Abstract

The Kitsault molybdenum deposit is related to the 54-m.y.-old Lime Creek Intrusive Complex which is hosted by sedimentary rocks along the eastern margin of the Coast Plutonic Complex. The Alice Arm intrusive rocks, of which the Lime Creek Complex is a member, are probably related to the latest intrusive phase of the Coast Plutonic Complex.The Lime Creek Complex is a series of nested stocks that intrude the Bowser Lake Group graywackes and argillites of Jurassic age. A broad zone of biotite hornfels developed in the sedimentary rocks as a result of the intrusive activity. The oldest member of the Complex is the East Lobe. It in turn is followed by the Border, Southern, and Central stocks, and the Intramineral dikes and the related Northeast Porphyry. These intrusions vary from diorite of the East Lobe to quartz monzonite of the Northeast Porphyry, suggesting a differentiation trend. Postmineral lamprophyre and basalt dikes are common.Mineralization is related to the Central stock and Northeast Porphyry. The molybdenite shell generally occupies the contract zone of the Central stock. Quartz-pyrite, with or without, scheelite veins occurs on the hanging wall of the molybdenite zone, while barren quartz veins occupy the footwall. A series of postmolybdenite polymetallic sulfide quartz veins have a northeast trend and a greater lateral extent than any other vein type. Four ages of mineralization have been identified. The first three are molybdenite bearing, whereas the last consists of polymetallic sulfides.Hydrothermal alteration is directly related to the mineralization. A central silicified zone occurs on the footwall side of the molybdenite zone. There is a close correlation between molybdenite and potassium silicate alteration. Peripheral to the molybdenite zone and associated with the quartz-pyrite veins, phyllic alteration is common. All alteration is vein related as envelopes with the intervening areas being altered to propylitic to argillic assemblages.There appear to be several significant similarities and differences between the Kitsault-type deposits and those of the Climax type (White et al., 1981). The similarities appear to be in the style and nature of the intrusive activity and associated hydrothermal events. Both types of deposits are characterized by multiple igneous and hydrothermal events. Another common feature is the presence of intramineral dikes and related stocks. The significant differences appear to be the smaller size and lower grade of the Kitsault deposit, which may have had a smaller and less concentrated hydrothermal system. The other significant difference is in the composition of the source intrusions. The Kitsault deposits are characterized by siliceous quartz monzonites and granodiorites whereas the Climax-type deposits are characterized by rhyolites and granites. Alteration and trace element assemblages are similar in both types of deposits except that alteration is not as pervasive and trace elements are not as abundant in the Kitsault deposits.

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