Geologist's advice needed

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	Geologist's advice needed « on: September 14, 2010, 10:21:25 pm »

The geologic structure in question appears to be a mudstone conglomerate extinct volcano (background of photo P1000112.jpg). I estimate it to be about 70 feet high. There are seashell fragments embedded in the mudstone conglomerate at lower levels near the base, and it is the only structure poking out from the mangrove area. I surmise that it rose from the sea bed and/or was exposed due to tectonic plate upheaval/dropping water levels.

This may be a tough question for anyone to answer without analyzing rock samples, but normally speaking do such volcanoes bring up any minerals or gems worthwhile of extraction?

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	Re: Geologist's advice needed « Reply #1 on: September 15, 2010, 03:12:27 am »

I've never heard of a mudstone conglomerate extinct volcano with shells in it. Most likely you have a pipe of limestone with fossilized shells in it. All volcanoes leave igneous rock pipes with minerals like gold in them but never shells. Nature of the beast.

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	Re: Geologist's advice needed « Reply #2 on: September 15, 2010, 04:02:50 am »

	Quote:	Posted by GoldDigger1950
I've never heard of a mudstone conglomerate extinct volcano with shells in it. Most likely you have a pipe of limestone with fossilized shells in it. All volcanoes leave igneous rock pipes with minerals like gold in them but never shells. Nature of the beast.

Here's the thing: the visible bits of seashells are found near the base. They aren't seen further up that structure, though I'd not exclude the possibility that there may be more shells present further up hidden within the rocks.

I climbed barehanded up as high as I could (approx 15 feet up from a lumpy portion that protruded from what I can best describe as the base of the structure) onto a ledge, and pulled up the Nokta. As the ledge was not wide, I ground balanced the machine on the rock above my head (which rose at an approx 50-60 degree angle) as I leaned out and away from the ledge, no easy feat considering the damned weight of the detection head and rod. The ledge was scanned thrice with similar results: gold and cavity. Being wary of possibly false results due to the unsatisfactory ground-balancing done, I keep my reservations on the scans' accuracy. I wasn't the first one there though (see attached photo). Someone had left behind a makeshift cooking implement fashioned from a powdered milk tin and some thick wire. Whatever they were trying to cook, I doubt it was food.

Anyways, one day I shall return to the spot with mountaineering gear and rock picks. If there's more seashells up there, then limestone pipe it is. If some enthusiastic rock bashing produces the yellow stuff, hooray!

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	Re: Geologist's advice needed « Reply #3 on: September 15, 2010, 05:43:00 am »

Your climb was quite ambitious. Was there any igneous rock up there or was it more crumbling limestone? It would be a very odd rock formation if igneous was atop limestone and shells.

Do you trust the readings on the Nokta?

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	Re: Geologist's advice needed « Reply #4 on: September 15, 2010, 08:40:08 am »

Been scanning through the HD vids I made for good shots of the rock. Attached is a still frame from the base of the structure. Is that limestone? Was rushing under a time constraint; had to leave the place before big seas hit the area at 3PM, would have swamped the small boat, and I had minerals on the brain. Didn't bother taking photos of the seashell bits, but in the upper center of the frame, there seems to be the apex of a gastropod's shell embedded in the whitish rock.

The rock on the ledge and above it is very tough. Repeated hard blows using a sandak (basically it's a flat blade of tough steel welded on a pipe handle we use to chop through tree roots before digging) only resulted in small chips and scratches and a blunted sandak edge. Please refer to photo P1000120.jpg. That triangular stone was found in the leaf litter and debris that had collected on that ledge (the ledge is roughly concave). Before any of you Yam hunters say it, NO that is not a treasure sign! Both triangular stone and the underlying rock surface are of equal hardness and are not the least bit crumbly.

As for the Nokta's readings in this case, no I do not trust them entirely. The machine has proven itself in soils, but has yet to do so on rock.

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	Re: Geologist's advice needed « Reply #5 on: September 16, 2010, 06:15:41 am »

What kind of rock do you think it's made from? The hard rock, that is. The seashell encrusted crumbly rock is no doubt rotted limestone.

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	Re: Geologist's advice needed « Reply #6 on: September 16, 2010, 06:51:27 am »

The pics make it difficult to tell exactly what kind of rock it is. But from what you've described I believe you're looking at a sedimentary rock (the fracturing looks off for limestone but it's difficult to tell from the pics). And as far as your original question...yes, volcanic activity does produce gems and valuable metals. It depends on it's composition, depth, and rate of cooling. Here in East TN (and western NC) we commonly see out cropping's of and weathered fields of gems (ruby's etc.) from skarns.

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	Re: Geologist's advice needed « Reply #7 on: September 16, 2010, 07:39:54 pm »

	Quote:	Posted by GoldDigger1950
What kind of rock do you think it's made from? The hard rock, that is. The seashell encrusted crumbly rock is no doubt rotted limestone.

I'm totally unfamiliar with that kind of hard rock; first time I ever seen it in Borneo. In past decades I've mainly stuck to the inland regions and it's only this year that I'm exploring the coastal portions. The whitish rock/rotted limestone was only seen at the base of the structure. I've submitted the same photos to a geology forum in hope of more opinions. I may avail of the university's geology dept after I return next month and hack off some sample pieces of rock.

	Quote:	Posted by tndirtdigger
The pics make it difficult to tell exactly what kind of rock it is. But from what you've described I believe you're looking at a sedimentary rock (the fracturing looks off for limestone but it's difficult to tell from the pics). And as far as your original question...yes, volcanic activity does produce gems and valuable metals. It depends on it's composition, depth, and rate of cooling. Here in East TN (and western NC) we commonly see out cropping's of and weathered fields of gems (ruby's etc.) from skarns.

Thank you for your input, and I can understand it's hard to tell anything with absolute certainty from photos. There is one more facet to this area which I did not divulge before: I was brought to the place by a weathered old boatman. His son and him had explored the base of the structure before, and the 29 year old son had found a translucent red rock. His son took the rock home with them, fell into a coma that evening and died without regaining consciousness 3 days later. Typical of some communities here, they rely on traditional shaman's cures and eschew hospitals. The boatman blamed evil spirits for the death and returned the red rock to the place of origin. With due respect to others' cultural beliefs and norms, I find that hard to swallow. The young man could have been exposed to anything ranging from leptospirosis (rat urine disease) to radiation poisoning. Have volcanoes been known to emit radioactive material?

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