Hi Steve,

We have anhydrite and gypsum in the Sarcheshmeh Porphyry Copper deposit, Iran.

There are hydrothermal anhydrite, less magmatic anhydrite in the Sarcheshmeh Porphyry Copper deposit, and also gypsum exist mostly in upper parts of the deposit that can confirm the high oxygen fugacity.

Prescence of hydrothermal and magmatic anhydrite and also gypsum is reported in many PCDs of the world (Stern et al., 2007; Cooke et al., 2011; Ling et al., 2013).

Hopefuly, it is useful.

Kind regards,

Mohammad

Dear Steve,

Anhydrite can be found associated with alteration zones of porphyry copper deposits and can be the indicator of physicochemical characteristics of these zones.

You can find some worthful information here:

https://pubs.geoscienceworld.org/segweb/economicgeology/article/114/1/143/569145/evidence-for-magmatic-anhydrite-in-porphyry-copper

http://archives.datapages.com/data/atlantic-geology-journal/data/035/035001/pdfs/86a.pdf

Regards,

Rahim

I think it opens up the possibility of endoskarns. If you don’t have carbonates sulfates will do. It is a sign there may be internal high grade zones...like at Lihir.

It’s my understanding that.Anhydrite is the result of hydrolytic processes, water provides the oxygen, silica competes for it. you either get a quartz rich product silicon dioxide or ionized sulfur-oxide species...the calcium and potassium ”float”. If you get calcium sulfates watch where the potassium might be if anywhere. Fortunately we get cobaltinatrate yellow-stain potassium alteration everywhere. There is calc-silicate sedimentary within the breccia mix. So?

Still...is the abundance of anhydrite in a “conventional” Au-Cu porphyry a sign of size or grade or is it subject to unusual contamination? Kay reported the Infiernillo igneous suite shows contamination. Presumably because of hi thorium geochem anomalies. So is abundant anhydrite merely a sign of something accidental to a differentiating melt in a relatively hydrous environment (Contaminated by wallrock) or is abundant anhydrite a fluke of trapping or level of exposure as part of a normal suite from a calk-alkaline melt?

Since anhydrite has to my knowledge received only modest interest by orthomagmatists, and others I am inclined to think it is an indication of contamination by “wet deep” warm wall rock, (calc-silicates?) presumably not merely warm or even hot dry basalt or andesite volcanic material.

The isotope folks say the oxygen and sulfide species in actual Cu porphyry mines are magmatic. Ok? But...What about ones with known mineralized skarns...grasberg might be a good example. Does the chemistry still show a strongly magmatic influence? Are the “teasers“ less magmatic. @@@

I say the presence of abundant anhydrite is or at least could be the sign of assimilation of something unusual...and a skarn might pop up somewhere in the magmatic/structural system. That seems likely...especially when we can see blocks of what seems like calc-silicate sedimentary material on 3500 ft sharp cliff faces at 17,000 ft (with google earth) And we have support...shallow level indicators of reaction... hornfels reports, are abundant.

The local paleoz-Mesozoic stratigraphic system straddles the intrusion and the structures where something like a dacite dome complex was squeezed up through sed. beds bounding a major fault zone. The magmatic system is in the right place...in a “duplex basin“ formed by major fault zone intersections. See image...target is in Chile right on the tip of a big structural promontory bounding Chile and Argentina.

@loan Pintea

Some mines such as Toquepala in Southern Peru have very significant amounts of gypsum/anhydrite. So much so that locally the medium grained sulphides (chalcopyrite, pyrite...) are essentially supported by a medium grained gypsum/anhydrite matrix (I've attached a photo example of pyrite+gypsum/anhydrite). Also, some of the largest fault zones in this deposit have a high proportion of gypsum/anhydrite as matrix to the fault breccia, and this increases with depth. I like the paper by Henley et al (2015), but I wonder whether it can fully account for the very large volumes of gypsum/anhydrite in such deposits.

Yes, i just read the paper. It is not only essential, the paper explains the paragenetic associations I have identified anhydrite, chalcopyrite, azurite, quartz and possibly barite, bornite and malachite. It was weird. It also explains the abundance...a hundred meters of anhydrite bearing core over 1 sq km. and adjacent to andesite

Unfortunately, The two paper attachments didn’t open. Links in text work. Henly’s paper worked. We thought about sulfur isotopes but we don’t know how well it really works. We are new at this.

I think that S isotope geochem would be strongly affected if sulphates from a sedimentary source were incorporated into a porphyry magma. the sources of the S could probably be fairly readily identified. Have a look at the paper which could be a useful background.

https://pdfs.semanticscholar.org/4fe5/17bd29156a6918431813600299bf701a7937.pdf

There is a lot of anhydrite at the Cerro Colorado porphyry copper deposit in Panama. The abundance of anhydrite is controlled by the alteration zone. It is present in the two mineralized host rocks (QFP and granodiorite) plus the andesite country rock. Anhydrite is the most abundant in the sericite zone and least abundant in the illite zone with intermediate frequencies in the other alteration zones. Above the "anhydrite surface" or highest level of anhydrite, it is frequently altered to gypsum.

