Ah Ha....I found some publications on Magmatic garnets reported from a granitoid...and from other lithologies described in the article. Are any ecologitic? It does not seem so. No pyroxenes reported...nothing like serpentine or some otherwise bedraggled remnant of processes from below the 40km Garnet IN line.

The Iranian garnets in granitic material described below seem too "pristine" to be residuals from depth. But at least a good argument is made they are "Magmatic" and from I type granites. That is good.

Where is the copper now?

We are still hunting for the proverbial "garnet-in" material responsible for oxidizing magmas considered favorable for porphyry coppers....but this is a start.

Magmatic garnet in the Triassic (215 Ma) Dehnow pluton of NE Iran and its petrogenetic significance (zaminazmoon.com)

FYI..Include an interesting breccia dome...does it have any bits of ecologite preserved...I will take beat up garnets inside pyroxenes.

Limited published thin section studies of this lithology show no garnets...but maybe they did not know what to hunt for.

Something made these iron titanium? knots. They are also found within miocene dikes from the unknown..."Permotriassic" breccia dome.

Is there something dragged up from 40 km down?

Here is a little discussion of ultramafic/mafic/garnetiferous pyroxenite/dunite assemblage...preserving processes alleged from a "foundered arc keel" in so many words. The mineral assemblage is reportedly consistent with systems at 1-2 Gpa systems at 20-40 km depth and the proposed intrusive relationships are worked out well. I attach an image from that paper of a pyroxenite showing garnet in contact with amphiblole containing Fe/ilmenite symplectite. See the referenced publication below.

The system is not apparently undergoing the copper liberating process I am hunting for but it seems interesting. The tiny iron granules reported by Sun at Qulong and others from Bingham (above) might have come from similar amphibole grains associated with garnet that have been broken up and segregated from silicate host material. The visible "woody" Fe-Ti intergrowth seems consistent with the process of Fe oxide segregation leading to magma chemistry favorable to models of porphyry Cu formation being currently developed. The cumulates are deep and the porphyry system is "shallow". If you have a magnetic anomaly at 4 km... and nothing below it...I can only suppose the magnetic anomaly is what gives rise to porphyry fingers and "hydrothermal leakage" from the 4 km "chamber" giving rise to material at the surface.

(PDF) Primitive Arc Magmatism and Delamination: Petrology and Geochemistry of Pyroxenites from the Cabo Ortegal Complex, Spain | Michel Gregoire - Academia.edu

I attach an outcrop image of eclogite at the surface from the Caledonites showing silicate symplectitite. What is happening to the copper?

You don't get 100 million ton copper concentrations out of nothing.

Hi Steve, thanks for your interesting thoughts! However, if you are looking at ”adakites” you cannot expect magmatic garnets to be present, because ”adakitic” magmas typically form from low degrees of partial melting of upper mantle reservoirs where garnet remains as a residual phase in the mantle (i.e., residual mantle). This is the reason why ”adakitic” magmas are characterized by high whole rock La/Yb ratios. The HFSE such as Yb remain in the residual mantle phases (e.g., garnet) during the partial melting process. Please note that the term ”adakite” has been coined in an island arc setting at Adak Island and it should not be used in a continental arc setting such as the Chilean Andes. At least this is my humble opinion.

Sorry, Yb is a HREE of course. Please replace HFSE with HREE in my previous reply. That happens when I get too excited! :‐)

Hi Steve,

Actual garnet crystals (as oposed to the geochemical signature of residual garnet) have been very elusive in the study of adakites, but there are a few examples. To my knowledge, none directly related to porphyry copper systems, though.

In my opinion, one should not expect to see relict metamorphic garnets (unless accidental), but rather magmatic garnets, which are quite rare. And there are good reasons for this: if garnet crystallizes at all, it will do so at significant depth, and given their high density, they will be easily lef behind upon ascent. If some crystals manage to stay in the magma, they will tend to be resorbed as thet ascend, especially in wet magmas.

