Tom Price Research Articles

The association of carbonate alteration of banded iron formation with the Carajás high-grade hematite deposits

The Carajás iron ore deposits in the eastern part of the Amazonas Craton contain approximately 18 000 Mt of hematite ore with > 66%Fe. These deposits are hosted by jaspilitic banded iron formation (BIF) of the Carajás Formation which together with metavolcanic rocks comprise the ~2·8 Ga Grao Para Group of the Itacaiunas Supergroup in the ~1000 km long by 100 km wide, eastwest trending Carajás Synclinorium. The Carajás Formation comprises discontinuous layers and lenses of partly dolomitised jaspilitic BIF (17-43%Fe and 35-61%SiO2), bodies of jaspilitic BIF and lenses of high-grade iron ore, cut by mafic sills and dykes. Dolomitisation of the BIF occurs mainly at the base of the Carajás Formation. With increasing amounts of dolomite, the BIF lamination (microbanding) and other fine primary structures are progressively obliterated resulting in irregular alternating carbonate and iron-oxide mesobands. The high-grade iron ores occur as tabular bodies of soft friable hematite with smaller lenses of hard (compact) massive hematite. The hard hematite lenses typically occur at the contact with the underlying metavolcanic rocks of the Parauapebas Formation surrounded by an aureole of hydrothermal carbonate alteration in both overlying and underlying rocks. The common association of carbonate altered and jaspilitic BIF with the Carajás hematite ore bodies is similar to the Mount Tom Price deposit where carbonate altered BIF has been recognised below massive hematite ore and a jaspilitic halo occurs above the ore body. This indicates that, as at Mount Tom Price, hydrothermal carbonate alteration and associated loss of silica from BIF may be an important step in the formation of the giant Carajás hematite deposits.

From banded iron-formation to iron ore: geochemical and mineralogical constraints from across the Hamersley Province, Western Australia

Several major iron ore deposits occur in deformed regions of the Hamersley Province, Western Australia, where banded iron-formation (BIF) of the Dales Gorge Member has been converted to martite and microplaty hematite. The genesis of these high-grade hematite ores remains controversial, in part because no study has systematically documented variations on the chemistry and mineralogy of stratigraphically equivalent rocks from undeformed regions into the deposits. In this study, we examine the powder colour, chemistry and mineralogy of 177 samples of the Dales Gorge Member and surrounding shales from the type section near Wittenoom and the Mt. Whaleback mine near Newman. Profound chemical and mineralogical changes suggest that after early diagenesis, low-grade metamorphism converted clays in black shales to stilpnomelane and talc. Coincident with or following these changes, reduced metamorphic fluids altered phyllosilicates and K-feldspar in these rocks to clinochlore and muscovite around Mt. Whaleback. These metamorphic fluids did not significantly affect BIF. However, subsequent acidic and oxidizing fluids around Mt. Whaleback converted magnetite to martite and dissolved carbonates and silicates from BIF. In black shales, these fluids also dissolved quartz and converted clinochlore and muscovite to hematite and kaolinite, respectively. Late in the paragenetic sequence, BIF or altered BIF was converted to highly porous high-grade hematite ore by the dissolution of Si, a process not requiring iron addition. Our observations in and around Mt. Whaleback suggest that BIF was oxidized prior to silica removal so we infer that the bulk of this oxidation was related to ore formation. However, regionally, this sequence is probably more complicated because rocks previously described at Mt. Tom Price show a stage involving carbonate replacement of silica prior to oxidation that is not evident at Mt. Whaleback. Also, the oxidation stage could (at least in part) have formed by weathering sometime since the Proterozoic. In any case, (1) no single process can produce all of the altered rocks at Mt. Whaleback, (2) oxidation of magnetite to hematite can occur independently of silica removal or replacement and (3) the main mineralization event postdates metamorphism. A model explaining the differences between these two deposits requires either a local carbonate addition step at Mt. Tom Price, or the complete removal (by oxidation) of previous carbonate–magnetite bearing ore at Mt. Whaleback.

