Dear Colleague: As far as I know one of the best studies were carried out on Mn deposits by Dr. Márta Polgári, professor at Eszterházy Károly University in Hungary. May I propose you the looking for her papars on microbial processes forming Mn deposits. With the best: Szaniszlo Berczi

Dear colleague thank you very much for your attention to my question

Here I send you one of them:

http://real.mtak.hu/152952/1/PolgariMetal_minerals_2022.pdf

titled: Comparative Study of Formation Conditions of Fe-Mn Ore

Microbialites Based on Mineral Assemblages: A Critical Self-Overview.

written by Márta Polgári and Ildikó Gyollai.

OK many thanks

Dear Dr. Rad

If you want to distinguish sedimentary and hydrothermal Mn deposits you must have an overview of the Mn deposits on a whole, because Mn forms a great variety of minerals and deposits due to its polyvalent state and the incorporation of many elements like Pb in coronadite which is a sedimentary deposits forming straight from groundwater oscillation without any mediating effect of organic matter, fairfieldite is a Mn phosphate of late stage phosphate hydrothermal mineralization in granite pegmatite, coulsonite is an oxide in metamorphosed igneous rocks, alabandite is a sulfide in epithermal polymetallic sulfide mineralizations and especially in low-temperature manganese deposits, kutnohorite is a Mn carbonate with Fe manganiferous sediments and polymetallic manganese, iron, zinc, etc. deposits, tinzenite a Mn borate occurs in veinlets cutting stratiform manganese deposits or metachert and also found in a granite pegmatites and rhodochrosite, one of the common Mn carbonates is met as primary gangue mineral in moderate- to low-temperature hydrothermal veins, also in high-temperature metasomatic deposits and sedimentary manganese deposits or as a late stage hydrothermal mineral in pegmatites, especially lithiophilite-bearing ones.

These examples may give you an idea how variable the concentration of Mn is.

Below you find a classification of Mn deposits on worldwide basis

(1) Magmatic manganese deposits

(1) Sedimentary/volcanic-exhalative marine Mn deposits (SEDEX to VOLCEX) (8b BC-8c B-8c D)

(2) Volcano-sedimentary lacustrine (8b D)

(3) Epithermal Mn in places with gem quality rhodochrosite (8d D)

(4) Rhodonite skarn (8e D)

(2) Structure-related manganese deposits

(1) Hydrothermal unconformity-related vein-type deposits (8a G)

(2) Mixed-type unconformity-related vein-type deposits (8b GH-8b K)

(3) Rhodochrosite veins (8c G)

(3) Sedimentary manganese deposits

(1) Shallow marine Mn deposits with /without remobilization in subaerial regimes (8a I-8a K)

(1) Clastic-hosted deposits (8a I)

(2) Carbonate-hosted (8a K)

(2) Mn deposits in black shales (8c J)

(3) Mn nodules in deep-marine depositional environments (in parts endogenous) (8a M)

(4) Supergene manganiferous deposits (8a H)

(1) Bog iron ores on siliciclastic bedrocks

(2) Manganiferous replacement deposits hosted by calcareous rocks

(4) Metamorphic manganese deposits (prevalently sedimentary protore)

(1) Manganiferous Banded Iron Formation (8a BCD-8a J)

(2) Rhodonite gemstone deposits (8 bJ)

See

DILL, H.G. (2010) The “chessboard” classification scheme of mineral deposits: Mineralogy and geology from aluminum to zirconium.- Earth Science Reviews, 100: 1-420.

DILL, H.G. (1985) Terrestrial ferromanganese ore concentrations from Mid-European Basement Blocks and their implication concerning the environment of formation during Late Cenozoic (N Bavaria / F.R. Germany). - Sedimentary Geology, 45: 77-96

DILL, H. G. and ULRICH, H.-J. (1987) Geoelectric deep sounding - A contribution to constrain the genesis of siliceous ferromanganese duricrusts on deeply weathered Paleozoic basement rocks (N Bavaria, F.R. Germany).- Zeitschrift für Geomorphologie., N.F., 31: 361-370.

DILL, H.G., PÖLLMANN, H. and TECHMER, A. (2013) 500 Million years of rift- and unconformity-related Mn mineralization in the Middle East: A geodynamic and sequence stratigraphical approach to the recycling of Mn.- Ore Geology Review 53: 112-133.

I wish you much success

HGD

ِDear Professor Dill

Hi

Many thanks for your excellent and complete answer to my question about Mn ore deposits.

With best wishes and thanks again : Dr Gholamreza Fotoohi Rad

Dear Prof. Harald G. Dill , can you please specify among the cited deposit types, where do Mn-dendrites belong? I usually see them along joint walls in limestone, one time in Ni-silicate metasomatic veins in limestone.

Dear Dr. Kurešević,

the first image shows “cauliflower-like” coatings of fissure plains. The second one are vein-like mineralizations in garnierites top-down. The last image shows dendritic Mn limonite (?) on fissure plains. It is a non-rotative breccia or incipient crack-and-seal structure (dynamic processes not involved).

With kind regards H.G. Dill

So, these aren't Mn-dendrites at all? Thank you.

Otherwise, do real Mn-dendrites (such as:

https://en.wikipedia.org/wiki/Dendrite_%28crystal%29#/media/File:Dendrites01.jpg)

form from hydrothermal solutions or exogenic ones (weathering processes)?

The cited wiki article states: "These pseudofossils form as naturally occurring fissures in the rock are filled by percolating mineral solutions. They form when water rich in manganese and iron flows along fractures and bedding planes between layers of limestone and other rock types, depositing dendritic crystals as the solution flows through.", however, it doesn't state whether the solutions come from weathering processes (exogenic) or they are hydrothermal.

To be honest dendritic is a purely descriptive term which has no special genetic connotation and runs from Mn oxide-hydroxide dendrites to dendritic drainage systems. In the latter usage it has relation to bedrock, physical-hydraulic flow patter. As such dendritic texture as plain coating which evolve when fissures closed and not directly exposed to the atmospheric impact can also be interpreted in terms of physical changes in the flow regime. But this is a hard nut to crack and express a stark warning to avoid a simple comparison of pattern. The width of the cracks, the filling of them, local ruptures and marks may have a stronger influence than expected.

HGD

P.S. I would call them dendritic "limonitisation" texture (can involve Fe and Mn)

Dear Prof. Dill

Many thanks for your excellent and complete answer related to Mn deposits.

Best wishes and thanks

Reza