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Gold/Mining/Energy : Manhattan Minerals (MAN.T)
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To: Jeff Dickson who wrote (3702)9/13/1999 9:09:00 PM
From: Bruce Robbins  Read Replies (1) of 4504
 
Jeff,

I think everyone is a little confused re massive sulfides. There are no magmas and lavas directly involved in the sulfide deposition. Sulfide magmas do exist IMO, but are very rare. In massive sulfides, the sulfides are thought to deposit from the cooling of superheated water exiting from vents on the seafloor (they are hydrothermal deposits). The theory is that gold and copper remain dissolved in only very hot water (and also dissolve into), while zinc can stay dissolved in cooler water. That is part of the reason why you get a copper-zinc zonation: the water is hotter near the vent, and as such you get most of your copper and gold dropping out near the vent; the zinc drops out further along. Part 2 of the reason for a zonation is that it is thought that the system heating the water is very hot at the beginning of the venting and then cools off with time and later vents. This theoretically means that massive sulfide black smoker 1 will be copper rich while black smoker 100 will be zinc rich. There may be variations due to source of metals etc. The words to keep in mind are "hydrothermal" and "exhalative".

To answer your question, the gold/silver values probably reflect the fact that the underlying source for the metals picked up by the hydrothermal solution were richer than average in gold and silver. The zinc mineralization may represent the waning stage of the TG-3 hydrothermal system.
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