Folks, here's a great essay explaining more of the true potential of diamond exploration in Alberta!
[--posted with consent--]
Marum president, Rick Boulay:
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Re: Your questions on the significance of the recent Ashton and New Claymore news releases, I have put together a few thoughts on the matter of "bedded" kimberlite deposits. Its complicated. By the way, none of the comments below incorporate any information from our current field program since we are running a really tight program and have not yet received a written report from the project manager. You can post this. Be sure to attribute it directly to me.
[Of course!]
I suppose we have always thought of the Alberta Diamond Play as being primarily a horizontal play with dragline mining potential as opposed to small shovels on small vertical pipes. The vertical pipes are very important both as deposits in their own right and, very likely, as ore guides to much larger layered or "bedded" deposits. These layered bodies are just beginning to emerge out of the mass of geological data that is being compiled by the ADP explorers. It will take a while for the perception to change, probably another six months to a year before the cartoon concept of a crisply defined vertical pipe fades into well deserved obscurity, to be replaced with a more accurate concept of erratically defined volcanic vents genetically related to volumetrically massive bedded deposits. However, this transition will not occur without misconceptions because the sedimentary and volcanic makeup of Alberta is very complex. This is because the Western Canadian or "Prairie" diamond play is unique in that the Saskatchewan and Alberta volcanic complexes are exposed, under the till, at erosional surfaces that coincide almost exactly with the original eruptive surfaces on ancient late-Cretaceous age sea floors. Violent volcanic vents blew episodically into the sea floors between 100 and about 75 million years ago and built up complex stacks of pyroclastic ejecta and sediments. These complete volcanic superstructures appear to be preserved and are just now being identified. There is a very close and complex interrelationship between the kimberlites and the host marine sediments. In our area to the west, in the Chinchaga and Peace River areas, it is more complicated because three different surface environments existed to "receive" the volcanics, namely: near-shore marine, tidal lagoon/deltaic and sub-areal or "dry land" environments. In the sub-areal environment actual volcanic ash piles or cones could actually form and remain stable over short periods, maybe a couple of million years. We know there was kimberlitic volcanic activity in the Chinchaga area and we have been defining longshore beach deposits for some time. However, for the moment anyway, the "horizontalization" of the ADP is being defined by pyroclastic rocks; by Marum last year, then a few days ago by Ashton and today by New Claymore. Expect to hear a lot more about this large tonnage diamond exploration alternative over the next few years.
Leaving aside the issue of whether or not sub-marine volcanic cones ever existed in the Ashton area, (not likely, but we don't know for sure) the bedded deposits referred to in the recent Ashton release are almost certainly pyroclastics, i.e. "hot grainy rocks", which were dumped at or near their current location after being blown out of the vent. They certainly may have been re-sorted a bit by water action but they are essentially in the same place they were a few minutes or hours after they were blown out and fell back to the sea floor. In current cross section, they probably resemble grey or brown clay-rich "sandstones" interbedded with darker mudstones (i.e. shales). When they are less altered to clays (i.e. weathered) the kimberlitic components consisting of micas and olivine give them a medium- to dark-green colour. The tonnage potential of these bedded deposits in a place like Alberta are orders of magnitude higher than for pipe deposits and their geometry is amenable to "Alberta-style" mining, that is, gigantic scale mining operations using draglines. The rocks are indistinct layered units and the mining is entirely driven by tailings disposal and reclamation costs. This is not very picturesque, but if the ore grade is present these operations can be very profitable over long periods of time as demonstrated by the coal and oilsand industries.
In Alberta, there is growing evidence that these structures are quite large. They were generated by episodic ejection of mantle derived material over long periods of time. To picture these structures, imagine a small turbine shaft aligned vertically with many rows of turbine blades arranged in a circular pattern. As the vent pulsates and throws out material into the shallow sea the material form "petals" or "blades" depending on wind and current conditions and the "turbine assembly" grows upward as the sedimentary pile thickens. The pipe, or vent, will be small, but over time it will build up a prodigious tonnage of "turbine blades" interbedded with marine or deltaic sediments. Its a good exploration model. It is supported by current geological evidence and that evidence will grow rapidly during the next year. Expect to hear a lot more about massive "bedded" kimberlite deposits and huge stacks of pyroclastic kimberlite slabs along with their production centres, the relatively small kimberlite pipes with diameters of only one kilometre or less.
For a while, the location of pyroclastic production pipes will be important as ore guides to the big layered deposits. In fact, our current exploration programs are focused on locating pipe vents (aka "kimberlite pipes"). There are valid technical reasons for this and explorers cannot ignore that the market is currently "pipe oriented" and does not yet appreciate the complex nature of these volcanic systems or their real tonnage potential. A 10 metre thick pyroclastic layer will contain roughly 30 tonnes per square metre or 30 million tonnes per square km. There is preliminary evidence for township sized bodies, or bodies in the billion ton range. At overburden depths of, say, less than 10 or 15 metres, dragline economics similar to the oilsand economics start to apply. The New Claymore pyroclastics occur at surface. Last year we defined some systems in the Chinchaga that were under only one to four metres of soil or overburden. The potential is staggering and the story will begin to unfold as exploration shifts into a "horizontal" gear.
I hope this helps. We are still learning. It is really interesting work. /
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Excellent discussion, Rick! Thanx.
Wow-- such tonnage potential.
(A township is about 6 miles by 6 miles).
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Have a great day!
-j
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