The Mutooroo Copper Deposit: Geology, Alteration and Petrogenesis Graham S. Teale Consultant t Andrew T. Price Havilah Resources NL
The speaker would like to thank Havilah Resources NL for the opportunity to present this information at the SA Explorers Conference 2009
Geology NNE trending sequence of amphibolites, garnet amphibolites, granitic gneisses, meta-sediments, Potosi-like gneiss and sulphide-rich rock-types In the Mutooroo Mine area the sequence and associated mineralisation dips at 45º-50º 50º to the NW The Mutooroo Gneiss (Crooks and Fanning, 2006) close to the Mutooroo Mine has been dated at 1696 ± 17Ma with a metamorphic overprint at ~1575Ma (Crooks and Fanning, 2006) The Mutooroo Gneiss and adjacent amphibolites were most likely introduced as sills into the meta-sedimentary sequence
Mutooroo Copper Project Summary Drill Section MTDD116
Mutooroo Copper Project Summary Drill Section MTDD128
Amphibolite immediately adjacent to sulphide lens which contains abundant alteration biotite DDH MM21A-157.20m
The S 3 fabric observed here has been crenulated (D 4 ). Sample contains the retrograde assemblage quartz-muscovite-staurolite-biotite-tourmaline DDH MM21A-130.40m
Intensely retrogressed meta-pelite. Retrograde muscovite + staurolite are shown with the latter containing folded inclusion trails of quartz Mag. x 20; length of photomicrograph = 65mm; 6.5mm; PPL DDH MM21A-130.40m
Clasts and Gangue in Mineralisation Monomineralic quartz, biotite, apatite, gedrite and hornblende aggregates and single grains Clasts of blue quartz (quartz-sillimanite ± rutile or quartz-rutile), gedrite-quartz ± plagioclase ± biotite ± staurolite ± cordierite ± sulphides (usually Na and K-poor) poor), altered amphibolite, disaggregated and sericitised pegmatite, white quartz and plagioclase-biotite gneiss Thin magnetite, chalcopyrite and pyrite-rich lodes which contain a gangue dominated by abundant allanite Abundant monazite noted in the more chalcopyrite-rich mineralisation
In part milled, pyrrhotite breccia containing blue quartz clasts DDH MM05-310.20m
Milled pyrrhotite breccia containing rounded clasts of blue quartz and clasts of quartz-plagioclasebiotite ± epidote gneiss DDH MM18-168.10m
Milled breccia containing large white quartz clasts (as well as blue quartz clasts), contained within much finer grained rock fragments and abundant groundmass pyrrhotite and chalcopyrite DDH MM18-170.50m
Disaggregated, g sericitised pegmatite contained within mineralisation. The green colour is caused by sericite development MTDD130-265.7m
Mineralisation 8.7 mill. tonne @ 1.8% Cu (Broken Hill South, 1973) at a 1% Cu cut-off (non JORC). Havilah have drilled 228 RC and diamond drill-holes which have confirmed and extended this resource Mineralisation slightly transgressive but overall stratabound. Tested over 800m. The lodes display a sinusoidal character along strike and down dip. Plunge is highly variable from 45º SW to sub-horizontal Dominant sulphides are pyrrhotite, chalcopyrite and pyrite with lesser to rare molybdenite, gold, sphalerite, galena, bismuthinite, native bismuth, pentlandite and?cobaltite Dominant Fe-Ti oxides are magnetite, ilmenite, ferrian ilmenite, titan-hematite. The latter two phases develop at the margins of the mineralisation (often contained as inclusions in pyrite)
Sulphides are coarse grained (chalcopyrite up to 1cm, pyrite up to 1.5cm and pyrrhotite in the 2mm-4mm range) and exhibit well developed polygonal textures Pyrite contains from 0.17% to 4.1% Co (average 2.78%) and pyrrhotite contains 0.2% to 0.5% Co (average 0.26%). There is no Mn, Ni or Cu in pyrite. Silicates and oxides contain no Co Bi, Ag, Au, Pb, Zn, Mo As tend to concentrate at the margins of the massive mineralisation. Sporadic gold (up to 1m @ 11.5g/t; hole MTDD163) occurs in the immediate footwall in some areas The upper 30m-40m of the mineralisation is oxidised to a goethite-quartz gossanous breccia with local development of malachite, atacamite and chrysocolla. This is underlain by a vughy secondary pyrite-quartz t zone
Large milled quartz clast exhibits coarse chalcopyrite which has developed in a pressure fringe domain MTDD128-276.2m
Unusual eutectoid-like texture of intergrown pyrrhotite and quartz MTDD128-277.4m
Polygonal textured quartz-pyrrhotite-magnetite Mag. x 20; length of photomicrograph = 6.5mm; Reflected light MTDD128-277.4m
