Sudbury has no nickel left. They mined the rim out 20 years ago. Maybe under the Onaping tuff buried 4 miles down, or deeper there is some stuff. There is this big trapezohedral mag shadow-block showing deep under the mid basin. In the middle of the tuff zone, in the centre of the basin (the Sudbury oval formation, 100 miles long and 50 wide, is a giant volcanic caldera filled with tuff-ash and outside the rim, south and along the rim are felsic pyroclastic flows that constitute the largest such outpouring of pyroclastic debris ever found. -
The myth you will hear is that the Sudbury basin was formed by a giant meteor, that blasted out a crater. In fact it was a giant volcano perhaps 15,000 feet high rising out of an inland sea called Ojibway Barlow, with a sea bed base in a caldera depression as large as the basin is now. The volcano was superheated with trapped steam from the sea water and when its main vent plugged with felsic lava, it blew its top like Mt. St. Helens, covering the entire area for 1000 miles around with 50 feet thick of volcanic ash. The force was about 1000 times greater than Mt. St. Helens. There was only one major volcanic explosion that came close to its size in North American and that was in Kansas. The ash explosion there covered most of the state to a similar depth. A good portion of the ash fell back into the hole left by the explosion and filled the basin about 3 km deep. Before that explosion, the volcano had been felsic, erupting constantly and violently with volcanic bombs that fell about 2 to 7 miles south of the southern rim, in the direction of the prevailing winds.
Lahars, nuee ardentes and felsic rhyolite flows flowed from the main vent down the southern side of the volcano into the rim area due south. Then the volcano went up. Before the deep basin was filled there were pulses of volcanism laying down lava flows at the edges of the entire basin, which did not escape the caldera. Gradually, after the main felsic and mafic pulses of the volcano, the system's feeders began to choke. It was during a hiatus between these two pulses of caldera filling lava flows that the ore was formed coming out of sea floor super-heated vents, which were laid down on the sediments of the sea bed. The lava flows came out of nearby feeders and covered the ore. Later the volcano exploded and the ash covered the ore still further. Still later the southern rim got pushed up by the Grenville orogeny or mountain building period. Tectonic movement of a craton trying to weld together to form the Pangea super continent pushed the basin into an oval shape from its original circular shape that most cinder-cone volcanoes adhere to.
The Grenville Mountains that pushed the southern rim flat rose 6 miles above the basin and perhaps 5 miles above the sea. Crystallographic geobarythermometry tells us the height from the metamorphic back-pressure from uplift isostasy that formed the mineral crystals of the Grenville rock. They were the largest mountains ever built on the planet, and would tower twice as high as Everest above their base. Denali, at near 20,000 feet above its base, the largest mountain mass in the world, would be dwarfed by the giant Grenville Scarp which stretched from Michigan to New Brunswick in one massive metamorphic uplift. (The Himalayas exist on a plain 17,000 feet high. Many peaks of the Cordillera are almost as high above their base as Everest.) In a little more than one half one billion short years, the Grenville Mountains were gone. Their very height and steepness contributed to their fast decay.
You can see the radial sea shock quench structures in pyrite nodules from the Creighton mine. If the ore had been formed by other than vents pouring out into sea water the nodules would not have those radial structures. They would not even be nodules. Fast quenching would not occur with cracks filled with lava.
Further still, all the ore occurs at embayments in the sedminentary sublayer.. the resting bed of the ore.. now if the sed sublayer were an ocean bottom, the embayments would be valleys in the sea floor, which we now see uplifted by the Grenville push, so we now see the end on of the valley. Naturally sea floor vents would drop their ore precipitates chilled by cold seas on the valley beds.. not the hills.. so the structure fits. Why would the ore be in the valleys now uplifted if the ore were emplaced in later vertical valleys along planes of weakness between the old possible sea bottom and the overlying rock.. proven younger now by age dating.. what fortuitous planar effect was there to make concave outward contacts more productive than convex.. of course that is a stretch of the contact base isn't it? And your credulousness... planes of weakness and pushing in lavas favour "out-oomphs" not in, 100%.. and the leakage into the fractured sublayer... that could happen with both systems, so there is no denial to the more consistent sedimentary theory.. Fans of the old weak plane system of ore emplacement do not explain how the ore did not push the folds in the rock into the more yielding inward basin, which did not yet have the late tuff on it.. and why it instead perhaps pushed into the miles of sublayer around the basin to form the putative perhaps late embayments by force.. balderdash embayments of confounded weakness one could call them. Geological deus ex machina to save lava man.
