Boss Mountain Mine, Williams Lake, Cariboo Mining Division, British Columbia, Canada

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Ref.: Mining Annual Review(1985):94,308. A molybdenum property owned by Noranda Mines.
The Boss Mountain molybdenum deposit is situated near the eastern margin of the Early Jurassic Takomkane batholith which intrudes Upper Triassic Nicola Group volcanic rocks on the south and west and is in fault contact with Lower Jurassic volcanic and sedimentary rocks to the east and north. A syenodiorite phase, a granodiorite phase and a porphyritic biotite granodiorite phase make up the Takomkane batholith. Intruding the batholith about 450 metres northeast of the deposit is the Cretaceous Boss Mountain Stock of porphyritic quartz monzonite. Related to this intrusion is a complex sequence of rhyolite porphyry and rhyolite dike emplacement, breccia development and molybdenum introduction.

Molybdenum mineralization is contained within quartz veins and to a somewhat lesser extent in breccia bodies within the granodiorite phase of the batholith. Three phases of breccia, known as Phase 1 Breccia, Quartz Breccia and Phase III Breccia, are found at the deposit. Fracturing can be grouped into eight distinct periods with six of these being genetically related to vein formation and ore deposition. The following six ore zones have been outlined at the deposit: 1. Main Breccia zone - composed of Quartz Breccia and Phase III Breccia with molybdenite occurring along fragment boundaries and within quartz veins cutting the breccia. 2. Fracture Ore zone - re-brecciated upper part of the Quartz Breccia and adjacent overlying granodiorite in the Main Breccia zone. Molybdenite with only a very minor amount of quartz comprise the matrix. 3. South Breccia zone - composed of Phase I and Phase III breccias with ore-grade mineralization occurring erratically as pods in fractures and the matrix. 4. Stringer zone - a subparallel swarm of veins around the northwest and west margins of the Main Breccia zone. 5. Southwest Stringer zone - a zone of subparallel veins about 300 metres south of the Main Breccia zone. Bounded at least partly on the southwest by what appears to be a major fracture zone which has been localized along an intensely altered and mineralized andesite dike. 6. High-Grade Vein - a system of quartz-molybdenite veins localized in a sheared and intensely altered andesite dike north of the Main Breccia zone.

All the ore zones are composed of more than one stage of molybdenite mineralization. Molybdenite is the only mineral of economic importance in the deposit. Pyrite is the most abundant and widespread accessory mineral, with chalcopyrite, sphalerite, scheelite, tetrahedrite, rutile, ankerite, bismuthinite, pyrolusite, magnetite, hematite and anatase also present.

Six alteration assemblages have been recognized in the deposit. Four of these are related to molybdenum mineralization and from oldest to youngest are: 1) garnet-hornblende, 2) biotite, 3) quartz-sericite-pyrite-potassium feldspar-chlorite, and 4) chlorite- talc. An epidote-chlorite assemblage had both a pre-mineralization stage and a stage coincident with mineralization. A zeolite-calcite- clay assemblage is post-mineralization.

Mineral List

Anatase Ankerite Biotite Bismuthinite Bornite Calcite

Chalcopyrite 'Chlorite Group' Epidote 'Feldspar Group' 'Garnet' Hematite

'Hornblende' Magnetite Molybdenite Muscovite var: Sericite Pyrite Pyrolusite

Quartz Rutile Scheelite Sphalerite Talc Tetrahedrite

24 entries listed. 18 valid minerals.