Henley’s work regarding Ca extraction from plagioclase and hydrolitic oxidation of a H2S sulfide to Anhydrite makes complete sense because hydrolysis and sulfur oxidation consumes all the water...so you get dessication of the reaction products...Anhydrite is what happens if the supply of water is depleted and there is plenty of Ca and H2SNow what’s interesting is the possible

That tourmaline( boron) is a boon because it helps drive the reaction. Henley’s paper says we should see carbonates in a dry anhydrite-precipitating system going to completion and we do. I enclose a photo. Malachite below the gyosum front. If anhydrite means “hot and dry“ because the water is hydrolytically consumed...is that good or bad? High grade, deep, small, large dispersed?

Anhydrite (a= without, hydro= water, -ite=rock)

Anhydrite is consistent with potassic alteration somewhere in the system. (Yes NASA “martians” found cold water anhydrite. can form on mars...but there isn’t any sign of coy/tourmaline...or other high temp phases.). My magmachem take is that increased salinity in a solidifying heat liberating mass leads to decreased anhydrite In solution and mineral ppt.

Hydrolytic alteration under confined (lithostatic load) conditions favors Cl ionic species at the expense of the sulfate “ligand”...because clorides tend to be more soluble than sulfates. In short the decreased activity of water as salinity increases , KCl ,NaCl to borates etc drops sulfates out of solution. The hot salt spring escaping porphyry shell to shell leaves an anhydrite fingerprint. If the water isn’t salty enough or hot enough the water is not saturated with regard to sulfate and anhydrite does not ppt. It stays fluid and is lost. The fingerprint is not formed.

Of course, the hotter and saltier fluids get the closer you are Lillis to be to the potassic zone. Depending on relatively high sulfur abundance, low water supply and the extent of hydrolysis,, anhydrite ppt increases as it gets knocked out of solution..

As water temp drops and with meteoric dilution salinity decreases anhydrite is returned to solution via its relatively high cold water solubility...(like carbonates) by way of its hydrated form, gypsum. Low temp leaching should remove the two

if there is enough water, time and there isn’t too much anhydrite to leach With regard to erosional rates. So, excess hydrothermal anhydrite is the hi Ca analogue of alunite rich systems and the sulfate equivalent of carbonate deposition in oceans above the CCD, the carbonate compensation depth.

it is an indicator to the likelihood of excess chlorides in solution, heat, anomalous magmatic sulfur either as remnants in crystals or as a disequilibrium phase. It should be expected in a mafic sulfur copper rich system evolving to a /shallow silicate melt transitioning to a hydrothermal system right around the time the lithostatic seal leaks.

For example, 30 million tons of igneous to volcanic and cataclasite rock systems bearing anhydrite at .24% is a good sign that a synmineral metallic magmatic phase is present, has been breached...and needs to be hunted down Like oil traps in an overthrust belt.

The weakly mineralized quartz latite feeder dikes of Bingham come to mind as a feeder/“conduit“ to the mineral “trap”.

What would one thin feeder dIke caught up in a 2km wide cataclasite look like? It would look like what we have on the surface at milenamining.com.(a big wide smeared out prot-ore anhydrite alteration done that is just full of core porphyry minerals that don’t seem right, are full of cockade mixtures and do not have an intact magmatic source). The system confuses everybody until likely intact Feeder” dike sources are found intact between the anhydrite barite cpy, bornite, tourmaline magnetite filled “veins”.

The first video above shows a "felsic" breccia-dike crosscutting a coarser intrusive within a cooling system...that did not lead to formation of an alteration contact between them. Both are then crosscut by chalcopyrite bearing vein material showing a potassic feldspar like "selvedge". The imagery does not do justice to the chalcopyrite. I am hunting for signs of magmatic mineralization. The whole anhydrite story seems entirely dependent on finding "magmatic" anhydrite. What is in veins is nice but not necessarily compelling one way or another. Apparently isotope studies of vein material are of questionable value...because of x-contamination and isotopic dilution. It is OK to do isotope work if you want to risk finding contaminated isotopic indicators and can explain. Apparently Anhydrite isotope work needs to be conducted in something considered definitely magmatic, apatite...or failing that...another euhedral magmatic mineral...amphibole or pyroxene. Biotite is OK but apparently less compelling. The stories from Ladolam were my inspiration for the study. I think I am capturing the workings of mineralization from a medium grained "diorite" to a derived vein/dike/breccia all below the anhydrite on the surface. It's too altered to expect to find magmatic anhydrite, fresh dike or granoblastic rock is what is needed. The generation of a sulfate escape gas in the non-eruptive system is apparently what triggers formation of mineralizing ore forming fluids. I think that is marking the onset of potassic phase alteration. According to Sillitoe, you should see a volume change and fracturing. The loss of the sulfate phase then changes the system, it cools, depressurizes and deposits as veins, caps, breccias etc. Sillitoe argued that was why you got late stage vents/blowouts that sometimes destroyed the system. His claim was that you should find pieces of that system in the breccia. Well, they should be in the vein fragments too. Veins are plenty fragmental.

Here is a closer video of the same mineralizing system. Regarding fluid inclusion indications in previous videos, thanks.

I can use also apatite crystals for geochemical microscopy. In the Video below I show imagery of quartz-anhydrite matrix of drill hole core vein like material. It has been described as a "vein breccia", some of which definitely host tourmaline. It may be a rubbly trashy "latite" or quartz diorite breccia dike. Both fine-grained matrix material and coarse grained "vein fill" material are present.

