Abstract
In northern Chile, between 27 and 33°S, there are numerous deposits where residual petroleum is associated with Cu-(Ag) mineralisation (the most famous being El Soldado). All of these deposits are hosted by Lower Cretaceous volcanic or volcanoclastic facies along the axis of a former backarc basin. This close relationship suggests that the generation, migration and emplacement of hydrocarbons in the Cretaceous volcanic units is a regional process, associated with the evolution of the Cretaceous backarc basin and points to the importance of pyrobitumen as an exploration tool for similar Cu–(Ag) deposits. The present work analyses four small strata-bound copper deposits located along a north–south belt approximately 10 km east of Copiapó in northern Chile. These deposits are typically hosted by pyrobitumen-rich andesitic volcanic to volcanoclastic rocks intercalated with the marine carbonate Pabellón Formation, the youngest formation within the Chañarcillo Group. The strong genetic and spatial relationships between the pyrobitumen-rich lavas and the mineral deposits allow us to define this volcanic belt as the Ocoita-Pabellón Metallotect. Two hydrothermal events can be distinguished based on the mineralogical, textural, fluid inclusion and isotope data of ore and gangue and on the optical properties of residual petroleum. During the early event, petroleum was mobilised from the source rocks into the primary and secondary porosity of the lavas by Fe-rich hydrothermal fluids, which precipitated pyrite as an early sulphide phase. The second event is characterised by Cu-rich hydrothermal fluids, which induced three successive sub-stages of Cu-sulphide precipitation. The hydrothermal fluids chemically and thermally altered the first-stage bitumen, transforming it into pyrobitumen. The present work documents similarities between the Ocoita-Pabellón Metallotect and the El Soldado ore deposit and emphasises important differences. In the El Soldado host rocks, a petroleum reservoir existed prior to the arrival of the mineralising hydrothermal fluids, the framboidal pyrite was formed by assistance of bacteria, the S of the Cu sulphides was inherited from the pyrite, and the fluid source was basin connate-metamorphic brine. In the Ocoita-Pabellón Metallotect, the hydrocarbons were mobilised into the host rocks by hydrothermal fluids; the pyrite is epigenetic, the δ34S values of pyrite and copper sulphides are very different, with distinctive light δ34S signature of Cu sulphides (δ34S between −44.7 and −17.9‰), and the calculated δ18O of hydrothermal fluids indicates the participation of meteoric water in the late phases of the hydrothermal system.
Similar content being viewed by others
Notes
The physical and optical characteristics of bitumen and pyrobitumen are explained in the next section (“Solid hydrocarbons: bitumen and pyrobitumen”).
References
Aberg G, Aguirre L, Levi B, Nystrom O (1984) Spreading subsidence and generation of ensialic marginal basins, an example from the early Cretaceous of Central Chile. In: Kokelaar BP, Howels MF (eds) Marginal basin geology. Geological Society of London, special publication, vol 16. Blackwell Scientific, London, pp 185–193
Arévalo C (1994) Mapa geológico del cuadrángulo Los Loros. Documentos de Trabajo N° 6. SERNAGEOMIN. Scale 1:100.000
Arévalo C (1995) Mapa geológico de la Hoja Copiapó, Región de Atacama. Documentos de Trabajo N° 6. SERNAGEOMIN. Scale 1:100.000
Arévalo C (1999) The Coastal Cordillera/Precordillera boundary in the Copiapó area, northern Chile and the structural setting of the Candelaria Cu–Au deposit. Ph.D. thesis, University of Kingston, p 205
