AboutJoe Norris Expertise I am an economic geologist. An economic geologist does mineral evaluations and appraisals of mineral or mining properties. I can tell you if your deposit has value - remember that a mineral deposit, no matter how good, only has value when mined. Any value assigned to a mineral deposit, in the ground, is only the speculative value that deposit.
Experience I have been a economic geologist for most of my 35 year career. Although I have done work in perhaps 45 states and numerious countries much of my work has been in Appalachian coal, intermountain west gold and silver, and Arizona uranium.
Organizations Past President of the Virginia Section of the American Institute of Professional Geologists and a certified geologist in twelve states.
Education/Credentials BS Degree from Eastern Kentucky University. Work on MS Degree @ Eastern Kentucky University, Colorad School of Mines & Marshall University
Numerious short courses on the value of mineral deposits and how to value same. Also several short courses dealing with the different types of geologic processes; sedimentary, igneous, metamorphic along with the mineral associated with each.
Question 2 questions of wording for a history programme we are making:
Is there a more exciting and easier way to explain why the granite in the Sierra Nevada mountains of CA / NV is so hard to penetrate?
"Formed from volcanic magma 20 million years ago, the granite of the Sierra Nevada is embedded with even harder xenoliths of crystalline rock, trapped in the granite as the magma cool" - would prefer not to use words like xenolith! And would like to be more snappy if possible.
Second question is concerning the gold deposits in the Sierras:
A hundred million years ago, Magma in the eart's crust coold and solidifes to form the rocks of the Sierra Nevada. In the volcanic cauldron, a unique element, gold, is laid down in veins of quartz in concentrations 200,000 times higher than elsewhere on earth. Over hundreds of thousands of years, as the peaks of the Sierra Nevada push upwards, ice, rain and wind erode the rocky peaks. Water washes mountain debris along rivers and streams. Flakes of gold, seven times heavier than quartz, accummulate as nuggets in the riverbeds of California." This is long and also wring in parts - particularly the whole distillation process that concentrates the gold. I would like to make it more magical and illustrative and perhaps include how gold follows fault lines - hence its prevalence in California.
Can you please help? Thanks so much!
Answer I'm not a writer but a geologist. Geology has certain terms that describe formation to geologists. One of these terms is xenoliths. Xenoliths are a fragments of country rock within a plutonic or volcanic rock. The term country rock means the rock type that was there before the plutonic rock was in-placed. Below is another description you may find things that you like better.
The well-known granite that makes up most of the southern Sierra started to form in the Triassic period. At that time, an island arc collided with the West coast of North America and raised a set of mountains, in an event called the Nevadan orogeny.[8] At roughly the same time, a subduction zone started to form at the edge of the continent. This means that an oceanic plate started to dive beneath the North American plate. Magma from the melting oceanic plate rose in plumes (plutons) deep underground, their combined mass forming what is called the Sierra Nevada batholith. These plutons formed at various times, from 115 million to 87 million years ago.[9] By 65 million years ago, the proto-Sierra Nevada was worn down to a range of rolling low mountains, a few thousand feet high.
Image of the Sierra Nevada and Owens Valley from the International Space StationTwenty million years ago, crustal extension associated with the Basin and Range Province caused extensive volcanism in the Sierra.[10] About 4 million years ago, the Sierra Nevada started to form and tilt to the west. Rivers started cutting deep canyons on both sides of the range. The Earth's climate cooled, and ice ages started about 2.5 million years ago. Glaciers carved out characteristic U-shaped canyons throughout the Sierra. The combination of river and glacier erosion exposed the uppermost portions of the plutons emplaced millions of years before, leaving only a remnant of metamorphic rock on top of some Sierra peaks.
Uplift of the Sierra Nevada continues today, especially along its eastern side. This uplift causes large earthquakes, such as the Lone Pine earthquake of 1872.
There are a few things that need to be understood about gold.
1) The specific gravity of gold varies somewhat but generally is around 21 as opposed to water, which is the standard, at 1 and quartz having a specific gravity of 2.65. So gold is 21 times heavier than the equivalent quantity of water. To make this a little more understanding a gallon of water weights about 7 pounds if you had a gallon of gold it would weigh about 147 pounds. This is why gold can be panned because it is so much heavier than water and falls to the bottom.
2) The statement that "gold, is laid down in veins of quartz in concentrations 200,000 times higher that elsewhere on earth". A very mis-leading and ambiguous statement. This statement is probably true of places on earth that do not have any gold content but it is not true of the whole earth. There are many places on earth where the concentration of gold is greater that the concentration in the Sierra-Nevadas.
3) Gold has an affinity for gold. In other words gold attracts gold. This is, at least in-part the reason that one finds nuggets.
As far as gold following fault lines I'm not sure in what respect you are referring:
are you talking about the deposition of gold, related to faults, relative to mountain-building or relative to placer gold. But either does not make California unique. Science has certain principals and if these principals are met the same thing will occur anywhere. The island of Fuji is somewhat similar to the Sierras and has one of the highest concentrations of gold on earth. Other areas that you may be more familiar with that have similar scenarios are the Rockies and the Andes.
