The University of British Columbia

Current Thesis: Mid-Cretaceous magmatism and mineralization in the southwestern Northwest Territories and southern Yukon: a geochronological, geochemical, and isotopic approach towards a model for the Cretaceous tectonic, magmatic, and metallogenic evolution of the northern Cordillera

Location:  Selwyn Basin and Cassiar Platform, Yukon and Northwest Territories

Start Date:  January 2005

Expected Completion Date:  December 2011

Sponsors:  Parks Canada, Northwest Territories Geoscience Office, Yukon Geological Survey

Supervisor:  Dr. James K. Mortensen

Committee Members:  Dr. Richard M. Tosdal, Dr. Gregory Dipple, Dr. Craig J. R. Hart

Background:  This PhD thesis aims to examine the petrogenesis of voluminous, 115-90 Ma felsic magmatism and related mineralization emplaced into Laurentian and peri-Laurentian terranes in the Yukon and the Northwest Territories (NWT).

Objectives:

1.  To better understand the petrogenesis of the magmatism and the nature of basement rocks, and to suggest possible melt, metal, and ligand sources.
2.  To add to our current, but limited, understanding of the tectono-magmatic and metallogenic regime in northern Cordillera throughout the Cretaceous.

Research Methods:

• fill gaps in dataset for the Cretaceous granitoids by analyzing 65 samples for geochronological-geochemical-isotopic data from over 50 intrusions
• produce one of the largest published S ± O isotopic datasets of plutons (~80 samples) and selected mineralization
• apply LA-ICP-MS to determine trace element and Lu-Hf isotopic compositions in zircon
• examine the evolution of magmatic volatiles (F-Cl) in intrusions regionally, and locally in tungsten mineralizing magmatic systems
• compile all relevant datasets  to combine with these data to test the existing model for the tectonic, magmatic, and metallogenic evolution of the northern Cordillera in the Cretaceous

Products - Thesis Chapters:

• Radiogenic and stable isotopic compositions of Cretaceous intrusions in the Selwyn Basin and Cassiar Platform, Yukon and NWT
• Whole Rock and Zircon Chemistry, and Hf-isotopic Composition of Zircon for Cretaceous Intrusions in the Selwyn Basin, northern Cordillera
• Magmatic fluid compositions relative to fluorine and chlorine in W-mineralizing intrusive systems: case studies from the northern Canadian Cordillera
• Lead and sulphur isotopic compositions of selected mineral deposits in the Selwyn Basin and the Cassiar Platform, northern Cordillera
• An alternate model for mid-Cretaceous magmatism in the northern Cordillera

SELECTED PUBLICATIONS

Peer-Reviewed:

• In Progress:

  - Zircon U-Pb Ages and Textures of Cretaceous to Eocene Granitoids, south-central Yukon. Yukon Open Report, 2011

  - Zircon U-Pb Ages and Textures of Cretaceous Granitoids, Mackenzie Mountains, NWT. NWT Open File, 2011

  - Apatite and Biotite Compositional Data for W-Mineralizing Intrusions, Mackenzie Mountains. NWT Open File, 2011

• In Review: Rasmussen, K.L., Lentz, D.R., and Falck, H. Felsic magmatic phases and the role of late-stage aplitic dykes in the formation of the world-class Cantung W-skarn deposit, Northwest Territories. Ore Geology Reviews.
  

• In Review: Rasmussen, K.L., Leslie, C., and Ootes, L. Chapter 4; Intrusive rocks. In: Geology of the northern central Mackenzie Mountains, Sekwi Mountain (105P) and Mount Eduni (106A) and northwestern part of 95M map areas, Northwest Territories. Geological Survey of Canada.

• Accepted: Rasmussen, K.L., Mortensen, J.K., and Falck, H., 2010.  Magmatic fluid compositions (F-Cl-SO₃) as an exploration tool for Cretaceous intrusion-related mineralization in the Selwyn and Mackenzie Mountains, southwestern NWT. GNWT Open Report.

• Rasmussen, K.L., Arehart, G., and Mortensen, J.K., 2010. Preliminary S-O isotopic compositions of Cretaceous granitoids in the Selwyn Basin and the Cassiar Platform, Yukon and Northwest Territories. Yukon Exploration and Geology 2009.

• Rasmussen, K.L., 2009. New geochemical, geochronological, isotopic, and apatite composition data for Cretaceous magmatism, NTS 105P, Northwest Territories. GNWT Open Report.