The interval being researched in the video below is at about 230m below ground adjacent of a very large Miocene intrusive in Chile. The sample preserves open spaces with euhedral quartz blades. Rhyolite dikes also preserve open spaces to considerable depths...so the presence of open spaces is not diagnostic between vein and dike. The video shows floating clasts of magmatic segregation minerals (magnetite-chalcopyrite-cubanite-digenite?) in a varied fine and coarse anhydrite-quartz matrix. The clasts include both polycrystal aggregates and clasts with a greenish chlorite matrix in which magnetite crystals seem to grow and exsolved cpy etc..

The blocky black minerals are likely magnetite. It is possible euhedral trigonal hexagonal tourmaline fragments exist in polycrystal aggregates. The dull black "magnetite" aggregations and polycrystalline blocks show clear exsolution of magmatic minerals, cpy, possible euhedral bronze bornite crystals, interlaminated greenish blue digenite and a spongy black material with possible graphic textures of white material.

It was not clear what to do or how to think about the coarse blocky slightly lavender anhydrite matrix material. Isotopic work and Sr/Y ratios require considerable background. Apparently, analysis of hydrothermal minerals is not particularly useful without knowing the exact source of the minerals.

The "diorite-tonalite" world differs from the quartz monzonite world of Butte and Bingham. Chilean intermediate to mafic units apparently work in a different way. They hold much more sulfur, apparently more oxygen together with less pyrite and less quartz. Mineralization shows two different pathways to a metallic endpoint.

For example gas phases are apparently different:

Some of the minerals in the video below show a spongy texture. The spongy texture is a sign of degassing and the white material enclosed by black material may be primary magmatic anhydrite. My experience shows monzonite systems show reduced sulfur phases....pyrite for example. Note: In the video, some of the ambiguous black material associated with cpy crystals are relatively vitreous and have blocky crystallographic cleavage, suggesting tourmaline is mixed with obvious magmatic magnetite fragments.

I was concerned that surficial anhydrite on site represents the exposure of a deep phase and that the ore zone is eroded away. Conversely if it represents a very shallow ephemeral phase the sulfide zone is likely out of reach...+1000m deep. At Bingham anhydrite is found deep below the high grade zone 1500+ meters below the pre mining surface. The images of the site include below shows the situation, anhydrite adjacent to a large intrusive. Sillitoe was on site, reviewed the core and confirmed d-veins" on site at the surface but said nothing about the significance of anhydrite, the particulars of the porphyry at hand or the depth to mineralization.

Regarding depth to sulfide accumulation, the enclosed paper on quartz monzonite systems by Redmond/Einaudi at Bingham and the attached diagram indicates d-veins are "shallow". It is possible to speculate on depth to our diorite system target sulfide zone by using known temp/veinlet style and correlating with Bingham's original pit level. Our drilling starts in d-vein material and goes down 300m. The cartoon enclosed shows we got down to within 200m of the Bingham pre-mining elevation.

Anhydrite indicates a potassic zone exists and confirms yellow potassic staining of cores.

The project explained systematics of a diorite based porphyry. Because a diorite system can host much more sulfur than a quartz monzonite system and because it is too oxidized to deposit sulfide phases it appears that Diorites must evolve off excess sulfate. This seems likely to happen upon switchover to high salinity potassic alteration. Bingham quartz monzonite systems are not known for evolving a sulfate gas system. Perhaps they have not been recognized because of weathering over...38my not merely 14 my as in Miocene systems at hand. It is my conclusion that the lack of pyrite in dioritic systems is because the whole magmatic differentiation pathway for Chilean diorites are high oxygen... magnetite based pathways. Sulfide deposition in a mafic system apparently requires a sudden or distinct loss of excess sulfur and oxygen by "flashing off" the sulfates. We see that event not only in the existence of anhydrite but in the abundance of hematite iron on site. It actually shows up in geomagnetic work as a low.

Structural analysis provides support for the overall conclusions. The enclosed images show 1-2 ft thick anhydrite Veins x-cutting the lithocap...an exposed intrusive face. The whole intrusive system appears to occupy a graben corner within a cataclasite. It appears the anhydrite is a geochemical alternative to alunite. The presence of anhydrite in late veins suggests the system "fracked" as a result of a change in volume, likely due to K-spar alteration.

As previously discussed, geochemically the anhydrite was kicked out of the fluid system during increased salinity and temperature. It was squeezed/ driven out mechanically during post mineralization collapse. Anhydrite and silica therefore fill long post mineral fractures in the lithocap, leaked silica and anhydrite around the edges of the lithocap and apparently sealed up the cataclasite zone. The gypsum visible on the surface is from weathering of the reaction/collapse results...anhydrite to gypsum.

Teck ran PIMA over this core. They did not report potassic alteration. They reported "advanced argillic". I enclose a few representative shots. The veins host sulfidic clasts in a quartz-anhydrite matrix within an "advanced argillic" material.

