Komatiites and nickel sulfide ores of the Black Swan area, Yilgarn Craton, Western Australia. 2: Geology and genesis of the orebodies
Tóm tắt
The Black Swan Ultramafic Succession hosts a number of magmatic Fe–Ni–Cu–PGE sulfide ore shoots, ranging from high grade massive ore to low grade disseminated sulfides. Of these, the most economically significant is the Silver Swan massive sulfide orebody, associated with the basal contact of the succession. The deposit varies in thickness between 5 and 20 m, reaches a N–S strike length of 75 m, extends for at least 1.2 km of vertical plunge and is open at depth. Overlying matrix (net-textured) ore is rare. Inclusions of dacite are abundant within the lower 5 m of the massive sulfide. They range from angular fragments through smooth sinuous and plumose morphologies to fine lace-like intergrowths with the sulfide matrix, and comprise variable proportions of cores of porphyritic dacite and carapaces with skeletal plagioclase phenocrysts. Dynamic crystallisation and kinetic melting textures in the carapaces indicate that the inclusions have been heated to various temperatures, some well above their liquidus temperature. The composition of the inclusions ranges from a perfect match with the immediate footwall dacites to mixtures of dacite with up to 30% komatiite. The consistent thickness of the inclusion-bearing basal layer within the massive sulphide is interpreted as the extent of 3-D physical connectivity between the inclusions and a partially molten underlying hybrid layer. Primary contacts between the Silver Swan massive sulfide orebody and overlying ultramafic rocks are marked by thin rinds containing coarse-grained chevron-textured chromites with skeletal textures. Compositions of these chromites match those from Kambalda, Perseverance and other localities, and are inconsistent with a metamorphic origin. They are interpreted as markers of primary magmatic contacts. The combination of this feature with the general paucity of matrix ore implies that the massive ore accumulated and solidified before the accumulation of the overlying thick sequence of olivine cumulates. Taken together with observations on the internal fractionation of platinum group elements within the massive ores, these observations are consistent with a model where the massive ore were emplaced at the floor of a small partially drained lava tube. The floor of the tube had been previously heated by passage of large volumes of lava, such that it had reached its melting range. The felsic inclusions within the ore are the result of buoyant ascent of partially molten substrate into the ore magma. This constitutes strong evidence for the operation of thermo-mechanical erosion during ore emplacement. The disseminated Cygnet and Black Swan orebodies show a number of distinctive features. Cygnet contains a assemblage of clasts and inclusions which are interpreted as the result of rip-up, transport and redeposition of sulfides from a pre-existing massive sulfide orebody, of which Black Duck may be a remnant. The Black Swan orebody, by contrast, does not show xenolithic features, but is characterised by an association of sulfide blebs with segregation vesicles, and by unusually coarse-grained olivine. The Black Swan orebody is interpreted as the result of transport of sulfide droplets within a lava charged with a suspended load of coarse olivine crystals.
