As most people know, I don't thought, I just hold forth. If I thought, I would be wrong or right, not just dimissable politically for cant and have agend. It is morally wrong to have agend, that I must, as I am not selling stock, so I must either be pro mining or anti, as the liberals are. (steps carefully off soapbox ... it's the takedown kind, which he begins to dissemble. When he finished folding it to billfold size and opens his trenchcoat to put it in an inside pocket, it is revealed he is wearing nothing but socks and a hip flask underneath.)
Gravitas animals are strange. They should by field laws (shape of body and square law recession of field by Maxwell/Newton calcule.. simple stuff) reveal mineral deposits of mass differentiae. Do they? hmmmmm Gravitas machines were first developed in the 19 teens by Gulf for oil probing in Lousiana and Texas. By 1920 they were finding salt domes, and oil traps galore. They had the facility of that. Phelps Dodge and St. Joes tehn applied them to Lead and copper bodies with alacrity. Trouble is in copper the felse rock is light and with porphyry, the copper itself few and far between. It's 4 to 10 million ton mass will not change the background that much. Lead is a bit different. PbS is 8 SG. And lead bodies go to 30% Pb. Missouri and Utah lead roll fronts have to show right? Yep they do. So one such body was mined out and they tried the gravity on it after. LO.. the gravity anomaly was still there!. For 50 years they did gravity all over the States and Canada, and while orebodies have gravity anomalies beside them, they are often so large it is hard to tell if the anomaly is related to the ore or not. And to top it off, no mine found in NA so far has been the result of drilling a gravity anomaly. AND no gravity anomaly yet drilled has been found to be ore!!! With the maddening exception of oil, where gravity anomalies have turned up 100's of salt plugs. Why? I think it is because the ore is not that differentiable and it is too close to surface. Overburden effects of hills and valleys you cannot account for without an expensive seismic survey, mask the fields. (Corrections for gravity are minute station to station for tiny mass effects .... the effect of a 50 foot high ridge near surface underneath a 150 foot clay layer is major ... and NOT accounted for in any surveys I have done.. In other words, why correct for a rock cliff 10 feet high 75 feet away, if you are standing over a buried valley 100 feet deep..) Large gabbroic and hidden felses and huge kilometres deep intrusives, part of the volcanic pile, end up distorting the anomalies. In oil, you are looking at 3 miles deep of "quiet" more or less uniform layers of sediments, not a huge number of intrusive bodies of all sorts here and there. Things are far away.. about 5000 feet down, so they stand out.
99% of the time the anomaly is a heavy gabbro, or dense komatiite. They are always nearby. Even 100 million tons of 4.5 SG ore cannot compete with a 15 billion ton SG 3.5 basaltic plug. There is a gravity high near the Kidd Creek brass mine of 150 million tons. It is not the orebody as it is now mined out 90% and they gravity high is still there... !
BUT the IOCG thingies are different. For some reason .. they seem to ALL be gravity anomalies .. again they do not know precisely why .. this stuff does NOT work out in practice so far in volanic terranes.
EC<:-} |