Barker CE, Pawlewicz MJ (1994) Calculation of vitrinite reflectance from thermal histories and peak temperatures. A comparison of methods. In: Mukhopadhyay PK, Dow WG (eds) Vitrinite reflectance as a maturity parameter: applications and limitations. ACS Symp Ser 570:216–229
Boric R, Holmgren C, Wilson NSF, Zentilli M (2002) The geology of the El Soldado manto-type Cu (Ag) deposit, Central Chile. In: Porter TM (ed) Hydrothermal iron oxide copper–gold and related deposits: a global perspective, vol 2. PGC, Adelaide, pp 163–184
Bustin RM, Cameron A, Grieve D, Kalkreuth W (1985) Coal petrology, its principles and applications. Geological Association of Canada, short course notes, 2nd edn. Geological Association of Canada, St. John’s, p 230
Cisternas ME, Diaz L (1990) Geologic evolution of the Atacama basin during the Lower Cretaceous. In: Fontboté L, Amstutz CG, Cardozo M, Cedillo E, Frutos J (eds) Stratabound ore deposits in the Andes. Springer, Berlin Heidelberg New York, pp 496–504
Cisternas ME, Frutos J (1996) Importancia metalogénica del volcanismo extensional del Cretácico Inferior en la Región de Copiapó, Chile. In: XXXIX Congresso Brasileiro de Geologia, vol 7. Anais, Salvador, pp 303–306
Cisternas ME, Frutos J, Spiro B, Galindo E (1999a) Lavas con bitumen en el Cretácico Inferior de Copiapó: petroquímica e importancia metalogénica. Rev Geol Chile 26(2):205–226
Cisternas ME, Haggan T, Parnell J (1999b) Andesita-hosted copper sulphide-bitumen mineralization in a back arc Andean Basin, North Central Chile. In: Stanley CJ et al. (eds) Mineral deposits: processes to processing, vol 1. Balkema, Rotterdam, pp 223–226
Cucurella J, Canut de Bon C, Cisternas ME (2005) Pyrobitumen related to silver–copper deposits in a Cretaceous volcanic–sedimentary sequence: Talcuna district, Coquimbo, Chile. Mineral Pol 36(1):21–29
Davis DW, Lowenstein TK, Spencer RJ (1990) Melting behavior of fluid inclusions in laboratory-grown halite crystal in the system NaCl–H2O, NaCl–H2O–KCl, NaCl–H2O–MgCl2, and NaCl–H2O–CaCl2. Geochim Cosmochim Acta 54:591–601
Goodarzi F, Gentis T, Jackson G, Macqueen RW (1993) Optical characteristics of head-effected bitumens from the Nanisivik mine, NW Baffin Island, Arctic Canada. Energy Resour 15:359–376
Haggan T, Parnell J, Cisternas ME (2003) Fluid history of andesite-hosted CuS-bitumen mineralization, Copiapó district, North Central Chile. J Geochem Explor 78–79:631–633
Hermosilla J (2001) Rol de la materia orgánica en la formación de los depósitos minerales del Metalotecto Ocoita-Pabellón. Copiapó, III Región de Atacama. Undergraduate Thesis, Departamento de Ciencias de la Tierra, Universidad de Concepción, p 213
Hoefs J (1987) Stable isotope geochemistry. Springer, Berlin Heidelberg New York, p 236
Hunt JM (1978) Characterization of bitumens and coals. Am Assoc Pet Geol Bull 54:249–273
Jacob H (1989) Classification, structure, genesis and practical importance of natural solid oil bitumen (“migrabitumen”). Int J Coal Geol 11:65–79
Landis CR, Castaño JR (1995) Maturation and bulk chemical properties of a suite of solid hydrocarbons. Org Geochem 22:137–149
Larson R, Pitman WC (1972) World-wide correlation of Mesozoic magnetic anomalies and its applications. GSA Bull 83:3645–3662
Lewan MD (1983) Effects of thermal maturation on stable carbon isotopes as determined by hydrous pyrolisis of Woodford shale. Geochim Cosmochim Acta 47:1471–1480
Longstaffe FJ, Ayalon A (1987) Oxygen-isotope studies of clastic diagenesis in the Lower Cretaceous Viking Formation, Alberta: implications for the role of meteoric water. In: Marshall JD (ed) Diagenesis of sedimentary sequences. Geological Society, special publication, vol 36. Oxford University Press, Oxford, pp 277–296
Marschik R, Fontboté L (2001) The Punta del Cobre Formation. Punta del Cobre-Candelaria area, northern Chile. J South Am Earth Sci 14:401–433
