Controls on Ore Deposition Flashcards
Controls on Ore Deposition
Chemical
Lithologic
Stratigraphic
Structural
Chemical Controls
temp change
pressure change
reaction between solution and wallrocks
chem changes due to solution mixing
Temperature Change (Cooling)
will
affect mineral solubilities
affect stabilities of aqueous metal bearing complex ions
influence io-pairing hydrolysis constants of ions
affect oxygen fugacity
loss of volatiles disabling metal transport
Boiling
change in pressure regime from lithostatic to hydrostatic across an obstruction
Throttling
loss of H+ and H2O, increase Na+ and Ca+2
hydrolysis and hydration
loss of volatiles disabling metal transport without change in temperature
Retrograde
can cause precipitation by causing dissociation of some metal complexes and recombination
Dilution
T & P drop will result in precipitation from aqueous solution
Solubility
separation of one mineral from another in a natural solution
Exsolution
certain microbes are agents of mineral precipitation
Bacterial Precipitation
simultaneous capillary solution and deposition by which new minerals are substituted for earlier minerals or rocks
Replacement
loss and gain of electrons to specific ions
Oxidation and Reduction (redox)
certain substances cause precipitation from solution without themselves entering into solution
Catalytic Action
taking up of one substance at the surface of another
kaolin absorbing copper to form chrysocolla
Adsorption
occurs between solids and liquids whereby cations are exchanged, producing changed characteristics of both
Base Exhchange
ratio of pore volume to the total volume of rock
Porosity
necessary for passage of solution through host rock to depositional sites
Permeability
High Permeable Rocks
Rhyolite/Quartzite/Limestone/Silicified Rocks
Less Permeable Rocks
Shale/Schist/Basaltic Rocks/ Chloritized Rocks
some constituents in rocks are more reactive
Composition
thick accumulation of sediments in orogenic environments
Geosynclines
regional loci of ore deposition
-deposits cluster within or about stocks or batholiths
Igneous Intrusions
it is related to uplift, folding, faulting, and intrusion
geosynclines
control location of syngenetic sedimentary deposits
Unconformitites
are permeable pathways
replacement or metasomatic deposits extend or deposit along it
Bedding
serve as barriers for mineralizing solutions: Concentrate deposition in strata below or above
Impervious Layers (Covers and bases)
most important loci of ore
Structural Control
broader localization of ore belts/mineral districts
Regional
immediate localization of ore
Detailed
provide zones of porosity and permeability
structural control
deposits can be located if fluid is lighter than magma
Structural highs - cupolas (cut of a stock dome)
sulfide melt is heavier than silicate melt so located at bottom of intrusive
Structural Lows -lopoliths
axes with increased fracturing provide channelways for pre-ore depostion
Folds
control deposition of ore deposits
can result from regional stresses
Fractures/Lineaments
favorable for deposition
increased permeability
loci for interaction of different fluids
Structural Intersections
controlling structure
Syngenetic
a high velocity volcanic explosion vent
diatreme
physical and chemical properties of host rocks
exact properties are seldom evident
operate along with structural features
lithologic control
cut and displace ore bodies
change attitude, width, and grades of ores
Epigenetic
