Especially for porphyry deposits, ore is closely related with the late-stage of magmatic event. Can be related with the compatibility of ore-forming elements or chemical reaction between fluid and hostrock (like boiling mechanism) or remobilization of ore which was transported previous pulses?
Hi Zehra, most porphyry Cu-Au deposits are hosted by intrusions with intermediate compositions which typically range from quartz-diorites to granodiorites in calc-alkaline magmas or monzodiorites to quartz-monzonites in high-K calc-alkaline to shoshonitic magmas. However, at that stage the underlying magma chamber continues to fractionate and it can still release late-stage pulses of highly evolved magmas (that underwent plagioclase fractionation) which can cross-cut, and locally even stope out, the porphyry mineralization. Cheers Daniel
Of course there is a direct relationship between the intrusive magmas and copper porphyries and veins of hydrothermal origin of gold and copper.
Ore minerals can be formed in the late stage of magmatization as a result of fluid segregation between the rock forming minerals and also formed from the hydrothermal solution at its early and late stages.
Dear Dr. Aral:
It is widely known that so-called “incompatible elements” which cannot be accommodated into the lattice of the (host) rock-forming minerals (plagioclase, pyroxene...) are enriched in the course of a magmatic differentiation, see , e.g., Sn, W, B, F, Li, U, Nb/Ta in acidic magmas, giving rise to late-stage mineralizations with cassiterite, scheelite, tourmaline.. It is a very well-known one of a wide range of processes accountable for the formation of mineral deposits, see also metasomatism…. This common trend can be applied to a wide range of ore-forming processes elsewhere.
I wish you much success
H.G.Dill
This paper colud give you a answer:
https://www.researchgate.net/publication/301660096_Triggers_for_the_formation_of_porphyry_ore_deposits_in_magmatic_arcs
zehra
there is a relation between late magmatic stage and porphyry, especially at subductiuon zones , within the evolution of magmatic arcs along convergent plate margins where subduction of oceanic crust and arc-type magmatism generates hydrous, oxidized upper crustal granitoids genetically related to ores
Depends on what you mean by "late stage". Originally it was thought that Cu was mainly, or only, introduced in porphyry Cu deposits during the initial high T event that produces hydrothermal biotite and K-feldspar (potassic alteration). This is certainly the case in some deposits (eg. Bingham). However, some porphyry deposits have an overprint of chlorite-white mica alteration (Far Southeast, etc.), and it is now (1998) known that this stage is lower T magmatic, not due to meteoric water (as thought in the 1970s and 80s). Many of these deposits show evidence that much of the Cu is introduced at this later stage, with evidence indicating that Cu deposition is largely due to cooling below 400 C. However, as you ask, is it possible that some of this Cu has been remobilized from greater depths. This is a question that still needs study, looking for evidence of remobilization of early-formed Cu sulfides at depth. I also wonder about this.
Hi Jeff, many thanks for your interesting comments. The chlorite-sericite alteration that you documented at Far Southeast in the Philippines is also found in Chilean porphyry Cu deposits (e.g. Cerro Colorado). At Cerro Colorado, the bulk of the Cu mineralization is associated with Chl-Ser alteration assemblages, rather than with biotite-magnetite alteration. However, this seems to be a very rare case, at least in Chile.
Hi. The formation of ore deposits results from a chain of process, related to the interaction of lithosphere and crust, regional and local tectonics, magmatism and geochemistry, which eventually lead to fluid focusing and metal precipitation . One important variable in these processes is the time. Apparently, the time influences not only the geochemistry but also the fertility of magma and magmatic-hydrothermal system . it is important to choose the most reliable methods which will allow not only to date the ore-formation but also to distinguish the age of precipitation from that of the consequent overprinting processes.
It depends on the nature of the magma, each type of magma from calc-alkaline to peraluminous and alumina has different effects
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