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There are two major types of iron ore deposits in the Pilbara Province of Western Australia—banded iron formation (BIF)-hosted iron ore deposits and bedded iron deposits (BID), respectively, named martite–goethite and martite–microplaty hematite and the channel iron deposits (CID). These deposits consist mainly of iron oxides such as magnetite, hematite and goethite; the latter have been subdivided into vitreous and ochreous goethite. Combining spectral scanning of diamond drill core, drill chips and pulps collected from these deposits provides a rapid and relatively inexpensive means of assessing the potential mineral makeup within a deposit to make informed qualitative decisions. Additionally, the full width half maximum (FWHM) of the 900 nm 6A1→4T1 crystal field absorption feature within the goethite-dominated region is shown to be related to the type of goethite, namely ochreous and vitreous. The assessment capabilities of the combined metrics are presented in a visual format named as the iron boomerang because of its distinctive manifold. This provides the identification of at least two spectral endmembers comprised of hematite and vitreous goethite, the identification of samples that are moving from a pure hematite to mixed hematite/goethite and lastly into a goethite-dominant-driven regime. [ABSTRACT FROM AUTHOR]

Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image analysis is a proven method for mapping mineral and geochemical zonation associated with a variety of ore types, including ore-genic Au, porphyry Cu-(Mo), porphyry-skarn, Pb-Zn-Au, and Mn systems. Only recently has this technique been applied, in a general sense, to mineral alteration mapping and exploration for Fe ore deposits hosted by banded iron formations (BIFs). For this reason, the Archean Weld Range greenstone belt that hosts the Beebyn and Madoonga Fe ore deposits has been chosen as a case study area to test the effectiveness of ASTER imaging techniques for the identification of Fe orebodies. Banded iron formations in the Weld Range district crop out as a series of parallel, 10- to 500-m-wide, <150-m-high, ENE-trending ridges that continue along strike for up to 70 km. Individual ridges of BIFs are surrounded by mafic igneous rocks, whereas felsic volcanic and volcaniclastic rocks and granitoid intrusions are exposed as rounded low-lying mounds in the northern and eastern areas of the district. All outcrop is at least moderately weathered. Thick layers of unconsolidated alluvial and colluvial sediments dominate low-lying areas. The Beebyn and Madoonga high-grade (>55 wt % Fe) iron ore deposits host Archean hypogene magnetite and specular hematite orebodies that are locally replaced by more recently formed, supergene goethite-hematite ore within several hundred meters of the present erosion surface. A common feature of all ore types hosted by BIFs is a high Fe content relative to SiO2. Consequently, all types of Fe ore in the Weld Range district are best identified by the ferric iron to silica index and the opaques to silica index, for the reason that these ASTER image products detect surfaces that are rich in (opaque) Fe oxide minerals and have a low silica abundance. Gabbro, dolerite, and basalt country rocks located within 20 m of high-grade Fe ore zones in BIFs are altered to hypogene Fe-rich chlorite and, more rarely, are altered by Fe-rich talc. These hypogene alteration zones are best detected by the ferrous iron content in MgOH minerals and carbonates and the FeOH group abundance products, which identify hypogene Fe chlorite and Fe talc. This study demonstrates that integrated remote spectral sensing techniques (ASTER, airborne hyperspectral, and radiometric) used in conjunction with geophysical surveys (aeromagnetic and gravity) are useful for district-scale exploration for Fe orebodies hosted by BIFs. The spectral sensing techniques are a rapid, cost-effective, and efficient means for generating and ranking exploration targets that are located in areas with restricted physical access. [ABSTRACT FROM AUTHOR]

This study demonstrates how mineralogy generated from spectroscopic visible, near, and shortwave infrared reflectance data, collected using rapid drill core logging systems, can be used to build one-, two- and three-dimensional models of the architecture of ore systems, with applications toward exploration and mining. In particular, this study examines both spectroscopic and traditional mining data (laboratory geochemistry and field geologist logging) from 180 drill holes through the Rocklea channel iron deposit in the Hamersley region of Western Australia. Valuable infrared reflectance spectroscopy-based mineralogy includes: the types and abundances of iron (oxyhydr-)oxides (hematite, vitreous goethite, and ochreous goethite); clays (well- and poorly ordered kaolin, Al and Fe smectite); and carbonates (calcite and dolomite). Algorithms to determine the abundance and composition of these minerals from infrared reflectance spectra were validated in an associated study by Haest et al. (2012) and were found to be accurate (e.g., root mean square error (RMSE) for Fe (oxyhydr-)oxide abundance prediction of 9.1 wt % Fe). Petrographic analysis and validated infrared reflectance spectroscopy-based mineralogy constrained the stratigraphy in the paleochannel and the Para genetic history of each horizon. The Rocklea channel iron deposit developed over weathered basalt and met sedimentary rocks, with an internal channel stratigraphy dominated from bottom to top by the following: (1) well-ordered (in situ) kaolinite and a partially deuaturated channel iron deposit, (2) poorly ordered (transported) kaolinite, (3) ochreous goethite with scarce ooidal textures, no clays, and late-stage vitreous goethite/silica replacement, (4) mostly poorly ordered kaolinite, and (5) calcrete with associated Fe smectite. The mineral Para genesis of the Rocklea deposit was compared against current models for channel iron deposit formation. A key finding is the relationship between parent rock composition, superimposed regolith cover, and channel iron deposit ore quality, which are linked through ground-water interactions and the physic-chemistries of both the parent rock and the deposit. This has implications for both exploration and ore deposit characterization: (1) ore-grade channel iron deposits can develop several kilometers downstream (50 km, in this case) from the proposed source rock areas above mafic volcanic and met sediments, (2) vitreous goethite, calcrete, Al and Fe smectite cover the Rocklea deposit and are proposed as potential vectors to channel iron deposit mineralization at depth, (3) improved mineralogy from hyperspeetral data in terms of iron (oxyhydr-) oxide and clay content/composition can improve iron ore resource delineation, iron ore processing (separation of vitreous and ochreous goethite), and pit design (differentiating "swelling" smectite (requiring pit walls with lower slopes) from kaolin or white mica). [ABSTRACT FROM AUTHOR]

