I agree with you. Biotite content can sometimes turns out to be phlogopite. However i believe that this can sometime be very difficult to differentiate it visually. One of the things that I have experienced is the spectral geology. In spectral geology the Fe and Mg content can easily differentiate two different contents. Would you agree?

Dear Elif, yes I completely agree. Spectral methods are very efficient tools to map hydrothermal alteration assemblages both on the ground and in drill core. In many cases, the distinction between phlogopite and biotite is also possible in hand specimen based on their different colours. Phlogopite is commonly brown while biotite is pitch black.

Dear Daniel,

Could you please describe what minerals are present in this picture?

Dear Michael, the mineralization in this sample consists of chalcopyrite-bornite and the monzodiorite host rock is overprinted by a strong sil-phl-Mt alteration assemblage. The sample was collected from a high-grade zone underground at Grasberg.

Your observations are very valuable!

I faced a similar problem with biotite alteration that turned out to be phlogopite after X-raying and the flame structure of phlogopite ("flame-rock") came out clearly in the thin section.

That was in the calc-alkaline porphyry Cu-Mo deposit in Panama (about 5 Ma old).

There is both orthoclase and phlogopite with pyrite in the so-called potassic alteration zone in two separate intrusions (an older QFP and a younger granodiorite).

There is a magnetite-sericite-chalcopyrite alteration peripheral to the potassic and sericite alteration zones, but is of a lower, marginal grade.

However, the porphyry Au deposits in the Archean in Canada (Abitibi, Quebec) have biotite (definitely not phlogopite) - K-feldspar alteration with quartz-calcite-Au-bearing pyrite. The host intrusion is everywhere altered (not fresh) and has been described as syenite by some or granodiorite by others. There are basically two alteration zones: the potassic zone (with the ore) and the propylitic (low grade) zone around it.

Dear Daniel Müller

Currently I am dealing with the alteration products of a porphyry Mo deposit in Iran, in which the monzo-syenitic (shoshonitic) host rock is strongly altered and texture-destroyed. I documented disseminated magnetite as inclusion inside secondary K-feldspar+albite and considerable amount of secondary annite with some phlogopite as disseminated and along weakly developed irregular veins. Apparently annite overprinted phlogopite and is associated with some ilmenite.

Do you have any idea why there is a conversion of phlogopite toward annite?

Thanks in advance

please see the attached image.

Dear Ahmad, many thanks for your good question! I think that "biotite" refers to a solid-solution series between annite (Fe-rich) and phlogopite (Mg-rich) endmembers. Where I referred to biotite in my original question I actually meant annite! It seems that the parental intrusions in your studied porphyry Cu deposit contain primary phlogopite which is overprinted by an annite-magnetite alteration assemblage. At the Ladolam gold deposit at Lihir Island in PNG you can make similar observations. The gold mineralization at Ladolam has formed during the transition from porphyry- to epithermal conditions, probably triggered by an earthquake and the sector collapse of the stratovolcano above. Best regards, Daniel

I advocate no longer using these simple summary terms, largely developed during the 1960s in the infancy of porphyry study. Rather, simply report the mineral assemblage, as analytical capability has improved markedly over the last 5-6 decades (from hand lens and thin section plus XRD to microprobe and SEM, then SWIR as well as Qemscan and MLA); still, start with a hand lens. One problem is that different people use some terms differently (e.g., argillic and intermediate argillic). In the case of "advanced argillic", there are 5 distinct environments of formation of minerals that Meyer and Hemley (1967; based on Hemley and Jones work in 1964) included in this term. Just using this term misses all of the information to be gathered from mineralogy, texture, morphology, etc. Please, determine and describe the mineralogy of various assemblages, and the variation between different deposit styles and types. Jeff

I think these terms are relative and not substantial. being present the detailed investigation, one can present new divide for each type of deposits.

Can I ask if the Perth 2019 Symposium produced any abstracts/ publications?