Here's one documented case of igneous garnets: https://academic.oup.com/petrology/article/42/10/1813/1567445?login=false

And here's a case closer to Chile that a student of mine was able to document: https://repositorio.unab.cl/xmlui/handle/ria/7747

And yet another case of "geochemical garnet", well modeled during magma evolution: https://academic.oup.com/petrology/article/48/11/2033/1563926?login=false

Hope this helps.

Daniel

Dear Daniel, please keep in mind that the term adakite has originally been defined by Defant and Drummond (1990) who described fresh island arc basalts from Adak Island in the Aleutians, Alaska. However, these volcanic rocks are completely fresh and unaltered. It is very misleading to compare them to parental intrusions that host porphyry Cu mineralization in the Chilean Andes even though the latter typically also contain high whole rock La/Yb and Sr/Y ratios. It seems to me like comparing pears and apples just because both are green!

Just to be precise, Defant and Drummond defined the adakites looking at a number of arc volcanoes in continental subduction zones, including the Cascades and the Austral Andes. But yes, the term comes from Adak island, originally studied by Kay and Kay. But I agree with your point, we should refer to these rocks as 'adakitic' rather than 'adakites' because of the heavy genetic implications of the term.

Thanks for the responses, note, I am looking for disequilibrium assemblages high up in the magmatic stratigraphy where the copper porphyry is...4km etc.. dragged up from the "root" zone.

Garnets are part of the new notion of oxidative segregation of iron +2 from +3 by garnet formation and gravity separation. Therefore we should expect to find something left of the process somewhere in some kind of rock, dike, pebble breccia clast or enclave. Hopefully not something that requires high-teck geochemistry...just ordinary observations. After all, chrome garnets are apparently good signs of diamondiferous pipes even if they do take a bit of lab work to confirm.

The oxidized magmatic fractionate created by garnet "fluxing" as it were, is thought by some to be essential to development of the copper rich tops of fertile metallogenic systems. As such there should be bits and pieces here and there of the deep reaction process that tell the story. Think poor pig-iron smelting.

Some remnants of that garnet/clinopyroxene Ti-Fe/hematite-magnetite in and out process could easily be trapped and preserved...even as solid mineral inclusions within, say feldspars, zircons of some kind. Fluid inclusions are surprisingly informative but do take fancy equipment.

I enclose a very fine writeup of sulfide silicate systematics in the cumulate fraction...the roots. So...can we follow a path? I proposed Iron aggregates...but I think they need more of a track record than I have found to convince folks that they have a solid target...as apparently some in the Qulong area seem to think.

The responsible garnets may be out of equilibrium...but there should be something left of them...be they magmatic/metamorphic or whatever as remnant symplectites maybe. ..just not in skarn garnets...those things are not magmatic/metallogenic source rock indicators.

The iron intergrowths in the "adakite sun intergrowths" image below, said by Sun et al to be unique to fertile systems, should...by theory, have come from say 40 km down and might carry with them interesting material that might show up on the surface and be somewhat observable...hopefully not merely tiny rims in zircons or zoned plagioclase...please.

And...I do not care if the rock is adakitic/kimberlitic/lamprophyric granodioritic or amphibolite of some kind. The idea is to develop an overall observational trail of evidence from "source rock". The oil patch folks have developed a very sophisticated model....the "golden zone" theory for development of oil patches. I suppose it works pretty well...and we do seem to be heading in that general direction.

My concern is that the good Fe/Mg or Ti mineral aggregates indicating fertility might be hard to tell from "tramp iron" or "microtectites" whatever...see below. If the iron with chalcopyrite inclusions is attached to say, remnant garniferous omphacite...I say we have a hit. If it is all gnarly...maybe more so.

Here we can see garnet (isotropic black) under x-nichols exsolving from clinopyroxene from a mafic enclave in kimberlite. Notice there is a 40% volume expansion! That might drive convection processes. Maybe the famous garnet/iron reaction associated formation of oxidized magmas looks like this.

So...we should look at remnant clinopyroxene in enclaves and at inclusions within clinopyroxene to see remnants of the hypothetical garnet-iron self-oxidation process. Notice there is a bright reaction boundary! SEM anybody?

Maybe this is step one.