Remotely sensed hyperspectral datasets were integrated with petrographic data to map the distribution of sedimentary rocks in order to infer grain size variations within the siliciclastic, Paleoproterozoic Bresnahan Group in Western Australia. Finer sandstones have greater compositional variation compared to coarser sandstones, with higher modal proportions of mudstone intraclasts, K-feldspar, and muscovite laths, and lower modal quartz. Partial Least Squares modelling indicates a link between visible to shortwave infrared spectral data collected on samples and their average grain size. Specific electronic absorptions are important for defining this relationship, particularly in the blue-green visible spectra, wavelengths related to water or hydroxyl bonds, along with certain wavelengths in the shortwave infrared (SWIR) spectra. The results from field samples were compared to airborne hyperspectral datasets which showed broad scale regional variations in composition could be discerned from processed white mica abundance maps and images that use spectral bands 2350 nm and 2200 nm. The remotely sensed compositional variations are relatable to changes in sandstone grain size. Diagenetic alteration and surface weathering may influence the absorption spectra, although the effect of the latter can be reduced by using processed white mica abundance maps. Overall, the results show that airborne hyperspectral datasets, particularly the SWIR part of the spectra, can be useful to remotely map spatial compositional variations associated with sandstone grain size. This shows the method can be used to remotely map siliciclastic successions in other sedimentary basins by aiding recognition of grain size trends and significant stratal surfaces associated with changes in composition. However, the important wavelengths may differ due to other controls on sandstone composition such as uplift history of the source region, changes in sediment dispersal, and transport mechanisms. • Sample spectral data detect compositional change linked to sandstone grain size. • Compositional change with grain size is detected in airborne spectral data. • Study indicates grain size of siliciclastic successions can be remotely inferred. [ABSTRACT FROM AUTHOR]

Abstract: Determining the spatial relationships between various geological features and mineralisation is not only important for understanding the ore genesis of mineral deposits, but can also help to guide mineral exploration by providing predictive mineral maps. In this GIS-based study, we quantify the spatial relationships between gold mineralisation and plausible controlling factors in the central part of the St Ives area, Western Australia. We weigh plausible control factors including rock types, lithological boundaries and faults, using gold occurrences in drill-cores, and then apply the weights to the geological data to generate a predictive map for the entire St Ives area. The three major findings of this study are: (1) all major gold deposits are controlled by faults, and small-scale fault systems have a stronger correlation with gold mineralisation than large faults; (2) felsic to intermediate intrusive rocks show strong correlations with gold mineralisation, whereas metamorphic mafic rocks (greenstones) possibly acted as part of the broad regional environment for the mineral province rather than as a factor controlling the exact locations of the deposits; and (3) our predictive mapping indicates that the southeast part of the St Ives goldfield has a high potential for discovering new gold mineralisation. [Copyright &y& Elsevier]

An understanding of the nature of the facies heterogeneity is crucial for successful exploration and development of shale reservoirs. However, shale is a very fine-grained sedimentary rock and it is challenging to understand its heterogeneity through conventional techniques. This paper addresses this challenge for Ordovician Goldwyer Formation (Goldwyer-III shale) through a unique approach by integrating core data with high-resolution image logs (SCMI); petrographic information; Fourier transform infrared (FTIR); and hyperspectral drill core reflectance spectra acquired using a HyLogger3. The petrographic and FTIR data validates the usage of HyLogger3 as a tool to examine high-resolution vertical variations in the shale mineralogy. The results indicate that the Goldwyer-III shale is highly heterogeneous in terms of sedimentary features, organic richness and mineral composition. The studied shale is divided into four facies based on colour, sedimentary features, mineral composition and lithology. The facies include thinly laminated siliceous shale (TLSh), concretionary-banded calcareous shale (CSh), massive black shale (MBSh) and heterolithic shale (HSh). The total organic carbon varies from 0.35 to 4.5 wt% due to variation in facies as a result of fluctuation in oxic-anoxic conditions. The TLSh, MBSh and HSh facies have a higher TOC value (up to 4.5 wt %), T max (up to 450 °C), hydrogen index (up to 250 mgHC/g) and brittleness index (>0.4) comparatively. Whereas, the CSh facies has least TOC, Tmax, hydrogen index and brittleness index. Continuous high-resolution hyperspectral core log data, combined with petrography and conventional core logging, provides a much better understanding of heterogeneity in Goldwyer-III shale. This study offers a new workflow for rapid, continuous and accurate recognition of optimum facies for hydraulic fracturing. This approach can improve economic decisions when developing shale gas reservoirs. Based on TOC and mineralogical derived brittleness index cut-offs values, the high-quality brittle zones are recognised in TLSh and HSh facies deposited in medial (proximal to distal) depositional setting. • The marine shale is highly heterogeneous even at μm scale. • The integration of high resolution data provided a unique workflow for facies classification scheme in shale. • A continuous vertical facies heterogeneity is obtained. • HyLogger3 data with petrography and FTIR is validated for shale. • The influence of depositional setting on shale reservoir potential is discussed. [ABSTRACT FROM AUTHOR]

