Volcanic red-bed copper mineralisation related to submarine basalt alteration, Mont Alexandre, Quebec Appalachians, Canada (original) (raw)

Abstract

Two types of native copper occur in Upper Silurian basaltic rocks in the Mont Alexandre area, Quebec Appalachians: (1) type 1 forms micrometric inclusions in plagioclase and is possibly magmatic in origin, whereas (2) type 2 occurs as coarse-grained patches rimmed by cuprite in altered porphyritic basalt. Type 1 has higher contents of sulphur (2,000-20,263 ppm) and arsenic (146-6,017 ppm), and a broader range of silver abundances (<65-2,186 ppm Ag) than type 2 (149-1,288 ppm S, <90-146 As, <65-928 ppm Ag). No mineral inclusions of sulphide or arsenide in native copper were observed at the electronmicroprobe scale. Primary igneous fabrics are preserved, but the basaltic flows are pervasively oxidised and plagioclase is albitised. Chlorite replaces plagioclase and forms interstitial aggregates in the groundmass and has Fe/ (Fe+Mg) ratios ranging from 0.29 to 0.36 with calculated temperatures between 155°C and 182°C. Copper sulphides in vacuoles and veinlets are associated with malachite, fibro-radiating albite and yarrowite (Cu 9 S 8 with up to 0.3 wt% Ag). Bulk-rock concentrations of thallium and lithium range from 70 to 310 ppb and 10 to 22 ppm, respectively, and thallium is positively correlated with Fe 2 O 3 . Such concentrations of thallium and lithium are typical of spilitisation during heated seawater-basalt inter-action. Spilitisation is consistent with the regional geological setting of deepwater-facies sedimentation, but is different from current models for volcanic red-bed copper, which indicate subaerial oxidation of volcanic flows. The volcanic red-bed copper model should be re-examined to account for native copper mineralisation in basalts altered by warm seawater.

Figures (13)

Fig. 1 Location of the cupriferous occurrence investigated (Mont Alexandre) and major stratigraphic units of the Gaspé Appalachians (modified from Malo 2004)

Fig. 1 Location of the cupriferous occurrence investigated (Mont Alexandre) and major stratigraphic units of the Gaspé Appalachians (modified from Malo 2004)

Fig. 2 Depositional environments during Silurian time for the Mont Alexandre region (after Bourque and Lachambre 1980; Bourque 2001) tensional event in an orogenic foreland setting (Bédard proportion of normative albite may be attributable to sodic alteration (Morin and Simard 1987). Primary flow textures are preserved, but the rocks are pervasively altered to secondary minerals, such as albite, chlorite, epidote, calcite and quartz (Bédard 1986a; Dostal et al. 1993). The lavas are more oxidised towards the top of the sequence (Bédard 1986b). The basalts were probably erupted during a tensional event in an orogenic foreland setting (Bédard

Fig. 2 Depositional environments during Silurian time for the Mont Alexandre region (after Bourque and Lachambre 1980; Bourque 2001) tensional event in an orogenic foreland setting (Bédard proportion of normative albite may be attributable to sodic alteration (Morin and Simard 1987). Primary flow textures are preserved, but the rocks are pervasively altered to secondary minerals, such as albite, chlorite, epidote, calcite and quartz (Bédard 1986a; Dostal et al. 1993). The lavas are more oxidised towards the top of the sequence (Bédard 1986b). The basalts were probably erupted during a tensional event in an orogenic foreland setting (Bédard

Fig. 3. Location of the study area and simplified geological map of a portion of the Mont Alexandre syncline (modified after Duffours 2000)

Fig. 3. Location of the study area and simplified geological map of a portion of the Mont Alexandre syncline (modified after Duffours 2000)

Native copper mineralisation has been known to be hosted in mafic volcanics of the Mont Alexandre area since 1936 (Fig. 3; Jones 1938; Duffours 2000). A quarry, in an area designated ‘Triangle d’Argent’, exposes basaltic rocks overprinted by alteration, which is more intense in the central, mineralised portion of the quarry (Figs. 3 and 4). The least-altered basalt, at the margin of the quarry and

Native copper mineralisation has been known to be hosted in mafic volcanics of the Mont Alexandre area since 1936 (Fig. 3; Jones 1938; Duffours 2000). A quarry, in an area designated ‘Triangle d’Argent’, exposes basaltic rocks overprinted by alteration, which is more intense in the central, mineralised portion of the quarry (Figs. 3 and 4). The least-altered basalt, at the margin of the quarry and

