Petrography and Mineral Chemistry of Magmatic and Hydrothermal Biotite in Porphyry Copper-Gold Deposits: A Tool for Understanding Mineralizing Fluid Compositional Changes During Alteration Processes

Arifudin Idrus


DOI: 10.17014/ijog.5.1.47-64

This study aims to understand the petrography and chemistry of both magmatic and hydrothermal biotites in porphyry copper-gold deposits, and to evaluate the fluid compositional changes during alteration processes. A total of 206 biotite grains from selected rock samples taken from the Batu Hijau porphyry Cu-Au deposit was analyzed. Detailed petrography and biotite chemistry analysis were performed on thin sections and polished thin sections, respectively, representing various rocks and alteration types. A JEOL JXA-8900R electron microprobe analyzer (EMPA) was used for the chemistry analysis. The biotite is texturally divided into magmatic and hydrothermal types. Ti, Fe, and F contents can be used to distinguish the two biotite types chemically. Some oxide and halogen contents of biotite from various rocks and alteration types demonstrate a systematic variation in chemical composition. Biotite halogen chemistry shows a systematic increase in log (XCl/XOH) and decrease in log (XF/XOH) values from biotite (potassic) through chlorite-sericite (intermediate argillic) to actinolite (inner propylitic) zones. The y-intercepts on the log (XCl/XOH) vs. XMg and log (XF/XOH) vs. XFe plotted for biotite from potassic and intermediate argillic zones are similar or slightly different. In contrast, the y-intercepts on the log (XCl/XOH) vs. XMg and log (XF/XOH) vs. XFe plotted for biotite from inner propylitic zone display different values in comparison to the two alteration zones. Halogen (F,Cl) fugacity ratios in biotite show a similar pattern: in the potassic and intermediate argillic zones they show little variation, whereas in the inner propylitic zone they are distinctly different. These features suggest the hydrothermal fluid composition remained fairly constant in the inner part of the deposit during the potassic and intermediate argillic alteration events, but changed significantly towards the outer part affected by inner propylitic alteration. High halogen content, particularly Cl, in hydrothermal biotite may portray that copper and gold were transported in mineralizing fluids in the form of chloride complexes CuCl2- and AuCl2-, respectively.


biotite; fluid composition change; halogen F and Cl; mineral chemistry; petrography; porphyry Cu-Au deposits


Afshooni, S.Z., Mirnejad, H., Esmaeily, D., and Asadi Haroni, H., 2013. Mineral chemistry of hydrothermal biotite from the Kahang porphyry copper deposit (NE Isfahan), Central Province of Iran. Ore Geology Reviews, 54, p.214-232.

Babcock, R.C., Jr., Ballantyne, G.H., and Phillips, C.H., 1995. Summary of the geology of the Bingham District, Utah. In: Pierce, F.W., and Bolm, J.G., (eds), Porphyry Copper Deposits of the American Cordillera. Arizona Geological Society Digest, 20, p.316-335.

Bao, B., Webster, J.D., Zhang, D-H., Goldo, B.A., and Zhang, R-Z., 2016. Compositions of biotite, amphibole, apatite and silicate melt inclusions from the Tongchang mine, Dexing porphyry deposit, SE China: Implications for the behavior of halogens in mineralized porphyry systems. Ore Geology Reviews, 79, p.443-462.

Beane, R.E., 1974. Biotite stability in the porphyry copper environment. Economic Geology, 69, p.241-256.

Turner, S.J., 1995. Fluid inclusion study of Batu Hijau porphyry Cu-Au deposit, Southwest Sumbawa, Indonesia: implications for mineralisation and metal patterns around a major porphyry stock. Unpublished Newmont Nusa Tenggara company report, 49pp.

Zhang, W., Lentz, D.R., Thorne, K.G., and Mc- Farlane, C., 2016. Geochemical characteristics of biotite from felsic intrusive rocks around the Sisson Brook W-Mo-Cu deposit, west-central New Brunswick: An indicator of halogen and oxygen fugacity of magmatic systems. Ore Geology Reviews, 77, p.82-96.

Zhu, C. and Sverjersky, D.A., 1991. Partitioning of F-Cl-OH between minerals and hydrothermal fluids. Geochimica et Cosmochimica Acta, 55, p.1837-1858.

Zhu, C. and Sverjersky, D.A., 1992. Partitioning of F-Cl-OH between biotite and apatite. Geochimica et Cosmochimica Acta, 56, p.3435-3467.

Full Text: PDF


  • There are currently no refbacks.

Creative Commons License
Indonesian Journal on Geoscience by is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.


Indexing Site :

Follow us on:

shopify visitor statistics
View My Stats