New Zealand Gold Prospecting & Metal Detecting Forums Archive

Gold deposition is frequently associated within what are called “Fault Zones”.

These are areas where the surrounding ground has been shattered by earth movements and contains lots of, lets say, “Cracks”, these very often point out to you ,that, where these cracks have occurred in some abundance, then there is every likely hood that the area is well mineralized, and hopefully auriferous.
Even better is, if it is loaded with “Stringer” veins, or a “Stockwork” of smaller little veins that run through the rock of the area like a bunch of crazy little networked lines of quartz.
Most of the time these areas are quite difficult to find, or even to see when you are out in the country happily prospecting, or fossicking away, especially if in a bush covered landscape.

Topographical or geological maps show fault lines as pencil like lines, or as dotted, dashed lines, but they generally only depict the larger and more recognizable ones of an area.
But this is not what you will see in the field if you are looking for them as an indication of possible mineralized ground in the area that you are in at the time.

One of the signs to look for in the field, are areas of “Shattered” rock, especially if they have been re-cemented together with silica (quartz) (this is often referred to as Breccia, or Brecciated rock. Bit of a misnomer for N.Z. conditions really) which forms the veins running sort of higgledy-piggledy throughout the rock, and crisscrossing over themselves here and there, forming a network (Stockwork) of interlacing quartz veins. But, bear in mind that all gold veins “Do not” occur in breccias, especially in N.Z.

Earthquakes are associated with faults and fault zones, because when the strains and pressures of some other underground movements, are forced upon already in place rocks, it becomes too much for them to handle, so they move suddenly. (This is generally caused by the pressures associated with what is called a “Reverse” fault, which represents the “Overriding” (called the hanging wall) part of a faults movement.) or they may break and snap apart causing the sudden lurching, or jarring motions of an earthquake. The strength of the earthquake is strictly a measure of how much energy is released by this snapping apart scenario.

The “Original” actual faults themselves are (to me), seemingly caused by the pressures of “Igneous” eruptions which generally break through to the surface as volcanoes, with the associated rupture and cracked areas surrounding the volcanoes cones. Later in time, these associated ground cracks (which may have been completely hidden by erosion debris over time) form very convenient pathways for future underground pressure sources to easily force their way to the surface causing earthquakes.

One of the things that fault zones do for us, is that because they shatter the rock, they form excellent plumbing pipelines to convey hot and dissolved mineralized hydrothermal fluids up from the depths of the earth, and deposit them in places where the heats and pressures of these fluids diminishes to a point where they can no longer be held in suspension. They are therefore precipitated out of the fluids (as native metals, or minerals) once they reach a temperature that is below their respective boiling points.

Faults also cause weaknesses in the surface of the earth, and as most things always choose the path of least resistance (if they get that choice), then faults present the ideal opportunity for water, as with its great powers of erosion it can use these fault lines if they are situated within its pathway to the sea. This is a feature of the landscape that water is always ready to take advantage of.

I know that we are told at school that valleys are carved out by running water. Of course they are!
But we were not told that “Practically all rivers and streams follow ancient fault zone factures.” because this is the easiest way to go for the water!
Also, the faults associated with river and stream passages, are often the largest faults to be found in any immediate area.
(Forget glaciation forces, as these are after all, just frozen water that flows because of weight motivation) .

Faults are generally always present where the country rock changes to another different type of country rock. (this is often sequential) This feature is often noticeable by color, or a texture change of adjacent and abutting formations.
Remember also, that wherever you see a vein, or reef in a rock, you are looking at a “Fault” fracture.

Gold seems to prefer to precipitate out of solution, where Easterly/Westerly trending “Smaller” fault fractures, intersect, and cross through Northerly/Southerly trending “Larger” major fault fractures.

It is in the veins associated with the smaller fault fractures that seem to produce the larger gold bits.

Its like reverse psychology really---“Small“, means “Big“, and vice-versa.

As an aside: The biggest fault line that we have in N.Z. is the “Alpine” fault, but it is not apparent as it runs alongside the “Southern Alps” so we can’t see it. But if you look at the weather map for “Wellington” on TV, and take notice of the near straight line that runs along the Western side of the harbor (by the motorway), what you are looking at represents a visual part of the extension of the Alpine fault.

Cheers---Colin.

Edited by user Wednesday, 8 September 2010 3:12:52 PM(UTC)  | Reason: Not specified

Thanks for the thanks Jason. : )

Actually I had forgotten that I had written that piece! so I actually read it!

Sometimes I even surprise myself with the crap I write?

Cheers---Colin.

Edited by user Thursday, 21 October 2010 2:02:42 PM(UTC)  | Reason: Not specified

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Edited by user Saturday, 9 July 2011 3:19:59 AM(UTC)  | Reason: Not specified

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Edited by user Saturday, 9 July 2011 3:20:15 AM(UTC)  | Reason: Not specified

JW, yah that bit has been done to death. It needs a decent flood to rip some more gravel over it....
Macetown is bad for junk...... Everything from horseshoes to bits off 4wds lol