week 1 Flashcards
what are chalcophiles
react with sulphur
what are siderophiles
react with iron
why do prices for resources drop in 2008 and rise in 2020
global financial crash in 2008
greater need for technology due to covid in 2020
describe gold and the USD
- gold is a commodity (e.g. electronics, jewellery, dentistry)
- it is a store of value, especially as an insurance policy against political upheavals
- a falling USD increases the value of other countries’ currencies. this increases the demand for and price of commodities including gold.
- when the USD starts to lose its value, investors look for alternative investment sources to store value. gold is an alternative
describe indium
a rare metal generally found in ores of zinc and produced from residues generated during zinc ore processing
describe lithium
mainly used in the manufacture of lithium-ion batteries. the demand for these batteries is growing rapidly as they are used in electric vehicles and for power storage from renewable energy sources.
what is a mineral deposit
an aggregate of a mineral in an unusually high concentration
what is an ore deposit
a mineral deposit that can be extracted at a profit. market factors change continually so a given mineral deposit may sometimes be an ore deposit but at other times, it may be uneconomic and hence not an ore deposit.
many ore deposits are large in volume but low in concentration (grade)
what is the relationship between an ore and mineral deposit
all ore deposits are mineral deposits but not all mineral deposits are ore deposits. an ore deposit is an economic term, mineral deposit is a geologic term
factors that affect mining
- shape of the deposit
- depth below the surface
- geographic remoteness
- access to transportation
- political stability of the region
- environmental considerations
- market factors e.g. price of the metal, costs of borrowing money needed to develop the mine
what is a mineral resource
an occurrence of intrinsic economic importance
what is a mineral (ore) reserve
an economically extractable measured or indicated mineral resource
grade of copper ores
most copper ores contain only a small % of Cu metal bound up in ore minerals, with the remainder of the ore being unwanted gangue minerals, typically silicates or oxides. the average grade of Cu ore in the 21st century is <0.6%
what does syngenetic mean
- formed at the same time as the igneous rock
-magmatic and sedimentary/surficial deposits are often syngenetic
what does hydrothermal mean
analogue for metamorphism - involves modification of igneous or sedimentary rocks, plus heat and mass transfer and pressure fluctuation
igneous and sedimentary ore type deposits can be altered and redistributed by hydrothermal solutions
are ore deposits randomly distributed?
ore deposits are not randomly distributed, they are linked to the global tectonic cycle. major periods of crustal growth occurred in the Late Archaean (~3000-2500 Ma) and Late Phanerozoic (~540 Ma to present). there was a global ‘quiescence’ in the Mesoproterozoic (~1600-1000 Ma).
describe orogenic (mountain-building process at convergent plate margins) deposits
- volcanogenic base metal sulphides
- porphyry-epithermal base and precious metals
- occur principally in the Late Archaean or Phanerozoic
- very few deposits in the proterozoic
describe anorogenic (free from mountain-making disturbance) deposits
- layered mafic intrusions
- sediment-hosted ores
- stratiform (sedimentary) Cu deposits
- occur principally in Proterozoic rocks
- ore formation might be closely linked to the “supercontinent cycle” - the broad-scale amalgamation and dispersal of the major continental fragments with time
- anorogenic and continental sediment-hosted metal deposits coincide with periods of crustal stability and the existence of large, stable amalgamations
- period of large-scale continental fragmentation give rise to volcanism and tectonism, which favour magmatic-hydrothermal ore formation
what is continental freeboard
the relative elevation of the continental land masses with respect to sea level or the geoid i.e. the area of the exposed continents vs the area covered by the oceans
what leads to higher/lower continental freeboard
tectonic stability -> increase in area of the continents -> deeper oceans -> higher continental freeboard
continental dispersal -> creation of oceanic crust -> shallower oceans -> marine transgression and flooding -> lower continental freeboard
how does continental freeboard affect the nature and preservation of continental shelf sediments
- marine transgressions flood the shelf and preserve sediments with deposits such as Pb-Zn ores, BIFs, bedded Mn and mineral beach placers
- oceanic lowstands result in shelf exposure and erosion with possible destruction of any ore deposits present in the sedimentary sequence
describe extensional tectonics and mineral deposits
- incipient rifting of stable continental crust, potentially related to hotspot activity. possible related to alkaline and kimberlitic magmatism
- magmatism is often localised along old sutures that might have been reactivated during hotspot-driven extension
-as continental rifting extends to the point that incipient oceans begin to open, basaltic volcanism marks the site of a mid-ocean ridge.
