Tahera Diamond Corporation (TAH:TSX) is a Canadian diamond mining company headquartered in Toronto, Ontario. Tahera's Jericho Diamond Mine represents Canada's third, and Nunavut's first, diamond mine.  

Question asked on Jun 12, 2007 by Rene Sugar <rene_sugar2 @gmx.net> I've got a question that you might want to ask Tahera.  From what I understand, RC drilling breaks up the kimberlite. In one of Tahera's reports, they mention the grade being affected by the type of drill bit used. Also, from what I have read, the 2005 Muskox test results were based upon samples from core drilling and not RC drilling. The 2006 Muskox test used large diameter RC drilling.

Corporate Head Office Tahera Diamond Corporation P.O. Box 1020, T.D.C. Postal Station 77 King Street West Toronto, Ontario Canada M5K 1P2 Tel: (416) 777-1998 Fax: (416) 777-1898 Toll Free: 1-877-777-2004 Email: investor_relations@tahera.com Email: resume@tahera.com

Given the test results based upon core drill sampling, the test results based upon RC drill sampling could be significantly under reporting the grade of the Muskox kimberlite depending upon the type of drill bits used.

What type of drill bits were used by "North West Sequoia drilling of Calgary" to collect the last Muskox sample?

 From Tahera's own data, using RC drilling, the grade returned varies significantly depending upon the type of drill bit used.

Bit        Grade
---        -----
Drag       119 cpht
Mission     47 - 65 cpht
Ballistic   29 - 49 cpht
Digger      12 - 17 cpht

http://tahera.com/Theme/Tahera /files/OtherReports/rocking .pdf

Here is the excerpt from the report:

"Information received late in 2005 from De Beers indicates significant breakage of stones during the RC drilling and sampling program. A number of different drill bits were used in the program resulting in a wide range of diamond breakage and recovered grade. The
two drill holes which used a Drag bit had a sample grade of 119 cpht while the Mission bit
intervals graded between 47 to 65 cpht. The intervals using a Ballistic bit averaged between 29 and 49 cpht and the Digger bit intervals averaged between 12 and 17 cpht. Recoveries also varied depending on the type of drill bit used. In total, 37% of the diamonds recovered in the RC sample were significantly broken (as defined by more than 5% of the original stone being removed, due to fresh breakage).
This RC sample may have pulverised the rock to the point of crushing larger diamonds. The De Beers report states that suggestions of stone breakage are much more evident in the drill chip [RC] sample." 

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