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Martison |
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Ontario, Canada |
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P Nb
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Super Porphyry Cu and Au
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The Martison carbonatite-phosphate-niobium deposit is located 70 km northeast of Hearst, and 15 km southwest of Martison Lake, Ontario, Canada, and lies within the Superior Province of the Canadian Shield, #Location: 50° 19 52"'N, 83° 24' 52"W.
The Martison carbonatite is overlain by a high grade secondary residual phosphate deposit, where Cretaceous weathering and dissolution of the soluble minerals in the host carbonatite rock has left behind a residue of the insoluble minerals, largely apatite crystals, accompanied by a well-developed karst topography, now buried under glacial lake deposits of lacustrine clays, and boulder tills of Pleistocene age.
The Martison carbonatite complex lies within the Ontario Carbonatite Province of northern Ontario and western Quebec, the only known concentration of carbonatite complexes in North America. This petrographic province is made up of some 50 known carbonatite complexes over an area of 1.3 million sq. km, almost all of which occur along recognisable major tectonic features. They all contain 5 to 25% apatite in the carbonatite phase, with some having undergone significant enrichment of apatite through leaching of carbonates, as at Martison. Based on their ages, the carbonatites belong to four groups; the two younger, dated at 120 and 570 Ma, are restricted to the Ottawa graben, whereas the two older groups, dated at 1100 and 1700 Ma, are distributed along the Kapuskasing and the Albany Forks gravity highs. All of these gravity highs/structures are major tectonic features that are probably related to the Mid-Continent Gravity High, the geophysical expression of the Mid-continental Rift mafic to ultramafic intrusive and extrusive masses (Erdosh, 1979).
The Martison carbonatite lies ~150 km west of the Kapuskasing Structural Zone and gravity anomaly which hosts numerous alkalic-carbonatite complexes (e.g., Cargill), and as such is unlikely to be related to that structure. It is a similar distance SE of the Albany Forks gravity highs. However, it lies along the NE extension of the Garden River fault zone, the western end of which is one of the bounding faults for the northwestern margin of the Neoproterozoic Lake Superior basin.
The carbonatite complex is situated in the large expanse of 'low ground' SW of Hudson Bay, characterised by a very gently rolling terrain dominated by muskeg and black spruce swamp. Neither the carbonatite or its enclosing wall rocks are exposed, with the nearest outcrop 25 km to the south, and all geological data is from drilling information and geophysical interpretations. It is overlain by Cretaceous sediments, Pleistocene glacial till and a thin layer of peat.
The basement country rock to the carbonatite and ultramafic rocks surrounding it, is Archaean to Palaeoproterozoic granite and granite gneisses. Structural drilling has shown that the Palaeozoic sequence, regionally comprising up to 800 m of shallow marine sediments, chiefly arkose, shale, limestone and dolomite covering these basement rocks is missing over an area of at least 10 km radius around the Martison carbonatite. Regionally, the basement and Palaeozoic sequence are overlain by Middle Cretaceous non-marine sands, silts and clays with occasional lignite seams and kaolin beds. Several Mesozoic kimberlitic dykes are also known within the region.
The mafic to ultramafic halo to the carbonatites covers an area of at least ~10 x 15 km and includes serpentinised olivine-calcite-phlogopite kimberlitic and ultramafic porphyry diatreme rocks.
Differential weathering of the carbonatite complex has produced an irregular upper surface, the depth of which varies considerably over short distances. Depressions within this surface are filled with the weathered carbonatite residuum that represents the bulk of the economic phosphatic material. Numerous NW-striking faults are interpreted from magnetic data, block-faulting both the carbonatite and ultramafic rocks and influencing the distribution of irregularities in the base of the residuum (i.e., influencing palaeo-surface drainage and possibly karstic weathering of the underlying carbonatite).
The complex has been interpreted to comprise three separate but related carbonatite intrusions over an area of about 56 sq. km, designated as (i) Carbonatite A, which covers an area of ~12.5 sq. km, (ii) Carbonatite B, which is located about 5 km to the SE, and has an area of ~4 sq. km, and (iii) Carbonatite C, located ~3 km to the ESE of Carbonatite A and is ~2 sq. km in size.
Carbonatite A, which contitutes the main resource, is overlain by 0 to 135 m of Mid-Cretaceous sediments, chiefly lignitic sediments and a highly weathered lateritic profile. These are followed by 30 to 82, averaging 47 m of Pleistocene glacial till that ranges from coarse gravel size sediment to clay, which is in turn blanketed by 0.5 to 4, averaging 2 m of peat.
Carbonatite A is a massive, white, medium to coarse grained rock composed mainly of calcite, dolomite, phlogopite, magnetite, apatite and pyrochlore with the composition of a sovite and silicocarbonatite at different locations. It has subvertical banding and local brecciation. The upper contact between the carbonatite and residuum is marked by a thin zone of partially leached carbonatite that ranges form 1 to to 55 m in thickness, averaging 11 m, with generally very low P2O5 and Nb2O5 contents.
Above Carbonatite A, the residuum material occurs in two main types, one of which is brownish, soil-like and unconsolidated (0.0 to 58.5 m thick) generally with a medium P2O5 content and higher Nb2O5, and an underlying consolidated (re-cemented) residuum (0.0 to 91.6 m thick), generally with a high P2O5 content and lower Nb2O5. A third and minor type of material comprises partially weathered carbonatite, which occurs as "lenses" within the residuum. The residuum is basically a horizontal layer confied to part of Carbonatites A and C, but not over Carbonatite B . The larger accumulation over Carbonatite A is butterfly shaped and 2 x 3 km in area. It has a flat top but an irregular base with keel-like projections filling depressions in the underlying weathered carbonatite.
The minerals of the residuum have been classified as primary, secondary and detrital. The principal primary minerals are apatite, magnetite, pyrochlore, calcite, dolomite, barite, columbite and occasional quartz. The secondary minerals, which are the result of the breakdown of the primary minerals, replacements of the primary minerals or redeposition of elements after dissolution of the primary minerals, and include francolite, calcite, dolomite, ankerite, siderite, limonite, goethite, hematite, ilmenite, phlogopite, pyrite and pyrochlore. The detrital minerals include kaolin, crandallite, feldspars and quartz.
Concentrate from the unconsolidated residuum contains 25 to 75% fluorapatite; 5 to 25% each of crandallite, magnetite, goethite and chlorite; 1 to 5% each of hematite, carbonates, limonite, mica, quartz and feldspar; and identified ilmenite, pyrochlore, anatase, pyrite and garnet, while concentrate from the consolidated material is composed of 25 to 75% fluorapatite; 5 to 25% each of crandallite, magnetite, chlorite; 1 to 5% each of goethite, hematite, carbonates, limonite, mica, quartz and feldspar; and identified ilmenite, pyrochlore, anatase, hornblende and garnet.
The resource over Carbonatite A trends at ~150° with a length of ~1700 m and width varying from 300 to 600 m, with sharp NE and SW margins. The residuum over Carbonatite C is generally >100 m thick, covering an area of ~2 x 1 km.
Geological resource estimates for Carbonatite A (Spalding, 2007 for Phoscan Chemical Corporation) include:
Measured + indicated mineral resource - 62.3 Mt @ 23.55% P2O5 0.34% Nb2O5;
Inferred mineral resource - 55.7 Mt @ 21.87% P2O5 0.34% Nb2O5.
These resources are calculated within lithological boundaries with an effective ~10% P2O5 cut-off,
The information in this summary was largely derived from Spalding, 2007 and Potapoff 1989.
The most recent source geological information used to prepare this decription was dated: 2011.
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.
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