kimberlite Genesis

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Kimberlite Genesis – a continuing story, Part 1. (external - login to view)

Posted on December 11, 2013 (external - login to view) by Louis Hissink (external - login to view)
It seems a previous post on the Ubehebe Crater (external - login to view) raised interest among some geological peers in that it lacked ‘scientific evidence or based on non peer reviewed science’. In addition we have an example of geological nomenclature evolution in that the crater has now evolved into a ‘maar’. A maar is a broad, shallow crater, typically filled by a lake, formed by the volcanic eruption with little lava, so my dictionary states. But maars lacking lakes are simply craters, and the Ubehebe crater can hardly be described as shallow either.

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There also remains an ideological war between the dark-suit diamond geologists (De Beers camp) who interpret kimberlites as essentially deep seated intrusive-extrusive magmatic eruptions, (The Clement-Skinner model), to the earth’s surface, and the Lorenzians, who favour the phreatomagmatic model of eruption in which ascending magma encounters water saturated cover rock before eruption to the surface. (Incidentally I’m a member of the dark-suit camp, but not dogmatically inclined from long experience in the mineral exploration profession, in that when the facts change, I will change my mind).
We dark-suiters have a well tested rule of thumb concerning kimberlite occurrence gained from 150 years of mining and exploring for kimberlites over the world, and that is that kimberlites are essentially spatially random occurrences with the diamond rich varieties uniquely restricted to the crystalline basement or stable cratons. Put simply kimberlites occur where you find them, the Hawthorne-Hissink model. This model goes against the geological grain of most mainstream geologists, especially the Australians, who adamantly assert that all volcanic eruptions are structurally controlled, and hence kimberlites must also be so controlled, and hence ‘predictable’ from a structural perspective. This structural dogmatism seems to be derived from the almost religious devotion to the belief of ‘plate tectonics’.
It’s interesting to note that the Western Australian Geological Survey has recently published a book on “The Birth of Super Continents and the Proterozoic assembly of Western Australia” by Simon P Johnson. On page 42 ending the discussion of the Proterozoic alkaline intrusions including the diamondiferous Argyle Lamproite, as well as the younger lamproites of the Canning Basin in the west Kimberley, is the sentence “The tectonic driver for prolonged and punctuated melting in this region is currently unknown”.
In other words mainstream geology hasn’t a clue what natural processes formed these peculiar, occasionally diamondiferous, alkaline intrusions. It certainly can’t be attributed to ‘plate tectonic’ processes.
A seminal scientific paper written by Barbara H Scott Smith, Near-Surface emplacement of Kimberlites by Magmatic Processes but not published in the peer censored journals because “much of the data for kimberlites are collected by economic geologists”,”whose priority is not publication” summarises the two dominant kimberlite genesis models, most of which isn’t in the public domain. This debate over emplacement model has lasted at least two decades, (as of 2006), and continues to the present day.
Scott Smith suggests an impartial, independent review of the two models is required, which I would interpret the same way that the late Fred Hoyle wrote last century, but paraphrasing him, that when a scientific problem continues to be the object of acrimonious debate, then perhaps both sides are thinking with the wrong ideas.
So what prompted me to suggest that the Ubehebe crater might be a proto-kimberlite associated with an electrical discharge? This story started during the late 1980′s when I was in charge of diamond exploration for a small-cap exploration company near Kununurra in the east Kimberley region of Western Australia. Previous exploration recovered anomalous diamonds from the alluvial gravels in the Ord River, and exploration during 1988 concentrated on repeating those results by resampling and processing the source gravels near the Kimberley Research Station.
Two styles of diamonds are known to occur in the Kununurra valley – small rounded octahedra ubiquitously found in the gravels used for construction purposes in the Ord river itself, usually averaging about 10 to 20 points (100 points to a carat), and larger, clear to a brown tinge, often fractured, diamonds in active river trap sites and exceeding 1 carat in size. These larger diamonds are not derived from the Argyle AK1 diamond pipe 150 km upstream from Kununurra, but from an unknown source located in the Kununurra Valley.
Upon confirmation of the earlier results, an airborne magnetic survey was completed over valley upstream of the anomalous sample site in the Ord River. It was interpreted by a very competent geophysicist who noted the existence of a specific magnetic anomaly of interest, which I suggested was probably a buried kimberlite pipe.
The usual exploration procedure is to drill test targets to identify them, but before this could be done, one had to complete an aboriginal heritage survey over the proposed area of work. A competent anthropologist was brought in and given authority to conduct an “at arms length” survey over the exploration tenement. This took a couple of days.
On completion of the survey the anthropologist briefed me on the results which he divided into good and bad news, bad news being sites not to be disturbed, and of which there were a couple, but of no geological interest, and good news being the rest of the tenement area, which was of immediate relief. However he discovered a potential snag.
During the survey the anthropologist was quite surprised to be spontaneously informed to let the client know (me and the company I worked for) about the existence of the place known to the Aboriginals as ‘Malawon’, the place where the Barramundi jumped into the ground. Not knowing what this ‘barramundi’ story was about, I was soon to learn that it was related to the Argyle AK1 story which, according to the local aborigines, was the place where the barramundi jumped out of the ground. The problem was that the location of where the barramundi jumped in, called Malawon, was also the location of the anomalous magnetic anomaly identified from the geophysical survey. This survey result caused an immediate problem of understanding how tribal aborigines could have possibly known of a geological event occurring over 11,000 million years ago before any humans, or for that matter life, appeared on the earth according to the prevailing paradigm of neo-Darwinism and biological evolution. Coincidence?
To be continued
Mafics and ultra mafics don't just happen because there is volcanism. Greenstone deposition requires very specific conditions.
I appreciate your sentence but could you expand it and make a paragraph please. Why do you deprive us? Magnetic anomalies are caused by electrical anomalies, current makes diamonds.
Any EM would be from Si with very low current. Nothing major. The electric phenomenon of pyroclasts is all together different.

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