|
Morrison |
|
|
British Columbia, Canada |
| Main commodities:
Cu Au Mo
|
|
 |
|
|
 |
Super Porphyry Cu and Au
|
IOCG Deposits - 70 papers
|
All available as eBOOKS
Remaining HARD COPIES on
sale. No hard copy book more than AUD $44.00 (incl. GST) |
|
|
The Morrison porphyry copper-gold-molybdenum deposit is located 21 km north of the Bell mine, north Babine Lake, and 86 km east of Hazelton in central British Columbia, Canada. (#Location: 55° 11' 40" N 126° 18' 55" W).
Published reserve and production figures include:
95 Mt @ 0.42% Cu, 0.02% Mo, 0.34 g/t Au, (Res. 1976, Carson and Jambor, 1976),
190 Mt @ 0.40% Cu, 0.21 g/t Au (Indicated + Inferred Resource to 330 m, 1993)
123 Mt @ 0.38% Cu, 0.20 g/t Au (drill indicated resource, 1998)
12.4 Mt @ 0.53% Cu, 0.26 g/t Au (Measured plus indicated reserves, 2003),
86.9 Mt @ 0.45% Cu, 0.26 g/t Au (open pit resource, 2004).
Morrison is a strongly zoned, annular porphyry copper deposit that is largely within a multi-phase Eocene 'Babine-type' biotite-hornblende-plagioclase porphyry plugs, sills and dykes, enclosed within Middle to Upper Jurassic Ashman Formation (Bowser Lake Group)s iltstone, silty argillite, and minor conglomerate.
These sediments are massive and strongly altered and bedding has been largely obliterated, although where observed, the strike is north to northwest and dips steeply. On the outer margin of the deposit are the sediments have considerable introduced carbonate and a fawn to medium grey colour. As the copper zone is approached, the rocks become darker greyish green and fawn, indurated, chlorite-carbonate-rich greywackes and argillites, while in the copper zone these are dark grey and jet-black as a result of biotite alteration. Conglomerates are evident at a few localities distant from the porphyry plug.
The main porphyry body at Morrison, prior to faulting, was roughly circular in plan, with a diameter of approximately 500 m. It now occurs as a NW oriented elliptical multiphase plug with dimensions of 900 x 150 to 300 m, and near vertical sides. Numerous dyke and sill offshoots of the plug are common in the surrounding Hazelton Group sediments. The unaltered porphyry comprises abundant 0.25 to 1 mm phenocrysts of plagioclase (zoned oligoclase-andesine), biotite and hornblende in a fine grained matrix of the same components as well as K-feldspar and quartz (Carson & Jambour, 1976).
The Morrison deposit lies within the central part of a major graben that is part of the regional northwest trending block-fault structural framework of the region. The dominant structure in the deposit area is the NNW trending, Morrison fault, which bisects and offsets both the porphyry plug and copper zone with an apparent a dextral throw of approximately 300 metres. The vertical displacement is believed to be considerable. The fault is a linear zone of parallel shears and fractures that averages about 25 m in width, but ranges from 50 m in the central portion to only a few metres at the extremities.
At Morrison, chalcopyrite, pyrite and minor bornite occur in the copper zone with a large pyrite halo, with three very strong segments peripheral to the copper zone. The orebody was a vertical, annular cylinder that conforms to the shape of the porphyry plug, but has been dextrally displaced along the NNW trending Morrison fault. Its restored outer dimensions, as defined by a 0.3% Cu cut-off, are of the order of 700 x 400 m, with the central barren core being around 250 x 50 to 100 m. The copper zone is bounded by inner and outer grade boundaries of 0.3% Cu. In most places the outer margin is relatively sharp with a decline outwards to <0.1% Cu in about 40 m. The low grade core has 0.15 to 0.2% Cu. Within the ore annulus, which is 15 to 150 m wide, Cu grades exceed 0.5%, with >0.7% Cu over appreciable widths, and an average of 0.42% Cu. Mo averages 0.01%, and Au and Ag, 0.3 and 3 g/t respectively. The pyrite halo, which also contains minor pyrrhotite, is of the order of 50 to 250 m wide, but lenses out on the western extremity. The >0.3% Cu ore is predominantly within the plug, with only around 10% within the surrounding sediments (Carson & Jambour, 1976).
Chalcopyrite is the main Cu mineral, with minor to moderate amounts of bornite. Anomalous quantities of pyrite (>1%) are ubiquitous in all rock types, although the most pronounced concentrations (5 to 15%) are found in three segments of the pyrite halo surrounding the copper zone. Chalcopyrite predominantly occurs as thin seams and veinlets with or without quartz, and is distributed chiefly in fracture stockworks, while around 20 to 30% occurs as disseminations in the porphyry plug matrix and in peripheral sedimentary rocks. Very minor molybdenite accompanies some chalcopyrite-pyrite seams but also occurs as minute disseminated flakes.Some iron-bearing sulphides are altered to iron oxides and minor jarosite. Minor marcasite is present and is most commonly associated with pyrite, arsenopyrite, galena, sphalerite, geocronite, and boulangerite which occur with quartz and carbonate in small vuggy veinlets and pockets in minor faults and in the clay-carbonate altered rocks of the Morrison fault zone. Where exposed the copper minerals are oxidised to malachite, brochantite, and small amounts of pale blue copper silicates.
Pyrite and chalcopyrite exhibit a well-defined zonal relationship, with pyrite predominating in the pyrite halo, with the transition closely corresponding to the 0.3% Cu contour. While pyrite decreases toward the centre of the deposit, disseminations persist throughout and into the low grade core, where magnetite and minor bornite are also found.
Hydrothermal alteration is characterised by biotite-chlorite zoning. Biotitisation (dated at 52.1 Ma) is directly related to Cu grades, with >0.3% Cu being within the centrally located biotite zone, while chlorite-carbonate alteration is strongest in peripheral pyritised rocks. Minor K-feldspar alteration is evident on the inner rim of the copper zone. Disseminated fine-grained apatite is anomalously abundant in the porphyry plug and in some large dykes. In the fault zone, and along subsidiary shears, late stage clay-carbonate alteration and associated Pb and Zn sulphides are superimposed on the earlier biotite and chlorite alteration (Carson and Jambour, 1976).
Along the Morrison Fault, where it cuts the ore, there is a 5 to 20 m thick zone that has been downgraded to about 0.2 to 0.25% Cu due to dilution by sheared rock during fault movement, and by leaching by late hydrothermal solutions and possibly by ground-water. Irregularly distributed quartz-chalcopyrite veinlets and small blobs of chalcopyrite occurring along the fault zone may have originated from such leaching (Carson & Jambour, 1976).
The most recent source geological information used to prepare this decription was dated: 2000.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
|
|
|
Selected References:
|
Carson D J T and Jambor J L, 1976 - Morrison: Geology and evolution of a bisected annular porphyry copper deposit: in Sutherland Brown A (Ed.), 1976 Porphyry Deposits of the Canadian Cordillera, Canadian Institute of Mining and Metallurgy, Special Volume 15, pp 264-273
|
|
Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
|
Top | Search Again | PGC Home | Terms & Conditions
|
|