Unfortunately reports speculations and offhand comments of copper in eclogite and kimberlite seem missing. Why is that? The copper must come from somewhere. Is it just leached out of ordinary magma chamber wall rock at a higher elevation?

PII: 0012-821X(89)90191-X (colorado.edu)

The attached link to an abstract in American Mineralogist suggests discovery of and documentation of the iron eclogite garnet association I seek. It may document the very iron oxide titaniferous "spheroid" granules discovered in what Sun et. al indicated were unique to fertile porphyry systems at least around Qulong.

Ref:

Immiscible melt droplets in garnet, as represented by ilmenite–magnetite–spinel spheroids in an eclogite-garnet peridotite association, Blanský les Granulite Massif, Czech Republic | American Mineralogist | GeoScienceWorld

Abstract

Interlayered eclogite and symplectitic garnet rock that is interpreted as former garnetite are found in the Gföhl Unit of the Bohemian Massif. They show unusual Fe–Ti-rich compositions, characterized by TiO2 contents up to 2.34 wt%, and Mg# of 59.8 and 51.6, respectively. Equilibration conditions of 1250 °C and 4.0 GPa are calculated for eclogite. The petrogenesis of this rock association can be best explained as high-temperature and ultrahigh-pressure magmatic cumulates. Highly decoupled Sr-Nd isotopic composition with nearly constant radiogenic 87Sr/86Sr values and a slightly negative e Nd value suggests interaction of aqueous fluid most likely derived from a subducting slab and/or from parental magmas. The garnetite contains large (up to 0.5 mm) Fe–Ti-rich spheroids of ilmenite–magnetite–spinel, interpreted as frozen droplets of a melt incorporated in the growing garnet. The interstices between these garnet crystals are filled by ilmenite–magnetite–spinel aggregates, with concave outer surfaces with trapped Fe–Ti-rich melt. These ilmenite–magnetite–spinel spheroids represent possibly the first record of such an oxidized assemblage in mantle rocks, and probably the first description of Fe–Ti-rich melt in eclogite-garnetite mantle rocks. (emphasis SMJ). A calculation based on mineral proportions in the spheroids and mineral composition indicates that the immiscible Fe–Ti-rich melt consisted of 28.7 TiO2, 3.7 Al2O3, 0.2 Cr2O3, 27.9 Fe2O3, 37.0 FeO, 0.8 MnO, and 1.7 MgO wt%. Petrology and geochemistry of the garnetite indicates an unusual composition for an upper mantle melt with a high oxygen fugacity and relatively high Fe content. (emphasis SMJ).

I attach a copy of the full article posted in Researchgate by the author together with convenient snips from that article clearly documenting the observation of spheroid Iron-Ti minerals as immiscible droplets in symplectites adjacent to garnet as part of a proposed decompression reaction in an exposed high temperature pressure material interpreted as magmatic cumulate in garnetite/eclogite mantle material of the Bohemian Massive Czech Republic.

Now we seem to have field evidence of how magmas become oxidized. Now to put something like this in association with a porphyry copper.

Note...we do not need for the porphyry to be part of a single magmatic/volcanic event...the idea from Cin-ty-lee of an "arclogite" for instance, requires the base or keel of a tall mountain chain. Such a tall mountain chain drives a "metamorphic" process at depth by gravity and so transforming basaltic material in the keel into "metamorphic" eclogite. The process of arclogite isostatic overpressurization is simply a consequence of isostatic compensation and burial pressurization. The theory is somewhat akin to development of the "golden zone" theory for petroleum genesis.

The driving force could come from an unrelated plate-driven collision and ancient/prior mountain uplift entirely disconnected with later copper porphyry metallogenesis.

We do not need subduction...just elevation and isostatic pressurization and then later depressurization, say from tectonic rollback. Maybe there is subduction...maybe not. The hypothetical cumulate consisting of dense metaliferous segregates...somehow later transported, trapped and sulfidized in some cases, might have been from a previous collision, for example, the permotriassic collision in the Andes that made the chilean "high andes" tectonic slice.

