Who the hell knows in this cockeyed world? The people who run the Aviat play told me that the chemistry thing is a mystery, as there is both eclogitic and perdotitic chemistry in both the Aber pipe AND the Diamet pipe. They said the eclogitic (non pyrope) element of the chemistry is "more important" than the pyrope. (a better indicator?.. i.e. the pyrope can be ignored to a degree if it does not conform classically say to Yakuts standard... in other words the pyrope could have more calcium and less chrome and still be "good"? We are guessing ..)
I would say that all the various elements do is indicate pressure and temperature, so they are just indicators, not contributors.. If they both exist in the same pipe, so be it.( but which do you depend on?) It is strange for this to happen, but in theory both components are "down there" in the chromite harzburgite layer where diamonds come from. The strange thing is that there is not more eclogitic chemistry in peridotitic pipes, as most authorities agree that the primary contributor of diamomd to the kimeberlite, no matter what chemistry it is, is the rock eclogite. But we have this thing about diamonds containing inclusions of extremely subcalcic pyrope in 90% of the economic pipes. Where did they come from? Go figure.
You never hear people following eclogitic garnet trains with nickel thermometry, and announcing it. It is the single best technique, an accurate grade predictor, and cheap too. They just don't know how for the most part. They can sell G-10's in fact, so they do that. Aviat I am told is an eclogitic area, with some pyrope too.
The nomenclature G-10 is the categorization developed by Dawson many years ago, before it could be thought of being applied to kimberlites and diamonds. In fact, Dawson's G-10 pyrope is not a pyrope from a kimberlite but may come from a metamorphic rock as well. It is merely a high chrome magnesian garnet, which may or may not be that low in calcium. Kimberlitic garnets are special creatures. They are usually rounded, not faceted with crystal faces, display a blackish reaction rim of kelyphite, may be very deep purple and are deficient in calcium compared to other garnets. This G-10 stuff is just news announcment pap to drive stock. If they want to impress me they will show pictures of the garnet and the position of a statistical group on a graph of calcium against chromium contained. And if they really want to show me competence, they can show the contained nickel and zinc of all their garnets not just the pyrope on a pressure/temperature graph. They they are cooking with gas. Then I will buy stock.
EC<:-} |
