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Gold/Mining/Energy : Trump's 12 Diamond Picks, Discussions Limited
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To: gg cox who wrote (1204)8/27/1998 12:29:00 AM
From: Walt  Read Replies (3) of 2251
 
Greetings all, just in town for a couple of days.
Lets see if I can sort out this strike and dip thing for you, because that explaination I find a tad confusing.
Imagine that we are out walking across a dessert and we come across an old paved road. The strike if the direction that the road is going.
As for dip I put a level onto the road at right angles to its strike and that is the dip. In the case of the road its dip could be zero (flat lying) or it may have a slight dip say 1 degree. Now if the road were running north south then the dip would be either east or west. Dip is ninety degrees to strike.
Now if we put a hole into the road at niety degree to the dip we get the roads true thickness.
So strike is the direction that the road is going and dip is the angle of the road to horizontal.
As we walk along the road taking our measurements the strike and dip will no doubt change. So might the thickness of the road.
If you put the strikes dips and distances on a map, then we would have mapped the road.
Now if we could remove all the overburden from snap lake then we could walk along the kimberlite dyke taking strike measurements and apparently it runs N-S. If we turned at right angles and could walk down throught the kimberlite into the ground (or if a tunnel were put in removing the kimberlite) then we would be walking east down the dip.
So strike is the direction a thing is going and dip is the angle at which it is lying and strike and dip can change over distance as can thickness.

So in geology in the field you find something. In this case its a dyke that lies under overburden so it was found by drilling. You put in a hole hit a width of kimberlite but you really dont know its true strike dip or thickness. You know the angle of your hole you can measure angles on the core so you can do some calculation so you may know its apparent strike and dip and thickness. Each time you put in a whole you learn more. By this process you are mapping the body three dimensionally.
You develope a model of what you have but with widely spaced somewhat random holes into it it is an aproximation.
Lets say you dig a hole down through the overburden to the kimberlite where it comes closest to surface. Now if you went along stike 100 paces and dug down through the overburden you would expect to hit the kimberlite. If you didnt you would dig a little to the east or west and hope to hit it sooner rather then latter and you would revise your strike accordingly.
You could start to dig down dip or you could say ok lets do some more drilling. We take a drill and move it along surface to the east and set it up. We think the dyke dips at ten degrees, so try to drill down at eighty degrees, so we will hit the dyke at right angles or ninety degrees and this will give us our true thickness. If we do our measuring correctly and our model is working then we should hit the drill at lets say two hundred feet. If it is less then that the dyke has flattened out to a dip of say five degrees or it might be steeper then predicted and changed to a dip of 15 degrees.

To drill another hole you could move the drill further east and test the dyke deeper, down dip or you could move it north and drill the dyke along strike.

By now I'm sure I only have the dedicated reader with me.
What WSP is doing is detailed grid drilling. As they drill the holes a fairly accurate picture or model of the dyke will immerge then tonnage calculations can be made with some degree of accuracy.
Gut feeling or statistics will tell you how accurate your being. If you drill the dyke and its strike, dip and true thickness are constant then you can be very safe in you calculations. The more the strike dip and thickness vary the less sure you will be. SO if fifty holes were drilled and things were constant including grade then one could say ah yes we have so many tons at this grade with a variablity of plus or minus 1%. The more variable it is It could be X number of tons plus or minus 20% and a grade of Y plus or minus 10%.

Hope this clears things up for people a little.
regards Walt

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