Skip to main content

Conglomerate-hosted copper mineralization in Cretaceous Andean molasse: the Coloso Formation of northern Chile

  • S. Flint (a1), H. Clemmey (a1) and P. Turner (a2)

Alluvial fan sediments of the Lower Cretaceous Coloso Formation of northern Chile were deposited during the evolution of a half-graben, arid, intra-arc basin. The sediments were derived from an andesitic volcanic arc and show compositional variation which can be interpreted as an unroofing sequence. Copper mineralization is stratigraphically restricted to the upper 150 m of the sequence in conglomerates of predominantly granodioritic composition. The presence of mineralized clasts at this level indicates the erosion of bedrock mineralization. Lead isotopic signatures of ore sulphide support the sedimentological evidence for derivation of the sediments and metals from an island arc volcano-plutonic complex to the west of the basin.

A genetic model is proposed in which uneconomic metal concentrations were transported into the basin as detrital phases and released by diagenetic reactions. The precipitation of copper minerals followed authigenic formation of quartz, feldspar, analcime and calcite and also some secondary parosity generation. Copper minerals include the oxychloride atacamite, and the suphides bornite, digenite, djurleite and covellite. Sulphur isotope values for the sulphides are relatively heavy isotope-enriched (δ34S = −3.6 to −12.8‰). Although these results could be interpreted in terms of closed-system bacterial sulphide reduction there is no known occurrence of organic material within the Coloso basin. An alternative explanation involving the mixing of diagenetically derived copper-rich brines and sulphur-rich hydrothermal fluids is proposed to account for the Coloso mineralization.

