To: WillP who wrote (315 ) 12/20/2002 12:48:02 PM From: E. Charters Read Replies (1) | Respond to of 16206 I think the confusing issue is -- what is good chemistry in xenocrysts, how is it determined, and what statistics must the xenocrysts have with regard to that chemistry? If a promoter says "great chemistry" or "we have G10's" I will grant you that the chances of economics are not assured. However good chemistry is more than G10's. The factors that agur well statistically for pipe economics are: (these are biased towards non-eclogitic kimberlite) 1. pipe being in a regionally low geotherm (<40 mw heat radiation per sq metre). 2. pipe being about ~50+ miles of craton/archon edge, or in euogeosyncline. 3. large size of pipe. 4. other economic pipes being in proximity 5. high diamond content of pipe field. 6. tendency for pipe to be crater or at least diatreme facies at surface. 7. uniform lithology of pipe (some pipes are dual lithology). 8. low oxygen fugacity of pipe (low diamond resorbtion on ascent). 9. tendency of pipe to form large diamonds. 10. presence of eclogite in rock mass. 11. copious micro diamond content (rough indicator and lack thereof does not rule anything out). 12. presence of large number of deep purple, unfaceted pyrope. Kelyphitic rims is a good sign. 13. 14% or thereabouts of the pyrope having greater than 5.1% chrome and less than 2.6% calcium. 14. general garnet population being high in nickel if pipe is low in pyrope. 15. chromite population including ones with greater than 68% chrome. 16. presence of huge macrocrysts. 17. pipe being high in magnesium, high in potassium; low in calcium and aluminum by whole rock analysis. 18. presence of perovskite. 19. mica with reaction rims of reibeckite. 20. highly serpentinized olivine. 21. deep colour index of kimberlite rock mass (not a universal indicator and may be misleading) 22. high quality of diamonds found. 23. presence of rare diamond types. 24. lots of diamonds of large size found :) With all these factors, or many being present, the probability that you are not in an economic pipe, no matter where the pipe may be found in the world is starting to be fairly low. Note that certain groups of indicators in the above list are by themselves very important and can lead to very firm conclusions as to whether to spend money determining pipe economics. I am keeping that list to myself. It is also true that there are other omitted indicators. When is a pipe known to be NOT economic. This is the far thornier question. At what point do you stop sampling the pipe? With many eclogitic pipes of probably good economicsx this is very tough. This is why nickel thermometry is an imperative. It is probably true that many eclogitic pipes have been left behind, solely because they had poor small sample diamond counts and were low in pyrope. With a possible wildly economic eclogitic pipe, the diamond counts may be as low as .25 carats per tonne. With sample sizes of less than 5,000 tonnes, this grade and its economics may be impossible to determine. No testing in Canada so far would have discovered or revealed the economics of the Premier Mine pipe, which is the most economic kimberlite so far found, despite its grade of 0.35 carats per tonne. It is also very tough to recover diamonds in small plants. For complete recovery a plant has to have several carefully setup recovery techniques. One wrong headed plant in Canada used solely a "sortex" or x-ray fluorescence sorter to recover diamonds in bulk testing. Less than 30% of diamonds x-ray-fluoresce. The plant also needs very expert setting to get recovery of those diamonds. A possibly economic diamond field was left behind in Canada, perhaps forever. EC<:-}