Post on 01-Apr-2020
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Magmatic Processes
• Within the magma chamber• During magmatic ascent• During volcanic venting• The role of water
– Magmatic water– Ground water
Old Faithful Geyser, Yellowston NP, WY
Mt St Helens, May 1982
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https://pubs.usgs.gov/fs/1997/fs113-97/
Mount Pinatubo, The Philippines, June 12, 1991
https://pubs.usgs.gov/fs/2005/3036/fs2005-3036.html
Mt St Helens Ash and Steam Eruption, March 8, 2005
Hundreds Protest Global Warming In London this Week
Water: polar, high dialectric constant, high heat capacity, high surface tension, maximum density above 32°F
PLUTON
3. Hydrothermal settings- as magmas crystallize, the water present in the liquid magma is driven off into fractures or permeable beds within the host rock. Minerals species that are water-soluble will thus be carried away from the parent magma body. As the water encounters lower temperatures and pressures, it may boil. Sulfide ores will precipitate in the order shown in this diagram, beginning with zinc or lead if present, and ending with a sinter of silica and or carbonate. The host rock may thus become host to hydrothermal deposits. Hydrothermal waters may also be derived from the circulation of ground water in deep basins. If the resulting brines ascend to shallow depths, the same order of precipitation of dissolved sulfides may occur.
Hydrothermal settings Sinter (Silica/Carbonate) Arsenic
Antimony
Mercury
Gold
Silver
Copper
Zinc-Lead
Order of precipitation ofhydrothermal mineralsbetween pluton andsurface
Contact metamorphic aureole settingSkarns-formed at high temperatures with both addition and
subtraction of material within contact aureole. Most economic skarnsoccur in carbonate country rocks, which are converted to marble. Oresinclude copper, iron, tungsten, zinc-lead, molybdenum, tin, talc, Au, Ag.
AUREOLE
CarbonateCountryRock
Intrusive rock
Robb (2005) An Introduction to Ore Forming Processes
Model of three stage skarn deposition
Copper porphery and skarn ores,Bingham Copper Mine, Utah
South Sister Volcano: the surface expression of magmatism
Solfaterra Caldera, Napoli
Solfaterra Hot Spring & Sulfur
Broken Top: shallow volcanic plumbing
Phantom Ship, Crater Lake, Or: shallow plumbing below vent
Beacon Rock: shallow plumbing below volcanic vent
River Mountains Lake Mead Mount Wilson Pluton
River Mountains, Henderson, Las Vegas
12 Ma Wilson Ridge Pluton (near Las Vegas) shallow plumbing
12 Ma Wilson Ridge Pluton: quartz monzonite shallow plumbing
12 Ma Wilson Ridge Pluton with riebeckite hydrothermal alteration
Mt Davidson,18 Ma granodiorite plutonComstock Lode,Virginia City, NV
Plutonism: aka deep volcanic plumbing Cretaceous Granite Dome, Texas
Coarse grained plutonic rock���Cretaceous Granite Dome, Texas
Mono Lake
Tioga Pass
Yosemite National Park, Sierra Nevada, Mono Lake
Gaylor Lakes
Gaylor Lakes Basin, Sierra Nevada, CA
Toulumne Intrusive Suite
Gaylor PeakU Triassic-JurassicMetamorphicRocks
U Triassic-JurassicMetamorphic RocksDana, CA
Fracture filled with quartz at Dana, CA
Plutonic Plumbing:���
1.7 Ga���Granitic veins���
cutting schist & gneiss ���
Black Canyon of the Gunnison
River