Tài liệu tham khảo
Barnes SJ (2000) Chromite in komatiites, II. Modification during greenschist to mid-amphibolite facies metamorphism. J Petrol 41:387–409
Barnes SJ (2004) Komatiites and nickel sulfide ores of the black swan area, Yilgarn Craton, Western Australia. 4. Platinum group element distribution in the ores, and genetic implications. Miner Deposita, this issue, DOI 10.1007/s00126-004-440-1
Barnes S-J, Naldrett AJ (1986) Variations in platinum group element concentrations in the Alexo mine komatiite, Abitibi greenstone belt, northern Ontario. Geol Mag 123:515–524
Barnes SJ, Roeder PL (2001) The range of spinel compositions in terrestrial mafic and ultramafic rocks. J Petrol 42:2279–2302
Barnes SJ, Gole MJ, Hill RET (1988) The Agnew nickel deposit, Western Australia: part I. Stratigraphy and structure. Econ Geol 83:524–536
Barnes SJ, Hill RET, Evans NJ (2004) Komatiites and nickel sulfide Ores of the Black Swan area, Yilgarn Craton, Western Australia. 3. Komatiite geochemistry, and implications for ore forming processes. Miner Deposita, this issue, DOI 10.1007/s00126-004-439-7
Beresford SW, Cas RAF, Lambert DD, Stone WE (2000) Vesicles in thick komatiite lava flows, Kambalda, Western Australia. J Geol Soc 157:11–14
Cowden A (1985) The effects of metamorphism upon the mineralogy, textures and geochemistry of the Kambalda nickel ores. Can Mineral 23:325
Cowden A (1986) The geochemistry, mineralogy and petrology of the Kamblada iron-nickel sulphide deposits, Western Australia. PhD (unpublished) Thesis, The University of Western Austalaia
Cowden A, Archibald NJ (1987) Massive-sulfide fabrics at Kambalda and their relevance to the inferred stability of monosulfide solid–solution. Can Mineral 25:37–50
Cowden A, Roberts DE (1990) Komatiite hosted nickel sulphide deposits, Kambalda. In: Hughes FE (ed) Geology of mineral deposits of Australia and Papua New Guinea. Australian Institute of Mining and Metallurgy Monograph. Australian Institute of Mining and Metallurgy, Melbourne, pp 567–581
Dobrovinski IE, Esin OA, Barmin LN, Chuchmarev SK (1969) Physicochemical properties of sulphide melts. Russ J Phys Chem 43:1769–1771
Donaldson MJ (1981) Redistribution of ore elements during serpentinisation and talc-carbonate alteration of some Archaean dunites, Western Australia. Econ Geol 76:1698–1713
Doyle CD, Naldrett AJ (1987) The oxygen content of ‘sulphide’ magma and its effect on the partitioning of nickel between coexisting olivine and molten ores. Econ Geol 82:208–211
Eckstrand OR (1975) The Dumont serpentinite: a model for control of nickeliferous opaque assemblages by alteration products in ultramafic rocks. Econ Geol 70:83–201
Eckstrand RO, Williamson BL (1985) Vesicles in the Dundonald komatiites. In: Program and abstracts, Geological Association of Canada—Mineralogical Association of Canada annual meeting, vol 10, p A-16
Ewers WE, Graham J, Hudson DR, Rolls JM (1976) Crystallisation of chromite from nickel–iron sulphide melts. Contrib Mineral Petrol 54:61–64
Frost KM, Groves DI (1989a) Magmatic contacts between immiscible sulfide and komatiitic melts; implications for genesis of Kambalda sulfide ores. Econ Geol 84:1697–1704
Frost KM, Groves DI (1989b) Ocellar units at Kambalda: evidence for sediment assimilation by komatiite lavas. In: Jones MJ (ed) Magmatic sulphides—the Zimbabwe volume. Institute of Mining and Metallurgy, London, pp 207–214
Gillies SL (1993) Physical volcanology of the Katinniq Peridotite complex and associated Fe–Ni–Cu–(PGE) mineralisation, Cape Smith Belt, Northern Quebec. MSc Thesis, University of Alabama, Tuscaloosa, p 146
Groves DI, Hudson DR, Hack TBC (1974) Modification of iron-nickel sulphides during serpentinisation and talc-carbonate alteration at Black Swan, Western Australia. Econ Geol 69:1265–1281
Groves DI, Barrett FM, Binns RA, McQueen KG (1977) Spinel phases associated with metamorphosed volcanic-type iron–nickel sulfide ores from Western Australia. Econ Geol 72:1224–1244