Copper sulphides are present in sub-economic amounts (compared to native copper) in altered basalts without coarse-grained native copper. The most abundant copper sulphides are yarrowite and chalcocite. Yarrowite, CuoSg, with up to 0.3 wt% Ag (Table 2), occurs mainly as independent crystals in veinlets of malachite and fibro- radiating albite (Fig. 5c). Yarrowite is also found as independent crystals in calcite-filled vesicles. Chalcocite is disseminated within the basaltic matrix (Fig. Sc) and co- exists with malachite and fibro-radiating albite, together with barite, as void infillings (Fig. 5d). Calcite-filled vesicles contain bornite, chalcopyrite, a Cu—S phase compositionally analogous to geerite, CugS; (Fig. Se, Table 2), digenite, chalcocite, yarrowite (Fig. 5f) and covellite. Chalcopyrite forms exsolution spindles in a triangular or reticulated pattern in bornite (Fig. Se).

Copper sulphides are present in sub-economic amounts (compared to native copper) in altered basalts without coarse-grained native copper. The most abundant copper sulphides are yarrowite and chalcocite. Yarrowite, CuoSg, with up to 0.3 wt% Ag (Table 2), occurs mainly as independent crystals in veinlets of malachite and fibro- radiating albite (Fig. 5c). Yarrowite is also found as independent crystals in calcite-filled vesicles. Chalcocite is disseminated within the basaltic matrix (Fig. Sc) and co- exists with malachite and fibro-radiating albite, together with barite, as void infillings (Fig. 5d). Calcite-filled vesicles contain bornite, chalcopyrite, a Cu—S phase compositionally analogous to geerite, CugS; (Fig. Se, Table 2), digenite, chalcocite, yarrowite (Fig. 5f) and covellite. Chalcopyrite forms exsolution spindles in a triangular or reticulated pattern in bornite (Fig. Se).

Table 1 Electron-microprobe analyses of chlorite n.a.: not analysed “Temperature calculated using the equation by Cathelineau and Nieva (1985)

Table 1 Electron-microprobe analyses of chlorite n.a.: not analysed “Temperature calculated using the equation by Cathelineau and Nieva (1985)

Table 2 Electron-microprobe analyses of copper sulphides apfu: atoms per formula unit; /—3: yarrowite, CuoSg; 4-5: bornite, CusFeS,; 6: chalcopyrite, CuFeS,; 7: covellite, CuS; 8—9: chalcocite, Cu,S; /( geerite, CugSs5

Table 2 Electron-microprobe analyses of copper sulphides apfu: atoms per formula unit; /—3: yarrowite, CuoSg; 4-5: bornite, CusFeS,; 6: chalcopyrite, CuFeS,; 7: covellite, CuS; 8—9: chalcocite, Cu,S; /( geerite, CugSs5

haematite (white). b Reflected-light photomicrograph (air) of coarse- grained, type 2 native copper, which is replaced by cuprite. c S vs As and d S vs Ag plots of electron-microprobe analyses of native copper Fig. 6 a Backscattered electron (BSE) image of type 1 native copper (arrows) along the c-axis of a plagioclase phenocryst (dark grey). The groundmass of the basaltic rock is spotted with titanium oxide and

haematite (white). b Reflected-light photomicrograph (air) of coarse- grained, type 2 native copper, which is replaced by cuprite. c S vs As and d S vs Ag plots of electron-microprobe analyses of native copper Fig. 6 a Backscattered electron (BSE) image of type 1 native copper (arrows) along the c-axis of a plagioclase phenocryst (dark grey). The groundmass of the basaltic rock is spotted with titanium oxide and

Table 3. Bulk-rock chemical analyses

Table 3. Bulk-rock chemical analyses

Table 3 (continued) Analytical methods: 7, INAA; 2, INAA/total digestion ICP-MS; 3, total digestion ICP/total digestion ICP-MS; 4, INAA/total digestion ICP; 5, total digestion ICP; 6, total digestion MS; 7, ICP-OES; 8, FA-MS; 9, titration. The following elements were sought, but were not detected (analytical method in parenthesis): Re, <0.001 ppm (6); Ir, <5 ppb (1); Hg, <1 ppm (1); W, <1 ppm (1); In, <0.1 ppm (6); Br, <0.5 ppm (1); Pd, <0.5 ppb (8). Sample numbers correspond to those indicated in Fig. 4. n.a.: not analysed

