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Kev

Terrane Convergence = Contact Zone?

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Hi,

    I've got a query for one of the resident geologists please.

Can the covergence of two tectonostratigraphic terranes (both schists) be considered a contact zone, such that minerial empacement is possible locally along the abutment?  

 

Thanks

Kev.

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Kev,

 

Welcome to the forum! :)

 

Geology can be viewed from two different scales; macro and micro. From a macro-geological scale, we can note that plate tectonics play a major role in creating crustal deformation from California to Alaska. Folding, metamorphism, temperature and pressure all play into formation of schist. 

 

On a micro-geological scale, the effects of folding of stratigraphic sequence can make formations conformable and unconformable. Does any of this lead to creation of a structure that improves the probability of emplacement of mineralization? Yes, it does.

 

I recently published the title of a document on another thread that discusses gold models and relates the models to the associated geology. Although there are millions of contacts, veins, vents, volcanogenic and intrusive geological events, there are very few that became sources of gold.  They represent a good place to begin looking.

 

- Geowizard 

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Thanks Guys for taking the time to reply.

An unconformity of sorts is evident in places, I think mainly textural zone schistosity differences. Perhaps I should look for local shears.

 

Best regards

Kev.

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Kev,

 

Are you prospecting for shears?

 

Your profile and question doesn't offer any clues. Are you in Romania, Pakistan or Southern California?

 

There is schist everywhere. What is the significance of schist?

 

Just curious. :)

 

- Geowizard 

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Hi Geowizard,

                      I'm in the South Island of New Zealand, schist is one of the predominant gold hosts.

 

Well I spent a couple of weeks looking at various points along a 15km stretch of differing textural zone contact, and I think terrane boundary interfaces do make, as the picture shows.

 

Since the contact of the two terranes is not totally vertical but more low angle to almost horizontal as one zone has been forced to slide up and over another, is it possible that any remaining lodes are also flat lying?
 

Regards

Kev.

 

Some of the Au found along a raised portion of the terrane boundary.

16195777960_c4ef073e8e_b.jpg

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Kev,

 

Great photos!

 

And... nice looking gold. :)

 

The answer to your question depends on the timing of the gold intrusion.

 

Was the gold introduced before the fault event or after?

 

You need to find the answer to that question!

 

If the gold formed as a result of pre-fault deposition/intrusion, there is likely a source nearby that was "sheared" and carried gold with the displacement of the shear.

 

The displacement will provide a measure of the distance to the lode.

 

If the gold entered the shear zone and migrated along the shear zone after the fault/shear event, it is potentially in and on or embedded within the shear zone at great length.

 

The shear zone may intersect a pre-existing gold "conduit". You have more work to do to find the source.

 

You are probably very close. Continued careful observation as you have already done will probably direct you to the source.

 

Good luck!  

 

Note: I want to be clear about this, so I invite follow-up questions and postulations!

 

- Geowizard

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Kev,

You can also be on a Widely Low Grade Disseminated Schist Deposit that when overthrown could have Redissolved/Melted the Micron Gold and Then Redeposited it IN-AT-Near your "Contact Zone", by any of the common methods, without Quartz being present.

Just some Thoughts to mull over.

 

Sincerley

Bill "Lost Adams"

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