User:EmlyCole/Iron oxide copper gold ore deposits

Deposit Features
A feature of IOCG ore deposits is the large variability between deposits regarding the ore grades, alteration styles, and fluid inclusion characteristics that leads to the lack of a complete model for the deposits formation.

An important feature of these deposits is the depth of formation, which ranges from the deep crust at depths of over 10km, to paleosurfaces. This main feature sets apart IOCG type deposits from porphyry skarn Cu-Au deposits which are from origins of shallow formation (<5km depth). The formation at deeper depths has implications such as ore fluids from a deep source.

Ore Fluids Formation
One of the biggest factors in the formation of IOCG deposits is the presence of ore fluids. The driving factor for the fluids movement in the upper crust is the present paleogeothermal gradients, as well as regional hydrothermal systems responsible for the for the alteration within these deposits. IOCG deposits have a distinctive set of two fluids vital in their formation :


 * Highly oxidized fluids such as a meteoric or ground waters
 * Brines of magmatic hydrothermal fluid or fluids that have reacted with metamorphic rocks, that are deep sourced and high temperature

There is also evidence of other fluids that are volatile rich in the formation of these deposits.

Economic Mineral Occurrence
IOCG ore deposits containing economic quantities of both copper and gold originate from the Precambrian. Larger deposits with >100 tons of resources occur towards Paleoprotozoic and Archean cratons. These large deposits formed by mantle underplating impacts to metasomatized lithospheric mantle, and smaller deposits form by tectonic settings replication of this process in more recent times.

The content of gold within these deposits is largely variable, and can be a factor in the economic value of the deposit. The gold contents of deposits averages 0.41 g/t Au, with the majority of worldwide deposits averaging less than 1 g/t Au.

The contents of gold can appear in three different forms in these deposits :


 * Native gold
 * Electrum
 * Gold–bismuth–antimony–tellurium alloy

World class IOCG deposits contain consistent Cu grades, between 0.7-1.5% Cu, higher copper grades than that of most world class gold-rich porphyry copper deposits.

Factors of Ore Formation
There is controversy in regards to the factors that control the formation of the ore in these deposits, as they display a lot of variety between deposits in regards to the ore grades, alteration styles, fluid inclusion characteristics, and their links to their tectonic settings, and nearby intrusions. This has led to the lack of a complete model for the deposits formation.

There is a variety of models that have been made to try and model the formation of these deposits, such as IOCG deposits as the lower root potion of iron oxide-apatite formation, or models of complex interactions between more than two fluids of magmatic, surficial, sedimentary, or metamorphic origin. There is still controversy to these origins but using tracing of fluid sources has opened exploration possibilities in recent years to large deposits in Australia, such as the Olympic Dam deposit, where using fluorites REE chemistry, the fluids in the formation of the deposits were identified.