• Genetic processes are examined for supergene and hypogene iron ores at Mt Richardson. • Iron ores form by reactivation of hypogene-altered shear zones. • Oxidized supergene fluids removed primary and hypogene quartz from BIF. • Resulting in the formation of high-grade goethite–hematite ores. The Mt Richardson deposit contains high-grade (>57 wt% Fe total) iron ore zones hosted by several banded iron-formations (BIFs) in the c. 3504 Ma Illaara greenstone belt. The BIFs and intervening mafic igneous rocks are exposed along a 700 m-wide, 140 m-high, NNW-trending ridge that demarks the eastern limb of a greenstone belt-scale tight, upright, moderately SSE-plunging syncline. Local expressions of this fold generation include parasitic metre-scale fold hinges, an axial planar fabric, and intersection lineation in BIFs. Margins of tightly folded BIFs are commonly sheared and altered by hypogene magnetite and quartz. Although primary bands are strongly overprinted by disseminated magnetite, the concomitant growth of quartz translates to a negligible increase in the iron content of hypogene-altered BIFs. Reactivation of magnetite–quartz-altered shear zones and interaction with more oxidized fluids led to the replacement of magnetite by martite, precipitation of crystalline hematite, and recrystallization of quartz. Mafic igneous rocks are altered to fine-grained chlorite via replacement of igneous amphibole, biotite, and plagioclase within 30 m of sheared and hypogene-altered BIFs. Hypogene-altered mafic igneous rocks are enriched in Fe 2 O 3total and W, and depleted in MnO, K 2 O, Ca, Na 2 O, and Sr compared to least altered rocks. Subsequent reactivation of shear zones and the circulation of supergene fluids led to dissolution and replacement of primary and hypogene quartz by goethite, and further oxidation of magnetite to martite. Resultant goethite–hematite ore zones are silica-poor, iron-rich, porous, and friable. Alteration indices for supergene-modified, hypogene ore zones in BIFs include hypogene magnetite and hematite in BIFs, chlorite-replacement of primary minerals in mafic igneous rocks, intense supergene goethite–hematite–kaolinite alteration, thinning of primary quartz bands in BIFs, and the presence of broad high-strain zones. Prime exploration targets in the Illaara greenstone belt are areas where these alteration indices coincide with fold-thickened BIFs. Given the friable nature of high-grade iron ore zones, mineralized occurrences are often at least partly hidden and require remote detection methods, followed by drilling, for testing. Mt Richardson differs from most iron deposits in the Yilgarn Craton by the absence of early hypogene carbonate mineral replacement of primary quartz bands in BIFs. Instead, Mt Richardson demonstrates the greater role of supergene fluids that exploit existing structures and permeability via reactivation of hypogene magnetite- and hematite-rich shear zones. In this regard, the Mt Richardson deposit has greater affinity with iron deposits in the Pilbara Craton. [ABSTRACT FROM AUTHOR]

Abstract: Quantitative iron (oxyhydr-)oxide (Fe-Ox), AlOH-clay and carbonate abundance maps of the Rocklea Dome in Western Australia have been derived from hyperspectral visible-near to shortwave infrared (VNIR–SWIR) airborne data that were compensated for the influence of vegetation cover. The quantitative mineral maps were validated against field data, including ~5500 VNIR–SWIR spectra and ~300 portable X-ray fluorescence measurements. The error on these airborne mineral abundance estimates averages 13.4wt.% Fe for the Fe-Ox abundance, 4.0wt.% Al2O3 for the AlOH-clay abundance and 0.025 for the 2320D parameter used to quantify the carbonate abundance. The unmixed quantitative mineral abundance maps improve geological mapping, including characterisation and exploration for channel iron deposits (CID). In particular, some areas with outcropping CID, which appear subeconomic from the airborne Fe-Ox abundance map without vegetation removal, show as potentially economic CID resources when the influence of vegetation cover is unmixed from the airborne hyperspectral data. These results show that seamless maps of mineral contents can be achieved using data collected from both proximal (drill core and field) and remote (airborne and satellite) hyperspectral sensing systems. [Copyright &y& Elsevier]