EAST TENNESSEE GEOLOGICAL SOCIETY
January 2009 Meeting


Monday, January 12, 2009
6:00 - 7:30 pm

Pellissippi State Technical Community College
10915 Hardin Valley Road, Knoxville
J.L. Goins Administration Building, Cafeteria Annex

JANUARY PRESENTATION

Introduction to Karst Features in a Peatland Complex, Northern Ontario, Canada

by
Dr. Barry F. Beck, Dr. Wanfang Zhou, and Arthur J. Pettit
P.E. LaMoreaux & Associates, Inc.
Oak Ridge, Tennessee

The peatland complex of interest is within the Hudson Bay Lowland Physiographic Region of Canada. Underlying the muskeg is a series of glacial, marine and fluvial deposits overlying flat-bedded Silurian limestone formations. This series of deposits reflects the dynamic nature of the region over the relatively recent geologic past of approximately 8,000 years. Poor surface drainage and continuous isostatic uplift (1-1.2m per 100 years) have created a unique environment for karst development. Fluvio-karst has developed in the exposed bedrock along the major rivers as they entrench into the limestone; whereas organo-karst has developed inland in bioherms protruding through the peat. In the 1980&rsquos, discovery of kimberlite boulders nearby on a riverbed led to extensive prospecting for kimberlite pipes that are common host structures for diamonds. Mine development feasibility studies carried out over several years at two diamond-bearing pipes revealed karst features in the subsurface. Exploratory boreholes encountered voids and vugs of less than 50mm in diameter in the limestone. The majority of the voids are filled by fine sediments. Foundation excavations for a process plant revealed sediment-filled features that may be sinkholes and cave passages. Several large springs were discovered flowing into a major river. A 250m deep &ldquobedrock trench,&rdquo which is filled with interlayered till, peat, and glacio-fluvial and glaciolacustrine sands and silts may result from polygenetic processes including bedrock dissolution. The 220m open pit diamond mine started operation in July 2008, using large diameter wells to lower the water level of the karst aquifer. A program to monitor water in the bedrock, muskeg and rivers, and to monitor subsidence at critical facilities has been recommended to further understand how the karst features impact the dewatering effort and how the dewatering impacts characteristics of the karst features. The logistical difficulties of working in muskeg terrain in Northern Ontario may also be of interest.


NOTE: The following animation (approximately 25 minutes long) summarizes the formation of the kimberlites, as well as plans for mining, processing, and reclamation: www.discoverabitibi.com/animation/Geology.swf.


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