The Geology of Metallic Mineral Deposits (L20) Flashcards
what form was the metals first used by humans in?
pure elemental or native form
what was smelting methods developed to do?
seperate metal from impure forms
what are all metals united by having?
high electrical conductivity, lustre, and malleability, and the ability of their atoms to lose electrons to form positive ions
what does the term “metal” generally refer to in our culture?
refers to “fusible metals” - metals of moderate hardness that can be fused with other metals to form alloys (metal mixtures)
what are the 2 main categories we classify fusible metals in?
Precious metals and Base metals
What are precious metals and why are they desireable?
metals of high intrinsic value (silver, gold, platinum)
desireable for the manufacture of electrical components due to their resistance to corrosion and oxidation
what are base metals?
metals of low intrinsic value (iron, lead, copper, zinc, tin)
most base metals oxidize in air
what was the term “base metals” derived from and what is it referred to now?
derived from the practice of alchemists to attempt to make gold from less valuable metals
the “base” part of the term now refers to base metals being common and inexpensive
the metals that we think of as exceedingly common, are ____
actually scarce
what is essential to the discovery of metal-rich deposits?
knowledge of the geological processes that lead to enrichment of metals, and of the geological environments in which the processes operate
what is an important aspect in determining the feasibility of extracting any given metal?
cost of extraction
a mineral body mined at a profit is called ___
an Ore
What are some economic factors that qualify a mineral body to be called an Ore?
the concentration of the metals of interest and the size of it
the cost associated with mining and transportation
market value of the metal
some metals, such as iron and chromium can be concentrated by _____
gravitational setting
what is an example of gravitational setting?
heavy oxide minerals are formed during the earliest stages of cool and sink to the bottom of the magma champer
the rest of the minerals fill the remaining spaces, and the least dense minerals can actually float to the top of the magma chamber
What is immiscibility?
an “unmixing” or seperation of metal-rich liquid from silicate-rich liquid
how does immiscibility work?
as the molten material rise to the surface, metal-rich liquid seperate from the silicate liquid by settling to the bottom while the silicate material floats to the top
what is one of the best-known and most important ore deposits? How is it created?
ore deposits formed from hydrothermal (hot-water) solutions
these solutions may be left over fluids of cooled magma, or generated by the warming of groundwater or seawater that seep into rock below the surface by heat
what is a critical factor in the ability of hot water to dissolve metals?
its “saltiness”
higher the water temp, _____?
greater the amount of material the water can dissolve and hold in solution
what can be generated from the pressure from the intrusion of an igneous body?
it can generate lots of microscopic cracks into which residual fluid from the intrusion can penetrate and cool
these dissemenated ore deposits low in grade but mined at a profit
how are mineral-filled veins created?
fluids super-concentrated in metals penetrate larger fractures
what is another word for Vein Deposits?
Lode Deposits - comes from “Mother Lode”
what can be found in these mineral-filled veins?
native gold and silver can be found in the spaces between quartz crystals within these veins
how are the gold-bearing quartz veins made of?
made of minerals that percipated in large cracks in the rock when it was still deep undergound
why is gold found in close association with quartz?
quartz crystallizes at low temps. the fluids containing dissolved gold are left over after the main rock-forming minerals have crystalized into plutonic igneous rocks
what is Pegmatite?
rock type associated with late crystalization that crystalizes from water-rich residual magma that tends to occur on the borders of large intrusions and can also be injected into smaller scale fractures
how are the huge crystals found in pegmatites?
the huge crystals are due to the very fluid-rich nature of the magma
b/c ions are able to move around easily and react with each other, crystals grow to huge sizes