• Invited: Rasmussen, K.L., Mortensen, J.K., Falck, H., and Ullrich, T.D., 2007. The potential for intrusion-related mineralization within the Nahanni MERA area, Selwyn and Mackenzie mountains, Northwest Territories. In: Mineral and Energy Resource Potential of the Proposed Expansion to the Nahanni National Park Reserve, Northern Cordillera, Northwest Territories, GSC Open File 5344.

• Rasmussen, K.L., Mortensen, J.K. and Falck, H., 2007. Morphological and compositional analysis of placer gold in the South Nahanni River drainage, Northwest Territories. Yukon Exploration and Geology 2006.

• Rasmussen, K.L., Mortensen, J.K. and Falck, H., 2006. Geochronological and lithogeochemical studies of intrusive rocks in the Nahanni region, southwestern Northwest Territories and southeastern Yukon. Yukon Exploration and Geology 2005.

Non-Peer-Reviewed:

• Rasmussen, K.L., 2008. Geochemistry, Petrography, and Geochronology of Porphyritic Intrusive Phases at the RNT Zone, Newmont Lake Property, Galore Creek Project, Northern BC: implications for associated Cu-Au mineralization. Consulting Report, 31p.

• Rasmussen, K.L., 2007. Sweden Field Trip Report. UBC Society of Economic Geology Student Chapter, Report on Annual Field Trip, 30p.

International Meeting Presentations:

• Rasmussen, K.L., Arehart, G., and Mortensen, J.K., 2010. Radiogenic and Stable Isotopic Compositions of mid-Cretaceous Intrusions in the Selwyn Basin, Yukon and Northwest Territories; GAC-MAC Annual Meeting, Calgary.

• Rasmussen, K.L., Lentz, D.R., and Falck, H., 2009. Aplitic dykes at the world-class Cantung tungsten skarn deposit: indicators of fluid flow and mineralizing processees; International Applied Geochemistry Symposium, Fredericton. 

• Rasmussen, K.L. and Mortensen, J.K., 2008. Magmatic fluid compositions relative to fluorine and chlorine in tungsten-mineralizing intrusive systems; Goldschmidt Conference, Vancouver.

• Rasmussen, K.L., Mortensen, J.K. and Falck, H., 2007. Magmatic fluid compositions (F-Cl-SO₃) as an exploration tool for Cretaceous intrusion-related mineralization in the Selwyn and Mackenzie Mountains, southwestern NWT; GAC-MAC Annual Meeting, Yellowknife.

Awarded: Julian Boldy Certificate Award, Mineral Deposits Division, Geological Association of Canada: “for the most significant and creative papers presented at the Mineral Deposits Division session at the annual meeting”

• Rasmussen, K.L., Mortensen, J.K. and Falck, H., 2006. Geochronology and geochemistry of intrusive rocks in the Nahanni Region, southwestern Northwest Territories and southeastern Yukon. 102^nd Annual Meeting - GSA Cordilleran Section, Anchorage.

• Rasmussen, K.L., 2004. The aplitic dykes of the Cantung mine, NWT: petrography, geochemistry and implications for mineralization processes; CIM Annual Mining Industry Conference and Exhibition, Edmonton.

§  Rasmussen, K.L., Arehart, G., and Mortensen, J.K., 2010. (in progress) Preliminary S-O isotopic composition of Cretaceous granitoids in the Selwyn Basin and Cassiar Platform, Yukon and Northwest Territories. In: Yukon Exploration and Geology 2009.

§  Rasmussen, K.L., 2009 (in review). New geochemical, geochronological, isotopic, and apatite composition data for Cretaceous magmatism, NTS 105P, Northwest Territories; Open Report 

§  Rasmussen, K.L., Leslie, C., and Ootes, L., 2009 (in review). Chapter 4; Intrusive rocks; in: Geology of the northern central Mackenzie Mountains, Sekwi Mountain (105P) and Mount Eduni (106A) and northwestern part of 95M map areas, Northwest Territories, edited by E. Martel, S. Gordey, and C. Roots; Geological Survey of Canada.

§  Invited:  Rasmussen, K. L., Mortensen, J. K., and Falck, H., 2009 (in press). Magmatic fluid phase compositions (F-Cl-SO3) as an exploration tool for Cretaceous intrusion-related mineralization in the Selwyn and Mackenzie Mountains, southwestern NWT; GAC Mineral Deposits Division, the Gangue Newsletter.