I think they can be some rocks such as andesites, dacites and basaltic andesits and granitic intrusive rocks to intermediate intrusive rocks.

Rock type is not particularly important...it's geochemical history, depth of crust, gold content and the timing of events are much more important. Think more like a petroleum explorationist. Source rock, thermal history, fluids, pathways of transport, reservoir rock etc. Economic mineralization for copper relies on the same kind of process thinking. There are many recent authors reporting their belief that the existence of a deep flat generative tectonic slab is favorable and there is a world of trace element studies that distinguish large from small targets in otherwise identical rock types. Previous thinking was that flat slabs were unfavorable. Indeed, "volcanic gaps" might well indicate the presence of "failed eruptions". That seems to be a good thing. I attach some images below.

I enclose some interpretive images of my own porphyry copper system and a more famous one, Pelambres, as an example.

For what it's worth, Copper seems to be sourced deeply and gold is shallow. Where I work there are actual geomorphic signs of stepwise exhumation of a system proceeding from copper rich to gold rich as a segment of the Andes is lifted too high and undergoes a progressive block failure process extending over 5-15 million years.

I have a bit of work to that effect on my researchgate pages...look at the question and answer section for a reasonably popular discussion.

I enclose an open access article discussing recent thinking about the importance of recognizing the passage of distinct geo-chemical phases. Accordingly, the evolution of an oxidizing brine "gas" evolved off a magmatic system driven by advance and retreat of plate edges and the gas's entrapment by a relatively porous host itself sealed off by a relatively impermeable envelope and the invasion of that reservoir by a disproportioning sulfurous gas from a hotter more mafic source is reportedly a good way to fix the earlier trapped metalliferous brines hosting sulfosalt remnants of the oxidized supercritical fluid/gas event into ore common sulfides. Your clue to the extent of completion of the process seems to be the evolution of a mass of sodic feldspars from previously calcic ones and the presence of a reaction byproduct, anhydrite. Anhydrite is soluble enough for cold water erosion to virtually destroy whatever volcanic edifice might be present and expose the system's "roots". Geophysics can divert one's attention to the albitic residual products near the "roots" enough to miss the favorable zone of copper sulfidation.

A carbonate host rock is a nice thing to find. I highly recommend finding it.

Dear Doctor

Go To

Porphyry Copper Systems

RICHARD H. SILLITOE

©2010 Society of Economic Geologists, Inc. Economic Geology, v. 105, pp. 3–41

[Abstract Porphyry Cu systems host some of the most widely distributed mineralization types at convergent plate boundaries, including porphyry deposits centered on intrusions; skarn, carbonate-replacement, and sedimenthosted Au deposits in increasingly peripheral locations; and superjacent high- and intermediate-sulfidation epithermal deposits. The systems commonly define linear belts, some many hundreds of kilometers long, as well as occurring less commonly in apparent isolation. The systems are closely related to underlying composite plutons, at paleodepths of 5 to 15 km, which represent the supply chambers for the magmas and fluids that formed the vertically elongate (>3 km) stocks or dike swarms and associated mineralization. The plutons may erupt volcanic rocks, but generally prior to initiation of the systems. Commonly, several discrete stocks are emplaced in and above the pluton roof zones, resulting in either clusters or structurally controlled alignments of porphyry Cu systems. The rheology and composition of the host rocks may strongly influence the size, grade, and type of mineralization generated in porphyry Cu systems. Individual systems have life spans of ~100,000 to several million years, whereas deposit clusters or alignments as well as entire belts may remain active for 10 m.y. or longer. The alteration and mineralization in porphyry Cu systems, occupying many cubic kilometers of rock, are zoned outward from the stocks or dike swarms, which typically comprise several generations of intermediate to felsic porphyry intrusions. Porphyry Cu ± Au ± Mo deposits are centered on the intrusions, whereas carbonate wall rocks commonly host proximal Cu-Au skarns, less common distal Zn-Pb and/or Au skarns, and, beyond the skarn front, carbonate-replacement Cu and/or Zn-Pb-Ag ± Au deposits, and/or sediment-hosted (distal-disseminated) Au deposits. Peripheral mineralization is less conspicuous in noncarbonate wall rocks but may include base metal- or Au-bearing veins and mantos. High-sulfidation epithermal deposits may occur in lithocaps above porphyry Cu deposits, where massive sulfide lodes tend to develop in deeper feeder structures and Au ± Ag-rich, disseminated deposits within the uppermost 500 m or so. Less commonly, intermediate- sulfidation epithermal mineralization, chiefly veins, may develop on the peripheries of the lithocaps. The alteration-mineralization in the porphyry Cu deposits is zoned upward from barren, early sodic-calcic through potentially ore-grade potassic, chlorite-sericite, and sericitic, to advanced argillic, the last of these constituting the lithocaps, which may attain >1 km in thickness if unaffected by significant erosion. Low sulfidation-state chalcopyrite ± bornite assemblages are characteristic of potassic zones, whereas higher sulfidation-state sulfides are generated progressively upward in concert with temperature decline and the concomitant greater degrees of hydrolytic alteration, culminating in pyrite ± enargite ± covellite in the shallow parts of the lithocaps. The porphyry Cu mineralization occurs in a distinctive sequence of quartz-bearing veinlets as well as in disseminated form in the altered rock between them. Magmatic-hydrothermal breccias may form during porphyry intrusion, with some of them containing high-grade mineralization because of their intrinsic permeability. In contrast, most phreatomagmatic breccias, constituting maar-diatreme systems, are poorly mineralized at both the porphyry Cu and lithocap levels, mainly because many of them formed late in the evolution of systems. Porphyry Cu systems are initiated by injection of oxidized magma saturated with S- and metal-rich, aqueous fluids from cupolas on the tops of the subjacent parental plutons. The sequence of alteration-mineralization events charted above is principally a consequence of progressive rock and fluid cooling, from >700° to

Dear All,

Steve Steve Johnson ,

Congratulation , It counts as a surprise how good a comment you posted.

The attached description by Sundus F Hantoosh is also excellent... Anyone who knows how gold nuggets are formed can immediately use the two comments as evidence.

The Gholamreza Fotoohi Rad 's comment is supported by the presence of the intercalations that caused the formation of the golden porphyry copper of the Central Mountains of Transylvania!

Regards,

Laszlo

We did not have to wait very long. Rad answered his own question and organised his mates to recommend his answer. This bloke is not interested in your answers. He is just gaming the system.

It forms from large-scale hydrothermal systems associated with igneous rocks.