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TitlePorphyry indicator minerals in tills of the Highland Valley copper-molybdenum mine area, south-central British Columbia
AuthorFerbey, T; Plouffe, A; Bustard, A
SourceRoundup 2016, abstracts, Technical sessions: Tuesday; by Association for Mineral Exploration British Columbia; 2016 p. 4
LinksOnline - En ligne (PDF 582 KB)
Alt SeriesEarth Sciences Sector, Contribution Series 20150384
MeetingRoundup 2016; Vancouver, BC; CA; January 25-28, 2016
Mediaon-line; digital
File formatpdf
ProvinceBritish Columbia
NTS92I/05; 92I/06; 92I/09; 92I/10
Lat/Long WENS-121.5000 -120.5000 50.7500 50.2500
Subjectsmetallic minerals; geochemistry; surficial geology/geomorphology; porphyry deposits; mines; copper; molybdenum; Wisconsinian glacial stage; glaciation; tills; glacial deposits; assays; gold; sulphides; mineralization; trace element geochemistry; dispersal patterns; ice movement directions; Highland Valley mine; Guichon Creek batholith; Quaternary
ProgramIntrusion/Porphyry Ore Systems, Targeted Geoscience Initiative (TGI-4)
AbstractIn total, 97 subglacial till samples were collected within a 1000 square kilometre area roughly centred on Highland Valley copper-molybdenum mine, which consists of five porphyry copper-molybdenum centres-Bethlehem, J.A., Valley, Lornex and Highmont. Hosted by the Late Triassic calcalkaline Guichon Creek batholith, these centres are largely covered by Late Wisconsinan glacial and older nonglacial sediments. This study was designed to determine if the buried porphyry copper-molybdenum mineralization could be detected using the mineral assemblage and trace-element geochemistry of subglacial tills. Silt plus clay (<0.063 millimetre size) and clay (<0.002 mm size) fractions of till were analyzed for trace-element geochemistry by aqua regia followed by inductively coupled plasma-mass spectrometry and lithium metaborate/tetraborate-inductively coupled plasma emission and mass spectrometry. Additionally, heavy and mid-density mineral concentrates from the till (0.25-2 mm size fraction; >2.8-3.2 and >3.2 SG) were examined for porphyry indicator minerals (PIMs).
During the Late Wisconsinan, the Cordilleran Ice Sheet flowed south and southeast through the study area toward its terminus in northern Washington state. There is no evidence of an early eastward iceflow out of the Coast Mountains, despite the proximity of the study area to this major ice-accumulation centre. Glacial dispersal from the Highland Valley porphyry district is clearly demonstrated in copper and molybdenum concentrations in till. The two highest values in the silt-plus-clay fraction (1579 and 1707 parts per million copper; 23 and 29 ppm molybdenum) occur directly southeast of Valley and Lornex centres. Immediately up ice from here, copper and molybdenum values drop to background (178 ppm copper; 1.1 ppm molybdenum). Copper and molybdenum values decrease down ice from these centres and approach background concentrations approximately 20 km to the southeast. The spatial distribution of chalcopyrite grains in till (0.25-0.5 mm; >3.2 SG) is similar but more restricted, with the highest counts (107-4630 grains/10 kg) located down ice of the Valley, Lornex and Bethlehem centres; background for chalcopyrite is 1 grain/10 kg. Other PIMs recovered from subglacial till samples include apatite, malachite and epidote. Gold and jarosite grains were also recovered from the tills adjacent to Highland Valley mineralization but their relationship is unclear.
Porphyry copper-molybdenum mineralization at the Highland Valley mine is detectable in the matrix mineralogy and trace-element geochemistry of subglacial till samples. The regional glacial dispersal train (or 'footprint') from the Highland Valley district, including a cluster of economic and sub-economic deposits, is one of the most extensive (about 20 km long) and better defined in British Columbia, based on contrast in element concentrations and mineral grain counts. The dispersal pattern reflects simple ice flow from multiple mineralized bedrock sources. This survey was a collaborative project between the Geological Survey of Canada (Targeted Geoscience Initiative 4), the Canadian Mining Innovation Council (Cu Footprints Project) and the B.C. Geological Survey.
Summary(Plain Language Summary, not published)
We have conducted a sampling survey of glacial sediments in the region of a large copper deposit in British Columbia with the objective of developing mineral exploration methods in regions with an extensive glacial sediment cover. Our results demonstrate that the geochemical composition (e.g. determine how much copper is in the sediment) and the presence of indicator minerals in the sediments provide an indication of the presence of a buried mineral source. These results have major implications for mineral exploration.