Geology

[Sandman]

Hi everyone,

Reading this forum, I realize just how little I know about geology and how the rocks and minerals we seek are formed. To find gold, one must first know the processes involved in the creation of pockets and veins that are accessable. Does anyone have suggestions on some literature to assist in my quest for knowlege? Thanks in advance.

P.S. I'm most interested in the copper based derivitives such as tourquoise, malochite, azurite and chrisocholla but gold and silver also have my interest.

[oroblanco]

Hola amigo,

I am no expert in geology but have been a student of this fascinating science for a while, and may be able to answer some questions.

Copper as well as gold, silver, tin, lead, etc most of the metals are deposited by the actions of hot water. Strange as this may sound, it is how most metallic minerals are deposited in the host rock. The quartz and other minerals are also deposited by hot water. Water has its greatest solvent power when it is under pressure and intense heat, in these conditions many otherwise insoluable minerals and materials suddenly become soluable. This very hot, pressurized water deep in the earth slowly circulates around, dissolving various minerals and metals, until it reaches some "fault" or crack/void in the rock layers which cover it - then it pushes up into these voids because it is under pressure. As it rises in these cracks or voids, the temperature drops and the pressure is lowered, making the waters rather suddenly NOT quite so good at being a solvent, and the minerals and metals which are dissolved in the waters precipitate out, forming crystals and grains that solidify into veins. The difference in depth (meaning really the pressure and temperature) at which this occurs makes the difference in what type of ore deposit we find - those which formed at shallow or near surface depths are referred to as "epithermal" and these have characteristics which geologists <or a prospector> can readily identify. Mesothermal is formed at "medium" depths and Hypothermal is formed deep in the earth.

The biggest difference in these different types is in the size of the grains of the minerals which make up the ore - Epithermal having the tiniest grain size, <and generally tiniest gold particles> at the other end of the spectrum Hypothermal has the largest grain size and often coarse gold particles. The gold does not form into true crystals, it simply fills the voids between the mineral grains - there are crystals of gold which are actually "casts" of gold that filled a void which was left when a mineral crystal dissolved away. Epithermal gold veins are the most common type found in Arizona and they can be quite rich in gold, but a feature of this type of deposit is that they rarely run to any great depth, usually "pinching out" at a shallow depth. Mesothermal and Hypothermal deposits often run to considerable depths - in some cases over a mile and still no end found.

The Audobon Society Field Guide to North American Rocks & Minerals by Charles W. Chesterman is one of the best single-volume books on geology IMHO and is made to fit in a pocket with a tough vinyl cover, I highly recommend it for anyone interested in geology.

Google Books has several very good geology books (free) in full text, here is a short one which is helpful for a beginner: Geology by James Geikie
http://books.google.com/books?id=Vs8JAA ... q=&f=false

For concentrating on metallic ore deposits, Google books has this volume (free, full text) Geology of Western Ore Deposits by Arthur Lakes
http://books.google.com/books?id=wB9DAA ... q=&f=false

There are many good websites on Geology too, such as:

Geology.com http://geology.com/

Geology at About.com http://geology.about.com/

The United State Geological Survey has a large selection of publications and maps available, many are free downloads, check out
http://www.usgs.gov/pubprod/
<They also have many of the former United States Bureau of Mines pubs, which were excellent>

Some states also have considerable libraries of publications including many free downloads,

Arizona Geological Survey
http://www.azgs.state.az.us/publications.shtml

Nevada Bureau of Mines and Geology online publications
http://www.nbmg.unr.edu/dox/dox.htm

Utah Geological Survey publications
http://www.mapstore.utah.gov/ugs/index.htm

California Geological Survey
http://www.conservation.ca.gov/CGS/Pages/Index.aspx

Colorado Geological Survey
http://geosurvey.state.co.us/

New Mexico Bureau of Geology and Mineral Resources
http://geoinfo.nmt.edu/publications/

I hope this is of some help to you amigo and for anyone reading our discussion here. Good luck and good hunting, I hope you find the treasures that you seek.
Roy ~ Oroblanco

[Plays In The Dirt]

Hi everyone,

Reading this forum, I realize just how little I know about geology and how the rocks and minerals we seek are formed. To find gold, one must first know the processes involved in the creation of pockets and veins that are accessable. Does anyone have suggestions on some literature to assist in my quest for knowlege? Thanks in advance.

P.S. I'm most interested in the copper based derivitives such as tourquoise, malochite, azurite and chrisocholla but gold and silver also have my interest.

Darn Sandman I've got just the book you're looking for but it's where I'm not right now and I can't remember the title. As soon as I get my hands on it I'll post it.

[roc2rol]

Great subjects and posts guys!

Enjoyed your writing Roy!
I could see the earth digesting churning creating
mineral & metals
but boy -I get my thermals confused
sometimes deep
most the time shallow

[Sandman]

Wow. Thanks Roy. I happen to own a copy of the Audobon Field guide sitting right here. It's a little worn from an encounter with a kangaroo rat but it only chewed the corner. Great pictures in that one. My library also includes "A field guide to Rocks and Minerals" written by Pough. I found a pretty good description of the process you described complete with illustrations in "The History of the Smokey Valley" by Robert McCracken.

I was out walking some familiar ground looking at some dirt and rock in a completely different way yesterday. There's an old prospect hole here and there.......if only I had x ray vision!

Thanks for the sources. This should keep the lights burning into the night as I attempt to gain more understanding of the geological procecces. It's interesting for sure.

[oroblanco]

Hola amigo,
I am still learning it too - but you are right, it does change how you look at the country around you. I am trying to figure out why Wyoming and Colorado got so many diamond-bearing kimberlite pipes while the Black Hills which are similar volcanics have none. Then there are those diamonds in California, with zero kimberlite pipes and they surely didn't get carried there by glaciers from Canada so...? It is quite a science, sure wish I had studied it in college when I was still young - seems like things are a lot harder to learn as we get older.
Roy