GENESIS OF HIGH-GRADE HEMATITE OREBODIES OF THE HAMERSLEY PROVINCE, WESTERN AUSTRALIA—A DISCUSSION

Sir: We have read with interest the paper of Taylor et al. (2001), which suggests a new genesis for the hematite deposits of the Hamersley province via an intermediate hypogene carbonate-rich phase structurally controlled by high-angle normal faults (e.g., Southern Batter fault at Tom Price). In attempting to apply their genetic model to the Mount Whaleback deposit, they have invoked a large but unspecified rotation (implied 40°–60°) by listric rotation along the late Mount Whaleback fault to re-orientate low-angle faults and folds to a high angle, in keeping with the geometry seen at Tom Price. This appears to have been based on the critical requirement for high-angle faults in their preferred genetic model, rather than the flat lying Central and East Footwall faults that developed at Mount Whaleback. …

GENESIS OF HIGH-GRADE HEMATITE OREBODIES OF THE HAMERSLEY PROVINCE, WESTERN AUSTRALIA—A DISCUSSION

Sir: Taylor et al. (2001) have presented a hypogene-supergene model for the genesis of the premium martite-microplaty hematite ores derived from banded iron formation (BIF), to replace the supergene-metamorphic model (Morris, 1980, 1985, 1998; Harmsworth et al., 1990). The new model is based on hydrothermal features in two of ten Tom Price hematite deposits, recorded previously as carbonate metasomatism of BIF (Ewers and Morris, 1981), and as localized postore metasomatism (Harmsworth et al., 1990; Morris, 1998). From new data, Taylor et al. (2001) proposed that hypogene leaching of free silica with addition of further siderite in BIF, followed by compaction, produced a general hematite ore precursor. During deep weathering episodes, or even within Tertiary weathering profiles, oxidation of magnetite to martite, and siderite to microplaty hematite and ankerite, followed by leaching of residual gangue, enriched this modified BIF to martite-microplaty hematite ore. In contrast, in the supergene-metamorphic model, martite-microplaty hematite ore genesis is linked to metamorphism of precursor ores of the Phanerozoic supergene martite-goethite type. These comprise about 90 percent of the Hamersley BIF-hosted resource, and deposits range to over a billion tonnes (Harmsworth et al., 1990) and >250 m deep, with high phosphorus levels (0.07–0.17% P). Although stratigraphically thinned by leaching (~35%) they maintain primary BIF banding and texture, with gangue minerals altered to phosphorus-bearing goethite pseudomorphs. Their martite-microplaty hematite analogues (< 0.06 % P) are attributed to Proterozoic supergene enrichment of BIF, with burial metamorphism partly converting the goethite pseudomorphs to secondary, largely microplaty, hematite, yet preserving the primary banding. Some 20 known deposits of this type range from small pockets of enrichment to the massive Mount Whaleback (1700 Mt). Later re-exposures of the microplaty hematite deposits produced further stratigraphic thinning (total ~45–50 %), with loss of phosphorus by leaching of remnant goethite. However, significant …

Hydrothermal origin for the 2 billion year old Mount Tom Price giant iron ore deposit, Hamersley Province, Western Australia

Giant iron-ore deposits, such as those in the Hamersley Province of northwestern Australia, may contain more than a billion tonnes of almost pure iron oxides and are the world's major source of iron. It is generally accepted that these deposits result from supergene oxidation of host banded iron formation (BIF), accompanied by leaching of silicate and carbonate minerals. New textural evidence however, shows that formation of iron ore at one of those deposits, Mount Tom Price, involved initial high temperature crystallisation of magnetite-siderite-iron silicate assemblages. This was followed by development of hematite- and ferroan dolomite-bearing assemblages with subsequent oxidation of magnetite, leaching of carbonates and silicates and crystallisation of further hematite. Preliminary fluid inclusion studies indicate both low and high salinity aqueous fluids as well as complex salt-rich inclusions with the range of fluid types most likely reflecting interaction of hydrothermal brines with descending meteoric fluids. Initial hematite crystallisation occurred at about 250 °C and high fluid pressures and continued as temperatures decreased. Although the largely hydrothermal origin for mineralisation at Mount Tom Price is in conflict with previously proposed supergene models, it remains consistent with interpretations that the biosphere contained significant oxygen at the time of mineralisation.

