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Minerals
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
Botryoidal - consisting of spheroidal aggregations, somewhat resembling a bunch of grapes; e.g. chalcedony. The curved surfaces are boundaries of the ends of many crystal fibres arranged in radiating clusters.
Geometallurgical characterisation of Mn ores
Published in Applied Earth Science, 2021
Michael John Peterson, James Robert Manuel, Sarath Hapugoda
Particles composed entirely of Mn oxides were sub-divided into ‘hard’ and ‘moderately hard to friable’ sub-types based upon estimated particle microporosity and texture, mineral microporosity and texture and mineral association (e.g. Figure 1(a–d)). Mineral microporosity was qualitatively estimated based upon the mineral’s optical properties (colour, shade, reflectivity, internal reflections under crossed polars and texture, e.g. botryoidal, colloform, fibrous, etc.). Binary Mn oxide-gangue and gangue particles were not sub-divided into hardness types. Where a particle consisted of more than two mineral phases, e.g. Mn Oxide + quartz + clay, it was counted in the category it most represented (i.e. group 4s or 4c if Mn oxide was the predominant particle phase – see Table 2).
Petrography of martite–goethite ore and implications for ore genesis, South Flank, Hamersley Province, Western Australia
Published in Australian Journal of Earth Sciences, 2021
All the mineralisation in SF6921RE (N3 extends from 12 to 21 m vertical depth) has been subject to a weathering overprint that has altered the texture and mineralogy. Colloform intergrowths of Stage 4 goethite and very fine-grained hematite (possibly hydrohematite—pale grey rather than bright white reflectance) are the characteristic minerals deposited near surface within the vadose zone and these minerals line voids within the rock (Figure 10). The colloform goethite ranges from coarse-grained and botryoidal (acicular grains >100 µm in length; Figure 10a) to very fine-grained and commonly intergrown with the colloform (hydro)hematite (<10 µm; Figure 10b). There is evidence for significant leaching and the creation of macro-porosity (centimetre-sized or larger).
Alteration and mineral zonation at the Mt Lyell copper–gold deposit, Tasmania
Published in Australian Journal of Earth Sciences, 2018
The botryoidal texture of some of the hematite suggests at least partial precipitation in open space from solution. This led Solomon (1967) to propose that the hematite formed as a gossan. The geology, morphology and chemistry of the massive pyrite, particularly the interplay between two fluids, suggested by barite distribution and the clear spatial relationship between the high-grade facies and the faulted volcanic–conglomerate contact suggest that fluids were channelled along faults in the subsurface. This implication is inconsistent with formation of a strictly superficial gossan; however, it is concluded that the hematite, ‘chert’ and high-grade Cu–Ag were deposited very close to the surface.