Table 3 (continued) Analytical methods: 7, INAA; 2, INAA/total digestion ICP-MS; 3, total digestion ICP/total digestion ICP-MS; 4, INAA/total digestion ICP; 5, total digestion ICP; 6, total digestion MS; 7, ICP-OES; 8, FA-MS; 9, titration. The following elements were sought, but were not detected (analytical method in parenthesis): Re, <0.001 ppm (6); Ir, <5 ppb (1); Hg, <1 ppm (1); W, <1 ppm (1); In, <0.1 ppm (6); Br, <0.5 ppm (1); Pd, <0.5 ppb (8). Sample numbers correspond to those indicated in Fig. 4. n.a.: not analysed

diagram to discriminate affinity (MacLean and Barrett 1993). ¢ The Th-Zr—Nb diagram with the fields for different tectonic settings from Wood (1980) Fig. 7 Geochemistry of Mont Alexandre and other basalts from the Lac McKay Member. a Classification using the Zr/TiO, vs Nb/Y diagram (Winchester and Floyd 1977; Pearce 1996). b The Y vs Zr

diagram to discriminate affinity (MacLean and Barrett 1993). ¢ The Th-Zr—Nb diagram with the fields for different tectonic settings from Wood (1980) Fig. 7 Geochemistry of Mont Alexandre and other basalts from the Lac McKay Member. a Classification using the Zr/TiO, vs Nb/Y diagram (Winchester and Floyd 1977; Pearce 1996). b The Y vs Zr

Fig. 8 Variation of bulk-rock contents of Fe203/FeO, Cu, Na and Li from the margin to the centre of the quarry. Numbers refer to samples located in Fig. 4. Lithium abundance of unaltered MORB used as reference from Staudigel (2003)

Fig. 8 Variation of bulk-rock contents of Fe203/FeO, Cu, Na and Li from the margin to the centre of the quarry. Numbers refer to samples located in Fig. 4. Lithium abundance of unaltered MORB used as reference from Staudigel (2003)

Fig. 9 Distribution of Fe.03 and TI in the basaltic rocks (Table 3; Fig. 4). Unaltered oceanic basaltic glasses contain less than 13 ppb Tl (McGoldrick et al. 1979)

Fig. 9 Distribution of Fe.03 and TI in the basaltic rocks (Table 3; Fig. 4). Unaltered oceanic basaltic glasses contain less than 13 ppb Tl (McGoldrick et al. 1979)

Loading...

Loading Preview

Sorry, preview is currently unavailable. You can download the paper by clicking the button above.

References (51)