Such oxidized material intersecting metalliferous cumulates, if they exist within the scope of younger magmatic influence, might be caught up in much later miocene or in general cenozoic magmatic/tectonic events...such as those that are copper bearing. Can we find them?

So...I believe there might be remnant bits of the tiny metallic spheroids preserved...perhaps in abundance in the vicinity of the fertile porphyry systems...even in material eroded from their surface expression.

Such microdroplets in symplectites might be common...but unrecognized...like the spheroidal tectites and micrometeorites that have relatively recently become so essential to working with meteorite deposits. See below.

Maybe folks have already found them but have no unifying concept to attach them to. Porphyry copper microspherules...impact microtectites..microgranules of some kind.

Here is where the eclogites of subduction origin fit into the model, using seismic tomography. I enclose the links and a PDF of that work. Apparently, they come from 60-100 km down according to seismicity. Note the fluids would have to pass through the serpentinized wedge area. My question is...do any porphyry systems show signs of such a deep source or transit through the serpentinized zone? It's easy to say one way or another...but my question is whether such a pathway is favorable for segregation of metals. Think smelting chemistry.

What would that material look like after floating up from 60-100 km, reacting and getting stuck at, say, 4km, the bottom of brittle crust?

(1) (PDF) Along-Dip Segmentation of the Slip Behavior and Rheology of the Copiapó Ridge Subducted in North-Central Chile (researchgate.net)

Howell et al in his recent posting, Jan. 2022 (see below) show the process of sulfide/magnetite cumulate formation and segregation under natural conditions within pyroxene/amphibole sill complexes in northern Italy. This does not discuss the formation of iron oxide droplets enough but there is a reference to the association of iron oxides and sulfide droplets and how buoyancy works. The formation of microdroplets of liquid copper rich sulfides and their migration under gravitational separation is likely associated with magnetite crystal bubbles. Dikes and sills associated with the process should not only show remnant features but might help understand the extent to which magmatic smelting has proceeded and perhaps the overall favorability of a particular magmatic system underlying the proverbial subcrustal and syncrustal porphyry apophysis.

The bubbles of sulfides and iron oxides apparently follow each other....like in some "froth flotation" system. How prospective would such an observation be? Can't say but if you can't see any of the process....likely the dikes don't tap the right stuff. Find other dikes...if you can.

(PDF) Mobilisation of deep crustal sulfide melts as a first order control on upper lithospheric metallogeny (researchgate.net)

Here's one documented case of magmatic garnet: https://academic.oup.com/petrology/article/62/4/egaa099/5937830?login=true

Here is a paper focusing on magmatic garnet in ore-forming porphyries. Hope it would be helpful for you. Cheers and regards.

Article High Sr/Y Magma Petrogenesis and the Link to Porphyry Minera...

Looking through candidates for the deep roots of porphry copper systems at the 40-60 km depth, conveniently exposed copper rich mafic/ultramafic material shows no sign of garnet minerals. Below are relevant differentiated copper rich mantle melt "plumes" mined for copper in Okiep and the Brazilian equivalents across the South Atlantic Ocean. Not only that...the copper mineralized host rock geochemistry seems wrong for having a Ca-garnet bearing source...apparently the cupriferous norites/hypersthenites hosting the copper as chalcopyrite and bornite is described as being sufficiently Ca poor to eliminate sources consistent with garnet bearing pyroxenites (ecologites). Mafic material from the "source depth" is actively being mined for copper but is still hard to connect to the oxidative mantle "smelting" systematics of garnet and iron species that are theoretically important in copper solubility, movement and accumulation. Something needs to feed the upper crust "chamber" from which the proverbial copper porphyry would be sourced and someone should find clear indications of the "copper smelting" process needed for generation of porphyry copper deposits sourced from fertile reservoirs 4 km down in the upper crust.

There are apparently tiny crystal inclusions that show a garnet signature...but there seems no obvious copper bearing source rock or iron oxidation process to be found. But don't give up yet. The feedstock and the processes leading to fertile if not actually copper rich magma chambers should be present. There are garnets reported in small "fiamme" within the "metasomatized" mantle wedge but that is for another post.

