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Gold/Mining/Energy : Winspear Resources

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To: VAUGHN who wrote (3308)	10/6/1997 2:36:00 PM
From: Walt	of 26850

Unfortunately Vaughn a little information can be misleading. The general rule of thumb is that glaciers like streams or rivers tend to round rocks the longer they work on them. So the farther a glacier moves a rock the more rounded it gets. Weathering, in the form of rain, freeze thaw weathers according to rock type etc. A rounded granite boulder will spall off sheets and maintain its rounded shape. A angular shale boulder will break along its bedding and cleavage planes as will most rocks with bedding and cleavage. Banded or bedded rocks will also have some bands or beds softer then others and you get differencial weathering. Conglomerites often lose their matrix and you are left with the cobbles. Kimberlites and other soft rocks tend to crumble. Pieces just get weathered crumble and fall off. They may get smaller but since the weathering is roughly equal on the outside surface you get a smaller version of original boulder ie they roughly maintain there shape. So different rock types weather differently, that also is a well known geological fact. To confuse the issue the north has seen several different periods of glaciation and the glaciers seemed to move in different dirrections and moved different distances. So if you study glacial striations (scatches on rocks) you often see two or three different sets. So you could get a long train of indicator minerals going off in one direction and a train of boulders going off in another, both from the same source. Usually the closer to the source you get the narrower the train gets and the number of boulders increases and the larger and more angular they get, that is also a rough rule of thumb.Having mapped a few boulder trains in the north I will also add that old ma nature can throw some real twists and turns into these general rules of thumb. I would also add that the rounding of boulders during glaciation is often due more to water erosion then the ice, ie most really rounded glacial boulders come from eskers, out washes etc. Most boulders trapped under ice and moved get (or got) crushed to rubble regards Walt

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