Depth is not the only factor in mineral alteration and weathering (oxidation, etc.). Mineral alteration may occur for physical or chemical reasons or (often) for both reasons at the same time.

An example of physical alteration is when a given mineral (or rock) leaves the geotectonic environment in which it was formed. Minerals that are stable at high temperature and pressure at great depth in the Earth become unstable at lower temperature and pressure during uplift and erosion of the overlaying near-surface zone.

An example of chemical alteration is when a mineral (or rock) meets a different chemical environment relative to the environment in which it was formed. Sulphides become oxidized when in contact with Oxygen (or Oxygen bearing water). Oxides become reduced when their environment turns to reducing.

At the famous Tsumeb mine, Namibia, three oxidized zones exist, one at surface, and two additional zones at depth where oxidizing water percolated at several hundred meters of depth (http://www.tsumeb.com/en/geology/).

Dear Asoori, Weathering (combined hydration and oxidation processes) can affect parent rock minerals up to 100 m depth under the effect of meteoric waters pecolating through connected fracture networks. For example biotite or olivine hydration (with formation of chlorite and/or serpentine, e.g., lizardite) and oxidation (with formation of Fe oxyhydroxides, goethite and/or hematite) at such depth and even deeper is very well known. All the best, Anicet

Der Asoori: Not much to add to Roberto's answer, perhaps that the deep chemical weathering at world famous Tsumeb mine occurs as deep as 1,5 km below the surface, since the host limestone was deeply faulted and the fault plane was permeable enough to allow meteoric water, laden with oxygen and CO2 (among other anions...), to create outstanding oxydation zones, which produced incredibly beatiful specimens of Cu-Zn-Pb minerals of the carbonate, arsenate and phospate classes, such as azurite, cerussite, malachite, rodochrosite, smithsonite, and hundreds. Also have to be considered the processes which occur during diagenesis, some of them quite similar to those ocurring during weathering, and also dependant on the redox chemical conditions of the altering fluids. Regards. Sebastian.

 Asoori, If you refer to supergene weathering, may be you know the manganese ore deposit of Sandur in Peninsular India. We recently show that supergene cryptomelane (K rich Mn oxide) as old as 35 Ma crystallized between 100 and 140 m depth. Lateritic weathering profiles can be also as thick as 130 m, e.g., bauxitic (see the books of Bardossy and Aleva, 1990, or Valeton, 1972). Such thick lateritic deposits exist in peninsular India (e.g., on Trapps, or upon the Southern massifs Nilgiris, Shevaroy hills, ...). Also peridotite of New Caledonia are deeply weathered with occurrences of Ni rich lizzardite, talc and smectite and even goethite among others minerals (oxides) at depths > 100 m (Co rich Mn oxyhydroxides like lithiophorite or asbolan also crystallize at such depths).  Another point is that meteoric waters warm up when moving down, leading to specific minerals to form, which do not result necessarily from pure hydrothermalism but rather from exothermic water-rocks interactions. Best wishes, Anicet

May be this paper can help you

https://digital.library.adelaide.edu.au/dspace/bitstream/2440/52597/8/02chapters1-2.pdf

Sebastian, Tsumeb is interesting in that it has two oxidation zones and two supergene sulphide enrichment zones with hypogene sulphides between and below. The lower oxidation zone was best developed at about 2600-3500 feet below surface where a thrust fault carrying oxygenated meteoric water from surface intersected the pipe (I haven't bothered to convert units), and was pretty much gone by about 3600 feet. So very deep, if not perhaps as deep as 1.5 km, closer to 1.0 km. Roberto, I am not aware of a third oxidation zone, but we were down to about 5000 feet, if not opened out (in unoxidised and rather impermeable silica alteration below 3600 feet) when I was mine geologist.

Quoting from http://www.tsumeb.com/en/geology/ :

Tsumeb’s vast array of secondary mineral species would not have formed if it were not for the three vertical zones of oxidation that occurred in the mineralised pipe structure.

First oxidation zone:  Surface to 11 Level represented by the vadose zone and influenced by fluctuations of the water table. Oxide minerals are found in much reduced quantities between 11 Level and 15 Level.

Second oxidation zone:  24 to 35 Level – centred around the intersection of the North Break Horizon with the Tsumeb pipe on 29 Level.

Third oxidation zone:  From 42 Level downwards. Note: The third zone of oxidation was not officially recognised when the author undertook the drilling on 40 level in 1984. Later, deeper level exploration, followed by mining, revealed evidence of oxidation in the lower levels (Gebhard, 1999; Melcher, 2003).

That explains the third oxidation level - we did not have much development at those depths when I was there, although what we had showed little oxidation (although I take it that when it says "revealed evidence of oxidation in the lower levels" that it was subordinate to the uper two oxidation zones).

Hughes MJ “The Tsumeb ore body, Namibia, and related dolostone-hosted base metal ore deposits of Central Africa”, 1987, PhD thesis, University of the Witwatersrand- Published, University Microfilms, Ann Arbor, Michigan.

Dear Asoori,

May I draw your attention to the detailed publication by P. Moeller et al. 1997 on the topic "Paleofluids and Recent fluids in the upper continental crust ...". The fluids cause all these possible alterations of the minerals in the earth's crust. Here it is shown very clearly in which depths of the crust these alterations reach and which processes have caused these alterations.

Please find attached the corresponding PDF.

Best regards

Guenter Grundmann

Thank you all for your valuable guidence