Chalcopyrite develops along pyrrhotite-pyrrhotite grain boundaries Mag. x 50; length of photomicrograph = 2.6mm; Reflected light DDH MM05-316.00m
General textural view of pyrrhotite-chalcopyrite Mag. x 20; length of photomicrograph = 65mm; 6.5mm; Reflected light DDH MM05-296.15m
Fractured and brecciated cobaltian pyrite annealed by chalcopyrite Mag. x 100; length of photomicrograph = 13mm; 1.3mm; Reflected light DDH MM08-168.10m
General textural view of cobaltian pyrite associated with pyrrhotite, chalcopyrite and gangue (black) Mag. x 50; length of photomicrograph = 2.6mm; Reflected light DDH MM05-296.15m
Thin magnetite and pyrite-rich lode. The magnetite (dark grey) occurs in linear arrays which parallel coarse pyrite grain boundaries. These lodes are rich in allanite. MTDD128-309.2m
Coarse tabular crystals of allanite sit within magnetite, pyrite and siderite Mag. x 50; length of photomicrograph = 2.6mm; PPL MTDD128-309.2m
Molybdenite develops towards the rims of chalcopyrite Mag. x 500; length of photomicrograph =.26mm; Reflected light DDH MM05-316.00m
Fine inclusions of galena (grey-white) and rare sphalerite contained within chalcopyrite. Accessory phases are often present at the margins of mineralised lodes Mag. x 200; length of photomicrograph = 0.65mm; Reflected light DDH MM05-319.00m
Pre-metamorphic Alteration K-silicate alteration in amphibolite as mineralisation is approached (biotite, K-feldspar) Scapolite replaces plagioclase in amphibolite as mineralisation is approached Ilmenite is replaced in amphibolite by ferrian ilmenite + titan-hematite as mineralisation is approached. It also develops within mineralisation close to ore-body margins All enclosing lithotypes can be extremely altered immediately adjacent to and within mineralisation. Sillimanite-quartz ± rutile, quartz ± rutile ( blue quartz ) and quartz-gedrite-cordierite ± staurolite assemblages are common on the flanks of lodes and as clasts within mineralisation
Mutooroo Copper Project Summary Drill Section MTDD163
Blue quartz rock from within a thick mineralised domain. It contains ~30% sillimanite. DDH MM05-304.90m
Intensely altered amphibolite now composed of sillimanite, quartz and abundant rutile. The latter replaces ilmenite. MTDD128-287.2m
General textural view of sillimanite-quartz rock developed via intense (pre-metamorphic) alteration Mag. x 50; length of photomicrograph = 2.6mm; PPL DDH MM05-304.90m
Extremely sillimanite-rich, sillimanite-quartz rock developed at the immediate margin of massive mineralisation. Mag. x 20; length of photomicrograph = 6.5mm; PPL MTDD128-287.2m
Ferrian-ilmenite and titan-hematite inclusions in pyrite. These oxidised phases only develop within pyrite with ilmenite in adjacent pyrrhotite (at margins of mineralisation). Mag. x 200; length of photomicrograph = 0.65mm; Reflected light DDH MM05-319.00m
Titan-hematite with abundant exsolution of ferrian ilmenite. These oxidised phases develop within amphibolite as mineralisation is approached. Mag. x 50; length of photomicrograph = 26mm; 2.6mm; Reflected light MTDD128-281.95m
Staurolite and gedrite inclusions within retrogressed cordierite. The sample contains the assemblage quartz-cordierite-gedritestaurolite-pyrrhotite-chalcopyrite Mag. x 50; length of photomicrograph = 26mm; 2.6mm; PPL MTDD163-241.2m
Summary Mutooroo is a significant body of sulphide mineralisation averaging 1.8% Cu (BH South, non JORC). It has been tested over ~800m strike length The sulphide mineralisation is pyrrhotite-rich with lesser pyrite and chalcopyrite and trace to rare molybdenite, gold, sphalerite, galena, bismuthinite, native bismuth, pentlandite +?cobaltite. Bi, Mo, As, Ag, Au, Zn and Pb are concentrated at the margins to massive mineralisation The sulphide mineralisation has been deformed, metamorphosed and remobilised. Remobilisation most likely occurred during D 1 /D 2 with mineralisation present pre-syn D 1 Intense alteration of wallrocks occurred prior to metamorphism. Highly acidic fluids stripped most elements (Na, K, Mg, Fe) from the non-metamorphosed precursors to the quartz-rutile and quartz-sillimanite rocks. These rock-types can also contain high gold concentrations. In addition, quartz-cordieritegedrite staurolite rocks are viewed as metamorphosed alteration assemblages