99/02279 Two-bed catalytic system for NO x/SO x removal : Blanco, J. et al. Catal. Today, 1998, 42, (1–2), 85–92

Hydrogen-lean kerogens (atomic H/C<0.4) isolated from the 2.5-billion-year-old (Ga) Mt. McRae Shale, Hamersley Group, at Tom Price, Western Australia, were studied via hydropyrolysis, a continuous-flow technique that degrades organic matter in a stream of high-pressure hydrogen assisted by a dispersed Mo catalyst. The hydropyrolysates yielded predominantly phenanthrene and pyrene, and higher polyaromatic hydrocarbons and alkylated homologues were generated in low relative concentrations. Saturated hydrocarbons were not detected. The molecular and carbon isotopic compositions of the hydropyrolysates are very similar to aromatic hydrocarbons obtained by solvent extraction of the host rocks. Because molecular structures covalently attached to kerogen are unaffected by contamination, this indicates that both the bound and extractable aromatic fractions are syngenetic with the host rocks. Therefore, the results of the hydropyrolysis experiments provide compelling evidence for preserved bitumen of Archean age. The very high proportion of nonalkylated polyaromatic hydrocarbons in the hydropyrolysates is consistent with hydrothermal dehydrogenation of the kerogen, and a marked concentration difference of pyrene in rock extracts and hydropyrolysates might be explained by hydrothermal redistribution of the bitumen. The kerogen and bitumen composition is therefore consistent with models suggesting a hydrothermal origin for the giant iron ore deposits at Mt. Tom Price. Comparison of the Archean samples with hydropyrolysates from immature Mesoproterozoic kerogens from the Roper Group, McArthur Basin, Northern Territory, and with pyrolysis experiments on Proterozoic kerogens in the literature suggests that Precambrian kerogens are frequently highly aromatic and lipid-poor regardless of their degree of thermal preservation.

99/02280 U.S. Department of Energy's high-temperature and high-pressure particulate cleanup for advanced coal-based power systems: Dennis, R. A. Proc., Annu. Meet. Air Waste Manage. Assoc., 1997, 90, MP501, 1–12

Hydrogen-lean kerogens (atomic H/C<0.4) isolated from the 2.5-billion-year-old (Ga) Mt. McRae Shale, Hamersley Group, at Tom Price, Western Australia, were studied via hydropyrolysis, a continuous-flow technique that degrades organic matter in a stream of high-pressure hydrogen assisted by a dispersed Mo catalyst. The hydropyrolysates yielded predominantly phenanthrene and pyrene, and higher polyaromatic hydrocarbons and alkylated homologues were generated in low relative concentrations. Saturated hydrocarbons were not detected. The molecular and carbon isotopic compositions of the hydropyrolysates are very similar to aromatic hydrocarbons obtained by solvent extraction of the host rocks. Because molecular structures covalently attached to kerogen are unaffected by contamination, this indicates that both the bound and extractable aromatic fractions are syngenetic with the host rocks. Therefore, the results of the hydropyrolysis experiments provide compelling evidence for preserved bitumen of Archean age. The very high proportion of nonalkylated polyaromatic hydrocarbons in the hydropyrolysates is consistent with hydrothermal dehydrogenation of the kerogen, and a marked concentration difference of pyrene in rock extracts and hydropyrolysates might be explained by hydrothermal redistribution of the bitumen. The kerogen and bitumen composition is therefore consistent with models suggesting a hydrothermal origin for the giant iron ore deposits at Mt. Tom Price. Comparison of the Archean samples with hydropyrolysates from immature Mesoproterozoic kerogens from the Roper Group, McArthur Basin, Northern Territory, and with pyrolysis experiments on Proterozoic kerogens in the literature suggests that Precambrian kerogens are frequently highly aromatic and lipid-poor regardless of their degree of thermal preservation.

99/02282 Application of gas chromatography-isotope ratio mass spectrometry to source coal-derived polycyclic aromatic hydrocarbons in the environment: McRae, C. et al. Prepr. Ext. Abstr. ACS Natl. Meet., Am. Chem. Soc., Div. Environ. Chem., 1998, 38, (2), 139–143