Quote:

"A basic magma impoverished in calcium must necessarily be derived from a Ca-depeleted mantle source having few or no calcium-bearing minerals such as garnet, amphibole or clinopyroxene. Harzburgite or ortho-pyroxenite from the sub-continental lithosphere would be compatible with this requirement. (PDF) Genesis of the Precambrian copper-rich Caraiba hypersthenite-norite complex, Brazil.

Available from:

https://www.researchgate.net/publication/226320784_Genesis_of_the_Precambrian_copper-rich_Caraiba_hypersthenite-norite_complex_Brazil [accessed Apr 20 2022].

High Sr/Y Magma Petrogenesis and the Link to Porphyry Mineralization as Revealed by Garnet-Bearing I-Type Granodiorite Porphyries of the Middle Cauca Au-Cu Belt, Colombia | Request PDF (researchgate.net)

To be determined:

Here I attach a few images and files....the garnet in question is hydrothermal. Not the right material. We should see signs of Cin Ty Lee's Arclogites somewhere even if the material is attacked in shallow magma chambers at 4km I suspect that signs of the dewatering/arclogite/ecologite transformation and the development of oxidizing magmatic conditions should be present. Note...I am trying to look "through" the effects of sulfidation and find pre-sulfidation material before water undergoes dissociation and confuses magmatics with hydrothermal processes.

We are hunting for the "cumulate" from which garnets and magnetite/hematite undergo the critical "magnetite crisis". If all goes well we might see where chalcophyllic minerals "float" through a cracked network while temperature and viscosity are just right. Think mineral processing/flotation.

(99+) Petrology and geochemistry of the shoshonite-hosted Skouries porphyry Cu-Au deposit, Chalkidiki, Greece | Tilo Kroll, Thomas Seifert, and Albrecht Schneider - Academia.edu

(99+) Petrographic Characteristics of Porphyry Indicator Minerals from Alkalic Porphyry Copper-Gold Deposits in South-Central British Columbia (NTS 092, 093) | Antonio Celis - Academia.edu

Below are 3-D stains of Azurite in a foliated granite "gneiss" from outcrops not too far from the mountain K2 in Pakistan/Himalayas. It is a commercial decorative stone and is described a fair amount in MinDat. However, those who do the petrography and post it in Mindat seem to have missed the altered nature of the material. What Fe-Mg minerals remain are merely greenish patches. Why the 3-D copper is a mystery to some but I contend it is the sign of having been somehow associated with a magmatic carbonate source that leached enough copper to make both Azurite and malachite. The process of moving copper as spherical...yes...spherical bubble-stains through a squeezed mush of "gneissic" material suggests there might be an unrecognized copper mobilizing process that somehow got frozen in place without deformation. I think there is actually one image that shows a "garnet". Forgive me but I did not buy it when it was available. Could we be seeing some kind of high level process stratigraphically well removed from the cumulates below? Or maybe there is just a big block of limestone that got stoped into the granitic material during emplacement. Still...I want to see a bit of the proverbial cumulate segregation process associated with pyroxenites etc. If there are "mafic enclaves" with garnet...so much the better. I suspect folks working in the mining sector might have seen the right material...veined mafic rock with cpy and relegated it to merely some hydrothermal process before loading it on a truck. Anyway...I want to see sulfates...but I will accept carbonates if I have to as an extremely differentiated oxidative float of a magmatic cumulate under destruction.

Oh...it's called K2 Jasper because it takes a good polish. The silica content is high and the remnant biotite is not prominent. It is feldspathic and it is pseudoblastic...meaning the biotites seem to make porphyroblastic ghosts. It's an altered granite gneiss and the quartz is not euhedral. Some quartz appears secondary andis mildly like a cockscomb...and it actually seems to have a garnet or two in some slabs.

Finally....thanks to Ming-Liang Huang above we have a pretty good hit. Thank you for the link.