Groves DI, Korkiakoski EA, McNaughton NJ, Lesher CM, Cowden A (1986) Thermal erosion by komatiites at Kambalda, Western Australia and the genesis of nickel ores. Nature 319:136–139
Hicks JD, Balfe GD (1998) Silver Swan, Cygnet and Black Swan nickel deposits. In: Mackenzie DH (ed) Geology of Australia and Papua New Guinea mineral deposits. Australasian Institute of Mining and Metallurgy, Melbourne, pp 339–346
Hill RET, Barnes SJ, Dowling SE, Thordarson T (2004) Komatiites and nickel sulfide Orebodies of the Black Swan area, Yilgarn Craton, Western Australia. 1. Petrology and volcanology of host rocks. Miner Deposita, this issue, DOI 10.1007/s00126-004-437-9
Hudson DR, Travis GA (1981) A native nickel–heazlewoodite–ferroan trevorite assemblage from Mount Clifford, Western Australia. Econ Geol 76:1686–1697
Keele RA, Nickel EH (1974) The geology of a primary millerite-bearing sulfide assemblage and supergene alteration at the Otter Shoot, Kambalda, Western Australia. Econ Geol 69:1102–1117
Lesher CM, Groves DI (1986) Controls on the formation of komatiite-associated nickel-copper sulfide deposits. In: Friedrich GH (ed) Geology and metallogeny of copper deposits. Springer, Berlin Heidelberg NewYork, pp 63–90
Lesher CM, Arndt NT, Groves DI (1984) Genesis of komatiite-associated nickel sulphide deposits at Kambalda Western Australia: a distal volcanic model. In: Jones MJ (ed) Sulphide deposits in mafic and ultramafic rocks. Institute of Mining and Metallurgy, London, pp 70–80
Lesher CM, Burnham OM, Keays RR, Barnes SJ, Hulbert L (2001) Trace-element geochemistry and petrogenesis of barren and ore-associated komatiites. Can Mineral 39:673–696
Libby JW et al (1998) Perseverance Nickel Deposit. In: Mackenzie DH (ed) Geology of Australian and Papua New guinean mineral deposits. Monograph. Australian Institute of Mining and Metallurgy, Carlton, pp 321–328
Lofgren G (1980) Experimental studies on the dynamic crystallization of silicate melts. In: Hargraves RB (ed) Physics of magmatic processes. Princeton University Press, Princeton, pp 487–551
Lofgren GE, Usselman TM (1977) Dynamic crystallisation experiments bearing on the origin of textures in impact generated liquids. Lunar Sci 8:589–592
Marston RJ, Kay BD (1980) The distribution, petrology and genesis of nickel ores at the Juan complex, Kambalda, Western Australia. Econ Geol 75:546–565
McQueen KG (1979) Metamorphism and deformation of volcanic associated nickel deposits: a study of mineralization around the Widgiemooltha Dome, Western Australia. PhD Thesis, University of Western Australia, p 280
McQueen KG (1981) The nature and metamorphic history of the Wannaway nickel deposit, Western Australia. Econ Geol 76:1444–1468
McQueen KG (1987) Deformation and remobilization in some Western Australian nickel ores. Ore Geol Rev 2:269–286
Naldrett AJ (1969) A portion of the system Fe-S-O and its application to sulfide ore magmas. J Petrol 10:171–202
Naldrett AJ (1973) Nickel sulphide deposits: their classification and genesis, with special emphasis on deposits of volcanic association. Can Inst Mining Metallurgy Bull 66:45–63
Sack RO, Ghiorso MS (1991) Chromian spinels as petrogenetic indicators: thermodynamic and petrological applications. Am Mineral 76:827–847
Stone WE, Archibald NJ (2004) Structural controls on nickel sulphide ore shoots in Archaean komatiite, Kambalda, WA: the volcanic trough controversy revisited. J Struct Geol 26:1173–1194
Stone MS, Stone WE (2000) A crustally contaminated komatiitic dyke-sill-lava complex, Abitibi greenstone belt, Ontario. Precambrian Res 102:21–46
Stone WE, Crocket JH, Fleet ME, Larson MS (1996) PGE mineralization in Archaean volcanic systems: geochemical evidence from thick, differentiated, mafic-ultramafic flows, Abitibi Greenstone Belt, Ontario, and implications for exploration. J Geochem Exploration 56:237–264
Usselman TM, Hodge DS, Naldrett AJ, Campbell IH (1979) Physical constraints on the characteristics of nickel-sulfide ore in ultramafic lavas. Can Mineral 17:361–372