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May 8th 2009 <br />The Chilcotin Basalts and Neogene landscape evolution of the Interior Plateau: implications for mineral...
Mineral Deposits in south-central BC<br /><ul><li>The Chilcotin Group (~22 – 0.1 Ma) covers >35,500 km2of the Interior Pla...
Mineral Deposits in south-central BC<br /><ul><li>The Chilcotin Group (~22 – 0.1 Ma) covers >35,500 km2of the Interior Pla...
It obscures basement likely to host epithermal Au and Cu-Au-Mo porphyry deposits.
The CG is wholly within the MPBB infestation zone.
It is extensively covered by ?? m of drift.</li></ul>Nicola Arc<br />Cariboo Mountains<br />Cariboo Mountains<br />Interio...
Mineral Deposits in south-central BC<br /><ul><li>The Chilcotin Group (~22 – 0.1 Ma) covers >35,500 km2of the Interior Pla...
It obscures basement likely to host epithermal Au and Cu-Au-Mo porphyry deposits.
The CG is wholly within the MPBB infestation zone.
It is extensively covered by ?? m of drift.</li></ul>It’s thickness and distribution are very poorly constrained.<br />Nic...
Mineral Deposits in south-central BC<br /><ul><li>The Chilcotin Group (~22 – 0.1 Ma) covers >35,500 km2of the Interior Pla...
It obscures basement likely to host epithermal Au and Cu-Au-Mo porphyry deposits.
The CG is wholly within the MPBB infestation zone.
It is extensively covered by ?? m of drift.</li></ul>It’s thickness and distribution are very poorly constrained.<br />Nic...
L. Eocene-Oligocene unconformity<br />Takomkanebatholith<br />Thuyabatholith<br />adapted from Massey (2006)<br />
L. Eocene-Oligocene unconformity<br />Chilcotin Ranges – Coast Mountains<br />≥18 Ma sub-horizontal unconformity – now 5° ...
CG - physical volcanology<br />Andrews and Russell (2007)<br />sub-aerial lavas<br />e.g. Hanceville<br />sub-aqueous pill...
e.g. Dog Creek<br />1. sub-aerial lavas<br />massive interior<br />sub-aerial lavas are typically:<br /><ul><li> columnar-...
 coherent,
 laterally restricted <100 km2,
 highly vesicular,
single lavas <20 m thick,
 sequences <60 m thick,
 often emplaced onto / into wet sediment</li></ul>basal breccia<br />columnar-jointed lava<br />0.5 m<br />vesicular top<b...
2. sub-aqueous successions<br />sub-aqueous successions are:<br /><ul><li> exposed in Present-day drainages
 always restricted to paleo-valleys (e.g. Mio-Plio Chilcotin Valley),
 typically associated with capping sub-aerial lavas,
 ≤80 m thick,
 typically repetitive sequences:
 repeated pillow-breccia  peperite  sub-aerial lava,
 indicates gradual damming, infilling, and breaching of valleys / lakes with short-lived highstands (sub-aerial lavas).</l...
sub-aqueous successions<br />transport direction<br />cross-bedded sediment trapped within peperite<br />Gordee et al. (20...
sub-aqueous successions<br />sub-aerial lava<br />hyaloclastite pillow-breccias<br />e.g. Chasm Prov. Park<br />Gordee et ...
paleovalleys<br />characterized by:<br /><ul><li> coincidence of sub-aqueous and sub-aerial lithofacies,
 areally-restricted (<100 km2),
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The Chilcotin Basalts: implications for mineral exploration

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This is a presentation I gave at the GSA Cordilleran Meeting in Kelowna, BC, in May 2009. It presents advanced results from geological studies of the Chilcotin Group basalts in south-central BC, and their impact on mineral exploration activities.

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The Chilcotin Basalts: implications for mineral exploration

  1. 1. May 8th 2009 <br />The Chilcotin Basalts and Neogene landscape evolution of the Interior Plateau: implications for mineral exploration<br />Graham Andrews – UBC<br />co-workers: Kelly Russell, Jackie Dohaney, Sarah Brown, Sarah Caven, Randy Enkin, Bob Anderson<br />
  2. 2. Mineral Deposits in south-central BC<br /><ul><li>The Chilcotin Group (~22 – 0.1 Ma) covers >35,500 km2of the Interior Plateaux.</li></ul>Nicola Arc<br />Cariboo Mountains<br />Cariboo Mountains<br />Interior Plateaux<br />Coast Mountains<br />adapted from Massey (2006)<br />
  3. 3. Mineral Deposits in south-central BC<br /><ul><li>The Chilcotin Group (~22 – 0.1 Ma) covers >35,500 km2of the Interior Plateaux.