Hydrogen-lean kerogens (atomic H/C<0.4) isolated from the 2.5-billion-year-old (Ga) Mt. McRae Shale, Hamersley Group, at Tom Price, Western Australia, were studied via hydropyrolysis, a continuous-flow technique that degrades organic matter in a stream of high-pressure hydrogen assisted by a dispersed Mo catalyst. The hydropyrolysates yielded predominantly phenanthrene and pyrene, and higher polyaromatic hydrocarbons and alkylated homologues were generated in low relative concentrations. Saturated hydrocarbons were not detected. The molecular and carbon isotopic compositions of the hydropyrolysates are very similar to aromatic hydrocarbons obtained by solvent extraction of the host rocks. Because molecular structures covalently attached to kerogen are unaffected by contamination, this indicates that both the bound and extractable aromatic fractions are syngenetic with the host rocks. Therefore, the results of the hydropyrolysis experiments provide compelling evidence for preserved bitumen of Archean age. The very high proportion of nonalkylated polyaromatic hydrocarbons in the hydropyrolysates is consistent with hydrothermal dehydrogenation of the kerogen, and a marked concentration difference of pyrene in rock extracts and hydropyrolysates might be explained by hydrothermal redistribution of the bitumen. The kerogen and bitumen composition is therefore consistent with models suggesting a hydrothermal origin for the giant iron ore deposits at Mt. Tom Price. Comparison of the Archean samples with hydropyrolysates from immature Mesoproterozoic kerogens from the Roper Group, McArthur Basin, Northern Territory, and with pyrolysis experiments on Proterozoic kerogens in the literature suggests that Precambrian kerogens are frequently highly aromatic and lipid-poor regardless of their degree of thermal preservation.

99/02285 Arrangement of gasifier spout tube for delivering feedstock and gasifying/fluidizing medium: Dennison, G. et al. Brit. UK Pat. Appl. GB 2,316,089 (Cl. C10J3/56), 18 Feb 1998, Appl. 96/16,401, 3 Aug 1996, 23 pp.

Hydrogen-lean kerogens (atomic H/C<0.4) isolated from the 2.5-billion-year-old (Ga) Mt. McRae Shale, Hamersley Group, at Tom Price, Western Australia, were studied via hydropyrolysis, a continuous-flow technique that degrades organic matter in a stream of high-pressure hydrogen assisted by a dispersed Mo catalyst. The hydropyrolysates yielded predominantly phenanthrene and pyrene, and higher polyaromatic hydrocarbons and alkylated homologues were generated in low relative concentrations. Saturated hydrocarbons were not detected. The molecular and carbon isotopic compositions of the hydropyrolysates are very similar to aromatic hydrocarbons obtained by solvent extraction of the host rocks. Because molecular structures covalently attached to kerogen are unaffected by contamination, this indicates that both the bound and extractable aromatic fractions are syngenetic with the host rocks. Therefore, the results of the hydropyrolysis experiments provide compelling evidence for preserved bitumen of Archean age. The very high proportion of nonalkylated polyaromatic hydrocarbons in the hydropyrolysates is consistent with hydrothermal dehydrogenation of the kerogen, and a marked concentration difference of pyrene in rock extracts and hydropyrolysates might be explained by hydrothermal redistribution of the bitumen. The kerogen and bitumen composition is therefore consistent with models suggesting a hydrothermal origin for the giant iron ore deposits at Mt. Tom Price. Comparison of the Archean samples with hydropyrolysates from immature Mesoproterozoic kerogens from the Roper Group, McArthur Basin, Northern Territory, and with pyrolysis experiments on Proterozoic kerogens in the literature suggests that Precambrian kerogens are frequently highly aromatic and lipid-poor regardless of their degree of thermal preservation.

New Pipelines in Australia

In 1895 the government of Western Australia considered a project to bring sweet water from a reservoir to be constructed in the Darling Range near Perth. The water was to go to Kalgoorlie, then a rapidly growing goldmining center with very limited and inferior local water supplies. Construction of a 966-kilometer-long pipeline with eight pumping stations was required. Skeptics doubted the technical and economic feasibility of the project, but it was constructed and came on stream in 1903. It has since supplied Kalgoorlie and other mining centers and small agricultural settlements. Indeed, the pipeline has been crucial in the development of a large segment of southwestern Australia. Now construction of another pipeline of about equal length is proposed for northwestern Australia. But it is to transport natural gas that has been discovered but not extracted from the Carnarvon Basin in the Timor Sea, an area that is within 161 kilometers of the northwesternmost land area of Australia. The pipeline terminus will be Port Headland, the nearest city and port, and gas will be distributed to a large mining area that includes Tom Price and Paraburdoo, iron ore-mining centers already long in operation, and to other potential mineral-resource areas located to the south and the east. It will terminate at Kalgoorlie. The existing mines now rely for energy on fuel oil or diesel oil that is trucked in over unsatisfactory roads that are sometimes flooded or covered by sand. The cost is great. The proposed pipeline will also provide energy for distilling some of the poor-quality local water into better-quality substances. Furthermore, a recently perfected process to use natural gas to transform iron ore into steel may be relevant. The pipeline may prove to be as instrumental in the development of the northern interior of Western Australia as was the water pipeline in the southwestern part of the state. Despite doubts, construction of some sections of the pipeline is under way, including eight intermediary pumping stations and residential areas for the permanent workforce.

