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Gold/Mining/Energy : Gold and Silver Juniors, Mid-tiers and Producers -- Ignore unavailable to you. Want to Upgrade?

To: marcos who wrote (61370)	9/27/2008 11:56:04 AM
From: E. Charters	Respond to of 78435

I knew earth was never that hot. When I went to town on saturday nite there were always a lot fewer fights per hour than people claimed. The same applies to geology. If there were that many volcanoes and hot rocks we would find an annealed area beneath all the seds. Of course a lot of it had to be above the eutectic, as you can see heat sigs in alteration everywhere, but these alteration regimes are relatively subdued and extend only a few feet from the vein. i.e. the rocks had to be a lot colder and more solid than the injected steam or magma. I believe most gneisses were formed from gold pressure, over a long period of time. Most sulfide orebodies from the time of the archean formed at around 375 C degrees, to 700 C degrees. Relatively few were formed hot. About the temp of super heated steam or water, showing ocean floor quenching from 2.8 billion on. If there was deep water and islands it could more or less have been like hawaii or the pacific, or iceland. 100 million years of that and we have loads of volcanic islands. Spread the CDN shield volcanoes over 1 billion years and you have a regime that is no more active than mexico and italy are today, geologically. And there are as many black smokers spread over 4,000 miles of pacific ocean floor today as there ever have been. Sudbury and Timmins were among the most active Plinian areas of the world with more felsic phreatomagmatic (explosive) rhyolites than any where else in the world. The most common volcanic rock, spread 100's of miles from the volcano center, is a tuff, which is a cold ash or hot ash flow. Tuffs are the most common sheared sediment/volcanic which contains gold and other ore. They form competent to semi competent fracture and shear conduits upon the inevitable orogenic to non orogenic deformation processess of uplift and tectonic transpressoin and movement. This implies a long history of explosive volcanism formed the core of most volcanic rock areas of the world for the last 2.8 billion years. The most common rock at depth and in old mountain building regions is a gneiss. These are layered rocks transformed by pressure and mild to high heat. their mafic and felsic areas tend to segregate on squeezing and they form new minerals from heat and pressure. down about 8 miles most rocks are gneisses. so if we see gneisses on the surface we may assume that the tectonic pressures were extreme and the resulting orogenies formed from this pressure must have given rise to very high isostatic uplift.. probably plus 4 miles or more, possibly 6. grenvillean orogenies near sudbury would be an example. this probably explains why the Sudbury basin is now oval. the mountains at its edge would have been 3 times higher base to top than everest. This is explained by the degree of metamorophic grade of pressure evinced by southerly gneisses. marbles and silicates of copper indicate this. Just about all sediments and volcanics of the archean and proterozoic have been pressurized and heated to a degree so they are in part metamorophosed, leading to their appelation, meta-volcanics and meta-seds. If a sed is not metamorphosed it is likely only weakly consolidated! the very act of consolidation of grains causes a degree of metamorphism. most rocks put out of a volcano are in fact sensu strictu sediments as by definition a sediment is a rock that is formed on the surface by deposition. all volcanic rocks fit that description so we may say their character is sedimentary, particularly where it comes to tuffs, as air or water born tuffaceous rocks really do get transported and laid down on the surface in a random fashion influenced more by gravity than earth pressures. When searching for gold mines, 95% of which are proximal to mafic volcanic vents we find them most of the time near a tuffaceous sub aqueous vent system that also emanates blob lava called pillow lavas. these systems are almost always accompanied by mica minerals both primary and metamorphically - hydrothermally formed. much of the time we find them at the base of island arc chains, formed under about 5,000 feet of sea water, and near felsic porphyries. an identical regime accompanies sulfide orebodies often. they are closely associated with layers of volcanic rock and are often found at the contacts of two surface laid rocks emanating from a volcano or near a volcano. For this reason we may suspect that they are also laid down at the surface as to assume they were formed at planes of weakness is perhaps too fortuitous an origin. otherwise they would always seem to have a vein character and if very voluminous to be coarse grained and obviously intrusive. For this reason a sea floor origin of most massive sulfides is favoured. And if you check out the temperature of formation of the minerals you will find it to be close to a super heated water or steam. The origin of mine quality minerals being found near volcanic vents has been observed since Roman times and is described as the most common source of mines in de Re Metallica written in 1450. Hydrothermal veins being aqueous in origin and of volcanic flows and found in fissures near vents was intimately known by this period. EC<:-}