Mineralium Deposita

, Volume 41, Issue 4, pp 301–321 | Cite as

Mineral zoning and gold occurrence in the Fortuna skarn mine, Nambija district, Ecuador

  • Agnès Markowski
  • Jean Vallance
  • Massimo Chiaradia
  • Lluìs Fontboté


The Fortuna oxidized gold skarn deposit is located in the northern part of the Nambija gold district, southern Ecuador. It has been subdivided into four mineralized sites, covering a distance of 1 km, which are named from north to south: Cuerpo 3, Mine 1, Mine 2, and Southern Sector. Massive skarn bodies occur in K–Na metasomatized volcanic and volcaniclastic rocks of the Triassic Piuntza unit. They appear to result from selective replacement of volcaniclastic rocks. Very minor presence of bioclast relicts suggests the presence of subordinate limestone. Endoskarn type alteration with development of Na-rich plagioclase, K-feldspar, epidote, actinolite, anhedral pyroxene, and titanite affects a quartz–diorite porphyritic intrusion which crops out below the skarn bodies in Mine 2 and the Southern Sector. Endoskarn alteration in the intrusion grades into a K-feldspar ± biotite ± magnetite assemblage (K-alteration), suggesting that skarn formation is directly related to the quartz–diorite porphyritic intrusion, the latter being probably emplaced between 141 and 146 Ma. The massive skarn bodies were subdivided into a dominant brown garnet skarn, a distal green pyroxene–epidote skarn, and two quartz-rich varieties, a blue-green garnet skarn and light green pyroxene–garnet skarn, which occur as patches and small bodies within the former skarn types. The proximal massive brown garnet skarn zone is centered on two 060° trending faults in Mine 2, where the highest gold grades (5–10 g/t) were observed. It grades into a distal green pyroxene–epidote skarn zone to the North (Cuerpo 3). Granditic garnet shows iron enrichment from the proximal to the distal zone. Diopsidic pyroxene exhibits iron and manganese enrichment from proximal to distal zones. The retrograde stage is weakly developed and consists mainly of mineral phases filling centimeter-wide veins, vugs, and interstices between garnet and pyroxene grains. The main filling mineral is quartz, followed by K-feldspar, epidote, calcite, and chlorite, with minor sericite, apatite, titanite, hematite, pyrite, chalcopyrite, and gold. Metal and sulfur contents are low at Fortuna, and the highest gold grades coincide with high hematite abundance, which suggests that retrograde stage and gold deposition took place under oxidizing conditions. Fluid inclusions from pyroxene indicate precipitation from high temperature—high to moderate salinity fluids (400 to 460°C and 54- to 13-wt% eq. NaCl), which result probably from boiling of a moderately saline (∼8-wt% eq. NaCl) magmatic fluid. Later cooler (180 to 475°C) and moderate to low saline fluids (1- to 20-wt% eq. NaCl) were trapped in garnet, epidote, and quartz, and are interpreted to be responsible for gold deposition. Chlorite analysis indicates temperature of formation between 300 and 340°C in accordance with fluid inclusion data. It appears, thus, that gold was transported as chloride complexes under oxidizing conditions and was deposited at temperatures around 300°C when transport of chloride complexes as gold carriers is not efficient.


Fortuna mine Nambija district Gold Skarn Zonation Endoskarn 



This work was supported by the Swiss National Science Foundation project n° 2000-062 000.00, the Académie Suisse des Sciences Naturelles, and the Society of Economic Geologists grants. We thank Fortuna Gold Mining Corp, Quito, Ecuador, for granting access to the Fortuna mine. Tom Shepherd and Fernando Tornos are also acknowledged for discussion and suggestions. This paper benefited from the fruitful comments of J. Hammarstrom, S. Redwood, L. Meinert, and D. Lentz.


