Geology and Mineral Deposits of the Sulphurets Area
(NTS 104A/5,12; 104B/8,9)
Open File 1988-04 presents the geology, major mineral deposits, mineral occurrences and gossans in the Sulphurets area (NTS 104A/5, 12; 104B/8, 9), one of British Columbia’s newest gold-silver camps. The map sheet is published at 1:50 000 scale and covers 1000 square kilometres at the eastern end of the Iskut River gold belt. Two mines are under development in the area and current reserves are tabulated for five precious metal deposits. The region is underlain by Lower to Middle Jurassic calcalkaline volcanic and associated sedimentary rocks of the Hazelton Group.
The area is underlain by Lower to Middle Jurassic Hazelton Group volcanic and sedimentary rocks that have been folded, faulted and weakly metamorphosed, mainly during Cretaceous time. Three episodes of intrusive activity produced small synvolcanic plutons, satellitic stocks of the Coast plutonic complex and minor dykes and sills.
The Hazelton Group consists of four lithostratigraphic map units in the Sulphurets area. Map unit 1 is a thick sequence of interbedded sedimentary and volcanic rocks. The sediments include sandstones, fine-grained conglomerates, rhythmically banded siltstones and mixed epiclastic/pyroclastic rocks. Quartz-poor lithic or arkosic wackes predominate. Intermediate pyroclastic comprise the volcanic component. Unit 2 consists of red, green and purple heterogeneous pyroclastic and epiclastic rocks. Unit 3 is light coloured and consists predominantly of felsic pyroclastic rocks, including welded tuffs. Unit 4 consists of marine, dark grey siltstone and fine-grained sandstone. It is well bedded but displays complex disharmonic folding.
Intrusive rocks are not abundant but are spatially and temporally associated with mineralization. Jurassic (?) quartz monzonite comprises the largest intrusion in the area, the Lee Brant stock. A wide variety of syn and post-volcanic hypabyssal stocks is concentrated near the Sulphurets and Mitchell glaciers. Most are quartz-poor and have alkaline affiliations; many are porphyritic with potassium, feldspar, hornblende and biotite. These intrusions are similar in composition to the volcanic rocks. Post-volcanic intrusions are generally more phaneritic and clearly cut the country rocks. Compositions differ from enclosing rocks and some are associated with copper and gold mineralization.
Only one syndepositional fault was recognized but they could be more numerous and important in controlling distribution of rock types in units 1 and 2.
More than 60 mineral occurrences are known in the area. Six types of veins are identified: base metal quartz, silver-rich base metal, precious and base metal quartz, precious metal quartz, carbonate, and barite. Other deposit types include: porphyry-style copper-molybdenum; disseminated gold (silver) in alteration zones; gold-bearing skarn; and stratabound pyritic zones.
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