Lecture 20# - Mineral Resources
Rocks of the crust have a small amount of valuable metals disseminated throughout their crystalline structure. These small concentrations can not be extracted economically. Before a mineral deposit can be worked profitably, the percentage of valuable metal in the deposit must be greatly enriched above its average percentage in igneous rocks of the Earth's crust.
Ore - an aggregate of minerals from which one or more minerals can be extracted profitably. In ore deposits the valuable metals have been enriched above their average percentage in igneous rocks of the Earth's crust.
Gangue - non valuable minerals such as quartz and feldspar in which the ore is found.
Concentration of Ore Elements:
Element-------------------- Concentration ---------------Concentration ---------------Concentration
-------------------------------in Igneous rocks --------------- (%) in Ores --------------- (%) Factor
Aluminum -------------------------8.0 ------------------------------35 ------------------------------4
Iron ---------------------------------5.0------------------------------ 50 ------------------------------10
Copper --------------------------0.007 --------------------------0.5 - 5 -------------------------70 - 700
Zinc ------------------------------0.013 --------------------------1.3-13 -------------------------100-1000
Lead-----------------------------0.0016 -------------------------1.6 - 16 ---------------------1000 - 10,000
Silver --------------------------0.00001 --------------------------0.05 -----------------------------5000
Origin of Mineral Deposits:
1.) hydrothermal mineral deposits - concentration by hot, aqueous solutions flowing through fractures and pore spaces. - (copper - Bisbee, Arizona; tin - Cornwall, England)
2.) magmatic mineral deposits - concentration by partial melting and fractional crystallization. - (lithium, beryllium - pegmatites) (chromium - crystalline settling)
3.) evaporate deposits - precipitation from evaporation of sea water. (sodium carbonate, halite, gypsum)
4.) iron deposits - iron was deposited as a chemical sediment in sea water and later concentrated by metamorphism (iron ore of Minnesota)
5.) strata bound deposits - these ores are found in sedimentary layering when hydrothermal solution invades and reacts with a muddy sediment (lead, zinc, copper - Missouri)
6.) placers - concentration by flowing surface water (gold - California)
7.) residual mineral deposits - chemical weathering leads to mineral concentration through the removal of soluble materials in solution and the concentration of less soluble residue (aluminum [bauxite] - tropical climates).