Hi all
The dyke swarm that makes up the Walhalla to Woods Point gold field is a roughly even spaced series of vertical dykes within a sequence of horizontal sedimentary layers.
The sedimentary layers were crumpled up into a series of anticlines and synclines from north to south and at each buckle they cracked.
The hot fluids that formed the dykes flowed up those cracks for probably 10s of kms vertically. The dykes hardened. Some of the sedimentary layers were softer so in some layers the dyke bulged out but in some it necked in. Thus going down from the surface each dyke necks then bulges then nexts then bulges, again at regular intervals.
Later geologically the entire sedimentary area was buckled again and that fractured the dykes horizontally. That happened within each sedimentary layer and like all rock the fractures were at 30 and 60 degrees and all either went all across the dyke or intersected each other.
This is the relatively symmetrical structural setting and drilling and mining shows us the pattern. Obviously much more complexity exists and that’s what is needed to find the gold veins within a part of one mine but this story is about finding a mine.
Next more fluids come into the dyke and fill the fractures. This time the fluids carry quartz and gold. Most of the fractures fill with quartz. Gold precipitates out of the melt due to some change in physical or chemical conditions (cooling, change of direction, flow slowing, chemical mix, pH etc).
In these dykes the gold preferentially deposited on the top of the quartz vein (hanging wall) at the edge of the dyke bulge. Have a look at the various pictures of the whole mine and you will see.
Now the best gold grades and tonnages are historically in the bulges.
Erosion since the dykes were emplaced 10 to 50 million years ago or more has left some necks at surface and some bulges.
100 years ago they had no electricity there or water pumps and needed ounce per tonne dirt. If they found a bulge that mine went deep (day 200m) if a neck then they abandoned it early.
So numerous dykes have been found but potentially abandoned at water level most probably not far above a bulge.
Get the idea?
I posted once that AULs ground could yield 5 mines all with multi million ounces at over 20g/t.
I stand behind that statement.
Thats a company making approach.
I would also abandon the MStar deeps and use them as a tailings sump for these new mines. Why - because the 3 mines that did reach 1km deep showed a decline in gold grade plus st 1km the tectonic stress increases and the rock is crushed. Also need space for tails so have 3 big mines running and use them for tails once finished.
Cheers Krum