  4. 4. It obscures basement likely to host epithermal Au and Cu-Au-Mo porphyry deposits.
  5. 5. The CG is wholly within the MPBB infestation zone.
  6. 6. It is extensively covered by ?? m of drift.</li></ul>Nicola Arc<br />Cariboo Mountains<br />Cariboo Mountains<br />Interior Plateaux<br />Coast Mountains<br />adapted from Massey (2006)<br />
  7. 7. Mineral Deposits in south-central BC<br /><ul><li>The Chilcotin Group (~22 – 0.1 Ma) covers >35,500 km2of the Interior Plateaux.
  8. 8. It obscures basement likely to host epithermal Au and Cu-Au-Mo porphyry deposits.
  9. 9. The CG is wholly within the MPBB infestation zone.
  10. 10. It is extensively covered by ?? m of drift.</li></ul>It’s thickness and distribution are very poorly constrained.<br />Nicola Arc<br />Cariboo Mountains<br />Cariboo Mountains<br />Interior Plateaux<br />Coast Mountains<br />adapted from Massey (2006)<br />
  11. 11. Mineral Deposits in south-central BC<br /><ul><li>The Chilcotin Group (~22 – 0.1 Ma) covers >35,500 km2of the Interior Plateaux.
  12. 12. It obscures basement likely to host epithermal Au and Cu-Au-Mo porphyry deposits.
  13. 13. The CG is wholly within the MPBB infestation zone.
  14. 14. It is extensively covered by ?? m of drift.</li></ul>It’s thickness and distribution are very poorly constrained.<br />Nicola Arc<br />Cariboo Mountains<br />Cariboo Mountains<br />Interior Plateaux<br />Coast Mountains<br />adapted from Massey (2006)<br />
  15. 15. L. Eocene-Oligocene unconformity<br />Takomkanebatholith<br />Thuyabatholith<br />adapted from Massey (2006)<br />
  16. 16. L. Eocene-Oligocene unconformity<br />Chilcotin Ranges – Coast Mountains<br />≥18 Ma sub-horizontal unconformity – now 5° NE-dipping<br />Cardtable Mtn. – 6400 ft<br />~18 Ma paleo-valley fill<br />Battleship Peak<br />6000 ft<br />5800 ft<br />Mesozoic meta-sedimentary succession<br />Relay Mtn.<br />Andrews et al. (in prep)<br />
  17. 17. CG - physical volcanology<br />Andrews and Russell (2007)<br />sub-aerial lavas<br />e.g. Hanceville<br />sub-aqueous pillow delta<br />Eocene rocks<br />Extensive sub-aerial / sub-aqueous successions along the tributaries of the Fraser River.<br />Complex horizontal stratigraphic transitions between sub-aerial and sub-aqueous lithofaciesat the margins of paleovalleys.<br />
  18. 18. e.g. Dog Creek<br />1. sub-aerial lavas<br />massive interior<br />sub-aerial lavas are typically:<br /><ul><li> columnar-jointed,
  19. 19. coherent,
  20. 20. laterally restricted <100 km2,
  21. 21. highly vesicular,
  22. 22. single lavas <20 m thick,
  23. 23. sequences <60 m thick,
  24. 24. often emplaced onto / into wet sediment</li></ul>basal breccia<br />columnar-jointed lava<br />0.5 m<br />vesicular top<br />massive interior<br />3 m<br />basal breccia<br />
  25. 25. 2. sub-aqueous successions<br />sub-aqueous successions are:<br /><ul><li> exposed in Present-day drainages
  26. 26. always restricted to paleo-valleys (e.g. Mio-Plio Chilcotin Valley),
  27. 27. typically associated with capping sub-aerial lavas,
  28. 28. ≤80 m thick,
  29. 29. typically repetitive sequences:
  30. 30. repeated pillow-breccia  peperite  sub-aerial lava,
  31. 31. indicates gradual damming, infilling, and breaching of valleys / lakes with short-lived highstands (sub-aerial lavas).</li></li></ul><li>sub-aqueous successions<br />SW<br />NE<br />sub-aerial lavas<br />peperites<br />pillow breccias<br />basement<br />basement<br />basement<br />e.g. 6 Ma Chilcotin River Valley<br />Gordee et al. (2007)<br />