  1. Alt JC, Honnorez J (1984) Alteration of the upper oceanic crust, DSDP site 417: mineralogy and chemistry. Contrib Mineral Petrol 87:149-169
  2. Alt JC, Laverne C, Vanko DA, Tartarotti P, Teagle DAH, Bach W, Zuleger E, Erzinger J, Honnorez J, Pezard PA, Becker K, Salisbury MH, Wilkens RH (1996) Hydrothermal alteration of a section of upper oceanic crust in the eastern equatorial Pacific: a synthesis of results from Site 504B (DSDP Legs 69, 70, and 83, and ODP Legs 111, 137, 140, and 148). Proc Ocean Drill Program Sci Results 148:417-434
  3. Bédard JH (1986a) Les suites magmatiques du Paléozoïque supérieur en Gaspésie. Ministère de l'Énergie et des Ressources du Québec, ET 84-09, 111 pp
  4. Bédard JH (1986b) Pre-Acadian magmatic suites of the southeastern Gaspé Peninsula. Geol Soc Amer Bull 97:1177-1191
  5. Bellehumeur C, Valiquette G (1993) Synthèse métallogénique du centre nord de la Gaspésie. Ministère de l'Énergie et des Ressources du Québec, ET 92-03, 65 pp
  6. Bourque PA (1975) Lithostratigraphic framework and unified nomen- clature for Silurian and basal Devonian rocks in eastern Gaspé Peninsula, Québec. Can J Earth Sci 12:858-872
  7. Bourque PA (2001) Sea level, synsedimentary tectonics, and reefs: implications for hydrocarbon exploration in the Silurian-lower- most Devonian Gaspé Belt, Québec Appalachians. Bull Can Pet Geol 49:217-237
  8. Bourque PA, Lachambre G (1980) Stratigraphie du Silurien et du Dévonien basal du sud de la Gaspésie. Ministère de l'Energie et des Ressources du Québec, ES-30, 123 pp
  9. Bourque PA, Brisebois D, Malo M (1995) Gaspé Belt. In: Williams H (ed) Geology of the Appalachian-Caledonian orogen in Canada and Greenland. Geological Survey of Canada, Geology of Canada 6, pp 316-351
  10. Brown AC (2005) Refinements for footwall red-bed diagenesis in the sediment-hosted stratiform copper deposits model. Econ Geol 100:765-771
  11. Brown AC (2006) Genesis of native copper lodes in the Keweenaw district, northern Michigan: a hybrid evolved meteoric and metamorphogenic model. Econ Geol 101:1437-1444
  12. Cathelineau M, Nieva D (1985) A chlorite solid solution geo- thermometer: the Los Azufres (Mexico) geothermal system. Contrib Mineral Petrol 91:235-244
  13. Chan LH, Alt JC, Teagle DAH (2002) Lithium and lithium isotope profiles through the upper oceanic crust: a study of seawater-basalt exchange at ODP sites 504B and 896A. Earth Planet Sci Lett 201:187-201
  14. Cornwall HR (1956) A summary of ideas on the origin of native copper deposits. Econ Geol 51:615-631
  15. Dostal J, Laurent R, Keppie JD (1993) Late Silurian-early Devonian rifting during dextral transpression in the southern Gaspé Peninsula (Quebec): petrogenesis of volcanic rocks. Can J Earth Sci 30:2283-2294
  16. Duffours, C (2000) Minéralisations Cuprifères du Mont Alexandre, Gaspésie. M.Sc. thesis, Université du Québec à Montréal, 125 pp Gablina IF, Semkova TA, Stepanova TV, Gor'kova NV (2006) Diagenetic alterations of copper sulfides in modern ore-bearing sediments of the Logatchev-1 hydrothermal field (Mid-Atlantic Ridge 14°45′N). Lithol Miner Resour 41:27-44
  17. Goble RJ (1980) Copper sulfides from Alberta: yarrowite Cu 9 S 8 and spionkopite Cu 39 S 28 . Can Mineral 18:511-518
  18. Hofmeister AM, Rossman GR (1985) Exsolution of metallic copper from Lake County labradorite. Geology 13:644-647
  19. Humphris SE, Thompson G (1978a) Trace element mobility during hydrothermal alteration of oceanic basalts. Geochim Cosmochim Acta 42:127-136
  20. Humphris SE, Thompson G (1978b) Hydrothermal alteration of oceanic basalts by seawater. Geochim Cosmochim Acta 42:107-125
  21. Hussak E (1906) Ueber das Vorkommen von gediegen Kupfer in den Diabasen von São Paulo. Centralb Mineral, pp 333-335
  22. Jolly WT (1974) Behavior of Cu, Zn, and Ni during prehnite- pumpellyite rank metamorphism of the Keweenawan basalts, northern Michigan. Econ Geol 69:1118-1125
  23. Jones IW (1938) Région du Mont Alexandre, Péninsule de Gaspé. Ministère de Mines et de Pêcheries, Québec, Rapport Annuel du Services des Mines de Québec pour l'Année 1936, Partie D, pp 5-28
  24. Kimata M, Nishida N, Shimizu M, Saito S, Arakawa Y (1997) Geochemical aspects of aventurine labradorites "sunshine" with inclusions of native copper: implication for continental-margin magmatism. Sci Rep Inst Geosci Univ Tsukuba Sect B 18:39-56
  25. Kirkham RV (1995) Volcanic redbed copper. In: Eckstrand OR, Sinclair WD, Thorpe RI (eds) Geology of Canadian mineral deposit types. Geological Survey of Canada, Geology of Canada 8, pp 241-252