High Sr/Y Magma Petrogenesis and the Link to Porphyry Mineralization as Revealed by Garnet-Bearing I-Type Granodiorite Porphyries of the Middle Cauca Au-Cu Belt, Colombia | Request PDF (researchgate.net)

The article is not an open publication yet. If you review the slide below note there are definitely signs of the working of garnet, completely enclosed by plagioclase and preserved from destruction. The idea is that early pre mineral dikes host garnet but intermineral dikes do not...more or less. You have to go to Economic Geology and find it. It was released in 2017 and is about on page 551-558 of that year.

It makes good sense. The paper has a lot of high level backing by major players in the industry. So...it appears the non mineral Garnet-bearing dikes predate the intermineral dikes by several hundred thousand years according to age dating reported in the article.

So...first the garnet and the magnetite crisis...then comes copper mineralization...simplifying things of course and making reference to the "arclogite" concept of Cin-ty-lee. The presence of the magmatic garnet is not an indicator of "ore" but it is a sign...probably, that you have hit a "premineral dike". My guess is that there will be confusion and contamination but still....that is what I get from the paper.

So it takes a while for the magmatic system to "cook" once it has become oxidized. The garnet phase seems to be happening at about .7-1.2 GPa...which puts us at the 40km depth...and then, presumably it goes up to a more shallow level where presumably the copper is accumulated...as some kind of oxidized species and is later sulfidized during emplacement as water undergoes decomposition.

According to the authors...Bissig et al...the main ingredient is water...and evidently thick crust is nice but maybe not as important.

I attach a figure that is in powerpoint form. Maybe it works on Researchgate. And...

I ask another question...will the plagioclases surrounding the garnet be aluminized and host anomalous copper?..

see image below.

So...apparently garnets come first in dike sequencing from a rising melt system..and evidently zircon preserves later conditions....it can come relatively late.

So the garnetiferous eclogite bearing mantle material I am searching for undergoes a transformation as it rises and goes away, perhaps to be preserved within newly made plagioclase as mineral relicts. On the other hand...the proverbial "keel" of an uplifted collision zone undergoes the opposite transformation as it sinks. Keel garnet appears "metamorphically" from a calcic/aluminous non-eclogite source as it sinks below the proverbial 40 km "slag/sludge" line of crustal metamorphic/metasomatic processes.

So...does the sinking mass in an orogenic "keel" sinking under gravity (isostatic connditions) might look more like a "skarn" and the floating stuff might look more like an intrusion?

The difference might be seen in those relict crystals preserved in Quartz or plagioclase. Is it more like a "skarn" assemblage or is it more like a magmatic differentiate. I think maybe the remnant grains found in newly grown crystals might be different depending on if it is full of "sinker" garnet or "floater" garnet.

(fancy words aside...I say we are analyzing natural smelter... floating stuff that is shallow...is "slag"...stuff that is deep is "sludge"). Using simple words... Sinking stuff that is shallow...mere "feedstock" sinking stuff that is deep....well that would be sludge. The garnets however should be different.

Unfortunately the smelting systematics are not thought through on garnets...like they are on zircons.

Zircon: The Ce+4/Ce+3 ratio of zircons is a pretty good sign of fertility...in the relatively uncontaminated "magmatic slag" floating component.

The famous europium anomaly thought to indicate garnet fractionation might just be a sign of Ca plagioclase formation. Likely it depends on whether you are testing the "slag/foam" or the "magmatic sludge" of a natural tectonic "smelting" system.

PS..."Zircon grains may crystallize late, during the solidification of granitic magmas..."

Orogenic garnet caught up in a porphyry intrusion might seem like eclogite. Included is a presentation showing orogenic garnet from the worlds largest Orogenic Belt...(apparently), together with a discussion of how to identify garnet origins based on texture. The quick answer is that orogenic garnets should be zoned and in my opinion, carry hornblende or biotite remnants from previous associations. Magmatic systems hosting eclogite garnet should not carry hornblende or biotite to my thinking. Eclogite garnets should carry clinopyroxene remnants...or signs of mantle material. Of course that should affect the mineralogical/geochemical signature significantly.

The claims that metamorphic processes should be zoned because they are "slow" and igneous processes are not as well zoned because the rate of growth is "fast" is hard to reconcile with the widespread use of zoned minerals, plagioclase, zircon etc. in magmatic systems as indications of chemical processes.

