Geology TV Documentary
12 messages in this thread
Hello All,
I'm a freelance writer/director working on a series of six documentary TV
programmes on the Geological History of Ireland, presented by Dr. Padhraig
Kennan from University College, Dublin. The programmes cover Sedimentary
Layers, Folding & Earthquakes, Volcanoes & igneous rock, Movement & Collision,
The Ice Age and Society & Geology.
I'm just posting this note to say that I may be asking some dumb questions over
the next couple of months, and will appreciate any help I can get!
Regards,
Gerry Hoban.
Gerry-
That sounds like a nice series. Are you addressing mineral deposits and
mining? We have the story here in the states that the high kings of Tara had
large gold and silver mines that were rather "lost" until just a few decades
ago. Of course, now there is again exploration and mining. Is this a true
representation?
Steve
Steve,
>>Are you addressing mineral deposits and mining?<<
Yes, we'll be looking at mining and mineral deposits from two main angles: the
processes that gathered the resouces into seams in the first place (black
smokers, continental collisions, tropical vegetation etc), and the finite
nature of those reserves within a human timespan (we're taking the stuff out
quicker than the earth can produce new resources).
>>…gold and silver mines that were rather "lost" until just a few decades
ago…<<
Most of the precious artefacts that have been found are indeed made of "Irish"
gold, but probably came from very rough and basic surface mining.
I think people are beginning to discover "new" seams of gold and silver.
Whether they're economically viable or not has yet to be proved. The one
instance I know of is Croagh Patrick, a holy mountain in the West of Ireland.
Commercial prospectors found gold there a few years back, built an access road
without planning permission, and then had the wrath of the local and national
clergy come down on them. They backed off, and what is regarded as the best
seam in Ireland has been left untouched. Priests, huh!
Gerry
Hi, Gerry–
Welcome to the forum!
Please feel free to ask any and all questions about geology and related
subjects. This is still a small section, thus you may need a bit of luck to
find someone here who knows the specific geology of Ireland. If none come
forward, there is always the Internet mail-list rocks-and-fossils to be tried
(though it has been off-line for a week or two); see INTERN.TXT in the library
for details.
You might want to keep half an eye out for info about the geology of
Newfoundland and southern Greenland, since they were neighbors of Ireland a
"short" time ago (140 million years is not long to a geologist). I am not a
pro geologist (though others who "hang out" here are), just an amateur mineral
collector – I am aware of a number of minerals from England and am keenly
interested in those from the alkalic igneous intrusions of southwest Greenland,
and am wondering why I have not heard of similar minerals from Ireland. Have
you folks been hiding something?
Happy hunting!
–Doug
Doug,
Thanks for your words of welcome & encouragement. As for your question about
alkalic igneous intrusions, once I look up what that means (!!), I'll check
with our programme presenter, the bona fide expert…
Regards,
Gerry.
Hi, Gerry–
In case you have not had time to look it up, molten rock that erupts onto the
surface is an extrusive (extruded from the Earth) igneous rock; if it does not
make it to the surface, cooling slowly inside the Earth, it forms an intrusive
igneous rock.
Igneous rocks may be rich in silica (quartz and relatives), giving them a
somewhat acidic nature in a technical sense, or may have instead of silica some
minerals with more of an alkaline character (carbonates would be found in such
rocks). Thus an "alkalic igneous intrusion" is a rock sort of like granite in
that it cooled underground and thus has a similar texture, but unlike granite
is short on silica, letting a different suite of minerals dominate.
–Doug
Hi, Doug
> Thus an "alkalic igneous intrusion" is a rock sort of like granite in that
> it cooled underground and thus has a similar texture, but unlike granite is
> short on silica, letting a different suite of minerals dominate.
Now I'm confused (so what else is new <g>). I was under the impression that
the rocks in the Washington Pass area were alkaline, but I have one specimen
that has a couple of smoky quartz micros in a tiny vug. I suppose they could
have formed later. The other possibility is that I've been a victim of thread
drift (again). Lanny, Help!
Regards, Guy
Hello, Guy:
Strictly speaking in terms of igneous petrology, the classifications of
igneous rocks as "alkalic", "calc-alkaline", "peralkalic", etc., are based on
the ratios of Na2O, K2O, CaO (alkali and alkaline earth elements, no?) in the
total normative (oxide) composition. Silica saturation (SiO2) is a related,
but not identical, compositional means of classification. A rock w/ the same
content of alkalis (Na2O, K2O, etc.), as a granite, but that was
silica-undersaturated would be a *syenite*, for example.
Scott M.
Thanks, Scott. Time to go read some of the fine print in the field guide
<sigh>.
Guy
Hi, Scott–
Thanks, you have made me realize my understanding of the term alkalic needs
some refining.
There is a diagram I have seen in several places that defines the various
igneous rock types on a two-dimensional diamond-shaped graph that has a
horizontal axis with Na+K on one end and Ca on the other; the vertical axis was
from high-silica to highly-feldspathic (I am visiting CA again, away from my
references, so I am paraphrasing the text that is in the diagram from memory).
I have always identified that highly-feldspathic endpoint with "alkalic", I
guess because of fuzzy memories that "acid" rocks as meaning high-silica was
used in my intro geo class decades ago. The other axis ranging from alkali
metals to alkaline earth metals (Ca) seemed irrelevant to the meaning of
"alkalic" since both endpoints would be involved in that other sense of the
word. But I know there is at least one more dimension, mafic (Mg+Fe) through
the opposite, as evidenced by another box separated from the main diamond,
containing the ultramafic rocks.
Perhaps "alkalic" could be taken as the opposite of mafic? Hmm, magnesium is
an alkaline earth element, but not on your list (Na,K,Ca) as defining
"alkalic". As long as I can regard the less common metals and aluminum as
irrelevant to this dimension, alkalic seems equivalent to anti-mafic. Or is
"alkalic" best regarded as yet another independent dimension? Alkalic =
anti-mafic would answer my earlier question as to why alkaline igneous rocks
seem to include a disproportionate number of fluorescent minerals – less iron!
Ferrous iron is a major poisoner of fluorescence.
It seems trying to fit that diagram onto two-dimensional paper left it able to
communicate much to me, but not a complete picture. I look forward to the
invention of three-dimensional and four-dimensional paper (electronic
publication with animated holograms?)!
–Doug
Hi Guy!
I've been out of sink for a while (Montana Rendezvous the 30th-1st, then
immediately off to Utah [Thomas Range] for a full week, home a couple days then
back to Montana to look at my new natrolite locality [in the first winter storm
for the season]) but am home again, at last.
As you probably note from the other messages in this thread that in the
"alkalic" and similar terms we are talking about various degrees of
alkaline/acid. There are few absolutes. An alkaline intrusive rock is loaded
with Na, K, Ca, and short on SiO2. An alkaline granite has to have SiO2
(quartz) or it isn't a granite, so an alkaline granite like the one at
Washington Pass, WA is about the same a s a "regular" granite, except it has
more Na and K than is necessary to make the feldspars, so it is on the alkaline
side, but not really an alkaline intrusive rock. As a granite, it still has
quartz grains in the rock and typically quartz crystals in the cavities.
Lanny
Thanks, Lanny! That backs up what I thought I knew. See you in Vancouver next
month…
Guy