  26. Large RR, McGoldrick PJ (1998) Lithogeochemical halos and geochem- ical vectors to stratiform sediment hosted Zn-Pb-Ag deposits, Part 1. Lady Loretta Deposit, Queensland. J Geochem Explor 63:37-56
  27. Large RR, Bull SW, McGoldrick PJ (2000) Lithogeochemical halos and geochemical vectors to stratiform sediment hosted Zn-Pb- Ag deposits, Part 2. HYC deposit, McArthur River, Northern Territory. J Geochem Explor 68:105-126
  28. Laurent R, Bélanger J (1984) Geochemistry of Silurian-Devonian alkaline basalt suites from the Gaspé Peninsula, Quebec Appalachians. Marit Sediments Atl Geol 20:67-78
  29. LeHuray AP (1989) Native copper in ODP site 642 tholeiites. Proc Ocean Drill Program Sci Results 104:411-417
  30. Lindgren W (1933) Mineral deposits. McGraw-Hill, New York, p 930
  31. MacLean WH, Barrett TJ (1993) Lithogeochemical techniques using immobile elements. J Geochem Explor 48:109-133
  32. Malo M (2001) Late Silurian-early Devonian tectono-sedimentary history of the Gaspé Belt in the Gaspé Peninsula: from a transtensional Salinic basin to an Acadian foreland basin. Bull Can Pet Geol 49:202-216
  33. Malo M (2004) Paleogeography of the Matapédia basin in the Gaspé Appalachians: initiation of the Gaspé Belt successor basin. Can J Earth Sci 41:553-570
  34. McGoldrick PJ, Keays RR, Scott BB (1979) Thallium: a sensitive indicator of rock/seawater interaction and of sulfur saturation of silicate melts. Geochim Cosmochim Acta 43:1303-1311
  35. Morin R, Simard M (1987) Géologie des régions de Sirois et de Raudin, Gaspésie. Ministère de l'Énergie et des Ressources du Québec, ET 86-06, 69 pp
  36. Munhá J, Kerrich R (1980) Sea water basalt interaction in spilites from the Iberian Pyrite Belt. Contrib Mineral Petrol 73:191-200
  37. Murao S, Itoh S (1992) High thallium content in Kuroko-type ore. J Geochem Explor 43:223-231
  38. Nagle F, Fink LK, Boström K, Stipp JJ (1973) Copper in pillow basalts from La Désirade, Lesser Antilles island arc. Earth Planet Sci Lett 19:193-197
  39. Nielsen SG, Rehkämper M, Norman MD, Halliday AN, Harrison D (2006) Thallium isotopic evidence for ferromanganese sediments in the mantle source of Hawaiian basalts. Nature 439:314-317
  40. Pearce JA (1996) A user's guide to basalt discrimination diagrams. In: Bailes AH, Christiansen EH, Galley AG, Jenner GA, Keith JD, Kerrich R, Lentz DR, Lesher CM, Lucas SB, Ludden JN, Pearce JA, Peloquin SA, Stern RA, Stone WE, Syme EC, Swinden HS, Wyman DA (eds) Trace element geochemistry of volcanic rocks: applications for massive sulphide exploration. Geological Asso- ciation of Canada, Short Course Notes 12, pp 79-113
  41. Seyfried WE Jr, Janecky DR, Mottl MJ (1984) Alteration of the oceanic crust: implications for geochemical cycles of lithium and boron. Geochim Cosmochim Acta 48:557-569
  42. Spooner ETC, Fyfe WS (1973) Sub-sea-floor metamorphism, heat and mass transfer. Contrib Mineral Petrol 42:287-304
  43. Staudigel H (2003) Hydrothermal alteration processes in the oceanic crust. In: Rudnick RL (ed) The crust. In: Holland HD, Turekian KK (eds) Treatise on geochemistry, volume 3. Elsevier, New York, pp 511-535
  44. Uytenbogaardt W, Burke EAJ (1971) Tables for microscopic identification of ore minerals. Dover, New York, 430 pp
  45. Vaughan DJ, Craig JR (1978) Mineral chemistry of metal sulfides. Cambridge University Press, Cambridge, 493 pp
  46. Wheat CG, Mottl MJ, Rudnicki M (2002) Trace element and REE composition of a low-temperature ridge-flank hydrothermal spring. Geochim Cosmochim Acta 66:3693-3705
  47. White WS (1968) The native-copper deposits of Northern Michigan. In: Ridge JD (ed) Ore deposits of the United States, 1933-1967: the Graton-Sales volume. American Institute of Mining, Metal- lurgical and Petroleum Engineers, New York, pp 303-325
  48. Whiteside LS, Goble RJ (1986) Structural and compositional changes in copper sulfides during leaching and dissolution. Can Mineral 24:247-258
  49. Winchester JA, Floyd PA (1977) Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chem Geol 20:325-343
  50. Wood DA (1980) The application of a Th-Hf-Ta diagram to problems of tectonomagmatic classification and to establishing the nature of crustal contamination of basaltic lavas of the British Tertiary volcanic province. Earth Planet Sci Lett 50:11-30
  51. Yang K, Scott SD (1996) Possible contribution of a metal-rich magmatic fluid to a sea-floor hydrothermal system. Nature 383:420-423