The analytical group did not report anhydrite in the PIMA results and the project geologists did not really understand its significance. The material I photographed appears to be a "vein" in "advanced argillic" material. If so, it may be a "clastic" vein. I do not think it is a "hydrothermal vein". It comes from a strongly "veined" area adjacent to large "fins" of silicified "rock dust"...probably clastic dikes...large ones.

On another nearby hole Teck stained several hundred feet and got strong dusting of "yellow". Potassic feldspar flooding pink islands of plagioclase. It appears potassic alteration is overprinted to retrograde propylitic and PIMA missed it. I think the vein clasts are rip up pieces of magmatic sulfide zone following a change in load stresses to hydrostatic loading.

Previous geologists did not seem to consider vein clasts relevant. They were testing around what they considered was a "blowout". They looked for lithic clasts in rock breccia material and found low grades...max. 0.5% Cu peak. No "high grade" but lots and lots of 0.24-0.35 over hundreds of meters...mostly A veins and dustings of cpy and bornite with digenite and cpy. Magnetite was strong in some areas and tourmaline was "spotty".

Mineralization consisted of traces of sulfides in clasts and in a dirty quartz matrix filling mostly clast supported greenstone fragments and occasionally rounded pebbles. I analyzed some of the clasts and decided many of the "veins" are interclast sulfide fill and that the clasts show zonation. I enclose one I annotated. The project was halted due to winter in "0.65% in yellow staining potassic alteration at about 200m.

I don't understand the systematics of a diorite halo like I do around quartz monzonites but I'm willing to bet there is a difference due to SiO2 and sulfur solubility in an oxidized magma/magnetite dominated system.

The clear material is lavender anhydrite, the beige material is barite, the light material is a mix. Some of the rock fragments are cockade, others are granodiorite and some are felsites of some kind.

We do have some "tonalite" quartz diorite dikes that carry Cu. The system hosts tourmaline and round magnetic clasts...pebble dike material. I enclose a photo from the internet of cockade. I can't tell if our long sections of cockade-like "greenstone" material is merely recrystallized cataclasite, silicified "ash" or if there is a cementing magmatic material in some breccia areas. The enclosed bridge over icy water shows what I think. Large "dirty" clasts with dirty crusts sometimes cut by magmatic dike rock material...tonalites etc. adjacent to a thick andesite/diorite intrusive wedge. The tall mountain cliff face shows bimodal, white xcutting black and black within tan material with apparent cementing granite material between giant dacite dome fragments. It all is enclosed by intruding Miocene felsic granite and black hornfels like material encircling the sides of a 5120m mountain.

Nobody at Sernangeomin or Teck really understands if the peak is paleozoic or miocene. It seems like both.

We find large round magnetite clasts in the bottom of our last hole. I enclose an image. The magnetite is very strong...a supermagnet is hard to remove from the clasts.

Work at Bingham suggests D-veins are shallow...600m above the main ore zone. The presence of large rounded zoned pebble clasts of magnetite in breccia seems hopeful. We are looking at a magmatic system and according to Bingham modelling...600 m away. Drilling seems to get within 200m of the target elevation I established based on geomorphology and which has since been casually affirmed by others.

The structural work says we might be in a small "graben". I enclose an image. Finally, it seems to me that the crustiform textures go deep...I show some of our crustiform bornite-anhydrite-chalcopyrite material at maybe 200m. Fluid inclusion work on this material would show we are "above" the boiling zone. The hole bottoms in 0.35% Cu. at approximately 300 meters below the surface. We are within the degassing zone. We have tonalitic quartz rich dikes with Cpy. I think we are in an "escape" structure that makes a pie shaped "graben" extending away from a tectonic "indentor". I show an analysis.

So, regarding fluid inclusions...it seems we start in epithermal like material with digenite & covellite and cpy etc. We do not see obvious "sinter". We think it is eroded off. The last image shows surface material from an undrilled pad in strongly veined material with gypsum. We hit the anhydrite front at 100 meters or so. There are breccias everywhere. Now I believe degassing is essential to sulfide deposition. We are degassing a 16my hornblende diorite that crosses a cataclasite at the headwall of a graben/escape structure. The degassing event cooled enough to leave an Ar-Ar date of 14 my. We have almost every sign of a good system except a discovery hole and a large host batholith. We have older batholiths immediately adjacent and "aplites" on site. We have discovery hole grade material over 2-3 meters at the bottom of the last hole drilled right where it enters a corner of a 60 million ton .24%Cu mineralized prism and we have room for 50-100 hectares of 1% just outside our prism...it's even marked with geophysics. The anhydrite indicates a degassing event from a potassic zone alteration process. We have the potassic zone...100 meters of yellow stain in our last hole...right before work ceased virtually in "ore".

It is clear to me that fractionating metals can go into oxides or sulfides but that metal rich fractionate still has to accumulate. Using the buoyancy model I believe a light metal rich fractionate in a hot mafic fluid is more likely to float to the top. Iron oxides float better than iron sulfides. If you see anhydrite in a mafic to felsic system think oxygenation as a result of disproportionation of Iron oxides to zero valent iron and ferric iron in a deep mafic system high in sulfur and breakdown of apatite often associated with magmatic iron. Iron disproportionation should be just as effective at facilitating scavenging, separation and or accumulation of metals as a felsic system undergoing hydrolytic alteration at a more shallow depth. The net result might be a richer...at least that's what sulfur solubility work on Granite hosted gold systems seem to say. Plus, the CODES folks say mafic systems may be comparatively higher grade anyway, so to prevent losing too much to the sulfide fraction look to the iron system and hope it has depleted the sulfide phase enough to mobilize and accumulate a lighter copper saturated iron oxide phase that floats better and might be accessible. The sulfide rich mafic systems are probably full of "sinkers"...that fall to the bottom of the fluid chamber and never get entrained in any kind of hydromagmatic process.

