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Gold/Mining/Energy : BET YOUR ASSAY - Mining Terms Explained
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To: Ed Pakstas who wrote (384)4/2/1998 10:55:00 PM
From: Walt  Read Replies (2) of 463
 
Greeting Ed,
There are basically two minerals which are magnetic: magnetite and pyrrhotite. Black sands or magnetic sands are thus composed of grains containing these minerals. In placer mining the old timers will tell you that when you hit the black sands you are getting close to the gold. The reason being that these black sands are dense or heavy and thus end up at aproximately the same area as the gold. Being a little less dense then the gold you tend to hit them before the gold.
Sedimentary deposites particularly alluvial ones (paid down by running water) thus can have layers of black or magnetic sands. This topic has come up recently in two contexts. I believe some companies drilling for diamonds have mistaken magnetic sands in the overburden for kimberlite targets. King or Terry C. could explain the difference in magnetic signiture between the two. Both will give a magnetic anomaly but the kimberlite should continue to depth. Presumably if you had a magnetic kimberlite which had weathered alot you could get a layer of weathered magnetic overburden over a magnetic kimberlite.
The other signifigance for magnetic black sands is some people are looking at them for other minerals associated with them iridium and osmium I believe. In other cases blsck sands, gold and even platinum are associated because of their densities.
hope that helps a little
regards Walt
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