The ore-lava theorists would have you believe that the entire basin was intruded at one and only one horizon between the mafic and the felsic norite, fortuitously for 200 miles of rim. Quite the amazing plane of weakness not to have one other afterthought of mineral emplacement. Sort of like two layers of rock with all other layers having contacts of cement but the two norites having peanut brittle at the contacts -- allowing no other zones of emplacement before them. And then the age dating progressively from oldest to youngest from rim to inner basin is: sediment sublayer, norite one, norite two, and then tuff.
In other words, the order from bottom rock layer to top fits if you have sedimentary succession. If the layers are intrusions, the age from rim or bottom edge of the volcanic basin to interior of the caldera which looks all the world like a filled upside down layer cake, is purely accidental. Two accidents or logical succession? The 1964 PhD thesis was that the the basin was a sediment subaqueous layer cake. The 1948 thesis was that it had to be hydrothermal. (Hot water deposited perhaps in veins) The tempterature of formation of all the pentlandite is 270 degrees centigrade. The exact temperature of nickel if is vent dissolved in a super heated acid and cooled/precipitated on hitting seawater. The same process as the copper zinc vents of the Straits of Jaun de Fuca. Today being deposited on the sea bed at 4000 feet deep. And what do we have in the center of this Sudbury basin? Obvious vent hot water sea bed copper zinc in the Onaping tuff. The Vermillion River deposits, briefly explored by Falconbridge. Long acknowledged as subaqueous sea-floor type. But in an about-face, the pundits of post 1948 would have us believe that despite the copper-zinc in the center being laid down later in a subaqueous way, that process could not operate at all in the same basin for the nickel, 30 miles away and perhaps 5 million years earlier. Why not? Same basin, and it was apparently sea water covered over for the tuff not much later by geologic time in its history...
The inconsistencies of the lava flow thesis are embarassing to CDN geology and it's time these texts were quietly burned in a lava flow, say off Hawaii, or Indonesia, where sea bed processes presently lay down ore, in blatant and high handed defiance of postulated theory -- it would seem.
These sea floor processes are the only "evidentiary" processes we know of that create massive sulfides. All other attempts to come up with ore bodies by other processes have problems with access to conduits, temperature of flow of the necessary sulfide veins, etc.. If anyone has ever tried to pour molten pyrite, you find you cannot do it without a flux. It will not course thru veins like water. The minute it hits cold rock it will freeze as solid as a glacier. As a matter of fact if you heat pyrite to 1900 F degrees it will simply crust up and pour in blocky blobs of crap. I tried it. I fire assayed for 20 years. If you want a "water pour" you have to add silica by twice the 'stoichiometric weight' to pyrite and lead oxide stoichetrically half equal to one quarter the silica. Add borax and sodium carbonate, or sodium hydroxide quarter equal to the silica. This will be what is called a bi-silicate melt. The minor constituent with the oxides is not the pyrite.
Without the oxides of silica, lead and hydroxide, the pyrite will not pour. And when it does it will be a mass of silicates, not massive sulfides. Otherwise by itself pyrite will congeal like putty. The question is do these fluxes or their equivalent allow the pyrite in the postulated massive sulfide lava vein to first fractionate at the base of a deep melt, then mix with a suitable flux for transport, then drop out of the flux to enter the vein under pressure? I think not. The only way sulfide gets to the surface is either disseminated in some granitic melt, or as acid water-leached precipitates.
The Sudbury basin veins are either a normal vein-type or a hydrothermal sea-bed vent-type sub-aqueous surface-deposited low-temperature VMS. Volcanigenic Massive Sulfides, or, take your pick, to go way out on a limb, SEDEX. Sedimentary exhalative. Geologists may seethe, but they are the same thing. Only difference is the supposed distance from the volcano. This fits exactly with the known laboratory-determined temperature of formation of the Pentlandite. If you ask the lava theorists why the nickel sulfide was formed 800 degrees centigrade cooler than the lava it supposedly came from -- when the sulfide precipitated, all you get is glissades away from the topic. They have no answer.
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