  1. Allen J, Aslund T (1998) The Wabu gold skarn, Irian Jaya, Indonesia: the Gangue, newsletter of the mineral deposit division. Geol Assoc Can 59:9–11Google Scholar
  2. Bakker RJ, Brown PE (2003) Computer modeling in fluid inclusion research. In: Ian Samson, Alan Anderson, Dan Marshall (eds) Fluid inclusion analysis and interpretation. Min Assoc Can Short Course Series 32:175–212Google Scholar
  3. Bodnar RJ, Vityk MO (1994) Interpretation of microthermometric data for H2O–NaCl fluid inclusions. In: De Vivo B, Frezzotti ML (eds) Fluid inclusions in minerals, methods and applications. Virginia Tech, Blacksburg, VA, pp 117–130Google Scholar
  4. Brooks JW (1994) Petrology and geochemistry of the McCoy gold skarn, Lander County, Nevada. Ph.D. thesis, Washington State University, Pullman, Washington, p 607Google Scholar
  5. Brooks JW, Meinert LD, Kuyper BA, Lane ML (1991) Petrology and geochemistry of the McCoy gold skarn, Lander County, NV. In: Raines GL, Lisle RE, Schafer RW, Wilkinson WH (eds) Geology and ore deposits of the great basin. Geological Society Nevada, Reno, pp 419–442Google Scholar
  6. Burt DM (1977) Mineralogy and petrology of skarn deposits. Soc It Min Pet Rend 33:859–873Google Scholar
  7. Cathelineau M (1988) Cation site occupancy in chlorites and illites as a function of temperature. Clay Miner 23:471–485CrossRefGoogle Scholar
  8. Cathelineau M, Nieva D (1985) A chlorite solid solution geothermometer. The Los Azufres geothermal system (Mexico). Cont Miner Pet 91:235–244CrossRefGoogle Scholar
  9. de Caritat P, Hutcheon I, Walshe JL (1993) Chlorite geothermometry: a review. Clays clay miner 23:219–239CrossRefGoogle Scholar
  10. Doebrich JL, Theodore TG (1996) Geologic history of the Battle Mountain mining district, Nevada, and regional controls on the distribution of mineral systems. In: Coyner AR, Fahey PL (eds) Geology and ore deposits of the American Cordillera. Geological Society Nevada, Reno, pp 453–483Google Scholar
  11. Doebrich JL, Wotruba PR, Theodore TG, McGibbon DH, Felder RP (1996) Field trip guidebook for Trip H—geology and ore deposits of the Battle Mountain mining district. In: Green SM, Struhsacker E (eds) Field trip guidebook compendium. Geological Society Nevada, Reno, pp 327–388Google Scholar
  12. Einaudi MT, Meinert LD, Newberry RJ (1981) Skarn deposits. Econ Geol 75:317–391Google Scholar
  13. Feininger T (1987) Allochthonous terranes in the Andes of Ecuador and northwestern Peru. Can J Earth Sci 24:266–278CrossRefGoogle Scholar
  14. Fontboté L, Vallance J, Markowski A, Chiaradia M (2004) Oxidized gold skarns in the Nambija District, Ecuador. In: Perrello J, Sillitoe R, Vidal C (eds) Andean metallogenesis. SEG Special Publication 11:341–357Google Scholar
  15. Gammons CH, Williams-Jones AE (1997) Chemical mobility of gold in the porphyry-epithermal environment. Econ Geol 92:45–59Google Scholar
  16. Gendall IR, Quevedo LA, Sillitoe RH, Spencer RM, Puente CO, Leon JP, Povedo RR (2000) Discovery of a Jurassic porphyry copper belt, Pangui area, southern Ecuador. SEG Newsletter 43(1):8–15Google Scholar
  17. Gustafson LB, Hunt JP (1975) The porphyry copper deposit at El Salvador, Chile. Econ Geol 70:856–912Google Scholar
  18. Hammarstrom JM (1992) Mineralogy and chemistry of gold-associated skarn from Nambija, Zamora Province, Ecuador: a reconnaissance study. Adv US Int Min Res USGS 107–118Google Scholar
  19. Hughes RA, Pilatasig LF (2002) Cretaceous and Tertiary terrane accretion in the Cordillera Occidental of the Andes of Ecuador. Tectonophysics 345:29–48CrossRefGoogle Scholar
  20. Jaillard E, Benitez S, Mascle GH (1997) Les déformations paléogènes de la zone d’avant-arc sud équatorienne en relation avec l’évolution géodynamique. Bull Soc Geol Fr 168:403–412Google Scholar
  21. Jowett EC (1991) Fitting iron and magnesium into the hydrothermal chlorite geothermometer. GAC/MAC/SEG Joint Annual Meeting (Toronto). Program with Abstracts 16, p 62Google Scholar
  22. Kranidiotis P, MacLean WH (1987) Systematics of chlorite alteration and the Phelps Dodge massive sulfide deposit. Matagami, Quebec. Econ Geol 82:1898–1992CrossRefGoogle Scholar
  23. Litherland M, Fortey NJ, Beddoe-Stephens B (1992) Newly discovered Jurassic skarn fields in the Ecuadorian Andes. J South Am Earth Sci 6:67–75CrossRefGoogle Scholar
  24. Litherland M, Aspden JA, Jemielita RA (1994) The metamorphic belts of Ecuador. BGS, Overseas Memoir 11, Keyworth UK, p 147Google Scholar
  25. Markowski A (2003) The gold skarn of Fortuna, (Nambija District, Cordillera del Cóndor, Ecuador). Ms thesis, University of Geneva, 184 p. Also accessible on line under
