Still have more questions than answers, thanks to ASTROBLEME and Diamond Digger I think I'm getting closer Options

[TheRookie]

Thanks to ASTROBLEME and Diamond Digger for the responses in my previous thread. I really do appreciate the time you've taken to answer some of my questions.

I still have many more questions, but I think I'll start with just a couple and some observations.

Is this what I'd be looking for as far as kimberlitic type material?



Most of it is very black until after it's been exposed to the weather, at that point a yellowish and in some areas a rusty red sort of film starts to form on the outer surface. It's very crumbly, I can break up a lot of it with just my hands, or a light tap or two with a hammer. Most of it is fine-grained, but there are chunks that look more like concrete, and then there are some with more of a crystalline appearance. It's fairly heavy and has a lot of iron in it. After breaking it up about 1/3 to 1/2 can be picked up with a magnet. I also have a lot of nasty yellow clay mixed in with the sand/gravel, which is quite different from the reddish brown clay that I'm used to seeing in this area. If you wash the sand/gravel with water you get a nasty yellowish muck that takes quite a while to settle. Is that what you guys refer to as yellow ground?

[ASTROBLEME]

Hello TheRookie,

First a little background to help everyone understand more about diamond deposits. Prospectors, from the first diamond discoveries near Kimberly Africa, refer to any igneous rock containing diamond as kimberlite. This practice survives to this day although many geologists break out the types in detail and apply the proper nomenclature to the rock. Ideally, for kimberlite that has $ values, you'd want to have rock from the very deep diamond-stability zone that has erupted through the crust very quickly in order to keep most of the diamond crystals preserved. I think this eruptive process is triggered by large meteorite impacts so searching near those impact sites is what I would recommend.

The problem that modern diamond prospectors have is kimberlite rocks are complex hybrids consisting of crystals originating from 3 very deep mantle sources. The overall minerology of any given kimberlite type rock from each of the 3 mantle sources varies widely and accounts for the thousands of different compositions observed world-wide. This means that kimberlite looks different between locations and many times even within the same pipe emplacement. I have collected a wide variety of kimberlite specimens to help me better understand what to look for. You could also use kimberlite photos found on the www but an in-hand speciment is best. Garnets are a key component found in kimberlite but not all garnets are indicators of kimberlite. The minerals common to kimberlite include garnet lherzolite, garnet harzburgite, chromite harzburgite, spinel lherzolite, websterite, eclogite, grosspydite. You may also find peridotites containing phlogopite, potasium richterite, yimengite and hawthorneite. This mineral identification is far beyond what most diamond prospectors are accustomed to. I've spent lots of time and money running analysis and employing diamond savvy geologists to make sure I am finding what I need to when I'm out in the field. Most folks don't have the persitence in order to do that work but if you can seek to understand and look for what is referred to as the MARID suite of minerals, you will have a good handle on the more easily identified components of a kimberlite rock. MARID stands for mica, amphilbole, rutile, ilmenite and diopside. If your yellow ground or blue ground samples show these MARIDs... along with the proper garnet chemistry... then you likely have a kimberlite rock. MARIDs are best observed under high magnification and ideally by examination of a thin section prepared from the rock sample. Unfortunately, from the photo, I cannot see any MARIDs. If you are in a location where diamondifeous kimberlite has eroded, you should be able to find diamond(s) by using basic panning techniques. After all, the best indicator for diamond is diamonds.

Keep in mind that there are about 5,500 kimberlite pipes world-wide. Out of those known pipes, about 500 contain diamond. Only 50 or so pipes have enough diamond to profitably mine. If you can locate what is called a pan that develops over an eroded pipe, you can recover substantial quantities of diamonds that have been concentrated by Mother Nature. I would encourage you to have a competent geologist examine a specimen or two of your rock finds to formulate a proper answer to the "is it kimberlite" question.

Best Wishes,

ASTROBLEME