Scientific Quarterly Journal of Geosciences

Scientific Quarterly Journal of Geosciences

Role of pyroclastics in localizing hydrothermal alteration in the Ab-e-Torsh Volcanic district

Document Type : Original Research Paper

Authors
Ali Darvishzadeh 1
Abbas Asiyabanha 2
1 Geology Department, Science Faculty, Tehran University , Tehran, Iran
2 Geology Department, Faculty of Sciences, Imam Khomeini International University, Qazvin, Iran
Abstract
The Ab-e-Torsh volcanic district contains the Paleogene outcrops of trachyandesitic and dacitic lava flows and fall out pyroclastic deposits (equivalent to Karaj Formation) which have been hydrothermally altered. The, abundant fractures and faults produced a cauldron subsidence. Subsequently, fissure eruptions occurred and later hydrothermal solutions were intruded through the country rocks.
    One the basis of the formation of the sulfate mineral (alunite), it seems that the acidic solutions (e.g., H2S and H2SO4) have been formed by the interaction of hypogene volcanic vapours with hot solutions. Because of the interaction of the acidic solution with the country rocks and their chemical leaching, silicic, allunitic, argillic and advanced argillic alteration zones were developed.
    The high permeability and reactivity of the pyroclastic deposits with respect to the hydrothermal fluids facilitated the chemical reactions and hence the alteration products have been well developed in the latter unit. However, due to the presence of fractures the other units (e.g., trachyandesitic and dacitic lava flows) were also intruded by the solutions and altered.
Keywords
hydrothermal alteration
alteration zones
cauldron subsidence
Paleogene volcanics
acid-sulfate deposits

Subjects

Annells, R.N.; Arthurtun, R.S.; Bazley, RA and Davies, A.G., 1975- Explanatory text of the Qazvin and Rasht quadrangle map, 1 :250000 G.S.I.Rep. no E3, E4, 94
Carey, S. and Sparks, R.S.J., 1986- Quantitative models for the fall- out and dispersal of tephra from volcanic eruptions columns. Bull. Volcanoe, 48, pp.109-125
Dedual, E., 1967- Zur geologie des mittleren und unteren karaj-Tales, Zentral Elburz (Iran). Thesis Univ. Zurich 123p.
Dill, H.G.; Boss, R.; Henning, K.H.; Fricke, A. and Ahrendt, H., 1997- Mineralogical and chemical variations in hypogene and supergene kaolin deposits in a mobile fold belt, the central Andes of northwestern Peru. Mineralium Deposita, 32(1997) 149-163
Elston, W.E., 1994- Siliceous volcanic centers as a guide to mineral exploration: review and summary. Econ. Geel. 89(1994) 1662-1686.
Fisher, R.V. and Schmincke, H.U., 1984- Pyroclastic rocks, Springer Verlag, 472p.
Francis, P., 1992- Volcanoes, a planetary perspective, Clarendon Press 443p.
Goodman, R.E., 1989- Introduction to Rock Mechanics; John Wiley and Sons, 562p.
Hassanipak, A.A; Ghazi, A.M.; Vanke, D.A. and Wampler, J.M., 1994- Fluid inclusion study of the Ghoncheh- khoran and Zeh-Abad Pb-Zn deposit and KJAr ages of associated rocks, Qazvin, Iran
Heald, P; Foley, N.K. and Hayba, D.O., 1987- Comparative anatomy of volcanic - hosted epithermal deposits: acid-sulfate and adularia-sericite types. Econ.Geel. 82, 1-26.
Jebrak, M., 1997- Hydrothermal breccias in vein-type ore deposits. Ore Geel. Rev. 12(1997) 111-134
Kesler, S.E., 1997- Metallogenic evolution of convergent margins: selected ore deposit models. Ore Geel. Rev. 12(1997)153-171.
Stocklin, J. and Eftekhar Nezhad, J., 1969- Explanatory text of the Zanjan quadrangle map. G.S.I. Rep. no. D4.
Stoffregen, R., 1987- Genesis of acid-sulfate alteration and Au-Cu-Ag mineralization at Au-Cu-Ag mineralization at Summitvile, Colorado. Econ.Geol.82(1987)1575-1591.
Scientific Quarterly Journal of Geosciences
Volume 10, 37-38
Autumn & Winter 2001, Vol. 10, No. 37-38
Winter 2000
Pages 48-59