Hide All
Berg, K., Breitkruez, C., Damm, K. W., Pichowiak, S. & Zeil, W. 1983. The North Chilean coast range – an example for the development of an active continental margin. Geological Rundschau 72, 715–31.
Coira, B., Davidson, J., Mpodozis, C. & Ramos, V. 1982. Tectonic and magmatic evolution of the Andes of northern Argentina and Chile. Earth Science Reviews 18, 303–32.
Coleman, M. L. & More, M. P. 1978. A method for the direct reduction of sulphates to SO2 for isotopic analysis. Analytical Chemistry 50, 1594–5.
Davidson, C. F. 1965. A possible mode of origin of strata-bound copper ores. Economic Geology 60, 942–54.
Dickinson, W. R. 1982. Compositions of sandstones in circum-Pacific subduction complexes and fore-arc basins. Bulletin of the American Association of Petroleum Geologists 66, 121–37.
Entwistle, L. P. & Gouin, L. O. 1955. The chalcocite ore deposits at Corocoro, Bolivia. Economic Geology 50, 555–70.
Espinoza, S. R. 1983. Geologia y genesis de la mineralizacion cuprifrea del sector de Caleta Coloso, al sur de Antofagasta. Revistas Geologia e Chile 20, 8191.
Flint, S. 1985 a. Sedimentary and diagenetic controls on red bed ore genesis: the San Bartolo copper deposit, Antofagasta Province, Chile. Economic Geology (in press).
Flint, S. 1985 b. On the paragenetic position of atacamite in low temperature red bed ore deposits of northern Chile. Zentralblatts Geologie Palaontologie (in press).
Flint, S., Clemmey, H. & Turner, P. 1986. The Lower Cretaceous Way Group of northern Chile: an alluvial fan–fan delta complex. Sedimentary Geology 46, 122.
Goble, R. J. & Smith, D. G. W. 1973. Electron microprobe investigation of copper sulfides in the Precambrian Lewis Series of S.W. Alberta, Canada. Canadian Mineralogist 12, 95103
Gustafson, L. B. & Williams, N. 1981. Sediment-hosted stratiform deposits of copper, lead and zinc. Economic Geology, 75th Anniversary Volume, 179213.
Harrington, H. 1961. Geology of parts of Antofagasta and Atacama Provinces, north Chile. Bulletin of the American Association of Petroleum Geologists 45, 169–97.
Holmes, I., Chambers, A. D., Ixer, R. A., Turner, P. & Vaughan, D. J. 1983. Diagenetic processes and the mineralization in the Triassic of central Engand. Mineralium Deposita 18, 365–77.
Ixer, R. A. & Vaughan, D. J. 1982. The primary ore mineralogy of the Alderley Edge deposit, Cheshire, Mineralogical Magazine 46, 485–92.
Jurgan, V. H. 1974. Die marine kalkfolge der unterkreide in der quebrada El Way–Antofagasta, Chile. Geologisches Rundschau 63, 490516.
Liou, G. J. 1971. P-T stabilites of laumontite, lawsontite and related minerals in the system Ca-Al, Si, O, –SiO2–H2O. Journal of petrology 12, 320–36.
Ljunggren, P. Meyer, H. C. 1964. The copper mineralization in the Corocoro basin, Bolivia. Economic Geology 59, 110–25.
Peters, E. 1976. Direct leaching of sulphides: chemistry and applications. Metallurgical Transactions 7B, 505–17.
Potter, R. W. 1977. An electrochemical investigation of the system copper–sulfur. Economic Geology 72, 1524–42.
Renfro, A. R. 1974. Genesis of the evaporite-associated stratiform metaliferous deposits – a sabkha process. Economic Geology 69, 3345.
Richards, D. T. 1971. The chemistry of copper in natural aqueous solutions. Stockholm Contributions in Geology no. 23, 64 pp.
Ripley, E. M., Lambert, M. W. & Berendsen, P. 1980. Mineralogy and paragenesis of red-bed copper mineralization in the lower Permian of South Central Kansas. Economic Geology 75, 722–9.
Robinson, B. W. & Kusakbe, M. 1975. Quantitative preparation of SO2 for 34S/32S analysis from sulphides by combustion with cuprous oxide. Analytical Chemistry 47, 1179–81.
Rose, A. W. 1976. The effect of cuprous chloride complexes in the origin of red bed copper and related deposits. Economic Geology 71, 1036–48.
Roseboom, E. H. Jr. 1966. An investigation of the system Cu-S and some natural copper sulfides between 25° and 700°C. Economic Geology 61, 641–72.
Rye, R. O. & Ohmoto, H. 1974. Sulfur and carbon isotopes and ore genesis: a review. Economic Geology 69, 826–42.
Sillitoe, R. H. 1973. The tops and bottoms of porphyry copper deposits. Economic Geology 68, 110.
Surdam, R. C. & Boles, J. R. 1979. Diagenesis of volcanic sandstones. In Aspects of Diagenesis (ed. Scholle, P. A. and Schluger, P: R.), pp. 227–42. Society of Economic Paleontologists and Mineralogists Special Publication no. 26.
Turner, P. 1980. Continental Red Beds. Developments in Sedimentology Series no. 29. New York: Elsevier. 562 pp.
Turner, P., Clemmey, H. & Flint, S. 1984. Palaeomagnetic studies of a Cretaceous molasse sequence in the Central Andes (Coloso Formation, northern Chile). Journal of the Geological Society of London 141, 868–76.
Walter, T. R., Waugh, B. & Crone, A. 1978. Diagenesis in first cycle desert alluvium of Cenozoic age, southwestern United States and northwestern Mexico. Bulletin of the Geological Society of America 89, 1932.
Woodward, L. A., Kaufman, W. H., Schumacher, O. L. & Talbott, L. W. 1974. Strata-bound copper deposits in Triassic sandstone of Sierra Nacimiento, New Mexico. Economic Geology 69, 108–20.
Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

Geological Magazine
  • ISSN: 0016-7568
  • EISSN: 1469-5081
  • URL: /core/journals/geological-magazine
Please enter your name
Please enter a valid email address
Who would you like to send this to? *


Altmetric attention score

Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed