Dear Mrs.Huang,

if you have a continuous alteration from the hypogene stage into the supergene one any discrimination between the various stages can only be achieved if you have done a proper geological and mineralogical study prior to chemical investigations.Using chemical indices for whatever type of  mineralogical or geological processes they may have been designed without this stepwise approach means pocking around in fog and you will not hit the mark. In combination you will, however, obtain reasonable results, I am certain about this.

Best regards

H.G.Dill

Dear Harald G,

Thanks for your suggestion, it makes sense.

Best regards,

Zongying

Hello,

this is the conclusion of the original paper which introduced the CIW:

The proposed CIW index has been successfully applied to a number of modern soils as well as Precambrian paleosols. It can be applied to silicate rocks of felsic to mafic composition, and is superior to other weathering indices in that it involves a restricted number of components which have simple, well-known and consistent geochemical behaviour during weathering.

From that conclusion I would be very cautios to apply the CIW to alteration and metamorphism events. The detailed field work is very important to do before the application of weathering and alteration indices. Because otherwise you don't what elements could be mobile and or not.

I think it is better to figure out elements, which behave immobile (after the field work) like Zr (mostly) and to relate their content relative to the gains and losses of other elements.

Some years ago I found an excel application for this. I will search it and upload it in this discussion when I find it.

Best regards

Dear Christian,

Thanks for your comments and hoping for the excel application. 

Best Regards,

Zongying

I do not think this the chemical index can be applied to assess such kiind of element mobility because the chemical index CIW was established for rock weathering on the surface of the earth, and it is applied to under the assumption that the parent rocks are chemically homogeneous.  

Dear Bo,

Thanks for the discussion.

It indeed needs to be caustious to use the CIW, as Harald G. and Christian mentioned, unless the sampels have received detailed field work and mineralgical studies.

Best Regards,

Zongying

Dear Mrs.Huang,

The study of element mobility can be done using a few simple methods initially developped in Gresens, R. L. (1967) Composition-volume relationships of metasomatism. Chemical Geology 2(C):47-65.

A few papers discuss about that in volcanic rocks, but this can be applied to any magmatic rock. Most of them are based on the identification of immobile elements (usually Zr, Ti, other HFSE, HREE...). The methods for such identification are explained in some of the following papers.

Grant, J. A. (1986) The isocon diagram; a simple solution to Gresens' equation for metasomatic alteration. Economic Geology 81(8):1976-1982.

MacLean, W. H., and Kranidiotis, P. (1987) Immobile elements as monitors of mass transfer in hydrothermal alteration; Phelps Dodge massive sulfide deposit, Matagami, Quebec. Economic Geology 82(4):951-962.

MacLean, W. H., and Barrett, T. J. (1993) Lithogeochemical techniques using immobile elements. Journal of Geochemical Exploration 48(2):109-133.

Barrett, T. J., and MacLean, W. H. (1994) Chemostratigraphy and Hydrothermal Alteration in Exploration for VHMS Deposits in Greenstones and Younger Volcanic Rocks. Alteration and Alteration Processes Associated with Ore-Forming Systems, (Short Course Notes: 11), Lentz, D. R. (Édit.) Geological Association of Canada, p 433-466.

Grant, J. A. (2005) Isocon analysis: a brief review of the method and applications. Physics and Chemistry of the Earth, Parts A/B/C 30(17):997-1004.

In highly deformed and metamorphosed rocks, I would not recommand methods based on density or volume changes of the rock to identify pre-deformation processes.

Dear Antoine,

Thanks so much for your informative response. I will read the papers.

All the best,

Zongying

Hello,

sorry for the late answer. This is the excel application:

Hello -

I see that a previous respondent has recommended Jim Grant's papers on the isocon method - these are excellent. In addition, the effects of K metasomatism on paleosols can be evaluated through judicious application of the A-C*N-K plot, as described in the attached paper which I published recently. Take a look, and if you have further questions, please feel free to contact me.

Sincerely,

Gordon Medaris, Jr.

Hi Christian,

Thanks for your effort on the topic.

Best Regards,

Zongying

Hi Levi Gordon,

Thanks for the discussion and the paper, I will read it.

Best Regards,

Zongying

Dear Mrs Huang,

 the correct treatment of mass balance during open system-processes (such as alteration, metamorphism or weathering)  needs to take into account the changes in overall mass/volume of the whole system, which would also apparently alter the concentrations of immobile elements, whose abundances in reality did not change at all.

I agree with Antoine and Gordon that isocon method is commonly employed remedy to this problem. But unfortunately it does suffer from two drawbacks: 1)  it does not take into account a variability of the protolith (only a pair of rocks is assessed at the time) and 2) it is subjective in that the individual elements are scaled , i.e. multiplied by arbitrary coefficient, in order to obtain more legible results. 

I would like to bring to your attention an alternative, called Wedge plots, defined by prof. J.J. Ague. They are  superior in that they take into account the overall variability of the whole dataset (both of the putative protolith and the altered product) and not just a selected whole-rock pair, and do not introduce any subjective aspects, such as arbitrary scaling.

Ague JJ (1994) Mass transfer during Barrovian metamorphism of pelites, south-central Connecticut; I, Evidence for changes in composition and volume. Amer J Sci 294:989-1057

BTW, they can be plotted by GCDkit, gcdkit.org.

I trust that this helps,

Vojtech Janousek

Dear Vojtech,

Thanks so much for the suggestions and hints.

Best Regards,

Zongying