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Gold/Mining/Energy : Gold and Silver Juniors, Mid-tiers and Producers
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To: hank2010 who wrote (32228)2/8/2007 12:12:57 AM
From: E. Charters   of 78419
 
I have talked to Naldrett from time to time about this. Whereas I think the jury is out vis a vis Dietz's conclusions about exogenous nature of the shatter cones, exhibited in some of the only 168 impact craters known to exist, I disagree with Naldrett's nickel melt emplacement hypothesis. Naldrett favours an endogenous origin for the nickel sulfide but says it was emplaced by intrusive force of a sulfide magma into fractures and shears always at the same plane of weakness, that of the norite along the rim, and sometimes in "feeder dykes" crossing the structure (Whistle Dyke, Nickel Offsets). The nickel cannot be related to impact of a meteor, because the ore forming processes take much longer and are much more complex, having a relationship to the surrounding fabric that cannot be explosive. To postulate that a nickel melt suddenly introduced was then remobilized slowly to form, is stretching the point as it requires a continuing newly introduced heat source to be mobile over ore forming periods.

There is a possibility that the Grenville Uplift created compressional folds, but the embayment pattern of ore formation was indeed fortuitous if it ore were subsequent to it. As well there are plentiful examples of Ni and Pt (River Valley) in differently-than Rim-aged Grenville-associated rocks, which implies a long term endogenous nickel source that continued to be emplaced for megennia after the nickel formation at the Norite-sublayer boundary.

EC<:-}
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