Marschik R, Fontignie D, Chiaradia M, Voldet P (2003) Geochemical and Sr–Nd–O isotope composition of granitoids of the Early Cretaceous Copiapó plutonic complex (27°30′ S), Chile. J South Am Earth Sci 16:381–398
Mpodozis C, Ramos V (1990) The Andes of Chile and Argentina. Circum Pacific council for energy and minerals resources. Earth Sci Ser 11:59–90
Ohmoto H (1972) Systematics of sulfur and carbon isotopes in hydrothermal ore deposits. Econ Geol 67:551–578
O’Neil JR, Clayton N, Mayeda TK (1969) Oxygen isotope fractionation in divalent metal carbonates. J Chem Phys 51:5547–5558
Potter RW, Clynne MA, Brown DL (1978) Freezing point depression of aqueous sodium solutions. Econ Geol 73:233–244
Rye RO, Ohmoto H (1974) Sulphur and carbon isotopes and ore genesis. A review. Econ Geol 69:826–842
Segerstrom K (1960) Cuadrángulo Quebrada Paipote. Inst Inves Geol Carta Geológica de Chile.Vol.7, N° 1, scale 1:50.000
Segerstrom K (1968) Geología de las hojas Copiapó y Ojos del Salado. Provincia de Atacama. Inst Inv Geol Boletín 24:58
Thomas H (1958) Geología de la Cordillera de la Costa entre el valle de La Ligua y la cuesta Barriga. Ins Inv Geol Boletín 2:86
Ullrich TD, Clark AH, Kyser KT (2001) The Candelaria Cu–Au deposit, III region, Chile: product of long-term mixing of magmatic–hydrothermal and evaporite-source fluids. GSA annual meeting, Boston, 1–10 November 2001
Vaughan APM (1995) Circum-pacific mid-Cretaceous deformation and uplift: a superplume-related event? Geology 23:491–494
Vergara M, Nystrom JO (1996) Geochemical features of Lower Cretaceous backarc lavas in the Andean Cordillera, Central Chile (31–34°S). Rev Geol Chile 23(1):97–106
Wilson NSF (1998) The role of petroleum in the formation of the El Soldado copper deposit, Chile: hydrothermal replacement of a biodegraded petroleum reservoir. Ph.D. Thesis, Dalhousie University, p 418
Wilson NSF (2000) Organic petrology, chemical composition, and reflectance of pyrobitumen from the El Soldado Cu deposit, Chile. Int J Coal Geol 43:53–82
Wilson NSF, Zentilli M (1999) The role of organic matter in the genesis of the El Soldado volcanic-hosted manto-type Cu deposit, Chile. Econ Geol 94:1115–1136
Wilson NSF, Zentilli M, Reynolds PH, Boric R (2003a) 40Ar/39Ar geochronology of K-feldspar from the El Soldado manto-type copper deposit, Chile. Chem Geol Isot Geosci Sect 197:161–176
Wilson NSF, Zentilli M, Spiro B (2003b) A sulfur, carbon, oxygen, and strontium isotope study of the volcanic-hosted El Soldado manto-type copper deposit, Chile: the essential role of bacteria and petroleum. Econ Geol 98(1):163–174
Wilson NSF, Zentilli M (2006) Association of pyrobitumen with copper mineralization from the Uchumi and Talcuna districts, central Chile. Int J Coal Geol 65(1–2):158–169
Zentilli M, Boric R, Munizaga F, Graves MC (1994) Petroleum involvement in the genesis of some strata-bound copper deposits of Chile, VII Congreso Geológico Chileno, vol 2. Concepción pp 1542–1546
Acknowledgements
Funding for this research was provided by the Fondo Nacional de Desarrollo Científico y Tecnológico Grant 1010825 from the Chilean Commission for Scientific and Technological Research. This manuscript was greatly improved by the constructive comments of Dr. Georges Beaudoin, Dr. Slawornir Oszczepalski, Dr. Nicholas Wilson and Dr. Alex Brown.
Author information
Authors and Affiliations
Corresponding author
Additional information
Editorial handling: G. Beaudoin
Rights and permissions
About this article
Cite this article
Cisternas, M.E., Hermosilla, J. The role of bitumen in strata-bound copper deposit formation in the Copiapo area, Northern Chile. Miner Deposita 41, 339–355 (2006). https://doi.org/10.1007/s00126-006-0063-9
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00126-006-0063-9