Frontiers | Gem-Grade Garnet With Metamorphic Origin in the Tiemurt Orogenic-Type Deposit, Chinese Altay Orogen: Texture, Chemistry, and Physicochemical Condition | Earth Science (frontiersin.org)

Below are PDF's and jpg's of the article cited above, for convenience. :

The orogenic garnets plotted according to chemical analysis:

"As exhibited in the Figure 6, (see text) most of the garnet grains are plotted from the spectrum of spandite (spessartite–almandine) with compositions ranging from Alm49.31Gro18.42 to Alm76.56Gro11. It is notable that no analysis is plotted in the field of spessartite + andradite + uvarovite."

This is what "arclogite" might look like. Will it be "fertile". Perhaps, but the orogenic belt deposits of the Central Asian Orogenic Belt are not large.

Remnants of garnet bearing rock in a copper deposit seems like the "kiss of death"...skarn, orogenic deposit etc. for hunters of magmatic porphyry systems.

An interesting deposit might pass for a valuable Cu porphyry because of the existence of a previous volcanogenic/orogenic magmatic system and it's dikes and plugs. Tectonic stacking over geologic intervals is confusing. Telling a small metamorphosed "orogenic" system from the "keel" of a tall mountain belt that is not longer present from a legitimate intrusive porphyry coming much later might be done based on the garnets somehow being or not being associated with a skarn system. But just dismissing the prospect because of the presence of garnet might be presumptive.

Are there any prospects where a fertile magmatic porphyry affinity is masked by a skarn? Maybe.

I am guessing the metamorphosed keels of orogenic belts will produce copper bearing systems but they might not be very big.

So.. garnets are found in a porphyry system...may not be the "kiss of death"...it could be a strange eclogitic remnant. However, so far there are few reports of eclogite material surviving in a magmatic system with deep roots that tap into a subduction system. Expect them to be present as crystal inclusions, as discussed above.

My take is that if diamonds and kimberlites exist...then we should see signs of deep source igneous activity around a porphyry system of significant size. However, such signs of deep seated activity are likely pre-mineral and seem unlikely to have been reported.

Hence...my question in the first place. Garnets in porphyry copper systems are probably from skarn assemblages...but not necessarily.

A unique example from Columbia "High Sr/Y magma petrogenesis and the link to porphyry mineralization as revealed by Garnet-Bearing I-type granodiorite porphyries of the Middle Cauca Au-Cu Belt, Colombia"

This is what we are dealing with...dikes from "hell?". Here...like Dante...we have

A nice diagram with a scale! Thank you Searle, 2015.

Those garnets...so when they get resorbed...then what?

Does the system get "aluminized" somehow and can we make the case that the "fertile" ones show something like the high aluminum zones in plagioclase that I showed before? What does that aluminum represent that garnets are gone and that you are looking at a "properly cooked" intermineral (copper bearing) fractionate that post-dates the so called "pre mineral" garnet bearing fractionates (dikes).

Finding those aluminous rims might be easier than hunting all over for garnetiferous samples and then...even worse...hunting for "non-garnetiferous" material.

Gee...I can always find "non-garnetiferous material". It is very easy.

Followup work on the story of excess aluminum in fertile copper porphyry systems suggests the observed aluminum excess might have been an artefact of long dwell time by the microanalytical technique where ablated Na contributed to anomalous aluminum. The followup work was done in 2018 by a powerful research group. I include several links to the open access article below and to the original. It certainly seemed like a good thought and the connection with the disappearance of Garnet and the appearance of plagioclase on stability diagrams lent a certain credibility to the idea.

The influence of water in silicate melt on aluminium excess in plagioclase as a potential hygrometer (cugb.edu.cn)

The influence of water in silicate melt on aluminium excess in plagioclase as a potential hygrometer | Scientific Reports (nature.com)

And the original link:

(99+) Porphyry copper enrichment linked to excess aluminium in plagioclase | Fredy Montalvo Enriquez - Academia.edu