Palaeomagnetism and magnetic anisotropy of Proterozoic banded-iron formations and iron ores of the Hamersley Basin, Western Australia

Rock magnetic properties and palaeomagnetism of weakly metamorphosed banded-iron formations (BIFs) of the Palaeoproterozoic Hamersley Group, Western Australia, and Proterozoic BIF-derived iron ores have been investigated. The BIF units sampled here are slightly younger than 2500 Ma. At Paraburdoo, Mount Tom Price and Mount Newman iron ore formation was completed before 1850 Ma. Sampling was mainly from the Mount Tom Price and Paraburdoo mining areas and for the first time a palaeomagnetic fold test on fresh (unweathered and unaltered) BIF samples has allowed the nature of the remanence of the BIFs to be defined. The remanence of the BIFs is carried by late diagenetic/low-grade metamorphic magnetite after primary haematite. This remanence is pre-folding and is unlikely to be greatly affected by the high anisotropy because the palaeofield inclination was demonstrably low. Determination of palaeofield directions from measured remanence directions is complicated by self-demagnetization effects in strongly magnetic, highly anisotropic BIF specimens. We present a method for correcting measured directions for the effects of self-demagnetization and anisotropy. For typical BIFs, the effect of magnetic anisotropy on measured remanence inclinations and inferred palaeolatitudes is minor for low palaeolatitudes, but can lead to large errors in calculated palaeopoles for intermediate to moderately steep palaeolatitudes. Anisotropy also causes cones of confidence to be underestimated, due to compression of the range of inclinations. In principle, deflection of post-folding remanence towards the bedding plane by high magnetic anisotropy can produce an apparent syn-folding signature, with best agreement between directions from different fold limbs after partial unfolding. Thus high anisotropy cannot only bias estimated palaeofield directions and cause underestimation of errors, but can also mislead interpretation of the time of remanence acquisition. The anisotropy of anhysteretic remanent magnetization (ARM) probably yields an upper limit to the anisotropy of the chemical remanent magnetization (CRM) carried by the BIFs. Therefore, from the anisotropy of ARM, a maximum inclination deflection of 9° is suggested for the sampled BIFs. This corresponds to less than 5° change of palaeolatitude. The palaeomagnetic pole position calculated for BIFs at Paraburdoo is 40.9°S, 225.0°E (dp=2.9°, dm=5.8°) after tilt correction, but without correction for anisotropy. Other pole positions reported include that from flat-lying BIFs from Wittenoom at 36.4°S, 218.9°E (dp=4.6°, dm=9.1°), from Mount Tom Price iron ore at 37.4°S, 220.3°E (dp=5.7°, dm=11.3°) and from Paraburdoo ore at 36.4°S, 209.9°E (dp=4.7°, dm=8.8°). The poles from the BIFs, the Paraburdoo ore and the part of the Tom Price deposit that was sampled in this study are indistinguishable from each other and from the Mount Jope Volcanics overprint pole. The magnetization of the BIFs was probably acquired during burial metamorphism of the Hamersley Group, soon before the main folding and uplift event in the southern part of the Hamersley Province. This tectonic event exposed magnetite-rich BIFs to near-surface oxidizing conditions, producing extensive martite-goethite orebodies and also appears to have produced the syn-folding overprint magnetization recorded by the Mount Jope Volcanics of the underlying Fortescue Group. Ages of magnetization are tentatively interpreted as ∼ 2200±100 Ma for the BIFs, ∼ 2000±100 Ma for the supergene enrichment of BIF to martite-goethite ore, recorded by the Parabudoo and Mount Tom Price orebodies, and ∼ 1950±100 Ma for the metamorphic martite-microplaty haematite ore, recorded as an overprint by the Tom Price orebody and as the only surviving magnetization of the Mount Newman orebody.

