Everything in the "shield", or just about everything, is pre-Cambrian.
That is probably why the call it the Pre-Cambrian Shield.
The Cambrian era starts at only 500 million years. This is classically the beginning of macroscopic life in the geologic time scale. It is now accepted that even the early proterozoic, extending from 1.8 billion to 1.1 billion years ago, had microscopic life such as may be recorded in algal stromatolites, and in the consolidated radiolarian ooze of ancient sediments. These soft bodied very ancient creatures were not preserved except as echoes of their former selves; metamorphosed, petrified ghosts in microscopic rock formations.
Two billion to 4 billion year old ore vents would later be host to bizarre life forms, which to this day occupy the unique ecological niche of living off these hot water vents. Underwater geysers, super saturated in metals, now lay their valuable sediment in nearby basins when their superheated fluids contact the cold ocean. The resultant ore deposits have been continually formed at the edge of colliding continental plates where the rocks becomes molten at depths between 15 and 100 kilometers.
Far before that, when the earth did not have oxygen in its atmosphere, and when the rock surfaces often would boil lead, the ancient vast ore deposits we mine today were formed on a sea bed supposedly barren of life. These deposits are called VMS, and Sedex. VMS stands for volcanigenic massive sulphide, and Sedex stands for sedimentary exhalative. Iron formations, both sulphidic and oxide, (the latter being called taconites), were formed in the same way; in shallow sea bays, a few miles from a volcano, laid down rhythmically by hot water vents. Most sulphide ore bodies formed as the result of metals precipitating out of hot water geysers, which were on the bottom of the ocean floor. The time they took to form may have only been 50,000 years. Special conditions of burial and uplift had to take place in order for them to be preserved for 3 billion years.
Nearly ever ore body mined in Canada was once laid down at the base of an island chain of exploding Volcanoes, from 3 billion to 1.1 billion years ago. When I say exploding, I mean that precisely. When these volcanoes got to a certain state, they plugged up with acid rock, and then they went bang in a most horrendous way. One in Kansas exploded and covered the surrounding 4 states with ash about 50 feet deep. The size of this explosion has been calculated as equal to a billion one megaton hydrogen bombs. Probably the resultant ash cloud covered the sky for a few thousand years, and caused many animal extinctions.
The ore bodies formed then were laid down flat. Nearly all of them today stand on their edge, indicating that the degree of compression and folding of the rocks since then borders on the catastrophic. Ore that was on the seabed at one time was raised up to a height of between 6,000 and 30,000 feet ASL, and then buried perhaps 1 to 5 miles below the surface. If New York City had been on the planet then, it would now be a silcate-iron-copper-aluminum ore body about 200 feet thick and 20 miles long, wrapped sinuously around a few east-west trending faults. We might see the odd remnant girder or traffic light.
God was only thinking about building man and chicks at the time. What he was busy with then was whipping up fancy mineral bodies for his later complex self-determining carbon based robot-beastie to use in innovative ways. Two thousand, 800 million years later man would come along, believing he was the key to the universe. Great events gone before him, for two thousand times longer than he has been around, should tell him that he is really of no consequence to the evolving planet. A proper sense to have in the study of geology is one of awe at the incredible history of the sphere, written out before us in the rocks. Once a mass of land was centered on the earth, then it split apart and it drifted and spun away into continents, spreading itself across the globe. As the earth cooled more life formed, and gradually grew to enormous size and complexity. The the planet cooled still further, and in the last .06% of its history, apes began to scratch their head and say "whuffo?" So here we are. Still cooling, and worried about getting warmer.
Although most of the rocks laid down then were complexly folded, some are still preserved near their original attitudes. I have seen the roots of ancient volcanic mountains still sitting on their bases. One such monster I observed had a base about 6 miles wide, but it was only about 200 feet high. At one time it was 15,000 feet high. Near its base was sign of copper, and felsic rocks. It has bever been drilled, and the odd conductor is about. The target is in between the rocks that gave birth to Kidd Creek and the Horne Mine some of the world's largest and richest ore-bodies.
Ever throughout time these zones of subduction and continential plate collision have been giving birth to orebodies. Later the ore is folded into the earth's crust, preserved by mountain building, and then moved inland as the plates continue their westward march.
At these folded-in, preserved volcanic-sedimentary horizons we prospect today, looking for the signs that we are in the same basin, fault, or age of a previously-found productive body. If we looked at the contemporary deposits and their heat engines, we would see what our target was clearly.
The ore has to have been deposited in basins once parallel to a coastline, and thence compressed and folded perhaps once from east-west pressure, and thence north-south. The source of the heat, volcanism, or the surface expression of the main rock vent does not have to be nearby the vent-source as was once thought.
150 miles from a contemporary explosive volcanic regime, (Mt. St. Helens) an orebody is forming today, 1500 metres beneath the Straits of Jaun de Fuca, fed by a hot water vent pregnant with copper. If one considered that Timmins was a volcanic centre of a certain age, then considering this modern scale, one would be quite comfortable exploring for related copper-zinc deposits from North Bay to Moosonee, and from Kapuskasing to
Val d'Or
-- ed ...
