ◽  
Jan Cempírek
Keyword(s):  
British Columbia ◽  
Fluid Inclusions ◽  
Hanging Wall ◽  
Oscillatory Zoning ◽  
Stage Iii ◽  
Fine Grained ◽  
Melting Temperatures ◽  
Homogenization Temperatures ◽  
Intrusive Suite ◽  
Cathodoluminescence Imaging

ABSTRACT The Deer Horn deposit, located 150 km south of Smithers in west-central British Columbia, is an Eocene polymetallic system enriched in Au-Ag-Te with lesser amounts of Bi-Pb-W; the Au and Ag are hosted in Te-bearing minerals and Ag-rich gold (Au-Ag alloy). A quartz-sulfide vein system containing the main zones of Au-Ag-Te mineralization and attendant sericite alteration occurs in the hanging wall of a local, spatially related thrust fault and is genetically related to the nearby Eocene Nanika granodiorite intrusive suite. Tellurium-bearing minerals commonly form isolated euhedral to subhedral grains or composite grains (up to 525 μm in size) of Ag-, Bi-, Pb-, and Au-rich tellurium-bearing minerals (e.g., hessite, tellurobismuthite, volynskite, altaite, and petzite). Panchromatic cathodoluminescence imaging revealed four generations of quartz. Within remnant cores of quartz I, local oscillatory zoning occurs in quartz II. Fine-grained veinlets of quartz III and IV crosscut quartz I and II, showing evidence of at least two deformation events; late-forming veinlets of calcite crosscut all generations of quartz. The tellurides and Ag-rich gold occur in stage III quartz. Three types of fluid inclusions were observed in stage III and IV quartz: (1) aqueous liquid and vapor inclusions (L-V); (2) aqueous carbonic inclusions (L-L-V); and (3) carbonic inclusions (vapor-rich). Primary fluid inclusions related to the telluride mineralization within quartz III were tested with microthermometry, along with a few primary inclusions from quartz IV. Homogenization temperatures are 130.0–240.5 °C for L-V inclusions and 268.0–336.4 °C for L-L-V inclusions. Aqueous carbonic inclusions had solid CO2 melting temperatures from –62.1 to –56.8 °C, indicating the presence of ≈1 to 30 mol.% dissolved methane in these inclusions. The Deer Horn Au-Ag-Te-(Bi-Pb-W) deposit is a reduced intrusion-related gold system characterized by sheeted veins, metal zoning, low salinity aqueous-carbonic fluids, and a genetic relationship to an Eocene granodiorite. Values of δ34S of pyrite vary from –1.6 to 1.6 per mil and are compatible with a magmatic source of sulfur.

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