I find so little FeS2 that I am concerned the system is an Iron Oxide Gold Copper system. It emanates from a mafic intrusion adjacent to a big fault zone. IOGC systems seem characterized by multiple fluid steps but the magmatic stories seem consistent. How good is anhydrite for an IOGC?

Here is an interesting study....for sulfide depleted/oxide rich systems. It appears magnetite precipitates sulfur saturation. The anhydrite is a consequence of the magnetite...which further oxidizes to hematite. So...the anhydrite indicates the system probably went through the "magnetite crisis"....described below. The lack of pyrite in our particular system is because it is Iron Oxide dominated. If it were less oxidized the whole area would be distinctly pyritic. The chalcopyrite we see in core samples actually exsolves from magnetite. It isn't exactly an IOGC but it is a strange thing, emanating from mafic material. Likely it is just part of an Iron Oxide porphyry system. When it has gold and Copper it's hard to not call it an IOGC. According to the work below, Mafic rock less than 60% SiO2 can host copper but it will be dispersed. If phases are found in the field that exceed 60% SiO2 with an abundance of Cu IN Magnetite with other sulfosalts, they are the metal rich fractionate. That fractionate is where the economic concentrations will be, as dikes and fingers, some of which may be "pegmatitic" and show up geophysically. There will be barren source rock to be found but it will have been depleted as part of an iron disproportion event. Mostly the whole process seems to be pressure related. I would imagine the oxygen comes from increasing the Si-O coordination from olivine to pyroxene to hornblende to biotite etc. Oxygen will be evolved off in a stepwise fashion. A deep mafic pool that breaks out of say a "flat slab" area as a result of a tectonic shift...say in the Andes High Cordillera about 16-18 my bp about the time of the Miocene shift should undergo this kind of process.

No, just started.

I went through all the core at the latest SEG meeting in Santiago 2019 looking for anhydrite or other unidentified fluorescent minerals that might help navigate a porphyry lithocap...like “hard” Red fluoresing Zunyite. There was one good hit, soft red material...anhydrite...in ATEX’s core “ore grade” intercept at 1500 meters!

Anhydrite seems essential.

At Qulong, Tibet, a new large post collision porphyry, the anhydrite is early and hot...associated with quartz-k-feldspar+- anhydrite and the next alteration step down.

Abs: "...Early potassic alteration, characterized by quartz–K feldspar (± anhydrite), pervades the P porphyry and Rongmucuola pluton. Laterally, this alteration grades into quartz–biotite–anhydrite (± K feldspar), which affects all Miocene intrusions except the latest dioritic porphyry. Wall rocks of Rongmucuola pluton and Jurassic andesitic–dacitic volcanics within 1–1.5 km of the porphyries are dominated by pervasive potassic alteration."

Article Geology of the Qulong porphyry copper–molybdenum deposit in Tibet

UV illumination of a shallow "high grade" interval from Milena at about 76m showing 0.6% Cu over a few meters shows clear and distinct association between anhydrite and Cu minerals that has not been reported before. UV illuminated images show red fluorescing anhydrite as late fracture fill and as inter grain cementing material. The bright orange yellow specks are chalcopyrite (Chalcopyrite can be confirmed visually in the NON UV image as yellow patches within pyrite and is confirmed because the reflectance of Cpy in long UV is unusually high! See attached paper by Wood and Stren.) (the blue is cutting oil). Black is likely Chalcocite or digenite. The pyrite is brownish.

I have seen anhydrite at many of the PCD I have worked on, but not at Bingham, which I think is recognized as one of the best by any standard.

I said the exact same thing to Ken with that citation but did not know if the observation was was still current. I thought Keith might have some news. People are hunting. Apparently magmatic anhydrite is more rare than I thought. Frikken reported in a CODES Dissertation 2003...

https://eprints.utas.edu.ay/17677/frikken.thesis.pdf

That anhydrite sulfur AND oxygen had positive del values. The only negative values were in sulfides within the ore zones of Rio Blanco/Los Brinces.

Frikken said the anhydrite was likely wall rock sourced. How many other stems show high del values on anhydrite?

I am hunting for indications of relict magmatic cu oxide sulfates? Probably not likely but I have an oxidized system am picking up a mixed bag of cu oxides and fe oxides (intermixed mag-hem) together with bornite/cpy/cov grains and tiny loose pieces chalcanthite blue material in a hbl microcline? Plagioclase porphyry with k-spar CuSO4? replacing pyroxene.proxene

I think my anhydrite is all probably hydrothermal but have never seen isotopic work on metal sulfates or carbonates. There is an interesting cu carbonate bearing granite in Pakistan called “K-2 jasper”. Look it up in mindat. The big blue spheres are probably growing around sulfides. I suspect someone will find primary cu-sulfosalt/carbonate/sulfates one day. I figured an anhydrite ruch system would be a good candidate.