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Kwestione 64 dollaramus -- Whuffo Worthington-Totten 1 and 2?
Date: Sat, 7 Feb 2004 08:48:24 -0800
To: E. Charters <echarters@sympatico.ca>
Subject: sudbury
"Hi;
Totten 2 is a mine of INCO's on care and maintenance. It is SW end? of the offset from Creighton.
Creighton, Gertrude, Lockerby, Aero-Kidd-Crowflight, Worthington,
Totten 1, Totten2 from NE toSW With Crean Hill a splay off this offset. All these offsets seem to be radial ore bearing fractures."
# what do you mean "seem to be radial ore etc.." Either they are or they aren't. Make up my mind.
"Around the N and E rim the ore seems to be in concencentric fractures.
Mialex appears to be the radial fracture from Murray mine, North
mine, South mine, Kelly Lake mine intersecting the concentric fracture of Makada Lake. The Murray fault runs through Lively and a radial fault runs from the Murray to Makada Lake which in turn has parrallel faults. The Grenville front collision no doubt produced other ore bearing fractures such as the Manchester, ESE of the basin."
-- Junior Bit Reamer (with # comments)
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I hear yah reamer and I second that opinion -- (with a 13 no-trump sed theory)
I guess jeeallohgee is an imperfect art, not a deterministic science.
All these jeeallohgists going around trying to prove they are "right"! Kurt Godl could have told them that it is impossible to prove the rightness of a system of reasoning from within that system. So geology will never be "right". It can only validate its pre-set terms of reference. A good set of terms to start with is "this system is always right, even if it seems wrong". Such a frame of reference is religion. No religion tries to justify itself, which proves they already know what they are up against, unlike science. Religion is therefore more advanced logically than science.
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My geological religion believes that the ores of Studbury are hydrothermal as the gent who wrote the book on Studbury fully believed. Those at the rim of the basin are see bed sedimentary-exhalative or volcanigenic (Take your pick. They are the same process) and some of the rim and offset dike ones are vein hydrothermal injected, such as the Strathcona.
At the time, the 1948 observer said that the Studbury area was the largest area of phreatomagmatic (violently explosive) felsic volcanism in the world. He also stated that if the basin were to be magmatic, it would have to have been overturned. It is unlikely with its successions that it was, since younger rocks overlie older as you progress inwards to the center of the basin. The age of the norites is very near the presumed age of the ore, and the age of the felsic norite and the mafic norite is impossible to differentiate within the bounds of the error of the age determination. This, with the extremely fine grained nature of the two norites, is consistent with them both being flows that covered the ore just after it was exhalatively laid down in the emabyments along the basin rim it is nearly always found in.
This natural succession is much more compelling and consistent with the interior basin sedimentary processes and the later known volcanigenic copper-zinc in the interior of the basin, than the almost impossibly co-incidental and fortuitous deus ex machina of having the ore inject itself along a contact "plane of weakness" all along the rim as the magmatic theorists say.
The "plane of weakness" canard has some support in that the Whistle and Worthington offset dyke systems do control ore, and some veins do look dendritic in plan, offering the possibility of injection. Hydrothermal injection is just as powerful a possibility as magmatic, and it explains the extensive flow, and low temperature characteristics of the pendlandite much more persuasively than magmatic theories. In all fairness, contacts that are squeezed that may have gross differences in plasticity, such as felsic norite and the highly fractured sublayer sedimentary zone, do evince in many areas, preferred loci of injected deposition. You would expect with the highly fractured nature of the sublayer for it to be veritably flooded with intrusion. The fairly quiet nature of the sulphide encroachment onto the sublayer does not speak powerfully that it was intruded so violently by high pressure magmatics.
The whole magmatic theory ignores several important structural elements, invokes will nilly a huge unexplained fortuity of emplacement, and is very weak on how massive sulphide flows, or fractionates from its very low % silicated nature all at once in such a massive event. All over the world layered separated massive copper-nickel and copper-zinc has proven exhalative and volcanigenic origins in sea bed basin embayments, but Studbury has to the a hold-out on the very weak underpinning of geochemical grounds.
How so?
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That said, the Grenville and its long history may have much more to do with the Studbury basin than has previously been loudly said. Certainly the extreme deformation of its once towering mountain ranges (30,000 feet of more above their base or 2.5 times higher than Everest) -- must have had much to do with laying out permissive dilationary structures in the basin. What lies outside the basin proper in the Grenville? Pacific Northwest Capital has struck it rich in an intrusive far outside the basin. Is there more? How far may we be from a volcanic centre to reap related ore vents? Contemporary experience tells us that 150 miles is not too far. In the straits of Jaun de Fuca off the left coast, sea bed orebodies are forming this very day at least that distance from Mt. St Helens and the Coastal volcanic extrusions. If you draw a 150 mile circle around Studbury you are in Kirkland Lake, Chapleau, Blind River, Sultan, Elliot Lake, Temiscaming, South River, or Midland. That is quite an area to look for related ore.
It might be there.
-- ed ...
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