  32. 32. sub-aqueous successions<br />transport direction<br />cross-bedded sediment trapped within peperite<br />Gordee et al. (2007)<br />
  33. 33. sub-aqueous successions<br />sub-aerial lava<br />hyaloclastite pillow-breccias<br />e.g. Chasm Prov. Park<br />Gordee et al. (2007)<br />
  34. 34. paleovalleys<br />characterized by:<br /><ul><li> coincidence of sub-aqueous and sub-aerial lithofacies,
  35. 35. areally-restricted (<100 km2),
  36. 36. complex vertical and along-valley stratigraphy,
  37. 37. ≤150 m thick, 100 – 2000 m wide,
  38. 38. rapidly filled (10s – 100s years)  multiple, single eruptions.</li></ul>They are typically sub-parallel to modern river valleys (e.g. the Chilcotin, Nazko, Fraser, and Taseko Rivers).<br />Many seem to follow Eocene paleo-valleys (e.g., Selina Tribe)<br />
  39. 39. paleovalleys – 3 Ma Chilcotin River<br />e.g. Anahim IR<br />
  40. 40. paleovalley environment - model<br />“perched” lavas<br />tributary-filling lava – “escaped”<br />valley-fill lithofacies association<br />e.g. Dog Creek<br />
  41. 41. paleovalley environment - model<br />7<br />1.1<br />7<br />2.9<br />2.9<br />
  42. 42. duration of valley-filling eruptions<br />Bull Canyon – 6.2 Ma<br />Dog Creek – 3.1 Ma<br />Enkin et al. (Round-Up 2008)<br />clustered, non-polar paleomagnetic mean directions<br />rapid (&lt;&lt; 10 kyr), un-interrupted in-filling  single, short-duration, proximal eruptions <br /><ul><li> probably mono-genetic  many vents, cones, in a single field</li></li></ul><li>Chilcotin Group sources<br />inferred Chilcotin Group sources<br />Holocene volcanic field<br />Nazko area<br />Wells-Grey VF<br />there are probably 100s of ‘missing’ vents – 1 vent for each lava<br />
  43. 43. Chilcotin Group – buried channels<br /><ul><li> BC Prov. Govt. water-well log data
  44. 44. CG locally up to 50 m thick around 100 Mile House (092P) and Miocene (093A)
  45. 45. typically <20 m across 092P
  46. 46. elsewhere, limited data suggests CG is <20 m thick
  47. 47. can also constrain drift thickness and bedrock type</li></ul>MPBB<br />40<br />10<br />0<br />50<br />10<br />0<br />Andrews & Russell (2008)<br />
  48. 48. schematic cross-section<br />Thuyabatholith<br />adapted from Massey (2006)<br />
  49. 49. Implications for exploration<br />Thuyabatholith<br />Extreme thickness variations (0 – 100 m) require many ‘basement windows’ and greatly reduced areal extent.<br />
  50. 50. New Distribution Map<br />Dohaney (in prep.)<br />
  51. 51. New Distribution Map<br />X<br />X<br />X<br />X<br />X<br />Dohaney (in prep.)<br />
  52. 52. Basement Prospects – Windows<br />Several deposits identified within windows or adjacent to CG margins:<br />How are mineral trends / geochemical anomalies traced below the basalt? <br />How are geophysical signals modified?<br />How many similar deposits lie hidden under thin basalts elsewhere?<br />Windows can be delineated by careful mapping, supported by regional- and property-scale geophysical surveys. <br />ARIS Report 25740 - Bonaparte<br />Mb – Chilcotin basalt<br />Tv – Nicola volcanics<br />Mzi - pluton<br />Mb – Chilcotin basalt<br />1 km<br />
  53. 53. Implications for exploration<br />Thuyabatholith<br />Extreme thickness variations (0 – 100 m) require many ‘basement windows’ and greatly reduced areal extent.<br />Identifying paleo-drainages (esp. Pliocene / Pleistocene) reveals major drainage direction changes  what are the implications for regional-scale detrital mineral / till and geochemical sampling? --- POTENTIALY A BIG PROBLEM!!!<br />