As i indicated earlier when discussing Lihir, It does not really matter if anhydrite is magmatic or hydrothermal. It may well be the karst process that counts! At Lihir it is it’s karst-like anhydrite solubility that matters for gold concentration! Anhydrite is supposedly not soluble in hot water but soluble in cold water. There is a paper by Blount and Dickinson In 1969 IN Rabbia et al Mineral Deposita Jan 2009 pointing out that anhydrite is relatively soluble in saline hot water.

Audete et al found calcite and anhydrite in fluid inclusions at Santa Rita. How long before we start seeing the whole process...Copper out of silicates/iron oxides, into fluxing agents...sulfates, carbonates, borates etc. then destruction of the fluxing agent and metal concentration into suldifes

Where it is trapped.

It appears high Del S34 values in sulfates can be magmatic. The enclosed slide shows a close association between sulfides and anhydrite in what is probably potassic zone minerals in a D-vein hosting free Molybdenite. Botroidal anhydrite seems to host internal growth rings with possible sulfate minerals. Space filling sulfides appear to show exsolution features of bornite/cpy/cov. Unfortunately I am limited to medium power reflected light petrography. The systematics below suggest there COULD be isotopic fractionation even in such a close paragenesis. Rio Blanco/Los Bronces positive del S34 could be magmatic and other Andean systems such as at the Milena project the abundant hydrothermal anhydrite could just be remobilized magmatic material and the botroidal deposits do seem to be carrying some kind of copper bearing mineral even in direct paragenetic association with sulfides.

https://digitalcommons.unl.edu/usgsstaffpub/345/?utm_source=digitalcommons.unl.edu%2Fusgsstaffpub%2F345&utm_medium=PDF&utm_campaign=PDFCoverPages

For those who wonder about magmatic indicators, Bingham, usually reported as having no anhydrite actually does have anhydrite in it...not much but it is reported convincingly in the attached file from Zhang and Audetat 2017, Econ. Geology V 112, No. 2.

It seems the presence of anhydrite is necessary but is not a good indicator of theoretical economic potential. Size and depth of a magmatic system seem more important. According to Zhang and Audetat above there are consistent reports that volcanic magma chambers are "too small", being only about 200cukm. They indicate you need 5-10x that for enough source rock. The presence of anhydrite in such a good sized system with copper bearing breccia pipes is probably compelling. (someone else agreed and is mining one now onsite)

Enclosed is a x-section showing how what I call a "sulfikarst" system works...domes and dikes carrying hydrothermal anhydrite derived from magmatic differentiates invade a large fault as in the image below and blowouts develop. Enclosed is an image of what is likely a "young" dacite-like magmatic invasion of a very large mineralized fault zone on x-section taken from Google Earth imagery. The anhydrite and gypsum spar we found on site during road construction shows minerals in the upper hydrothermal zone, see image below from outcrop sampling shows chalcanthite and probably tourmaline/pyrite/biotite/cpy etc.. It is my belief that Anhydrite is good in part because it transforms to gypsum and changes permeability. Leached fluids follow secondary permeability paths to develop secondary enrichment zones somewhere...just like what was reported at Lihir.

So...magmatic or supergene...mineralization is definitely facilitated by the development of secondary porosity associated with anhydrite. Minerals carried with meteoritic leachate is trapped as supergene concentrations below the water table. The whole process works like a "leaky landfill".

attached file from which chart above is published.

Zhang and Audetat show tiny FeO inclusions at Bingham that looks just like the larger zoned FeO xenocrysts in a Miocene porphyry dike matrix. See attached image. I suspect such relatively large Miocene xenocrysts are Melt Inclusion Fragments with the same re-dox history as in tiny inclusions from Bingham. If this is so what next...a magmatic source for other things...particularly with reports of magmatic clinoatacamite? It should not be such a stretch to think blue copper sulfate like grains in a porphyry dike such as shown below might not be merely authigenic "hydrothermal" minerals but could also include allogenic resistates from melt sources. I enclose an image with tiny blue crystals of "cu-sulfate" together with what looks like Alunite. I grant the alunite as being authigenic but what is the story of clinoatacamite with anhydrite?

The mineral assemblage of oxidized metallogenic intrusions so prospective for Porphyry Copper deposits might be ripe for the discovery of oxide resistates. It makes sense because the Redox conditions are unstable...as we can see in the FeO grains. If anhydrite is magmatic and if the story about magmatic clinoatacamite from Tubauf seamount near Lihir/Ladolam in the paper listed above for MgHastingsite is right then we should set our sights to thinking not all "supergene" mineralization (copper sulfates) are necessarily deposited as authigenic hydrothermal "encrustations" but that there may be room for say potassic zone remnants of metaliferous oxides from magmatic sources, especially where the final stage of sulfate reduction to sulfides is, for one reason or another incomplete or somehow inadequate. Volcanic events and structural failures come to mind. I until reading the story of Tubauf I had automatically assumed blue copper-like minerals have to be automatically hydrothermal but I am not so sure.

The sample from 127m in Mil-011 below is, to the limit of my microscopy, host to the same oxide sulfide sulfosalt mineral suite as in intercepts at double that depth of the same porphyry material.

