GEOLOGIC HISTORY
About 380 million years ago, the African Continent was being forced toward the Ancestral Eastern North American Continent by plate tectonic force. The subduction, or forcing down of the Oceanic Crust underneath the North American Continent produced tremendous friction-generated heat from the two colliding continents. This friction-generated heat, in excess of 2000 degrees, melted the surrounding rock 9-15 miles below the surface. This igneous molten rock was generated under intense pressure that forced the molten rock into cracks and fissures of pre-existing rock. This molten rock under pressure is similar to hot hydraulic fluid being forced into a chamber. Due to the pressure exerted on the molten fluid, it hydraulically pushed its way through the cracks of the host rock. This opened the rock up, along with melting contact areas of the host rock and sucking up rich mineral forming fluids. As these cooled, they crystallized and became a mineral rich buried treasure.
It then took an estimated 100 million years for this deeply buried (and insulated) mass to cool and crystallize. The slowly cooling mineral crystals grew within the Spruce Pine District to some of the largest feldspar and mica crystals in the world. After molten emplacement and cooling, it took millions of more years of Appalachian Mountain building and subsequent erosion to expose the deposits we see today.
MINE ROCKS
FELDSPAR
Feldspar was first mined in North Carolina in 1911 in the Spruce Pine district, the main feldspar-producing district in North America. Original mining was from pegmatite bodies but current mining is from alaskite,a very coarse-grained, light-colored, feldspar-quartz-muscovite rock.
Feldspar is by far the most abundant group of minerals in the earth's crust, forming about 60% of terrestrial rocks. Most deposits offer sodium feldspar as well as potassium feldspar and mixed feldspars. Feldspars are primarily used in industrial applications for their alumina and alkali content. The term feldspar encompasses a whole range of materials.
Feldspar minerals are essential components in igneous, metamorphic and sedimentary rocks, to such an extent that the classification of a number of rocks is based upon feldspar content. The mineralogical composition of most feldspars can be expressed in terms of the ternary system Orthoclase (KAlSi3O8), Albite (NaAlSi3O8) and Anorthite (CaAl2Si2O8). Chemically, the feldspars are silicates of aluminium, containing sodium, potassium, iron, calcium, or barium or combinations of these elements.
QUARTZ
Quartz is a mineral composed of silicon and oxygen atoms in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar.
Quartz had no use when this mine operated and was thrown on the dump. Much of the Quartz in this mine is gray Smoky Quartz, caused by exposure to Uranium in the mine.
MICA
Mica is a mineral name given to a group of minerals that are physically and chemically similar. They are all silicate minerals, known as sheet silicates because they form in distinct layers. Micas are fairly light and relatively soft, and the sheets and flakes of mica are flexible. Mica is heat-resistant and does not conduct electricity. There are 37 different mica minerals.
GNEISS
Gneiss is a common and widely distributed type of metamorphic rock. Gneiss is formed by high temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Orthogneiss is gneiss derived from igneous rock (such as granite). Paragneiss is gneiss derived from sedimentary rock (such as sandstone). Gneiss nearly always shows a banded texture characterized by alternating darker and lighter colored bands and without a distinct foliation.
FLUORESCENT MINERALS
Some of the rocks in this mine are highly fluorescent when exposed to ultraviolet light. Here is a list of many of these minerals and the color they glow under UV light:
Albite - Red
Beryl - Orangy Yellow
Calcite - Pink
Halite Opal - Green
Kaolin - Yellowish White
Oligoclase - Yellow
Orthoclase - Orange
Quartz - Bluish White
MINE AREAS
MAIN MINE STOPE
Feldspar was mined here from the light-colored rock called Pegmatite. Pegmatite is molten rock that was forced into the older, original dark-brown mountain rock. These pegmatites range in size from small pockets to hundreds of feet across as you see in this mine. When large pegmatites were mined by underground methods, it was called "stope mining", and the room or cavern that was created was called a "stope".
ADIT
Entry into underground mines are either down a vertical shaft or a horizontal opening called and "adit".
LOGGING REQUIREMENTS
In order to log this EarthCache, send me your answers to the following questions either through email from my profile page.
1. As soon as you leave the lower level and walk past the "Dump" you will come to 4 numbered rocks (from 2-5). Match the numbers with the type of rock: Feldspar, Gneiss, Mica and Quartz. NOTE: Pay close attention to the rocks, you will need this information for question 2.
2. Make your way into the mine. As soon as you enter the mine, you will be in the main stope. Look around and estimate what percentage of the ceiling and walls of the stope are made up of each of the 4 types of rocks from question 1.
3. In the back of the main stope you will find an adit. The adit is lit by fluorescent lights. Identify the type of rock in the adit and what color is it under the fluorescent lights?
4. Pictures are not required but are appreciated. Please post a pic of you or your GPS with anything you find interesting inside the cavern.
sources:
www.fluomin.org
deq.nc.gov
pubs.geoscienceworld.org
Geologyof the Spruce Pine Mining District
Your Guide to the North Carolina Mining Museum at Emerald Village