Hole to hole explosive interaction in production blasting at Mount Tom price : Bulow, B M; McKenzie, C K Proc 3rd International Symposium on Rock Fragmentation by Blasting, Brisbane, 26–31 August 1990P325–333. Publ Parkville: AusIMM, 1990

Hole to hole explosive interaction in production blasting at Mount Tom price : Bulow, B M; McKenzie, C K Proc 3rd International Symposium on Rock Fragmentation by Blasting, Brisbane, 26–31 August 1990P325–333. Publ Parkville: AusIMM, 1990

Current drilling and blasting practice at Mount Tom Price Mine, Western Australia : Hancock, A W J; Lilly, P A Proc International Conference of the South African Institute of Mining and Metallurgy: Planning and Operation of Open-pit and Strip Mines, Pretoria, 9–13 April 1984, 213–223. Publ Johannesburgh: South African Institute of Mining and Metallurgy, 1986

Current drilling and blasting practice at Mount Tom Price Mine, Western Australia : Hancock, A W J; Lilly, P A Proc International Conference of the South African Institute of Mining and Metallurgy: Planning and Operation of Open-pit and Strip Mines, Pretoria, 9–13 April 1984, 213–223. Publ Johannesburgh: South African Institute of Mining and Metallurgy, 1986

The vector competence of Australian Culex annulirostris with Murray Valley encephalitis and Kunjin viruses.

Australian populations of Culex annulirostris Skuse from 10 localities, Brisbane, Townsville, Cairns, Charleville, Kowanyama (Queensland), Darwin (Northern Territory), Mildura (Victoria) and Port Hedland, Karratha and Mt. Tom Price (Western Australia) showed considerable heterogeneity in response to oral infection with low passage level Murray Valley encephalitis (MVE) and Kunjin (KUN) viruses. However, there was no consistent pattern of either high or low vector efficiency for populations collected from different regions. Overall, Cx annulirostris was a more competent vector of MVE virus than KUN virus, both in oral susceptibility (suckling mouse intracerebral ID50 of 10(1.7)-10(3.9) compared to 10(2.7)-10(4.8)/mosquito, respectively) and in ability to transmit virus to chicks after 10 d extrinsic incubation (50-89% compared to 0-55%). High or low susceptibility with one virus did not correlate with susceptibility for the other. Although these date were probably subject to some seasonal variation, they generally support the view that Cx annulirostris is the principal vector of MVE in Australia. Poor to moderate susceptibility with KUN suggests that (1) it is only a minor vector in some localities, (2) vertebrate hosts have high viraemias or (3) the strain used may have been atypical.

Studies of the Dales Gorge Member of the Brockman Iron Formation, Western Australia

A drill core consisting of unaltered banded iron-formation from Paraburdoo, Western Australia, representing the entire Dales Gorge Member of the Brockman Iron Formation, has been analyzed in short units of about 300 mm or in groups of units of up to 1 m. These analyses have been combined to give average compositions for each of the 33 macrobands of the member. The average compositions for the 17 oxide facies BIF macrobands and the 16 intercalated chert-carbonate and silicate facies S macrobands are, respectively, 43.15 and45.78 percent SiO 2 , 0.09 and 2.04 percent Al 2 O 3 , 46.37 and 27.77 percent Fe 2 O 3 (total iron), 2.69 and 5.21 percent MgO, 1.65 and 2.85 percent CaO, 0.04 and 0.02 percent Na 2 O, 0.01 and 0.09 percent TiO 2 , 0.21 and 0.16 percent P 2 O 5 , 0.05 and 0.02 percent MnO, and 0.03 and 0.32 percent S. The analyses are similar to those reported by Trendall and Pepper (1977) for a part of the Dales Gorge Member at Wittenoom, 130 km away. These data, together with documented evidence of lateral continuity of both major and minor banding across the Hamersley Iron Province, support an assumption that the primary deposits were chemically similar throughout the area. Mineralogical variations between sites indicate low but variable metamorphism in the area, and magnetite-hematite ratios and textural relations suggest increasing grade from Paraburdoo to Wittenoom to Tom Price.A short length of drill core from Tom Price, representing two complete macrobands and parts of two others, was also analyzed, and the results were found to vary significantly from the Paraburdoo and Wittenoom data. These differences are attributed to metasomatism of the rocks at Tom Price.Primary precipitation of iron in BIF macrobands was caused by oxidation and was dominated by gels containing iron(III) hydroxyoxides and silica in varying proportions, depending both on seasonal conditions and on supply. These variations were responsible for the wide range in composition and in thickness of banding, from tens of micrometers (submicrobanding), to millimeters (microbanding), to tens of millimeters (mesobanding). Preservation of micro- and submicrobanding within specific mesobands is due to very early consolidation and accentuation of primary depositional layering during diagenesis. In other mesobands, crystallization was evidently delayed and, under deeper burial conditions, tended to destroy primary lamination. In S macrobands, iron was precipitated as siderite and silicates. Mineralogical and chemical data show that the apparently sharp lithological boundaries between BIF and S macrobands are in fact gradational. Such contacts are attributed to a more or less continuous precipitation of silica and iron, interrupted periodically and changed in character by increase in pH and/or f (sub CO 2 ) . These changes were initiated by additions of volcanic ash. S macrobands are characterized by increases in the overall content of CO 2 , Ca, Mg, Mn, Al, Ti, K, and Zr.Podding, and other localized distortion, of mesobands is attributed mainly to lateral flow of silica during compression. It appears to have been inhibited in mesobands where early crystallization of components, particularly iron oxides, enhanced the mechanical stability of the dehydrating gel.The logistics of supplying sufficient iron to the Brockman Iron Formation, together with the absence of terrigeneous material in the deposits, suggests open access of the depositional area to a large and constantly replenished reservoir of dissolved iron. A shelf model is preferred.

