«

»

Apr 15 2013

Print this Post

Types of Ore Deposits

Notes: Not all ore deposits will contain secondary minerals. The epigenetic (different times) and syngenetic (at the same time) is based on the time frame for the formation of the host rock and the ore. Some ores cab be classified as both syngenetic and epigenetic.

Placer Deposit

Syngenetic
Primary: Gold
Secondary: Platinum, Uranium, Silver, diamonds
Other: NA
Host: magmatic basalt
Process: Magmatic intrusion and later transported by fluids
Examples: Gold Rush (India and any country river or flowing water)

Soil Deposits

Syngenetic and Epigenetic
Primary: Aluminum
Secondary: Iron
Other: NA
Host: Kaolinite
Process: Chemical and physical weathering due to erosion
Examples: in the tropical areas

Kimberlite Deposits

Epigenetic
Primary: Diamond
Secondary: NA
Other: Kimberlite Indicator Minerals (KIM)
Host: Kimberlite
Process: Formed in depths over 100 km under the temperature of 900 – 1200 C and high pressure. Ideal conditions are in the old, cold, thick Archean (>2.5 Ga). Rapid igneous intrusions known as Kimberlite pipes.
Examples: Ekati, Diavik and Snap Lake (unusual kim. sill), Canada

Mafic Igneous Intrusion Associated Deposits

Syngenetic
Primary: Nickle
Secondary: Gold, Copper, Molybdenum, (PEG)
Other: sulphides
Host: mafic and ultramafic magma and the type of rock depends on the degree of melting and the type of country rock.
Process: Magmatic intrusions result in partitioning of elements and contamination of the melt by assimilation of the host rock. Gravitation segregation of sulphur result in sulphide ore to form at the bottom of the melt. It is also possible to produce this type of ore through the meteorite impacts, rift/continental flood basalt-associated sills and dykes, volcanic flows and troctolite intrusions.
Examples: Sudbury (meteorite impact-unusual), Voisey’s Bay and Thompson, Canada

Greenstone Related Quartz Veins

Epigenetic
Primary: Gold
Secondary: Silver
Other: Chlorite, Actinolite, Amphiboles
Host: quartz vein
Process: Intrusion of epithermal fluids and regional metamorphism. Usually associated with areas of wide spread regional metamorphism.
Examples: Abitibi Greenstone Belt

Porphyry Deposits

Epigenetic and Syngenetic
Primary: Copper
Secondary: Molybdenum and Gold
Other: Chalcopyrite, Bornite, Chalcocite
Host: magmatic rocks, stockwork (veins and breccias)
Process: Intrusion of heavy mineral rich fluids in subduction zones (leading to hydrothermal alterations). Stockwork texture, veins amd breccia are typical types of rocks. If the formation is caused due to hydrothermal alternation, then the ore is classified as an epigenetic formation.
Examples: El Teniente, Chile

Volcanogenic Massive Sulphide (VMS) Deposits

Syngenetic
Primary: Zinc, Copper, Gold, Silver, Lead
Secondary: Cobalt, Tin, Barium, Manganese, Cadmium, Selenium, etc
Other: Sulphides
Host: stockwork sulphides and ophiolite
Process: Magmatic process which result in geothermal fluids (“black smokers”)
Examples: Since they form in tectonic settings, it has an age range between the modern seafloor materials to as far as 3.4 Ga. Therefore, the deposits are globally distributed along old and young spreading centers.

Sedimentry Exhalative Deposits (SedEx)

Syngenetic
Primary: lead, zinc, silver
Secondary: barite, gold, copper, tungsten
Other:
Host: Underwater sedimentary rocks
Process: Mid-Ocean Ridge (MOE) hydrothermal fluids (“black smokers”)
Examples: Sullivan, Canada

Mississipi Valley Type Deposit (MVT)

Epigenetic
Primary: zinc, lead
Secondary: carbonate
Other: sulphides
Host: carbonate hosted sulphides
Process: precipitation from circulating groundwater at relatively low temperature (brines transported)
Examples: edges of the sedimentry basin in Canada.

Unconformity Associated Deposit

Epigenetic
Primary: uranium
Secondary: lead, radium, cadmium, thorium and REE
Other: NA
Host: Uraninite
Process: Unconformities in the basins, but there are 14 different types have been identified. In Canada, they are usually found in unconformities between Proterozoic silliclastic basins and metamorphic basement.
Examples: Athabasca Basin, Canada

Permanent link to this article: http://sanuja.com/blog/types-of-ore-deposits