  54. 54. Mio-Pliocene Fraser River Basin<br />?<br />inferred paleo-channel flow direction<br />approx. present watershed<br />Stage 3<br />age constraint<br />10 Ma<br />6 Ma<br />Fraser River<br />8 Ma<br />6 Ma<br />?<br />3 Ma<br />10 Ma<br />11 Ma<br />3 Ma<br />6 Ma<br />?<br />9 Ma<br />7 Ma<br />9 Ma<br />
  55. 55. Present Fraser River Basin<br />Nechako River<br />reversal<br />approx. present watershed<br />new<br />un-changed<br />Fraser River<br />abandoned<br />0.2 Ma<br />direct to sea<br />ChilcotinRiver<br />&lt;1 Ma<br />Fraser Canyon<br />Thompson & Clearwater Rivers<br />
  56. 56. Aid for Interior explorationists<br />New distribution and thickness maps of the Chilcotin Group tested against regional-scale geophysical data-sets. <br />Identification / estimation of basement affinities in the new ‘windows’.<br />Use of the Chilcotin Group as a “clock” to quantify:<br /><ul><li> Neogene uplift and erosion  Barkerville placer gold release and exhumation of Eocene epithermal systems,
  57. 57. paleo-landscapes and changes in drainage networks  constraints on geochemical ‘vectoring’.</li></ul>Database of physical properties (e.g., mag. sus; resistivity; density; seismic velocity) tied to CG lithology and lithofacies.<br />
  58. 58. Thank you – questions?<br />
  59. 59. Neogene uplift<br />X<br />The ‘high’ Coast Mountains have significant (&gt;2 km) Mio-Pliocene uplift<br />This is linked to Cordilleran-scale uplift across the Interior Plateau and into the Omineca Mountains<br />The Interior Plateau is warped:<br /><ul><li> the ‘corners’ goes up (100s – 1000s m)
  60. 60. the ‘middle’ goes down (100s m)</li></ul>X<br />X<br />X<br />X<br />X<br />V – 0 masl<br />
  61. 61. Fraser River Basin base-level change<br />0 m change<br />25 m change<br />50 m change<br />&gt;100 m change<br />-ve change<br />25<br />&gt;100<br />0<br />&gt;100<br />“warping” recognized by Mathews (1989)<br />
  62. 62. Chilcotin Prospects – Placer / U<br />lava<br />Buried Miocene channels are known locations of basal U deposits (e.g., Blizzard site, Kelowna).<br />Buried Miocene channels are probable hosts for placer deposits (Au, PGE)<br />most Barkerville / Fraser placers are Miocene in age <br />Mapping the courses of buried channels is a first step towards further exploitation.<br />volcanic breccia<br />fluvial gravels<br />
  63. 63. l. Eocene peneplain<br />The Cordillera has a widespread late-Eocene – Oligocene unconformity:<br /><ul><li> post major transtensional regional extension (core complexes, etc),
  64. 64. synchronous with minor transtensional basin formation (e.g., Hat Creek, Merritt, Tulameen),
  65. 65. very few l. Eocene & Oligocene rocks,
  66. 66. preserved l. Eocene drainage network in southern BC (Tribe, 2003, 2005),
  67. 67. l. Eocene – Present drainage across the ‘high’ Coast Mountains,
  68. 68. extensive u/c overlain by sub-horizontal Neogene basaltic lavas (Chilcotin Group & Maitland Frm).</li></ul>“perched” outliers<br />extensive coverage<br />“perched” outliers<br />Neogene Chilcotin Grpvolcs<br />
  69. 69. Outstanding questions<br /><ul><li> How does Neogene vertical tectonics link to plate-margin processes?
  70. 70. What causes Fraser River reversal after 1 Ma?
  71. 71. Balance between post-glacial rebound / base level drop / uplift
  72. 72. Are there un-recognized neotectonic landforms across the Interior Plateau (e.g., fault scarps, alluvial fans, truncated valleys)? – YES there are!</li>

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