Geology of Quesnel and Stikine terranes and associated porphyry deposits. Jim Logan Paul Schiarizza

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1 Geology of Quesnel and Stikine terranes and associated porphyry deposits Jim Logan Paul Schiarizza

2 Quesnel and Stikine terranes Major cordilleran terranes characterized by similar Late Triassic Early Jurassic volcanic-plutonic arc complexes Well-endowed with Cu (Au Mo) porphyry deposits, including Aurich alkalic types Associated younger rocks also host porphyry deposits Large areas are covered by Qal and/or young rocks need to explore under cover

3 Outline: -Overview of tectonic setting -Geology and porphyry deposits of Quesnel terrane -Geology and porphyry deposits of Stikine terrane -Late Mesozoic Cenozoic porphyry deposits

4 Tectonic Setting 1 General Geology Quesnel terrane bounded to east by oceanic Slide Mountain terrane and pericratonic rocks; separated from Stikine terrane to west by oceanic Cache Creek terrane

5 Tectonic Setting 2 Quesnel terrane Part of a long-lived arc system that formed along the western margin of North America Late Paleozic arc formed outboard of associated Slide Mountain marginal basin Overlying Mesozoic arc formed along continental margin after collapse of Slide Mountain basin

6 Tectonic Setting 3 Stikine terrane Characterized by Triassic-Jurassic arc complex that is markedly similar to that of Quesnel terrane, and is similarly well-endowed with alkaline and calc-alkaline porphyry deposits Oroclinal model (Nelson and Mihalynuk, 1993) suggests that Quesnel and Stikine arcs are parts of the same system; anticlockwise rotation of the Stikine arc brought it into parallelism with Quesnel arc, enclosing Cache Creek terrane Stikine terrane was in present relative position along the continental margin by early Middle Jurassic time

7 Middle Jurassic Cretaceous Episodic contractional deformation Clastic basins; local arc volcanic and plutonic rocks with porphyry Cu-Mo (Au) and porphyry Mo deposits Tectonic Setting 4 Late Cretaceous Eocene Dextral strike-sip and normal faults Paleocene - Eocene volcanic, sedimentary and plutonic rocks; porphyry Cu-Mo deposits Protracted deformation: porphyry deposits may be tilted, dismembered, and variably strained

8 Quesnel Terrane Mainly Upper Triassic submarine volcanic and volcaniclastic rocks of Nicola and Takla groups Main belt characterized by pyroxene-phyric shoshonitic basalt, and alkaline to calc-alkaline intrusions Locally developed southwestern belt of calc-alkaline basalt to rhyolite and calc-alkaline intrusions

9 Main Belt: Quesnel Terrane representative Triassic succession taken from the Nicola Group in the Thuya Creek Woodjam Creek area, mapped in and Nicola Group Middle and Upper Triassic, submarine succesion; locally unconformably overlain by Lower Jurassic sandstone and conglomerate

10 Nicola Group: Lemieux Creek unit Basal unit along eastern margin of group Deposited, in part, on Slide Mountain terrane Mainly black phyllite, slate, siltstone, quartzite, limestone Quartz-rich units probably derived from pericratonic rocks to east Middle and Late Triassic conodonts

11 Nicola Group: Volcaniclastic unit Volcanic breccia/basalt subunits Siltstonelimestone subunit Chert-rich subunit Widespread, heterogeneous unit, dominated by volcanic sandstone, conglomerate and breccia Also includes pyroxene-feldspar-phyric basalt, volcanic breccia, limestone, siltstone, chert Scattered Late Triassic (mainly Carnian) macrofossils and conodonts Interfingers? with upper part of Lemieux Creek unit

12 Nicola Group: Basalt Breccia unit Pyroxene-phyric basalt, pillowed basalt and basalt breccia Locally includes feldsparpyroxene sandstone, and limestone

13 Nicola Group: Polylithic breccia unit Uppermost unit, not everywhere recognized Mainly polylithic breccia, conglomerate and feldspathic sandstone; breccias contain feldspathic plutonic and volcanic fragments Commonly red Locally includes pyroxene-phyric and coarse plagioclase-phyric basalt Late Triassic age constrained by underlying successions and cross-cutting Late Triassic plutons

14 Intrusive suites and associated porphyry depostis Southern Quesnel terrane: Intrusive rocks in southwest and main belts define 4 linear belts of alternating calc-alkaline and alkaline plutons, younging to the east All belts host important mineral occurrences

15 Late Triassic calc-alkaline belt Late Triassic Guichon Creek batholith in southwest calc-alkaline belt; hosts the major Highland Valley porphyry Cu-Mo deposits ~ 210 Ma Is the Late Triassic Granite Mountain batholith, within Cache Creek terrane, host to the Gibraltar Cu-Mo porphyry deposit, part of the same belt? Intervening interval mainly covered

16 Late Triassic monzodiorite belt In western part of main belt Mainly ~ Ma monzodiorite, diorite, monzonite, syenite Host to numerous alkalic Cu-Au porphyry deposits

17 Early Jurassic granodiorite belt Large batholiths (Takomkane, Thuya, Wild Horse, Pennask, Bromley) of mainly Early Jurassic ~ Ma granodiorite, monzogranite, quartz monzodiorite Hosts past-producing Brenda Cu-Mo clac-alkaline porphyry deposit, and recently discovered Woodjam SE zone (calc-alkaline Cu-Mo-Au porphyry)

18 Early Jurassic alkaline belt Diorite, monzonite, syenite, quartz monzonite, quartz seyenite; and Alaskan-type ultramafic-mafic complexes Co-spatial and east of EJ granodiorite belt; coeval and younger than EJ granodiorite belt (~ Ma) Associated Cu-Au skarns and some porphyry-style mineralization

19 Intrusive suites and porphyry deposits farther north, in Nation Lakes Omineca River area Same intrusive suites that are recognized in the main Quesnel belt in southern BC, but eastward-younging spatial distribution not apparent Major porphyry Cu-Au mineralization associated with monzonite and syenite of the Early Jurassic alkaline belt (Mt. Milligan, Lorraine, Kwanika? Note strong northwest-trending structural grain to many intrusive units