The fluids that generate IOCG deposits are thought to be saline and highly oxidized and would be capable of leaching and transporting significant uranium. The reasons for uranium enrichment in certain IOCG deposits remain speculative but could include the composition of mineralization-related magmas, of the wall rocks altered by hydrothermal fluids or of the fluids mixing at the site of mineralization.

U is leached out of granite by fluids and precipitate it when the fluids encounter carbon in graphite for example. When magmas intrude/extrude into an area with mafic volcanics their Au-bearing fluids may leach some more gold out of (mafic) volcanics and precipitate it in native form or within pyrite.

Therefore, both metals have an origin in magmas.

I have encountered one vein system in metamorphic rocks that was very rich in both U and Au, but it was limited in size and obviously of epigenetic origin.

Interesting following

Dear Colleagues,

I maintain the classical structural description of deposits and call the most important U mineralization associated with gold " Breccia Pipes"

Makes up 66% of Australias reserves plus resources. The deposit occurs in a hematite-rich granite breccia complex in the Gawler Craton. It is overlain by of flat-lying sedimentary rocks of the Stuart Shelf geological province. Virtually all the economic copper-uranium mineralisation is hosted by hematite-rich breccias. This broad zone is surrounded by granitic breccias extending up to 3 km beyond the outer limits of the hematite-rich breccias. The deposit contains Fe, Cu, U, Au, Ag, REE (mainly La and Ce) and F Only Cu, Au, U, Ag are recovered. Uranium grades average from 0.08 to 0.04% U3O8, Copper grades average 2.7% for proved reserves, 2.0% for probable reserves, and 1.1% for indicated resources. Gold grades vary between 0.3-1.0 g/t. Principal mechanisms which formed the breccia complex are hydraulic fracturing, tectonic faulting, chemical corrosion gravity collapse. Much of the brecciation occurred in near surface eruptive environment of a crater complex during eruptions caused by boiling and explosive interaction of water from lake, sea or groundwater with magma. Examples: Olympic Dam, Prominent Hill, Ernest, Henry, Starra, Osborne, Australia; Candelaria,Chile, Salobo, Sossego, Brazil; Michelin and Sue-Dianne, Canada.

The second one is the so-called "Au-U quartz pebble conglomerate"

Witwatersrand, South Africa, Elliot Lake, Canada, Sierra do Jacobina, Brazil, Tarkwa, Ghana and the Guyana Shield area in Colombia Earth’s atmosphere was a different one from today’s oxidizing conditions Archaean to the Early Proterozoic (3,100-2,200 Ma), some also extending into the Middle Proterozoic such as the Tarkwa (1,900 Ma) oligomictic mature conglomerates intercalated with sequences of less mature conglomerates and sandstones sedimentary to hydrothermal mobilization Archaean granite-greenstones Braided streams in alluvial fans (Au) Carbonaceous layers (algal mats) = low-energy regime deposit with U and fine Au Quartz, gold, pyrite, uraninite, brannerite, zircon, chromite, monazite, Ru-Os-Ir-Pt-Fe alloys, sperrylite.

I present them in some short remarks.

Further details you will find with Dill (2010) "The chessboard classification scheme of mineral deposits..."

H.G.Dill

"Au-U quartz pebble conglomerate"

Witwatersrand, South Africa, Elliot Lake, Canada, Sierra do Jacobina, Brazil - OK. However, Tarkwa, Ghana has gold but no uranium (and is much younger than WITS).

Dear

My opinion is that uranium deposits are generally present along with batholite granite intrusion, whereas gold deposits are formed by the presence of hydrothermal solutions, both deposits may be present together, if the geological conditions support the formation of gold in granite intrusion, especially the geological structure that makes the pathway for formation hydrothermal deposits and the area is around a volcanic zone

Uranium deposits are not always around granitic intrusions, i.e. Colorado Plateau deposits. There occur some roll-type deposits, i.e. in Wyoming in USA, but these granites are alkaline types from which uranium was transported under atmospheric conditions, at 25 degrees Centigrade. So there are no relationship between Au and U.Witwatersrand, uranium-gold deposit in South Africa is placer-type under reducing atmospheric conditions.

I think the answer is that in some places, e.g. Olympic Dam, gold and uranium are found together, but in many other places gold is found without uranium, and in quite a few uranium deposits there is no recoverable gold. It depends on the type of chemical system that was operating.

There is an interesting unconformity related U-Au deposit at Coronation Hill, NT Australia, which is well worth reading about. A paper by Stuart Needham and Peter Stuart-Smith is a recommended reference.

Depends fully on deposit type and if we have shallow or deep seated fault systems as fluid conduits. In a typical roll front type U deposit (shallow faults)there is rarely gold with U, where in IOCG (Olympic Dam, Great Bear Lake) and SSD (Copperbelt) we have deep seated fault systems we also have gold.

Dear Khaled,

Geochemically, Au and U have different behaviors. U can appear in +4 and +6 valencies whereas Au is usual in +1 and +3 valencies. It makes the behavior of these elements variable. Uranium is transported in +6 state with different complexes such as OH, SO4, F, CO3, and some other species, and is deposited in +4 state. Au is transported with some complexes such as Cl, S, and sulfosalts. In my opinion, the same complexes between U and Au can be caused to the contemporary occurrence of these elements in an environment.

Regards,

Rahim

cross relationship.

U content increases with increasing Au content

Take a look at Mawson's Rompas deposit in northern Finland. High grade U and Au mineralisation, yet nuggety

In proterozoic age, both U and Gold were transported as placer deposits in elliote lake deposits in Canada (oligomectic conglomerate deposits), as well as witwatersrand in southern Africa. The main factor controlling the transportation of U minerals as placer without oxidation is the non-oxyginated climate at that time. but later they found permitive alge, which means there is oxegen during the deposition. Finally , they interpreted by glacial period prevailing during this period, this galciation presereve the U- minerals from oxidation. Therefore, under glacial condition both uranium and gold can be transported and deposition as placer deposits.