Anhydrite is known to be magmatic, so look for more clinoatacamite.

Magmatic anhydrite: Hutchinson, 2019

Hydrothermal anhydrite (?): Henley, 2015

Estimado Steve, pienso que la importancia de la porosidad secundaria radica principalmente a eventos de sobreimpresión,en donde la anhidrita sufrió eventos previos de exsolución, más no a una primera etapa tipo pórfido, esto indica Sykora, 2017.

Yo prefiero darle una mayor importancia al trabajo realizado por Henley, 2015.

An example from Perú

I've opened up a newi discussion directing research on this project to water. "Growing Glaciers for Sustainability" by hydro-mineral solar cogeneration. Finding water lost to the sun and the wind...and sending it to Chilean farms.

Si, pero las possibilidad! Anhydrite magmatico es conoce. Aya pseudo karst en el cap intrusive?.

Si? Es verdad? I will look into it. Merci pour ton avis.

Hello sir, what is the fundamental role of anhydrite in a copper porphyry model?

It is an oxygen buffer. It is the cause of and consequence of high fO2. I think it shows that oxidation is extensive. The question I have is where did the oxygen come from. I believe that the coordination chemistry of Si-O bonding goes from octahedral with an overall Si-O ratio of 1:4 in nesosilicates like olivine to 1:2...Quartz...SiO2. It makes sense in a simplistic way. I got the idea in a class I took in Silicate chemistry long ago. I assume the idea has been better developed among magmachem theorists. It is my belief that the presence of sulfate shows the extent of mineral differentiation within the underlying magmatic body. Think slag chemistry. Anhydrite is hydrothermal "slag" if you will. It's how I think. I show below pieces of the process...the calcium comes from breakdown of feldspars...most likely.

Anhydrite is soluble in magmas. It is not just hydrothermal.

If so, we might see primary copper sulfates in magma.

Here are a few lines excerpted from a new preprint paper attached below.

"Since most arc magmas have a considerable fraction of sulphur present as S6+

223 , they may instead saturate in anhydrite, which is much more soluble in silicate melts

224 ."

Below we see a link to interesting copper bearing granite from Pakistan. It is called "K-2 Jasper". It comes from near the peak "K-2". Jasper...it is not.

https://www.google.com/search?q=k-2+jasper&oq=k-2+jasper&aqs=chrome..69i57.4657j0j7&sourceid=chrome&ie=UTF-8

The blue teardrop material in the K-2 Jasper image below was tested and determined to be azurite. See photo below.

There is a green mineral too. undoubtably malachite.

It's easy to claim they are merely carbonate hydrothermal alteration features but there is probably more to the story. Is there a sulfide grain in paragenetic relationship?

The granite is distinct and is sold as a dimension stone. Are some of these so called highly oxidized granites bearing primary oxide coppers? Check it out on "mindat". I tried to make some deductions but they are entirely speculative. The teardrop features are new to me.

Carbonate and maybe Anhydrite in oxidized copper bearing granite in Pakistan. There does not seem to be any description of the situation in a scientific publication.

So much for "lithologic work".

Regarding theoretical general magma fertility indicators: The new pre-print paper attached below gives a good explanation for the Sr/Y anomaly and discusses the inverse relationship between copper bearing magmatic sources and porphyry fertility. The database is big and the implications seem significant. Is there a way to predict size and grade? I could not see it. It is declared that amphibole is critical. My bet is that that zonation in amphibole porphyroblasts might have preserved the mineralizing process. I attach the paper in hopes it might stir up some interesting discussion.

My limited take is that The porphyry potential seems to be improved with relatively thick crust etc. but the paper does not specifically state that Anhydrite is a good sign. The authors have not taken that step. Given the extent of surface mineralization on site at Milena I would argue we have a porphyry...fertility? Yes...you can see it. Dikes show plagioclase and amphibole, both good signs but not really much if any quartz...although it is hosted by a deep blanket of "patchy wormy" material that needs to be addressed.

In any case...I include for fun, a little perspective from flat slab tectonics in Central Chile where I work.

See below: The big "flat slab" of the central Andes about 30deg. S. is mapped at 80km depth. I simply got tired of seeing an old figure/map of the Pampas flat slab reprinted over and over with no updating. So I include an updated mapping.

For what it's worth, the porphyry mineralizing system described in the enclosed paper occur entirely above the pampas "flat plate" 80 km down. Tomographic x-section is marked accordingly.

I believe slab Dewatering and magmatic activity above the flat slab seems perfectly possible. The image below I recently prepared out of sheer frustration from failure of scientific papers to update to newer maps shows the updated flat slab geometry and for perspective I marked several copper properties...pelambres etc. They seem to be on the "wings" and "stem" of the slab. The flat slab is marked on plan view and x-section.

I suspect like in the oil business...there are many kinds of porphyry copper trapping mechanisms. Is there a way to predict good ones? I can't see it yet from the new research paper, but like in the oil business you can't really tell how big the elephant will be.

Oh...the blue droplets are completely 3-D. Many have assumed they were painted on...until they cut the rock.