A textural and mineralogical study of the relationship of iron ore to banded iron-formation in the Hamersley iron province of Western Australia

Microscope studies of a wide range of ores and fresh, oxidized, or partly iron-enriched, banded iron-formation (BIF) have shown a consistent sequence of alteration of the primary constituents, chert, magnetite with or without hematite, carbonates, and silicates, leading to the formation of martite-(hematite)-goethite ores which form the bulk of the reserves of the Hamersley Iron Province. Primary hematite survives with little change; magnetite oxidizes to hematite (martite) or in part to lacunar phases between magnetite and maghemite (kenomagnetite), which in turn commonly is altered by hydration to goethite. Subsequent leaching of this goethite in preference to martite leads to a variety of skeletal textures which may help identify the original magnetite, despite destruction of martite lamellae by recrystallization. Chert, carbonates, and silicates are either replaced by goethite or leached from the system, resulting in thinning of the orebodies with respect to their parent banded iron-formations. Preservation of macroscopic features, such as mesobanding, and microscopic features, such as pseudomorphs, is compelling evidence of supergene enrichment which, together with residual upgrading by leaching of these iron-formations, produces ores which typically assay 62 percent Fe, ignition loss of 4 to 6 percent, and >0.07 percent P. With increasing maturity, part of the goethite has converted to fine-grained hematite in some of these martite-(hematite)-goethite ores. Though overall the secondary hematite is quantitatively unimportant, some deposits may be significantly upgraded by this process, and it is this variability that is implied by the use of brackets in the classification.A second ore type, characteristic of the Tom Price and Whaleback mines, consists essentially of residual primary components, martite and hematite, with abundant secondary hematite, most of it platy but some anhedral. These martite-hematite ores appear to have formed by a low-temperature process in which some of the goethite or its precursor, in ores of the martite-(hematite)-goethite type, has converted to platy hematite in contrast to the fine-grained and often cryptocrystalline material of the normal ores. This partial transformation has resulted in increased permeability of the deposits which in turn has allowed leaching of the remnant goethite. The Paraburdoo 4E mine represents an arrested stage of development in which a large proportion of this unconverted goethite is still present, whereas the Tom Price and Whaleback deposits represent the most mature ores in the province. In these, leaching has removed the bulk of the goethite, leading to typical assay values of >64 percent Fe, 1 percent loss on ignition, and <0.05 percent P.The supergene ores of the province can be classified in terms of a maturity scale based on the type and amount of secondary hematite replacing goethite. Thus martite-goethite ores without significant secondary hematite are considered to be the least mature. Examples of these have been found in a limited survey of the Marra Mamba Iron Formation ores. The Brockman Iron Formation deposits at Koodaideri, the Brockman syncline, and Metawandy provide examples of more mature ores with increased secondary hematite and are classified as martite-(hematite)-goethite ores. Ancient deposits (early to middle Proterozoic) with abundant secondary platy hematite but with significant residual goethite are classified as the Paraburdoo type. Substantial leaching of this goethite leads to the most mature ores of the province, the martite-hematite deposits of the Tom Price-Whaleback type.