  26. McKelvey GE, Hammarstrom JM (1991) A reconnaissance study of gold mineralization associated with garnet skarn at Nambija, Zamora Province, Ecuador. In: Good EJ, Slack JF, Kotra RK (eds) USGS research on mineral resources—1991, program and abstracts. US Geol Surv Circ, vol 1062, p 55Google Scholar
  27. Meinert LD (1989) Gold skarn deposits—geology and exploration criteria. In: Groves DI, Keays R, Ramsay R (eds) Proceedings of Gold ‘88, Economic Geology Monographs, vol 6. pp 537–552Google Scholar
  28. Meinert LD (1992) Skarns and skarn deposits. Geosci Can 19:145–162Google Scholar
  29. Meinert LD (1993) Igneous petrogenesis and skarn deposits. In: Kirkham RV, Sinclair WD, Thorpe RI, Duke JM (eds) Geol Assoc Can Special paper 40:569–583Google Scholar
  30. Meinert LD (1997) Application of skarn deposit zonation models to mineral exploration. Explor Min Geol 6:185–208Google Scholar
  31. Meinert LD (1998) A review of skarns that contain gold. In: Lentz DR (ed) Mineralized porphyry/skarn systems. Min Assoc Can Short Course Series, 26:359–414Google Scholar
  32. Meinert LD (2000) Gold in skarns related to epizonal intrusions. In Hagemann SG, Brown PE (eds) Gold in 2000. Rev Econ Geol 13:347–375Google Scholar
  33. Meinert, LD, Dipple, GM, and Nicolescu, S (2005) World Skarn Deposits: in Hedenquist, JW, Thompson, JFH, Goldfarb, RJ, and Richards, JP (eds) Economic geology 100th anniversary volume, society of economic geologists, Littleton, Colorado, USA, includes supplementary appendices on CD-ROM (filename: Meinert), pp 299–336Google Scholar
  34. Mining Magazine (1990) Campanilla gold mine. Min Mag 163:322–323Google Scholar
  35. Myers GL (1994) Geology of the Copper Canyon–Fortitude skarn system, Battle Mountain, Nevada. Ph.D. thesis, Washington State University, Pullman, p 356Google Scholar
  36. Nakano T (1998) Pyroxene geochemistry as an indicator for skarn metallogenesis in Japan. In: Lentz DR (ed) Mineralized porphyry/skarn systems. Mineral Assoc Can Short Course Series 26:147–167Google Scholar
  37. Newberry RJ, Allegro GL, Cutler SE, Hagen-Leveille JH, Adams DD, Nicholson LC, Weglarz TB, Bakke AA, Clautice KH, Coulter GA, Ford MJ, Myers GL, Szumigala DJ (1997) Skarn deposits of Alaska. In: Goldfarb RJ (ed) Ore Deposits of Alaska. Econ Geol Monogr 9:355–395Google Scholar
  38. Paladines A, Rosero G (1996) Zonificación mineralogénica del Ecuador: Ed. Laser, Quito, p 146Google Scholar
  39. Pearce JA, Harris NBW, Tindle AG (1984) Trace element discrimination for the tectonic interpretation of granitic rocks. J Petrol 25:956–983Google Scholar
  40. Prodeminca (2000) Depósitos porfídicos y epi-mesotermales relacionados con intrusiones de la Cordillera del Cóndor: Evaluacion de distritos mineros del Ecuador: UCP Prodeminca Proyecto MEM BIRF 36-55 EC 5Google Scholar
  41. Ray GE, Dawson GL, Webster ICL (1996) The stratigraphy of the Nicola Group in the Hedley district, British Columbia and the chemistry of its intrusions and Au skarns. Can J Earth Sci 33:1105–1126Google Scholar
  42. Shepherd TJ (1981) Temperature programmable heating-freezing stage for microthermometric analysis of fluid inclusions. Econ Geol 76:1244–1247CrossRefGoogle Scholar
  43. Skirrow RG, Walshe JL (2002) Reduced and oxidised Au–Cu-Bi iron–oxide deposits of the Tennant Creek Inlier, Australia; an integrated geologic and chemical model. Econ Geol 76:1167–1202CrossRefGoogle Scholar
  44. Sterner SM, Bodnar RJ (1984) Synthetic fluid inclusions in natural quartz. I. Compositional types synthesized and applications to experimental geochemistry. Geochim Cosmochim Acta 48:2659–2668CrossRefGoogle Scholar
  45. Sterner SM, Hall DL, Bodnar RJ (1988) Synthetic fluid inclusions. V. Solubility relations in the system NaCl–KCl–H2O under vapor-saturated conditions. Geochim Cosmochim Acta 52:989–1006CrossRefGoogle Scholar
  46. Vallance J, Markowski A, Fontboté L, Chiaradia M (2003) Mineralogical and fluid inclusion constraints on the genesis of gold-skarn deposits in the Nambija district (Ecuador). In: Eliopoulos D et al (eds) Proc. of Seventh Biennal SGA Meeting, Mineral exploration and sustainable development, Millipress, Athens Greece, pp 399–402Google Scholar
  47. Winchester JA, Floyd PA (1976) Geochemical magma type discrimination: application to altered and metamorphosed basic igneous rocks. Earth Planet Sci Lett 28:459–469CrossRefGoogle Scholar
  48. Zharikov VA (1970) Skarns. Int Geol Rev 12:541–559, 619–647, 760–775CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2006 2006

Authors and Affiliations

  • Agnès Markowski
    • 1
    • 2
  • Jean Vallance
    • 1
  • Massimo Chiaradia
    • 1
  • Lluìs Fontboté
    • 1
  1. 1.Section des Sciences de la TerreUniversity of GenevaGenevaSwitzerland
  2. 2.Isotopengeologie und Mineralische Rohstoffe, ETH-ZentrumZürichSwitzerland

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