Anhydrite In the proper magmatic context is a Good sign of deep favorable magmatic auto-oxidation. See Cin-ty Lee’s magnificent 10 minute synopsis on you-tube!

according to his work auto oxidation happens when continental crust base deepens and crosses into the Garnet stability field. He says Garnets like ferrous iron and splits the iron component. Ferric iron is excluded so the oxidized magmatic fluid component. is rendered mire efficient at scavenging metals.

The system undergoes auto oxidation at depth as a result of the iron crisis (Reported earlier). A reduced cumulate fractionate develops and sinks and the oxidized component sucks up metals and floats. Like in a steel mill! Plagioclase, a sign of relative dryness contains high heat energy and the system moves Plastically up From the cumulate Entraining indications of its deep arclogite source.

Note this can only happen when the crust is thick! I attached sim images from his video! That would be at the end of a subduction cycle. Magmatic activity is cut off when a continental crustal leading edge is so “bunchy”. Rollback happens.

This is a epiphany situation!

The thickning eventually ends a subduction cycle And the crust is too far too wide too whatever to allow deep tapping magmatic plumes to tap the arclogite cumulate-heat oxygen zone.

I had hoped to hear Audetet speak in this at SEG 2019 in Santiago. But he did not show. Cin-ty Lee’s work is excellent.

it certainly provides the basis for what I see at Milena...too much oxidation, too much Anhydrite, strange tectonic location And gives me encouragement to do Sr/Y and REE work. More work coming! Ioan Pintea

The presence of anhydrite in a porphyry system is essential not accidental. It comes from apical intrusive stalk-like rock material containing plagioclase!

The amount of anhydrite formed indicates the presence of sufficient plagioclase as a reactant (Ca-supplier) to drive the system by "mass action" to form Anhydrite and drive Cu/Mo to ppt as a sulfide. See below

The anhydrite present in a copper target illustrates the extent of rock alteration, its temperature and pressure as well as whether reaction proceeded as a vapor or a liquid and to some extent how long the process continued, assuming anhydrite loss is insignificant.

The abundance of Ca available from plagioclase needed to drive the de-sulfating of the system may be an indicator of whether the system is Cu rich or Cu-Mo rich. The particular Cu minerals formed is an indicator of the extent to which biotite and magnetite participated in buffering the level of oxidation created during the hydrolytic transformation of water.

The existence of "primary" covellite and chalcocite rather than chalcopyrite and bornite suggests high oxidation with regard to the NNO line. Note the photomicrographs.

For an example, picture what happens In clay systematics, think of the effect of KCl water on reducing the Cation Exchange Capacity of a montmorillonite clay. Evidently plagioclase releases Ca upon exposure to KCl constituents just as a Na Montmorillonite gives up much of its "stickiness" as part of an ion exchange process. So, the presence of KCl in a "mineralizing brine" apparently does much of the same thing, it degrades the plagioclase and potassium rich "k-spars" are the result.

The article made available by Jianping Li1, Weihua Liu2, Long Su3, Dengfeng Li4, Shitao Zhang5, and Huayong Chen1,6,7 below shows Ca being removed from plagioclase and presumably joined with metal rich "formation fluid" containing SO4-- to make anhydrite.

So the presence of anhydrite is essential to deposition of sulfides. The plagioclase alteration process is described succinctly as favored in vapor phase reactions. The presence of nearby vapor release structures (breccia pipes) adjacent to a porphyry system of interest indicates the confinement of a significant vapor phase. That would be good.

See above and below for core micro photos from a porphyry exploration test from 2010 that illustrate the process described in the 2023 paper below.

Recent drone images show that the anomalous light-colored accumulations seen in the WV2 image below are actually natural features, likely from mass wasting from nearby cliffs, avalanche deposits of some kind. There is no dam...just an eroded pile of debris. The initial photo interpretation from WV2 imagery suggested that there had been placer mining in the area and that the "scalloped" features were spoil piles and there were signs of excavation and water retention facilities. They are not present. The scene was misleading and a drone image shown below taken in 2023 shows a better 3-D perspective view. In any case, the odd bluish cast to the soil was tested by IR instruments and is reportedly the mineral Lazulite, an iron mg phosphate mineral. The white cast may very well be anhydrite but the claim that there was gold mining and that the presence of anhydrite is very good is based on old and now new drilling but there is no sign of historic gold mining in the image and the connection between anhydrite and economic mineral is not supported by this particular scene. The conclusion that anhydite is very good, if not essential is supported, nonetheless. Further information is expected.

The article below shows the authors found anhydrite to have been a fluid trapped within a silicate liquid that later produced high Al Amphiboles. The signature wormy texture of the amphibole were reported by them long ago, 2008 (see below). The authors of that article suggests that the abundance of Sulfur species likely stems from the co-existence of a liquid anhydrite. Some lower Al amphiboles exist with "dry" inclusions anhydrite.

The article cited below is the best answer to my question about the significance and importance of anhydrite in porphyry coppers, however it is relatively old. By now there should be more reports of the significance of the wormy anhydrite as an indicator of processes that lead to economic mineralization.

(13) (PDF) Sulfate Saturated Hydrous Magmas Associated with Hydrothermal Gold Ores (researchgate.net)

How about this geochemical nomogram as an indicator of Cu content? Any comments. I suspect it is related to anhydrite systematics. It certainly looks important if it works.