Nuclear activation logging for aluminium in iron ores and coal

Aluminium in shale bands associated with iron ores at Mt. Tom Price, Western Australia, and in sandstone and mudstone formations associated with coal seams at Blair Athol, Queensland, has been logged with probes equipped with 252Cf and PuBe sources and stratigraphy established precisely by the neutron activation technique. Alumina in the iron ore has also been quantitatively assayed. Aluminium was excited with a 252Cf neutron source, and the intensity of the activation radiation from successive contiguous intervals within the hole was regressed against alumina concentrations obtained from assays of corresponding core sections. The results were fitted by a simple linear expression yielding 95% confidence intervals for prediction of grade for individual 122 cm logging intervals of ± 1.8% Al 2O 3, and for the mean grade of the whole drillhole section of ± 0.5% Al 2O 3. These results pertain to the concentration range 1–18.8% A1 2O 3. Comparison of results between neutron activation and quantitative natural gammaray logging shows that the confidence intervals for the former are narrower by a factor greater than 3.

Genetic implications of shales in the brockman iron formation from Mount Tom Price and Wittenoom Gorge, Western Australia

Abstract Mineralogically complex shale horizons interbedded with, and underlying, the Brockman Iron Formation at Mt Tom Price, Western Australia, are compared with equivalent sections at Wittenoom and Yampire Gorge. Despite the alteration by fairly intense post‐depositional folding, faulting and weathering, very limited evidence favouring a primary pyroclastic source is indicated. By acting as effective seepage horizons for percolating meteoric waters, the upturned shale bands, which are part of the truncated synclinal folds in the Brockman Formation, have actively promoted supergene enrichment of the iron ore during lateritization and have themselves undergone considerable mineralogical reconstitution. By means of semi‐quantitative mineralogical data from samples in a reconstructed weathering profile, it is postulated that the formation at Mount Tom Price was subjected to two periods of lateritization separated by a period of diagenesis. Of these cycles the first was probably the most intense and hence r...

Palaeomagnetism of Australian Hematite Ore Bodies--II Western Australia

Summary Iron ore deposits of the Lake Superior type within the Archaean and Proterozoic banded iron formations of Western Australia show consistent and stable directions of remanent magnetization. The palaeomagnetic poles of the ores do not correlate with poles of Post-Cambrian Australian rocks, which suggests a Pre-Cambrian age for the ore formation. Magnetic anisotropies of the ores are low and the distribution of the principal susceptibility axes tends to reflect the magnetic fabric of the host rocks. In a previous publication (Chamalaun & Porath 1967) we reported the results of a palaeomagnetic study on the hematite ore bodies of the Middleback Ranges in South Australia. It was found that these were consistently and stably magnetized with a Pre-Cambrian direction. We therefore extended the study to the Western Australian ore bodies, the results of which are reported here. A large number of high-grade hematite ore bodies are known to occur in the Archaean and Proterozoic banded iron formations of Western Australia, but in order to obtain fresh subsurface samples we have sampled only those that are actively mined. The localities of the ore bodies sampled are shown in Fig. 1. The Mt Goldsworthy and Koolyanobbing deposits occur in Archaean banded iron formations, whilst the host rocks for the Mt Tom Price and Mt Newman ore bodies are Proterozoic iron formations. 2. Results (a) Mt Goldsworthy. The Mt Goldsworthy deposit is located at the northern extremity of the Western Australian Archaean shield. A folded and faulted banded iron formation, which consists of alternating layers of silica and hematite, forms the host rock of a number of high-grade hematite ore bodies of varying origins. Brandt (1964, 1966) makes a distinction between lode ore and crust ore deposits. Lode ores are deep lenses of massive finely crystalline hematite (average grain size about 20p). The major deposit at Mt Goldsworthy consists of lode ore and is controlled by a steep angled transcurrent fault. Pebbles of massive hematite ore occur in the basal Proterozoic conglomerate indicating that the ore formed in Pre-Proterozoic times (Brandt 1964). Brandt (1966) favours a hypogene origin of the lode ore along the lines suggested by Dorr (1965) for the Brazilian ores. Crust ores form shallow cappings of hematite and goethite on the upturned