-the site is accompanied by exhalative hydrothermal activity and formation of Volcanogenic Massive Sulphide (VMS) deposits e.g. Cu, Zn, Pb - also suitable environments for chemical sedimentation and precipitation of Banded Iron Formation (BIFs)
what are mineral deposits formed in continental rifting setting
-anorogenic granites
-kimberlites (diamonds)
-SEDEX-type (sedimentary exhalative) Pb-Zn-Ba-Ag deposits
describe compressional tectonics and mineral deposits
- Andean-type collisional margins are the sites of large porphyry Cu-Mo deposits as well as signification Sn-W granitoid-hosted mineralisation
- volcanic regions above the porphyry systems are also sites of epithermal precious metal mineralisation
- zones of continent-continent collision such as the Alps and the Himalayas are not significantly mineralised
- this could be due to insufficient exhumation of mineralised zones
- older examples (e.g. the Appalachians) preserve Sn-W-U mineralisation in granites and hydrothermal vein-related Au deposits in their orogenic roots
evolution on the hydrosphere and atmosphere
- transition from Archean to Proterozoic at 2500 Ma broadly coincided with a major increase in O2 due to the evolution of primitive life and photosynthesis
- later event at the Cambrian boundary was related to the start of multicellular life
- the changing budget of atmospheric O2 and CO2 has been important in the formation of mineral deposits e.g. redox processes, weathering and erosion of the crust
how were banded iron formations formed
- in the Archean there was very little O2. the reduced atmosphere allowed mobility of Fe2+, which remained in solution in the oceans
- From the Proterozoic, oxidation of more soluble Fe2+ to insoluble Fe3+ -> precipitation -> formation of banded iron formations
type of ore deposits in impact structure settings
- progenetic (pre-impact) deposits that existed in the target rocks prior to impact - and may have been exposed by the impact
- syngenetic (syn-impact) deposits that result directly from the impact process
- epigenetic (immediately post-impact) deposits that results from impact-induced thermal/hydrothermal activity
the ‘late veneer’ hypothesis for Au and Pt
- in the early stages of Earth evolution, the originally homogeneous, molten planet differentiated into a metallic Fe-Ni core and silicate mantle
- as this differentiation took place, the siderophile metals (with a strong affinity for Fe, e.g. Au and PGEs) were partitioned into the core
- but today, concentrations of these siderophile elements in the crust and mantle are higher than expected and their abundance ratios are similar to those in chondritic meteorites suggesting that a substantial proportion of the precious metals in the mantle-derived from meteorites that impacted the Earth after the core and mantle had differentiated.
- If so, then much, if not all the mined Au and Pt ultimately had an extraterrestrial origin
- this is syngenetic
describe the Subury complex, Canada
- world’s leading producer of Ni with substantial Cu and PGE deposits
- product of a meteorite impact at 1850 Ma
- Ni-Cu sulphides found along basal contacts and in the brecciated floor of the impact structure - ‘differentiated impact melt sheet model’
-thought to have derived from lower crustal or upper mantle target rocks - this is progenetic
describe the post-impact mineralisation at Sudbury
- extensive, regional hydrothermal alteration pervasively affected Sudbury, particularly the breccia
- thought to have lasted about 4 Ma after impact
- produced large alteration zones and Zn-Cu-Pb mineralisation, similar to that found in volcanic/magmatic systems
